Compton gamma -ray imaging probes for prostate and breast.

Abstract

Radionuclide imaging provides valuable functional information that cannot be obtained using anatomical imagers. Consequently, it has been successfully used in detecting tumors and monitoring disease recurrence and response to therapy. However, conventional single photon imaging systems have spatial resolution in the 1--2 cm range for imaging objects at distances 8 to 10 cm. It is important to improve spatial resolution in order to detect tumor as early as possible when treatment is more effective. However, conventional imaging system can improve spatial resolution only at the expense of sensitivity and increased statistical image noise. The proposed Compton imaging technique does not require collimators to form images so that sensitivity is decoupled from spatial resolution. Furthermore, Compton imagers have better performance as gamma-ray energy increases in direct contrast to collimator performance. Probes based on the Compton imaging technique can achieve simultaneous high spatial resolution and high sensitivity over a wide range of energies from 141 keV and above. In this thesis, potential Compton probe designs and their performance in prostate and breast imaging are evaluated using data generated by clinical situation. Images reconstructed using EM algorithm are evaluated using both resolution and sensitivity criteria and observer models to predict detection sensitivity. Results show that the proposed prostate imaging probes achieve absolute detection efficiency of 0.17%, a two-order-magnitude improvement over the mechanically collimated systems, and spatial resolution of 2.4 mm FWHM for <super> 111</super>In. An 8 mm tumor with TB ratio of 5:1 is clearly detectable in the reconstructed prostate images, but invisible in the single photon emission computed tomography (SPECT) images. With the same imaging time, the prostate probes have an improved SNR of 3--3.5x over the SPECT for detecting both 5 mm and 8 mm tumors. The probe for breast imaging reveals a moderate improvement over a dedicated scintimammographic system in detecting a 5 mm tumor and comparable performance in the detection of an 8 mm tumor.