Performance characteristics of the SMARTZOOM® collimator

The IQ·SPECT system released by Siemens in 2010 was developed to improve the efficiency of myocardial perfusion imaging using conventional large-field-of-view SPECT and SPECT/CT systems. In this paper we present sensitivity and resolution characteristics of IQ·SPECT, measured according to or similar to NEMA and IEC standards. Measurements were performed on fully integrated clinical SPECT/CT systems (Symbia T series) with state-of-the-art digital detectors. We measured planar sensitivity and resolution of the variable-focus SMARTZOOM
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collimator using a NEMA/IEC like testing setup. Planar sensitivity was measured using a 50 mm diameter flat Petri dish containing calibrated Tc99m and aligned with the center of the field of view. Planar data were acquired at both the NEMA/IEC specified distance of 100 mm from the face of the collimator and at the IQ·SPECT clinical scan radius of 280 mm. System spatial resolution in air was measured using two thin-walled glass capillaries in the center of the field of view at a NEMA/IEC specified distance of 100 mm. Data for reconstructed tomographic resolution in air and in scatter were acquired using a clinical cardio-centric orbit with a fixed scan radius of 280 mm, using a point source in air and a line source in scatter medium aligned to the axis of rotation, respectively. Projection data were reconstructed using iterative reconstruction. A total of 12 collimators on three different systems were characterized. Data analysis and calculation of sensitivity and resolution FWHM were performed in compliance with NEMA/IEC standards. The planar sensitivity of the SMARTZOOM
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collimator was found to be ≥285 cpm/Ci at a distance of 100 mm and ≥810cpm/Ci at 280 mm. The system spatial resolution at 100 mm was measured to be ≤7.5 mm. The transaxial and axial reconstructed resolution in air were ≤10.2 mm and ≤10.8 mm and the reconstructed resolution in scatter ≤10.7 mm.