Radiology Syllabus

On what physical principle does diagnostic ultrasound imaging depend?

Ultrasound uses high-frequency sound waves (typically 2-15 MHz) emitted by a piezoelectric transducer; echoes reflected at tissue interfaces (from acoustic impedance differences) are detected and used to build the image (pulse-echo principle).

State the relationship between ultrasound transducer frequency, image resolution, and depth of penetration.

Higher frequency gives better spatial resolution but less penetration (attenuates faster). Lower frequency penetrates deeper but with lower resolution. Thus high-frequency probes are used for superficial structures and low-frequency probes for deep abdominal imaging.

What is the Doppler effect as applied to ultrasound, and give the Doppler equation.

The Doppler effect is the frequency shift of echoes reflected from moving blood, used to measure flow velocity: $$\Delta f = \frac{2 f_{0} v \cos\theta}{c}$$ where $f_0$ is transmitted frequency, $v$ is blood velocity, $\theta$ is the insonation angle, and $c$ is sound speed in tissue.

Define the ultrasound terms anechoic, hyperechoic, and hypoechoic, with an example of each.

Anechoic: no internal echoes, appears black (e.g., simple cyst, urine-filled bladder). Hyperechoic: brighter than surrounding tissue (e.g., bone surface, calculi with shadowing). Hypoechoic: darker than surrounding tissue (e.g., many solid tumors, lymph nodes).

What is the underlying principle of nuclear medicine imaging, and how does it differ from CT/MRI?

Nuclear medicine uses radiopharmaceuticals (radioactive tracers) administered to the patient; the emitted gamma radiation is detected to form functional/physiological images. Unlike CT/MRI (primarily anatomical), it images metabolism and function.

What radiotracer is most commonly used in PET oncology imaging, and what does its uptake reflect?

$\text{}^{18}\text{F}$-fluorodeoxyglucose (FDG), a glucose analog. Uptake reflects glucose metabolic activity, which is elevated in most malignancies (as well as inflammation and infection).

What radionuclide is most widely used in general nuclear medicine, and what is its physical half-life and principal gamma energy?

Technetium-99m ($\text{}^{99m}\text{Tc}$). Physical half-life ≈ 6 hours; principal gamma photon energy ≈ 140 keV, ideal for gamma-camera imaging.

Define interventional radiology and give three common procedures.

Interventional radiology uses image guidance (fluoroscopy, US, CT) to perform minimally invasive diagnostic and therapeutic procedures. Examples: angioplasty/stenting, embolization (e.g., uterine fibroid embolization, GI bleed), image-guided biopsy, and drain/catheter placement.

What is the Seldinger technique?

A method of gaining safe percutaneous access to a vessel or hollow structure: needle puncture, insertion of a guidewire through the needle, removal of the needle, then passage of a catheter/sheath over the wire into the lumen.

What is TIPS and what is its main indication?

Transjugular Intrahepatic Portosystemic Shunt — an IR procedure creating a channel between the portal and hepatic veins to reduce portal hypertension. Main indications: refractory variceal bleeding and refractory ascites in cirrhosis.

In neuroimaging of acute stroke, why is non-contrast CT performed first?

Non-contrast CT rapidly and reliably excludes intracranial hemorrhage, which is a contraindication to thrombolysis. It also detects early ischemic changes (loss of gray-white differentiation, hyperdense vessel sign), guiding treatment decisions.

How do acute (hyperacute) ischemic infarcts and acute hemorrhage appear on non-contrast CT?

Acute ischemic infarct: subtle hypodensity with loss of gray-white differentiation and sulcal effacement (may be normal in the first hours). Acute hemorrhage: hyperdense (bright, ~50-80 HU) collection.

On brain MRI, which sequence detects acute ischemic stroke earliest, and how does the infarct appear?

Diffusion-weighted imaging (DWI) detects acute infarction within minutes: the infarct core shows restricted diffusion — bright on DWI and dark on the ADC map.

Describe the classic imaging appearance and shape of epidural versus subdural hematomas on CT.

Epidural hematoma: biconvex (lentiform) hyperdensity that does not cross suture lines, usually arterial (middle meningeal artery). Subdural hematoma: crescent-shaped hyperdensity that crosses sutures but not the midline, usually venous (bridging veins).

What is the imaging modality of choice for suspected pulmonary embolism, and what is the classic finding?

CT pulmonary angiography (CTPA). Classic finding: an intraluminal filling defect within a pulmonary artery. A V/Q scan is an alternative when CT/contrast is contraindicated.

List classic chest radiograph signs of pleural effusion and of pneumothorax.

Pleural effusion: blunting of the costophrenic angle, meniscus sign, layering on decubitus views. Pneumothorax: visible visceral pleural line with absent lung markings peripherally; tension pneumothorax shows mediastinal shift and diaphragm depression.

On a chest X-ray, describe the silhouette sign and its diagnostic use.

The silhouette sign: loss of a normal soft-tissue border occurs when an adjacent opacity is of the same density and in anatomic contact. It localizes pathology — e.g., loss of the right heart border indicates right middle lobe disease; loss of a diaphragmatic border indicates lower lobe disease.

What is the imaging modality of choice for suspected acute appendicitis in adults, and list classic CT findings.

CT of the abdomen and pelvis (ultrasound preferred in children/pregnancy). CT findings: dilated appendix >6 mm, wall thickening/enhancement, periappendiceal fat stranding, appendicolith, and possibly abscess.

Describe the classic imaging findings that distinguish small-bowel obstruction from large-bowel obstruction on abdominal radiograph.

Small-bowel obstruction: dilated central loops >3 cm with valvulae conniventes (lines crossing the full lumen), air-fluid levels. Large-bowel obstruction: peripheral dilated loops >6 cm (cecum >9 cm) with haustra (not crossing the full lumen).

What imaging modality and view best demonstrate free intraperitoneal air (pneumoperitoneum), and what is the sign?

An erect chest X-ray (or left lateral decubitus abdomen) best shows free air as a lucent crescent under the diaphragm. On supine films, Rigler's sign (air on both sides of the bowel wall) suggests pneumoperitoneum.

What is the first-line imaging modality for suspected acute cholecystitis, and give key ultrasound findings.

Ultrasound. Findings: gallstones, gallbladder wall thickening (>3 mm), pericholecystic fluid, and a sonographic Murphy's sign (maximal tenderness over the gallbladder under the probe). HIDA scan can confirm cystic duct obstruction.

Describe the Salter-Harris classification of pediatric physeal (growth plate) fractures.

Type I: through the physis; II: through physis and metaphysis (most common); III: through physis and epiphysis; IV: through metaphysis, physis, and epiphysis; V: crush injury of the physis. Mnemonic SALTR — Slipped, Above, Lower, Through, Rammed.

What is the standard first-line imaging for suspected bone fracture, and when is MRI or CT added?

Plain radiography (X-ray) in at least two orthogonal views is first-line. CT is added for complex/occult fractures and surgical planning; MRI is added for occult fractures, stress fractures, and soft-tissue/ligament/marrow assessment.

Name three imaging features suggesting an aggressive (malignant) versus benign bone lesion.

Aggressive: wide zone of transition (ill-defined margins), permeative/moth-eaten bone destruction, aggressive periosteal reaction (sunburst, Codman triangle), and cortical breakthrough with soft-tissue mass. Benign: narrow well-defined zone of transition, sclerotic margin, no soft-tissue mass.

Why are children more radiosensitive than adults, and what principle governs pediatric radiation dose?

Children have more rapidly dividing cells, longer life expectancy for radiation effects to manifest, and smaller body size (higher dose per exposure). The ALARA principle ("As Low As Reasonably Achievable") governs dose minimization; ultrasound and MRI are preferred when possible.

What is the imaging test of choice for suspected intussusception in a child, and what is the classic sign?

Ultrasound is the diagnostic test of choice; the classic sign is the "target" or "doughnut" sign (and "pseudokidney" on longitudinal view). An air or contrast enema is both diagnostic and therapeutic (reduction).

What is the FAST scan in emergency radiology and what does it assess?

FAST = Focused Assessment with Sonography for Trauma. Bedside ultrasound checking for free fluid (hemorrhage) in four regions: perihepatic (Morison's pouch), perisplenic, pelvis (pouch of Douglas), and pericardium. E-FAST adds assessment for pneumothorax/hemothorax.

What is the ABCDE (or ABCs) systematic approach to reading a trauma chest/abdominal radiograph?

A common mnemonic for CXR is ABCDE: Airway (trachea), Breathing (lungs/pleura), Cardiac (heart size/mediastinum), Diaphragm (and below), Everything else (bones, soft tissues, lines/tubes). It ensures a structured, complete review.

What imaging modality is preferred for staging most solid tumors, and what does the RECIST criteria measure?

CT (often with PET/CT) is standard for staging. RECIST (Response Evaluation Criteria in Solid Tumors) measures tumor response by the change in the sum of the longest diameters of target lesions: complete response, partial response, stable disease, or progressive disease.

What is the imaging investigation of choice for aortic dissection, and describe the key finding.

CT angiography (ECG-gated) is the modality of choice in stable patients; transesophageal echo is used in unstable patients. Key finding: an intimal flap separating a true and false lumen. The Stanford classification divides dissections into Type A (involves ascending aorta) and Type B (does not).