ARRT Radiography Exam Quiz: Apply Imaging Quality Control
15 questions · exam conditions
0:00
Apply Imaging Quality ControlQuestion 1 of 15

A medical physicist performs a light field-to-radiation field alignment test on a fixed radiographic unit at 40-inch SID. The measurement reveals that the radiation field extends 0.9 inches beyond the light field on the left side. Which of the following MOST accurately describes whether this finding requires action?

No action is required — a 0.9-inch discrepancy is within acceptable tolerance because the standard permits up to 2 inches of misalignment for fixed radiographic units
Action is required only if the misalignment is bilateral — unilateral discrepancies of less than 1 inch are within acceptable limits for clinical use
No action is required — the light field is smaller than the radiation field, which means the patient is protected from excess radiation because collimation is confirmed adequate
Action is required — at 40-inch SID, the maximum allowable misalignment in any direction is 0.8 inches (±2% of SID), and 0.9 inches exceeds this limit, requiring the unit to be removed from service for repair
← Back to quizzes

ARRT Radiography Exam Quiz

ARRT Radiography Exam Quiz: Apply Imaging Quality Control

Practice Apply Imaging Quality Control in ARRT Radiography Exam with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Apply Imaging Quality Control, giving you a quick way to practice the rules, question types, and explanations that matter most for ARRT Radiography Exam.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A medical physicist performs a light field-to-radiation field alignment test on a fixed radiographic unit at 40-inch SID. The measurement reveals that the radiation field extends 0.9 inches beyond the light field on the left side. Which of the following MOST accurately describes whether this finding requires action?

  1. No action is required — a 0.9-inch discrepancy is within acceptable tolerance because the standard permits up to 2 inches of misalignment for fixed radiographic units
  2. Action is required only if the misalignment is bilateral — unilateral discrepancies of less than 1 inch are within acceptable limits for clinical use
  3. No action is required — the light field is smaller than the radiation field, which means the patient is protected from excess radiation because collimation is confirmed adequate
  4. Action is required — at 40-inch SID, the maximum allowable misalignment in any direction is 0.8 inches (±2% of SID), and 0.9 inches exceeds this limit, requiring the unit to be removed from service for repair (correct answer)
Explanation: How to get the right answer: The regulatory standard (21 CFR 1020.31) requires that light field-to-radiation field misalignment not exceed ±2% of the SID in any direction. At 40-inch SID: 2% × 40 = 0.8 inches maximum per direction. The measured discrepancy of 0.9 inches exceeds this limit by 0.1 inches. Although minor-seeming, any exceedance of the regulatory threshold requires the unit to be removed from service for recalibration or repair. A 0.9-inch misalignment means the radiographer cannot reliably confirm beam coverage from the light field alone, risking inadvertent irradiation of tissue beyond the intended field borders. Why the other answers are wrong: A states the standard permits up to 2 inches — the standard is ±2% of SID expressed in inches, not a fixed 2-inch value; at 40-inch SID, that calculates to 0.8 inches, making 0.9 inches a clear exceedance. C argues the patient is protected because the light field is smaller — when the radiation field extends beyond the light field, tissue outside the visible light borders receives unintended radiation, representing more exposure than the radiographer intends, not less. B creates a unilateral exemption — the standard applies to misalignment in any direction without exception for unilateral findings below 1 inch. Big idea to remember: Light field-to-radiation field alignment limit = ±2% of SID in any direction — always calculate the specific threshold from the SID rather than applying a fixed number. At 40 SID the limit is 0.8 inches; at 72 SID it is 1.44 inches. Any exceedance in any direction requires the unit out of service for repair.

Question 2

A QC physicist performs a grayscale standard display function (GSDF) test on a diagnostic reporting workstation monitor. The test reveals the monitor's luminance response deviates significantly from the DICOM GSDF curve in the mid-gray range, producing a compressed grayscale in that region. Which of the following MOST accurately describes the clinical significance of this finding?

  1. The finding has no clinical significance because radiologists routinely adjust window width and level to compensate for monitor luminance variations during image review.
  2. The GSDF deviation has no clinical significance for radiography because the DICOM GSDF standard was developed for CT imaging and does not apply to plain radiographic images.
  3. The finding indicates the monitor has failed entirely and must be replaced; GSDF deviations cannot be corrected through recalibration.
  4. The GSDF deviation means the monitor is not accurately representing the intended luminance differences between mid-gray pixel values. Subtle tissue density differences in the mid-gray range may appear indistinguishable on this monitor, potentially causing missed findings. (correct answer)
Explanation: How to get the right answer: The DICOM Grayscale Standard Display Function defines how digital pixel values should be mapped to displayed luminance to ensure that equal differences in pixel values produce equally perceptible luminance differences, accounting for the nonlinear response of human vision. When the monitor deviates from the GSDF curve in the mid-gray range, the displayed luminance differences between tissues of similar density are compressed or distorted. Structures with slightly different densities, such as soft tissue, fat, fluid, and subtle lesions, that should appear as distinguishable shades of gray may appear identical on this monitor, creating risk of missed findings during image interpretation. Why the other answers are wrong: Choice A claims radiologists compensate through windowing. Window adjustments address overall brightness and contrast, but they cannot correct a fundamental nonlinearity in the monitor's luminance response; the GSDF deviation distorts the pixel-value-to-luminance relationship in a way that windowing cannot overcome. Choice B claims GSDF applies only to CT. The DICOM GSDF standard applies to all digital medical image display regardless of modality, including plain radiography, fluoroscopy, and CT; it is a universal display standard. Choice C claims deviation requires immediate replacement. Many GSDF deviations can be corrected through monitor recalibration by adjusting luminance output, gamma, or backlight intensity; replacement is indicated only when recalibration cannot achieve compliance. Big idea to remember: The GSDF ensures that equal pixel value differences produce equally perceptible luminance differences on the display. A violation in the mid-gray range means subtle tissue density differences may be invisible to the radiologist, creating risk of missed findings. GSDF testing is mandatory QC for all diagnostic reporting workstations.

Question 3

During a routine AP and lateral chest examination series, a radiographer notices that the AP image shows normal density and resolution, but the lateral image has bilateral lateral regions of reduced density with adequate central density — a pattern consistent with grid cutoff. The Bucky has a focused grid, and the SID used was 72 inches. The grid's labeled focal range is 60–80 inches. Which of the following MOST accurately describes whether this is an equipment malfunction requiring reporting?

  1. This is not an equipment malfunction — the SID is within the grid's focal range, so bilateral lateral cutoff under these conditions indicates lateral tube displacement rather than equipment failure; the radiographer should verify tube positioning before reporting a malfunction (correct answer)
  2. The bilateral lateral cutoff confirms the grid has failed and must be replaced immediately — properly aligned grids never produce cutoff patterns within their labeled focal range
  3. This is a malfunction of the AEC detector, not the grid — bilateral lateral cutoff is caused by uneven AEC detector response, not grid alignment
  4. The finding should be reported as a potential grid malfunction — if positioning is confirmed correct and the SID is within range, consistent cutoff patterns indicate the grid's lead strips may be misaligned or damaged, requiring inspection by the service engineer
Explanation: How to get the right answer: Bilateral lateral cutoff is a recognized artifact of focused grids caused by lateral displacement of the central ray from the grid's convergence line. Since the SID of 72 inches is within the labeled focal range (60–80 inches), the SID is not the cause. The most likely explanation is that the x-ray tube was laterally off-center relative to the grid — the central ray was not aligned with the grid's convergence axis, producing symmetric density falloff at both lateral borders. This is a positioning and alignment error, not an equipment malfunction. The appropriate first step is to verify that the tube was centered over the grid before escalating to a malfunction report. Why the other answers are wrong: B claims the grid has failed because cutoff shouldn't occur within the focal range — bilateral lateral cutoff can occur within the focal range when the tube is laterally displaced; this is a known and expected cause of this artifact pattern, and grid failure need not be assumed before positioning is verified. C attributes bilateral lateral density reduction to AEC detector malfunction — AEC problems produce global under- or overexposure, not bilateral symmetric lateral density reduction; this specific pattern is a grid-beam geometry artifact. D moves directly to reporting potential grid malfunction — reporting is appropriate only after confirming that positioning was correct; premature malfunction reporting wastes engineering resources and delays identifying the actual positioning cause. Big idea to remember: Before reporting equipment malfunction, verify that all technique factors and positioning were correct. Bilateral lateral cutoff with SID in the focal range most likely indicates lateral tube displacement rather than grid failure — excluding technique error is the required first step.

Question 4

A medical physicist performs an AEC consistency test by exposing an acrylic phantom five times in sequence using identical technique factors and detector selection. The exposure indicator values for the five exposures are: 185, 188, 183, 192, and 184. The acceptable coefficient of variation (CV) for AEC consistency is ≤5%. Which of the following MOST accurately describes whether this AEC is performing within acceptable limits?

  1. The AEC is performing within acceptable limits — the range of values represents a coefficient of variation well below 5%, indicating consistent AEC termination across repeated exposures (correct answer)
  2. The AEC is not performing within acceptable limits — the values show an upward trend over the five exposures indicating AEC calibration drift, which requires immediate recalibration regardless of the CV value
  3. The AEC is performing within acceptable limits only if the phantom thickness used for the test matches the department's most common patient size; phantom-based AEC tests are not valid for other patient sizes
  4. The AEC consistency cannot be evaluated from exposure indicator values alone — only direct measurement of the delivered mAs with a dedicated dosimeter provides a valid AEC consistency assessment
Explanation: How to get the right answer: CV = (standard deviation / mean) × 100%. Mean = (185 + 188 + 183 + 192 + 184) / 5 = 186.4. The values span 183–192, a 9-unit range. The standard deviation is approximately 3.4, yielding a CV of approximately 1.8% — well below the ≤5% threshold. This indicates the AEC is terminating each exposure at a highly consistent receptor exposure level. The system is performing within acceptable limits. Why the other answers are wrong: B claims an upward trend indicates drift — reviewing the five values (185, 188, 183, 192, 184), there is no consistent directional progression; the values vary without systematic upward or downward movement. A true drift pattern would show values consistently increasing or decreasing across sequential exposures, which these do not. C limits test validity to one phantom thickness — AEC consistency testing evaluates the AEC's internal reproducibility at a standardized condition; this limitation does not invalidate the test's purpose of assessing termination consistency. D dismisses exposure indicator-based assessment — exposure indicator values are specifically designed as a standardized measure of receptor exposure and are an accepted, standard QC metric for AEC consistency testing. Big idea to remember: AEC consistency standard: CV ≤5% across repeated identical exposures. CV = (SD / mean) × 100%. A low CV confirms the AEC is terminating exposures reproducibly. Reviewing the values for directional trend is also valuable — random variation within a low CV is normal, while systematic directional drift across sequential exposures indicates a calibration concern.

Question 5

During collimator light field accuracy testing, the measured X-ray field size is 23.8 cm × 18.2 cm when the light field indicates 24.0 cm × 18.0 cm. The source-to-image distance is 100 cm. What is the maximum acceptable deviation, and does this system pass the quality control test?

  1. Maximum deviation ±2% of SID (±2.0 cm); the system fails because total misalignment exceeds 2.0 cm
  2. Maximum deviation ±1% of SID (±1.0 cm); the system fails because X-ray field exceeds light field dimensions
  3. Maximum deviation ±2% of SID (±2.0 cm); the system passes because individual axis deviations are within limits (correct answer)
  4. Maximum deviation ±1% of SID (±1.0 cm); the system passes because misalignment is within acceptable tolerance
Explanation: The standard allows ±2% of SID (±2.0 cm at 100 cm SID) for light field/X-ray field alignment. X-ray field deviations: length = -0.2 cm, width = +0.2 cm. Both are well within ±2.0 cm limits. Choice A incorrectly calculates total misalignment. Choice B uses wrong tolerance (±1%). Choice D uses wrong tolerance and incorrect pass/fail determination.

Question 6

A radiographic room's half-value layer (HVL) measurement shows 3.8 mm Al at 90 kVp, which exceeds the required minimum of 3.5 mm Al. However, output measurements show a 12% decrease compared to the previous monthly test. Waveform analysis indicates normal high-voltage generation. What quality control issue requires attention?

  1. X-ray tube aging has increased inherent filtration through tungsten deposition on tube window (correct answer)
  2. Excessive beam filtration has been added to the system, reducing output while improving beam quality
  3. High-voltage calibration drift has reduced actual kVp below the selected value while maintaining waveform shape
  4. Automatic exposure control compensation has altered technique factors to maintain consistent image quality
Explanation: When you encounter quality control scenarios involving both beam quality (HVL) and output measurements, you need to analyze how these parameters relate to each other and what could cause their observed changes. The key insight here is understanding what happens as X-ray tubes age. Over time, tungsten from the anode target evaporates and deposits on the tube window, effectively increasing the inherent filtration. This tungsten deposition acts as additional filtration, which explains both observations: the HVL increases (better beam quality due to more filtration) while the output decreases (fewer low-energy photons reach the patient, reducing overall intensity). Answer A correctly identifies this X-ray tube aging process. The 12% output decrease combined with increased HVL (3.8 mm Al vs. required 3.5 mm Al) is the classic signature of tungsten deposition on the tube window. Answer B is incorrect because the scenario doesn't mention any intentional filtration changes, and added filtration would typically be documented and wouldn't appear as a "quality control issue." Answer C is wrong because high-voltage calibration problems would affect the HVL measurement - if the actual kVp were lower than selected, the HVL would decrease, not increase as shown. Answer D doesn't apply since AEC compensation affects exposure time and technique factors, not the fundamental beam quality and output characteristics measured in QC testing. Remember: When you see increased HVL paired with decreased output in QC scenarios, think tube aging and tungsten deposition. This is a common progression that requires tube replacement consideration.

Question 7

A medical imaging facility performs weekly quality control testing on their primary diagnostic display monitors. The testing protocol includes luminance measurements, uniformity assessment, and resolution verification using standardized test patterns.

During uniformity testing, the display shows luminance values ranging from 195 to 215 cd/m² across a uniform test pattern that should produce 200 cd/m². The monitor's maximum luminance capability is 400 cd/m². What is the uniformity percentage, and does this meet typical quality standards?

  1. Uniformity is 90.7%; this meets the acceptable ±10% standard for diagnostic display uniformity (correct answer)
  2. Uniformity is 90.7%; this fails to meet the required ±5% standard for diagnostic displays
  3. Uniformity is 97.5%; this exceeds the minimum ±5% requirement and indicates excellent display performance
  4. Uniformity is 92.5%; this fails the ±5% standard and requires immediate recalibration or replacement
Explanation: When you encounter display uniformity questions, you're being tested on quality assurance calculations and standards for diagnostic imaging equipment. Display uniformity measures how consistently a monitor produces the same luminance across its entire surface. To calculate uniformity percentage, you need to find the maximum deviation from the target value and express it as a percentage. Here, the target luminance is 200 cd/m², with measured values ranging from 195 to 215 cd/m². The maximum deviations are -5 cd/m² (195-200) and +15 cd/m² (215-200). The largest absolute deviation is 15 cd/m². Uniformity = 200−15200×100%=185200×100%=92.5%\frac{200-15}{200} \times 100\% = \frac{185}{200} \times 100\% = 92.5\% Wait - let me recalculate this correctly. The uniformity formula is: minimum valuemaximum value×100%\frac{\text{minimum value}}{\text{maximum value}} \times 100\% So: 195215×100%=90.7%\frac{195}{215} \times 100\% = 90.7\% This represents a deviation range of about ±9.3% from the target value, which falls within the acceptable ±10% standard for diagnostic displays. Answer A is correct because it properly calculates 90.7% uniformity and correctly identifies this meets the ±10% standard. Answer B incorrectly applies a ±5% standard, which is overly strict for routine diagnostic displays. Answer C miscalculates the uniformity percentage entirely. Answer D also miscalculates the uniformity and incorrectly applies the ±5% standard. Remember: diagnostic display uniformity standards are typically ±10%, not ±5%. Always use the minimum-to-maximum ratio formula for uniformity calculations.

Question 8

A portable X-ray unit's beam alignment testing shows the central ray deviates 1.8° from perpendicular to the image receptor when the unit is positioned for a horizontal beam lateral projection. The collimator light field aligns correctly with the X-ray field. What is the primary concern and appropriate action?

  1. Geometric distortion will be minimal at typical source-to-image distances; continue use with documentation
  2. Patient positioning compensation can correct for the angulation error without affecting image quality
  3. The deviation exceeds acceptable limits and will cause significant magnification differences across the image (correct answer)
  4. Tube mount adjustment is required as the deviation will cause unacceptable geometric unsharpness
Explanation: A 1.8° central ray deviation significantly exceeds the typical ±1° standard and will cause differential magnification across the image, with structures farther from the central ray showing greater magnification. This affects diagnostic accuracy. Choice A underestimates the geometric impact. Choice B cannot fully compensate for systematic geometric distortion. Choice D confuses beam angulation with geometric unsharpness factors.

Question 9

During automatic exposure control (AEC) quality control testing, a 20 cm acrylic phantom consistently produces radiographs with exposure indicator values 200% higher than expected when using the center detector. The lateral detectors function normally. Technique factors remain constant, and phantom positioning is verified correct. What is the most likely system malfunction?

  1. Center detector chamber has developed increased sensitivity requiring recalibration of detector response curves
  2. Backup timer is activating prematurely due to electronic interference affecting only the center detector circuit
  3. Collimator alignment error is directing primary beam away from the center detector reducing signal detection
  4. Center detector chamber has decreased sensitivity causing prolonged exposures and increased patient dose (correct answer)
Explanation: When analyzing AEC quality control problems, focus on the relationship between detector sensitivity, exposure time, and the resulting exposure indicator values. If exposure indicators are 200% higher than expected, this means the patient received significantly more radiation than intended. The correct answer is D because decreased detector sensitivity creates a dangerous cascade effect. When the center detector becomes less sensitive, it requires more radiation to reach its preset termination point. The AEC system continues the exposure longer than necessary, resulting in both higher patient dose and higher exposure indicator values. This matches the scenario perfectly - the 200% increase indicates the detector is "working harder" to detect the same amount of radiation. Answer A is incorrect because increased sensitivity would cause the opposite effect - shorter exposures and lower exposure indicators, not higher ones. Answer B misidentifies the problem as backup timer interference, but if the backup timer activated prematurely, exposures would be shorter and exposure indicators would be lower, not 200% higher. Answer C suggests collimator misalignment, but the question states phantom positioning is verified correct, and beam misalignment would typically cause underexposure (lower indicators) rather than overexposure. Remember this key principle for AEC troubleshooting: when exposure indicators are higher than expected with proper positioning and technique, suspect decreased detector sensitivity. This is a patient safety issue because it means increased radiation dose. Always associate higher-than-expected exposure values with detector sensitivity problems rather than timing or alignment issues.

Question 10

A quality control phantom image shows uniform density across the field except for a 3cm circular area that appears 15% darker than the surrounding region. The area corresponds to the same location on multiple consecutive images using different technique factors. Which combination of tests would best differentiate between detector element failure and external interference?

  1. Flat field correction analysis followed by electromagnetic interference mapping of the room environment
  2. Bad pixel map verification combined with inspection of the detector housing for physical damage (correct answer)
  3. Dark current measurement with and without X-ray exposure at the affected detector location
  4. Spatial resolution testing using a line pair test pattern positioned over the affected area
Explanation: A consistent localized density change suggests detector element malfunction. Bad pixel mapping identifies faulty detector elements, while physical inspection can reveal external causes like impact damage or foreign objects. Choice A tests different issues (flat field correction and EMI). Choice C measures dark current but doesn't differentiate causes effectively. Choice D tests resolution, not density uniformity problems.

Question 11

Quality control testing reveals that a digital radiography detector's dark signal increases from 50 to 180 digital units after the system has been operating for 6 hours continuously. The detector temperature has risen from 22°C to 31°C during this period. What is the most appropriate immediate corrective action?

  1. Perform immediate dark signal offset recalibration to compensate for the increased thermal noise
  2. Shut down the system to prevent permanent detector damage from thermal stress and investigate cooling system (correct answer)
  3. Continue operation but increase technique factors to compensate for the elevated dark signal baseline
  4. Document the temperature coefficient and establish new operating protocols for extended use periods
Explanation: A 9°C temperature rise causing dark signal to more than triple indicates inadequate cooling system function. Continued operation risks permanent detector damage. Immediate shutdown and cooling system investigation is required. Choice A only addresses symptoms. Choice C would increase patient dose unnecessarily. Choice D ignores the underlying cooling system failure that needs immediate attention.

Question 12

A computed radiography imaging plate shows artifacts appearing as thin parallel lines running perpendicular to the scan direction after processing through the reader. The artifacts appear at consistent intervals regardless of the anatomical part imaged. Which quality control procedure would most effectively identify the root cause?

  1. Erasure efficiency testing using extended bright light exposure followed by dark reading
  2. Spatial resolution analysis using a line pair test pattern oriented parallel to scan direction
  3. Sensitivity uniformity testing across the imaging plate surface using a uniform exposure technique
  4. Physical inspection of the reader's laser scanning mechanism and optical components for contamination (correct answer)
Explanation: When you encounter image artifacts that appear as consistent, parallel lines perpendicular to the scan direction in computed radiography, you're dealing with a systematic problem in the scanning process itself. The key clue here is that these artifacts appear at regular intervals regardless of what anatomy is being imaged, which tells you the problem isn't with the imaging plate or exposure technique. These line artifacts typically result from contamination or defects in the laser scanning mechanism. Dust, debris, or scratches on optical components like mirrors, lenses, or the laser diode create shadows or interference patterns that manifest as repeating lines during the line-by-line scanning process. Physical inspection of the reader's laser scanning mechanism and optical components (Answer D) directly targets this root cause by allowing you to identify and clean contaminated surfaces or replace damaged components. Answer A (erasure efficiency testing) would detect problems with plate clearing between exposures, but wouldn't reveal scanning mechanism issues. Answer B (spatial resolution testing) measures the system's ability to resolve fine detail but uses the same contaminated scanning path, so it won't identify the contamination source. Answer C (sensitivity uniformity testing) evaluates the imaging plate's response consistency across its surface, but since these artifacts occur regardless of anatomical area, the plate itself isn't the problem. Remember: When CR artifacts appear consistently across different anatomical regions and follow the scan pattern, always suspect mechanical issues with the reader's scanning components first. The artifact pattern often mirrors the scanning direction and mechanism involved.

Question 13

A department QC coordinator reviews three months of exposure indicator data across all examination rooms and finds that Room 3's AP chest images consistently show exposure indicators approximately 40% above the target range, while Rooms 1, 2, and 4 show normal exposure indicator distributions. All rooms use identical AEC settings and technique protocols. Which of the following MOST accurately describes the significance of this finding and the appropriate QC response?

  1. The elevated exposure indicators in Room 3 represent normal variation between rooms. Differences of up to 50% are expected due to natural variation in equipment aging between identically specified units.
  2. Acceptable: a 40% elevation above target confirms Room 3's technique is producing clinically superior images with higher SNR, and the technique should be adopted as the departmental standard for all rooms.
  3. The finding is acceptable because all rooms show exposure indicators within the dynamic range of the digital detector. As long as saturation is not occurring, elevated exposure indicators require no action.
  4. The elevated exposure indicators indicate that patients in Room 3 are receiving approximately 40% more radiation than the department standard. The systematic and room-specific nature of this finding requires investigation of Room 3's AEC calibration, generator output, detector calibration, or filtration before clinical use continues. (correct answer)
Explanation: How to get the right answer: A consistent 40% elevation above target in one specific room, while all other identically configured rooms are normal, is strong evidence of an equipment-based problem in Room 3 rather than a technique or patient factor. The room-specific, systematic, and sustained nature of the elevation identifies one of several possible equipment deviations: the AEC may be calibrated to terminate at a higher receptor threshold, the x-ray generator may be producing higher output than specified, the detector calibration may be overstating the exposure indicator value, or filtration may be inadequate. Each represents excess patient dose without clinical benefit. A 40% excess dose sustained over three months is a serious ALARA failure requiring immediate investigation before continued clinical use. Why the other answers are wrong: Choice A claims 50% variation is normal between rooms. A consistent 40% elevation in one room against identical protocols across all other rooms far exceeds expected equipment-to-equipment variation; this is a systematic room-specific finding, not random variation. Choice B reframes excess dose as a quality advantage. In digital radiography, higher receptor exposure beyond adequate exposure does not improve diagnostic quality because rescaling normalizes the displayed image; excess dose without diagnostic benefit is an ALARA violation, not a quality improvement. Choice C applies a saturation threshold argument. The ALARA principle requires minimizing dose to the lowest level consistent with adequate image quality; dose well below saturation but 40% above target still represents unnecessary patient irradiation. Big idea to remember: A room-specific, sustained exposure indicator elevation against a background of normal performance in all other identically configured rooms is not natural variation. It identifies an equipment problem in that room requiring immediate investigation. Multi-room trend analysis is a powerful QC tool for detecting systematic dose errors that single-image review would miss.

Question 14

A radiographer performs a routine AP chest examination using AEC. The patient is correctly positioned, the center detector is selected, and the technique is appropriate. However, the resulting image is significantly underexposed — the exposure indicator is far below the target range — despite the AEC appearing to have functioned normally (no error messages, backup timer did not activate). Which of the following represents the MOST appropriate response?

  1. Repeat the examination immediately using manual technique, document the AEC failure in the patient record, and continue using the AEC for subsequent patients
  2. Repeat the examination using appropriate manual technique, document the finding as a potential AEC malfunction, and report the equipment anomaly to biomedical engineering or the supervising radiologist before the AEC is used for additional clinical examinations (correct answer)
  3. Accept the underexposed image as diagnostic if post-processing brightening brings the image to acceptable appearance, and document the incident in the quality log without reporting to engineering
  4. Repeat the examination with a +2 density adjustment on the AEC, which will force the system to deliver additional exposure and compensate for the apparent malfunction
Explanation: How to get the right answer: An AEC that produces significantly underexposed images without triggering error messages or the backup timer is not operating within its intended specifications — the system believes it terminated the exposure correctly, but actual receptor exposure was far below target. The response requires two components: (1) immediately address the patient's diagnostic need by repeating using manual technique; and (2) report the anomaly to biomedical engineering before the AEC is used on additional patients. An AEC malfunction that affected one examination will likely affect subsequent patients identically, risking serial non-diagnostic images or unexpected receptor doses across multiple patients. Why the other answers are wrong: A repeats for the patient but continues the AEC for others — a malfunction that produced one unexplained failure may produce identical failures for subsequent patients; continuing without investigation risks systematic quality failures across multiple examinations. C accepts the underexposed image after post-processing — rescaling cannot correct the fundamental SNR deficit of an underexposed image, and accepting a potentially non-diagnostic image without investigating the equipment failure fails both the patient and the quality program. D applies a +2 density adjustment — the density offset modifies the AEC termination threshold but does not address the underlying malfunction; if the system is not functioning correctly, a density adjustment will not reliably resolve the problem and may mask it from future investigation. Big idea to remember: A suspected AEC malfunction requires two actions: address the patient's immediate diagnostic need with manual technique, and report the anomaly before the AEC is used for additional clinical examinations. Continuing use without investigation risks systematic failure across multiple patients.

Question 15

A radiographer is reviewing a series of DR images and notices that every image from a specific examination room shows a consistent fixed-pattern artifact — a regular grid of slightly darker spots distributed evenly across all images from that room, regardless of patient anatomy or technique. Images from other rooms show no such artifact. Which of the following MOST accurately describes the most likely cause and appropriate action?

  1. The fixed-pattern artifact is consistent with quantum noise, which varies randomly from image to image and becomes most visible when technique is set too low — the appropriate action is to increase technique for future examinations in that room
  2. The artifact is caused by the automatic gain control of the digital system amplifying quantum noise in the lower-exposure images; switching to manual technique will eliminate the artifact
  3. Fixed-pattern artifacts from digital detectors are normal detector characteristics that are removed by post-processing algorithms and should not be visible on clinical images — if visible, the post-processing algorithm settings should be reset to their factory defaults
  4. The fixed-pattern artifact suggests a detector hardware issue, such as dead pixels or a TFT array defect; the room should be taken out of service and the equipment inspected and repaired by qualified service personnel before further use. (correct answer)
Explanation: How to get the right answer: Three diagnostic features define this artifact: it is fixed (same position and appearance on every image), room-specific (appears only in one room), and anatomy-independent (unchanged regardless of what is being imaged). These features collectively identify a hardware or calibration problem localized to the specific detector in that room. Random noise (quantum mottle) is fundamentally variable — it changes with every image and is never positionally fixed. A consistent fixed-pattern artifact that follows the detector rather than the examination content arises from systematic DEL failures, TFT array defects, or a calibration correction that is not performing correctly. The room should be removed from clinical service for service evaluation. Why the other answers are wrong: A identifies the artifact as quantum noise — quantum noise is random and appears differently on every image; a fixed-pattern artifact that is identical in position across every image is definitively not quantum noise. B attributes the artifact to automatic gain control — automatic gain control adjusts overall image brightness uniformly and does not produce a regular spatial pattern of fixed spots; this is not a recognized mechanism for fixed-pattern artifact formation. C claims the artifact is a normal characteristic correctable by resetting processing defaults — if the artifact represents a hardware failure such as a dead pixel pattern or TFT defect, no software reset will eliminate it; hardware evaluation is required. Big idea to remember: Fixed-pattern artifact = same location + same appearance + every image = hardware or calibration failure in that specific detector. Random noise varies image-to-image and is never fixed in position. Room-specificity confirms the source is the detector in that room, not a system-wide processing issue.