Abstract
PurposeThe study illustrates how a renewed approach to medical physics, Medical Physics 3.0 (MP3.0), can identify performance decrement of digital radiography (DR) systems when conventional Medical Physics 1.0 (MP1.0) methods fail.Methods MP1.0 tests included traditional annual tests plus the manufacturer's automated Quality Assurance Procedures (QAP) of a DR system before and after a radiologist's image quality (IQ) complaint repeated after service intervention. Further analysis was conducted using nontraditional MP3.0 tests including longitudinal review of QAP results from a 15‐yr database, exposure‐dependent signal‐to‐noise (SNR 2), clinical IQ, and correlation with the institutional service database. Clinical images were analyzed in terms of IQ metrics by the Duke University Clinical Imaging Physics Group using previously validated software.ResultsTraditional metrics did not indicate discrepant system performance at any time. QAP reported a decrease in contrast‐to‐noise ratio (CNR) after detector replacement, but remained above the manufacturer's action limit. Clinical images showed increased lung noise (Ln), mediastinum noise (Mn), and subdiaphragm‐lung contrast (SLc), and decreased lung gray level (Lgl) following detector replacement. After detector recalibration, QAP CNR improved, but did not return to previous levels. Lgl and SLc no longer significantly differed from before detector recalibration; however, Ln and Mn remained significantly different. Exposure‐dependent SNR 2 documented the detector operating within acceptable limits 9 yr previously but subsequently becoming miscalibrated sometime before four prior annual tests. Service records revealed catastrophic failure of the computer containing the original detector calibration from 11 yr prior. It is likely that the incorrect calibration backup file was uploaded at that time.Conclusions MP1.0 tests failed to detect substandard system performance, but MP3.0 methods determined the root cause of the problem. MP3.0 exploits the wealth of data with more sensitive performance indicators. Data analytics are powerful tools whose proper application could facilitate early intervention in degraded system performance.
Highlights
1.A | Traditional quality control by clinical medical physicists: Medical Physics 1.0In the routine course of clinical practice, the medical physicist performs tests and analyzes data intended to indicate whether imaging systems are producing adequate image quality at acceptable radiation doses
The most recent annual test was performed on August 5, 2014, in conjunction with the detector replacement, and it passed all of the required tests
The analysis revealed that the detector was operating within acceptable limits in October 2006, but an event occurred before the 2009 data were acquired that caused improper calibration of the detector as shown by abnormally high SNR2 values
Summary
1.A | Traditional quality control by clinical medical physicists: Medical Physics 1.0In the routine course of clinical practice, the medical physicist performs tests and analyzes data intended to indicate whether imaging systems are producing adequate image quality at acceptable radiation doses. A measurement within acceptable criteria is considered to “pass.” Once the system performance level is established, monitoring of its performance is not required until the inspection or service event.[5–7]. This pattern of QC support is what could be called “Medical Physics 1.0 (MP1.0),” the current standard of practice.[8–11]. Clinical medical physicists exceed this basic level of service as their time, resources, and individual preferences allow, but this description provides a reasonable minimum expectation for physicist testing. This level of QC support is consistent with the description of “Level 1 services” defined by the American Association of Physicists in Medicine (AAPM) Diagnostic Work and Workforce Study Subcommittee's Levels of Service model in Report 301.12 In this sense, MP1.0 tests are “well‐ defined, and there is a relatively high degree of agreement among medical physicists on procedures ... to perform them.”[12]
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