ABR DR Core flashcards

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

Half-value layer

The thickness of material that reduces the intensity of a radiation beam to half its original value; equals 0.693 divided by the linear attenuation coefficient.

CT dose index volume

CTDIvol equals CTDIw divided by pitch and estimates the average dose per slice in a CT volume; it is displayed on the scanner console.

Larmor equation

The precessional frequency of a nucleus in a magnetic field equals the gyromagnetic ratio times field strength; for hydrogen it is 42.58 MHz per tesla.

Photoelectric effect

Photon absorption by an inner-shell electron; probability scales with atomic number cubed and inversely with photon energy cubed, producing high bone contrast.

Compton scatter

Inelastic photon interaction with an outer-shell electron that ionizes the atom and deflects the photon; dominates in soft tissue at diagnostic energies and degrades image contrast.

Axial resolution

The minimum separation of two reflectors along the beam path that can be distinguished; approximately half the spatial pulse length, improving with higher ultrasound frequency.

Absorbed dose unit

The gray equals one joule per kilogram and quantifies energy deposited per unit mass, distinct from kerma, which describes energy transferred to charged particles.

Linear-quadratic model

Survival fraction equals e raised to the negative of alpha times dose plus beta times dose squared; the alpha/beta ratio characterizes tissue fractionation sensitivity.

Alpha-beta ratio

A parameter from the linear-quadratic model; about 10 Gy for early-responding tumors and about 3 Gy for late-responding normal tissues.

Law of Bergonié and Tribondeau

Radiosensitivity is greater in cells that are highly mitotic, undifferentiated, and immature; it declines as cells mature and become more differentiated.

Oxygen enhancement ratio

The ratio of dose under hypoxia to dose under normoxia producing the same biologic effect; approximately 3 for sparsely ionizing radiation.

Stochastic radiation effect

An effect, such as carcinogenesis, whose probability increases with dose but whose severity is independent of dose; no threshold is assumed.

Deterministic radiation effect

An effect with a dose threshold below which it does not occur; above threshold, severity increases with dose, as in skin erythema or cataract.

Relative biologic effectiveness

The ratio of a reference radiation dose to the dose of a test radiation producing the same effect; higher for high-linear-energy-transfer radiation such as alpha particles.

DNA double-strand break

The principal lethal radiation lesion; repaired mainly by nonhomologous end joining in interphase and homologous recombination in late S and G2 phases.

Fractionation rationale

Dividing dose into fractions exploits differential repair between early-responding tumors and late-responding normal tissues, whose low alpha/beta ratios make them sensitive to fraction size.

Sensitivity and specificity

Sensitivity is true positives divided by all diseased; specificity is true negatives divided by all nondiseased. Both are intrinsic to the test.

Positive predictive value

The proportion of test-positive patients who truly have disease; unlike sensitivity, it depends strongly on disease prevalence in the population tested.

ROC curve

A plot of true-positive rate against false-positive rate across thresholds; area under the curve of 0.5 means no discrimination, 1.0 means perfect discrimination.

ALARA principle

Radiation doses should be kept as low as reasonably achievable, considering economic and social factors, while achieving the diagnostic objective.

Justification and optimization

Core ICRP principles: a procedure must produce net benefit and be appropriate for the indication, and doses must be optimized to the diagnostic task.

Informed consent elements

Valid consent requires patient capacity, voluntary decision, and disclosure of the nature of the procedure, material risks, benefits, and alternatives.

Critical result communication

Findings requiring urgent action must be communicated directly to the responsible clinician with documented closed-loop confirmation of receipt.

Moderate contrast reaction

A reaction such as urticaria or mild bronchospasm requiring treatment but not airway support; managed with observation and antihistamines, with epinephrine ready.

Large-vessel occlusion imaging

Noncontrast CT excludes hemorrhage; CT angiography identifies the occlusive thrombus; CT perfusion defines infarct core and salvageable penumbra before thrombectomy.

CT pulmonary angiogram

First-line imaging for suspected pulmonary embolism; right ventricular enlargement relative to the left ventricle on CT suggests severe disease and worse prognosis.

Tension pneumothorax

A clinical diagnosis of hemodynamic compromise requiring immediate decompression; imaging must not delay treatment when the presentation is typical.

Small bowel obstruction signs

Dilated bowel loops greater than 3 cm with air-fluid levels and a transition point; closed-loop obstruction with reduced wall enhancement is a surgical emergency.

Bosniak classification

A system stratifying cystic renal masses from category I to IV by septation, calcification, and enhancement; higher categories carry greater malignancy risk.

BI-RADS category 4

A breast imaging assessment meaning suspicious for malignancy, subdivided 4A, 4B, and 4C by increasing likelihood; biopsy is generally recommended.

Zone of transition

The margin between a bone lesion and normal bone; a narrow zone suggests a slow-growing benign process and a wide zone suggests aggressive or malignant disease.

Ileus versus obstruction

Ileus shows diffuse, proportional bowel dilation without a discrete transition point; mechanical obstruction shows dilated proximal loops and a defined transition zone.