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We describe the electronics for a high performance Positron Emission Mammography (PEM) camera. It is based on the electronics for a human brain PET camera (the Siemens/CTI HRRT), modified to use a detector module that incorporates a photodiode (PD) array. An ASIC services the PD array, amplifying its signal and identifying the crystal of interaction. Another ASIC services the photomultiplier tube (PMT), measuring its output and providing a timing signal. Field programmable gate arrays (FPGAs) and lookup RAMs are used to apply crystal by crystal correction factors and measure the energy deposit and the interaction depth (based on the PD/PMT ratio). Additional FPGAs provide event multiplexing, derandomization, coincidence detection, and real-time rebinning. Embedded PC/104 microprocessors provide communication, real-time control, and configure the system. Extensive use of FPGAs makes the overall design extremely flexible, allowing many different functions (or design modifications) to be realized without hardware changes. Incorporation of extensive onboard diagnostics, implemented in the FPGAs, is required by the very high level of integration and density achieved by this system.

An electronics architecture for a PET camera is presented which utilizes a newly developed ASIC, CFD, and TDC to fully utilize the timing advantages of an LSO scintillation crystal. Measured intrinsic timing resolution for a LSO/PMT detector against plastic/PMT detector is 900 ps FWHM using the newly developed ASIC electronics. The energy and pixel location are derived using continuous sampling ADCs with FPGA digital processing algorithms. Sampled PMT signals are rescaled using the CFD trigger to recalibrate the energy and position since the ADCs are asynchronous with the events. The overall linearity of the energy channels is 1.8% for a 6:1 input dynamic range. The electronics are designed to be compatible with large and small area LSO or BGO detectors used in PET imaging. Index Terms--Continuous sampling, front-end electronics, nuclear pulse timing, positron emission tomography (PET).

A custom mixed-signal CMOS integrated circuit has been developed for high performance positron emission tomography (PET) front-end applications. The application specific integrated circuit (ASIC) contains four differential variable-gain constant bandwidth amplifiers, which receive buffered photomultiplier tube (PMT) voltage pulses. All four amplified PMT signals are summed by adding their outputs and feeding this sum to the timing channel of the ASIC. The timing channel, which consists of a constant fraction discriminator and subnanosecond time to digital converter, offers excellent PET count rate performance and randoms noise reduction through low deadtime (100 ns) and excellent timing resolution (312.5 ps LSB). Amplified PMT signals are also distributed to energy processing channels for lowpass filtering and buffering for subsequent digitization by external ADCs. The ASIC offers substantial size, power, and cost reductions over existing PET front-end discrete designs. Fabricated in a 5 V, 0.5 [micro]m, triple metal, double poly, n-well CMOS process, the new ASIC has a die size of 20 [mm.sup.2] and dynamic power dissipation under 425 mW. Index Terms--CMOS integrated circuits, constant fraction discriminator (CFD), front-end electronics, nuclear pulse processing, positron emission tomography (PET), time to digital converter (TDC), variable gain amplifier (VGA).

The ECAT HRRT is a three-dimensional (3-D) only dedicated brain tomograph employing the new scintillator lutetium-oxy-orthosilicate (LSO) and using depth of interaction (DOI) information to achieve uniform isotropic resolution across a 20-cm diameter volume. With its unique technological innovations it represents the prototype of a new generation of high-resolution brain tomographs. The physical performance with respect to count rate, live time, scatter, sensitivity, and resolution was evaluated with phantom studies and measurements with a point source. The HRRTs imaging performance was tested with phantoms and fluorodeoxyglucose (FDG) scans performed in animal and human brains. We find that due to the significantly improved resolution and the large solid angle covered by the panel detectors, several issues that have been adequately solved for older generation scanners demand new attention for the HRRT, like acquiring and handling large amounts of data effectively, strategies for optimal reconstruction, shielding, and correction of random coincidences. Index Terms--Brain tomograph, depth of interaction (DOI), lutetium-oxy-orthosilicate (LSO), phoswitch detector, positron emission tomography (PET).

We present observations of 40 asteroids taken mostly from Table Mountain Observatory, mostly from 1982, but with a few observations from late 1981 and early 1983. Several new or substantially revised periods are reported. Perhaps most interesting are observations of two asteroids, 288 Glauke and 3288 Seleucus, which are in 'tumbling,' or nonprincipal axis rotation, states. Glauke has the longest rotation period known, approximately 1200 h. Absolute photometry was performed on most objects, allowing us to derive phase relations and absolute magnitudes. For objects where these results are superior to previous values, we have revised the IRAS albedos using our absolute magnitude (H) values.

We present the results of photometric observations of the near-Earth asteroids(1943) Anteros, (2102) Tantalus, (2212) Hephaistos, (3199) Nefertiti, (5751) Zao= 1992 AC, (6322) 1991 CQ, (7474) 1992 TC, and 1989 VA made between 1982 and 1995.Synodic rotation periods in the range from 2.39 to 5.54 hr were derived for fiveof them, and we were able to place lower limits on periods of (2212) and (5751)- both > 20 hr. Only the period of the low amplitude case of (1943) was notconstrained. The most interesting results were obtained for the following objects:(2102), a fast rotator (period 2.39 hr) in an extremely inclined orbit (i [approximately equal to] 64 [degrees]); (2212), a low amplitude slow rotatorconsidered as an inactive cometary nucleus candidate; (3199), which showed similarlightcurves at quite different positions of the phase angle bisector, constrainingits rotational pole; and 1989 VA, an unusual Aten asteroid with a rotation periodof 2.51 hr and a relatively large amplitude. Overall, these results continue thepattern that NEO spins exhibit a bimodal distribution of spin rates. Key Words: asteroids; rotation; photometry; near-Earth objects; lightcurves.

New architectures for higher performance data acquisition in PET are proposed. Improvements are demanded primarily by three areas of advancing PET state of the art. First, larger detector arrays such as the Hammersmith ECAT[R] EXACT H[R.sup.++] exceed the addressing capacity of 32 bit coincidence event words. Second, better scintillators (LSO) make depth-of-interaction (DOI) and time-of-flight (TOF) operation more practical. Third, fully optimized single photon attenuation correction requires higher rates of data collection. New technologies which enable the proposed third generation Real Time Sorter (RTS III) include: 1) 80 M byte/sec Fibre Channel RAID disk systems, 2) PowerPC on both VMEbus and PCI Local bus, and 3) quadruple interleaved DRAM controller designs. Data acquisition flexibility is enhanced through a wider 64 bit coincidence event word. PET methodology support includes DOI (6 bits), TOF (6 bits), multiple energy windows (6 bits), 512x512 sinogram indexes (18 bits), and 256 crystal rings (16 bits). Throughput of 10 M events/sec is expected for list-mode data collection as well as both on-line and replay histogramming. Fully efficient list-mode storage for each PET application is provided by real-time bit packing of only the active event word bits. Real-time circuits provide DOI rebinning.

MicroPET is a high resolution positron emission tomography (PET) scanner designed for imaging small laboratory animals. It consists of a ring of 30 position-sensitive scintillation detectors, each with an 8 x 8 array of small lutetium oxyorthosilicate (LSO) crystals coupled via optical fibers to a multi-channel photomultiplier tube. The detectors have an intrinsic resolution averaging 1.68 mm, an energy resolution between 15 and 25% and 2.4 ns timing resolution at 511 keV. The detector ring diameter of microPET is 17.2 cm with an imaging field of view of 112 mm transaxially by 18 mm axially. The scanner has no septa and operates exclusively in 3D mode. Reconstructed image resolution 1 cm from the center of the scanner is 2.0 mm and virtually isotropic, yielding a volume resolution of 8 [mm.sup.3]. For comparison, the volume resolution of state-of-the-art clinical PET systems is in the range of 50 - 75 [mm.sup.3]. Initial images of phantoms have been acquired and are reported. A computer controlled bed is under construction and will incorporate a small wobble motion to improve spatial sampling. This is projected to further enhance spatial resolution. MicroPET is the first PET scanner to incorporate the new scintillator LSO and to our knowledge is the highest resolution multi-ring PET scanner currently in existence.

The subtropical convergence that separates East Australia Current water from the subantarctic water is unrelated to an enhanced micronekton abundance, and contains no single unique community, during the Australian winter. Diaphus danae is most abundant organism in the oceanic waters of Tasmania, Australia. The community structure of the area is similar to that of the East Australia Current (EAC) water. Lobianchia dofleini, Ceratoscopelus warmingi and Vinciguerria spp. are found in greater density in the EAC water whereas Lampichthys procerus is found in the subantarctic water.

The variations in the regional oceanography on seasonal and annual scales affect the presence and density of Nyctiphanes australis found in the coastal waters of eastern Tasmania. During the La Nina cold event, the non-availability of N. australis reduced the stock in T. declivis fishery. The inflow of subtropical northern waters with low nutrient content affected the growth of the plankton that this species of fish feeds on.

Photometric observations of asteroid 951 Gaspra taken prior tothe Galileo deep-space probe flyby were analyzed to determine the characteristics of the minor planet. The results showed that Gaspra had a solarphase angle dependence which exhibited a G value of around 0.29 for the lightcurve maxima. In combination with data obtained by the Galileo space probe, the information gathered from these images allowed a groundbased model of Gaspra to be formulated.

The feeding behavior and its impact on the prey populations of larval Trachurus diclivis were assessed during three summers in the coastal waters of Tasmania. The main components of the larvae'a diet were harpacticoids, cyclopoids, calanoids and calyptopis stage of the euphausiid Nyctiphanes autralis. Larvae fed during the day, with peaks observed during the early morning and late afternoon. Larval population and feeding habits, as well as the overall high densities observed for the prey species, showed that larval feeding does not have a highly significant impact on the prey populations.

Asteroid lightcurve observations from 1981 made by the Table Mountain Observatory are presented. Reports of over 59 asteroids observed in the V-band are given. The observations were used to determine rotation periods of the asteroids as well as the mean phase curves. Asteroids with moderate albedo have a good fit with the data, but those with small or large albedos have poor fit. A machine readable file of the observations is included.

An Application Specific Integrated Circuit (ASIC) has been designed and fabricated which implements many of the current functions found in the digital front-end electronics for a high resolution Positron Emission Tomography (PET) scanner. The ASIC performs crystal selection, energy qualification, time correction, and event counting functions for block technology high resolution PET scanners. Digitized x and y position, event energy, and time information are used by the ASIC to determine block crystal number, qualify the event based on energy, and correct the event time. In addition, event counting and block dead time calculations are performed for system dead time corrections. A loadable sequencer for controlling the analog front-end electronics is also implemented. The ASIC is implemented in a 37,000 gate, 1.0 micron CMOS gate-array and is capable of handling 4 million events/second while reducing parts count, cost, and power consumption over current board-level designs.