A vectorized Monte Carlo code for modeling photon transport in SPECT.

A vectorized Monte Carlo computer code has been developed for modeling photon transport in single photon emission computed tomography (SPECT). The code models photon transport in a uniform attenuating region and photon detection by a gamma camera. It is adapted from a history-based Monte Carlo code in which photon history data are stored in scalar variables and photon histories are computed sequentially.

Scatter compensation for digital chest radiography using maximum likelihood expectation maximization.

Rationale And Objectives: An iterative maximum likelihood expectation maximization algorithm (MLEM) has been developed for scatter compensation in chest radiography.

Methods: The MLEM technique produces a scatter-reduced image which maximizes the probability of observing the measured image. We examined the scatter content and the low-contrast signal-to-noise ratio (SNR) in digital radiographs of anatomical phantoms before and after compensation.

Bovine neurofilament-enriched preparations contain kinase activity similar to casein kinase I--neurofilament phosphorylation by casein kinase I (CKI).

Neurofilament (NF)-enriched preparations from bovine spinal cord contain regulator-independent kinase activities that phosphorylate NF subunits as well as alpha-casein. CKI-7 (N-2-amino ethyl, 5-chloroisoquinoline, 8-sulfonamide), a specific inhibitor of casein kinase I (CKI), inhibits the phosphorylation of NF subunits in the neurofilament preparation. This inhibition occurs at a concentration range identical to concentrations where CKI-7 inhibits rabbit reticulocyte CKI phosphorylation of alpha-casein.

Digital chest radiography with photostimulable storage phosphors: signal-to-noise ratio as a function of kilovoltage with matched exposure risk.

A photostimulable storage phosphor (PSP) digital radiography system was evaluated regarding the signal-to-noise ratio (S/N) on chest images acquired at differing peak kilovoltage settings but with matched risk from radiation exposure. Images of two chest phantoms were acquired by using bedside (portable) imaging equipment at tube voltages ranging from 60 to 120 kV. Exposure factors were set so that the effective dose equivalent, a risk estimator weighted for various organs, was approximately equal in all exposures.

Human pathologic correlation with PET in ischemic and nonischemic cardiomyopathy.

To assess the correlation between myocardial perfusion, metabolism and histologic findings in patients with cardiomyopathy, we evaluated myocardial perfusion and metabolism using positron emission tomography (PET) with 13NH3 (ammonia) and 18FDG (fluoro-2-deoxy-glucose) in nine patients prior to undergoing orthotopic cardiac transplantation. Four patients had ischemic cardiomyopathy (ISCM) and five had nonischemic cardiomyopathy (NISCM). Normalized circumferential profile analyses of representative mid-ventricular perfusion and metabolism PET images were performed for each patient.

An artificial neural network for lesion detection on single-photon emission computed tomographic images.

Rationale And Objectives: An artificial neural network (ANN) has been developed to detect nonactive circular lesions on single-slice, single-photon emission computed tomographic (SPECT) images reconstructed using filtered back projection (FBP).

Methods: The neural network is a single-layer perception which learns to identify features on the SPECT image using supervised training with a modified delta rule. The network was trained on a set of SPECT images containing clinically realistic levels of noise.

Measurement of scatter fractions in clinical bedside radiography.

The authors present measurements of scatter fraction (SF), the ratio of scattered to total imaged photons, from clinical bedside radiographs of 102 patients. These measurements were obtained by using a new posterior beam-stop technique that does not alter the diagnostic image but that simultaneously provides SF measurements at 224 locations in the image. The SF values in the lung were found to be consistent with previous measurements, while the SF values in the mediastinal and retrocardiac areas were larger than previously reported.

von Willebrand factor interacts with malignant hematopoietic cell lines: evidence for the presence of specific binding sites and modification of von Willebrand factor structure and function.

von Willebrand factor (vWf) mediates the adherence of platelets to exposed vascular subendothelium. During hematogenous metastasis in certain model systems, platelets are also deposited at endothelial surfaces in heterotypic aggregates with tumor cells. The role of vWf in this metastatic event was investigated by examining the interaction between purified iodine 125-labeled vWf and the human tumor cell lines, U937 and CA46.

Comparison of commercially available media for detection and isolation of Ureaplasma urealyticum and Mycoplasma hominis.

The Mycotrim Triphasic flask system (Irvine Scientific, Irvine, Calif.) was compared with a system composed of Mycotrim GU broth (Irvine Scientific) and A7 or A8 agar (Remel, Lenexa, Kans.) for the ability to detect Ureaplasma urealyticum and Mycoplasma hominis from 129 genital specimens.

Three-dimensional photon detection kernels and their application to SPECT reconstruction.

In single photon emission computed tomography (SPECT), three-dimensional photon detection kernels characterize the probabilities that photons emitted by radio-isotopes in different parts of the source region will be detected at particular projection pixels of the projection images. Monte Carlo modelling is used to study these kernels for the case of parallel hole collimators. The use of vectorized Monte Carlo computer code speeds the modelling computations.

Posterior beam-stop method for scatter fraction measurement in digital radiography.

The authors presented a new posterior beam-stop (PBS) technique for measuring the ratio of scattered to total-detected photon flux (scatter fraction) in a radiographic examination while preserving the diagnostic quality of the image. The scatter measurement was made using a standard imaging geometry with both beam stops and an additional x-ray detector placed behind the standard imaging detector. This PBS geometry differs from the standard beam-stop (SBS) technique for scatter measurement.

Reconstruction of SPECT images using generalized matrix inverses.

Generalized matrix inverses are used to estimate source activity distributions from single photon emission computed tomography (SPECT) projection measurements. Image reconstructions for a numerical simulation and a clinical brain study are examined. The photon flux from the source region and photon detection by the gamma camera are modeled by matrices which are computed by Monte Carlo methods.

Treatment of Compton scattering in maximum-likelihood, expectation-maximization reconstructions of SPECT images.

This paper studies the extent to which lesion contrasts and signal-to-noise ratios in maximum-likelihood, expectation-maximization estimates of SPECT images can be improved by considering Compton scattering when calculating the photon detection probability matrix. Matrices are generated using a Monte Carlo code that realistically models a SPECT imaging system. For cold lesions having true contrasts of one, thirty-six combinations of three lesion sizes, three lesion locations, and four projection-data count levels are considered.

Quantitative scatter measurement in digital radiography using a photostimulable phosphor imaging system.

X-ray scatter fractions measured with two detectors are compared: a photostimulable phosphor system (PSP) and a conventional film-screen technique. For both detection methods, a beam-stop technique was used to estimate the scatter fraction in polystyrene phantoms. These scatter fraction measurements are compared to previously reported film-based measurements.

Single-exposure conventional and computed radiography image acquisition.

A technique for simultaneously acquiring a conventional film-screen radiographic image and a digital computed radiography (CR) image with a single x-ray exposure is described. Measurements of image contrast, spatial resolution, and signal-to-noise ratios demonstrate that a modified film cassette in which the first intensifier screen has been replaced with a CR imaging plate permits dual-image, single-exposure imaging with only nominal degradation in film and CR image quality relative to the two standard image counterparts. This technique may be used to acquire matched image pairs for research or as a way to provide full-size conventional film images in the clinical environment, while retaining the advantages offered by computed radiography systems.

Effects of sleep deprivation on sleepiness and increased REM sleep in rats selectively bred for cholinergic hyperactivity.

In this study we employed a modification of the multiple sleep latency test (MSLT) to determine whether rats of a strain with increased cholinergic activity were sleepier compared to randomly bred control rats. Seven rats each from the Flinders sensitive line (FSL, hypercholinergic) and Flinders resistant line (FRL, age-matched controls) were kept awake for 20 min and then allowed to sleep ad libitum for 20 min. The regimen of 20 min of wakefulness followed by 20 min of sleep was repeated 12 times during the day.

Principal neurofilament-associated protein kinase in squid axoplasm is related to casein kinase I.

A cytoskeletal extract of pure axoplasm, highly enriched with neurofilaments (ANF), was prepared from the giant axon of the squid. This ANF preparation also contained potent kinase activities which phosphorylated the Mr greater than 400,000 (high molecular weight) and Mr 220,000 squid neurofilament protein subunits. High salt (1 M) extraction of this ANF preparation solubilized most of the neurofilament proteins and kinase activities and gel filtration on an AcA 44 column separated these two components.

Testing of local gamma-ray scatter fractions determined by spectral fitting.

The spectral-fitting method of correction for gamma-ray Compton scattering within objects separates the unscattered and scattered components of locally measured energy spectra. Here, we employ a third-order polynomial for the scattering and an approximately constant fitting window. A scatter fraction, defined as total scattered over total unscattered counts within a 20% window, is calculated for each point in our Anger camera images.

An artificial neural network for SPECT image reconstruction.

An artificial neural network has been developed to reconstruct quantitative single photon emission computed tomographic (SPECT) images. The network is trained with an ideal projection-image pair to learn a shift-invariant weighting (filter) for the projections. Once trained, the network produces weighted projections as a hidden layer when acquired projection data are presented to its input.

Scatter fractions in AMBER imaging.

Images of two phantoms were obtained with use of an advanced multiple-beam equalization radiography system, and scatter fractions were estimated with use of a photostimulable phosphor imaging system. Scatter fractions in the equalized images were lower in the mediastinum-equivalent areas and higher in the lung-equivalent areas, relative to images that were conventionally acquired with use of an antiscatter grid. The differences are attributed to a reduction in incident exposure in the lungs and the presence of cross-scatter between lung and mediastinal regions.

A structurally novel inhibitor of cGMP phosphodiesterase with vasodilator activity.

A novel, potent, competitive inhibitor of smooth muscle cGMP phosphodiesterase is described (Compound I, [4-[2-n-butyl-5-chloro-1-(2- chlorobenzyl)imidazolyl]methyl] acetate). The compound is highly selective for inhibiting cGMP phosphodiesterase compared with cAMP phosphodiesterase. Compound I inhibits the contraction of smooth muscle in response to a variety of agonists in the same concentration range to that which inhibits the enzyme.

Pontine cholinergic neurons simultaneously innervate two thalamic targets.

Cholinergic neurons located in the lateral dorsal tegmental (LDT) and pedunculopontine tegmental (PPT) nuclei have been shown to principally innervate the thalamus. In order to determine whether some of these neurons might simultaneously project to two thalamic targets we made microinjections of rhodamine-conjugated microbeads into the central-lateral nucleus of the thalamus and fluorescein isothiocyanate (FITC)-conjugated microbeads into the dorso-lateral geniculate nucleus. We then determined whether both tracers were found in immunohistochemically identified cholinergic somata in the LDT and PPT nuclei.

Characterization of neurofilament-associated protein kinase activities from bovine spinal cord.

1. A neurofilament-enriched preparation from bovine spinal cord contains endogenous protein kinases that phosphorylate high, middle, and low molecular weight neurofilament subunits (NF-H, NF-M, and NF-L), as well as certain other endogenous and exogenous substrates. 2.

Quantitative radiographic imaging using a photostimulable phosphor system.

We have evaluated a photostimulable phosphor x-ray imaging system [Philips Computed Radiography (PCR) system] for use in quantification of x-ray exposure in diagnostic radiography. An exponential function was fitted to data yielding quantitative x-ray exposure values as a function of digital pixel values. We investigated several factors that affect the accuracy of exposure measurement using the PCR including repeatability, background noise as a function of time delay between plate erasure and use, sensitivity variation between different plates, nonuniformity of sensitivity within a plate, decay of the latent image between time of exposure and readout (observed as a change in sensitivity), and the accuracy with which the (exponential) calibration function yields exposure values as a function of digital pixel values.