Whole-body adipose tissue analysis: comparison of MRI, CT and dual energy X-ray absorptiometry.

The aim of this study was to validate a recently proposed MRI-based T(1)-mapping method for analysis of whole-body adipose tissue (AT) using an established CT protocol as reference and to include results from dual energy X-ray absorptiometry (DEXA). 10 subjects, drawn from the Swedish Obese Subjects Sibling-pairs study, were examined using CT, MRI and DEXA. The CT analysis was based on 28 imaged slices. T(1) maps were calculated using contiguous MRI data from two different gradient echo sequences acquired using different flip angles. CT and MRI comparison was performed slice-wise and for the whole-body region. Fat weights were compared between all three modalities. Strong correlations (r > or = 0.977, p<0.0001) were found between MRI and CT whole-body and AT volumes. MRI visceral AT volume was underestimated by 0.79 +/- 0.75 l (p = 0.005), but total AT was not significantly different from that estimated by CT (MRI - CT = -0.61+/-1.17 l; p = 0.114). DEXA underestimated fat weights by 5.23 +/- 1.71 kg (p = 0.005) compared with CT. MRI underestimated whole-body volume by 2.03 +/- 1.61 l (p = 0.005) compared with CT. Weights estimated either by CT or by DEXA were not significantly different from weights measured using scales. In conclusion, strong correlations were found between whole-body AT results from CT, MRI-based T(1) mapping and DEXA. If the differences between the results from T(1)-mapping and CT-based analysis are accepted, the T(1)-mapping method allows fully automated post-processing of whole-body MRI data, allowing longitudinal whole-body studies that are also applicable for children and adolescents.

Measurement of lower-leg volume change by quantitative computed tomography.

BACKGROUND: Lower-leg edema is a common symptom in many diseases. A precise method with low variability for measurement of edema is warranted in order to obtain optimal conditions for investigation of treatment effects. PURPOSE: To evaluate computed tomography for precise measurement of lower-leg muscle and adipose tissue volumes using a very low level of effective radiation dose. MATERIAL AND METHODS: Eleven volunteers were examined three times during 1 day, either as two consecutive examinations in the morning and one single examination in the afternoon, or as one examination in the morning and two in the afternoon. Eleven scans with computed tomography were made at each examination, and lower-leg volumes were calculated from automatically measured scan areas and interscan distances. Volumes for muscle, adipose tissue, and bone were calculated separately. Minimal radiation dose was used. RESULTS: Mean difference between the repeated examinations was -0.1 ml for total volume, -1.4 ml for muscle, and 1.6 ml for adipose tissue volume. The corresponding 95% confidence intervals were -6.5 to 6.0 ml, -3.5 to 6.5 ml, and -7.0 to 4.0 ml, respectively. The resulting effective dose was 0.5 microSv to one leg. CONCLUSION: Computed tomography can be used as a precise quantitative method to measure small volume changes of the lower leg as a whole, and separately for muscle and adipose tissue. The results were obtained with a negligible effective dose, lower than that delivered by modern fan-beam dual-energy X-ray absorptiometry whole-body examinations and equal to a few hours of background radiation.

Digital chest radiography--comparing two types of CRT monitors in a ROC experiment with a chest phantom.

Two principally different 1000-line CRT (cathode ray tube) monitors connected to a digital image intensifier system for chest radiography were compared in terms of image quality and viewing comfort. Image quality was assessed by means of ROC analysis. Five observers tried to find simulated pathology positioned over the lungs and the mediastinum of an anthropomorphic phantom. The observers also graded the viewing comfort of the two CRTs in terms of flicker, light levels, and general comfort. No significant difference in the detection of simulated pathology was demonstrated between the two monitors. A slight preference for the newer CRT (Imlogix) was seen as compared to the older standard CRT (Siemens) regarding flicker and general comfort.

Digital chest radiography--optimizing image processing parameters for the visibility of chest lesions and anatomy.

The effect of varying the degree of contrast and edge enhancement upon the visibility of chest lesions and anatomy was evaluated in a digital image intensifier system for chest radiography. Visual grading analysis was used as method for the evaluation. Conventional radiographs served as reference images. Ten observers graded the visibility of four regions of interest: (1) fine linear structures, (2) mediastinal anatomy, (3) rounded opacities, (4) vessels, and also graded the overall quality of 17 chest images. The images had been subjected to three grades of image processing: one basic, one intermediate, and one extreme. In all, 2730 observations were made. The basic image processing was the best for the visibility of regions 2, 3, and 4 and for the overall quality. The intermediate image processing was best for the fine linear structures. The extreme image processing rated lowest for all regions and especially for the overall quality.

Does digital chest radiography assess regional ventilation?

Digital radiography of the chest was evaluated for estimation of regional ventilation disturbances. Thirty-three patients with suspected bronchial carcinomas were examined. Objective measurements of regional density changes during breathing correlated significantly with standardized regional lung function tests (133Xe ventilation scintigraphy), but did not permit reliable individual estimations of regional ventilation. About 35% of the density variations could be explained by regional ventilation. Thus, factors other than ventilation, e.g. changes in the geometry of the thorax, have a major impact on the density variation at digital radiography.

Image intensifier based digital chest radiography. Visibility of lesions and anatomy.

Contrast- and edge-enhanced digital monitor images from an image intensifier system for chest radiography were compared to conventional radiograms using visual grading analysis. Eleven observers graded the visibility of rounded opacities, the carinal region, fine line structures, and also compared the overall quality of images from 20 patients. The results showed significantly better visibility on the digital monitor for the rounded opacities and the mediastinum compared to the conventional radiograms. The overall quality of the digital images was also considered better. However, the digital images showed significantly inferior visibility for the line structures in comparison with the conventional radiograms. Our study indicates that the present contrast- and edge-enhanced digital images, with a spatial resolution of 1,024 x 1,024 pixels and a contrast resolution of 8 bits, are superior to conventional radiograms for the visualization of mediastinal anatomy and rounded opacities. The clinical importance of the inferior visibility of fine line structures is not clear.

Digital luminescence radiography using a chest phantom. Comparison between radiographs displayed on monitor and hard-copy.

Ninety-eight digital radiographs of a chest phantom with simulated tumors in the mediastinum and left lung and a pneumothorax-simulation in the right hemithorax were compared with the corresponding examinations saved on optical disk and viewed on a 1,000-line monitor. The examinations were reviewed by 7 radiologists with different experience, and receiver operating characteristic (ROC) curves were constructed. There was no significant difference between the hard-copy and the monitor results. A significant interobserver difference was seen only with the low attenuating 6 mm "tumor" and then only between the observer with the highest and the one with the lowest scores.

Digital chest radiography: should images be presented in negative or positive mode?

The observer performance for video monitor images presented in positive mode ('bones black') was compared to that of images presented in negative mode ('bones white') in a digital system for chest radiography based on a large image intensifier. In the first part of the study (I), the original, non-linear grey-scale reversal performed in the computer of the digital image intensifier system (DS1000) was studied together with fixed and variable settings of light and contrast. In the second part of the study (II), true grey-scale reversal performed in a minicomputer (Micro VAX II) where the images were also processed with edge and contrast enhancement, was studied. The time spent viewing the images was also recorded. Before the second part of the study, the image intensifier system was optimized with regard to spatial and contrast resolution and dose settings. Simulated pathology was randomly positioned over the lungs and the mediastinum of an anthropomorphic phantom. Observer performance was evaluated with Receiver Operating Characteristic (ROC) analysis on the digital images. In the first part of the study, a significant advantage for the positive images was seen, but no significant difference between fixed and variable settings of light and contrast. In the second part of the study, no significant difference in the detectability of the test structures was seen between positive and negative images. A significant improvement in the detectability was seen between the first and the second part of the study for the nodules over the mediastinum in both negative and positive images. No significant difference in the time spent observing positive and negative images, was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of optimization and image processing in digital chest radiography: an ROC study with an anthropomorphic phantom.

A digital system for chest radiography based on a large image intensifier was compared to a conventional film-screen system. The digital system was optimized with regard to spatial and contrast resolution and dose. The images were digitally processed for contrast and edge enhancement. A simulated pneumothorax and two simulated nodules were positioned over the lungs and the mediastinum of an anthropomorphic phantom. Observer performance was evaluated with ROC analysis. Five observers assessed the processed digital images and the conventional full-size radiographs. The time spent viewing the full-size radiographs and the digital images was recorded. For the simulated pneumothorax, the results showed perfect performance for the full-size radiographs and detectability was high also for the processed digital images. No significant difference in the detectability of the simulated nodules was seen between the two imaging systems. The results for the digital images showed a significantly improved detectability for the nodules in the mediastinum as compared to a previous ROC study where no optimization and image processing was available. No significant difference in detectability was seen between the former and the present ROC study for small nodules in the lung. No difference was seen in the time spent assessing the conventional full-size radiographs and the digital images. The study indicates that processed digital images produced by a large image intensifier are equal in image quality to conventional full-size radiographs for low-contrast objects such as nodules.

Conservative surgery for mitral valve prolapse with regurgitation: clinical follow-up and noninvasive assessment.

To evaluate the result of mitral valve repair in pure regurgitation due to mitral valve prolapse with or without chordal rupture, 11 patients were followed noninvasively for 2.0 to 3.5 years and clinically for at least 5 years in a prospective study. The patients were operated upon before ominous signs of left ventricular dysfunction appeared, all patients being in functional class III, with an ejection fraction of at least 0.50 and mean velocity of circumferential fibre shortening above 1.0. There was no operative mortality. No thrombo-embolic episodes occurred during follow-up. Ten of the 11 patients were alive 5 years postoperatively. One patient died 9 months after the initial repair shortly after reoperation for mitral and tricuspid regurgitation. The other patients all showed definite clinical improvement. Confirming the experience of others, the two patients with ruptured chordae to the anterior mitral leaflet and the only patient with a thick anterior mitral leaflet all had moderate mitral regurgitation postoperatively. Complete repair of mitral valve prolapse is feasible and gives a good functional result of long duration. The results of this study support early mitral repair when complete restoration of ventricular size and function is still possible.

Computer aided exercise electrocardiographic testing and coronary arteriography in patients with angina pectoris and with myocardial infarction.

A set of electrocardiographic criteria for the diagnosis of coronary artery disease was evaluated in two different groups of patients examined by computer aided 12 lead exercise electrocardiographic stress testing and coronary arteriography. One group consisted of patients with severe angina pectoris and the other of patients who had suffered a myocardial infarction three years before the study. Angiographically determined categories of patients could be identified with satisfactory precision by the electrocardiographic criteria under test in the patients with angina pectoris but not in those with infarction. A new method of classifying patients on the basis of data from coronary arteriography improved the correlation with ST segment analysis compared with conventional classification.

A program for processing of multiple-lead exercise ECGs in real time.

A computer program for continuous recording and real-time processing of 8-channel exercise ECGs is presented. Current average ECG complexes and trends of various morphological and rhythmic parameters can be displayed on a TV monitor during the stress test. Average complexes computed every 10 s, the time of occurrence and 6 morphological coefficients of all detected tentative QRS complexes, and data manually entered by the operator are stored in a file on disk. The operational procedures and the principal signal processing are briefly presented. The main attention is given to a description of the software structure, explaining the subdivision of the program into dedicated autonomous sections and the system for the coordination of simultaneous activities of different priority.

Computerized exercise ECG in the diagnosis of critical coronary lesions.

Different ECG criteria are evaluated with respect to their ability to identify individuals with critical lesions of the coronary arteries in a population of patients with severe angina. Six chest leads and the the limb leads were recorded in 85 patients by computer during maximal, symptom-limited exercise ECG testing. Averaging of ECG complexes enhances the signal quality and makes it possible to use measurements of the limb leads recorded during exercise. 14 patients with abnormal Q waves in lead V2 were excluded from ST analysis. In the remaining 71 patients, more than 1/3 mm ST depression in lead I and/or more than 2.0 mm ST depression in any of the chest leads had a sensitivity of 85% and a specificity of 67% for lesions in the main stem and/or proximal LAD and/or three-vessel disease. The predictive value of a positive test was 83%. This and other criteria were evaluated for different disease groups and a different stages during the exercise test.

Real-time processing of multiple-lead exercise electrocardiograms.

A system for continuous recording and real-time processing of eight-channel exercise ECGs is presented with emphasis on the algorithms performing the principal signal processing. The hardware and the operational procedures are briefly described. New methods have been developed for the detection, alignment, and selection of complexes to be used in the creation of eight-dimensional average ECG complexes every 10 s. These algorithms are based on digital filter functions approximating low-order Legendre polynomials in order to be robust in the presence of noise.