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Biomedical subjects

J M Kofler

Publications and source records attributed to J M Kofler.

11 recordsLinked to original sources
PubMed1999

Techniques for measuring radiographic repeat rates.

Radiographs that must be repeated, which are commonly referred to as "repeats," represent additional, non-billable costs due to increased film, chemistry, and equipment use as well as increased personnel time. Furthermore, patients receive additional radiation exposure from repeats and must remain on the premises until the second exam is completed. Compounding the overt negative financial impact on the department is an increased burden on the waiting room and support staff, and a decrease in patient throughput. A continuous improvement team was assigned to develop an improved technique for monitoring and reducing the number of repeated radiographs in a subset of our radiology department. This paper presents a novel method of accurately measuring the repeat rate through the use of radiographic repeat labels. The labels remove the guesswork from repeat analysis and heighten the technologists' awareness of common problems. Additionally, the labels allow for detailed analysis of the cause of repeated radiographs, which can provide insight for determining remedial actions. Repeat analysis data from our institution acquired using the labels before and after implementing remedial actions are presented.

Documentation↗
PubMed1998

Comparison of selected ultrasound performance tests with varying overall receiver gain and dynamic range, using conventional and magnified field of view.

Most ultrasound (US) scanner vendors currently offer a feature that allows a region of the ultrasound image to be magnified or zoomed. Although the methods of magnification vary among vendors, the ability to "zoom in" on a selected portion of the image has gained clinical acceptance. However, using this feature introduces additional steps in the quality assurance (QA) measurement procedures. No studies exist that demonstrate the advantage of a magnified field of view (FOV) over the conventional FOV for QA purposes. The purpose of this study was to investigate the influence of a magnified versus nonmagnified FOV on various common QA performance tests as a function of the overall receiver gain and dynamic range. Additionally, since the performance tests are subject to variations caused by scanner settings, sets of QC tests were recorded using several different scanner settings to investigate any change in the sensitivity of the QC measurements with respect to the magnified and nonmagnified fields of view. The lateral and axial resolution, slice thickness, and caliper accuracy (vertical and horizontal) as a function of varying overall receiver gain and dynamic range, were obtained using conventional (no zoom) as well as a magnified (zoom) field of view (FOV). Each measurement was performed three times by a single observer using a 4 MHz "vector" format transducer on a single diagnostic medical ultrasound scanner. The results show no statistical significance in the variability of most recorded masurements when using the conventional versus the magnified FOV. However, in some cases, such as lateral resolution, the average value measured using the magnified FOV was typically 0.5 mm lower than when using a conventional FOV.

Calibration↗
PubMed1996

Use of personal computers and digitized film angiograms to produce subtraction angiograms.

Digitization of film angiograms for subtraction purposes alleviates many of the problems associated with conventional film subtraction techniques. In this method, conventional film angiograms are digitized with a laser digitizer. An unenhanced image is subtracted from a contrast material-enhanced image with image processing software and a personal computer. Image registration and the contrast of the subtraction mask image are adjusted as necessary to obtain complete subtractions. Subtraction images produced with this method are superior to subtraction images produced with conventional film subtraction techniques; all areas and densities of a digitized subtraction image exhibit nearly perfect subtraction. Digitized film angiograms and image processing software provide a useful alternative to traditional techniques for producing subtraction angiograms. Digital film subtraction provides more control over image registration, eliminates the need for an intermediate subtraction mask image, and allows the user to control the contrast, window width, and window level of the final image.

Angiography, Digital Subtraction↗
PubMed1996

Technical exhibits.

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Exhibitions as Topic↗
PubMed1995

Quantitative evaluation of low-cost frame-grabber boards for personal computers.

Nine moderately priced frame-grabber boards for both Macintosh (Apple Computers, Cupertino, CA) and IBM-compatible computers were evaluated using a Society of Motion Pictures and Television Engineers (SMPTE) pattern and a video signal generator for dynamic range, gray-scale reproducibility, and spatial integrity of the captured image. The degradation of the video information ranged from minor to severe. Some boards are of reasonable quality for applications in diagnostic imaging and education. However, price and quality are not necessarily directly related.

Computers↗
PubMed1995

Blood flow velocity measurements: a comparison of 25 clinical ultrasonographic units.

A blood-mimicking flow phantom was used to evaluate the precision of velocity measurements acquired using 25 pulsed Doppler ultrasonographic units from four vendors. Measurements were made at four constant flow rates (12 to 50 cm/s peak velocity). The average standard deviation values of the peak and time-averaged velocities among all units and all flow rates were found to be 7 and 9% of the mean, respectively, while the corresponding values for a subgroup of 20 identical units were 5 and 8%. Considered in conjunction with other published data, this suggests that units should be calibrated to an institutional standard at the time of acceptance testing.

Blood Flow Velocity↗
PubMed1994

Spatial and temporal response characteristics of ionization chambers used in diagnostic radiology for exposure measurements and quality control.

The temporal and spatial (partial volume) response characteristics of ionization chambers used for measuring radiation exposures in x-ray quality control (QC) programs were evaluated. Five ionization chambers were evaluated using a pencil beam scanning x-ray source and a conventional radiographic system. The spatial response was determined by recording the exposure during scanning of the pencil beam or in increments using a slitted lead sheet on a conventional x-ray system. The temporal response was determined by recording x-ray wave forms using the different ionization chambers. The effects of partial volume irradiation of the chambers makes them unsuitable for use under these conditions, except those designed for exposure measurements in computed tomography. The temporal response of many chambers resembles that of a typical resistive-capacitive circuit, making them unsuitable for exposure time measurements or x-ray wave form evaluation. The appropriate ionization chamber must be selected for exposure measurements and quality control in diagnostic radiology.

Equipment Design↗
PubMed1994

Technical exhibits.

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Diagnostic Imaging↗
PubMed1991

Sensitometric responses of selected medical radiographic films.

Radiographic films produce different densities and contrast when processor changes occur, and the magnitude and rate of change vary with film type. The ability to detect and interpret the clinical importance of film density changes may depend on the method of sensitometry used. The characteristics of several medical radiographic films and various sensitometers were examined under three sensitometric variations and five processing variations. Of all variations used, only exposure with a single-versus a double-sided sensitometer caused a film type to have a marked different response. The results indicate that mismatching the sensitometer spectral output with the spectral sensitivity of the film in most cases does not affect the density changes of the film. The fact that a few films may be sensitive to differences in spectral content of the exposing light and dual- versus single-sided exposure and that only a limited number of film types were tested, however, leads to the prudent conclusion that the exposure conditions for quality control purposes should match clinical exposure conditions as closely as possible.

Technology, Radiologic↗
PubMedDate not supplied

Performance testing of a dedicated magnetic resonance peripheral blood flow scanner.

This work presents a novel investigation of an NMR device to measure blood flow. Continuous-wave magnetic resonance scanners are now available for noninvasive peripheral blood flow measurements. The appearance of dedicated peripheral blood flow scanners in the clinical setting requires analysis of system performance. No reports were found that explore methods or results of clinical MR blood flow scanner performance evaluation. This work was undertaken to identify the testing procedures and characteristics of a clinical, dedicated NMR blood flow scanner. The dependence of flow measurement on tubing size, material, offset from isocenter, and angulation was examined. In addition, the precision and accuracy of the scanner were investigated. The results demonstrate a strong dependence between the measured blood flow and both the tube size and flow rate. The tube offset results exhibited a region of weak dependence in the center of the bore, which becomes stronger near the edge. The measured flow rate was found to be relatively insensitive to tube angles less than 30 degrees to 55 degrees. The repeatability was typically better than 5% and the table positioning was found to be highly accurate.

Humans↗