Impact of Pinhole Collimation on SPECT Image Quality Metrics, and Methods for Patient-Specific Assessment of Noise and Standardization of Imaging Protocols

Dedicated cardiac pinhole SPECT camera designs offer improvements in overall sensitivity, thereby enabling the use of lower injected radiotracer activity and shorter imaging times than parallel-hole designs. The effect of these novel camera designs on image noise on a voxel-by voxel level has not previously been investigated. This work identifies position and orientation-dependent variability of spatial resolution in the field-of-view (FOV) of pinhole cameras. It also identifies a 1.7-fold gradient in the magnitude of image noise across the length of the heart which leads to a 1.3-fold gradient in standard deviation values for a normal database for attenuation corrected images acquired with a commercially available cardiac pinhole camera. This pattern of noise varies with different patients and with different positioning of the heart within the FOV. Thus, to assist with clinical interpretation, a new 1-minute post-processing technique is developed to provide a patient-specific image of the noise distribution which may augment normal database information. Changes in attenuation result in varying levels of noise between patients of different body habitus administered the same radiotracer activity. A method for creating weight-based protocols is developed that standardizes the average noise in cardiac perfusion images by tailoring the radiotracer activity and acquisition time to the body mass of each patient. Methods developed in this thesis allow for more patient-specific imaging protocols, thereby standardizing the image noise level and providing physicians with more information about the noise and spatial-resolution distribution to aide in image interpretation.