ABNM Nuclear Medicine flashcards

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

Photoelectric effect

Photon absorption by an inner-shell electron; probability rises with atomic number cubed and falls with photon energy cubed, dominating at low diagnostic energies.

Compton scattering

Photon interacts with an outer-shell electron, transfers part of its energy, and scatters; probability depends on electron density and dominates in soft tissue at diagnostic energies.

Half-life formula

Radioactive decay follows A equals A-zero times e to the minus lambda t; half-life equals natural log of two divided by lambda, and mean life equals one divided by lambda.

Gamma camera resolution

Collimator resolution improves as hole diameter decreases and as hole length or collimator-to-source distance changes; sensitivity generally falls when resolution improves.

Occupational dose limits

NRC limits are 50 mSv per year effective dose, 150 mSv per year lens dose, and 500 mSv per year extremity dose; public limit is 1 mSv per year.

Inverse square law

Radiation intensity from a point source decreases with the square of distance: doubling distance reduces intensity to one quarter, which supports distance as a radiation protection tool.

NaI(Tl) detector

Thallium-activated sodium iodide scintillation crystal converts gamma photons to light, with energy resolution near six to seven percent at technetium-99m 140 keV.

Tc-99m generator

Molybdenum-99 adsorbed on alumina decays to technetium-99m; saline elution removes pertechnetate, and the generator is usually eluted every 24 hours after equilibrium.

Technetium-99m properties

Technetium-99m has a 6-hour half-life and emits a 140 keV gamma ray without beta particles, giving favorable imaging statistics and low patient absorbed dose.

Stannous reduction

In technetium-99m kits, stannous ion reduces pertechnetate so it binds to the ligand; excess stannous ion can cause hydrolyzed reduced technetium impurity.

FDG mechanism

Fluorine-18 fluorodeoxyglucose enters cells by glucose transporters and is phosphorylated by hexokinase; the product is trapped because it cannot proceed through glycolysis.

MAA lung perfusion

Technetium-99m macroaggregated albumin particles lodge in pulmonary capillaries; particle size and number are controlled to avoid toxicity and to image regional perfusion.

Radiochemical purity

The fraction of radioactivity in the desired chemical form; it is measured by chromatography and must meet kit limits before patient administration to prevent unwanted uptake or toxicity.

F-18 half-life

Fluorine-18 has a 110-minute half-life and decays by positron emission to oxygen-18; the emitted positron annihilates to produce two 511 keV photons.

V/Q mismatch

A perfusion defect with preserved ventilation suggests pulmonary embolism; matching defects are less specific and may reflect parenchymal lung disease or prior infarction.

Bone scan superscan

Diffusely increased skeletal technetium-99m MDP uptake with faint renal and soft-tissue activity; it suggests widespread metastatic disease or metabolic bone disease.

MAG3 renogram

Technetium-99m MAG3 is secreted by renal tubules and permits evaluation of renal perfusion, function, and excretion; captopril challenge can reveal renovascular hypertension.

Meckel diverticulum scan

Technetium-99m pertechnetate is taken up by ectopic gastric mucosa; a focal abdominal activity appearing with the stomach and clearing with it supports Meckel diverticulum.

Hepatobiliary scan

Technetium-99m iminodiacetic acid agents are transported into bile; nonvisualization of the gallbladder supports acute cholecystitis, while biliary leak shows extrabiliary activity.

Collimator selection

Low-energy high-resolution collimators suit technetium-99m 140 keV imaging; medium-energy collimators are needed for indium-111 and iodine-123 to limit septal penetration.

PET annihilation

A positron emitted by a radionuclide travels a short distance, combines with an electron, and annihilates; two 511 keV photons are emitted nearly 180 degrees apart.

SUV definition

Standardized uptake value equals decay-corrected tissue activity concentration divided by injected dose per body weight; it is influenced by plasma glucose, uptake time, and body composition.

PET detector crystals

Clinical PET uses dense scintillators such as LSO, LYSO, GSO, or BGO; faster crystals improve timing and time-of-flight performance, while light output affects energy resolution.

Deauville score

A five-point visual scale comparing lymphoma fluorine-18 FDG uptake with mediastinal blood pool and liver; scores one to three generally indicate complete metabolic response.

FDG patient preparation

Patients fast for at least four to six hours, avoid vigorous exercise, and have blood glucose controlled; elevated glucose or insulin can alter tumor and background uptake.

Ga-68 DOTATATE

Gallium-68 DOTATATE binds somatostatin receptors and is used for PET imaging of neuroendocrine tumors; normal uptake occurs in pituitary, spleen, liver, adrenals, and kidneys.

I-131 therapy

Iodine-131 emits beta radiation and a 364 keV gamma ray; it treats hyperthyroidism and differentiated thyroid cancer by concentrating in thyroid tissue and delivering local dose.

Lu-177 DOTATATE

Lutetium-177 DOTATATE delivers beta and gamma radiation to somatostatin receptor-positive tumors; kidney protection with amino acid infusion and dosimetry monitoring are standard.

Ra-223 dichloride

Radium-223 is an alpha emitter that targets bone metastases; it is given every four weeks for six doses and can cause myelosuppression and diarrhea.

Y-90 microspheres

Yttrium-90 resin or glass microspheres are infused into hepatic arteries for liver tumors; beta radiation provides local dose, and lung shunt fraction must be assessed.

Thyroid remnant ablation

Radioiodine after thyroidectomy destroys residual normal thyroid tissue; adequate TSH stimulation and a low-iodine diet improve uptake and treatment efficacy.

Radiation release criteria

Patients receiving radioiodine may be released when measured dose rate and retained activity meet regulatory limits; written instructions cover close contact, children, pregnancy, and travel.