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J H Gallagher

Publications and source records attributed to J H Gallagher.

14 recordsLinked to original sources
PubMed1988

A computer-assisted instruction course to teach visual-field interpretation.

A computer-assisted instruction course for visual-field interpretation is described. A multiple-choice, question-and-answer drill was constructed using the VAX/VMS minicomputer and commercially available educational software. Medical and paramedical personnel can use this course to further their knowledge of visual-field description, the location of lesions which lead to visual-field defects, and the underlying processes that cause some of these defects. The advantages of using a particular computer terminal because of its graphic capabilities and screen layout are described. Other uses of computer-assisted instruction in ophthalmology are discussed and encouraged.

Computer-Assisted Instruction↗
PubMed1983

Simultaneous structural and functional imaging of the transplant kidney using digital subtraction angiography.

We herein describe our preliminary experience with digital subtraction angiography in the noninvasive evaluation of renal transplant structure and function. A single digital subtraction angiography study was obtained in 38 patients with transplant kidneys and various levels of renal function. The main renal artery was demonstrated well in all studies. Stored digital information was used to generate appearance and clearance rates of contrast medium to produce a functional renal image. There was good correlation between the functional image pattern on digital subtraction angiography and the known degree of renal functional impairment. No adverse effects resulted from the small dose of intravenous contrast material used for angiography. This initial study suggests that digital subtraction angiography is a rapid, safe and noninvasive method for visualization of the transplant kidney, and can afford clinically relevant structural and functional information.

Adult↗
PubMed1983

The effects of nuclear magnetic resonance on patients with cardiac pacemakers.

The effect of nuclear magnetic resonance (NMR) imaging on six representative cardiac pacemakers was studied. The results indicate that the threshold for initiating the asynchronous mode of a pacemaker is 17 gauss. Radiofrequency levels are present in an NMR unit and may confuse or possibly inhibit demand pacemakers, although sensing circuitry is normally provided with electromagnetic interference discrimination. Time-varying magnetic fields can generate pulse amplitudes and frequencies to mimic cardiac activity. A serious limitation in the possibility of imaging a patient with a pacemaker would be the alteration of normal pulsing parameters due to time-varying magnetic fields.

Magnetic Resonance Spectroscopy↗
PubMed1983

Comparison of five digital scintigraphic display modes. An ROC curve analysis of detection performance.

In the last decade diagnostic imaging departments, even those of moderate size, have experienced unprecedented growth. Much of this expansion can be attributed directly to technological developments, including systems for the acquisition of diagnostic images in digital format. In modern imaging departments, digital-based systems are quite common and are found across the specialities of nuclear medicine, ultrasound, transmission and emission computed tomography, and angiography. Nuclear magnetic resonance is the newest digital-based modality, and it appears destined to achieve its place in the diagnostic arsenal. These systems all have one trait in common, which is the topic of this paper. They offer the potential of increasing diagnostic accuracy by varying the methods used to process and display the acquired imaged data. We present the results of a nuclear medicine study designed to compare observer performance among five digital scintigraphic display modes. The observer's task was to detect artificially created lesions in brain scintigrams. Each mode is defined by a combination of an image processing function and a method of display. Using 40 trained observers, a receiver operating characteristic curve analysis was performed. The results support the use of color displays in nuclear medicine.

Brain Diseases↗
PubMed1981

Imaging capability of an experimental digital subtraction angiography unit.

We evaluated an experimental digital subtraction unit in terms of field uniformity, linearity of signal response to x-radiation, response of the log amplifier, and imaging capability as measured with the Rose phantom. For comparison, conventional film subtraction phantom measurements were made. Our results indicate that this unit exhibits greater sensitivity to contrast media than conventional film subtraction units.

Angiography↗
PubMed1981

Recirculation subtraction for analysis of left-to-right-cardiac shunts: concise communication.

The object of this study is to improve the techniques for describing the lung dilution curve for shunt quantification by separating the effects of systemic recirculation on the curve form those of direct shunt return. The time of the systemic recirculation peak was estimated by determination of transit times from the right and left ventricles and lung. A gamma variate fit based on the distribution of points at that segment was applied to the recirculation curve and subtracted from the original lung dilution curve. Similar gamma variate fitting was performed for both primary and shunt curves. Rather than fitting the gamma variate of the shunt curve by the leading edge only, a larger portion could now be used since the trailing edge of the curve is clearer following recirculation subtraction. The algorithm is completely automatic, requiring no operator intervention or selection of curve-fitting regions. The correlation coefficient for comparison of the dilution-curve analysis with oximetry determinations was 0.92 in a series of 29 patients.

Adolescent↗
PubMed1981

ROC analysis of diagnostic performance in liver scintigraphy.

Studies on the accuracy of liver scintigraphy for the detection of metastases were assembled from 38 sources in the medical literature. An ROC curve was fitted to the observed values of sensitivity and specificity using an algorithm developed by Ogilvie and Creelman. This ROC curve fitted the data better than average sensitivity and specificity values in each of four subsets of the data. For the subset dealing with Tc-99m sulfur colloid scintigraphy, performed for detection of suspected metastases and containing data on 2800 scans from 17 independent series, it was not possible to reject the hypothesis that interobserver variation was entirely due to the use of different decision thresholds by the reporting clinicians. Thus the ROC curve obtained is a reasonable baseline estimate of the performance potentially achievable in today's clinical setting. Comparison of new reports with these data is possible, but is limited by the small sample sizes in most reported series.

Colloids↗
PubMed1980

Contribution of computed tomography to relative costs in the operative management of patients with renal cell carcinoma.

Relative costs in 14 patients undergoing operative treatment for primary renal carcinoma were anlayzed to determine the contribution of "little ticket" items relative to so-called "high technology" items, such as computed tomography (CT). The major contributing categories of cost were daily room charges, physican fees, and charges for laboratory and pharmacy. In most of the categories, a large variation was encountered, primarily due to patient and disease-related factors. CT was a minor factor in cost.

Adenocarcinoma↗
PubMed1980

Abnormal left ventricular relaxation in hypertensive patients.

1. The maximum rates of left ventricular ejection and filling were derived (Fourier analysis) from the left ventricular volume curve (99m technetium-human serum albumin gated blood pool studies) in 12 normotensive subjects and 15 hypertensive patients of matched age groups. 2. Average values of cardiac output, ejection fraction, heart rate and left ventricular ejection rate were not significantly different in the two groups. 3. Hypertensive patients had a slower rate of left ventricular filling (P < 0.05), suggesting diminished left ventricular compliance in hypertension.

Adult↗
PubMed1980

Detection of low-contrast lesions in computed body tomography: an experimental study of simulated lesions.

Observer accuracy in the identification of low-contrast objects in computed tomography (CT) was studied. Thresholds were established for detection of lesions of various sizes and attenuation differences in CT images produced at different radiation doses. Noise reduction was important in identifying certain types of lesions. Detection was not accurate when the standard deviation of the mean of an organ exceeded the difference in the means of the lesion and the surround region.

Humans↗
PubMed1980

Digital subtraction angiography of the human cardiovascular system.

Initial clinical application of a system for digital subtraction angiography (DSA) to the human cardiovascular system in 88 patients is reported. The equipment consisted of a specially designed computer system integrated with a fluoroscopic and radiographic apparatus for digitization, manipulation, and display of data. After intravenous injection of contrast material, adequate visualization of the heart and carotid, thoracic, abdominal, and femoral arteries was obtained with sufficient quality to obviate conventional angiography in many clinical settings. In this mode, nonselective opacification is obtained. However, DSA was also used to extend the capability of selective angiography. The availability of quantitative information permitted the determination of rates of transit of contrast material in various organs which may give insights of their physiologic performance.

Aneurysm↗
PubMed1978

Computed tomographic evaluation of the breast.

Experience with a dedicated breast CT scanner (General Electric CT/M) using a contrast medium enhancement technique indicates that CT is superior to mammography, thermography, or physical examination for diagnosing both benign and malignant mammary disease especially in dense, thick, or fibrocystic breasts. CT is capable of diagnosing totally unsuspected early miniature carcinomas. It can identify and differentiate potential precancerous lesions from benign fibrocystic disease, and is the diagnostic tool of choice for evaluating and following severe fibrocystic disease. CT evaluation also affords definitive diagnostic help in instances where the mammographic, thermographic, and/or physical examinations are inconclusive. It can influence immediate surgical intervention or mitigate against an unnecessary biopsy. The study not only demonstrates morphologic changes in the breast but also accurately depicts an altered iodine pool in mammary tissues.

Adult↗
PubMed1977

Computed tomography of the breast. A preliminary report.

Initial studies indicate that computed tomography can detect both benign and malignant breast disease in both fatty and dense, thick breasts. CT may also be capable of diagnosing early cancer or a precancerous lesion in women with dysplastic breasts or patients who have had radiation therapy or surgery, whereas some of these lesions cannot be diagnosed by mammography because the breast is too dense.

Breast Diseases↗