Pneumothorax rate during CT-guided lung biopsies.
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Biopsy↗
Biomedical subjects
M S Rzeszotarski
Publications and source records attributed to M S Rzeszotarski.
The x-ray fovea, a device for reducing x-ray dose in fluoroscopy.
The x-ray fovea (U.S. patents pending) is a device for reducing x-ray dose to patients and operations during x-ray fluoroscopy. It consists of a semitransparent collimator with an open, circular, central hole. The fovea collimator is placed at the exit of the x-ray tube, and the attenuation of the peripheral x-ray beam reduces x-ray exposure to patients and operators. The shadow caused by the x-ray fovea can be compensated using real-time image processing hardware. Accurate compensation is demonstrated for both linearly and logarithmically acquired images using a model that accounts for beam hardening in the fovea collimator. The central fovea region has improved image quality due to reduced scatter and veiling glare from the periphery. From beam-stop measurements, a 40% reduction in scatter plus veiling glare is measured using the fovea. A contrast improvement ratio of 1.5 is measured throughout the central region. In the compensated periphery, noise is increased by a factor of 1.66 because fewer photons are detected, but a small amount of temporal filtering compensates this degradation. The Roentgen area product (RAP) exposure to patients is reduced by approximately 70%, while scattered exposure to operators is reduced by approximately 60%.
Equipment Safety↗
Stylized chromosome images.
Stylized chromosome images 1) serve as a format to test effects of preprocessing algorithms used in automated karyotyping; 2) enhance the ability of humans to perform quantitative analysis of chromosomal aberrations; 3) provide an alternative format for karyotype hard copies produced by automated systems. Stylized chromosomes are two-dimensional computer-generated images based on information extracted from one-dimensional width and density profiles. These profiles correspond to what cytogeneticists observe through the microscope as the shape and banding patterns of stained chromosomes. Stylized presentation sharpens chromosome band boundaries and perimeters, reduces "noise," and enhances gray level variations, which are difficult to distinguish by humans on photographic or computer generated karyotypes. Karyotyping accuracy using stylized images was used to detect difficult areas for automated chromosome identification. Landmark bands sufficient to classify chromosomes were identified; shapes of chromosomes reflected in width profiles were said to aid classification. A two-step automated karyotyping strategy proposed is: 1) classify chromosomes by landmarks, minimum information needed for identification; 2) subsequently employ the full banding pattern with maximum resolution to detect aberrations. Stylized images of abnormal chromosomes have potential for testing hypothesis regarding breakpoints and quantitative analysis, but improvements are needed in homologue normalization and definition of termini of chromosomes.
Algorithms↗
Comparison of magnetic resonance imaging and radionuclide bone imaging of vertebral fractures.
The following report summarizes the authors' initial experience with detecting and aging vertebral fractures in elderly patients with osteoporosis, emphasizing the use of an inversion recovery sequence with a short time to inversion (STIR) and comparing these results to that achieved using RBI.
Aged↗
A strategy for magnetic resonance imaging of the head: results of a semi-empirical model. Part I.
This paper is an introduction to lesion detection problems of MR. A mathematical model previously developed for normal anatomy has been extended to predict the appearance of any hypothetical lesion in magnetic resonance (MR) images of the head. The model is applied to selected clinical images to demonstrate the loss of lesion visibility attributable to "crossover" and "boundary effect". The model is also used to explain the origins of these problems, and to demonstrate that appropriate gray-scale manipulations can remedy these problems. Specifically, pulse sequences that cause lesions to be the brightest tissue in the image are shown to eliminate the problems of crossover and boundary effect.
Brain Diseases↗
A strategy for magnetic resonance imaging of the head: results of a semi-empirical model. Part II.
A semi-empirical model was used to identify specific pulse sequences that cause most lesions to appear distinctly brighter than normal tissues in magnetic resonance (MR) images of the head. Clinical trials confirm the utility of these sequences for patient screening. As a result, a strategy for effective and efficient MR imaging of the head is proposed. The previously described gray-scale model has been modified to account for the effect of image noise. By means of computer simulation, 13,800 different hypothetical cerebral lesions were imaged with a variety of pulse sequences. A number of conclusions resulted. First, two sequences are expected to be sufficient to visualize most intracranial lesions, a "diagonal" SE sequence (e.g., SE 2500/80) and an IR sequence with a short inversion time (e.g., IR 1800/200). These sequences are orthogonal, i.e., lesions missed by one are likely to be detected by the other. Second, signal averaging the screening sequences is expected to be more effective than optimized sequences when lesion tissue parameters differ little from brain. Finally, the effectiveness of unaveraged screening sequences suggests that improved signal-to-noise ratio (SNR) is not necessary for the detection of most large lesions. Therefore, the increased SNR achievable through signal averaging or increased field strength might best be utilized to improve spatial resolution so that smaller lesions can be detected.
Brain Diseases↗
Relationship between Y-chromosome length and first-trimester spontaneous abortions.
The hypothesis that variation in Y-chromosome length is associated with repetitive fetal wastage was tested. Chromosome lengths were objectively quantitated by scanning photographic negatives of metaphases with a computer programmed to (1) select boundary thresholds and (2) construct and measure centerlines with a cubic spline-fitting algorithm. Variation in Y length among cells of different individuals was standardized by use of the ratio of the length of the Y to the average of the lengths of the No. 20s (20) in the same cell. Three groups were studied: (1) men whose wives had three or more spontaneous abortions and no live-born infants, (2) men whose wives had both abortions and normal live-born infants, and (3) control men whose wives had normal live-born infants only. Although central tendencies were similar in the three groups, the distributions of Y lengths among the three groups were significantly different (chi 2(6) = 15.33, 0.025 greater than p greater than 0.010). This difference was primarily because more of the subjects with only repetitive loss had Y lengths in the "tails" of the distribution rather than in the center. Our observations suggest the existence of an optimal Y length with respect to reproductive performance.
Abortion, Habitual↗
Nuclear magnetic resonance: a gray scale model for head images.
The gray scale of nuclear magnetic resonance (NMR) head images is explained in terms of tissue and machine parameters. Tissue parameters considered here include the spin-lattice relaxation time, the spin-spin relaxation time, and the proton density. Machine parameters include the pulse sequence (saturation recovery, inversion recovery, or spin echo), the repetition time, and the delay time. The ability of the operator to alter the NMR gray scale predictably is examined by computer simulation. The simulation computes NMR pixel values for a selected combination of tissue and machine parameters. The computed values are compared with those extracted from clinical NMR images. The agreement between simulation and clinical pixel values implies that the operator can use the machine parameters to alter the NMR gray scale, and thereby control contrast, appropriate to the diagnostic requirements. The extent to which the NMR gray scale can be predictably controlled is illustrated through graphs, simulated contrast displays, and representative NMR images.
Brain Chemistry↗
Localization of the nucleolar organizer by computer-aided analysis of a variant no. 21 in a human isolate.
A variant chromosome no. 21 consisting of two stalks and two satellites in tandem was detected during a survey of a human isolate. The variant segregated in three generations of a large kindred. One male had the variant no. 21, a metacentric Y, and a 47,XXY complement; however, no other evidence of chromosomal nondisjunction was found. Computer-aided analysis of sequentially stained variant no. 21 chromosomes indicated that silver-stained material corresponded to the proximal stalk region (as defined by Giemsa), but often covered both the distal stalk and satellite (also as defined by Giemsa). These data support the hypothesis that human nucleolar organizers are localized to the stalks of acrocentric chromosomes.
Azure Stains↗
An MTF method immune to aliasing.
The variance derived from the images of cyclic bar patterns can be used to determine the modulation transfer function (MTF) of an imaging system. Unlike most MTF methods, it is applicable even when the imaging system undersamples the test object and generates aliasing errors. The validity of the variance method in the presence of aliasing is established theoretically and by computer simulation.
Analysis of Variance↗
Counting statistics.
The low radiation dose rates used in nuclear medicine necessitate image formation and measurements that are severely count limited. This limitation may mask our ability to perceive contrast in an image or may affect our confidence in quantitative functional measurements. The randomness of the signal can be described by using the Poisson probability distribution with its associated mean and variance. The validity of a measurement and uncertainties in a result can be determined by examining the count statistics. If multiple measurements are used to derive a result, confidence levels can be determined by examination of the propagation of errors. The statistical properties of the detected signal can also be evaluated to determine if the equipment is functioning properly. For example, the chi2 test can be used to determine if there is too much or too little variability in count samples. Finally, image formation with limited numbers of photons results in noisy images that may be difficult to interpret. An understanding of the trade-offs between contrast, noise, and object size is required to set proper image acquisition parameters and thereby ensure that the information required to make a diagnosis is contained in the final image.
Algorithms↗
Measurement of pituitary gland height with MR imaging.
From sagittal magnetic resonance (MR) images with 10 mm slice thickness, the mean vertical height of the pituitary gland in 42 normal patients was found to be 5.4 +/- 0.9 mm. Computed tomographic (CT) scans in the coronal plane showed the same. Measurements of pituitary size in 13 patients with tumors using both CT and MR were also essentially equivalent. The ease, comfort, and accuracy of the MR pituitary measurement supports its use as the examination of choice for measuring pituitary height.
Adult↗