A cost-effective high-resolution modular pixelated clinical SPECT detector based on small NaI (Tl) pixels with medium-size single-anode PMTs, utilizing spatial modulation of scintillation light output

Abstract

The current trend toward SPECT systems dedicated to imaging specific organs has created new pressures to improve gamma camera performance. A number of designs rely on projection minification to increase system sensitivity by acquiring multiple non-overlapping simultaneous views, placing stringent requirements on detector intrinsic spatial resolution (ISR). Curved detector geometries require modular assemblies, making monolithic slab detectors impractical due to their large dead areas at the edges. Previously, we described a modular detector based on a scintillator block comprised of 2.75 × 2.75 × 10 mm3 NaI(Tl) pixels in a 3 × 3 mm pitch and decoded by an array of 51 mm diameter single-anode PMTs. The event positioning accuracy of the curved detector, averaged over its entire area, exceeds that of a hypothetical monolithic slab detector with 2.75 mm ISR. To reduce the pixel size/pitch and thus increase linear sampling in the transaxial dimension (the dimension along which the detector is curved and minification is applied), we introduce scintillation light output modulation between neighboring pixels. A series of narrow absorbing stripes is applied at the exit surface of every other pixel column, producing a modulation in light output between adjacent pixels and allowing the use of energy discrimination to more effectively assign events to the correct pixel. Compared to the 3×3 mm pitch modules, our new detector, with 2.25 × 2.75 × 10 mm3 NaI(Tl) pixels (2.5 × 3 mm pitch), achieves the same event positioning performance in terms of the average event positioning error, while yielding 10.3% energy resolution. This translates to an improvement in linear sampling, without any loss in positioning accuracy (and, thus, effective spatial resolution), a mod