A high-sensitivity small animal SPECT system

Abstract

Medical imaging using single gamma ray emitting radionuclides typically makes use of parallel hole collimators or pinholes in order to achieve good spatial resolution. However, a tradeoff in sensitivity is inherent in the use of a collimator, and modern preclinical SPECT (single photon emission computed tomography) systems detect a very small fraction of emitted gamma rays, often less than 0.1%. A system for small animal SPECT imaging which uses no collimators could potentially achieve very high sensitivity-several tens of percent-with reasonably sized detectors. This would allow two significant improvements in preclinical studies: images could be obtained more rapidly, allowing higher throughput for screening applications, or for dynamic processes to be observed with very good time resolution; and images could be obtained with less radioactive tracer, making possible the in vivo imaging of low-capacity receptor systems, aiding research into new tracer compounds, and reducing the cost and easing the regulatory burden of an experiment. Of course, a system with no collimator will not be able to approach the sub-millimeter spatial resolutions produced by the most advanced pinhole and collimated systems, but a high sensitivity system with resolution of order one centimeter could nonetheless find significant and new use in the many molecular imaging applications which do not require good spatial resolution-for example, screening applications for drug development or new imaging agents. Rather than as an alternative to high resolution SPECT systems, the high sensitivity system is proposed as a radiotracer alternative to optical imaging for small animals. We have developed a prototype system for mouse imaging applications. The scanner consists of two large, thin, closely spaced scintillation detectors. Simulation studies indicate that a FWHM spatial resolution of 7 mm is possible. In an in vivo mouse imaging study using the 99m Tc labeled tracer MAG-3, the sensitivity of the system is measured to be 40%. Simple projection images created by analytically combining the two detectors' data show sufficient resolution to observe the dynamic distribution of the radiotracer in the mouse.

Un-collimated single-photon imaging system for high-sensitivity small animal and plant imaging

“…This system has potential for many imaging tasks which do not require excellent spatial resolution, for example: high-throughput screening applications, dynamic studies where very good temporal resolution is critical [Celler 2000, Mitchell 2009], counting of radiolabeled cells in vitro, in vivo imaging of easily saturated receptor systems [Kenanova 2009], or in planta imaging of radioisotopes at low concentrations.…”

“…An example of a preclinical nuclear imaging system designed for high-sensitivity applications was our prototype un-collimated detector single-photon imaging system [Mitchell 2009]. This system achieved 40% sensitivity with 99m Tc and 3 mm thick monolithic NaI(Tl) detectors, which is more than a one hundred-fold increase in sensitivity compared to existing preclinical SPECT scanners [Rowland 2008].…”

Optical simulation of monolithic scintillator detectors using GATE/GEANT4

“…et al , Cherry 2004, Mitchell and Cherry 2009, Schramm et al 2003, Van der Have et al 2009 and/or developing hybrid imaging modalities such as PET/MRI (Catana et al 2009, Judenhofer et al 2008, Shao et al 1997.…”

Development and Application of Gamma Camera in the Field of Nuclear Medicine

“…A system for small animal SPECT imaging which uses no collimators could potentially achieve very high sensitivity-several tens of percent-with reasonably sized detectors. [4]。Haining [5] developed a small gamma camera based on position sensitive photomultiplier. The spatial resolution of the 241Am source for the collimator of the 2mm diameter was ~4mm, and the resolution of the plane 57Co source was 27%.…”