ABR Nuclear Radiology flashcards

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

Photoelectric effect

Photon is absorbed by an inner-shell electron, which is ejected; probability rises with atomic number cubed and falls with photon energy cubed.

Compton scatter

Photon transfers part of its energy to a loosely bound electron and is scattered; probability depends mainly on electron density and dominates in soft tissue at nuclear medicine energies.

NaI(Tl) detector

Thallium-activated sodium iodide crystal converts gamma photons to light, which a photomultiplier tube converts to an electrical pulse; it has high light output but modest energy resolution.

Paralyzable dead time

In a paralyzable system each event extends the dead time, so observed count rate falls at high activity even though true rate keeps rising; this causes pile-up and count loss.

Tc-99m generator

Mo-99 adsorbed on alumina decays to Tc-99m, which is eluted with sterile saline; Mo-99 breakthrough and alumina content must be tested before use.

Radiochemical purity

Fraction of total radioactivity present in the desired chemical form; it is measured by chromatography and must meet the kit or monograph limit before patient administration.

FDG

Fluorine-18 fluorodeoxyglucose is a glucose analog trapped after phosphorylation; it accumulates in high-glucose-utilization tissues and has a 110-minute half-life.

DOTA chelator

Cyclic chelator that tightly binds trivalent metals such as Ga-68, Lu-177, and Y-90; it is used to attach these radionuclides to peptides for imaging or therapy.

ALARA

As low as reasonably achievable principle requires minimizing radiation dose through time, distance, and shielding while maintaining necessary diagnostic or therapeutic benefit.

Inverse square law

Photon fluence from a point source decreases with the square of distance; doubling distance reduces exposure rate to one quarter.

Declared pregnant worker

A worker who voluntarily declares pregnancy in writing; NRC dose limit to the embryo-fetus is 5 mSv over the entire gestation, and workload may be adjusted.

MIRD schema

Dosimetry method that combines time-integrated activity in source regions with S values to estimate absorbed dose in target regions.

Deauville score

Five-point PET scale comparing lymphoma uptake with mediastinal blood pool and liver; scores 4 and 5 are generally considered positive.

SUVmax

Maximum standardized uptake value in a lesion, normalized to injected dose and body size; it is sensitive to timing, glucose, and partial-volume effects.

PSMA PET

PET using prostate-specific membrane antigen ligands; physiologic uptake occurs in salivary and lacrimal glands, liver, spleen, kidneys, and bowel, so correlation with CT is needed.

DOTATATE PET

Gallium-68 DOTATATE binds somatostatin receptors; normal uptake is seen in pituitary, spleen, liver, kidneys, and adrenal glands, with high target-to-background in neuroendocrine tumors.

Sestamibi kinetics

Tc-99m sestamibi is a lipophilic cation taken up by mitochondria; myocardial extraction depends on perfusion and viability, and it shows minimal redistribution after injection.

Regadenoson

Selective adenosine A2A receptor agonist used for vasodilator stress; it increases coronary flow and can cause flushing, chest discomfort, and bronchospasm less often than adenosine.

Hibernating myocardium

Chronically ischemic myocardium with reduced resting perfusion but preserved glucose metabolism; FDG PET mismatch with perfusion identifies tissue likely to recover after revascularization.

Tc-99m PYP amyloid

Bone-seeking tracer used for cardiac transthyretin amyloidosis; grade 2 or 3 myocardial uptake on planar images, confirmed with SPECT, is strongly suggestive when AL amyloidosis is excluded.

Thyroid uptake

I-123 or Tc-99m pertechnetate uptake reflects thyroid trapping; Graves disease shows elevated uptake, while subacute thyroiditis and exogenous hormone show low uptake.

MAG3 renography

Tc-99m MAG3 is secreted by renal tubules and gives high target-to-background images; it is used to assess perfusion, function, obstruction, and transplant complications.

V/Q mismatch

A perfusion defect with normal ventilation suggests pulmonary embolism; matched defects are more typical of parenchymal lung disease such as COPD.

Hepatobiliary scan

Tc-99m iminodiacetic acid agents are taken up by hepatocytes and excreted into bile; nonvisualization of the gallbladder supports acute cholecystitis.

Three-phase bone scan

Flow, blood-pool, and delayed images after Tc-99m MDP; increased flow and blood pool with focal delayed uptake suggests osteomyelitis or active arthritis.

Labeled leukocyte scan

Autologous white cells labeled with In-111 oxine or Tc-99m HMPAO migrate to infection; it is useful for osteomyelitis, prosthetic joint infection, and inflammatory bowel disease.

Superscan

Diffuse symmetric skeletal uptake with faint or absent renal and soft-tissue activity; causes include widespread metastases, metabolic bone disease, and renal failure.

Gallium-67

Citrate tracer accumulates in infection, inflammation, and some tumors; normal uptake occurs in liver, spleen, bone marrow, salivary glands, lacrimal glands, and bowel.

DAT SPECT

I-123 ioflupane binds dopamine transporters in the striatum; reduced comma-shaped uptake supports Parkinsonian syndromes, while normal uptake argues against them.

Brain death scan

Tc-99m HMPAO perfusion study showing absent cerebral and cerebellar uptake with preserved scalp activity is consistent with brain death when clinical criteria are met.

Lu-177 DOTATATE

Peptide receptor radionuclide therapy that delivers beta and gamma radiation to somatostatin receptor-positive tumors; it is given in cycles with kidney and marrow monitoring.

Ra-223

Alpha-emitting calcium mimetic that deposits in bone metastases and causes double-strand DNA breaks; it is used for castration-resistant prostate cancer with symptomatic bone metastases.