Abstract
1860
Objectives Molecular Breast Imaging (MBI) using Digital Direct Conversion Gamma ImagingTM (DDCGITM) is a functional modality which uses two planar cameras that detect gamma ray emissions from an intravenous injection of Tc99m-sestamibi to identify abnormalities associated with breast cancer. A crucial improvement to this modality is the reduction of the radiation dose to the patient from current values of about 2 mSV down to 1 mSv, in which case it will be comparable to the radiation dose of X-ray mammography. We will present techniques that will allow for further dose reduction through improved radiation detector uniformity and innovative collimator design.
Methods DDCGI-MBI consists of a pair of opposed semiconductor Cadmium Zinc Telluride (CZT) gamma cameras that mildly compress the breast between them in standard planar mammographic views. These cameras are fabricated using an array of pixelated CZT detector modules and a tungsten parallel hole collimator. In this work, the collimators were further optimized to maintain spatial resolution while increasing sensitivity. The improvement to detector sensitivity was measured using a radioactive source and comparing old collimators versus new collimators. Furthermore, the uniformity of CZT detectors was improved by advances in manufacturing technologies. The impact of these improvements on image quality was measured using a specially-designed image quality phantom that simulated lesions of diameters from 3 mm to 10 mm and varying tumor to background contrast from 2 to 5.33.
Results Reducing collimator septa walls increases sensitivity by at least 10%, and potentially up to 26%, while optimizing the collimator height maintains the spatial resolution. Simultaneously, improving the uniformity of the CZT by a median of 30% increases the median image contrast by about 15%. These improvements directly yield in corresponding reductions of dose to the patient.
Conclusions Optimizing collimator design and construction along will improving CZT detector uniformity puts us on the path towards our goal of a patient effective dose 1 mSv comparable to digital mammography.