NMAA flashcards

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

Tc-99m half-life

Approximately 6.02 hours. About half the activity remains after 6 hours and about 6% after 24 hours, so elution timing and dose preparation must account for decay.

Mo-99 breakthrough limit

The eluate must contain no more than 0.15 kBq of Mo-99 per MBq of Tc-99m (0.15 microcurie per millicurie) at the time of patient administration.

Decay formula

Activity at time t equals initial activity multiplied by e raised to the power negative 0.693 t divided by half-life; used for precalibration and post-calibration corrections.

Radiochemical purity

The fraction of total radioactivity present in the desired chemical form. It is measured by chromatography and must meet the product monograph before administration.

Radionuclidic purity

The fraction of total radioactivity attributable to the intended radionuclide. It is assessed by gamma spectroscopy or by assaying for contaminants such as Mo-99.

Dose calibrator constancy

A daily check with a long-lived reference source, such as Cs-137, that verifies the instrument response is stable within the established tolerance before patient doses are measured.

NaI(Tl) crystal function

Thallium-activated sodium iodide absorbs gamma photons and emits visible light proportional to deposited energy; photomultiplier tubes convert the light into an electrical pulse.

Photopeak window

An energy acceptance range centered on the gamma emission, commonly 20% for Tc-99m at 140 keV, that excludes scattered photons and reduces image noise.

Collimator selection rule

Use low-energy high-resolution collimators for Tc-99m, medium-energy for In-111 and Ga-67, high-energy for I-131, and a pinhole collimator for small organs such as the thyroid.

SPECT iterative reconstruction

OSEM reconstruction models the imaging process and applies attenuation and scatter correction, yielding lower noise and better quantitation than filtered backprojection in most clinical settings.

PET coincidence detection

Two 511 keV annihilation photons emitted about 180 degrees apart are recorded only when detected within a narrow timing window, which localizes the annihilation event along a line of response.

SUV definition

Standardized uptake value equals decay-corrected activity concentration in tissue divided by injected activity per unit body weight; consistent uptake time and calibration are required for comparability.

Tc-99m MDP bone scan

The diphosphonate tracer adsorbs to hydroxyapatite in proportion to osteoblastic activity and blood flow, showing metastases, fractures, and infection as focal increased uptake.

Three-phase bone scan

Flow, blood-pool, and delayed images separate hyperemia from osteoblastic activity; focal delayed uptake with normal flow suggests osteomyelitis rather than cellulitis.

V/Q mismatch significance

Perfusion defects with preserved ventilation in a segment suggest pulmonary embolism; matched defects are more typical of parenchymal lung disease such as COPD.

Tc-99m MAG3 use

A tubular secretion agent used for renal perfusion and function imaging, including Lasix washout for obstruction and captopril challenge for renovascular hypertension.

Tc-99m sulfur colloid

A particulate agent taken up by the reticuloendothelial system; used for liver/spleen imaging, bone marrow imaging, gastrointestinal bleeding, and sentinel lymph node localization.

I-131 therapy precautions

Patients receive written radiation safety instructions, avoid prolonged close contact with others, and must stop breastfeeding; pregnancy is an absolute contraindication.

F-18 FDG patient preparation

The patient fasts, blood glucose is checked against protocol, and after injection rests quietly for about 60 minutes to limit physiologic muscle and brown fat uptake.

Extravasation documentation

Infiltration at the injection site is confirmed by imaging the site; residual syringe activity is subtracted and the event is recorded and reported per institutional policy.

Occupational dose limit

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

Inverse-square law

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

Declared pregnant worker

A worker who formally declares pregnancy is subject to a fetal dose limit of 0.5 mSv per month, and workload may be adjusted to stay within that limit.

Decay-in-storage

Radioactive waste is held until its activity is indistinguishable from background, commonly after about 10 half-lives, then surveyed and documented before disposal as non-radioactive.

Personnel dosimeter placement

A whole-body TLD or OSL badge is worn at collar level outside protective clothing; ring badges are worn when hand exposure is likely to approach dose limits.

Pregnancy screening

Pregnancy or breastfeeding status is documented before radiopharmaceutical administration, because radioiodine and many agents require postponement or alternative imaging.

Administered dose reconciliation

The activity remaining in syringe, tubing, and injection site is measured or estimated and subtracted from the prepared activity so the recorded dose reflects actual patient uptake.

Thyroid uptake agents

Tc-99m pertechnetate and I-123 are used for thyroid imaging and uptake; I-131 is reserved for therapy and for selected diagnostic or ablation follow-up studies.

Renal scan timing agents

Tc-99m DTPA is filtered and estimates glomerular filtration rate; Tc-99m MAG3 is secreted by tubules and estimates effective renal plasma flow with better image quality.

Count statistics rule

Image noise is inversely proportional to the square root of collected counts, so quadrupling acquisition counts halves relative noise and improves image quality.

CT attenuation correction

Hounsfield units from the CT component are converted to attenuation coefficients at the emission energy, enabling quantitative SPECT or PET and improved lesion localization.

Generator elution principle

Saline elutes Tc-99m from the alumina column as pertechnetate; ingrowth of Tc-99m from Mo-99 reaches transient equilibrium in about four Tc-99m half-lives.