TEMN Medicina Nuclear flashcards

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

Effective half-life formula

One divided by effective half-life equals one divided by physical half-life plus one divided by biological half-life. Effective half-life is always shorter than either component and determines retained dose.

Technetium-99m properties

A pure gamma emitter with a 140 keV photopeak and a 6-hour physical half-life, produced from a molybdenum-99 generator. Its energy suits low-energy high-resolution collimators and sodium iodide crystals.

Fluorine-18 half-life

Approximately 110 minutes, decaying by positron emission. This permits transport between cyclotron and imaging sites while requiring rapid, scheduled workflows and same-day labeling of FDG.

Radiochemical purity

The fraction of total radioactivity present in the intended chemical form. It is measured by chromatography and must be verified before administration because impurities alter biodistribution and increase unnecessary dose.

Radionuclide purity

The fraction of activity originating from the intended radionuclide rather than contaminating isotopes. It is assessed by gamma spectroscopy and is critical for generator eluates such as technetium-99m.

Collimator function

A lead or tungsten device with holes that restricts incoming photons to near-parallel paths, defining the field of view and spatial resolution. Hole size and septal thickness trade resolution against sensitivity.

Photopeak energy window

A pulse-height analyzer setting that accepts counts within a percentage range around the photopeak, typically 15 to 20 percent for technetium-99m. It reduces scatter while retaining most true events.

OSEM reconstruction

Ordered-subset expectation maximization is an iterative SPECT and PET reconstruction method that models attenuation, scatter, and detector response, improving image quality and quantitative accuracy over filtered back-projection.

Attenuation correction rationale

Photons from deep structures are absorbed before reaching the detector, causing false defects. Correction using CT or transmission sources restores uniform counts in homogeneous regions such as the myocardium.

FDG patient preparation

Fasting for at least four to six hours, avoidance of strenuous exercise, and blood glucose measurement before injection. These steps suppress physiologic myocardial and muscular uptake and improve lesion contrast.

Physiologic FDG distribution

Normal uptake includes brain cortex, liver, spleen, bone marrow, kidneys, bladder, tonsils, and salivary glands. Myocardial uptake varies with fasting state and should not be mistaken for disease.

Reversible perfusion defect

A myocardial region with reduced uptake on stress imaging that normalizes at rest, indicating stress-induced ischemia. A defect present at both stress and rest represents scar or infarction.

Ventilation-perfusion mismatch

A segmental perfusion defect with preserved ventilation on a V/Q scan, indicating pulmonary embolism. Matched defects more often reflect parenchymal lung disease such as chronic obstructive disease.

Three-phase bone scan

Sequential blood flow, blood pool, and delayed images after technetium-99m MDP injection. It distinguishes hyperemia and inflammation from osteoblastic bone remodeling and helps evaluate prosthetic infection.

Superscan appearance

Diffuse intense skeletal uptake with faint or absent renal and soft-tissue visualization, seen in widespread metastases or metabolic bone disease. It can mask lesions by saturating the display scale.

Sentinel lymph node technique

Injection of technetium-99m labeled colloid around a tumor, followed by lymphoscintigraphy and intraoperative gamma probe detection. It identifies the first draining node for targeted biopsy.

Renal tracer MAG3

Technetium-99m mercaptoacetyltriglycine is secreted by renal tubules and estimates effective renal plasma flow. It provides high target-to-background images even in impaired renal function.

DMSA renal scan

Technetium-99m dimercaptosuccinic acid binds to proximal tubular cells, giving cortical images. It detects scars, pyelonephritis, and differential renal function in children and adults.

Radioiodine therapy principle

Iodine-131 concentrates in thyroid tissue via the sodium-iodide symporter. Beta emissions deliver therapeutic dose to hyperplastic or neoplastic thyroid cells while gamma emissions permit imaging.

Lutetium-177 DOTATATE

A peptide receptor radionuclide therapy targeting somatostatin receptors in neuroendocrine tumors. It delivers beta radiation to receptor-expressing cells and requires dosimetry and renal protection.

Radium-223 mechanism

A calcium mimetic alpha emitter that localizes to bone metastases in castration-resistant prostate cancer. Alpha particles cause dense local DNA damage with limited marrow exposure compared with beta emitters.

Absorbed dose unit

The gray equals one joule per kilogram of tissue. It quantifies energy deposited by radiation and is converted to equivalent and effective dose using radiation and tissue weighting factors.

Effective dose concept

A whole-body dose surrogate that sums tissue-absorbed doses weighted by radiosensitivity. It allows comparison of stochastic risk across different imaging procedures and radionuclides.

Occupational dose limit

Twenty millisieverts per year averaged over five years, with no single year exceeding fifty millisieverts. The lens and extremity limits are higher and apply to specific tissues.

Inverse-square law

Radiation exposure from a point source decreases with the square of distance. Doubling the distance from a syringe or patient reduces exposure rate to one quarter.

Stochastic radiation effects

Cancer and heritable effects for which probability rises with dose but no threshold exists. Severity is not dose-dependent, and risk is estimated using the linear no-threshold model.

Deterministic radiation effects

Tissue reactions such as skin erythema, cataract, and marrow suppression that occur only above threshold doses. Severity increases with dose and can be prevented by dose limits.

Dose calibrator quality control

Daily constancy and accuracy checks plus periodic linearity and geometry testing verify activity measurement. Errors propagate directly into administered activity and patient dosimetry.

Gamma camera uniformity test

A flood field image assesses count uniformity across the detector. Intrinsic uniformity is measured without a collimator, while extrinsic uniformity includes the collimator response.

Pregnancy screening before tracer

Question women of reproductive age about last menstrual period and possible pregnancy before administering radiopharmaceuticals. Fetal dose and alternative imaging should be discussed when pregnancy is possible.

Breastfeeding interruption

The required pause after a radiopharmaceutical depends on its half-life and excretion. Technetium agents usually require hours, whereas iodine-131 generally requires cessation of breastfeeding.

Radiopharmaceutical extravasation management

Stop the injection, apply a cold compress, elevate the limb, and record activity and time. Local dose is estimated and the site is monitored for skin reaction.