A high-resolution, whole-body positron camera, POSICAM 6.5 BGO, has been designed, built, and tested; results from it are presented. The camera utilizes 1,320 BGO crystals and 720 PMTS in a staggered geometry to produce high resolution of 5.8 mm FWHM and 21 image planes simultaneously. The axial resolution of the camera is measured at 11.9 mm at the center. High axial sampling is achieved with 5.125 mm separation of the image planes such that three-dimensional imaging of an object can be carried out in a single scan. Recovery of volumetric distribution of radioactivity and object dimensions in axial and sagittal views is demonstrated by imaging spherical objects 13 mm to 39 mm in diameter.

The performance of the University of Texas TOFPET-I PET camera has been characterized. The camera has 720 fast cesium fluoride scintillators arranged in 5 rings to produce 9 slices images. The spatial resolution FWHM is found to be 9.0 mm, 11.0 mm and 12.0 at the center, 9 cm and 18 cm off center radius respectively. The time-of-flight resolution is about 9 cm. The true coincidence sensitivity for the outer and inner slices are about 8500 cps/ Ci/cc and 22,000 cps/ Ci/cc respectively for a 20 cm uniform source. The axial field-of-view spans 10.5 cm and allows the whole heart to be imaged at one time and a 3-D surface model of the heart to be displayed. The 3-D image is found to be more useful than the conventional slice image for interpretation and is being used for normal operation. Human studies have been carried out for both normal and MI subjects with YSRb. Fast 4 seconds dynamic images with 50% cardiac gating have been obtained.

One of the major design goals of the TOFPET I positron camera was to produce a high resolution whole body positron camera capable of dynamically imaging an organ such as the heart. TOFPET I is now nearing completion and preliminary images have been obtained to assess its dynamic and three dimensional imaging capabilities. Multiple gated images of the uptake of Rubidium in the dog heart and three dirensional surface displays of the distribution of the Rubidium-82 in the myocardium have been generated to demnstrate the three dimensional imaging properties. Fast dynamic images of the first pass of a bolus of radio-tracer through the heart have been collected with 4 second integration time and 50% gating (2 second equivalent integration time) with 18 mCi of Rb-82.

Positron emission tomography (PET) allows the in vivo assessment of biochemical activity in humans. The newer PET cameras can create several imaging planes, or slices, through an organ inside the body. The interpretation of two-dimensional (2-D) slices of an organ is often difficult for the clinician since he or she has to form a three-dimensional (3-D) mental composite of the structure of interest. We have developed a set of algorithms to reconstruct a functional three-dimensional surface model of the cardiac left ventricle from a set of two-dimensional cross-sectional image slices generated by PET. The theoretical techniques for this reconstruction method are applicable to most organs provided that the appropriate models for the organs are considered. An automatic boundary detection algorithm outlines the surface of the left ventricle from the 2-D images and assigns intensity values to the surface points whose level is proportional to the local activity. A 3-D surface of the intensity levels, with pseudocolor enhancement, is then displayed with the long axis of the heart in a vertical position. Such a display allows the 3-D myocardial tracer uptake to be clearly visualized by the clinician for better diagnosis.

Positron emission tomography (PET) with the added time-of-flight information has been shown to provide a better reconstructed image over conventional positron tomography. This improvement depends on the size of the object being imaged, the intrinsic resolution of the detector, and the time-of-flight resolution. Moreover, the signal-to-noise ratio of a PET image is related not only to the total number of counts in the image but also the event-locating uncertainties, the reconstruction filter function, and the recovered resolution in the image. This study provides a physical explanation for, and description of, the improvement in signal-to-noise ratio of a reconstructed image as a function of the crucial design parameters: time-of-flight timing resolution, intrinsic detector resolution, object size, and reconstructed image resolution.

TOFPET is a high resolution whole body positron camera which uses time-of-flight information to (a) improve the signal to noise ratio of a reconstructed image and (b) improve the sensitivity of the central slices by using all the interplane coincidences. The first phase of the construction of the camera has been completed, with all the detectors operational and data collected in the list format with a VAX 11/750 computer. Some of the preliminary results obtained with TOFPET such as resolution and sensitivity, as well as, images of Rubidium-82 in a dog heart are presented. The second phase of the construction, which involves the installation of the on-line microprocessors for faster image reconstruction, is being implemented at this time and is expected to be completed by early 1983, at which time the TOFPET camera will be used for routine clinical studies.

The implementation of data acquisition and real-time backprojection via a bit-slice microprocessor system places serious constraints on data format in TOF-PET systems. To minimize hardware costs and complexity and enhance processing speed, internal data representation is to be realized with a minimum number of bits without significant loss of accuracy. Specifically, we have examined in detail data formats necessary for the quantization of the TOF data and reconstruction filtering via integer FFT's. Estimates of data degradation as related to number of bits utilized have been obtained. It is shown that a significant reduction in image memory size and improvement in speed of computation can be achieved with the appropriate choice of data formats and algorithms.

Several researchers have proven the benefits of using time-of-flight data in Positron Emission Tomography (TOFPET). One of the characteristics of TOFPET which has not been previously explored is the ability to carry out real-time image reconstruction. The advantages of real-time reconstruction are four-fold: 1) Immediate visual feedback of image build-up, 2) Substantial savings of image memory, 3) Faster thoughput of patients through the system and 4) Region-of-interest reconstruction for further memory savings. We present a generalized mathematical model describing this technique together with computer simulations demonstrating its feasibility. We also discuss the implementation of this real-time reconstruction scheme in the TOFPET scanner currently under construction at our institution.