Search

Dead mice tell too few tales. Conventional animal imaging requires sacrificing multiple animals at numerous time points, then slicing and staining tissue to identify the location and state of particular [...]

In the framework of post-genomic era, computed tomography (CT) and positron emission tomography (PET) systems were recently adapted to the new requirements of small animal imaging. In order to combine ideally anatomical and functional informations, simultaneous acquisitions of the two modalities are necessary. In this context, we studied the tomographic reconstruction required by a new prototype of PET/CT micro-system where the X-ray source has to be off-centered. In contrast to conventional micro-CT where the source and detector rotate in the same plane, our configuration imposes that the source point and its orthogonal projection on the detector plane describe two parallel distinct circles. To address this specific geometry, we derive a new general formulation of the Feldkamp (FDK) algorithm. This formula, called [alpha]-FDK, with [alpha] representing the off-center angle of the source, is evaluated using computer simulations. While the image quality obtained for small values of [alpha] (< 17[degrees]) is comparable to that obtained in standard circular cone beam geometry, strong artifacts appear for higher values. In order to interpret these degradations, we first analyze the projection/reconstruction system in terms of the impulse response and show the insufficiency of ramp filtering. Second, the missing data problem due to the off-centered geometry is analyzed in the Radon space. Index Terms--Circular trajectory, computer tomography, cone beam.

We report on the design of a data acquisition (DAQ) module for a small animal PET camera developed at our institutes. During the design an important guideline was to develop a system which is built up from strictly identical DAQ modules, and which has no built-in hardware limitation on the maximum number of modules. The developed DAQ module comprises of an LSO scintillator crystal block, a position sensitive PMT, analog signal conditioning circuits, a digitizer, an field programmable gate array (FPGA) for digital signal processing, and a communication module through which the collected data are sent to a cluster of computers for postprocessing and storage. Instead of implementing hardware coincidence detection between the modules, we attach a precise time stamp to each event in our design, and the coincidence is determined by the data collecting computers during postprocessing. The digital CFD algorithm implemented in the FPGA gives a time resolution of 2 ns FWHM for real detector signals. Index Terms--Data acquisition (DAQ), digital CFD, Ethernet, PET, small animal.

High-resolution small animal single photon emission computed tomography (SPECT) with pinhole collimation has become well-established in preclinical research. Conventional scanner designs use custom fixtures that precisely attach and align pinholes to dedicated detectors. As a lower-cost alternative, we have developed a compact small animal SPECT device with integrated pinholes that is physically detached from gamma camera detectors and uses real-time calibration. The device consists of a shielded lead box with multiple integrated tungsten pinholes on the sides and with a rotating platform at the bottom. The animal or phantom to be imaged is positioned within a hollow cylinder mounted to the platform, with point source markers attached to the cylinder's outer surface. The entire device is placed on the patient table of a standard dual-head gamma camera system with collimators removed. Projection data are acquired with multiple energy windows to separate the point source data from the emission data. The complete geometric calibration is derived through analysis of the point source data. The system matrix is computed based on the calibration parameters and then applied to reconstruction of the emission data. Real-time calibration was found to be robust and accurate, even in the presence of downscatter from [sup.99m]Tc emission data or dual-isotope [sup.99m]Tc/[sup.111] In emission data. Successful calibration was consistently achieved in all pinhole configurations tried (up to seven pinholes per detector). Accuracy of real-time calibration was demonstrated in phantom studies and animal studies, where structures as small as 0.8 mm could be resolved in reconstructed images. Images appeared to be free of artifacts, and no cross-contamination from the calibration point sources was observed. Real-time calibration is feasible for pinhole SPECT, thus enabling standalone pinhole devices to be used without special alignment fixtures. The calibration accuracy is sufficient for high-resolution small animal studies. The hardware is compatible with nearly all gamma camera models and represents a lower-cost entry-level solution to the field of small animal SPECT. Index Terms--Calibration, pinhole, single photon emission computed tomography (SPECT), small animal.

A dual-modality compact SPECT/CT system for small animal imaging was developed. The SPECT system consisted of a pinhole collimator and continuous NaI(Tl) scintillation crystal coupled to a PSPMT. The CT system consisted of a microfocus X-ray tube and a CMOS flat-panel detector. The SPECT system was mounted perpendicular to the X-ray system. Individual projections of the SPECT and the CT were acquired by rotating the animal on a vertical axis in front of the detectors. The SPECT and CT images were reconstructed using OSEM and Feldkamp's cone-beam algorithms, respectively. Mouse and rat SPECT images demonstrated detailed activity distribution at the expected structures. ACT image obtained with 40 kVp and 0.5 mA presented high-resolution anatomic details. Fused SPECT/CT images demonstrated good agreement between the CT images and the corresponding uptake of the radiotracer. The SPECT/CT system developed in this study provides high-quality dual-modality images and could be useful to obtain functional images with high resolution morphology information. Index Terms--Multimodality imaging, small animal imaging, single photon emission computed tomography, X-ray imaging.

A Small Animal Imager (SAI) for PET has been designed, built, tested in phantoms, and applied to investigations in mice and rats. The device uses principles based on [gamma]-ray induced scintillation in crossed fiber optic detectors connected to Position Sensitive Photomultiplier Tubes (PSPMT). Each detector consists of an epoxied stack of 28 layers of 135 round 1 mm BCF-10 scintillating plastic fibers. The overlap region forms a 13.5 x 13.5 x 2.8 [cm.sup.3] detector volume. Scintillating light from the fibers is detected by two (X and Y directions) Hamamatsu R-2486 PSPMTs with 16 anode wires in each of two orthogonal directions. A centroid-finding algorithm gives the position of a light cluster on the face (photocathode) of a PSPMT. The accuracy of the reconstruction of an interaction position is essentially independent of light cluster position. This translates to a nearly isotropic photon response for the entire detector. The system has been used to test several 3D image reconstruction algorithms, software modifications, and improvements. The sensitivity (~12.6 cps/kBq at 9 cm inner diameter) and sub-millimeter spatial resolution (better than 1 mm in phantoms) obtained with an iterative algorithm incorporating system modeling make the SAI a relatively inexpensive high performance animal imager. The SAI is currently being used for imaging experiments in mice and rats. Index Terms--Antibodies, arsenic, FDG, image reconstruction, positron emission tomography, small animal imaging.