Improving the spatial resolution of the microPET scanner by wobbling the bed

Before the introduction of block detectors in PET many scanners had two modes of operation, one lower resolution mode with the detectors stationary and a higher resolution mode in which the detector array moved on a circular path known as "wobbling". Wobbling improves the spatial sampling, allowing an image to be formed with the full spatial resolution limited only by the detector pairs\´ response function. Experiments performed on the MicroPET R4 small animal PET scanner demonstrate significant variations in the FWHM measured in the sinograms suggesting that it undersamples the image space. We have implemented a continuous wobble motion of the bed of this scanner, as opposed to wobbling of the detector array formally used in human PET scanners. The wobble radius can be changed from 0.25 to 1.75 mm by changing the offsets in wheels which support the bed. The wobble mechanism, driven continuously at one revolution per ten seconds allows for the angular sampling to be doubled, and the linear sampling to be increased by factors of 3 or 5. Since the data is collected in list mode, and the reconstruction and display programs are driven by parameters in the file headers, only the histogramming program requires adaption for wobbled operation. Preliminary results indicate an improvement in spatial resolution of about 20%