{ "modality": "MRI", "spec_basis": "Effective February 1, 2025 (ARRT Board approved January 2024). ARRT has posted a revised MRI specification effective February 1, 2028 (board approval pending) that changes the counts to Patient Care 20, Safety 40, Image Production 86, and Procedures 54.", "how_to_use": "Study in order of question weight: Image Production (106 of 200, 53%) first, especially physics, parameter trade-offs, and artifacts; then Procedures (57, 28.5%), Safety (21, 10.5%), and Patient Care (16, 8%). For each topic, learn the must-know facts and key numbers, then read the board traps, since that is where wrong answers come from. Finish with the last-minute review list the day before the exam.", "chapters": [ { "id": "patient-care", "category": "Patient Care", "scored_questions": 16, "weight_pct": 8.0, "topics": [ { "subcategory": "Patient Interactions and Management", "title": "Ethics, patient rights, and legal terms", "must_know": [ "Informed consent needs a competent adult (or legal guardian) who understands purpose, risks, benefits, and alternatives; it can be written, oral, or implied (emergency).", "HIPAA protects patient health information; share only the minimum necessary with people directly involved in care.", "The AHA Patient Care Partnership covers privacy, extent of care (including DNR orders), access to information, advance directives (living will, health care proxy), and the right to refuse research participation.", "Battery is touching without consent; negligence is failing to meet the standard of care; malpractice is professional negligence; beneficence means acting for the patient's good.", "Respondeat superior makes the employer liable for an employee's acts on the job; res ipsa loquitur ('the thing speaks for itself') applies when the injury itself proves negligence.", "Verify identity with two identifiers and confirm the order matches the clinical indication and exam coding before scanning.", "Sponges and straps used as positioning aids to limit motion are not restraints; true restraints need a physician order and documentation.", "ARRT Standards of Ethics: the Code of Ethics is aspirational; the Rules of Ethics are mandatory and enforceable." ], "memory_tip": "Battery = Body touched without consent; Negligence = Not meeting the standard.", "board_traps": [ "Calling a restraint a positioning aid: if it restricts freedom of movement and isn't needed to position, it's a restraint.", "The Code of Ethics is not the enforceable part; the Rules of Ethics are." ], "key_numbers": [] }, { "subcategory": "Patient Interactions and Management", "title": "Communication and patient education", "must_know": [ "Explain the exam's purpose, length, noise, need to hold still, and what contrast does, in plain words without jargon.", "Use a qualified medical interpreter for language barriers, not a family member, when possible.", "Adjust for age, hearing or vision loss, cognitive impairment, and anxiety; nonverbal cues (eye contact, touch, tone) matter as much as words.", "Keep two-way contact during the scan via intercom and a squeeze ball; tell the patient before each loud sequence or breath-hold.", "Give pre-exam instructions (e.g., NPO for MRCP or enterography) and post-exam instructions (hydration, watch the IV site, delayed reaction signs).", "Review pertinent history: prior imaging, surgeries, cancer, renal disease, allergies, and current symptoms that change the protocol.", "Answer questions about other modalities honestly; MRI uses no ionizing radiation." ], "memory_tip": null, "board_traps": [ "Saying MRI uses radiation: it does not, but it does use RF energy that heats tissue." ], "key_numbers": [] }, { "subcategory": "Patient Interactions and Management", "title": "Physical assistance, monitoring, sedation, claustrophobia", "must_know": [ "Body mechanics: wide base of support, bend the knees, keep the load close, push rather than pull, and use transfer boards or slider sheets.", "Only MR Conditional/MR Safe oxygen tanks, IV poles, pumps, wheelchairs, and stretchers may enter Zone IV; move the patient to an MR stretcher outside.", "Normal adult vitals: pulse 60-100/min, respirations 12-20/min, SpO2 about 95-100%, oral temp about 98.6 F (37 C), BP below 120/80 is normal.", "Sedated or anesthetized patients need continuous monitoring with MR Conditional equipment (e.g., fiberoptic pulse oximetry) and someone trained to monitor them.", "Claustrophobia: explain, feet-first if the exam allows, eyes closed or covered, prism glasses or mirror, music, a screened companion, wider-bore or open scanner, or sedation per order.", "Prevent falls: lock stretchers, raise rails, never leave a sedated or confused patient alone on the table.", "Perform a time-out (patient, procedure, site) before invasive steps such as arthrogram injections." ], "memory_tip": null, "board_traps": [ "Bringing a standard ferromagnetic O2 cylinder or monitor into Zone IV; only labeled MR Conditional/MR Safe equipment goes in." ], "key_numbers": [ { "label": "Adult pulse", "value": "60-100 bpm" }, { "label": "Adult respirations", "value": "12-20/min" }, { "label": "Normal SpO2", "value": "about 95-100%" } ] }, { "subcategory": "Patient Interactions and Management", "title": "Medical emergencies", "must_know": [ "Cardiac or respiratory arrest: start CPR, call the code, and move the patient OUT of Zone IV to a prepared area; the code team and crash cart never enter Zone IV.", "An AED and standard defibrillator are not MR Safe; defibrillation happens outside Zone IV.", "RF burn: stop the scan, remove the patient, inspect the skin, notify the radiologist, and document and report the event.", "Seizure: protect from injury, remove from the scanner, do not restrain or put anything in the mouth, and turn on the side afterward.", "Hypoglycemia (shaky, sweaty, confused): give oral sugar if alert; hyperglycemia shows thirst, frequent urination, and fruity breath.", "Vasovagal reaction: hypotension with BRADYCARDIA; elevate legs, give IV fluids, and atropine if it persists; anaphylactic hypotension comes with TACHYCARDIA.", "Communicate critical findings (e.g., acute stroke, cord compression) to the radiologist and care team immediately and document who was told and when." ], "memory_tip": "Vasovagal = slow pulse; anaphylaxis = fast pulse.", "board_traps": [ "Running a code inside the magnet room.", "Mixing up vasovagal (bradycardia) and anaphylactic shock (tachycardia)." ], "key_numbers": [] }, { "subcategory": "Patient Interactions and Management", "title": "Infection control and hazardous materials", "must_know": [ "Chain of infection: pathogen, reservoir, portal of exit, mode of transmission, portal of entry, susceptible host; breaking any link stops spread.", "Hand hygiene is the single most important practice; use soap and water (not alcohol rub) for C. difficile and visibly soiled hands.", "Contact precautions: MRSA, VRE, C. difficile (gown and gloves). Droplet: influenza, pertussis, mumps (surgical mask). Airborne: TB, measles, varicella (N95 and negative-pressure room).", "Neutropenic (reverse) isolation protects an immunocompromised patient from you.", "Never recap needles; drop sharps in a puncture-resistant container; use a new needle and syringe for every injection.", "Disinfect coils, pads, and the table between patients; sterilization (not disinfection) is required for items entering sterile tissue.", "Safety data sheets (SDS) describe the hazards and handling of chemicals such as disinfectants; chemotherapy waste and body fluids follow hazardous-waste rules." ], "memory_tip": "Airborne = 'My Chicken Has TB': Measles, Chickenpox (varicella), TB.", "board_traps": [ "Using alcohol gel for C. difficile: it does not kill spores.", "Airborne precautions need an N95, not a surgical mask." ], "key_numbers": [] }, { "subcategory": "Patient Interactions and Management", "title": "Gadolinium contrast: agents, dosing, injection", "must_know": [ "GBCAs are paramagnetic; they shorten T1 (and T2) of nearby water, so enhancing tissue gets bright on T1-weighted images.", "Macrocyclic agents (e.g., gadobutrol, gadoterate, gadoteridol) bind Gd more stably than linear agents, lowering free-Gd release and retention.", "Ionic vs nonionic refers to the charge of the Gd chelate; macrocyclic vs linear (stability) matters more for safety.", "Typical dose is 0.1 mmol/kg for most agents; gadobutrol is 1.0 mmol/mL (0.1 mL/kg), most others are 0.5 mmol/mL (0.2 mL/kg); gadopiclenol uses 0.05 mmol/kg.", "Dose calc: weight (kg) x dose (mmol/kg) / concentration (mmol/mL) = mL; pounds / 2.2 = kg.", "Bolus timing methods: test (timing) bolus measures arrival time, automatic bolus tracking triggers when signal in a target vessel rises, fluoro-triggering lets the tech watch real-time images and start the scan.", "Power injectors must be MR Conditional and kept at their labeled distance or gauss line; follow with a saline flush.", "FDA requires a GBCA Medication Guide for outpatients receiving a GBCA for the first time." ], "memory_tip": null, "board_traps": [ "Doubling the volume for gadobutrol: it is twice as concentrated, so the mL dose is half that of a 0.5 mmol/mL agent." ], "key_numbers": [ { "label": "Standard dose", "value": "0.1 mmol/kg (most agents)" }, { "label": "Volume, 0.5 mmol/mL agent", "value": "0.2 mL/kg" }, { "label": "Volume, gadobutrol 1.0 mmol/mL", "value": "0.1 mL/kg" }, { "label": "Example", "value": "80 kg x 0.1 / 0.5 = 16 mL" } ] }, { "subcategory": "Patient Interactions and Management", "title": "Renal screening, NSF, reactions, special populations", "must_know": [ "NSF risk is highest with severe kidney disease (eGFR below 30 mL/min/1.73 m2), acute kidney injury, or dialysis, mainly after older linear (ACR Group I) agents.", "ACR Group II agents carry the lowest NSF risk; ACR considers eGFR screening optional for them, though many sites still screen at-risk patients.", "Gd retention in brain (dentate nucleus, globus pallidus) occurs more with linear agents; no harmful clinical effect has been proven.", "Mild reaction: limited hives, itching, nausea (observe, antihistamine). Moderate: diffuse hives, bronchospasm, facial swelling. Severe: laryngeal edema, hypotension, anaphylaxis, arrest.", "Epinephrine (IM) is the first-line drug for anaphylaxis; oxygen and albuterol help bronchospasm.", "Premedication for a prior allergic-like GBCA reaction (ACR oral regimen): prednisone 50 mg at 13, 7, and 1 hour before plus diphenhydramine 50 mg 1 hour before.", "Extravasation: stop the injection, elevate the limb, apply a compress per policy, notify the radiologist, and document; GBCA volumes are small, so injury is rare.", "Pregnancy: GBCA crosses the placenta, so give it only when essential. Breastfeeding: ACR says no need to stop; a mother may choose to pause 12-24 hours." ], "memory_tip": "Premed = 13-7-1.", "board_traps": [ "Thinking breastfeeding must stop for 24-48 hours: ACR says interruption is not necessary.", "Assuming shellfish or iodine allergy predicts a GBCA reaction; a prior reaction to a GBCA is the main risk." ], "key_numbers": [ { "label": "NSF high-risk eGFR", "value": "below 30 mL/min/1.73 m2" }, { "label": "Premed timing", "value": "13, 7, 1 h before" } ] } ] }, { "id": "safety", "category": "Safety", "scored_questions": 21, "weight_pct": 10.5, "topics": [ { "subcategory": "MRI Screening and Safety", "title": "Implant and device screening", "must_know": [ "Screen every patient and every non-MR person entering Zone IV with a written form plus a verbal interview; a second screen happens right before entry.", "Identify and document the device type, make, model, and implant year, then verify labeling and the device-specific conditions.", "MR Safe: no known hazards in any MR environment (green square or circle). MR Conditional: safe only under stated conditions (yellow triangle). MR Unsafe: hazardous in all MR environments (red circle with slash).", "MR Conditional labels can specify field strength, maximum spatial field gradient (T/m or G/cm), SAR or B1+rms limit, gradient slew rate, coil type, scan duration, and landmark position.", "Active implants (pacemakers, ICDs, neurostimulators, cochlear implants, pumps) usually need programming to an MR mode and a check before and after the scan.", "Non-conditional ('legacy') cardiac devices and abandoned leads are scanned only under a facility protocol with radiologist/cardiology risk-benefit review.", "Remove external insulin pumps and continuous glucose monitors unless they are labeled for MR use.", "Older aneurysm clips may be ferromagnetic; without exact make/model documentation, do not scan." ], "memory_tip": "Green = go anywhere, Yellow = conditions, Red = never.", "board_traps": [ "Scanning a 'conditional' implant at a field strength or SAR not on its label: conditions are specific, e.g., a 1.5 T-only device is not cleared at 3 T.", "Assuming 'non-ferromagnetic' means MR Safe: conductive implants can still heat." ], "key_numbers": [] }, { "subcategory": "MRI Screening and Safety", "title": "Foreign bodies, external items, pregnancy", "must_know": [ "A history of metal work, grinding, or eye injury from metal means orbital screening (radiographs, or a prior CT/MR of the orbits since the injury) before MRI.", "Bullets and shrapnel may be ferromagnetic; risk depends on composition and location (near eyes, spinal cord, vessels).", "Tattoos and permanent eyeliner with iron-oxide pigments can heat; a cold compress over the area lowers risk; tell the patient to report warmth.", "Remove medication patches with metallic backing (burn risk) after the prescriber or radiologist approves; remove jewelry, hairpins, hearing aids, and clothing with metallic threads.", "Change patients into facility gowns; athletic and 'cooling' fabrics may contain silver or copper fibers.", "Pregnancy: MRI without contrast may be done in any trimester when the benefit justifies it; avoid GBCA unless essential.", "Pregnant MR staff may work in the MR environment but should not stay in Zone IV during scanning (ACR guidance).", "Ferromagnetic detection systems help but never replace screening." ], "memory_tip": null, "board_traps": [ "Thinking first-trimester pregnancy is an absolute contraindication to MRI: it isn't.", "Relying on a walk-through ferromagnetic detector instead of a full screening interview." ], "key_numbers": [] }, { "subcategory": "MRI Screening and Safety", "title": "MR personnel levels and safety zones", "must_know": [ "Zone I: freely accessible public area. Zone II: interface where patients are screened and supervised. Zone III: restricted; access controlled by MR personnel. Zone IV: the magnet room.", "Zone IV should be clearly marked with a lighted sign and be visible from Zone III so staff can watch the door.", "Level 1 MR personnel: passed basic safety training to work safely in Zone III themselves.", "Level 2 MR personnel: extensive training (thermal loading, burns, neuromuscular stimulation from gradients); MR technologists are Level 2.", "Non-MR personnel (patients, visitors, untrained staff) enter Zone III/IV only after screening and under direct supervision of Level 2 personnel.", "The MR Medical Director, MR Safety Officer (MRSO), and MR Safety Expert (MRSE) are the ACR-defined safety roles.", "The 5 gauss (0.5 mT) line marks where the fringe field may affect pacemakers; it should stay inside controlled zones." ], "memory_tip": "Zones go I-II-III-IV, getting closer to the magnet; Level 2 = the techs.", "board_traps": [ "Calling Zone III the magnet room: Zone IV is the magnet room.", "Letting a Level 1 person supervise an unscreened visitor in Zone IV." ], "key_numbers": [ { "label": "Pacemaker fringe-field line", "value": "5 gauss = 0.5 mT" }, { "label": "1 tesla", "value": "10,000 gauss" } ] }, { "subcategory": "MRI Screening and Safety", "title": "Static magnetic field", "must_know": [ "The superconducting field is always on, even with power off; projectile risk never stops.", "Translational (pull) force depends on the spatial gradient and is strongest near the bore opening; rotational force (torque) is strongest at isocenter where B0 is highest.", "Fringe field spreads outside the magnet; active shielding (counter-windings) and passive shielding (steel) shrink it.", "Magnetohydrodynamic/magnetohemodynamic effect: flowing blood in B0 induces a voltage that elevates the T wave on ECG; it is not true ischemia.", "Moving the head quickly in a high field can cause vertigo, nausea, or metallic taste.", "FDA non-significant-risk limits: up to 8 T for adults, children, and infants older than 1 month; up to 4 T for neonates (1 month or younger)." ], "memory_tip": "Pull is at the door; twist is in the middle.", "board_traps": [ "Thinking translational force is greatest at isocenter: it peaks where the field changes fastest, near the bore entrance.", "Calling ECG T-wave elevation in the bore a sign of myocardial ischemia." ], "key_numbers": [ { "label": "FDA static field, adults/children/infants >1 month", "value": "8 T" }, { "label": "FDA static field, neonates", "value": "4 T" } ] }, { "subcategory": "MRI Screening and Safety", "title": "RF field: SAR, heating, burns", "must_know": [ "SAR (W/kg) measures RF energy absorbed; enter accurate patient weight because SAR limits are calculated from it.", "SAR rises with the square of field strength and the square of flip angle, and with more pulses per unit time (short TR, long ETL, 180-degree pulses, sat bands).", "FDA/IEC whole-body SAR: 2 W/kg in Normal Operating Mode, 4 W/kg in First Level Controlled Mode (needs medical supervision); head SAR limit 3.2 W/kg.", "Conductive loops (crossed ankles, clasped hands, thighs or arms touching the bore or each other) can cause burns; use pads to separate skin from skin and skin from bore.", "Keep ECG leads and coil cables straight, never looped, off the skin with padding, and away from the bore wall.", "Proximity burns can come from contact with the bore, coil cables, or metal-threaded clothing.", "Patients with fever, poor thermoregulation, or heavy blankets are at higher heating risk.", "The RF shield (Faraday cage, usually copper) keeps outside RF out; the door must be closed and the finger-stock seal intact." ], "memory_tip": "SAR goes as B0 squared: 3 T is about 4 times the SAR of 1.5 T.", "board_traps": [ "Thinking RF shielding blocks the magnetic field: the copper cage blocks RF only; magnetic shielding is separate.", "Entering the wrong weight: SAR will be miscalculated." ], "key_numbers": [ { "label": "Whole-body SAR, Normal Mode", "value": "2 W/kg" }, { "label": "Whole-body SAR, First Level", "value": "4 W/kg" }, { "label": "Head SAR", "value": "3.2 W/kg" }, { "label": "3 T vs 1.5 T SAR", "value": "about 4x" } ] }, { "subcategory": "MRI Screening and Safety", "title": "Gradient field: noise, nerve stimulation", "must_know": [ "Rapidly switching gradients (dB/dt) induce currents in tissue (Faraday's law), causing peripheral nerve stimulation: tingling or twitching.", "FDA limit: dB/dt must stay below levels that cause severe discomfort or painful nerve stimulation.", "Magnetophosphenes are flashes of light from induced currents in the retina.", "Acoustic noise comes from gradient coils vibrating against B0 (Lorentz force); it is loudest with fast sequences such as EPI/DWI and at higher field.", "Hearing protection (earplugs and/or headphones) is required for every patient, including sedated patients and infants.", "FDA acoustic limits: significant risk above 140 dB peak unweighted, or above 99 dBA with hearing protection in place." ], "memory_tip": null, "board_traps": [ "Blaming the RF field for knocking and noise: the gradients make the noise." ], "key_numbers": [ { "label": "FDA acoustic, peak", "value": "140 dB unweighted" }, { "label": "FDA acoustic, A-weighted rms with protection", "value": "99 dBA" } ] }, { "subcategory": "MRI Screening and Safety", "title": "Cryogens, quench, equipment, environment, emergencies", "must_know": [ "Superconducting magnets use niobium-titanium wire cooled by liquid helium near 4 K (about -269 C).", "A quench is the sudden loss of superconductivity: helium boils off and should vent through the quench pipe; the field ramps down over seconds to a minute or so.", "Liquid helium expands about 750 times to gas; helium in the room displaces oxygen (asphyxiation) and causes frostbite; an oxygen monitor alarms when O2 drops.", "Signs of a quench: loud bang or hiss, white cloud of vapor, O2 alarm. Evacuate the patient and staff immediately.", "Quench on purpose only when a person is pinned by a ferromagnetic object or for a fire needing firefighters with ferrous gear; a quench is costly and may damage the magnet.", "Fire: get the patient out, use only MR Conditional/MR Safe extinguishers in Zone IV, and keep firefighters out of Zone IV until the field is confirmed off.", "Keep temperature and humidity within manufacturer specs; high temp/humidity limits patient heat loss, very low humidity raises static discharge.", "Ancillary equipment (injectors, monitors, carts) needs MR labeling and must be kept at its labeled gauss line." ], "memory_tip": "Quench = 'Quick helium exit.'", "board_traps": [ "Quenching for a cardiac arrest: remove the patient instead; quench is for a pinned person or a fire emergency.", "Thinking turning off power or the E-stop (emergency power off) shuts off a superconducting field: only a quench does." ], "key_numbers": [ { "label": "Liquid helium temp", "value": "about 4 K (-269 C)" }, { "label": "Helium liquid-to-gas expansion", "value": "about 750:1" } ] } ] }, { "id": "image-production", "category": "Image Production", "scored_questions": 106, "weight_pct": 53.0, "topics": [ { "subcategory": "Physical Principles of Image Formation", "title": "Magnets, shims, and RF hardware", "must_know": [ "Faraday's law: a changing magnetic field induces a current in a conductor; this is how the receive coil picks up MR signal.", "Superconducting magnets: strong (1.5-3 T clinical, 7 T available), very homogeneous, field along the bore (horizontal), always on, need liquid helium.", "Resistive magnets: electromagnets, low field, use lots of power and make heat, can be switched off.", "Permanent magnets: low field, open design with a vertical field, no power or cryogens, very heavy, cannot be switched off.", "Homogeneity is measured in ppm; shimming improves it: passive (metal plates) and active (shim coils with current). Good shim is critical for fat sat, EPI, and spectroscopy.", "Volume coils (body, birdcage head) give uniform signal; surface coils give high SNR close to the coil that falls off with depth (roughly to a depth of the coil's radius).", "Phased-array coils combine several small elements for surface-coil SNR over a large FOV and make parallel imaging possible; quadrature coils improve SNR by about 1.4 (square root of 2).", "Most exams use the body coil to transmit and a local coil to receive; transmit/receive (T/R) coils do both and lower SAR outside the coil." ], "memory_tip": null, "board_traps": [ "Thinking a permanent magnet can be shut off in an emergency.", "Expecting uniform signal from a surface coil: SNR drops with distance from it." ], "key_numbers": [] }, { "subcategory": "Physical Principles of Image Formation", "title": "Gradient system", "must_know": [ "Three orthogonal gradient coils (X, Y, Z) add a linear field change so frequency varies with position.", "Gradient amplitude (strength) is measured in mT/m; higher amplitude allows thinner slices and smaller FOVs.", "Rise time is how long the gradient takes to reach full amplitude; slew rate = amplitude / rise time (T/m/s).", "Faster slew rate allows shorter TR, TE, and echo spacing (key for EPI) but raises peripheral nerve stimulation.", "Duty cycle is the percentage of time the gradients can run at full power.", "By convention Z runs along the bore (head-foot), X left-right, Y anterior-posterior: slice select is Z for axial, X for sagittal, Y for coronal." ], "memory_tip": "Slew = steepness: how fast the gradient climbs.", "board_traps": [ "Mixing slew rate (T/m/s) with gradient amplitude (mT/m)." ], "key_numbers": [ { "label": "Gradient amplitude unit", "value": "mT/m" }, { "label": "Slew rate unit", "value": "T/m/s" } ] }, { "subcategory": "Physical Principles of Image Formation", "title": "Nuclear magnetism and resonance", "must_know": [ "Hydrogen is imaged because it is abundant in water and fat and has a strong magnetic moment.", "Larmor equation: precessional frequency = gyromagnetic ratio x B0; for hydrogen, 42.58 MHz/T.", "In B0, slightly more protons align parallel (low energy) than antiparallel (high energy); that small excess forms net magnetization (M0) along B0, and it grows with field strength.", "Resonance: an RF pulse at the Larmor frequency gives energy to protons, tipping net magnetization and bringing their precession into phase (phase coherence).", "A 90-degree pulse puts all magnetization into the transverse plane; a 180-degree pulse inverts it or refocuses it.", "The free induction decay (FID) is the signal right after the RF pulse, decaying by T2*.", "Diamagnetic: weak negative susceptibility (water, most tissue). Paramagnetic: weak positive (gadolinium, deoxyhemoglobin, methemoglobin). Superparamagnetic: strong positive (iron oxide particles). Ferromagnetic: very strong, retains magnetization (iron, nickel, cobalt).", "SNR rises roughly in proportion to field strength (about 2x from 1.5 T to 3 T)." ], "memory_tip": "Larmor: Frequency = Gamma x B0 ('F = gamma B').", "board_traps": [ "Using 63.86 MHz at 3 T: 63.86 MHz is 1.5 T; 3 T is 127.7 MHz.", "Calling gadolinium superparamagnetic: it is paramagnetic; iron oxides are superparamagnetic." ], "key_numbers": [ { "label": "Gyromagnetic ratio, H", "value": "42.58 MHz/T" }, { "label": "Larmor at 1.0 T", "value": "42.58 MHz" }, { "label": "Larmor at 1.5 T", "value": "63.86 MHz" }, { "label": "Larmor at 3.0 T", "value": "127.7 MHz" } ] }, { "subcategory": "Physical Principles of Image Formation", "title": "Tissue characteristics: T1, T2, T2*, PD, flow, diffusion, perfusion", "must_know": [ "T1 (spin-lattice) recovery: time for longitudinal magnetization to regrow to 63% of its maximum.", "T2 (spin-spin) decay: time for transverse magnetization to fall to 37% of its starting value.", "T2* is decay from T2 plus field inhomogeneity and susceptibility; T2* is always shorter than T2, and T2 is shorter than or equal to T1.", "Fat has short T1 and is bright on T1; water/CSF has long T1 and long T2 (dark on T1, bright on T2).", "T1 lengthens at higher field; T2 changes little. Inversion times and TRs often need to be longer at 3 T.", "Proton (spin) density weighting shows the number of mobile hydrogen protons per voxel.", "Diffusion is random (Brownian) water motion; cytotoxic edema in acute infarct restricts it (bright on DWI, dark on ADC).", "Perfusion is capillary-level blood delivery, measured with gadolinium (DSC, DCE) or with arterial spin labeling (no contrast)." ], "memory_tip": "T1 = 63% up (recovery); T2 = 37% left (decay).", "board_traps": [ "Swapping the 63% and 37% definitions.", "Saying T2* is longer than T2." ], "key_numbers": [ { "label": "T1 definition", "value": "63% recovery of Mz" }, { "label": "T2 definition", "value": "decay to 37% of Mxy" } ] }, { "subcategory": "Physical Principles of Image Formation", "title": "Spatial localization and k-space", "must_know": [ "Slice selection: an RF pulse with a set transmit bandwidth is applied with a gradient on, exciting only one slab.", "Thinner slices come from a steeper slice-select gradient or a narrower transmit bandwidth.", "Phase encoding is applied after excitation and before readout; each TR (in conventional SE) fills one phase line with a different gradient step.", "Frequency (readout) encoding is applied while the echo is collected; the sampling rate is set by receive bandwidth.", "Smaller FOV requires a steeper frequency gradient (and steeper phase steps).", "K-space is raw frequency data: the center sets signal and contrast; the periphery sets edges and fine detail.", "Every point in k-space contributes to every pixel in the image; there is no one-to-one match.", "Number of phase-encoding steps (phase matrix) directly sets 2D scan time; frequency matrix does not." ], "memory_tip": "Center of k-space = Contrast; edges = Edges (detail).", "board_traps": [ "Thinking the top line of k-space is the top of the image.", "Thinking frequency matrix increases scan time in conventional SE." ], "key_numbers": [] }, { "subcategory": "Physical Principles of Image Formation", "title": "Artifacts I: aliasing, truncation, chemical shift, susceptibility", "must_know": [ "Aliasing (wrap): anatomy outside the FOV folds onto the opposite side in the phase direction (and slice direction in 3D). Fix: larger FOV, phase oversampling, swap phase/frequency, sat bands or coil placement.", "Gibbs/truncation: parallel bright and dark lines at sharp high-contrast edges (can mimic a syrinx in the cord), mostly in the phase direction. Fix: more phase steps, filtering.", "Chemical shift (first kind): fat and water precess about 3.5 ppm apart, so fat is shifted in the frequency direction, making a bright band on one side and dark band on the other (e.g., kidney edges).", "Chemical shift is worse at higher field and with narrower receive bandwidth; fix with wider receive bandwidth, fat suppression, or lower field strength; in EPI it appears in the phase direction.", "Chemical misregistration (second kind, 'India ink'): on out-of-phase GRE, a black line outlines fat-water interfaces in all directions. Fix: in-phase TE or a spin echo.", "Susceptibility: signal loss and distortion near metal or air-tissue interfaces; worst on GRE and EPI, at high field, and with long TE.", "Reduce susceptibility with spin echo/FSE, short TE, wide receive bandwidth, smaller voxels, lower field, and metal-artifact-reduction sequences." ], "memory_tip": "Aliasing and motion live in PHASE; chemical shift lives in FREQUENCY (except EPI).", "board_traps": [ "Expecting frequency-direction wrap on modern scanners: oversampling in frequency is built in, so wrap is a phase-direction problem.", "Narrowing bandwidth to fix chemical shift: narrower bandwidth makes it worse." ], "key_numbers": [ { "label": "Fat-water shift", "value": "about 3.5 ppm" }, { "label": "Fat-water shift at 1.5 T", "value": "about 220 Hz" }, { "label": "Fat-water shift at 3 T", "value": "about 440 Hz" } ] }, { "subcategory": "Physical Principles of Image Formation", "title": "Artifacts II: motion, RF, partial volume, cross-talk, and others", "must_know": [ "Motion and flow ghosts always propagate in the phase direction; periodic motion (heart, breathing, pulsatile vessels) makes discrete ghosts.", "Fix motion with immobilization, breath-hold or respiratory triggering, cardiac gating, sat bands, gradient moment nulling, swapping phase direction, faster sequences, or radial (blade-type) k-space.", "RF interference (zipper): a line of noise at one frequency running along the phase direction; causes include an open door, a broken RF seal, or an electronic device in the room.", "Partial volume averaging: thick slices blend tissues; fix with thinner slices.", "Cross-talk: imperfect slice profiles let neighboring slices excite each other, lowering SNR and contrast; fix with a slice gap or interleaved (odd then even) acquisition.", "Cross-excitation: where intersecting slice groups overlap (e.g., angled lumbar disc stacks), a dark saturation band appears; keep crossings outside the anatomy of interest.", "Moire (zebra) pattern: interference bands at the FOV edge on GRE, from aliasing plus field inhomogeneity. Parallel imaging artifact: residual aliasing in the image center when the FOV is smaller than the anatomy or calibration is poor.", "Eddy currents from fast gradient switching distort images (especially DWI/EPI); dielectric (standing-wave) effect causes uneven shading at 3 T, e.g., in abdomens with ascites or in pregnancy; fix with dielectric pads or multi-transmit RF." ], "memory_tip": null, "board_traps": [ "Swapping cross-talk (slice-profile overlap) and cross-excitation (intersecting stacks); check your textbook's usage.", "Putting the zipper in the frequency direction: it sits at one frequency and runs along the phase direction.", "Blaming dielectric shading on the coil: it comes from the RF wavelength at 3 T." ], "key_numbers": [] }, { "subcategory": "Physical Principles of Image Formation", "title": "Quality control", "must_know": [ "Center frequency is checked to confirm the system is on resonance; drift can signal a magnet or shim problem.", "Transmit gain (RF power/attenuation) is tracked; a sudden change suggests an RF or coil issue.", "Phantom tests (as in ACR accreditation) cover geometric accuracy, high-contrast spatial resolution, slice thickness, slice position, image uniformity, percent ghosting, and low-contrast detectability.", "SNR measurement: mean signal in a region divided by noise (standard deviation of background or difference image).", "Technologist QC is done at least weekly (ACR); the medical physicist/MR scientist does an annual survey.", "Visual checklist: coils and cables (fraying, cracks), table, door RF seals (finger stock), patient intercom, emergency buttons, oxygen monitor, and zone signage." ], "memory_tip": null, "board_traps": [ "Thinking slice thickness QC checks contrast resolution: it checks geometric slice width; low-contrast detectability checks contrast resolution." ], "key_numbers": [] }, { "subcategory": "Sequence Parameters and Options", "title": "TR, TE, TI, flip angle, and weighting", "must_know": [ "TR controls T1 weighting; TE controls T2 weighting.", "Spin echo T1: short TR (about 400-700 ms) and short TE (about 10-20 ms).", "Spin echo/FSE T2: long TR (2,000 ms or more) and long TE (about 80-120 ms).", "PD: long TR and short TE (about 20-40 ms) minimize both T1 and T2 effects.", "GRE: large flip angle with short TE gives T1; small flip angle with longer TE gives T2*; small flip with short TE gives PD.", "Longer TR increases SNR and allows more slices but lengthens scan time and reduces T1 weighting.", "Longer TE increases T2 weighting but lowers SNR.", "TI is the delay from the 180-degree inversion to the 90-degree pulse; a tissue is nulled at TI of about 0.69 x its T1." ], "memory_tip": "Short-Short = T1; Long-Long = T2; Long-Short = PD. ('TR = T1, TE = T2').", "board_traps": [ "Thinking a short TR with a long TE is useful: it gives poor SNR and mixed contrast.", "Assuming increasing TE improves SNR." ], "key_numbers": [ { "label": "Null point", "value": "TI = 0.69 x T1" }, { "label": "SE T1", "value": "TR ~400-700, TE ~10-20 ms" }, { "label": "SE T2", "value": "TR >=2000, TE ~80-120 ms" } ] }, { "subcategory": "Sequence Parameters and Options", "title": "SNR and CNR", "must_know": [ "SNR rises with larger voxels: bigger FOV, smaller matrix, thicker slices.", "SNR is proportional to the square root of NEX: doubling NEX raises SNR by about 1.41 and doubles scan time.", "Halving receive bandwidth raises SNR by about 1.41 but increases chemical shift and lengthens minimum TE.", "SNR also rises with longer TR, shorter TE, higher field strength, closer/better coils, and 3D acquisition.", "Doubling FOV in both directions (matrix fixed) makes the voxel 4 times larger, so SNR rises 4 times, but resolution drops.", "CNR is the signal difference between two tissues relative to noise; gadolinium, fat suppression, magnetization transfer, and proper weighting raise CNR.", "Parallel imaging and partial Fourier save time but cost SNR." ], "memory_tip": "NEX and bandwidth work by square root; voxel size works linearly.", "board_traps": [ "Thinking doubling NEX doubles SNR: it gives about 41% more.", "Thinking a wider bandwidth increases SNR: it lowers it." ], "key_numbers": [ { "label": "Double NEX", "value": "SNR x1.41, time x2" }, { "label": "Halve receive BW", "value": "SNR x1.41" }, { "label": "Double slice thickness", "value": "SNR x2" }, { "label": "Double FOV, both directions", "value": "SNR x4" } ] }, { "subcategory": "Sequence Parameters and Options", "title": "Spatial resolution: FOV, matrix, pixel, voxel, slices", "must_know": [ "Pixel size = FOV / matrix in each direction; voxel = pixel area x slice thickness.", "Smaller pixels/voxels (smaller FOV, larger matrix, thinner slices) improve spatial resolution but lower SNR.", "Example: 240 mm FOV / 256 matrix = 0.94 mm pixel; with 5 mm slices, voxel is about 4.4 cubic mm.", "Isotropic voxels (equal in all three dimensions) allow MPR in any plane without losing detail.", "Slice gap reduces cross-talk; many 2D protocols use a gap of about 10-30% of slice thickness or interleave slices.", "The number of slices per TR is limited by TR and TE: longer TR or shorter TE allows more slices.", "Increasing phase matrix lengthens scan time; increasing frequency matrix does not (but may raise minimum TE)." ], "memory_tip": null, "board_traps": [ "Thinking a smaller FOV raises SNR: it lowers it.", "Thinking more slices always add time in 2D: within one TR they are free until TR runs out." ], "key_numbers": [ { "label": "Pixel size", "value": "FOV / matrix" }, { "label": "Example pixel", "value": "240 / 256 = 0.94 mm" } ] }, { "subcategory": "Sequence Parameters and Options", "title": "Scan time: NEX, ETL, effective TE, concatenations", "must_know": [ "2D SE scan time = TR x phase steps x NEX.", "FSE scan time = TR x phase steps x NEX / ETL.", "3D scan time = TR x phase steps x NEX x number of slice partitions.", "Longer ETL shortens time but adds blurring, raises SAR, reduces T1 contrast, and allows fewer slices per TR.", "Effective TE is the TE of the echo placed in the center of k-space; it sets the image contrast in FSE.", "Fat stays bright on FSE T2 (J-coupling), so fat suppression is often added.", "Concatenations (acquisitions) split slices into more than one pass per TR so short-TR T1 scans cover more slices; each concatenation multiplies scan time." ], "memory_tip": "Time = TR x Phase x NEX (divide by ETL for fast spin echo).", "board_traps": [ "Forgetting to divide by ETL for FSE or to multiply by partitions for 3D.", "Thinking a longer ETL improves T1 weighting: it reduces it." ], "key_numbers": [ { "label": "Example SE", "value": "500 ms x 256 x 2 = 256 s (4:16)" }, { "label": "Example FSE", "value": "4000 ms x 256 x 2 / 16 = 128 s (2:08)" }, { "label": "Example 3D", "value": "10 ms x 256 x 1 x 128 = 328 s (~5:28)" } ] }, { "subcategory": "Sequence Parameters and Options", "title": "Bandwidth, b-value, and VENC", "must_know": [ "Transmit bandwidth is the frequency range of the RF pulse; with gradient slope it sets slice thickness.", "Receive bandwidth is the sampling frequency range (total kHz or Hz/pixel = total BW / frequency matrix).", "Wider receive BW: less chemical shift, less susceptibility distortion, shorter echo spacing and TE, more slices, but lower SNR.", "Chemical shift in pixels = fat-water shift (Hz) / BW per pixel; e.g., 220 Hz / 220 Hz per pixel = 1 pixel at 1.5 T.", "b-value (s/mm2) sets diffusion weighting; b = 0 is essentially T2-weighted, b = 1000 is typical for brain; higher b means more weighting and less SNR.", "VENC (cm/s) in phase contrast should be set just above the highest expected velocity; too low causes velocity aliasing, too high gives a weak flow signal.", "CSF flow studies use a low VENC; arterial studies need a much higher VENC." ], "memory_tip": null, "board_traps": [ "Setting VENC well below peak velocity: fast flow wraps and shows the wrong direction.", "Thinking a higher b-value increases SNR." ], "key_numbers": [ { "label": "Typical brain DWI b-value", "value": "1000 s/mm2" }, { "label": "Bandwidth per pixel", "value": "total BW / frequency matrix" } ] }, { "subcategory": "Sequence Parameters and Options", "title": "Image contrast types: T1, T2, PD, T2*, DWI, SWI", "must_know": [ "T1-weighted: fat bright, fluid dark, best for anatomy and gadolinium enhancement.", "T2-weighted: fluid bright, best for edema and most pathology.", "PD-weighted: high signal and detail; workhorse for knee menisci and other joints.", "T2*-weighted GRE: sensitive to blood products, calcium, and susceptibility (hemorrhage looks dark, 'blooms').", "DWI: restricted diffusion is bright on DWI and dark on ADC; bright on both is T2 shine-through, not true restriction.", "SWI: high-resolution 3D GRE combining magnitude and phase; most sensitive for microbleeds, small veins, and calcium vs blood (phase separates them); often viewed as minimum intensity projection (minIP)." ], "memory_tip": null, "board_traps": [ "Calling bright DWI with bright ADC an acute infarct: that is T2 shine-through.", "Expecting SWI to show acute infarct: DWI does." ], "key_numbers": [] }, { "subcategory": "Sequence Parameters and Options", "title": "Options I: 2D/3D, slice order, sat bands, flow comp, fat suppression, in/out of phase", "must_know": [ "3D gives thin contiguous slices, higher SNR, and isotropic reformats but takes longer and is more motion-sensitive.", "Interleaved slice order (odd, then even) reduces cross-talk; sequential is used when contiguous slices or timing matter.", "Spatial saturation bands null signal from a region before each excitation, reducing flow and motion ghosts (e.g., anterior to the spine); they add SAR and reduce slices per TR.", "Gradient moment nulling (flow compensation) rephases moving spins to cut flow and CSF pulsation artifact; it increases minimum TE.", "Spectral (chemical) fat sat: a frequency-selective pulse that needs a homogeneous field; fails near metal, at FOV edges, and at low field; fine after gadolinium.", "STIR: inversion recovery that nulls fat by T1; uniform and works near metal and at low field, but it also nulls anything with a short T1, so never use it after gadolinium.", "Dixon: in- and out-of-phase echoes are combined to make water-only, fat-only, in-phase, and out-of-phase images; robust fat suppression over large FOVs.", "In-phase/out-of-phase GRE: signal drop on out-of-phase means fat and water in the same voxel (fatty liver, adrenal adenoma); signal drop on in-phase (longer TE) suggests iron or susceptibility." ], "memory_tip": "STIR + gad = never.", "board_traps": [ "Using STIR after contrast: enhancing tissue gets nulled.", "Using spectral fat sat around hardware: it fails; use STIR or Dixon." ], "key_numbers": [ { "label": "Out-of-phase/in-phase TE, 1.5 T", "value": "about 2.2 / 4.4 ms" }, { "label": "Out-of-phase/in-phase TE, 3 T", "value": "about 1.1 / 2.3 ms" } ] }, { "subcategory": "Sequence Parameters and Options", "title": "Options II: gating, rectangular FOV, anti-aliasing, parallel imaging, filtering", "must_know": [ "ECG triggering uses the R wave; the effective TR equals the R-R interval (or a multiple); peripheral (pulse) gating lags behind the R wave.", "Respiratory triggering (bellows or navigator) acquires data during end-expiration; breath-holds are done at end-expiration for consistent positioning.", "Prospective triggering acquires after a trigger; retrospective gating records continuously and sorts data by cardiac phase (used for cine).", "Rectangular FOV cuts phase steps for anatomy narrower in one direction (e.g., sagittal spine); it saves time, keeps resolution, and lowers SNR.", "Anti-aliasing (phase oversampling) adds phase steps beyond the FOV and discards them; it can add time unless NEX is reduced.", "Parallel imaging (image-based or k-space-based) skips phase lines and uses coil sensitivity to fill them in; time divides by the acceleration factor, and SNR drops by at least the square root of that factor.", "Parallel imaging needs a phased-array coil and a calibration scan; it also shortens EPI echo trains, reducing distortion.", "Raw-data filters smooth noise and Gibbs ringing or sharpen edges; intensity normalization corrects surface-coil falloff." ], "memory_tip": null, "board_traps": [ "Thinking parallel imaging is SNR-neutral: it costs SNR.", "Placing rectangular FOV's short side in the frequency direction: it reduces phase steps." ], "key_numbers": [ { "label": "Parallel imaging factor 2", "value": "time / 2, SNR / at least 1.41" } ] }, { "subcategory": "Data Acquisition, Processing, and Storage", "title": "Spin echo and fast spin echo", "must_know": [ "Conventional SE: 90-degree pulse, then 180-degree refocusing pulse at TE/2; the 180 cancels fixed inhomogeneity, so contrast is true T2 (not T2*).", "One phase line per TR makes conventional SE slow; it remains a standard for T1 because of clean contrast.", "FSE (turbo SE) uses a train of 180-degree pulses, each echo with a different phase encoding, filling several lines per TR.", "Single-shot FSE (half-Fourier) fills all of k-space after one excitation; motion-resistant and useful for MRCP, fetal imaging, and uncooperative patients.", "FSE is less sensitive to susceptibility than GRE, so it is preferred around metal.", "Many 180-degree pulses raise SAR, especially at 3 T." ], "memory_tip": null, "board_traps": [ "Saying spin echo is T2* weighted: the 180-degree pulse removes the T2* effects." ], "key_numbers": [] }, { "subcategory": "Data Acquisition, Processing, and Storage", "title": "Inversion recovery: STIR, FLAIR, T1 prep", "must_know": [ "IR starts with a 180-degree inversion; after TI, a 90-degree pulse reads magnetization; the tissue crossing zero at TI is nulled.", "STIR nulls fat (TI about 150-170 ms at 1.5 T; longer at 3 T); great for marrow edema, orbits, and metal.", "FLAIR nulls CSF (TI about 2,000-2,500 ms at 1.5 T), making periventricular and cortical lesions (MS, edema) stand out.", "T1 FLAIR and 3D inversion-prepared T1 GRE improve gray-white contrast for brain anatomy.", "Double inversion recovery suppresses two tissues (e.g., CSF and white matter) for cortical lesions." ], "memory_tip": "STIR = Short TI (fat); FLAIR = Fluid, long TI.", "board_traps": [ "Using STIR after contrast (nulls enhancement)." ], "key_numbers": [ { "label": "STIR TI at 1.5 T", "value": "about 150-170 ms" }, { "label": "FLAIR TI at 1.5 T", "value": "about 2000-2500 ms" } ] }, { "subcategory": "Data Acquisition, Processing, and Storage", "title": "Gradient echo family and SSFP", "must_know": [ "GRE uses a gradient reversal (not a 180) to form the echo, so it is T2* sensitive, fast, and uses low flip angles.", "Spoiled (incoherent) GRE destroys leftover transverse magnetization for T1 weighting; 3D spoiled fat-sat GRE is the workhorse for dynamic liver, breast, and CE-MRA.", "Coherent (rewound) GRE keeps leftover transverse magnetization, adding T2*/fluid signal.", "Balanced SSFP: contrast depends on T2/T1, so fluid and blood are bright; used for cardiac cine, fast body imaging, and 3D high-resolution IAC/cranial nerve imaging; prone to banding from off-resonance.", "Fast GRE uses very short TR with prep pulses (inversion or saturation) for rapid T1 imaging, e.g., 3D inversion-prepared brain volumes.", "Because there is no 180-degree pulse, GRE shows more susceptibility and chemical misregistration than SE." ], "memory_tip": null, "board_traps": [ "Calling balanced SSFP T1-weighted: its contrast is T2/T1, so fluid is bright.", "Using GRE near metal hardware." ], "key_numbers": [] }, { "subcategory": "Data Acquisition, Processing, and Storage", "title": "MRA and MRV: TOF, phase contrast, contrast-enhanced", "must_know": [ "Time-of-flight: short TR saturates stationary tissue while fresh, unsaturated blood flows in bright; best when flow is perpendicular to the slice.", "2D TOF is better for slow flow (veins); 3D TOF gives high resolution for fast flow such as the circle of Willis but saturates slow flow in thick slabs (fixed with multiple thin slabs and ramped flip angles).", "Place a saturation band on the side blood comes from that you want to erase: superior band to kill venous flow for neck/head arterial TOF; inferior band to kill arterial flow for MRV.", "Short-T1 tissue (subacute hemorrhage/methemoglobin, fat) is bright on TOF and can mimic flow.", "Phase contrast uses bipolar gradients to encode velocity as phase; it gives flow direction and speed, suppresses stationary tissue, and needs a correct VENC.", "Contrast-enhanced MRA uses gadolinium T1 shortening with fast 3D spoiled GRE, timed so the center of k-space fills at peak arterial enhancement (bolus tracking, test bolus, or time-resolved).", "Flow dynamics: laminar flow is fastest in the vessel center; turbulent flow past a stenosis causes signal loss (dephasing) that can overestimate the stenosis on TOF." ], "memory_tip": "Saturate where the unwanted blood comes FROM.", "board_traps": [ "Putting the sat band on the wrong side (e.g., inferior band for carotid TOF erases the arteries).", "Calling bright subacute blood on TOF a vessel." ], "key_numbers": [] }, { "subcategory": "Data Acquisition, Processing, and Storage", "title": "EPI, DWI, SWI, perfusion", "must_know": [ "EPI fills k-space with rapid gradient switching after one (single-shot) or a few (multi-shot) excitations; fastest sequence but most prone to susceptibility distortion and to chemical shift in the phase direction (needs fat sat).", "DWI applies strong diffusion gradients on either side of the 180-degree pulse; moving water dephases and loses signal, restricted water stays bright.", "ADC map is calculated from at least two b-values; restriction is dark on ADC. Acute infarct restricts within minutes.", "Other restricted lesions: abscess, epidermoid, highly cellular tumors (e.g., lymphoma).", "SWI uses long-TE 3D GRE magnitude plus phase images to highlight veins, microbleeds, and calcium.", "DSC perfusion: rapid gadolinium bolus (often about 4-5 mL/s via a large-bore IV) tracked with T2* EPI; signal drops as contrast passes; maps include rCBV, rCBF, MTT, and TTP.", "DCE perfusion: repeated T1 imaging during contrast uptake (breast, prostate); ASL labels arterial blood water magnetically and needs no contrast." ], "memory_tip": null, "board_traps": [ "Thinking DSC perfusion uses T1 brightening: DSC uses T2* signal loss; DCE uses T1." ], "key_numbers": [] }, { "subcategory": "Data Acquisition, Processing, and Storage", "title": "MR spectroscopy", "must_know": [ "Spectroscopy displays metabolite peaks by chemical shift (ppm) instead of an image.", "Single-voxel (PRESS or STEAM) is fast and robust; multivoxel (chemical shift imaging) covers a grid.", "Good shimming and water suppression are essential; keep voxels away from fat, bone, and air.", "Key peaks: NAA 2.0 ppm (neuronal marker), creatine 3.0 ppm (energy, reference), choline 3.2 ppm (cell membrane turnover), lactate 1.3 ppm doublet (anaerobic metabolism), lipids about 0.9-1.3 ppm, myo-inositol about 3.5 ppm (short TE).", "Tumor pattern: choline up, NAA down; lactate/lipid suggests necrosis or high grade.", "Lactate doublet inverts below baseline at an intermediate TE (about 135-144 ms), separating it from lipid; short TE (about 30-35 ms) shows the most metabolites." ], "memory_tip": "Peaks rise left to right in a normal brain: Choline, Creatine, NAA ('Hunter's angle').", "board_traps": [ "Calling a rising choline peak a normal finding in tumor workups." ], "key_numbers": [ { "label": "NAA", "value": "2.0 ppm" }, { "label": "Creatine", "value": "3.0 ppm" }, { "label": "Choline", "value": "3.2 ppm" }, { "label": "Lactate", "value": "1.3 ppm (doublet)" } ] }, { "subcategory": "Data Acquisition, Processing, and Storage", "title": "K-space filling, FFT, Nyquist", "must_know": [ "Linear (sequential) filling goes top to bottom; centric fills the center first so contrast is captured right away (used for CE-MRA timing).", "Spiral and radial (blade-type) trajectories are less motion-sensitive; radial oversamples the center.", "Keyhole updates only central k-space lines in dynamic scans, borrowing the periphery from a reference scan.", "Partial (half) Fourier uses k-space conjugate symmetry to acquire about half the phase lines plus a few; saves time, costs SNR.", "Partial (fractional) echo samples part of the echo to shorten TE.", "The fast Fourier transform converts the raw time/frequency data in k-space into an image.", "Nyquist theorem: sample at least twice the highest frequency present; undersampling causes aliasing." ], "memory_tip": "Nyquist = 2x.", "board_traps": [ "Thinking half-Fourier cuts SNR in half exactly: SNR drops by roughly 30% (about 1/1.41), not by half.", "Thinking centric ordering affects resolution: it changes when contrast is captured." ], "key_numbers": [] }, { "subcategory": "Data Acquisition, Processing, and Storage", "title": "Postprocessing and informatics", "must_know": [ "MIP projects the brightest pixel along each ray; standard for MRA but small or overlapping vessels can be hidden, so review source images.", "MPR reformats a 3D (ideally isotropic) data set into any plane.", "Subtraction (post minus pre) removes bright background such as fat; misregistration from motion ruins it.", "ADC maps quantify diffusion; CINE loops images over time (cardiac, CSF flow, TMJ motion).", "DICOM is the standard file format and network protocol for medical images; HL7 carries text data among the hospital, radiology information system (RIS), and EMR.", "PACS stores and distributes images; the modality worklist pulls patient data from the RIS to avoid typing errors.", "Enter patient data accurately: name, ID, weight (needed for SAR), and orientation (head/feet first, supine/prone) so left/right labels are correct.", "Security: unique logins, log off, encryption, and role-based access protect PHI; lossless compression keeps all data, lossy compression discards some." ], "memory_tip": null, "board_traps": [ "Entering feet-first when the patient is head-first: image orientation labels will be wrong.", "Relying on MIP alone to rule out a stenosis." ], "key_numbers": [] } ] }, { "id": "procedures", "category": "Procedures", "scored_questions": 57, "weight_pct": 28.5, "topics": [ { "subcategory": "Neurological", "title": "Routine brain, MS, and seizure", "must_know": [ "Head coil, supine, head first; landmark at the nasion; axial slices parallel to the AC-PC line (or the genu-splenium line of the corpus callosum).", "Routine brain: sagittal T1, axial T2, axial FLAIR, axial DWI/ADC, axial T2* or SWI; post-gadolinium T1 when tumor, infection, or MS activity is the question.", "MS: sagittal FLAIR (2D or 3D) shows callosal and periventricular lesions perpendicular to the ventricles ('Dawson's fingers'); look in periventricular, juxtacortical/cortical, infratentorial, and spinal cord locations.", "Active MS plaques enhance on post-gadolinium T1; chronic plaques do not.", "Seizure: thin coronal T2/FLAIR perpendicular to the long axis of the hippocampus (and axials parallel to it) plus a 3D T1 volume.", "Mesial temporal sclerosis: small hippocampus with high T2/FLAIR signal, usually on one side.", "Acute stroke: DWI bright with ADC dark; hemorrhage blooms on T2*/SWI." ], "memory_tip": "Hippocampus: coronal slices perpendicular to it, axials along it.", "board_traps": [ "Angling seizure coronals to the AC-PC line instead of perpendicular to the hippocampus." ], "key_numbers": [] }, { "subcategory": "Neurological", "title": "Infant brain, perfusion, spectroscopy, CSF flow", "must_know": [ "Infants under 1 year have high brain water and little myelin, so gray-white contrast looks reversed compared with adults; longer TR and TE are used for T2.", "Myelination progress is easiest to judge on T1 in roughly the first 6 months and on T2 afterward.", "Infants: feed and swaddle ('feed and wrap') to avoid sedation, keep them warm, use hearing protection, and use MR Conditional monitoring.", "Brain perfusion (DSC) needs a fast power-injected bolus and a good IV; ASL is an option without contrast.", "Brain spectroscopy: place the voxel in the lesion away from scalp fat, bone, and sinuses; shim carefully.", "CSF flow: cardiac-gated (usually peripheral pulse) phase-contrast cine with a low VENC, sagittal through the aqueduct and axial perpendicular to it.", "CSF flow is used for normal-pressure hydrocephalus, aqueductal stenosis, and Chiari I malformation (cerebellar tonsils 5 mm or more below the foramen magnum)." ], "memory_tip": null, "board_traps": [ "Using a high arterial VENC for a CSF flow study.", "Reading a normal unmyelinated infant brain as abnormal white matter." ], "key_numbers": [ { "label": "Chiari I", "value": "tonsils >=5 mm below foramen magnum" } ] }, { "subcategory": "Neurological", "title": "IACs, pituitary, orbits, cranial nerves", "must_know": [ "IACs: thin (3 mm or less) axial and coronal T1 pre/post-gadolinium plus high-resolution 3D T2 (SSFP or 3D FSE) through CN VII and VIII.", "Vestibular schwannoma (acoustic neuroma) is an enhancing mass in the IAC/cerebellopontine angle.", "Pituitary: small FOV, thin (about 2-3 mm) sagittal and coronal T1 pre/post; dynamic coronal post-contrast finds microadenomas, which enhance later than normal gland and look darker early.", "The normal posterior pituitary is bright on sagittal T1 (the 'bright spot').", "Orbits: thin axial and coronal T1, fat-suppressed T2 or STIR, fat-suppressed post T1 (orbital fat is bright and hides enhancement); have the patient close eyes and keep them still; remove eye makeup.", "Coronal orbit coverage runs from the globe through the optic chiasm; optic neuritis enhances on fat-sat post T1.", "Cranial nerves: high-resolution 3D T2 shows nerves and vessels in the cisterns, e.g., vascular compression of CN V in trigeminal neuralgia." ], "memory_tip": null, "board_traps": [ "Skipping fat sat on post-contrast orbits: enhancement is lost in bright fat.", "Imaging the pituitary only after contrast: precontrast T1 is needed for comparison and the bright spot." ], "key_numbers": [] }, { "subcategory": "Neurological", "title": "Sinuses and soft tissue neck", "must_know": [ "Neck coil; cover skull base to thoracic inlet (or as directed); axial and coronal T1, T2 with fat suppression, and post-gadolinium fat-sat T1.", "Dixon fat suppression works well in the neck, where shape and air cause spectral fat sat to fail.", "Tell the patient not to swallow during acquisitions; sat bands help with swallowing and flow.", "Parotid: assess the facial nerve course; pleomorphic adenoma is very bright on T2.", "Sinuses: MRI separates inflammatory secretions from tumor and shows spread into the orbit or skull base; CT remains first-line for routine sinusitis." ], "memory_tip": null, "board_traps": [ "Relying on spectral fat sat in the neck: off-resonance makes it patchy." ], "key_numbers": [] }, { "subcategory": "Neurological", "title": "Vascular head and neck (MRA, MRV)", "must_know": [ "Intracranial MRA: 3D TOF of the circle of Willis with a superior sat band to suppress venous signal; MIP for review.", "Neck MRA: 2D or 3D TOF at the carotid bifurcation, or contrast-enhanced MRA from the aortic arch to the circle of Willis timed to arterial peak.", "Venous sat band goes superior for arterial imaging; arterial sat band goes inferior for MRV.", "Head MRV: 2D TOF (oblique coronal or sagittal to avoid in-plane flow), phase contrast, or contrast-enhanced 3D GRE for dural sinus thrombosis.", "TOF can overestimate stenosis because turbulent flow loses signal; contrast-enhanced MRA is less affected." ], "memory_tip": null, "board_traps": [ "Imaging the transverse sinus in-plane with 2D TOF: in-plane saturation mimics thrombosis." ], "key_numbers": [] }, { "subcategory": "Neurological", "title": "Cervical, thoracic, and lumbar spine", "must_know": [ "Spine (posterior) coil, supine, head first for C- and T-spine; landmarks roughly at the thyroid cartilage/mandible angle (C), mid-sternum (T), and just above the iliac crest (L).", "Core protocol: sagittal T1, sagittal T2, sagittal STIR (marrow edema, fracture, infection), axial T2 (and T1 for lumbar); add gadolinium for tumor, infection, MS, or prior surgery.", "Count thoracic levels with a large-FOV sagittal localizer that includes C2 (or count from the sacrum), noting transitional vertebrae.", "Place a sat band anterior to the vertebral bodies to remove swallowing, cardiac, aortic, and bowel motion ghosts.", "Flow compensation and cardiac gating reduce CSF pulsation artifact on T2.", "Post-op lumbar: scar (epidural fibrosis) enhances right away; recurrent disc does not enhance centrally (rim only), so scan soon after injection.", "Gibbs truncation can mimic a syrinx in the cord; increase phase matrix to confirm." ], "memory_tip": null, "board_traps": [ "Calling an enhancing epidural mass in a post-op spine a recurrent disc: scar enhances, disc doesn't.", "Miscounting levels without a localizer that includes C2." ], "key_numbers": [] }, { "subcategory": "Neurological", "title": "SI joints, sacrum/coccyx, total spine, lumbar plexus", "must_know": [ "SI joints: oblique coronal slices parallel to the long axis of the sacrum plus oblique axials; STIR or fat-sat T2 for bone marrow edema (sacroiliitis), T1 for erosions and fat.", "Sacrum/coccyx: sagittal and oblique planes along the sacral curve; STIR for insufficiency fractures.", "Total spine: multiple sagittal stations combined (composed) into one image for counting; used for metastases and cord compression.", "Lumbar plexus (roughly L1-L4 roots): coronal and oblique STIR/fat-sat T2 and T1, often 3D neurography sequences.", "Metastatic marrow replacement is dark on T1 compared with disc; normal adult marrow is brighter than disc on T1." ], "memory_tip": null, "board_traps": [ "Using straight coronal planes for SI joints instead of oblique coronal along the sacrum." ], "key_numbers": [] }, { "subcategory": "Body", "title": "Chest, vascular thorax, brachial plexus", "must_know": [ "Noncardiac chest (mediastinal or chest wall masses): cardiac gating and respiratory triggering or breath-holds; MRI is good at separating cyst from solid tissue and showing invasion.", "Vascular thorax: ECG-gated imaging and contrast-enhanced MRA for aortic aneurysm, dissection, and coarctation; non-contrast SSFP is an option.", "Brachial plexus (C5-T1 roots): roots, trunks, divisions, cords, branches.", "Brachial plexus imaging: coronal and sagittal oblique STIR or Dixon T2 and T1, large FOV covering both sides from the cervical spine to the axilla.", "Use Dixon or STIR rather than spectral fat sat near the neck-chest junction, where the field is uneven." ], "memory_tip": "Plexus order: Roots, Trunks, Divisions, Cords, Branches ('Read The Darn Chart, Buddy').", "board_traps": [ "Using spectral fat sat for brachial plexus: it often fails there." ], "key_numbers": [] }, { "subcategory": "Body", "title": "Breast", "must_know": [ "Prone in a dedicated bilateral breast coil, breasts hanging freely without compression; image both breasts.", "Cancer protocol: T2 (or STIR) plus dynamic 3D fat-suppressed T1 GRE before and several times after gadolinium, with subtraction.", "Schedule premenopausal patients in the second week (about days 7-14) of the menstrual cycle to reduce background enhancement.", "Kinetic curves: Type I persistent (usually benign), Type II plateau (indeterminate), Type III washout (suspicious for cancer).", "Silicone implant protocol: no contrast; silicone-selective sequences (fat and water suppressed) and silicone-suppressed images.", "Intracapsular implant rupture shows the 'linguine sign' (collapsed shell lines floating in silicone).", "ACR breast MRI accreditation calls for thin slices (3 mm or less) and in-plane pixel size of 1 mm or less." ], "memory_tip": null, "board_traps": [ "Giving gadolinium for a silicone implant integrity exam: it's not needed.", "Calling a Type III washout curve benign." ], "key_numbers": [ { "label": "Best cycle timing", "value": "about days 7-14" } ] }, { "subcategory": "Body", "title": "Liver, pancreas, adrenals, kidneys", "must_know": [ "Torso phased array, supine, breath-holds at end-expiration (or respiratory triggering); landmark at the xiphoid/lower costal margin.", "Liver protocol: in/out-of-phase GRE, T2 (fat-sat), DWI, and dynamic 3D fat-sat T1 GRE before and after gadolinium in late arterial, portal venous (about 60-70 s), and delayed phases.", "Gadoxetate (hepatobiliary agent) adds a hepatobiliary phase about 20 minutes after injection; normal liver turns bright, lesions without working hepatocytes stay dark.", "HCC: arterial phase hyperenhancement with washout and a capsule on later phases; hemangioma: very bright on T2 with peripheral nodular enhancement that fills in centrally.", "Fatty liver drops signal on out-of-phase; iron overload drops signal on in-phase (the longer TE) and on T2*.", "Pancreas is normally bright on fat-sat T1; adenocarcinoma is dark on fat-sat T1 and enhances less than normal pancreas.", "Adrenal adenoma loses signal on out-of-phase images (intracellular fat); pheochromocytoma is often very bright on T2.", "Kidneys: compare pre- and post-contrast (subtraction) to prove enhancement; angiomyolipoma contains macroscopic fat that drops out with fat sat." ], "memory_tip": null, "board_traps": [ "Mixing up which echo shows iron vs fat: fat drops on out-of-phase, iron drops on in-phase (longer TE).", "Breath-holding at inspiration inconsistently: expiration is more reproducible." ], "key_numbers": [ { "label": "Portal venous phase", "value": "about 60-70 s" }, { "label": "Gadoxetate hepatobiliary phase", "value": "about 20 min" } ] }, { "subcategory": "Body", "title": "MRCP and MR enterography", "must_know": [ "MRCP: heavily T2-weighted (very long TE) sequences so static fluid in bile and pancreatic ducts is bright and everything else is dark.", "Prep: NPO about 4 hours or more to reduce bowel fluid, distend the gallbladder, and reduce peristalsis.", "Negative oral agents (e.g., pineapple or blueberry juice, which contain manganese) darken overlying bowel fluid.", "Techniques: 2D thick-slab single-shot radial slabs and 3D respiratory-triggered FSE, reviewed with MIP; stones appear as dark filling defects.", "Enterography: drink a large volume of biphasic oral contrast over about 45-60 minutes, then glucagon or an antispasmodic to slow peristalsis.", "Enterography sequences: single-shot T2, SSFP, DWI, and post-gadolinium fat-sat T1 (enteric phase) for Crohn disease activity and complications.", "Glucagon is contraindicated with pheochromocytoma and insulinoma and with known glucagon allergy." ], "memory_tip": null, "board_traps": [ "Expecting stones to be bright on MRCP: they are dark filling defects in bright bile." ], "key_numbers": [] }, { "subcategory": "Body", "title": "Vascular abdomen and pelvis (MRA, MRV)", "must_know": [ "Renal and mesenteric MRA: contrast-enhanced 3D spoiled GRE, breath-hold, timed with bolus tracking or a test bolus; renal artery stenosis and fibromuscular dysplasia are common indications.", "Aorta and iliacs: aneurysm size, dissection, and pre-procedure planning.", "Non-contrast options include SSFP-based inflow techniques for renal arteries when gadolinium is unwise.", "MRV of IVC, iliac, and pelvic veins: delayed post-contrast phases, 2D TOF, or SSFP to evaluate thrombosis and compression syndromes.", "With sequential k-space ordering start the scan about half the acquisition time before peak arterial arrival; with centric ordering start at peak arrival." ], "memory_tip": null, "board_traps": [ "Starting a centric CE-MRA early 'to be safe': the center of k-space then catches the pre-peak contrast." ], "key_numbers": [] }, { "subcategory": "Body", "title": "Pelvis: female, male, bladder, rectum", "must_know": [ "Pelvic phased array; an antispasmodic (when ordered) reduces bowel motion; small FOV high-resolution T2 in planes angled to the organ.", "Uterus on T2: bright endometrium, dark junctional zone, intermediate outer myometrium; a junctional zone of 12 mm or more suggests adenomyosis.", "Image the uterus with sagittal plus true axial and coronal planes oriented to the uterine body; fibroids are usually dark on T2.", "Prostate (multiparametric, PI-RADS): high-resolution T2, DWI/ADC with high b-value (1400 s/mm2 or more), and DCE; cancer is dark on T2 and restricts diffusion.", "Prostate prep: empty rectum (evacuation or enema per site), antispasmodic; post-biopsy hemorrhage can obscure tumor, so waiting at least about 6 weeks is advised.", "Normal peripheral zone of the prostate is bright on T2; most cancers arise there.", "Rectal cancer staging: high-resolution T2 without fat sat, oblique axial perpendicular to the tumor; assess the mesorectal fascia.", "Bladder imaging works best with a moderately distended bladder." ], "memory_tip": null, "board_traps": [ "Using fat sat on rectal T2 staging images: the plain T2 shows the mesorectal fat planes best.", "Expecting prostate cancer to be bright on T2: it is dark." ], "key_numbers": [ { "label": "Adenomyosis", "value": "junctional zone >=12 mm" }, { "label": "Prostate high b-value", "value": ">=1400 s/mm2" } ] }, { "subcategory": "Musculoskeletal", "title": "TMJ, sternum, and SC joints", "must_know": [ "TMJ: bilateral small surface coils; oblique sagittal slices perpendicular to the long axis of each mandibular condyle and oblique coronals parallel to it.", "Image closed-mouth and open-mouth (PD/T2) to see disc position and motion; a bite block allows stepwise positions for CINE.", "The normal disc is a bow tie shape sitting on the condyle; anterior disc displacement is the most common finding.", "Sternum and SC joints: surface coil, axial and oblique coronal planes; prone positioning can reduce respiratory motion; STIR for edema and infection." ], "memory_tip": null, "board_traps": [ "Using true sagittal TMJ planes instead of angling to each condyle." ], "key_numbers": [] }, { "subcategory": "Musculoskeletal", "title": "Shoulder", "must_know": [ "Dedicated shoulder coil, arm at the side in neutral or slight external rotation (thumb up); internal rotation overlaps tendons.", "Shift the patient so the shoulder is as close to isocenter as possible; off-center positions hurt fat sat and SNR.", "Oblique coronal parallel to the supraspinatus muscle/tendon; oblique sagittal perpendicular to it (parallel to the glenoid face); axials from the AC joint through the inferior glenoid.", "Rotator cuff: supraspinatus, infraspinatus, teres minor, subscapularis; the supraspinatus is most often torn.", "MR arthrogram (with ABER position: abducted, externally rotated) best shows labral tears such as the anterior-inferior labrum.", "Magic angle: on short-TE sequences, tendon fibers at about 55 degrees to B0 look bright and mimic tendinopathy; check a long-TE T2." ], "memory_tip": "Cuff = SITS: Supraspinatus, Infraspinatus, Teres minor, Subscapularis.", "board_traps": [ "Calling magic angle signal on a PD image a tear.", "Positioning in internal rotation." ], "key_numbers": [ { "label": "Magic angle", "value": "about 55 degrees to B0" } ] }, { "subcategory": "Musculoskeletal", "title": "Elbow, wrist, hand, fingers, thumb, upper-extremity long bones", "must_know": [ "Elbow: arm extended and supinated at the side or overhead in a prone 'superman' position; coronal plane parallel to the humeral epicondyles.", "Elbow targets: ulnar collateral ligament, common extensor tendon (lateral epicondylitis), distal biceps tendon (flexed, abducted, supinated position helps).", "Wrist: dedicated wrist coil, superman position or at the side; thin coronal slices parallel to the radiocarpal joint, axials for the carpal tunnel and median nerve.", "Wrist targets: TFCC, scapholunate ligament (3D GRE helps), scaphoid fracture and proximal pole avascular necrosis (dark on T1).", "Thumb planes are prescribed to the thumb itself, which sits oblique to the hand; skier's (gamekeeper's) thumb is a tear of the ulnar collateral ligament of the 1st MCP joint.", "Fingers: small FOV, planes along the finger; evaluate tendons, pulleys, and collateral ligaments.", "Long bones: large FOV including the nearest joint for localization; place a marker over any palpable lump." ], "memory_tip": null, "board_traps": [ "Using hand planes for the thumb.", "Leaving out the nearest joint on a long-bone study." ], "key_numbers": [] }, { "subcategory": "Musculoskeletal", "title": "Hip, bony pelvis, lower-extremity long bones", "must_know": [ "Supine, feet internally rotated (about 15 degrees, taped) to elongate the femoral necks.", "Bony pelvis: large FOV bilateral coronal T1 and STIR for occult hip or pelvic fractures and avascular necrosis.", "Avascular necrosis of the femoral head: dark serpiginous line on T1; 'double-line sign' on T2.", "Dedicated hip: small FOV unilateral with oblique axial (along the femoral neck) and radial or oblique sagittal planes for labral tears; arthrography improves labral detail.", "Lower-extremity long bones: large FOV with a joint included; STIR shows stress fractures and marrow edema." ], "memory_tip": null, "board_traps": [ "Using only a small-FOV unilateral hip for suspected occult fracture: start with bilateral coronal T1 and STIR." ], "key_numbers": [] }, { "subcategory": "Musculoskeletal", "title": "Knee", "must_know": [ "Knee coil, supine, feet first, knee slightly flexed (about 5-10 degrees); landmark at the apex/lower pole of the patella (joint line).", "Sagittal slices angled parallel to the ACL (about 10-15 degrees from true sagittal, parallel to the inner surface of the lateral femoral condyle); coronal parallel to the posterior femoral condyles.", "Menisci are dark on all sequences; a tear is signal reaching an articular surface, best seen on short-TE PD images, on at least 2 slices.", "ACL tear clues: discontinuous fibers and bone bruises in the lateral femoral condyle and posterolateral tibial plateau.", "A Baker (popliteal) cyst sits between the medial head of the gastrocnemius and the semimembranosus tendon.", "Fat-suppressed PD/T2 shows bone bruises, edema, and cartilage defects." ], "memory_tip": null, "board_traps": [ "Calling meniscal signal that does not reach an articular surface a tear.", "Prescribing sagittals straight A-P: the ACL may not be seen along its length." ], "key_numbers": [] }, { "subcategory": "Musculoskeletal", "title": "Ankle and foot", "must_know": [ "Ankle coil, supine, foot in neutral (about 90 degrees) or slight plantar flexion, which also reduces magic angle on tendons.", "Ankle planes: axial, sagittal, coronal; the anterior talofibular ligament (most often sprained) is best seen on axials.", "Key tendons: Achilles, posterior tibial, peroneal (fibular) tendons.", "Foot planes are long axis and short axis to the metatarsals; diabetic foot osteomyelitis replaces marrow fat (dark on T1) with bright STIR and enhancement.", "Morton neuroma: between the 3rd and 4th metatarsal heads (most often); prone positioning can help.", "Plantar fasciitis: thickened plantar fascia with edema at the calcaneal attachment." ], "memory_tip": null, "board_traps": [ "Diagnosing osteomyelitis from STIR edema alone without T1 marrow replacement." ], "key_numbers": [] }, { "subcategory": "Musculoskeletal", "title": "Arthrogram, runoff MRA, soft tissue masses and infection", "must_know": [ "Direct arthrogram: time-out and sterile technique, then image-guided injection of dilute gadolinium into the joint (intra-articular use is off-label) followed promptly by fat-sat T1 in three planes plus a fat-sat T2.", "Indirect arthrogram: IV gadolinium, exercise the joint, then scan after a delay as contrast diffuses into the joint.", "Runoff MRA: multistation bolus-chase CE-MRA (abdomen, thighs, calves) with a moving table; time-resolved MRA of the calves/feet helps avoid venous contamination.", "Sub-systolic thigh compression cuffs can slow venous return during runoff.", "Soft tissue mass: skin marker over the lesion, large FOV covering the whole compartment, T1, STIR/fat-sat T2, and fat-sat post-gadolinium T1 with subtraction.", "Lipoma follows fat on every sequence (drops on fat sat); abscess shows rim enhancement and restricted diffusion centrally." ], "memory_tip": null, "board_traps": [ "Waiting too long after a direct arthrogram injection: contrast absorbs and the joint loses distention.", "Leaving the skin marker off for a palpable mass." ], "key_numbers": [] } ] } ], "last_minute_review": [ "Larmor: 42.58 MHz/T for hydrogen; 63.86 MHz at 1.5 T, 127.7 MHz at 3 T.", "T1 = 63% recovery of longitudinal magnetization; T2 = decay to 37% of transverse magnetization; T2* < T2 <= T1.", "TR controls T1 weighting, TE controls T2 weighting: short/short = T1, long/long = T2, long TR/short TE = PD.", "Null point TI = 0.69 x T1; STIR nulls fat (~150-170 ms at 1.5 T), FLAIR nulls CSF (~2000-2500 ms).", "Never use STIR after gadolinium; it nulls enhancing tissue.", "SNR goes up with bigger voxels, more NEX (square root), narrower bandwidth (square root), longer TR, shorter TE, higher field, better coils.", "Doubling NEX: SNR x1.41, time x2. Halving bandwidth: SNR x1.41, more chemical shift.", "Scan time: TR x phase steps x NEX (divide by ETL for FSE, multiply by partitions for 3D).", "Phase matrix sets scan time; frequency matrix does not.", "K-space center = contrast and signal; periphery = detail and edges.", "Aliasing, motion ghosts, and zipper run in the phase direction; chemical shift is in the frequency direction (phase direction in EPI).", "Fix aliasing: larger FOV, phase oversampling, swap phase/frequency.", "Chemical shift worsens with higher field and narrower bandwidth; fat-water shift is about 3.5 ppm (~220 Hz at 1.5 T).", "Out-of-phase signal drop = fat and water in the voxel (adrenal adenoma, fatty liver); in-phase drop = iron.", "Susceptibility is worst on GRE and EPI; use FSE, short TE, wide bandwidth near metal.", "Parallel imaging divides time by the acceleration factor and costs at least the square root of it in SNR.", "Acute infarct: bright DWI, dark ADC; bright on both = T2 shine-through.", "TOF: put the sat band where the unwanted blood comes from (superior for arterial head/neck, inferior for MRV).", "Phase contrast needs VENC set just above peak velocity; too low aliases.", "Spectroscopy: NAA 2.0, creatine 3.0, choline 3.2, lactate 1.3 ppm doublet (inverts at TE ~135-144 ms).", "Gadolinium: paramagnetic, shortens T1; 0.1 mmol/kg typical; 0.5 mmol/mL agents = 0.2 mL/kg, gadobutrol = 0.1 mL/kg.", "NSF risk: eGFR below 30, AKI, or dialysis, mainly with older linear Group I agents.", "Premed for a prior GBCA reaction: prednisone 50 mg at 13, 7, 1 h plus diphenhydramine 50 mg at 1 h.", "Zones: I public, II screening, III restricted (MR personnel control), IV magnet room.", "MR Safe green, MR Conditional yellow triangle, MR Unsafe red circle with slash.", "Whole-body SAR: 2 W/kg Normal Mode, 4 W/kg First Level; head 3.2 W/kg; SAR scales with B0 squared.", "FDA static field: 8 T for adults/children/infants over 1 month, 4 T for neonates.", "Translational pull is strongest at the bore entrance; torque is strongest at isocenter.", "Code in the scanner: CPR and move the patient out of Zone IV; quench only for a pinned person or fire.", "Hearing protection for every patient; gradients make the noise and cause nerve stimulation." ] }