Custom breast phantom for an accurate tumor SNR analysis

The capability of the scintimammography to diagnose subcentimeters sized tumors was increased by the employment of a dedicated gamma camera. The introduction of small field of view camera, based on pixellated scintillation array and position sensitive photomultiplier, allowed to enhance the geometric spatial resolution and contrast of the images due to reduced collimator-tumor distance. The aim of this paper is to investigate the realistic possibility of T1a tumors detection (∼5 mm size) by comparing the signal-to-noise ratio (SNR) values obtained by different imagers. To this end, we have utilized a self-designed solid breast phantom with different sized hot spots (tumors). The phantom consists of seven disks with different thickness, molded from resin epoxy activated with Co⁵⁷ isotope. The overlapped disks represent a pendula breast with about 800 cc volume. Hot spots have not wall. One disk has holes to fit the hot spots representing the different sized lesions. The imagers utilized were: a standard Anger Camera and three different cameras based on scintillator array, CsI(Tl) or NaI(Tl), coupled to position sensitive photomultiplier with different technologies, to make detectors with field of view of 3 and 5 inch. The experimental results are supported by Monte Carlo simulation. It was highlighted how spatial resolution is a predominant element in tumor visibility and how background causes a reduction of the image contrast. All gamma cameras show close results at SNR values less than 10 and a full detectability of 8 mm tumor size. However, the results show the 5 mm tumor size is lower detection limit for all cameras.