ABR Core Exam flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

Hounsfield unit of water

Water is defined as 0 HU on the CT scale, with air at -1000 HU; CT numbers are calculated from linear attenuation coefficients relative to water.

Half-value layer

The thickness of material that reduces beam intensity by half; equals 0.693 divided by the linear attenuation coefficient and reflects beam quality.

Larmor frequency equation

Precession frequency equals the gyromagnetic ratio times magnetic field strength; protons precess at about 63.9 MHz at 1.5 tesla.

Axial ultrasound resolution

Axial resolution equals spatial pulse length divided by two, which depends on wavelength and number of cycles per pulse; higher frequencies improve it.

CT pitch definition

Pitch is table travel per gantry rotation divided by collimator width; values above one reduce dose but may increase image noise.

Photoelectric versus Compton

Photoelectric absorption dominates at low energies and high atomic number, improving contrast; Compton scatter dominates in soft tissue and degrades image contrast.

Effective dose calculation

Effective dose sums equivalent doses to each tissue multiplied by its tissue weighting factor, expressed in sieverts, and estimates whole-body stochastic risk.

Nyquist limit Doppler

Aliasing occurs when blood velocity exceeds half the pulse repetition frequency; increasing PRF, shifting baseline, or using continuous wave avoids it.

BI-RADS category 4

Category 4 means suspicious for malignancy and warrants biopsy; it is subdivided into 4A, 4B, and 4C by increasing likelihood of cancer.

LI-RADS 5 criteria

In at-risk patients, definite hepatocellular carcinoma requires arterial phase hyperenhancement plus washout, enhancing capsule, or threshold growth on serial imaging.

Sonographic Murphy sign

Focal maximal tenderness over the gallbladder with the transducer during inspiration suggests acute cholecystitis, especially with wall thickening or pericholecystic fluid.

Dawson fingers

Ovoid T2-hyperintense white matter lesions oriented perpendicular to the lateral ventricles, characteristic of multiple sclerosis demyelination.

Adrenal adenoma washout

An adrenal mass with unenhanced attenuation under 10 HU or absolute washout above 60 percent at 15 minutes is likely a benign adenoma.

Codman triangle

Elevated periosteum at the margin of an aggressive bone lesion forms a triangular new-bone wedge, classically seen with osteosarcoma.

Uncal herniation effect

Medial temporal lobe displacement compresses the third cranial nerve causing a blown pupil, and may compress the posterior cerebral artery causing infarction.

PI-RADS 4 or 5

A focal peripheral zone lesion with marked diffusion restriction and early enhancement is suspicious to highly suspicious for clinically significant prostate cancer and warrants biopsy.

Sarcoidosis chest pattern

Bilateral symmetric hilar lymphadenopathy with perilymphatic nodules along bronchovascular bundles and fissures is the classic thoracic appearance of sarcoidosis.

Intussusception target sign

Transverse ultrasound of intussuscepted bowel shows concentric echogenic and hypoechoic rings resembling a target, often in children with colicky pain.

Clear cell renal carcinoma

The most common renal cell carcinoma subtype; it is hypervascular, enhances avidly, and is often T1-hyperintense and T2-heterogeneous on MRI.

Anaphylactoid contrast reaction

Severe hypotension, bronchospasm, or laryngeal edema after contrast requires intramuscular epinephrine 0.3 to 0.5 mg of 1:1000 plus airway support.

ALARA principle

Radiation dose should be kept as low as reasonably achievable while obtaining diagnostic images, using justification, optimization, and dose limits.

Informed consent elements

Valid consent requires patient capacity, disclosure of material risks, benefits, and alternatives, comprehension, and voluntary agreement without coercion.

Metformin and contrast

Current guidance holds metformin only when eGFR is below 30 or acute kidney injury is present; routine discontinuation before iodinated contrast is unnecessary.

Nephrogenic systemic fibrosis risk

Risk rises with impaired renal function and older linear gadolinium agents; macrocyclic agents are preferred when eGFR is below 30.

RADPEER peer review

A scoring system rating interpretive agreement from one to four, used to track radiologist performance and identify learning or system opportunities.

Negligence four elements

A malpractice claim requires duty to the patient, breach of that duty, causation of harm, and measurable damages proximately caused by the breach.

Critical result communication

Findings requiring urgent action must be communicated promptly to the responsible provider and documented with closed-loop confirmation of receipt.

Procedure time-out

Before an invasive procedure the team verifies patient identity, correct site and side, consent, allergies, and available equipment aloud.

RVU reimbursement formula

Payment equals total relative value units, combining work, practice expense, and malpractice components, multiplied by the geographic practice cost index.

Typical chest CT dose

A standard chest CT delivers roughly 7 mSv effective dose, compared with about 0.1 mSv for a frontal chest radiograph.

Contrast extravasation management

Most extravasations resolve with limb elevation and cold compresses; large volumes, blistering, or skin compromise require prompt surgical evaluation.