PCR-I and PCR-II: Ring and Cylinder
PET Devices

It soon became clear to many of those involved in PET development that a circular or cylindrical array of detectors was the logical next step in PET instrumentation. Although many investigators took this approach, James Robertson (Robertson et al 1973) and Z.H. Cho (Cho et al 1975) were the first to propose a ring system. The only drawback was the limited sampling provided by these geometries and a number of techniques such as wobbling the array were proposed to increase sampling (Huesman et al 1983). A Donner ring was developed in Berkeley (Derenzo et al 1979) that used a large number of detectors individually coded to small phototubes. However, it was the development of analog coding by Charles Burnham of the PRL at MGH (Burnham et al 1981 and 1985) that permitted the use of multiple small detectors identified by a smaller number of phototubes. The concept was applied to ring and cylindrical arrays to produce high resolution PET images without motion. This led to the development of two PET systems at MGH, PCR-I (Brownell et al 1985) (Figure 16) and PCR-II (Burnham et al 1988, Brownell et al 1989) (Figure 17). PCR-I used a ring design while PCR-II used a cylindridal design. PCR-I has been in continuous use for sixteen years producing high resolution images in a variety of studies centered on the brain, heart and cancer in mice (Kallinowski et al 1991), rats (Brownell et al 1991, Brownell et al 1998) (Figure 18), rabbits (Figure 19), dogs (Figure 20) and primates (Hantraye et al 1992, Brownell et al 1998 and 1999) (Figure 21). The single ring limitation of PCR-I has been overcome by use of a computer-controlled table and imaging a volume source in a step-and-shoot mode utilizing table motion as axial axis. This enables processing of transverse and sagittal slices in addition to coronal slices. The outcome of studies conducted with PCR-I led to world wide interest in developing special PET scanners for small animals.

fig16

Figure 16: PCR-I, a single ring positron emission tomograph using analog coding. Tomograph with cot and computer (left) and the electronic assembly (right).

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Figure 17: PCR-II, a cylindrical positron emission tomograph.

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Figure 18: Study of dopamine transporters with 11C – CFT and dopamine D2 – receptors using 11C– raclopride in a 6– OHDA lesioned (left striatum) rat brain using PCR-I. Note the decreased accumulation of 11C – CFT and increased accumulation of 11C– raclopride in the lesioned striatum (supersensitivity).

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Figure 19: Bone study of a rabbit skull using 18F and PCR-I. Coronal slices on the left, transverse slices at the middle and sagittal slices on the left.

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Figure 20: Gated studies of blood flow (13 NH3) and glucose metabolism ( 18F 2FDG) in infarcted dog heart using PCR-I.

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Figure 21: Study of dopamine transporters with 11C – CFT and glucose metabolism with 18F 2FDG in a primate brain using PCR-I.