Search

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.

The purpose of this exploratory study was to examine the relationship between school-, neighborhood-, and family-level resources and children's academic achievement, and to identify the role played by father involvement in mediating contextual influences on children's learning. A subsample of 1334 families with children between the ages of 5 and 12 was drawn from the 1997 Child Development Supplement of the Panel Study of Income Dynamics (PSID) for use in the analyses. Findings revealed a significant relationship between aspects of father involvement in their children's education and student achievement beyond that accounted for by mother involvement. The findings also lend partial support for a model outlining father involvement in school activities as a mediator of the relationship between contextual factors and children's school achievement.

A Macintosh-based signal processing system has been developed to support simultaneous respiratory and cardiac gating on the ECAT EXACT HR PET scanner. Using the Lab-View real-time software7 environment, the system reads analog inputs from a pneumatic respiratory bellows and an ECG monitor to compute an appropriate histogram memory location for the PET data. Respiratory state is determined by the bellows signal amplitude; cardiac state is based on the time since the last R-wave. These two states are used in a 2D lookup table to determine a combined respiratory-cardiac state. A 4-bit address encoding the selected histogram is directed from the system to the ECAT scanner, which dynamically switches the destination of tomograph events as respiratory-cardiac state changes. To test the switching efficiency of the combined Macintosh/ECAT system, a rotating emission phantom was built. Acquisitions with 25 msec states while the phantom was rotating at 240 rpm demonstrate the system could effectively stop motion at this rate, with approximately 5 msec switching time between states.

We characterize a 3x4 element imaging array consisting of 3x3x5 [mm.sup.3] CsI(Tl) scintillator crystals individually read out by 3x3 [mm.sup.2] PIN silicon photodiodes. The array is a prototype for larger modules (16x16 element) for use in single photon breast cancer imaging. The photodiode output signals are amplified with a 16 channel custom IC (

We present performance results for a prototype PET detector module consisting of 64 LSO scintillatot crystals (3x3x20 mm) coupled on one end to a single photomultiplier tube and on the opposite end to a 64 pixel array of 3 mm square silicon photodiodes (typical pixel parameters are 5 pF capacitance, 300 pA dark current, and 73% quantum efficiency at 415 nm). The photomultiplier tube (PMT) provides an accurate timing pulse and energy threshold for all crystals in the module, the silicon photodiodes (PD) identify the crystal of interaction, the sum (PD+PMT) provides a total energy signal, and the PD/(PD+PMT) ratio determines the depth of interaction. With 32 of the channels instrumented, the detector module correctly identifies the crystal of interaction (where 'correct' includes the adjacent 4 crystals) 79[+ or -]4% of the time with high detection efficiency. The timing resolution for a single LSO detector module is 750 ps fwhm, while its pulse height resolution at 511 keV is 24[+ or -]3% fwhm. The depth of interaction (DOI) measurement resolution is 8[+ or -]1 mm fwhm.

We present performance measurements of a 'Winner-Take-All' (WTA) CMOS integrated circuit to be used with a pixel based PET detector module. Given n input voltages, it rapidly determines the input with the largest voltage, and outputs the encoded address of this input and a voltage proportional to this largest voltage. This is more desirable than a threshold approach for applications that require exactly one channel to be identified or when noise is a significant fraction of the input signal. A sixteen input prototype has been fabricated using two 1.2 [[micro]meter] processes (HP linear MOS capacitance and Orbit double-poly capacitance). ICs from both processes reliably identify (within 50 ns) the maximum channel if [Delta]V (the difference between the two highest channels) is [greater than]20 mV. The key element in the WTA circuit is an array of high gain non-linear current amplifiers. There is one amplifier for each input channel, and each amplifier is composed of only two FETs. All amplifiers are supplied by a common, limited current source, so the channel with the largest input current takes all of this supply current while the other channels receive virtually none. Thus, these amplifier outputs become a set of logical bits that identify the maximum channel, which is encoded and used to select a multiplexer input. A voltage to current converter at each input channel turns this into a voltage sensitive device. This circuit uses very little power, drawing approximately 100 [micro]A at 5 V.