NMAA cheat sheet

Radiopharmaceutical decay follows A = A0·e^(−λt), with λ = ln2 / T½; activity at time t is obtained by multiplying the calibrated activity by the decay factor e^(−0.693t/T½).

Precalibration: activity needed at use time is divided by the decay factor from calibration time to use time; Tc-99m (T½ ≈ 6.02 h) loses about half its activity every 6 hours.

Mo-99/Tc-99m generator: Mo-99 (T½ ≈ 66 h) decays to Tc-99m; transient equilibrium is re-established in roughly 4 half-lives of Tc-99m (~24 h), and eluate Mo-99 breakthrough limit is 0.15 kBq Mo-99 per MBq Tc-99m (0.15 µCi/mCi) at administration.

Alumina column generator elution uses 0.9% NaCl; the first eluate after delivery may contain higher Mo-99 and is typically discarded or assayed before clinical use.

Radionuclidic purity is verified with a dose calibrator or gamma camera; radiochemical purity is verified by chromatography (paper, TLC, or column) and must meet the monograph limit before patient administration.

Common T½ values: F-18 ≈ 110 min, Ga-68 ≈ 68 min, Tc-99m ≈ 6.02 h, I-123 ≈ 13.2 h, Tl-201 ≈ 73 h, In-111 ≈ 67 h, I-131 ≈ 8.02 d, Lu-177 ≈ 6.7 d.

Dose calibrator constancy is checked daily with a long-lived source (e.g., Cs-137) and accuracy at clinical energies is verified at required intervals; geometry (volume and syringe type) affects measured activity.

Injection site infiltration is confirmed by imaging the injection site; residual activity in the syringe and tubing must be subtracted when calculating the administered dose.

Gamma camera: NaI(Tl) crystal converts gamma photons to light; PMTs convert light to electrical signal; the collimator defines the field of view and spatial resolution.

Collimator choice: low-energy high-resolution (LEHR) for Tc-99m; medium-energy for In-111 and Ga-67; high-energy for I-131; pinhole for small organs such as thyroid.

Energy resolution of NaI(Tl) is roughly 6–7% at 140 keV; a 20% photopeak window centered on 140 keV is standard for Tc-99m.

Spatial resolution improves with closer source-to-collimator distance; sensitivity and resolution trade off with collimator hole size and septal thickness.

Uniformity (flood) and energy-peak calibration are performed daily or per protocol; photomultiplier tube drift appears as ring or spot artifacts on uniformity images.

SPECT reconstruction uses filtered backprojection or iterative methods (OSEM); Butterworth and Hanning filters trade noise against resolution; attenuation correction improves myocardial and brain SPECT.

PET detection relies on annihilation photons (511 keV) detected in coincidence; time-of-flight and attenuation correction improve image quality; SUV = activity concentration / (injected dose / body weight).

Cardiac perfusion: Tc-99m sestamibi or tetrofosmin for SPECT; Tl-201 for viability; stress/rest comparison identifies reversible ischemia versus fixed scar.

Bone scan: Tc-99m MDP localizes to osteoblastic activity; three-phase imaging (flow, blood pool, delayed) distinguishes cellulitis from osteomyelitis.

V/Q scan uses Tc-99m DTPA or Technegas aerosol for ventilation and Tc-99m MAA for perfusion; mismatched defects suggest pulmonary embolism (modified PIOPED criteria).

Renal scan: Tc-99m MAG3 for tubular secretion and ERPF; Tc-99m DTPA for GFR; captopril challenge for renovascular hypertension; Lasix washout for obstruction.

Thyroid: Tc-99m pertechnetate and I-123 localize to thyroid; I-131 used for therapy; pregnancy and breastfeeding are absolute contraindications to radioiodine.

Hepatobiliary: Tc-99m mebrofenin/IDA agents trace hepatocyte uptake and biliary excretion; GI bleed: Tc-99m sulfur colloid or tagged RBCs.

Sentinel node and infection imaging: Tc-99m sulfur colloid for lymphoscintigraphy; Ga-67 and In-111 WBC for infection/inflammation; F-18 FDG PET for oncology staging.

ALARA: occupational dose limit is 50 mSv/year (5 rem) effective dose; lens of eye 150 mSv/year; extremity/skin 500 mSv/year under ICRP; public limit 1 mSv/year.

Pregnant declared worker: dose to fetus limited to 0.5 mSv per month (5 mSv over gestation); a declared pregnant worker may continue if limits are met.

Time, distance, and shielding: dose rate follows inverse-square law; doubling distance reduces exposure to one quarter; lead half-value layer for Tc-99m is about 0.3 mm Pb.

Personnel monitoring uses TLD or OSL badges worn at collar level (and ring badges for high hand exposure); badges are exchanged per institutional interval and not worn outside work.

Spills: contain, mark, and decontaminate; survey with a thin-window Geiger-Mueller or NaI probe; record removable contamination in Bq/cm² or dpm/100 cm² per license conditions.

Radioactive waste is held for decay-in-storage until activity is indistinguishable from background (commonly 10 half-lives) before disposal as non-radioactive; survey and document before release.

Patient release after therapy follows NRC/agreement-state criteria (e.g., 1.11 GBq I-131 or dose-rate limits) with written instructions; breastfeeding must stop after I-131 therapy.

Before any study, verify patient identity, pregnancy/breastfeeding status, allergies, renal function, and prior nuclear medicine or contrast procedures.

Radiopharmaceuticals are administered under an authorized user's order; the package insert and institutional protocol define dose, route, and timing.

Patient preparation is agent-specific: fasting for FDG PET, thyroid blockade or hydration for I-131 therapy, voiding before pelvic imaging, and hydration for renal scans.

For FDG PET, blood glucose should be controlled (commonly < 11.1 mmol/L or per protocol), uptake period is about 60 min, and the patient rests quietly to avoid muscle uptake.

Document administered activity, route, time, lot number, and any residual activity in the syringe; reconcile the prescribed and administered dose after injection.

Recognize and manage adverse reactions: anaphylactoid responses to radiopharmaceuticals are rare; vasovagal reactions and extravasation require prompt assessment and documentation.

Quality control: daily dose-calibrator constancy, generator eluate assay, radiochemical purity testing, and camera flood/energy checks must be recorded before patient imaging.

Image acquisition modes: static, dynamic, whole-body, SPECT, and gated; matrix size and zoom must match the required resolution and field of view.

Count statistics: noise decreases with the square root of counts; doubling counts improves signal-to-noise by about 1.41.

Reconstruction: filtered backprojection is fast but amplifies noise; iterative OSEM with attenuation and scatter correction is preferred for quantitative SPECT.

Registration and fusion of SPECT/CT or PET/CT improve localization; CT-based attenuation correction uses a bilinear conversion of Hounsfield units to attenuation coefficients.

Quantitation: SUV, standardized uptake ratio, and time-activity curves require decay correction, scanner calibration, and consistent uptake time.

Motion artifact (patient movement, respiration) produces blurring or misregistration; gating and patient immobilization reduce it.

Display and archiving follow DICOM standards; window/level, color maps, and annotation must be documented so images are interpretable and reproducible.