{
"id": "ct-procedures",
"modality": "CT",
"category": "Procedures",
"title": "CT Procedures: Protocols, Anatomy and Timing",
"minutes": 9,
"slides": [
{
"id": 1,
"diagram": "title",
"heading": "CT Procedures",
"bullets": [
"71 of 165 scored questions (43.0%)",
"Head, neck, chest, cardiac, abdomen and pelvis",
"Protocols, anatomy landmarks and contrast timing"
],
"narration": "Welcome to CT Procedures, the biggest category on the CT boards. It's 71 of the 165 scored questions, about 43 percent of your score. We'll move head to toe through the head, neck, chest, heart, abdomen and pelvis. For each region you'll learn the protocol choices, the anatomy landmarks the exam loves, and the contrast timing that makes or breaks a scan. Master this one category and you're almost halfway home. Let's begin.",
"svg": ""
},
{
"id": 2,
"diagram": "epidural-vs-subdural",
"heading": "Head CT and bleeds",
"bullets": [
"Noncontrast head first for trauma and stroke",
"Angle along supraorbitomeatal line to spare lenses",
"Epidural: lens shaped, arterial, stops at sutures",
"Subdural: crescent, bridging veins, crosses sutures",
"Acute blood about 50-80 HU"
],
"narration": "Head CT starts noncontrast for trauma and acute stroke, because you must rule out bleeding before clot-busting drugs, and contrast can hide or mimic blood. Angle the scan plane along the supraorbitomeatal line, or tilt the gantry, to keep the lenses out of the beam. Now the classic pair. An epidural hematoma is lens shaped, usually arterial from the middle meningeal artery, and stops at the sutures. A subdural is crescent shaped, from torn bridging veins, and crosses sutures. Acute blood measures about 50 to 80 Hounsfield units.",
"svg": ""
},
{
"id": 3,
"diagram": "perfusion-core-penumbra",
"heading": "Stroke CTA and perfusion",
"bullets": [
"Stroke CTA: aortic arch to vertex",
"Perfusion maps: CBF, CBV, MTT, Tmax",
"Core: CBV down; penumbra: MTT up, CBV kept",
"MTT = CBV / CBF"
],
"narration": "For stroke CTA, cover from the aortic arch to the vertex, usually with bolus tracking in the arch. CT perfusion scans the same slab over and over during the bolus and builds maps of cerebral blood flow, cerebral blood volume, mean transit time and time to maximum. The key distinction: dead infarct core has reduced blood volume, while the salvageable penumbra has a prolonged mean transit time with blood volume kept. Tie it together with the central volume principle: mean transit time equals blood volume divided by blood flow.",
"svg": ""
},
{
"id": 4,
"diagram": "neck-levels",
"heading": "Neck landmarks",
"bullets": [
"Hyoid about C3, thyroid cartilage C4-C5",
"Cricoid about C6: larynx ends, trachea begins",
"Phonation 'eee' tests vocal cord motion",
"Modified Valsalva distends pyriform sinuses",
"Shoulders down, quiet breathing, no swallowing"
],
"narration": "Neck questions love vertebral landmarks. The hyoid sits at about C3, and the thyroid cartilage at about C4 to C5. The cricoid cartilage, at about C6, is where the larynx ends and the trachea and esophagus begin. Special maneuvers help too. Phonation, having the patient say eee, tests vocal cord motion. A modified Valsalva, blowing against closed lips, distends the pyriform sinuses. And always pull the shoulders down, ask for quiet breathing, and tell the patient not to swallow during the scan.",
"svg": ""
},
{
"id": 5,
"diagram": "aortic-arch",
"heading": "Chest, aorta and PE",
"bullets": [
"Arch: brachiocephalic, L common carotid, L subclavian",
"Carina about T4-T5",
"Dissection: noncontrast first, then CTA",
"PE CTA: track main pulmonary artery, 4-5 mL/s"
],
"narration": "The aortic arch gives off three branches in order: the brachiocephalic, or innominate, artery, then the left common carotid, then the left subclavian. The carina sits at about T4 to T5, the level of the sternal angle. For suspected aortic dissection, run a noncontrast series first to catch intramural hematoma, then the CTA. For pulmonary embolism, put the bolus tracking region of interest in the main pulmonary artery and inject at about 4 to 5 milliliters per second with a saline chaser. Track in the aorta and you trigger too late.",
"svg": ""
},
{
"id": 6,
"diagram": "ecg-gating",
"heading": "Cardiac CT gating",
"bullets": [
"Target heart rate 60-65 bpm or less",
"Prospective: one phase, about 70-75% R-R, low dose",
"Retrospective: helical, low pitch, any phase, high dose",
"Calcium score: no contrast, 3 mm, 120 kVp"
],
"narration": "Coronary CTA needs a slow, steady heart, ideally 60 to 65 beats per minute or less, often helped by metoprolol and sublingual nitroglycerin. Prospective gating, called step and shoot, exposes only during one chosen phase, usually mid-diastole around 70 to 75 percent of the R to R interval. It's the low-dose option. Retrospective gating scans helically at low pitch with continuous exposure, so any phase can be reconstructed, but dose is higher. Calcium scoring uses no contrast, 3 millimeter slices at 120 k V p, scored by the Agatston method.",
"svg": ""
},
{
"id": 7,
"diagram": "liver-phases",
"heading": "Liver phases",
"bullets": [
"Dual supply: portal vein 75%, hepatic artery 25%",
"Late arterial 35-40 s: HCC, FNH, hypervascular mets",
"Portal venous 60-70 s: routine, hypovascular mets",
"Delayed 3-5 min: HCC washout, hemangioma fill-in"
],
"narration": "The liver has a dual blood supply, about 75 percent from the portal vein and 25 percent from the hepatic artery, and that drives its phases. The late arterial phase, about 35 to 40 seconds, lights up hypervascular lesions like hepatocellular carcinoma, focal nodular hyperplasia and hypervascular metastases. The portal venous phase, about 60 to 70 seconds, is your routine abdomen and best for hypovascular metastases such as colon cancer. The delayed phase, at 3 to 5 minutes, shows hepatocellular carcinoma washout and hemangioma filling in from the edges.",
"svg": ""
},
{
"id": 8,
"diagram": "adrenal-washout",
"heading": "Pancreas, adrenals, kidneys",
"bullets": [
"Pancreatic phase about 40-50 s, water as oral",
"Adrenal adenoma: 10 HU or less unenhanced",
"Washout at 15 min: absolute 60%, relative 40%",
"Nephrographic 80-120 s: best for renal masses"
],
"narration": "For a pancreas protocol, the pancreatic phase at about 40 to 50 seconds gives the best contrast between the bright gland and a dark adenocarcinoma, and water is the oral contrast so it doesn't hide the duodenum. On the adrenals, a noncontrast density of 10 Hounsfield units or less suggests a lipid-rich adenoma. Adenomas also wash out fast: at a 15 minute delay, absolute washout of 60 percent or more, or relative washout of 40 percent or more. For kidneys, the nephrographic phase, about 80 to 120 seconds, is best for finding masses.",
"svg": ""
},
{
"id": 9,
"diagram": "aortic-branch-levels",
"heading": "Vessel levels, stones, GI",
"bullets": [
"Celiac T12, SMA L1, renals L1-L2, IMA L3",
"Aortic bifurcation about L4",
"Stone CT: noncontrast, low dose; prone for UVJ",
"GI bleed CTA: no positive oral contrast",
"Bladder rupture: retrograde CT cystogram"
],
"narration": "Memorize the aortic branch levels: the celiac trunk at about T12, the superior mesenteric artery at L1, the renal arteries at L1 to L2, and the inferior mesenteric artery at L3. The aorta bifurcates at about L4. A renal stone CT is noncontrast and low dose, and scanning prone separates a stone stuck at the ureterovesical junction from one already in the bladder. For a GI bleed CTA, never give positive oral contrast, because it hides active bleeding. And for suspected bladder rupture, do a retrograde CT cystogram, filling through a Foley.",
"svg": ""
},
{
"id": 10,
"diagram": "summary",
"heading": "Lock these in",
"bullets": [
"Epidural = lens, arterial; subdural = crescent, venous",
"Perfusion core: CBV down; penumbra: MTT up, CBV kept",
"PE CTA: track in main pulmonary artery, 4-5 mL/s",
"Liver: late arterial 35-40 s, portal venous 60-70 s",
"Adenoma: 10 HU or less; washout 60% abs, 40% rel"
],
"narration": "Let's lock it in. Epidural is lens shaped and arterial; subdural is crescent shaped and venous. On perfusion, core has low blood volume, while penumbra has a long mean transit time with blood volume kept. For PE, track in the main pulmonary artery at 4 to 5 milliliters per second. Liver timing is late arterial at 35 to 40 seconds and portal venous at 60 to 70 seconds. And an adrenal adenoma is 10 Hounsfield units or less, with absolute washout of 60 percent or relative washout of 40 percent. Now hit Practice this chapter and test yourself.",
"svg": ""
}
]
}