R. Wojcik

SPECT-CT system for small animal imaging

The Detector Group at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) and the Biology, Physics, and Applied Sciences Departments at the College of William and Mary are collaborating on the development of a miniature dual modality SPECT-CT system for mouse imaging. The detector heads of the SPECT sub-system are designed to be capable of imaging the gamma- and X-ray emissions (28-35 keV) of the radioactive isotope iodine-125 (I-125). Two different sets of I-125 imaging detectors are configured on a gantry that has an open-barrel type design. One set of detector heads is based on the 1-in square Hamamatsu R5900-M64 position sensitive photomultiplier tube coupled to crystal scintillator arrays. The other detector heads configured on the gantry are two 5-in diameter Hamamatsu R3292-based compact gamma cameras. The X-ray radiographic projections are obtained using a LIXI Inc. model LF-85-503-OS X-ray imaging system that has an active area of 5.5 cm in diameter. The open-barrel shaped gantry facilitates the positioning of various mini gamma-ray imaging detectors and the X-ray system. The data acquisition and gantry control is interfaced through a Macintosh G3 workstation. Preliminary SPECT reconstruction results using the R5900 based detector are presented.

Analog readout system with charge division type output

Charge division readout provides a relatively simple electronic solution for data readout of position sensitive radiation detectors. Conventional charge division usually consists of some charge division media connected to the detector outputs to provide proportional charge division between two division chain outputs. Although offering some advantages such as simplicity and the reduction of the number of analog outputs, it reduces the detector spatial resolution and image quality, because of signal to noise reduction from the attenuation of the signal before reaching the amplifiers. An analog readout system with functionally the same output as common charge division, but without a division chain connected to the detector outputs before signal amplification was designed and evaluated. This readout system operates as a multi-channel analog signal converter which converts signals from multi-channel output position sensitive devices such as multianode PMTs or gamma cameras built of PSPMT arrays etc. to two per coordinate analog outputs with same amplitude correlation as common charge division position readout.

A restraint-free small animal SPECT imaging system with motion tracking

We report on an approach toward the development of a high-resolution single photon emission computed tomography (SPECT) system to image the biodistribution of radiolabeled tracers such as Tc-99m and I-125 in unrestrained/unanesthetized mice. An infrared (IR)-based position tracking apparatus has been developed and integrated into a SPECT gantry. The tracking system is designed to measure the spatial position of a mouses head at a rate of 10-15 frames per second with submillimeter accuracy. The high-resolution, gamma imaging detectors are based on pixellated NaI(Tl) crystal scintillator arrays, position-sensitive photomultiplier tubes, and novel readout circuitry requiring fewer analog-digital converter (ADC) channels while retaining high spatial resolution. Two SPECT gamma camera detector heads based upon position-sensitive photomultiplier tubes have been built and installed onto the gantry. The IR landmark-based pose measurement and tracking system is under development to provide animal position data during a SPECT scan. The animal position and orientation data acquired by the tracking system will be used for motion correction during the tomographic image reconstruction.

Optimized readout of small gamma cameras for high resolution single gamma and positron emission imaging

Using a novel resistive readout scheme and off-the-shelf PCI ADC data acquisition cards, a compact readout and control system for mini gamma cameras based on position sensitive photomultiplier tubes (PMTs) has been developed. This economical resistive readout incorporates a special fractional subtraction technique to greatly expand the useful field of view of the PMTs to the very edges of their active area as compared to standard resistive readout methods such as charge division or Anger logic. This allows one to obtain the same quality images as those obtained with much more expensive and bulky individual wire readout data acquisition systems. The four output signals from the readout circuit can be digitized by a PCI ADC card in a computer to achieve high counting rates. Results will be shown for this readout applied to a dual modality breast biopsy system currently undergoing clinical trials and an ultra high resolution single gamma small animal imaging system for studies on mice and rats.

Embedded waveshifting fiber readout of long scintillators

Abstract We have tested a method of reading out light from long scintillators by embedding waveshifting fibers in longitudinal grooves created in the scintillators which are then connected to a photomultiplier (PMT). With PMTs on both ends of the fibers we have obtained attenuation lengths of over 5 m and light outputs of over 5 photoelectrons per MeV from both ends of a 4 m long BC408 scintillator with five embedded 2 mm diameter BCF92 fast green waveshifting fibers using a Hamamatsu green extended R580-17 PMT. With a reflector at one end of the fibers, we have easily obtained over 10 m attenuation lengths. Also presented are results using inexpensive acrylic scintillators with this method and measurements of a new experimental scintillator from Bicron with over a 5 m attenuation length.

Performance Evaluation of a Dedicated Camera Suitable for Dynamic Radiopharmaceuticals Evaluation in Small Animals

As the result of a collaboration between the Detector and Imaging Group of Thomas Jefferson National Accelerator Facility (US), the Institute of Radioisotopes and Radiodiagnostic Products (IRRP) of N.C.S.R. ldquoDemokritosrdquo and the Biomedical Simulations and Imaging Applications Laboratory (BIOSIM) of National Technical University of Athens (Greece), a mouse sized camera optimized for Tc99m imaging was developed. The detector was built in Jefferson Lab and transferred to Greece, where it was evaluated with phantoms and small animals. The system will be used initially for planar dynamic studies in small animals, in order to assess the performance of new radiolabeled biomolecules for oncological studies. The active area of the detector is approximately 48 mm times 96 mm. It is based on two flat-panel Hamamatsu H8500 position sensitive photomultiplier tubes (PSPMT), a pixelated NaI(Tl) scintillator and a high resolution lead parallel-hole collimator. The system was developed to optimize both sensitivity and resolution for in vivo imaging of small animals injected with technetium compounds. The results of system evaluation in planar mode with phantoms are reported. Results are presented for in vivo dynamic studies of mice injected with > 100 muCi of two conventional and novel radiopharmaceuticals, namely Tc99m-MDP and Tc99m -Bombesin.

Integrated CT-SPECT system for small animal imaging

We are developing a scanner for simultaneous acquisition of x-ray computed tomography (CT) and single photon emission tomography (SPECT) images of small animals such as mice and rats. The scanner uses a cone beam geometry for both the x- ray transmission and gamma emission projections by using an area x-ray detector and pinhole collimator, respectively. The CT and SPECT data set are overlaid to form a coregistered structural-functional 3D image. The CT system includes a single CCD-based x-ray detector and a microfocus x-ray source. The SPECT scanner utilizes tungsten pinhole collimators and arrays of CsI(Tl) scintillation detectors. We describe considerations and the early performance of a prototype scanner.

Development and testing of a restraint free small animal SPECT imaging system with infrared based motion tracking

The development and initial evaluation of a high-resolution single photon emission tomography (SPECT) based system to image the biodistribution of radiolabeled tracers such as Tc-99m and I-125 in unrestrained/un-anesthetized mice. An infrared (IR) based position tracking apparatus has been developed and integrated into a SPECT gantry. The tracking system is designed to measure the spatial position of a mouses head at a rate of 10-15 frames per second with sub-millimeter accuracy. The high resolution, gamma imaging detectors are based on pixelated NaI(Tl) crystal scintillator arrays, arrays of compact position-sensitive photomultiplier tubes and novel readout circuitry for lower device cost while retaining high spatial resolution. Two SPECT gamma camera detector heads based on a 4 /spl times/ 8 array of Hamamatsu R8520-C12 position sensitive photomultiplier tubes have been built and installed onto the gantry. The IR landmark-based pose measurement and tracking system is under development to provide animal position data during a SPECT scan. The animal position and orientation data acquired by the IR tracking system is used for motion correction during the tomographic image reconstruction.

Optimization of breast imaging procedure with dedicated compact gamma cameras

Results are presented on studies conducted with various prototypes of a dedicated small field-of-view (SFOV) gamma camera for use in radiopharmaceutical studies of the breast. Since the experience in the clinical use of such instruments is limited, these experiments were conducted to test various clinical imaging implementations. Both planar and tomographic techniques were utilized to image various compressed and noncompressed breast phantoms. Lesion contrast was used to quantify the lesion visibility of each case. The results of this study indicate that lesion contrast is optimized with planar imaging of the compressed breast and that contrast is also dependent on lesion-to-detector distance. Based on these observations, planar imaging conducted with a system comprised of two opposed detectors providing compression to the breast would be optimal. The opposed views would ensure the minimization of lesion-to-detector distance, especially for lesions whose location is not known a-priori.

X-ray stereotactic lesion localization in conjunction with dedicated scintimammography

We are developing a dual modality system that combines digital X-ray mammography with gamma emission scintigraphy, on an upright mammography gantry in which the breast is held under mild compression by a support structure that is independent of the detectors. The X-ray source and detectors can be rotated around a fixed rotation axis permitting multiple views of the breast with fixed compression. Two such views can be combined as a stereotactic pair to obtain the three-dimensional location of breast lesions. Information about the location of the lesion within the breast permits corrections for attenuation and detector spatial resolution, resulting in more accurate estimation of the true lesion-to-background concentration ratio, based on the image lesion-to-background counts ratio. In this paper, we describe the model used to make these corrections, and present the results of phantom experiments designed to test the accuracy of our calculations.