Design and simulation of a high-resolution stationary SPECT system for small animals

Abstract

Exciting new SPECT systems can be created by combining pinhole imaging with compact high-resolution gamma cameras. These new systems are able to solve the problem of the limited sensitivity-resolution trade-off that hampers contemporary small animal SPECT. The design presented here (U-SPECT-III) uses a set of detectors placed in a polygonal configuration and a cylindrical collimator that contains 135 pinholes arranged in nine rings. Each ring contains 15 gold pinhole apertures that focus on the centre of the cylinder. A non-overlapping projection is acquired via each pinhole. Consequently, when a mouse brain is placed in the central field-of-view, each voxel in the cerebrum can be observed via 130 to 135 different pinholes simultaneously. A method for high-resolution scintillation detection is described that eliminates the depth-of-interaction problem encountered with pinhole cameras, and is expected to provide intrinsic detector resolutions better than 150 microm. By means of simulations U-SPECT-III is compared to a simulated dual pinhole SPECT (DP-SPECT) system with a pixelated array consisting of 2.0 x 2.0 mm NaI crystals. Analytic calculations indicate that the proposed U-SPECT-III system yields an almost four times higher linear and about sixty times higher volumetric system resolution than DP-SPECT, when the systems are compared at matching system sensitivity. In addition, it should be possible to achieve a 15 up to 30 times higher sensitivity with U-SPECT-III when the systems are compared at equal resolution. Simulated images of a digital mouse-brain phantom show much more detail with U-SPECT-III than with DP-SPECT. In a resolution phantom, 0.3 mm diameter cold rods are clearly visible with U-SPECT-III, whereas with DP-SPECT the smallest visible rods are about 0.6-0.8 mm. Furthermore, with U-SPECT-III, the image deformations outside the central plane of reconstruction that hamper conventional pinhole SPECT are strongly suppressed. Simulation results indicate that future pinhole SPECT systems are likely to bring about significant improvements in radio-molecular imaging of small animals.

Primer on molecular imaging technology

“…Unlike the pinhole , and thus photon sensitivityfor SPECT is relatively low compared with that for PET, limiting statistical quality of data for the same study duration. For SPECT systems that utilize pinhole collimation, efficiency may be significantly improved by increasing the number of pinhole apertures used [19,20] and, if appropriate, by bringing the tissue(s) of interest in close proximity to the pinhole apertures. This multipinhole SPECT approach has been applied successfully for small animal imaging [19,20], but not for human imaging.…”

An enhanced high-resolution EMCCD-based gamma camera using SiPM side detection

“…Rogulski et al (1993), Beekman and Vastenhouw (2004), Meng et al (2006), Rentmeester et al (2007), Shokouhi et al (2009) and Goorden et al (2009); recent work by Meng et al (2009a) validates the efficacy of high-resolution detectors in small-animal SPECT applications. High-resolution gamma-ray detectors have been developed for applications ranging from astronomy and particle physics to biomedical imaging.…”

Pixel-based subsets for rapid multi-pinhole SPECT reconstruction

“…The issue of subset choice turns out to be of particular concern in multi-pinhole SPECT systems (e.g. Beekman and Vastenhouw (2004), Furenlid et al (2004), Beekman et al (2005), Van der Have et al (2009)). For these systems, OSEM images exhibit artifacts already at a low number of subsets, as we will show in the next sections.…”