Nuclear Medicine Exam Questions & Answers 2026 (21–30)

Question 1

Integral uniformity on a gamma camera flood image is calculated as:

TheoryPractice · Accepted Answer

(Max − Min) / (Max + Min) × 100%. NEMA defines integral uniformity as [(Max − Min) / (Max + Min)] × 100%. This normalizes the range to the sum, giving a value between 0–100% that is independent of absolute count level. Acceptable values for clinical cameras are typically <5%.

Question 2

Daily QC for a PET/CT scanner most critically involves:

TheoryPractice · Accepted Answer

Blank scan normalization and well-counter cross-calibration verification. Daily PET QC includes a blank scan (detects broken crystals/PMTs and provides normalization data) and verification that scanner calibration matches the dose calibrator (cross-calibration). Co-57 floods and collimator checks are gamma camera procedures.

Question 3

What type of detector is used inside a dose calibrator?

TheoryPractice · Accepted Answer

Pressurized ionization chamber. Dose calibrators contain a pressurized (argon or nitrogen) ionization chamber that collects the ion current produced by radiation. The high pressure increases sensitivity over air-filled chambers, allowing accurate measurement of clinical radiopharmaceutical activities.

Question 4

NRC regulations require dose calibrator constancy checks to be performed:

TheoryPractice · Accepted Answer

Daily (or before first use each day) with a long-lived reference source. 10 CFR 35.60 requires constancy to be measured daily (before the first measurement of patient doses) using a sealed long-lived standard (e.g., Cs-137 or Co-57). Accuracy tests use at least two reference sources annually.

Question 5

A Geiger-Müller (GM) survey meter is most appropriate for:

TheoryPractice · Accepted Answer

Detecting contamination and low-level surface activity. GM tubes are extremely sensitive to ionizing radiation (useful for detecting low-level contamination) but saturate at high dose rates and cannot measure energy. Ionization chamber-based survey meters (cutie pie) are used for accurate dose-rate measurements.

Question 6

An ionization chamber survey meter (cutie pie) has a scale reading of 4.5 mR/h with a calibration factor of 0.95. What is the corrected dose rate?

TheoryPractice · Accepted Answer

4.28 mR/h. Corrected dose rate = Scale reading × Calibration factor = 4.5 × 0.95 = 4.275 mR/h ≈ 4.28 mR/h. Calibration factors adjust for instrument over- or under-response relative to an NIST-traceable standard.

Question 7

A scintillation well counter is used to measure a thyroid uptake standard. If the sample is placed directly at the mouth of the well instead of fully inside it, the measured count rate will:

TheoryPractice · Accepted Answer

Decrease significantly due to reduced geometric efficiency. Well counter sensitivity relies on the sample being surrounded by the crystal (near 4π geometry). Positioning the sample at the mouth reduces solid-angle coverage dramatically, lowering count rate by up to 50% or more. Reproducible, consistent geometry is essential for well counter measurements.

Question 8

What collimator is typically used on a thyroid uptake probe?

TheoryPractice · Accepted Answer

Flat-field (flat-face) collimator. Thyroid uptake probes use a flat-field (or open-face) collimator with a single bore designed to view the thyroid from ~30 cm distance. This geometry accepts photons from the entire gland without the complex hole patterns of imaging collimators.

Question 9

A 24-hour thyroid uptake calculation is: (Neck CPM − Background CPM) / (Standard CPM − Background CPM) × 100%. The neck counts 12,500 cpm, thigh (background) 500 cpm, standard 50,000 cpm, standard background 500 cpm. What is the uptake?

TheoryPractice · Accepted Answer

24.5%. Uptake = (12500 − 500) / (50000 − 500) × 100 = 12000 / 49500 × 100 = 24.24% ≈ 24.5% (rounding to 1 decimal). The thigh measurement estimates tissue background contribution not from thyroid uptake.

Question 10

As source-to-collimator distance increases for a parallel-hole collimator, spatial resolution:

TheoryPractice · Accepted Answer

Degrades because the geometric component of resolution worsens. Geometric resolution for a parallel-hole collimator = d(L + b)/L, where d = hole diameter, L = hole length, b = source-to-face distance. As b increases, geometric resolution degrades. Total system resolution combines intrinsic and geometric components in quadrature.

Nuclear Medicine Exam Questions & Answers 2026 (21–30)

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