A small-animal imaging system capable of multipinhole circular/helical SPECT and parallel-hole SPECT

Abstract

We have designed and built a small animal single photon emission computed tomography (SPECT) imaging system equipped with parallel-hole and multipinhole collimators and capable of circular or helical SPECT. Copper-beryllium parallel-hole collimators suitable for imaging the ~35 keV photons from the decay of 125I have been built and installed to achieve useful spatial resolution over a range of object-detector distances and to reduce imaging time on our dual-detector array. To address the resolution limitations in the parallel-hole SPECT and the sensitivity and limited field of view of single-pinhole SPECT, we have incorporated multipinhole circular and helical SPECT in addition to expanding the parallel-hole SPECT capabilities. The pinhole SPECT system is based on a 110 mm diameter circular detector equipped with a pixellated NaI(Tl) scintillator array (1×1×5 mm3/pixel). The helical trajectory is accomplished by two stepping motors controlling the rotation of the detector-support gantry and displacement of the animal bed along the axis of rotation of the gantry. Results obtained in SPECT studies of various phantoms show an enlarged field of view, very good resolution and improved sensitivity using multipinhole circular or helical SPECT. Collimators with one, three and five 1 mm diameter pinholes have been implemented and compared in these tests. Our objective is to develop a system on which one may readily select a suitable mode of either parallel-hole SPECT or pinhole circular or helical SPECT for a variety of small animal imaging applications.

Appropriate collimators in a small animal SPECT scanner with CZT detector

“…On SPECT imaging, sensitivity with MPH was about 5-fold higher than that with SPH, while PAH yielded about 21-fold higher sensitivity than SPH. The sensitivity was lower than with other scanners with NaI detector [10,12,14,15,17].…”

“…In other scanners, SPH provided 0.6-1.4 mm FWHM with NaI detector [12][13][14][15] [6,8]. PAH yielded about 8 mm FWHM with NaI detector [13].…”

“…In current SPECT scanners, cadmium zinc telluride (CZT) semiconductor detectors have been applied to improve energy and spatial resolution [4][5][6][7][8], as compared with sodium iodide (NaI) scintillation detectors, which were used in conventional SPECT scanners [9][10][11][12][13][14][15][16][17][18][19]. Planar and SPECT projection data are acquired using various collimators in clinical settings.…”

“…Planar and SPECT projection data are acquired using various collimators in clinical settings. Almost all small-animal SPECT is performed with pinhole collimators (PH), including single-PH (SPH) [8,[12][13][14][15][16][17] and multi-PH (MPH) [6,[8][9][10]15], as these collimators will provide good resolution for small objects when compared with parallel hole collimators (PAH), which are more commonly used in clinical settings [20]. Although we have to select appropriate collimator to obtain high-quality images and accurate analysis results, there have been no comparative studies on image quality with various collimators in small animal imaging.…”

In vivo small animal imaging: Current status and future prospects

“…93 Nowadays, several groups are working on the development or application of small gamma cameras based on pixilated scintillators coupled to PSPMTs. [94][95][96] The use of solid state ͑and mainly cadmium zinc telluride͒ systems offers an alternative to the combination of the scintillator-PMT module. Solid state detectors allow direct photon detection and they are characterized by significantly higher energy resolution.…”