Characterization of highly multiplexed monolithic PET / gamma camera detector modules

PET detectors use signal multiplexing to reduce the total number of electronics channels needed to cover a given area. Using measured thin-beam calibration data, we tested a principal component based multiplexing scheme for scintillation detectors. The highly-multiplexed detector signal is no longer amenable to standard calibration methodologies. In this study we report results of a prototype multiplexing circuit, and present a new method for calibrating the detector module with multiplexed data. A [Formula: see text] mm3 LYSO scintillation crystal was affixed to a position-sensitive photomultiplier tube with [Formula: see text] position-outputs and one channel that is the sum of the other 64. The 65-channel signal was multiplexed in a resistive circuit, with 65:5 or 65:7 multiplexing. A 0.9 mm beam of 511 keV photons was scanned across the face of the crystal in a 1.52 mm grid pattern in order to characterize the detector response. New methods are developed to reject scattered events and perform depth-estimation to characterize the detector response of the calibration data. Photon interaction position estimation of the testing data was performed using a Gaussian Maximum Likelihood estimator and the resolution and scatter-rejection capabilities of the detector were analyzed. We found that using a 7-channel multiplexing scheme (65:7 compression ratio) with 1.67 mm depth bins had the best performance with a beam-contour of 1.2 mm FWHM (from the 0.9 mm beam) near the center of the crystal and 1.9 mm FWHM near the edge of the crystal. The positioned events followed the expected Beer-Lambert depth distribution. The proposed calibration and positioning method exhibited a scattered photon rejection rate that was a 55% improvement over the summed signal energy-windowing method.

Evolution of the Design of a Second Generation FireWire Based Data Acquisition System

Our laboratory has previously reported on the basic design concepts of an updated FireWire based data acquisition system for depth-of-interaction detector systems designed at the University of Washington. The new version of our data acquisition system leverages the capabilities of modern field programmable gate arrays (FPGA) and puts almost all functions into the FPGA, including the FireWire elements, the embedded processor, and pulse timing and integration. The design is centered around an acquisition node board (ANB) that includes 64 serial ADC channels, one high speed parallel ADC, FireWire 1394b support, the FPGA, a serial command bus and signal lines to support a rough coincidence window implementation to reject singles events from being sent on the FireWire bus. Adapter boards convert detector signals into differential paired signals to connect to the ANB. In this paper we discuss many of the design details, including steps taken to minimize the number of layers in the printed circuit board and to avoid skewing of parallel signals and unwanted bandwidth limitations.

Arachidonic acid and nonsteroidal anti-inflammatory drugs induce conformational changes in the human prostaglandin endoperoxide H2 synthase-2 (cyclooxygenase-2)

By using the technique of site-directed spin labeling combined with EPR spectroscopy, we have observed that binding of arachidonic acid and nonsteroidal anti-inflammatory drugs induces conformational changes in the human prostaglandin endoperoxide H(2) synthase enzyme (PGHS-2). Line shape broadening resulting from spin-spin coupling of nitroxide pairs introduced into the membrane-binding helices of PGHS-2 was used to calculate the inter-helical distances and changes in these distances that occur in response to binding various ligands. The inter-residue distances determined for the PGHS-2 holoenzyme using EPR were 1-7.9 A shorter than those of the crystal structure of the PGHS-2 holoenzyme. However, inter-helical distances calculated and determined by EPR for PGHS-2 complexed with arachidonic acid, flurbiprofen, and SC-58125 were in close agreement with those obtained from the cognate crystal structures. These results indicate that the structure of the solubilized PGHS-2 holoenzyme measured in solution differs from the crystal structure of PGHS-2 holoenzyme obtained by x-ray analysis. Furthermore, binding of ligands induces a conformational change in the holo-PGHS-2, converting it to a structure similar to those obtained by x-ray analysis. Proteolysis protection assays had previously provided circumstantial evidence that binding of heme and non-steroidal anti-inflammatory drugs alters the conformation of PGHS, but the present experiments are the first to directly measure such changes. The finding that arachidonate can also induce a conformational change in PGHS-2 was unexpected, and the magnitude of changes suggests this structural flexibility may be integral to the cyclooxygenase catalytic mechanism.

Purification and characterization of the human recombinant histidine-tagged prostaglandin endoperoxide H synthases-1 and -2

We have used in vitro mutagenesis to introduce a six residue histidine sequence (His-tag) near the amino terminal end of the human PGHS-1 and -2 and have expressed these proteins using the baculovirus system. The His-tags are located one and two amino acids beyond the signal peptide cleavage sites of PGHS-1 and PGHS-2, respectively, positions that do not affect their activities or sensitivities to nonsteroidal anti-inflammatory drugs. When expressed in sf-21 cells, the His-tagged enzymes have K(m) values for arachidonate, and IC(50) values for inhibition by nonsteroidal anti-inflammatory drugs that are similar to values reported for the nontagged enzymes. The His-tags allowed for purification of the PGHSs by a simplified protocol involving nickel-affinity and anion exchange FPLC chromatography. The specific activities and recoveries for the purified enzymes were as good or better than those reported previously for purification of the non-tagged PGHS. These baculovirus constructs should provide a convenient source for pharmacologic and biophysical studies that require large scale preparation of human PGHSs.

Differentiation-associated expression of prostaglandin G/H synthase in monocytic cells

Significant progress in the investigation of the regulation of prostanoid formation has recently been made by cloning a second gene coding for prostaglandin G/H synthase (PGHS; EC 1.14.99.1). In this study we examined the expression of the two PGHS isoforms during phorbol ester induced monocytic differentiation of human myeloid leukemia cells (U937). Murine and ovine PGHS-1 probes hybridized to 2.8- and 5.5-kb mRNA species, whereas the murine PGHS-2 probe hybridized to a 5.3-kb species. Western blot analysis using antisera to mouse PGHS-1 and to a synthetic peptide derived from a mouse PGHS-2-specific region revealed a band of 70 kDa for PGHS-1 and a doublet of about 85 kDa for PGHS-2. Unlike PGHS-2, which was not expressed in U937 control cells, both PGHS-1 protein and mRNA were detected in untreated U937 cells. TPA strongly induced PGHS-2 protein and also increased the amount of PGHS-1 protein. Correspondingly, a marked induction of PGHS-2 mRNA was found, but virtually no change in the expression of the PGHS-1 2.8-kb mRNA occurred. The induction of both PGHS isoforms turned out to be dexamethasone-sensitive. The suppression of PGHS-2 induction was more pronounced. These results suggest that both PGHS-1 and to a larger extent PGHS-2 contribute to the upregulation of prostanoid synthesis during monocytic differentiation.

Diagnostic hysteroscopy

The hysteroscope is a valuable tool for selective viewing of the uterine cavity and the endocervical canal. With smaller-diameter scopes, hysteroscopy can be performed in the office setting, often without the need for cervical dilatation or local anesthesia. Controlled-rate CO2 insufflators allow safe distention of the uterine cavity with minimal side effects. Indications for office hysteroscopy include the evaluation of abnormal uterine bleeding, genital carcinoma and infertility and the investigation of a "lost" intrauterine device. Hysteroscopy is an adjunct to endometrial sampling, dilatation and curettage, hysterosalpingography and cervical cytology.

Occlusive disease of the middle cerebral artery

We studied 20 patients with severe occlusive disease of the mainstem middle cerebral artery (MCA) or its major division branches, and 25 patients with internal carotid artery (ICA) disease. MCA disease patients were more often black, female, younger, and had fewer TIAs than the ICA disease patients. Neurologic signs in patients with MCA disease evolved progressively during days to weeks, whereas ICA disease patients more often had an acute onset of nonprogressive deficits. CT commonly showed restricted subcortical or wedge-shaped infarcts in MCA disease patients. All MCA disease patients had stroke, but 40% of ICA disease patients had no infarction. MCA lesions usually affected the mainstem MCA or its major superior division. Patients with MCA disease seldom had recurrent ischemia in the same vascular territory as the stroke and had a low incidence of subsequent cardiac death.

Automated metabolic profiling of organic acids in human urine. II. Analysis of urine samples from "healthy" adults, sick children, and children with neuroblastoma

Normalized median, minimum, and maximum values (analytical concentration factors) are given for 134 organic acids in urine of nine adult control subjects, five juvenile control subjects, and five children with neuroblastoma. The organic acids, separated by anion-exchange chromatography, were analyzed by a gas chromatograph-mass spectrometer-computer system. Sixty substances in this fraction are positively identified, and, of these, mean absolute concentrations are listed for 20. An additional 81 substances, sought but not found by this method, and 16 other substances found in a subset of these urines by another analytical method, are also listed. Measured retention indices on 5% OV-17 and a selected discriminating ion are given for each of the total of 231 compounds. Results are compared for the three groups of subjects, and the value of normalizing the data is discussed.

Automated metabolic profiling of organic acids in human urine. II. Analysis of urine samples from "healthy" adults, sick children, and children with neuroblastoma

Normalized median, minimum, and maximum values (analytical concentration factors) are given for 134 organic acids in urine of nine adult control subjects, five juvenile control subjects, and five children with neuroblastoma. The organic acids, separated by anion-exchange chromatography, were analyzed by a gas chromatograph-mass spectrometer-computer system. Sixty substances in this fraction are positively identified, and, of these, mean absolute concentrations are listed for 20. An additional 81 substances, sought but not found by this method, and 16 other substances found in a subset of these urines by another analytical method, are also listed. Measured retention indices on 5% OV-17 and a selected discriminating ion are given for each of the total of 231 compounds. Results are compared for the three groups of subjects, and the value of normalizing the data is discussed.