Importance of Correct Photopeak Setting in Nuclear Medicine Imaging Procedures

Abstract

Most scintillation camera systems currently use an analog display for photopeak selection. A systematic evaluation of this peak setting procedure was undertaken to investigate its accuracy and effect upon the resultant image. The scintillation camera we selected provided both an analog and a multichannel analyzer (MCA) display of the spectrum. For each data collection, the investigator set the Co-57 peak symmetrically using the MCA. Polaroid images were taken of the resultant field flood. Several technologists were then asked to set the Co-57 peak using the analog display; additional Polaroid images were obtained of the ensuing field floods. The field flood images thus obtained were given to a panel for evaluation. The panel ranked as “best” those field flood images taken with the peak symmetrically aligned. In addition, a series of patient images was obtained at various peak settings. When this series was evaluated by the panel, the patient images obtained with the peak set too high were judged to be of unacceptable diagnostic quality. The accuracy needed for a diagnostically useful image is often not achieved by using an analog display for photopeak setting. The use of an MCA enables an accurate and objective method of selecting the peak.