Depth-of-Interaction Compensation Using a Focused-Cut Scintillator for a Pinhole Gamma Camera

Abstract

Preclinical SPECT offers a powerful means to understand the molecular pathways of drug interactions in animal models by discovering and testing new pharmaceuticals and therapies for potential clinical applications. A combination of high spatial resolution and sensitivity are required in order to map radiotracer uptake within small animals. Pinhole collimators have been investigated, as they offer high resolution by means of image magnification. One of the limitations of pinhole geometries is that increased magnification causes some rays to travel through the detection scintillator at steep angles, introducing parallax errors due to variable depth-of-interaction in scintillator material, especially towards the edges of the detector field of view. These parallax errors ultimately limit the resolution of pinhole preclinical SPECT systems, especially for higher energy isotopes that can easily penetrate through millimeters of scintillator material. A pixellated, focused-cut (FC) scintillator, with its pixels laser-cut so that they are collinear with incoming rays, can potentially compensate for these parallax errors and thus improve the system resolution. We performed the first experimental evaluation of a newly developed focused-cut scintillator. We scanned a Tc-99m source across the field of view of pinhole gamma camera with a continuous scintillator, a conventional “straight-cut” (SC) pixellated scintillator, and a focused-cut scintillator, each coupled to an electron-multiplying charge coupled device (EMCCD) detector by a fiber-optic taper, and compared the measured full-width half-maximum (FWHM) values. We show that the FWHMs of the focused-cut scintillator projections are comparable to the FWHMs of the thinner SC scintillator, indicating the effectiveness of the focused-cut scintillator in compensating parallax errors.

Inducible Nitric Oxide Synthase Drives mTOR Pathway Activation and Proliferation of Human Melanoma by Reversible Nitrosylation of TSC2

“…For Ki-67 staining of CAM tissue, the fractional area occupied by the immunoreactive ki-67 was quantified with the Bioquant image analysis system (BIOQUANT Image Analysis Corporation, Nashville, TN) as previously described (22). Random fields from seven independent sections were analyzed per sample and averaged.…”

NaI gamma camera performance for high energies: Effects of crystal thickness, photomultiplier tube geometry and light guide thickness

“…Different techniques have been studied to alleviate the DoI limitations affecting pinhole SPECT including software-based modeling and corrections, the use of curved fiber bundles to collimate light from a curved scintillator, and the application of a laser processed scintillator with converging pixels. [16][17][18][19] Another possible solution to mitigate this issue and preserve spatial resolution consists of estimating the 3D interaction position. This estimation would be useful for crystals thicker than what is currently available on the market, but it could also be beneficial for already existing gamma cameras.…”

“…This may lead to parallax errors for scanner geometries where the ɣ enters the detector under an angle, for example, for diverging, converging or pinhole collimators. Different techniques have been studied to alleviate the DoI limitations affecting pinhole SPECT including software‐based modeling and corrections, the use of curved fiber bundles to collimate light from a curved scintillator, and the application of a laser processed scintillator with converging pixels 16–19 . Another possible solution to mitigate this issue and preserve spatial resolution consists of estimating the 3D interaction position.…”

Cramer–Rao lower bound optimization of an EM-CCD-based scintillation gamma camera

“…Compact, high-resolution gamma imaging cameras are being developed by many research groups (Fiorini et al 2003, Kataoka et al 2005, Vavrik et al 2002, He et al 1999. In a subset of these gamma cameras, micro-columnar CsI(Tl) scintillators are being used in combination with electron multiplication (EM-)CCDs (de Vree et al 2005, Nagarkar et al 2006, Meng 2006, Miller et al 2006, Soesbe et al 2010, Alhassen et al 2011. In such CCD-based detectors, individual scintillation events can be detected in photon counting mode, enabled by readout at high frame rates.…”