Factors affecting cancer detectability in 99Tc MIBI scintimammography

Scintimammography shows strong potential in detecting and differentiating breast cancer. This scintigraphic technique, using a standard gamma camera, allows high sensitivity and specificity values (>95%) for detected tumors more than 1 cm size. However, the sensitivity of scintimammography using conventional gamma cameras is considerably less (40-50%) for tumors with smaller size. Recently, the authors demonstrated how the use of a small FOV dedicated gamma camera (Single Photon Emission Mammography, or SPEM camera), with very high intrinsic spatial resolution (1.7 mm FWHM), working with breast moderately compressed and positioned close to the breast tumor (i.e., analogously to X-ray mammography) increased sensitivity up to 80% for tumors sized between 0.5 and 1 cm (T1b). The aim of this paper is to demonstrate how the reduced breast thickness can play a primary role in small cancer detection. Five different methods were taken into account: clinical measurements, comparing tumor SNR values obtained from the same patients in prone scintimammography and in SPEM, comparing SNR values between compressed and uncompressed breast in craniocaudal projection, breast phantom measurements, Monte Carlo simulations and simplified theoretical model. Results confirm that the mechanism for the improvement in visualizing sub-centimeter lesions due to compression is a reduction of lesion-detector distance. As a result of this reduced distance there is a less reabsorption of signal by interposed breast tissue, and improved detector intrinsic spatial resolution.