Quality assurance in mammography: the Michigan breast phantom test experience.
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Female↗
Biomedical subjects
J P Windham
Publications and source records attributed to J P Windham.
Analysis of the evolution of focal cerebral ischemia in the rat using the eigenimage filter.
The eigenimage filter was used to evaluate the results of a MRI study of cerebral ischemia in a rat model. This linear filter segments a desired feature in an image sequence from other features which may interfere with its observation. The animals were imaged temporally, after occlusion of the middle cerebral artery, to investigate the evolution of the ischemic process. The temporal evolution of ischemia was evaluated by analysis of the "eigenimages," calculated T2 and T1 map images, and images for the angles between signature vectors defined in the eigenimage technique. The eigenimages and angle map images demonstrated an improved visibility of the lesion at all time points, as compared to the original images and T2 and T1 map images. The eigenimages also demonstrated signal intensity changes within the area of ischemia. These changes are speculated to be related to variations in local cerebral blood flow resulting in varying degrees of tissue damage. The eigenimage intensities and the angles between signature vectors demonstrated time-related changes similar to the T2 and T1 values. Since the eigenimage filter and angle calculations are not dependent upon physical models (like T2 and T1), and the errors associated with these models, they may be preferable as methods for tissue characterization.
Animals↗
Eigenimage filtering in MR imaging: an application in the abnormal chest wall.
A postprocessing linear filter was applied to spin-echo images on 10 patients with known or suspected chest wall invasion due to bronchogenic carcinoma. This technique known as eigenimage filtering allows selective feature extraction of suspected abnormalities from conventional MR images. The final result is an image with marked increased contrast range through enhancement of a desired process (tumor) with suppression of an interfering process (e.g., normal surrounding tissue). This preliminary work demonstrates the ease with which the technique may be implemented, the contrast enhancement obtained between the desired and the interfering feature in the final eigenimage, and its ability to correct for partial volume averaging effects. Also demonstrated are artifacts that can interfere with the interpretation of the eigenimage and a method for minimizing these artifacts in the final eigenimage.
Carcinoma, Bronchogenic↗
Computer model for simulation of first transit cardiac radionuclide curves--I.
A discrete-time, lumped-parameter mathematical model of the human cardiopulmonary circulation as it appears during a first-transit radionuclide study is developed. Eleven compartments, four delays, and 26 transfer paths are modeled, including the entire circulation from an input compartment before the vena cava to an output compartment after the aorta. The 26 transfer paths include forward and reverse flow through the heart valves, backflow from the atria into the veins, and five types of shunts. A method of modeling continuously-variable delay segments with only discrete-time sample points is devised to allow more versatility in specifying delays. The model simulates discrete time-activity curves for the various compartments of the cardiopulmonary system. The curves are obtained for end-systole and end-diastole. Simulation of curves indicative of a normal heart and several heart defects is presented. The use of this model for computer analysis of first-transit cardio-radionuclide curves is discussed.
Computer Simulation↗
Optimal fitting of computer model simulations to first transit cardiac radionuclide curves--II.
A discrete-time, lumped-parameter mathematical model of the human cardiopulmonary circulation as it appears during a first-transit radionuclide study has been described. An optimal fitting process is used to match curves obtained from the model to curves obtained from first transit studies in order to estimate the parameters of the subject's heart. The development of the optimization technique is described in this paper. The results of testing the effects of overlapping compartments and errors in delay estimates are presented. A parameter determination analysis is performed by applying the optimization algorithm to simulated data. This analysis technique provides a method of estimating many parameters of heart function using a single, simple, rapid procedure. Results of clinical studies will be presented subsequently.
Algorithms↗
Eigenimage filtration of intravenous digital subtraction angiograms of the heart. Work in progress.
The authors developed a postprocessing technique, eigenimage filtering, to extract phase-dependent information from digital subtraction angiograms of the heart. This technique suppresses the interference from the right ventricle and left atrium and produces an image of the left ventricle and aorta that is substantially free of these overlap artifacts. The resultant eigenimages of the heart appear more like conventional ventriculograms than do digital subtraction angiograms and matched filtered images.
Cardiac Catheterization↗
Captopril challenge with radionuclide assessment in two-kidney and one-kidney Goldblatt hypertension.
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Angiotensin-Converting Enzyme Inhibitors↗
Captopril renography in two kidney and one kidney Goldblatt hypertension in dogs.
In order to improve on the technique of noninvasive detection of renal artery stenosis, we studied the effects of angiotensin converting enzyme inhibition with captopril on individual kidney hemodynamics and function as assessed by technetium-99m diethylenetriaminepentaacetic acid [( 99mTc]DTPA) renal flow studies and iodine-131 orthoiodohippurate [( 131I]hippuran) renography in experimental Goldblatt's hypertension. In two-kidney, one-clip (renin-dependent) hypertension, captopril (1.5 mg/kg bolus with 1.5 mg/min infusion) reduced mean arterial pressure (MAP) and ipsilateral glomerular filtration rate (GFR) without changes in the contralateral kidney. Captopril infusion resulted in alterations in both the [99mTc]DTPA and [131I]hippuran studies, which were most evident in the 15-min [99mTc]DTPA renal flow studies. In one-kidney, one-clip (volume-dependent) hypertension, captopril reduced MAP but did not alter GFR, renal plasma flow, or the radionuclide studies. These studies suggest that the [99mTc]DTPA renal flow study coupled with captopril challenge may unmask intrarenal angiotensin II-dependent functional and hemodynamic changes of the stenotic kidney, and offers promise in the detection of renin-dependent hypertension.
Animals↗
Breast lesions: differential diagnosis using digital subtraction angiography.
To evaluate its potential for differentiating benign from malignant breast lesions, digital subtraction angiography of the breast (DSAB) was performed in 23 women with mammographic evidence of disease, and the results were compared with surgical biopsy findings. The DSAB technique employed breast immobilization with modest compression and bolus injection; following the injection of contrast material, 30-40 sequential subtraction images were obtained over a 5-minute interval. The average technical settings were 50 k Vp and 10 mAs, resulting in an estimated radiation dose to the breast of 0.05 mrad (0.5 mu Gy) per exposure. DSAB consistently demonstrated retention of contrast material and abnormal vasculature in malignant lesions but not in benign lesions. In the 22 breast lesions for which there was histopathologic correlation, DSAB correctly categorized eight of nine malignant and 11 of 13 benign lesions. Although this series is small, the initial results of DSAB suggest its potential for differentiating benign from malignant lesions.
Adenocarcinoma↗
Effect of captopril on 99mTc-diethylenetriaminepentaacetic acid renograms in two-kidney, one clip hypertension.
In an effort to improve on the noninvasive detection of renal artery stenosis, we investigated the effect of angiotensin converting enzyme inhibition on computer-assisted 99mTc-diethylenetriaminepentaacetic acid (DTPA) renal flow studies in a canine model of two-kidney, one clip hypertension and compared these findings with clearances of inulin and p-aminohippuric acid in the stenotic and contralateral kidney before and after converting enzyme inhibition. The 99mTc-DTPA renal flow study with the converting enzyme inhibitor captopril (1.5 mg/kg bolus with 1.5 mg/min infusion) showed an increased sensitivity in the detection of unilateral renal artery stenosis over the use of the 99mTc-DTPA study alone. Captopril induced striking alterations that were most evident in the 15-minute 99mTc-DTPA renal flow study, in which all nine curves exhibited severely blunted uptake and excretion of the radionuclide. These changes were reversed during a recovery study without converting enzyme inhibition and were not seen when blood pressure was lowered with nitroprusside to a level similar to that observed during converting enzyme inhibition. The changes shown by the 99mTc-DTPA study during converting enzyme inhibition correlated with a decrease in the glomerular filtration rate of the stenotic kidney. Captopril infusion significantly decreased the glomerular filtration rate of the stenotic kidney (16.0 +/- 3.1 vs 11.0 +/- 2.5 mg/min, p less than 0.03) but not of the contralateral kidney (32.4 +/- 2.6 vs 28.4 +/- 2.8 mg/min).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Technetium-99m DTPA renal flow studies in Goldblatt hypertension.
Computer-assisted dynamic renal studies were performed on a group of 14 mongrel dogs before and after the induction of unilateral renal artery stenosis. Ninety-second technetium-99m diethylenetriaminepentaacetic acid ( [99mTc]DTPA), 15-min [99mTc]DTPA, and 30-min iodine-131 orthoiodohippurate ( [131I]hippuran) time-activity curves were analyzed and correlated with reduction of renal blood flow as measured by electromagnetic flow probe and PAH clearance techniques. Parameters of the 90-sec [99mTc]DTPA curves found to be significantly different for the same kidney before and after stenosis were: upslope, curve width at 75% maximum, maximum activity value, and differential (stenotic/contralateral) maximum activity ratio. For blood flow reductions greater than 33%, the [99mTc]DTPA studies were judged diagnostic of unilateral renal artery stenosis in all cases, whereas the [131I]hippuran time-activity curves were indicative of stenosis in only six of ten studies. Thus, in this model we find the computer-assisted 90-sec [99mTc]DTPA renal flow study to be superior to conventional [131I]hippuran renography in the diagnosis of moderate-to-severe unilateral renal artery stenosis.
Animals↗
Improved computer-assisted nuclear imaging in renovascular hypertension.
Computer-assisted dynamic renal studies using both the 90 second 99mTc-DTPA and the conventional 30 minute 131I-Hippuran methods were performed in nine patients with angiographically proven renal artery stenosis. Time activity curves for both studies were derived from regions of interest selected from the computer-acquired dynamic images. The following parameters were used to assess renal blood flow: differential maximum activity, minimum/maximum activity ratio, and peak width. The computer-assisted DTPA study accurately predicted (9/9) the stenotic side documented angiographically, whereas the conventional Hippuran scan was clearly predictive in only 57% (5/9). The best discriminatory factors for the 90 second 99mTc-DTPA scan, when compared to a normal template synthesized from curves obtained from normal subjects (20), were differential maximum activity and peak width. In conclusion, the computer-assisted 90 second 99mTc-DTPA renal blood flow scan was superior to the conventional 30 minute 131I-Hippuran scan in demonstrating unilateral renovascular disease. The DTPA study was highly predictive of the angiographic findings, and this noninvasive study may prove useful in the diagnosis and serial evaluation following surgery or angioplasty in patients having renal artery stenosis.
Adult↗
The performance characteristics of radiographic equipment: compliance with federal regulations.
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Dose-Response Relationship, Radiation↗
Transport calculations of gamma ray flux density and dose rate about implantable californium-252 sources.
Gamma flux density and dose rate distributions have been calculated about implantable californium-252 sources for an infinite tissue medium. Point source flux densities as a function of energy and position were obtained from a discrete-ordinates calculation, and the flux densities were multiplied by their corresponding kerma factors and added to obtain point source dose rates. The point dose rates were integrated over the line source to obtain line source dose rates. Container attenuation was accounted for by evaluating the point dose rate as a function of platinum thickness. Both primary and secondary flux densities and dose rates are presented. The agreement with an independent Monte Carlo calculation was excellent. The data presented should be useful for the design of new source configurations.
Californium↗
Calculated neutron dose rates for implantable Californium-252 sources.
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Absorption↗
Brain tumor segmentation and characterization by pattern analysis of multispectral NMR images.
A major problem in tumor treatment planning and evaluation is determination of the tumor extent. This paper presents a pattern analysis methodology for segmentation and characterization of brain tumors from multispectral NMR images. The proposed approach has been used in 15 clinical studies of cerebral tumor patients who have been scheduled for surgical biopsy and resection. The tissue biopsy results, obtained at specific spatial coordinates determined in the analysis, have been utilized to validate the methodology. It was found that in all cases the lesion had extended into normal tissue, at least to the location where the sample was taken. In most cases, the proposed method suggested that the lesion had extended several millimetres beyond the point from where the biopsy sample was taken. In some cases, the extent of the lesion into normal tissue was well beyond the boundary seen on T1- or T2-weighted images. It is concluded that the proposed approach indicates brain tumor infiltration more precisely than what is visualized in the original NMR images and therefore its utilization facilitates proper treatment planning for the cerebral tumor patients.
Biopsy↗
Segmentation of the hippocampus from brain MRI using deformable contours.
The application of a discrete dynamic contour model for segmentation of the hippocampus from brain MRI has been investigated. Solutions to several common problems of dynamic contours in this case and similar cases have been developed. A new method for extracting the discontinuous boundary of a structure with multiple edges near the structure has been developed. The method is based on detecting and following edges by external forces. The reliability of the final contour and the model stability have been improved by using a continuous mapping of the external energy and limiting movements of the contour. The problem of optimizing the internal force weight has been overcome by making it dependent on the amount of the external force. Finally, the results of applying the proposed algorithm, which implements the above modifications, to multiple applications have been evaluated.
Algorithms↗
Eigenimage filtering in MR imaging.
This article presents the technical aspects of a linear filter, referred to as eigenimage filtering, and its applications in magnetic resonance (MR) imaging. The technique is used to obtain a single composite image depicting a particular feature of interest while suppressing one or more interfering features. The appropriate weighting components to be used in the linear filter are determined on the criterion that the desired feature is enhanced while the interfering features are suppressed. The criterion is expressed mathematically as a ratio. By applying Rayleigh's principle, the ratio is maximized by finding the eigenvector associated with the maximum eigenvalue of the corresponding generalized eigenvalue problem. The appropriate weighting factors for the linear filter are the elements of the eigenvector which maximize the ratio. The utilization of the technique is demonstrated in its application to a simulated MR image sequence as well as to acquired MR image sequences of a normal and an abnormal brain.
Brain↗