Design and Performance of a 1 mm³ Resolution Clinical PET System Comprising 3-D Position Sensitive Scintillation Detectors

Abstract

We are developing a 1-mm resolution, high-sensitivity positron emission tomography (PET) system for loco-regional cancer imaging. The completed system will comprise two cm detector panels and contain 4 608 position sensitive avalanche photodiodes (PSAPDs) coupled to arrays of mm LYSO crystal elements for a total of 294 912 crystal elements. For the first time, this paper summarizes the design and reports the performance of a significant portion of the final clinical PET system, comprising 1 536 PSAPDs, 98 304 crystal elements, and an active field-of-view (FOV) of cm. The sub-system performance parameters, such as energy, time, and spatial resolutions are predictive of the performance of the final system due to the modular design. Analysis of the multiplexed crystal flood histograms shows 84% of the crystal elements have>99% crystal identification accuracy. The 511 keV photopeak energy resolution was 11.34±0.06% full-width half maximum (FWHM), and coincidence timing resolution was 13.92 ± 0.01 ns FWHM at 511 keV. The spatial resolution was measured using maximum likelihood expectation maximization reconstruction of a grid of point sources suspended in warm background. The averaged resolution over the central 6 cm of the FOV is 1.01 ± 0.13 mm in the X-direction, 1.84 ± 0.20 mm in the Y-direction, and 0.84 ± 0.11 mm in the Z-direction. Quantitative analysis of acquired micro-Derenzo phantom images shows better than 1.2 mm resolution at the center of the FOV, with subsequent resolution degradation in the y-direction toward the edge of the FOV caused by limited angle tomography effects.

Advances in Detector Instrumentation for PET

“…Supplemental Figure 3A depicts an example of indirect detection of the measured PSF across 2 opposing detector modules, each consisting of 8 3 8 arrays of 0.9 3 0.9 3 1 mm 3 LYSO scintillation crystals coupled to a position-sensitive avalanche photodiode. An average CPSF of 0.84 6 0.02 mm was measured; the figure was extracted from a previous publication (33). Supplemental Figure 3C shows an example of the direct detection method using a monolithic CZT crystal arranged edge-on with respect to incoming photons, with intrinsic resolution determined by the 1-mm pitch of the anode electrode, which was segmented into strips; the reported CPSF averaged over 3 anode strips was 0.78 6 0.1 mm FWHM, including the 250-mm diameter of the point source.…”

“…The collimator had 30mm thickness and drilled holes 1.2 mm in diameter. The bottom panel of Supplemental Figure 3B shows the count histogram along the columns in the image of the data inside the red band, achieving an average (x,y) spatial resolution of 0.82 6 0.02 mm after taking into account the hole diameter, with significant degradations observed within a few millimeters from all 4 edges (33).…”

A new brain dedicated PET scanner with 4D detector information

“…Moreover, high sensitivity also allows for safer repeated scans for the same patient, decisive for early assessment of treatment progress and in depth physiological and pharmacodynamic occupancy studies. Also, organdedicated systems report better performance than standard WB-PET scanners, such as millimetric spatial resolution [4], small footprint and portable designs, higher patient throughput and also, a reduced cost [5]. A drawback of organ-dedicated PET systems is that, these scanners typically focus on the examination of a single organ thus reducing their usage by different areas or departments in a clinical centre.…”

A preclinical PET detector constructed with a monolithic scintillator ring

“…A major limiting factor in the performance of current preclinical PET scanners is the performance of the gamma detector (Berg and Cherry 2018). The conventional preclinical PET scanners were constructed with arrays of discrete scintillators and photosensors (Hsu et al 2018, Xie et al 2017b, Yang et al 2016.…”