A. Villanueva

Statistical 3D image reconstruction for the RatCAP PET tomograph using a physically accurate, Monte Carlo based system matrix

This work describes a fully 3D statistical image reconstruction for the RatCAP (Rat Conscious Animal PET) using a Monte Carlo based system matrix. The RatCAP consists of 12 Iutetium oxyorthosilicate (LSO)-avalanche photodiode (APD) detector blocks arranged in a ring of 41.2 mm diameter. Due to the small ring diameter and low number of total lines of response (LORs), the size of a complete system matrix is small in comparison to a typical small animal scanner. This allows incorporation of an accurate, RatCAP-specific physical model with the inclusion of crystal penetration, Compton scattering in both rats brain and detector, attenuation and the realistic event positioning errors. The trade off between the statistical accuracy and the matrix computational time as it relates to the accuracy of image reconstruction will also be discussed.

System performance simulations of the RatCAP awake rat brain scanner

The capability to create high quality images from data acquired by the Rat Conscious Animal PET tomograph (RatCAP) has been evaluated using modified versions of the PET Monte Carlo code Simulation System for Emission Tomography (SimSET). The proposed tomograph consists of lutetium oxyorthosilicate (LSO) crystals arranged in 12 4 /spl times/ 8 blocks. The effects of the RatCAPs small ring diameter (/spl sim/40 mm) and its block detector geometry on image quality for small animal studies have been investigated. Since the field of view will be almost as large as the ring diameter, radial elongation artifacts due to parallax error are expected to degrade the spatial resolution and thus the image quality at the edge of the field of view. In addition to Monte Carlo simulations, some preliminary results of experimentally acquired images in both two-dimensional (2-D) and 3-D modes are presented.

The RatCAP conscious small animal PET tomography

The RatCAP is a small, head mounted PET tomograph designed and built to image the brain of an awake rat. It allows PET imaging studies to be carried out on laboratory rats without the use of anesthesia, which severely suppresses brain functions and affects many of the neurological activities that one would like to study using PET. The tomograph consists of a 4 cm diameter ring containing 12 block detectors, each of which is comprised of a 4 times 8 array of 2.2 times 2.2 times 5 mm3 LSO crystals read out with a matching APD array. The APDs are read out using a custom designed ASIC and VME readout system. We have successfully performed a system integration test with a partially instrumented tomograph ring. We present the recent progress towards a fully integrated system

Initial performance of the RatCAP, a PET camera for conscious rat brain imaging

The first fully functional prototype of the RatCAP (Rat conscious animal PET) scanner has been constructed and preliminary evaluations have been performed. RatCAP is a miniature, high performance PET scanner designed specifically to image the brain of a rat while directly attached to its head. The goal is to eliminate the need for anesthesia which can confound quantitative brain studies and prevent simultaneous correlations of neurochemistry and behavior. RatCAP is a fully 3D tomograph with a transaxial (axial) field-of-view of 38(18) mm, outside diameter 72 mm, and weight <200 g which is supported by a small tether. A total of 384 LSO crystals are divided among 12 independent detector blocks, each of which contains an avalanche photodiode (APD) photosensor array and a custom-designed ASIC for highly integrated front-end processing. A custom FPGA-based time-stamp module has been designed and implemented, achieving a preliminary system resolution of 13.9 ns FWHM. With a point source in the FOV center, spatial resolution is 2.1 mm FWHM, energy resolution averages 23% FWHM, and sensitivity is 0.7% at an average threshold of 150 keV. Novel offline data processing algorithms have been developed including methods for time and energy calibrations, corrections for physical effects, and a highly accurate iterative image reconstruction. Initial phantom and rat brain images have been obtained

PDAQ - a fast data acquisition system for the RatCAP tomograph

We describe a custom data acquisition system for the RatCAP tomograph. It is a small, head-mounted PET detector designed to image the brain of an awake rat. At its core, the tomograph consists of a number of LSO crystals read out with an array of APDs. The data will be collected through a custom-designed ASIC, along with a custom VME board. We describe the design, implementation, and performance of a versatile VME-based data acquisition system which will be used to read out the VME board, as well as other off-the-shelf data acquisition electronics.

Front-end electronics for the RatCAP mobile animal PET scanner: timing discriminator and 32 line address priority serial encoder

We report on the development of the integrated front-end electronic for the RatCAP (Rat Conscious Animal PET). The RatCAP is a head-mounted, APD-based portable positron emission tomography scanner intended to perform brain imaging and behavioral studies of the awake rat. This paper focuses on the development and characterization of the zero-crossing discriminator (ZCD) and the 32 line address serial encoder for the miniature scanner. The ZCD, used as a time pick-off circuit for each APD detector, has a power consumption of only 300 /spl mu/W. The 32 line address serial encoder is used to multiplex the timing edge of every channel together with its address into a single output. The ASIC, realized in a CMOS 0.18 /spl mu/m process, has a maximum power dissipation of 125 mW. The electronic timing jitter, the time walk and the coincidence timing resolution of the ZCD measured at the encoder output are presented.

Noninvasive high-resolution detection of the arterial and venous input function through a PET wrist scanner

In order to assess the kinetics of radiotracer accumulation in tissue, the amount of radioactivity in the blood must be quantitatively measured as an input function to the kinetic model. Due to safety and comfort issues with invasive determination of the input function, a non-invasive method for arterial measurement of blood radioactivity is investigated using a wrist scanner. A prototype consisting of two detector pairs of LSO and APD detector arrays is used to obtain planar images of an anatomically correct wrist phantom. The spatial resolution and sensitivity of the prototype is determined. The results showed the detector was able to discriminate the arterial and venous flows from each other when using planar coincidence images.

A non-invasive LSO-APD blood radioactivity monitor for PET imaging studies

A study has been carried out to investigate the possibility of using a pair of LSO + APD detector arrays to obtain a non-invasive measurement of the arterial input function for use in PET. The main focus of this study was to determine the spatial resolution and sensitivity required to obtain a high quality image that would permit a precise determination of the region of interest around the wrist artery. From these data a quantitative arterial input function that has minimal interference from the tissue and vein background can be obtained. The detector arrays were operated in coincidence counting mode to obtain planar images of various phantoms to demonstrate the feasibility of the concept.