Appendix F — Image Quality & QC Tools
Purpose
This appendix provides a reference for evaluating image quality from an equipment and exposure standpoint, rather than positioning. It also introduces common tools used in radiographic quality control (QC), including acceptable limits and tolerances relevant to the ARRT exam. Students and preceptors can use this section to identify potential equipment-related issues and ensure compliance with quality standards.
Table 1: Image Quality Factors (Equipment-Related)
This table outlines key technical factors that influence image quality from an equipment and exposure perspective. Understanding how each factor affects the final image helps students recognize when poor image quality may be due to equipment settings rather than positioning errors.
| Factor | Description | Impact on Image | Common Issues |
|---|---|---|---|
| kVp | Controls beam penetration and contrast | Higher kVp = lower contrast; lower kVp = higher contrast | Incorrect contrast, over/under penetration |
| mAs | Controls beam quantity and image density | Higher mAs = darker image; lower mAs = lighter image | Noise, underexposure, overexposure |
| SID | Source-to-image distance | Affects magnification and density | Magnification errors, inconsistent density |
| Grid Use | Reduces scatter radiation | Improves contrast | Grid cutoff, misalignment |
| Focal Spot Size | Determines sharpness/resolution | Smaller focal spot = better detail | Blurring, loss of detail |
| Beam Filtration | Removes low-energy photons | Improves beam quality and patient dose | Increased patient dose, poor contrast |
| Receptor Exposure Index | Numeric value indicating exposure level | Helps assess image adequacy | Over/underexposure, inconsistent technique |
Table 2: Common QC Tools and Tests
This table introduces standard quality control tools and procedures used to evaluate radiographic equipment performance. These tests help ensure consistent image quality and patient safety, and students should be familiar with their purpose, frequency, and acceptable limits for the ARRT exam.
| Tool/Test | Purpose | Frequency | Acceptable Limits (ARRT) |
|---|---|---|---|
| Step Wedge / Penetrometer | Evaluates contrast and exposure consistency | Monthly or after service | Consistent density steps across exposures |
| Resolution Test Tool | Assesses spatial resolution | Annually | Must meet manufacturer specs |
| Beam Alignment Tool | Checks collimation and beam alignment | Semiannually | ±2% of SID for collimation; ±1° for alignment |
| kVp Test Tool | Verifies accuracy of kVp settings | Annually | ±5% of indicated kVp |
| Timer Accuracy Test | Checks exposure time accuracy | Annually | ±5% for exposures >10 ms |
| mAs Linearity Test | Ensures consistent output across mA/time combinations | Annually | ±10% variation |
| Reproducibility Test | Checks consistency of output for same settings | Annually | ±5% variation |
Table 3: Digital System QC
Digital imaging systems require regular quality checks to maintain diagnostic accuracy. This table highlights common QC procedures for digital detectors, monitors, and related components. Students should understand these tests to recognize digital system issues and meet ARRT expectations.
| Tool/Test | Purpose | Frequency | Acceptable Limits (ARRT) |
|---|---|---|---|
| Monitor Calibration | Ensures accurate display of grayscale and contrast | Monthly or per facility protocol | Consistent grayscale ramp; no missing steps |
| Detector Uniformity Test | Checks for consistent response across the detector | Monthly | No significant variation across image field |
| Dead Pixel Test | Identifies non-functioning pixels in the detector | Monthly | Within manufacturer’s tolerance (typically <0.1%) |
| Noise/Signal-to-Noise Ratio (SNR) | Evaluates image noise levels | Quarterly | SNR must meet manufacturer specifications |
| Exposure Index (EI) Consistency | Verifies accuracy of EI values across exposures | Monthly | ±20% of expected EI for given technique |
| Laser Printer QC (if applicable) | Ensures printed images match digital display | Monthly | Consistent grayscale and resolution |
Key References
American Registry of Radiologic Technologists. (n.d.). Examination content specifications: Radiography. https://www.arrt.org/pages/arrt-reference-documents/by-document-type/examination-content-specifications
Seeram, E. (2019). Digital radiography: Physical principles and quality control (2nd ed.). Springer. https://doi.org/10.1007/978-981-13-3244-9
Bushong, S. C. (2017). Radiologic science for technologists: Physics, biology, and protection (11th ed.). Elsevier.
Carlton, R. R., Adler, A. M., Balac, V., & Griswold, R. (2020). Principles of radiographic imaging: An art and a science (6th ed.). Cengage.
Image Gently Alliance. (n.d.). Radiologic technologist resources. https://imagegently.org/education
