External quality control of gamma cameras —results of an inter-laboratory comparison study in Austria

Abstract

Some 28 nuclear medicine departments out of a total of 40 participated in a nationwide Austrian interlaboratory comparison of the imaging quality of gamma cameras. The participation was voluntary, and confidentiality of the individual results was guaranteed. The survey was completed within 2 months, employing instructors to administrate the tests. An emission phantom simulating a flood field with non-uniformities was imaged by 43 cameras, and 54 images were evaluated. The test images were read by the participants using a graded rating scale to indicate the probability of the presence of a non-uniformity in the various parts of the image. The rating data were used to construct individual ROC curves for each image. The area under the ROC curve was used as the ranking parameter for image quality. The results show a spread of the ROC areas between 0.6 and 0.99, with a median of 0.81. A correlation was found between the year of installation and the ROC area obtained from the gamma camera, indicating improvements of performance in more recent cameras, which accounts for part of the variation of the ROC areas. The remaining variations are due to differences in the performance of the gamma cameras. Feedback was provided to the participants by describing individual performance with respect to the true structure of the phantom and by comparing this performance with that of the group. A questionnaire accompanying the test phantom yielded information about the practice of routine quality control and about details of the acquisition and analysis of images. The survey demonstrated the feasibility and usefulness of interlaboratory comparisons of this type even for a small number of participants. The feedback was found by the participants to be helpful and stimulated awareness of the importance of quality control.