Image Quality Control and Data Management

Once the imaging sites have been selected, the imaging protocol designed, and the technologists trained, image acquisition, transfer, and quality must be closely supervised to ensure a high-quality image set for analysis. Variability in image quality can be introduced either by the manner in which the subject is prepared for the examination and/or by improper calibration and maintenance of the imaging system. Device performance is documented and maintained by performing device quality control. One aspect of this is done by the imaging sites as part of their routine clinical quality control, but additional study-specific quality control must also be performed by the central radiology service. As mentioned above, this often requires the use of specialized phantoms (Figs. 19 and 20).

After the images are acquired according to the study-specific protocol, they are transmitted to the central radiologist(s) for review of protocol compliance, patient positioning, anatomical coverage, and image quality. This requires explicit image-quality (IQ) criteria. For example, serial radiographs of the knee for measuring joint-space narrowing (a marker of articular cartilage loss) in osteoarthritis must show reproducible projection of the anatomy, especially the region of the joint space to be measured. This is done both subjectively by an experienced reader visually comparing serial radiographs (Fig. 21) and by quantitative measurements of anatomical landmarks. For example, the distance between the anterior and posterior rims of the tibial plateau or between the suprior margin of the patella and

Figure 21 Quality control of serial radiography of the knee in osteoarthritis. Quality control includes assessment of the reproducibility of radioanatomical positioning. This is best done through side-by-side comparison of serially acquired images. (Courtesy of Synarc, Inc., with permission.)

Figure 22 Evaluating serial knee positioning. Lateral joint-space width is markedly more narrowed in (B) than it is in (A) in this patient with prior anterior cruciate ligament repair. However, this difference is due to greater flexion of the knee in (B) rather than actual cartilage thinning, as the images were acquired only minutes apart. Note the lower position of the patella relative to the articular surface of the femur on (B) compared to (A). This, along with narrowing of the distance between the apex of the fibula and the tibial plateau are indicative of increased flexion in B. Image B also shows greater external rotation of the knee, as indicated by the widening of the interosseous space between the fibula and tibia (*).

Figure 22 Evaluating serial knee positioning. Lateral joint-space width is markedly more narrowed in (B) than it is in (A) in this patient with prior anterior cruciate ligament repair. However, this difference is due to greater flexion of the knee in (B) rather than actual cartilage thinning, as the images were acquired only minutes apart. Note the lower position of the patella relative to the articular surface of the femur on (B) compared to (A). This, along with narrowing of the distance between the apex of the fibula and the tibial plateau are indicative of increased flexion in B. Image B also shows greater external rotation of the knee, as indicated by the widening of the interosseous space between the fibula and tibia (*).

Figure 23 Magnification error in knee radiography. The graphs show how variations in the distance from the x-ray source to the film (right graph) have only minor effect on magnification, but even small changes in knee-to-film distance (left graph) alter magnification markedly.
Figure 24 Image quality control in clinical trials. Shown is the process that a centralized clinical-trials radiology service uses to quality-control and analyze multisite image data.

the articular surface of the femur are measures of knee flexion, whereas the width of the interosseous space between the fibula and tibia is a marker of knee rotation (Fig. 22). Fiduciary phantoms (Fig. 17) and integrated image analysis software can also be used to verify knee side (right, left) and x-ray beam angulation on serial examinations to and quantify any changes in geometrical magnification (Fig. 23).

If the images are of acceptable quality, they are entered into the central study database. All processes performed by the central radiology service must be done in strict accordance with standard operating procedures (SOPs) and study-specific procedures (SSPs). If the image data do not pass the incoming quality inspection, a decision needs to be a made as to whether or not the data can be corrected, for example, by using information obtained from the instrument quality control. If the images cannot be salvaged, the imaging must be repeated or the data point discarded. The criteria applied are again controlled by SOPs, and data exclusions must be carefully documented. If repeat imaging is necessary a feedback loop must be designed with appropriate timing criteria. Final data consistency checks are applied before the data are submitted for filing and there may be an opportunity for a final adjustment if supported by appropriate instrument quality control information. The ultimate result of this process (Fig. 24) is a high-quality image set that conforms to rigorous quality assurance principles and can support high-quality image analysis.

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