Hand-held high resolution detectors

Aim High resolution scintigraphy ( HRS) can be useful in radio-guided surgery (RGS) and small animal imaging. Devices are generally based on arrays of sensible elements: room temperature semiconductor arrays or scintillating crystals arrays that can be coupled with position sensitive photomultipliers (PSPMT). Here we describe a small Field Of View (FOV) portable cameras based on 1 and 4 inches2 PSPMT. Materials & Methods These cameras show a peculiar crystal- collimator- PSPMT matching that allows the exact positioning of all the scintillating elements inserted in the square holes of a parallel Tungsten collimator. This arrangement ensures no crosstalk of ? rays or light among crystals. The scintillation light emerging from each crystal is revealed by a PSPMT (H8500 or R8520-00-C12). The anodes allow event positioning through the reconstruction of the maximum of the multiplied charge distribution by the centroid algorithm. Data are then selected with an appropriate energy window and transferred to a workstation. We studied the spatial resolution and the homogeneity of two cameras both equipped with 2.4x2.4x5 mm3 CsI (Tl) crystals and a 25 mm long collimator. A thin Plexiglas container filled with 99mTc was used to check homogeneity and pixel identification. A Derenzo phantoms with the diameter of the holes ranging from 2 to 4 mm was positioned at contact, at 1, 2, 3 cm distance from the collimator and filled with 99mTc to assess the camera spatial resolution. Results The energy resolution was 19.1 % FWHM of the 99mTc peak over the whole FOV area. Both cameras showed homogeneity within ± 5% between max and min pixel counts. Pixel identification showed average peak to valley ratio of 20:1. Spatial resolution was 3.3 mm at 1 cm, 4.9 mm at 3 cm, 6.0 mm at 5 cm and 10.9 mm at 10 cm distance. Conclusion Measurement of resolution were performed to foresee the working conditions of HR cameras. Actually when nuclear physicians show to surgeons sentinel nodes or parathyroid glands, they are on contact with the source or at few cm distance. Both detectors were used for RGS and showed hot nodes less than 2 mm large and distant 2.5 mm each other. In several instances a spot detected as single node by Anger camera showed the presence of two near nodes.