New approach for calibration of pixelated scintillation detectors of intraoperative gamma cameras

Introduction:SURGEOSIGHT is a dedicated intra-operative hand-held gamma camera designed and manufactured by our team to be used for lymphoscintigraphy. Although conventional gamma cameras are widely used, they lack the capability of the sentinel lymph node (SLN) imaging in the operation room. Like conventional gamma cameras it is necessary to calibrate SURGEOSIGHT for linearity distortion, energy and flood correction. Our main objective in this study is to develop and implement three techniques for linearity, energy and uniformity corrections. Methods: The camera is made up of a pixelated cesium iodide (sodium-activated) (CsI(Na)) scintillation crystal with 1 × 1 mm2 element size along with  a Hamamatsu H8500 flat-panel multi-anode (64 channels) photomultiplier tube. All triple corrections required lookup tables (LUTs). To generate all three LUTs, one uncalibrated acquisition is necessary. Linearity distortion correction was based on localization of physical pixels of crystal and thin plate spline interpolation to estimate the amount of distortion. Energy correction LUT was simply a photo-peak map of incoming events which was estimated using self-organizing map technique. Results: The results showed improvements qualitatively and quantitatively. The extrinsic energy resolution was enhanced from 50% to about 20.6%. Integral uniformity and the differential uniformity, after uniformity correction, in useful field-of-view (UFOV) was measured 9.5% and 4.5%, respectively. Conclusion: Results substantiated that the correction techniques guarantee uniform and accurate output of the SURGEOSIGHT which is desirable for intra-operative localization of the sentinel lymph nodes in breast cancer and also for imaging of other superficial tumors.