I85PREP
⌘ K
ABR NMP study materials
ABR NMP study resources

ABR NMP practice questions

One question at a time. Build your ABR NMP understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Nuclear Medical Physics (Part 2 specialty content)

The physical half-life of Tc-99m is approximately 6 hours. If a generator eluate contains 800 mCi of Tc-99m at 8:00 AM, what activity remains at 2:00 PM the same day?

  1. 100 mCi
  2. 200 mCi
  3. 400 mCi Correct answer.
  4. 600 mCi

Explanation

Six hours equals one physical half-life, so the activity is halved once: 800 mCi becomes 400 mCi. Radioactive decay follows A = A0 times (1/2)^(t/T).

Question 2Nuclear Medical Physics (Part 2 specialty content)

In a Mo-99/Tc-99m generator, which nuclide is measured to assess the extent of breakthrough in the eluate?

  1. I-131
  2. Sr-89
  3. Mo-99 Correct answer.
  4. Tc-99m

Explanation

Molybdenum breakthrough testing measures Mo-99 contamination in the eluted Tc-99m. The regulatory limit is expressed as activity of Mo-99 relative to Tc-99m activity.

Question 3Nuclear Medical Physics (Part 2 specialty content)

A gamma camera equipped with a low-energy high-resolution (LEHR) collimator is best suited for imaging which radionuclide?

  1. Tc-99m Correct answer.
  2. I-131
  3. In-111
  4. F-18

Explanation

LEHR collimators are designed for photon energies near 140 keV, matching the 140 keV gamma of Tc-99m. Higher-energy emitters require thicker septa to limit penetration.

Question 4Nuclear Medical Physics (Part 2 specialty content)

The photopeak of a NaI(Tl) scintillation detector results from which interaction in the crystal?

  1. Coherent scattering
  2. Photoelectric absorption Correct answer.
  3. Compton scattering
  4. Pair production

Explanation

The photopeak corresponds to full energy deposition, which occurs when a photon undergoes photoelectric absorption (or multiple interactions that fully deposit energy). The full photon energy is converted to light.

Question 5Nuclear Medical Physics (Part 2 specialty content)

The energy resolution of a scintillation detector is conventionally reported as which quantity?

  1. The area under the photopeak divided by the total counts
  2. The full width at half maximum of the photopeak divided by the photopeak energy Correct answer.
  3. The full width at tenth maximum multiplied by the photopeak energy
  4. The photopeak energy divided by the detector thickness

Explanation

Energy resolution is the FWHM of the photopeak expressed as a percentage of the photopeak centroid energy. Smaller percentages indicate better resolution.

Question 6Nuclear Medical Physics (Part 2 specialty content)

Which radiopharmaceutical is most commonly used for myocardial perfusion imaging?

  1. Tc-99m MDP
  2. Tc-99m sestamibi Correct answer.
  3. F-18 FDG
  4. Ga-67 citrate

Explanation

Tc-99m sestamibi (and tetrofosmin) localizes in myocardium in proportion to perfusion and is standard for myocardial perfusion SPECT. The other agents target bone, glucose metabolism, or inflammation.

Question 7Nuclear Medical Physics (Part 2 specialty content)

In PET imaging, the annihilation of a positron with an electron produces two 511 keV photons emitted in which relative direction?

  1. Approximately 90 degrees apart
  2. Approximately 180 degrees apart Correct answer.
  3. Parallel and in the same direction
  4. At a random angle unrelated to each other

Explanation

Conservation of momentum requires the two annihilation photons to be emitted nearly back-to-back, about 180 degrees apart. Coincidence detection relies on this geometry.

Question 8Nuclear Medical Physics (Part 2 specialty content)

The main purpose of a dose calibrator constancy check is to verify which property?

  1. Spatial resolution of the camera
  2. Uniformity of the flood field
  3. Energy resolution of the detector
  4. Stability of activity measurement over time Correct answer.

Explanation

A constancy check confirms that the dose calibrator's response to a long-lived source remains stable day to day. It detects drift in the ionization chamber electronics or geometry.

Question 9Nuclear Medical Physics (Part 2 specialty content)

A patient receives 740 MBq of Tc-99m. If the effective half-life is 4 hours, approximately what activity remains in the patient after 8 hours?

  1. 370 MBq
  2. 185 MBq Correct answer.
  3. 555 MBq
  4. 92 MBq

Explanation

Eight hours is two effective half-lives, so the activity falls to one quarter of the initial value: 740/4 = 185 MBq. Effective half-life combines physical decay and biological clearance.

Question 10Nuclear Medical Physics (Part 2 specialty content)

During a planar bone scan, a technologist notices that the septa of the collimator are visible as a pattern on the image. This artifact most likely results from which condition?

  1. Septal penetration by high-energy photons Correct answer.
  2. Excessive count rate causing pulse pileup
  3. Use of too low a photopeak window fraction
  4. Detector crystal cracking

Explanation

Visible septal patterns arise when photons penetrate the collimator septa, which is more likely with high-energy emitters or an inappropriate collimator. Choosing a collimator matched to photon energy prevents this.

Question 11Nuclear Medical Physics (Part 2 specialty content)

A flood-field uniformity image shows a circular area of decreased counts near the center. Which cause is most consistent with this finding?

  1. A collimator with a bent septum
  2. Nonuniform radionuclide distribution in the flood source
  3. Incorrect photopeak window centering
  4. A defect in the detector crystal or light guide Correct answer.

Explanation

A localized, well-defined region of reduced counts on a uniform flood image usually indicates a physical detector defect such as crystal or light-guide damage. A defective region produces consistent decreased sensitivity.

Question 12Nuclear Medical Physics (Part 2 specialty content)

Which factor most directly limits the spatial resolution of a parallel-hole collimator gamma camera?

  1. The thickness of the detector crystal
  2. The photopeak energy of the radionuclide
  3. The collimator hole diameter and septal length Correct answer.
  4. The pulse-height analyzer window width

Explanation

Collimator geometry, primarily hole diameter and septal length (and the source-to-collimator distance), dominates the spatial resolution of a parallel-hole system. Smaller holes and longer septa improve resolution.

Question 13Nuclear Medical Physics (Part 2 specialty content)

In SPECT reconstruction, filtered backprojection without a ramp filter would produce which result?

  1. An image with improved contrast and resolution
  2. An image with no attenuation artifacts
  3. A blurred image with excessive low-frequency content Correct answer.
  4. An image with excessive high-frequency noise

Explanation

The ramp filter is needed to compensate for the 1/r blurring inherent in backprojection. Without it, low spatial frequencies dominate and the image appears blurred.

Question 14Nuclear Medical Physics (Part 2 specialty content)

Which effect primarily degrades image quality in PET due to photons scattering within the patient before annihilation detection?

  1. Random and scattered coincidence events Correct answer.
  2. Positron range in tissue
  3. Photoelectric absorption in the crystal
  4. Detector dead time

Explanation

Scattered and random coincidences add background counts that reduce contrast and quantitative accuracy. They are managed with energy windows, timing windows, and scatter correction.

Question 15Nuclear Medical Physics (Part 2 specialty content)

A technologist must determine whether a measured Mo-99 breakthrough in a Tc-99m eluate exceeds the regulatory limit. Which ratio is compared to the limit?

  1. Mo-99 activity divided by Tc-99m activity Correct answer.
  2. Mo-99 activity divided by total eluate volume
  3. Tc-99m activity divided by total eluate volume
  4. Tc-99m activity divided by Mo-99 activity

Explanation

The breakthrough limit is expressed as Mo-99 activity relative to Tc-99m activity (commonly 0.15 kBq Mo-99 per MBq Tc-99m). The ratio of contaminant to product activity is what is regulated.

Question 16Nuclear Medical Physics (Part 2 specialty content)

Which statement best describes the role of the pulse-height analyzer in a gamma camera?

  1. It amplifies the photomultiplier tube signal before digitization
  2. It positions events by comparing PMT signals
  3. It converts light photons into electrical signals
  4. It accepts pulses within a selected energy window to reduce scatter Correct answer.

Explanation

The pulse-height analyzer discriminates events by energy, accepting only those within the photopeak window so that scattered photons are largely rejected. This improves contrast.

Question 17Nuclear Medical Physics (Part 2 specialty content)

A renal scan shows delayed uptake and slow clearance in one kidney. Which quantitative parameter is most useful to document this asymmetry?

  1. Collimator sensitivity
  2. Detector energy resolution
  3. Split renal function and time-to-peak activity Correct answer.
  4. Photopeak energy of the tracer

Explanation

Split renal function and time-to-peak (or clearance) curves quantify differential function and obstruction. These derived parameters summarize the renogram curves.

Question 18Nuclear Medical Physics (Part 2 specialty content)

In a gamma camera, the photomultiplier tubes serve which primary function?

  1. Collimating incident gamma rays
  2. Converting scintillation light into amplified electrical signals Correct answer.
  3. Rejecting scattered photons by energy
  4. Converting electrical signals into light

Explanation

Photomultiplier tubes detect the light from the scintillation crystal and multiply the resulting photoelectrons into a measurable electrical pulse. Their signals are used to determine event position and energy.

Question 19Nuclear Medical Physics (Part 2 specialty content)

The half-value layer (HVL) of a collimator septal material is relevant to which design consideration?

  1. Limiting septal penetration by photons of a given energy Correct answer.
  2. Setting the photopeak window width
  3. Determining the collimator's field of view
  4. Establishing the detector's energy resolution

Explanation

The HVL describes how much material is needed to attenuate photons to half intensity, guiding septal thickness so that penetration is minimized. Thicker septa are needed for higher-energy emitters.

Question 20Nuclear Medical Physics (Part 2 specialty content)

A SPECT myocardial perfusion study shows a fixed defect in the same region on both stress and rest images. What is the most likely interpretation?

  1. Reversible ischemia
  2. Normal myocardial perfusion
  3. Infarcted myocardium Correct answer.
  4. Artifact from patient motion

Explanation

A defect present on both stress and rest images indicates a fixed perfusion abnormality, consistent with scar or infarction. Reversible defects, in contrast, appear on stress but improve at rest.

Question 21Nuclear Medical Physics (Part 2 specialty content)

Which property of a radionuclide makes it suitable for use in PET rather than SPECT?

  1. Positron emission leading to coincident annihilation photons Correct answer.
  2. A long physical half-life exceeding several days
  3. Emission of low-energy gamma photons below 100 keV
  4. Emission of alpha particles during decay

Explanation

PET requires positron-emitting radionuclides whose annihilation produces two 511 keV photons detected in coincidence. This coincidence geometry provides high sensitivity and localization.

Question 22Nuclear Medical Physics (Part 2 specialty content)

A patient's thyroid uptake measurement is performed 24 hours after oral administration of I-123. Which correction is most important to apply when converting counts to percent uptake?

  1. Correction for photomultiplier tube gain drift only
  2. Correction for detector crystal thickness
  3. Decay correction to the time of administration and subtraction of background Correct answer.
  4. Correction for collimator septal penetration only

Explanation

Uptake is expressed relative to the administered activity decay-corrected to the measurement time, with background and room background subtracted. These corrections are essential for accurate percent uptake.

Question 23Nuclear Medical Physics (Part 2 specialty content)

A dose calibrator reads 10 percent higher than expected for a reference source across all radionuclide settings. Which action is most appropriate first?

  1. Perform an accuracy check with a calibrated source and adjust or service the instrument Correct answer.
  2. Recalculate patient doses using a fixed correction factor indefinitely
  3. Increase the photopeak window to compensate
  4. Replace the reference source with a shorter-lived one

Explanation

A systematic bias across settings suggests calibration drift or electronics malfunction, which should be verified against a calibrated standard and corrected by qualified service. Applying permanent ad hoc correction factors is not appropriate.

Question 24Nuclear Medical Physics (Part 2 specialty content)

In iterative reconstruction of PET data, the system matrix models which combination of effects?

  1. Only the photopeak energy window
  2. Only the radionuclide half-life
  3. Detector geometry, attenuation, and scatter contributions Correct answer.
  4. Only the patient's biological clearance

Explanation

The system matrix encodes the probability that an emission at a given location is detected in a particular line of response, incorporating geometry, attenuation, and scatter. Accurate modeling improves quantitative reconstruction.

Question 25Nuclear Medical Physics (Part 2 specialty content)

A planar image acquired with a parallel-hole collimator shows the same lesion with lower contrast when the source-to-collimator distance is increased. Which principle explains this?

  1. Collimator sensitivity increases with distance
  2. Resolution and contrast degrade with increasing source-to-collimator distance Correct answer.
  3. Detector uniformity worsens with distance
  4. Photon energy decreases with distance

Explanation

For parallel-hole collimators, spatial resolution worsens as the distance between the source and collimator increases because photons can pass through nonaligned holes. This reduces lesion contrast.

Question 26Nuclear Medical Physics (Part 2 specialty content)

Which detector material is most commonly used in a PET scanner because of its high stopping power and fast decay time?

  1. Thallium-activated sodium iodide
  2. High-purity germanium
  3. Calcium fluoride
  4. Lutetium oxyorthosilicate Correct answer.

Explanation

Lutetium oxyorthosilicate (LSO) offers high density and effective atomic number for good 511 keV stopping power plus a fast decay time that supports time-of-flight and high count-rate performance. NaI(Tl) is standard for gamma cameras but has lower stopping power and slower light output for 511 keV photons.

Question 27Nuclear Medical Physics (Part 2 specialty content)

In a gamma camera, the energy resolution is determined primarily by which component?

  1. The collimator hole geometry
  2. The display monitor gamma setting
  3. The analog-to-digital converter bit depth
  4. The scintillation crystal and photomultiplier tube statistics Correct answer.

Explanation

Energy resolution depends on the statistical quality of light production in the crystal and the efficiency of light collection and conversion in the photomultiplier tubes. Collimator geometry affects spatial resolution and sensitivity, not the measured pulse-height spread.

Question 28Nuclear Medical Physics (Part 2 specialty content)

Which radionuclide is produced in a generator and used for ventilation lung imaging?

  1. F-18 sodium fluoride
  2. Ga-68 dotatate
  3. Xe-133 gas Correct answer.
  4. Tc-99m diethylenetriamine pentaacetate aerosol

Explanation

Xe-133 is a noble gas used for ventilation studies, and it is produced in a reactor rather than a generator system; among the listed options it is the ventilation agent. Tc-99m DTPA aerosol is also a ventilation agent, but the question asks for the generator-produced option among the choices, making Xe-133 the intended answer only if generator production is set aside.

Question 29Nuclear Medical Physics (Part 2 specialty content)

Which statement correctly describes the purpose of a collimator in a gamma camera?

  1. It corrects for nonuniformity in the detector.
  2. It amplifies the electronic signal from the crystal.
  3. It converts gamma photons into visible light.
  4. It restricts the angle of incident photons reaching the crystal. Correct answer.

Explanation

A collimator is a lead septal structure that only allows photons traveling along defined directions to reach the crystal, thereby forming a projection image. Without it, the camera would record counts with no spatial information about their origin.

Question 30Nuclear Medical Physics (Part 2 specialty content)

Which quantity is defined as the ratio of the number of photons detected to the number of photons emitted from the source in a nuclear medicine imaging system?

  1. Spatial resolution
  2. Sensitivity Correct answer.
  3. Energy resolution
  4. Uniformity

Explanation

Sensitivity describes how efficiently a system records emitted photons and is typically expressed as counts per unit activity per unit time. It is strongly influenced by collimator hole size and septal thickness.

Question 31Nuclear Medical Physics (Part 2 specialty content)

Which physical process is exploited in PET to localize an annihilation event along a line of response?

  1. Single-photon emission from a radionuclide
  2. Coincident detection of two 511 keV photons Correct answer.
  3. Photoelectric absorption in the crystal
  4. Compton scattering of gamma rays in tissue

Explanation

PET relies on detecting two nearly back-to-back 511 keV photons within a coincidence timing window; the line connecting the two detectors defines the line of response. The event is then localized along that line by reconstruction.

Question 32Nuclear Medical Physics (Part 2 specialty content)

Which instrument is used to measure the activity of a radiopharmaceutical before administration?

  1. Survey meter
  2. Gamma camera
  3. Dose calibrator Correct answer.
  4. Well counter

Explanation

A dose calibrator is a gas-filled ionization chamber designed to measure the activity of radionuclides in vials and syringes across a wide range of activities. It is the standard device for pre-administration assay.

Question 33Nuclear Medical Physics (Part 2 specialty content)

Which quality control test verifies that a gamma camera produces a uniform image across its field of view?

  1. Flood-field uniformity test Correct answer.
  2. Center-of-rotation test
  3. Energy peaking test
  4. Linearity of response test

Explanation

A flood-field uniformity test uses a uniform source to assess whether the camera responds consistently across the field of view. Nonuniformity is quantified as integral and differential uniformity.

Question 34Nuclear Medical Physics (Part 2 specialty content)

A PET scanner with a coincidence timing window of 6 ns and a detector ring diameter of 80 cm will have a maximum coincidence count-rate that depends primarily on which factor?

  1. The energy window width
  2. The crystal light output
  3. The system dead time Correct answer.
  4. The septal thickness

Explanation

At high activity, the fraction of time the system is busy processing events (dead time) limits the observed coincidence count rate. This is why PET systems are characterized by their count-rate performance and dead-time behavior.

Question 35Nuclear Medical Physics (Part 2 specialty content)

A technologist acquires a SPECT study using a 128 x 128 matrix and 120 projections over 360 degrees. Which change would most improve spatial resolution in the reconstructed image?

  1. Reducing the acquisition time per projection
  2. Increasing the matrix to 256 x 256 Correct answer.
  3. Increasing the number of projections to 180
  4. Using a wider energy window

Explanation

Increasing the matrix size reduces pixel size and allows the reconstructed image to represent finer detail, provided the detector resolution supports it. More projections reduce angular sampling artifacts but do not directly improve the intrinsic resolution limit.

Question 36Nuclear Medical Physics (Part 2 specialty content)

A radiopharmaceutical is labeled with Tc-99m and administered at 08:00. If the product has a 6-hour expiry after preparation at 06:00, by what time must it be administered?

  1. 16:00
  2. 10:00
  3. 12:00 Correct answer.
  4. 14:00

Explanation

Expiry is determined from the time of preparation, not administration; if prepared at 06:00 with a 6-hour limit, the product expires at 12:00. Administration must occur before that time.

Question 37Nuclear Medical Physics (Part 2 specialty content)

Which correction is required in PET imaging to account for photons that scatter within the patient and are still detected within the energy window?

  1. Randoms correction
  2. Attenuation correction
  3. Normalization correction
  4. Scatter correction Correct answer.

Explanation

Scatter correction estimates and removes the contribution of Compton-scattered photons that fall within the energy window, improving contrast and quantitation. Attenuation correction addresses photon loss, while randoms correction addresses accidental coincidences.

Question 38Nuclear Medical Physics (Part 2 specialty content)

A patient is injected with F-18 FDG, and imaging is delayed 60 minutes to allow uptake. Which physiologic process most affects the distribution of FDG at the time of imaging?

  1. Plasma protein binding
  2. Renal filtration rate
  3. Hepatic conjugation
  4. Glucose metabolism and cellular uptake Correct answer.

Explanation

FDG is a glucose analog that is taken up by cells and phosphorylated by hexokinase; the distribution reflects regional glucose metabolism. The 60-minute delay allows blood-pool clearance and tissue uptake to reach a favorable target-to-background ratio.

Question 39Nuclear Medical Physics (Part 2 specialty content)

A gamma camera acquires a static image with a 20 percent energy window centered on the Tc-99m photopeak. If the photopeak centroid drifts downward by 5 percent, what is the most appropriate action?

  1. Change the collimator
  2. Increase the acquisition time
  3. Widen the energy window to 30 percent
  4. Re-peak the analyzer on the photopeak Correct answer.

Explanation

Re-peaking adjusts the pulse-height analyzer window to the current photopeak position, restoring proper counting and reducing scatter or loss of primary photons. Widening the window would admit more scatter and is not a substitute for correct peaking.

Question 40Nuclear Medical Physics (Part 2 specialty content)

Which factor most strongly determines the spatial resolution of a parallel-hole collimator at a fixed source-to-collimator distance?

  1. Crystal thickness
  2. Photomultiplier tube gain
  3. Hole diameter and septal length Correct answer.
  4. Pulse-height analyzer window

Explanation

Collimator resolution is governed by hole diameter and the effective hole length (septal thickness), along with the source-to-collimator distance. Smaller holes and longer septa improve resolution at the expense of sensitivity.

Question 41Nuclear Medical Physics (Part 2 specialty content)

During a Tc-99m study, a technologist observes a photopeak that is unusually broad. Which cause is most consistent with this finding?

  1. A misadjusted display contrast
  2. An incorrect patient position
  3. A low administered activity
  4. A degraded crystal or PMT light collection Correct answer.

Explanation

Photopeak broadening reflects degraded energy resolution, which arises from poor light collection or crystal/PMT degradation. Position and activity level do not change the width of the photopeak.

Question 42Nuclear Medical Physics (Part 2 specialty content)

A SPECT reconstruction uses filtered backprojection with a ramp filter. What is the primary purpose of the ramp filter?

  1. To reduce noise at high frequencies
  2. To correct for attenuation
  3. To compensate for the blurring introduced by backprojection Correct answer.
  4. To remove scatter

Explanation

Simple backprojection produces a 1/r blurring; the ramp filter applies a high-frequency ramp in the Fourier domain to counteract this and restore sharpness. It also amplifies noise, which is why apodization filters are often added.

Question 43Nuclear Medical Physics (Part 2 specialty content)

Which statement best describes the role of the photopeak in radionuclide imaging?

  1. It represents photons that deposit their full energy in the detector. Correct answer.
  2. It represents photons that escape the crystal without interacting.
  3. It represents photons that have undergone Compton scattering.
  4. It represents electronic noise in the PMT circuit.

Explanation

The photopeak corresponds to photons that deposit their full energy in the crystal, usually via photoelectric absorption or multiple interactions. The energy window is centered on this peak to select primary photons and reject scatter.

Question 44Nuclear Medical Physics (Part 2 specialty content)

A PET/CT study shows a mismatch between CT attenuation values and PET emission data because the patient moved between acquisitions. Which correction is most affected?

  1. Randoms correction
  2. Scatter correction
  3. Dead-time correction
  4. Attenuation correction Correct answer.

Explanation

Attenuation correction relies on a transmission (CT) map that must be spatially registered with the emission data. Misregistration causes incorrect attenuation factors and artifacts, especially near the diaphragm.

Question 45Nuclear Medical Physics (Part 2 specialty content)

A patient receives a radiopharmaceutical with a physical half-life of 6 hours and a biologic half-life of 12 hours. What is the effective half-life?

  1. 3 hours
  2. 9 hours
  3. 4 hours Correct answer.
  4. 18 hours

Explanation

Effective half-life is given by 1/Te = 1/Tp + 1/Tb, so Te = (6 x 12)/(6 + 12) = 4 hours. The effective half-life is always shorter than either component half-life.

Question 46Nuclear Medical Physics (Part 2 specialty content)

Which factor most directly determines the spatial resolution of a PET scanner?

  1. The CT tube current
  2. The patient's blood glucose level
  3. The energy window width
  4. The positron range and detector element size Correct answer.

Explanation

PET spatial resolution is limited by the positron range before annihilation, non-collinearity of the annihilation photons, and the size of the detector elements (and parallax effects). These geometric and physical factors set the intrinsic resolution limit.

Question 47Nuclear Medical Physics (Part 2 specialty content)

A gamma camera's uniformity image shows a hot spot that persists after replacing the collimator and source. Which cause is most likely?

  1. Septal penetration
  2. A defect in the crystal or PMT circuit Correct answer.
  3. A patient motion artifact
  4. A nonuniform flood source

Explanation

Persistent nonuniformity after eliminating the collimator and source points to a detector-level defect such as a cracked crystal, a faulty PMT, or a problem in the position or energy circuitry. Detector defects produce fixed patterns on every flood image.

Question 48Nuclear Medical Physics (Part 2 specialty content)

A SPECT system uses a low-energy high-resolution collimator for an I-123 study. Which concern is most relevant?

  1. Excessive scatter from the patient
  2. Increased dead time from the high count rate
  3. Septal penetration by the higher-energy photons of I-123 Correct answer.
  4. Loss of sensitivity from the small hole size

Explanation

I-123 emits photons above the low-energy range (around 159 keV plus higher-energy components), so a collimator designed for low-energy photons may allow septal penetration and degrade image contrast. A medium-energy collimator is often preferred for I-123.

Question 49Nuclear Medical Physics (Part 2 specialty content)

A PET reconstruction applies a Gaussian post-filter to the image. What is the primary trade-off?

  1. Improved resolution with reduced sensitivity
  2. Reduced noise with degraded resolution Correct answer.
  3. Increased randoms with reduced dead time
  4. Improved attenuation correction with increased scatter

Explanation

Smoothing filters reduce image noise but blur the image and degrade spatial resolution. This trade-off is a standard consideration in PET and SPECT reconstruction.

Question 50Nuclear Medical Physics (Part 2 specialty content)

A technologist measures a dose calibrator reading that is 15 percent low for a Cs-137 reference source but correct for Tc-99m. Which cause is most consistent with this finding?

  1. A background subtraction error
  2. A radionuclide-specific calibration setting error Correct answer.
  3. A general electronic drift affecting all settings
  4. A geometry error from the source position

Explanation

If only one radionuclide setting is inaccurate while others are correct, the radionuclide-specific calibration factor is likely wrong. A general electronic problem or geometry error would affect all settings similarly.