ABR DMP flashcards

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

Half-value layer

Thickness of material that reduces beam intensity by half; equals 0.693 divided by the linear attenuation coefficient and increases with filtration and beam energy.

Photoelectric effect

Photon absorption by an inner-shell electron, dominant at low energy and high atomic number; probability varies approximately as Z cubed over E cubed.

Compton scatter

Inelastic photon collision with an outer-shell electron; dominant interaction in soft tissue at diagnostic energies and nearly independent of atomic number.

Inverse-square law

Photon intensity from a point source decreases with the square of distance; doubling distance reduces intensity to one quarter of its original value.

Bremsstrahlung production

Radiation from electron deceleration in the target; output rises with tube current, exposure time, atomic number, and roughly the square of tube voltage.

Grid ratio

Ratio of lead strip height to interspace width; higher ratios improve scatter cleanup and contrast but require greater exposure and accurate centering.

Effective dose

Tissue-weighted sum of equivalent doses across organs; used for population comparisons and not for estimating an individual patient's risk.

Tc-99m generator

System producing technetium-99m from decaying molybdenum-99; eluate must be tested for Mo-99 breakthrough and aluminum contamination before patient use.

Decay equation

Activity at time t equals initial activity times e raised to minus 0.693 times t divided by half-life; after n half-lives activity is initial divided by 2 to the n.

PET annihilation

Positron combines with electron to emit two 511 keV photons about 180 degrees apart; coincidence detection of both defines the annihilation event location.

Collimator resolution

Spatial resolution of a gamma camera degrades as distance from the collimator face increases; sensitivity and resolution trade off with septal thickness.

Dead-time loss

Count loss at high count rates; paralyzable systems follow N equals n times e to the minus n tau, nonparalyzable systems follow N equals n over one plus n tau.

Cumulated activity

Time integral of activity in a source organ; combined with S-values in the MIRD schema to estimate absorbed dose to target organs.

F-18 half-life

Fluorine-18 decays with a half-life of about 110 minutes; this governs dose calibration timing and limits transport distance for FDG distribution.

Photopeak window

Energy acceptance range centered on the photopeak; a typical setting is a 20 percent window around 140 keV for technetium-99m imaging.

ALARA

Principle of keeping radiation doses as low as reasonably achievable, weighing social and economic factors; applies to occupational and public exposures.

Occupational dose limits

Annual limits for radiation workers: 50 mSv whole body, 150 mSv lens of eye, and 500 mSv to skin and extremities under ICRP recommendations.

Public dose limit

Annual effective dose limit for members of the public is 1 mSv above natural background, roughly one fiftieth of the occupational whole-body limit.

Declared pregnancy limit

Fetal dose limit for a declared pregnant radiation worker is 0.5 mSv in any month and 5 mSv over the entire gestation period.

Radiation weighting factor

Factor converting absorbed dose to equivalent dose; equals 1 for x-rays and gamma rays and 20 for alpha particles, reflecting biological effectiveness.

Lead apron attenuation

A 0.5 mm lead-equivalent apron attenuates scattered diagnostic x-rays by roughly 90 percent; 0.25 mm lead aprons provide less protection.

Shielding design goals

Dose targets for barrier design, commonly 0.1 mSv per week for controlled areas and 0.02 mSv per week for uncontrolled areas, per NCRP guidance.

Ring dosimeter

Extremity badge worn on the hand, typically under gloves, to monitor dose during procedures involving hands near the primary beam.

Anatomic position

Reference posture with the body upright, facing the observer, arms at the sides, and palms forward; right and left refer to the patient's sides.

Right main bronchus

Wider and more vertically oriented than the left main bronchus, making the right side a more common pathway for aspirated material.

Kidney location

Retroperitoneal organs lying near the T12 to L3 level; the right kidney sits slightly lower than the left because of the overlying liver.

Vertebral segments

The spine contains 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral, and 3 to 4 coccygeal segments; the spinal cord ends near L1 to L2.

GI tract order

Sequence is esophagus, stomach, duodenum, jejunum, ileum, cecum, ascending colon, transverse colon, descending colon, and rectum.

Hounsfield unit

CT number computed as 1000 times the difference between tissue and water attenuation coefficients divided by water's coefficient; water is 0 and air about -1000.

CT dose index

CTDIvol estimates dose per scan from tube output and pitch; dose-length product equals CTDIvol times scan length and supports effective dose estimation.

AEC reproducibility

Automatic exposure control should deliver consistent receptor exposure across repeated measurements, typically within about 10 percent of the mean value.

Detective quantum efficiency

DQE measures how efficiently a detector converts incident x-ray quanta into image signal; higher DQE indicates better dose efficiency and image quality.