ARRT Nuclear Medicine flashcards

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

Reversible myocardial perfusion defect

A stress image showing reduced tracer uptake that fills in on rest images; it indicates stress-induced ischemia rather than scarred myocardium.

V/Q mismatch

A perfusion defect with normal ventilation on lung scintigraphy; it raises suspicion for pulmonary embolism and is interpreted with clinical probability and chest imaging.

Three-phase bone scan

Dynamic flow, blood-pool, and delayed images after Tc-99m MDP; the sequence separates hyperemia from osteoblastic uptake and helps evaluate infection, fracture, or complex regional pain.

Hepatobiliary nonvisualization

Absence of gallbladder activity several hours after Tc-99m hepatobiliary tracer, especially with morphine augmentation, suggests acute cholecystitis when liver and bowel activity are present.

Meckel diverticulum scan

Tc-99m pertechnetate uptake in ectopic gastric mucosa in the right lower abdomen; it supports a Meckel diverticulum diagnosis, though other gastric or inflammatory lesions can mimic it.

Captopril renogram

Renal scintigraphy performed with an ACE inhibitor; a fall in relative function or prolongation of parenchymal transit suggests renovascular hypertension from unilateral renal artery stenosis.

Sentinel lymph node mapping

Injection of a radiolabeled colloid or tilmanocept near a tumor, followed by lymphoscintigraphy and gamma probe detection to identify the first draining nodes for biopsy.

Mo-99 breakthrough limit

The allowable Mo-99 activity in Tc-99m eluate is 0.15 kBq per MBq (0.15 µCi per mCi) of Tc-99m; exceeding it requires the eluate to be discarded.

Aluminum breakthrough

Alumina from a Tc-99m generator can appear in eluate; the limit is 10 µg/mL, and excess aluminum may cause particle aggregation and altered biodistribution.

Radiochemical purity

The fraction of total radioactivity present in the desired chemical form; it is measured by chromatography and must meet the package insert before a radiopharmaceutical is administered.

F-18 FDG half-life

Fluorine-18 has a 110-minute physical half-life; this limits shipping range and requires decay correction for dose calibration and PET scheduling.

MAA particle size

Technetium-99m macroaggregated albumin particles are typically 10 to 90 µm; they lodge in pulmonary capillaries after intravenous injection and must not be injected if clumped.

I-131 decay time

Iodine-131 has an 8.02-day half-life, so radioactive waste and patient precautions require decay through about 10 half-lives, or roughly 80 days, before release.

Photopeak energy window

A pulse-height analyzer accepts counts within a chosen energy range; for Tc-99m the 140-keV photopeak is commonly windowed at about ±10%, or 126 to 154 keV.

Center of rotation

The axis about which a gamma camera rotates during SPECT; misalignment produces ring or arc artifacts, so it is measured and corrected on a regular QC schedule.

Parallel-hole collimator

A collimator with parallel channels that preserves image size, increases resolution as hole length increases, and reduces sensitivity as septal thickness and hole length increase.

PET coincidence detection

Two 511-keV annihilation photons detected within a short timing window define an event; true coincidences localize the source, while scatter and random coincidences add background.

CT Hounsfield unit

A scaled CT attenuation value with water at 0 HU and air near -1000 HU; it allows tissue characterization and is used for attenuation correction in PET/CT.

Dead time

The interval after a detector event when the system cannot register another pulse; high activity causes count loss and can distort quantitation, especially in PET and first-pass studies.

Matrix and pixel size

Digital image dimensions define pixel size as field of view divided by matrix width; a larger matrix gives smaller pixels and finer display, but counts per pixel decrease.

Inverse square law

Radiation intensity from a point source varies inversely with the square of distance; doubling distance reduces exposure rate to one quarter of its original value.

Occupational dose limit

The annual effective dose limit for radiation workers is 50 mSv (5 rem), with a lens limit of 150 mSv and a skin or extremity limit of 500 mSv.

Fetal dose limit

After a worker declares pregnancy, the embryo-fetus dose limit is 0.5 mSv per month and 5 mSv over the entire gestation, with ALARA review of duties.

HVL lead for Tc-99m

The half-value layer of lead for Tc-99m gamma rays is about 0.3 mm; typical 0.5-mm lead aprons therefore attenuate a substantial but not complete fraction.

Radioactive waste decay

Short-lived waste is held for about 10 half-lives before release; Tc-99m requires roughly 60 hours, while I-131 requires about 80 days.

Contamination survey meter

A thin-window Geiger-Mueller or scintillation detector is used to find removable contamination; wipes are counted for gamma emitters and documented against release criteria.

Two-identifier patient check

Before radiopharmaceutical administration, staff verify at least two patient identifiers, such as name and date of birth, and match the dose label to the order.

Dose calibrator constancy

A daily check with a long-lived source verifies that the dose calibrator response is stable; accuracy, linearity, and geometry tests are performed on their own schedules.

Gamma camera uniformity QC

A daily flood image tests detector uniformity; nonuniformity appears as hot or cold spots and can produce ring artifacts, so corrections are applied before clinical imaging.

Breastfeeding after radiopharmaceutical

Lactating patients may need to interrupt breastfeeding and pump-and-discard for a period determined by the radiopharmaceutical, activity, and lactation guidance.

Extravasation response

If injection infiltrates, stop administration, estimate retained activity, apply local measures per protocol, document the event, and notify the authorized user and patient.

Renal function before contrast

Assess eGFR or creatinine when iodinated contrast or nephrotoxic drugs are planned; hydration and protocol adjustment reduce the risk of contrast-associated kidney injury.