Abstract
In the current PET/CT in-line system, high quality CT images not only provide better diagnostic values for anatomic delineation but also offer a shorter scanning time for the transmission scan. However, under standard operating conditions, the photon flux from a CT scan is greater than that from a typical PET transmission measurement obtained with germanium-68 rod sources by a factor of at least 104. This approach would potentially introduce more radiation burden owing to the higher radiation exposure. This situation is particularly severe for a whole-body protocol in which CT scans are obtained from the head to the pelvic region, though this is a relatively rare practice in typical diagnostic CT procedures. Ideal optimal operation protocols for routine PET/CT imaging must take diagnostic values, image quality, radiation doses, scanning time and practicability into consideration, and the question of how to reconcile all these factors is at present a hotly debated topic in nuclear medicine. By studying the potential effects on the corrected emission images obtained using various CT-based attenuation correction parameter settings, we can get more understanding of the relationship between image quality and radiation dose for different PET/CT diagnostic imaging purposes.The objectives of this study were: (1) to measure the radiation doses by the same technique during germanium-based and CT-based transmission scanning and to compare the doses received by brain, cardiac and whole-body scans, (2) to propose the imaging parameters that could best reduce these radiation doses to levels that permit scanning with all the advantages of current PET/CT imaging and yet without significantly degrading the accuracy of the diagnostic information that such scans provide, and (3) to estimate the expected decrease in dose. In order to improve the current clinical protocols, a new operational protocol is suggested based on the results of our present study. It is our belief that the revised PET/CT imaging protocol is able to maximize diagnostic information and minimize radiation risks.