Design and engineering aspects of a high resolution positron tomograph for small animal imaging

Abstract

We describe the Sherbrooke positron emission tomograph, a very high resolution device dedicated to dynamic imaging of small laboratory animals. Its distinctive features are: small discrete scintillation detectors based on avalanche photodiodes (APD) to achieve uniform, isotropic, very high spatial resolution; parallel processing for low deadtime and high count rate capability; multispectral data acquisition hardware to improve sensitivity and scatter correction; modularity to allow design flexibility and upgradability. The system implements the "clam-shell" sampling scheme and a rotating rod transmission source. All acquisition parameters can be adjusted under computer control. Temperature stability at the detector site is ensured by the use of thermoelectric modules. The initial system consists of one layer of 256 modules (two rings of detectors) defining 3 image slices in a 118 mm diameter by 10.5 mm thick field. The axial field can be extended to 50 mm using 4 layers of modules (8 rings of detectors). The design constraints and engineenng aspects of an APD-based PET scanner are reviewed and preliminary results are reported. * This work was supported in part by the Medical Research Council of Canada under Grant MA-8549. The first author is a senior scholar of Le Fonds de la Recherche en S a d did Qrribec.

Anatomical phenotyping in the brain and skull of a mutant mouse by magnetic resonance imaging and computed tomography

“…Medical imaging technologies are effective in depicting human anatomy and can likewise be used for anatomical phenotyping when adapted to the mouse scale (4,14,15,27,33,36). These technologies have the advantage of being noninvasive and repeatable for longitudinal in vivo examinations.…”

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“…Small animal PET systems based on rotating planar detectors are an alternative, cost effective research tool for molecular imaging, and posses some interesting advantages for high sensitivity, high resolution imaging [1][2][3][4][5][6][7][8][9]. The planar detectors are usually built around compact sensors with a high accuracy in the location of the event.…”

Temperature dependence of APD‐based PET scanners

“…More recently solid state detectors such as avalanche photodiodes (APDs) have been introduced as photodetectors for PET. 2,3 APDs have two important advantages over PMTs. They are insensitive to magnetic field variations, which makes it possible to use them in combined PET-MRI scanners.…”

“…[4][5][6] They are also considerably smaller than PMTs, making it easier to use them in small animal PET scanners and enabling one-to-one coupling between crystal and photodetector. 2,7 A disadvantage of APDs is the strong dependence of their gain factor on ambient temperature. 8 This is explained by increased lattice vibrations at higher temperatures, which in turn lead to a higher probability of electron-phonon interactions and a lower avalanche yield.…”