Compact trapezoidal pet detector with light sharing

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Positron Emission Tomography (PET) is a functional imaging technology developed during the latter half of the twentieth century. The first functional PET imager has been variously attributed to Michael E. Phelps at Washington University for a PET system known as PETT I, and to Sy Rankowitz and James Robertson at the Brookhaven National Laboratory in 1962. PET technology has continued to advance and has gained widespread adoption in nuclear medicine and in preclinical research. PET functional imaging is frequently combined with computed tomography or magnetic resonance imaging to obtain concurrent functional and structural image data.

Small animal imaging has emerged as an important research field. Currently, many research efforts have been devoted to multimodality imaging systems. For example, systems that incorporate both positron emission tomography (PET) and magnetic resonance imaging (MRI) provide information for combined functional and anatomic imaging. Due to the relatively small bore size in small animal PET detectors, it is desirable to provide three-dimensional (i.e., including depth of interaction (DOI) position) capability. Desirable characteristics in a small animal imaging PET system include (1) high image resolution; (2) high absolute sensitivity; (3) the ability to work in a strong magnetic field; and (4) a compact size.

The present inventors have created a novel high resolution, monolithic crystal small animal PET detector that provides a number of advantages over discrete crystal detector designs. Relatively large scintillation crystals are preferred for a monolithic crystal detector because of the challenges associated with positioning events near the edges of a crystal, which makes two-dimensional monolithic crystal geometry less than ideal for a compact PET detector. In order to maintain the advantages of monolithic crystal design, such as DOI decoding capability, while reducing the edge effects, the PET detector may use elongate trapezoidal slat crystals (TSC) to produce a compact annular detector. A PET detector suitable for use in a PET/MRI imaging system is disclosed in Xiaoli Li, et al., "Design of a trapezoidal slat crystal (TSC) PET detector for small animal PET/MR imaging," Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE (hereinafter, Li), which is hereby incorporated by reference in its entirety.

A front view of a prior art PET detector 50 is shown schematically in FIGURE 1.

The PET detector 50 includes a plurality of detector modules 52 assembled in an annular arrangement. During imaging, the subject is positioned generally along the center axis of the annular assembly.

A detector module 52 is shown in a detail view in FIGURE 1. The detector module 52 includes a scintillator body 51 that is shaped as an isosceles trapezoid. An optional optical window or light guide 57 is fixed to an outer end of the scintillator body 51, and two rows of coplanar photodetectors 60, for example, silicon photomultipliers (SiPM), are positioned to detect light released from scintillation events in the scintillator body 51. For example, a 2 X 12 array of photodetectors 60 may be provided on each scintillator body 51.

The scintillator body 51 comprises a plurality of elongate slat crystals 54 (8 shown) that are trapezoidal in cross section, and tapers in the radially inward direction. Light-blocking/reflecting elements 56 between each of the slat crystals 54 prevent (full length) or limit (less than full length) light sharing between adjacent slat crystals 54. Full length light-blocking/reflecting elements 56 cover both radial sides of the scintillator body 51. Light-blocking/reflecting elements 56 that extend only partially along the radial length of the adjacent slat crystals 54 permit some light from a scintillation event in one slat crystal 54 to be shared with an adjacent slat crystal 54. In particular, an outer portion of some of the interior slat crystal 54 faces are joined with transparent glue 108 (indicated by dashed lines), that allow light sharing internally within the module 52. This light sharing feature provides information that can be used to estimate the crystal of interaction of the scintillation event occurring in the detector module 52. However, this PET detector provides for light sharing only internally within a module 50, and requires two or more coplanar rows of photodetectors 60. The detector modules 50 are therefore relatively wide, to accommodate the two co-planar photodetectors 60, which limits the practical compactness of the scanner. The detector modules 50 do not incorporate light sharing between adjacent modules 52. It would be beneficial to have narrower detector elements to improve the resolution of the PET imager 50.