A prototype of very high-resolution small animal PET scanner using silicon pad detectors

Abstract

A very high resolution small animal positron emission tomograph (PET) which can achieve sub-millimeter spatial resolution is being developed using silicon pad detectors. The prototype PET for a single slice instrument consists of two 1 mm thick silicon pad detectors, each containing a 32 x 16 array of 1.4 mm x 1.4 mm pads read out with four VATAGP3 chips which have 128 channels low-noise self triggering ASIC in each chip, coincidence units, a source turntable and tungsten slice collimator. The silicon detectors were located edgewise on opposite sides of a 4 cm field-of-view to maximize efficiency. Energy resolution is dominated by electronic noise, which is 0.98% (1.38 keV) FWHM at 140.5 keV. Coincidence timing resolution is 82.1 ns FWHM and coincidence efficiency was measured to be 1.04 x 10(-3) % from two silicon detectors with annihilation photons of (18)F source Image data were acquired and reconstructed using conventional 2-D filtered-back projection (FBP) and a maximum likelihood expectation maximization (ML-EM) method. Image resolution of approximately 1.45 mm FWHM is obtained from 1-D profile of 1.1 mm diameter (18)F line source image. Even better resolution can be obtained with smaller detector element sizes. While many challenges remain in scaling up the instrument to useful efficiency including densely packed detectors and significantly improved timing resolution, performance of the test setup in terms of easily achieving submillimeter resolution is compelling.

A new PET resolution measurement method through Monte-Carlo simulations

“…Further, the poor spatial resolution of PET systems is a limiting factor for the accurate quantitative estimation of the PSF of structures more than three times smaller than the FWHM (partial volume effect) of the reconstructed image resolution [36]. The partial volume effect alternates the pixel values of a structure, by forcing lower activity peripheral tissues to gain uptake with higher activities from hot lesions spreading to the surrounding (spill-out effect) [44]. Thus, hot lesions will appear with reduced maximum values and the PSF will appear broader, with low-intensity tails.…”

“…In addition, it can be used as a longterm quality control method to identify the system's performance stability. Further, this method could be useful for comparing different PET scanners in multicenter PET studies and, in particular, for the accurate determination of image resolution of new technology PET scanners incorporating high-resolution detectors [44,46,48].…”

Optimization of silicon detector layout and associated front-end electronics for timing performance of a silicon PET through simulation

“…Abstract-There are indications that PET imaging may profit by incorporating position sensitive silicon detectors with intrinsic excellent spatial resolution into the scanner setup [1]. However, poor timing performance of detectors can compromise mentioned benefits.…”

Timing performance of the silicon PET insert probe

“…The most serious drawback is its low efficiency; only 2 % of incident annihilation photons interact in 1 mm of silicon with Compton scattering being the most common interaction. Although commonly used sensitive materials (for example, scintillators coupled with light detectors) exhibit higher efficiency, they have serious limitations when aiming for compact systems with high spatial resolution (2) . To improve the detection efficiency, thicker silicon detectors are used, causing extension of signal collection times.…”