Calibration procedure for a continuous miniature crystal element (cMiCE) detector

Abstract

We report on methods to speed up the calibration process for a continuous miniature crystal element (cMiCE) detector. Our cMiCE detector is composed of a 50 mm by 50 mm by 8 mm thick LYSO crystal coupled to a 64-channel, flat panel photomultiplier tube (PMT). This detector is a lower cost alternative to designs that use finely pixilated individual crystal detectors. It achieves an average intrinsic spatial resolution of ~1.4 mm full width at half maximum (FWHM) over the useful face of the detector through the use of a statistics based positioning algorithm. A drawback to the design is the length of time it takes to calibrate the detector. We report on three methods to speed up this process. The first method is to use multiple point fluxes on the surface of the detector to calibrate different points of the detector from a single data acquisition. This will work as long as the point fluxes are appropriately spaced on the detector so that there is no overlap of signal. A special multi-source device that can create up to 16 point fluxes has been custom designed for this purpose. The second scheme is to characterize the detector with coarser sampling and use interpolation to create look up tables with the desired detector sampling (e.g., 0.25 mm). The intrinsic spatial resolution performance will be investigated for sampling intervals of 0.76 mm, 1.013 mm, 1.52 mm and 2.027 mm. The third method is to adjust the point flux diameter by varying the geometry of the setup. By bringing the coincidence detector array closer to the point source array both the spot size and the coincidence counting rate will increase. We will report on the calibration setup factor we are able to achieve while maintaining an average intrinsic spatial resolution of ~1.4 mm FWHM for the effective imaging area of our cMiCE detector.

Figure 1

Picture of cMiCE detector with 8 mm thick LYSO crystal and white paint.

Figure 2

Multi-point source setup to provide multiple electronically collimated point fluxes.

Figure 3

Contour plots of the FWHM for point fluxes with 2.026 mm spacing. Fluxes got to within 4 mm of the edge of the crystal. LUTs were calibrated with different numbers of point sources: (a) 4 sources; (b) 8 sources; and (c) 12 sources.

Figure 4

Contour plots of the FWHM for point fluxes with 2.026 mm spacing. LUTs were created from data sets using 8 point sources and with different sampling intervals: (a) 0.76 mm; (b) 1.013 mm; (c) 1.52 mm; and (d) 2.026 mm.

Figure 5

Contour plot of the FWHM for point sources with 2.026 mm spacing. LUT was generated using 12 sources, 2.026 mm sampling interval and 0.52 mm diameter spot size.

Figure 6

Contour plot of the FWHM for point sources with 2.026 mm spacing. LUT was generated using 8 sources with 1.013 mm sampling interval and 0.7 mm FWHM point flux diameter.