Clinical Practice: Neuroradiology
Core concepts
Head CT remains the first study for acute neurologic presentations. Know the signs of acute infarction (loss of gray-white differentiation, insular ribbon sign, hyperdense MCA sign) and that CT is often normal in the first hours. Understand the Alberta Stroke Program Early CT Score (ASPECTS) as a scoring system for MCA territory ischemia and its role in treatment decisions. For hemorrhage, distinguish hypertensive basal ganglia hemorrhage from lobar hemorrhage (amyloid angiopathy in older patients).
Traps in questions
- Calling a hyperdense MCA sign hemorrhage; it reflects thrombus.
- Missing a subdural hematoma because it is isodense to cortex on a subacute scan.
- Overlooking posterior fossa pathology on CT due to beam-hardening artifact; MRI is more sensitive.
- Misinterpreting a ring-enhancing lesion as tumor without considering abscess.
Rule of thumb
On CT, acute blood is hyperdense (about 60-80 HU); if a hyperdensity persists on follow-up, consider that it may be calcification or contrast rather than acute hemorrhage.
Worked example
An elderly patient on anticoagulation presents with headache. Noncontrast CT shows a crescentic extra-axial collection crossing sutures. This is a subdural hematoma; epidural hematomas are biconvex and limited by sutures.
Clinical Practice: Musculoskeletal Imaging
Core concepts
MSK questions test fracture description (location, displacement, angulation, intra-articular extension) and recognition of classic patterns. Know the Ottawa ankle and knee rules as decision tools that reduce unnecessary radiography. Understand that MRI is the modality of choice for internal derangement (meniscal tear, ACL tear) and for occult fractures (hip, scaphoid) when radiographs are negative.
Traps in questions
- Missing a scaphoid fracture on initial radiographs; repeat imaging or MRI is indicated if snuffbox tenderness persists.
- Confusing a normal growth plate with a fracture in pediatric patients.
- Overlooking posterior shoulder dislocation (lightbulb sign, trough line).
- Calling a lytic lesion benign without considering metastasis or myeloma in older adults.
Rule of thumb
Ottawa ankle rule: imaging is indicated only if there is pain near the malleoli plus bone tenderness at the posterior edge or tip of either malleolus or inability to bear weight four steps, in patients aged 55 or older or with tenderness.
Worked example
A young athlete has a twisting knee injury and a positive Lachman test. Radiographs are normal. The next step is MRI to evaluate the ACL, since physical examination already suggests ligamentous injury and radiographs cannot exclude it.
Clinical Practice: Ultrasound and Obstetric Imaging
Core concepts
Obstetric ultrasound questions emphasize dating, viability, and ectopic pregnancy. Know that a gestational sac is visible transvaginally at about 5 weeks, a yolk sac at about 5.5 weeks, and an embryo with cardiac activity at about 6 weeks. Understand the discriminatory zone (serum hCG level above which an intrauterine sac should be seen) and that a pseudogestational sac in ectopic pregnancy lacks a double decidual sign.
Traps in questions
- Diagnosing a nonviable pregnancy from a single scan without follow-up criteria.
- Missing an ectopic pregnancy because a pseudogestational sac was called normal.
- Confusing a corpus luteum cyst with an adnexal mass requiring surgery.
- Overlooking an ectopic pregnancy in a patient with an intrauterine device.
Rule of thumb
A gestational sac with a yolk sac or embryo confirms an intrauterine pregnancy; if the hCG is above the discriminatory zone and no intrauterine sac is seen, ectopic pregnancy must be excluded.
Worked example
A patient with pelvic pain has a positive pregnancy test and an empty uterus on transvaginal ultrasound with an adnexal mass. This is a pregnancy of unknown location or ectopic until proven otherwise; follow-up hCG and repeat ultrasound are indicated.
Clinical Practice: Nuclear Medicine and Molecular Imaging
Core concepts
Nuclear medicine questions test tracer physiology and clinical indications. Know FDG PET/CT for oncologic staging and response assessment, and that physiologic uptake occurs in brain, myocardium, liver, kidneys, and bowel. Understand ventilation-perfusion scanning for pulmonary embolism and the criteria for high probability (mismatched defects).
Traps in questions
- Calling physiologic uptake pathologic (e.g., brown fat, muscle after exercise).
- Forgetting that FDG PET is not specific for malignancy; infection and inflammation also take up FDG.
- Misinterpreting a V/Q scan in a patient with prior PE or chronic lung disease.
- Overlooking that a normal V/Q scan effectively excludes PE in appropriate pretest probability.
Rule of thumb
A high-probability V/Q scan shows two or more segmental mismatched perfusion defects with normal ventilation; a normal scan excludes PE in most patients.
Worked example
A patient with suspected PE and normal chest radiograph has a V/Q scan showing a single subsegmental mismatched defect. This does not meet high-probability criteria; further evaluation with CTPA may be needed.
Imaging Physics: Radiography, CT, and Radiation Safety
Core concepts
Physics questions test the production of x-rays (bremsstrahlung and characteristic radiation), beam quality (kVp affects penetration and contrast), and detector technology. Understand CT reconstruction (filtered back projection versus iterative reconstruction), pitch, and the relationship between pitch and dose. Know the ALARA principle, the linear no-threshold model, and typical dose ranges.
Traps in questions
- Confusing kVp with mAs effects on contrast versus noise.
- Assuming higher pitch always lowers dose without considering image quality.
- Forgetting that CT dose is higher than radiography and that pediatric patients require adjusted protocols.
- Misapplying the inverse square law to non-point sources.
Rule of thumb
Increasing kVp raises beam energy and penetration but lowers contrast; increasing mAs raises dose and reduces noise without changing contrast.
Worked example
A CT protocol uses pitch 1.5 instead of 1.0. Higher pitch shortens scan time and generally reduces dose but may increase noise; the tradeoff must be evaluated for diagnostic quality.
Imaging Physics: MRI and Ultrasound Physics
Core concepts
MRI questions test T1 and T2 relaxation, sequence weighting, and safety. Know that fat is bright on T1 and T2, fluid is dark on T1 and bright on T2, and that gadolinium shortens T1. Understand the static magnetic field, gradient fields, and radiofrequency hazards, and the absolute contraindication of certain implants.
Ultrasound questions test the piezoelectric effect, frequency-resolution tradeoffs, and artifact recognition (shadowing, enhancement, reverberation).
Traps in questions
- Confusing T1 and T2 weighting; check TR and TE.
- Assuming all gadolinium agents behave identically; nephrogenic systemic fibrosis risk differs.
- Forgetting that higher ultrasound frequency improves resolution but reduces penetration.
- Misidentifying artifact as pathology (e.g., reverberation from bowel gas).
Rule of thumb
Short TR and short TE produce T1 weighting; long TR and long TE produce T2 weighting; fluid is bright on T2.
Worked example
An ultrasound of a gallbladder shows shadowing from gallstones. Shadowing occurs because stones reflect and absorb sound, reducing echoes deep to the stone; this is a true finding, not artifact.
Noninterpretive Skills: Quality, Safety, and Communication
Core concepts
Noninterpretive questions test quality improvement, patient safety, communication, and professionalism. Know the distinction between a diagnostic error, a near miss, and an adverse event, and the role of root cause analysis in systems failures. Understand informed consent elements, HIPAA privacy rules, and appropriate reporting of critical results.
Traps in questions
- Blaming an individual for a systems error.
- Forgetting that critical results require documented communication to the responsible clinician.
- Misapplying HIPAA to permit disclosure without patient authorization.
- Confusing informed consent with a signed form alone; the discussion matters.
Rule of thumb
A critical result must be communicated directly to the responsible clinician and documented, including time, recipient, and content.
Worked example
A radiologist identifies a tension pneumothorax on a chest radiograph. The finding must be communicated immediately to the treating clinician and documented, not simply entered in the report and left for later review.
Noninterpretive Skills: Ethics, Law, and Practice Management
Core concepts
Questions test the ethical principles of beneficence, nonmaleficence, autonomy, and justice, and how they apply to imaging utilization. Know the concept of appropriate use criteria and the radiologist's role in stewardship. Understand malpractice elements (duty, breach, causation, damages), peer review protections, and conflicts of interest.
Traps in questions
- Choosing autonomy over beneficence when a patient refuses a necessary study; autonomy generally prevails for competent adults.
- Confusing standard of care with best possible care.
- Overlooking that self-referral and financial conflicts are regulated.
- Assuming peer review records are always discoverable; protections vary by jurisdiction.
Rule of thumb
A malpractice claim requires all four elements: duty, breach, causation, and damages; missing any one defeats the claim.
Worked example
A competent adult declines a recommended contrast-enhanced CT. The radiologist should respect the decision after explaining risks and benefits, document the discussion, and offer alternatives; proceeding without consent is not appropriate.