ABR DMP cheat sheet

Half-value layer (HVL) relates to linear attenuation coefficient by HVL = 0.693/μ; a beam's HVL rises as filtration increases and beam energy hardens.

Photoelectric absorption probability scales approximately with Z^3/E^3; Compton scatter dominates at diagnostic energies in soft tissue and is nearly independent of Z.

Attenuation follows I = I0·e^(−μx); mass attenuation coefficient μm = μ/ρ removes density dependence, and μ/ρ = τ/ρ + σ/ρ + κ/ρ.

Bremsstrahlung output scales with tube current, exposure time, and roughly Z·kV²; characteristic x-rays require kV above the K-shell binding energy of the target.

The inverse-square law applies to a point source in air: intensity falls as 1/d²; entrance skin exposure rises as field area increases (output factor).

Grid ratio = height/gap; contrast improvement factor and Bucky factor quantify grid performance, and grid cutoff results from lateral decentering or wrong focal distance.

Effective dose is the tissue-weighted sum of equivalent doses; effective dose is not a patient-specific risk and should not be used for individual risk estimates.

Beam quality in mammography is specified by HVL (typically 0.3–0.45 mm Al) and by the half-value layer plus kVp combination; AEC controls exposure to the receptor.

Technetium-99m: 140 keV gamma, 6.02 h half-life, produced from a Mo-99/Tc-99m generator; Mo-99 breakthrough must be below regulatory limits.

Activity decays as A = A0·e^(−0.693t/T½); after n half-lives activity is A0/2^n.

PET annihilation produces two 511 keV photons emitted ~180° apart; coincidence timing window and scatter fraction determine image quality.

F-18 FDG half-life is 109.8 min; Tc-99m is 6.02 h; I-131 is 8.02 d; Ga-68 is 68 min; these govern dose calibration and imaging windows.

Gamma camera energy resolution is typically ~10% FWHM at 140 keV; photopeak window centering and width affect scatter and sensitivity.

Collimator resolution degrades with distance from the collimator face; sensitivity and resolution trade off inversely with septal thickness and hole length.

Dead-time losses in gamma cameras are modeled as paralyzable (N = n·e^(−nτ)) or nonparalyzable (N = n/(1+nτ)); high count rates reduce observed counts.

Absorbed dose from internally administered radionuclides depends on cumulated activity (∫A dt), the S-value, and the medical internal radiation dose (MIRD) schema.

ALARA principle: keep doses as low as reasonably achievable, considering social and economic factors; dose limits apply to workers and public, not to patients for justified exams.

Occupational effective dose limit is 50 mSv/y (whole body); lens of eye 150 mSv/y; skin/extremities 500 mSv/y; public limit is 1 mSv/y (ICRP).

Pregnant radiation workers: declared pregnant woman fetal dose limit is 0.5 mSv per month / 5 mSv total gestation (NCRP).

Shielding design uses controlled/uncontrolled area dose goals (e.g., 0.1 mSv/wk controlled, 0.02 mSv/wk uncontrolled) and transmission factors from attenuation data.

Lead apron attenuation: 0.5 mm Pb reduces scatter by roughly 90% at diagnostic energies; 0.25 mm Pb offers less protection and is used for lighter aprons.

Personnel dosimeters (TLD, OSL, film) measure equivalent dose at body locations; ring badges are used for extremity dose and should be worn under gloves.

Radiation weighting factor for x-rays and gamma rays is 1; for alpha particles it is 20; equivalent dose (Sv) = absorbed dose (Gy) × radiation weighting factor.

Inverse-square and barrier transmission: shielding thickness is calculated from workload (W), use factor (U), occupancy (T), and distance d² per NCRP Report 147.

Standard anatomic position: patient upright, facing observer, arms at sides with palms forward; right and left refer to the patient's sides.

The diaphragm separates thoracic and abdominal cavities; the liver lies in the right upper quadrant and the spleen in the left upper quadrant.

The airway divides into right and left main bronchi; the right main bronchus is wider and more vertical, making it a common aspiration path.

The heart lies in the mediastinum with the apex directed anteriorly and to the left; the aortic arch and pulmonary artery form the mediastinal contours.

Kidneys are retroperitoneal at approximately T12–L3; the right kidney sits slightly lower due to the liver.

The vertebral column has 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 3–4 coccygeal segments; the conus medullaris ends near L1–L2.

The gastrointestinal tract order: esophagus, stomach, duodenum, jejunum, ileum, cecum, ascending/transverse/descending colon, rectum.

Bone density and composition: cortical bone is dense and highly attenuating; trabecular bone is less dense; the growth plate (physis) appears as a lucent line in pediatric images.

Radiographic tube output (mR/mAs) is measured at a fixed distance and kVp; output should be linear with mAs within ±10% over the clinical range.

AEC performance: detector response should be uniform across the field, and exposure reproducibility should be within ±10% (varies by standard).

kVp accuracy is typically required within ±5% of indicated value, measured with a noninvasive kVp meter.

Mammography QC: phantom image score, AEC reproducibility, compression force, and mean glandular dose limits are specified; ACR phantom requires minimum passing scores.

CT number (Hounsfield unit) = 1000·(μtissue − μwater)/μwater; water is 0 HU and air is approximately −1000 HU.

CT dose index (CTDIvol) and dose-length product (DLP) estimate dose; DLP = CTDIvol × scan length; effective dose ≈ DLP × k-factor.

Fluoroscopy: high-level control produces up to 20 R/min at the skin in high-level mode; typical fluoroscopic entrance exposure is ~1–5 R/min under normal mode.

Digital detector QC includes flat-field/gain calibration, dead pixel mapping, and evaluation of detective quantum efficiency (DQE) and modulation transfer function (MTF).