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Automated interpretation of complex images requires elaborate knowledge and model-based image analysis, but often needs interaction with an expert as well. This research describes expert interaction with a multiagent image interpretation system using only a restricted vocabulary of high-level user interactions. The aim is to minimize inter- and intra-observer variability by keeping the total number of interactions as low and simple as possible. The multiagent image interpretation system has elaborate high-level knowledge-based control over low-level image segmentation algorithms. Agents use contextual knowledge to keep the number of interactions low but, when in doubt, present the user with the most likely interpretation of the situation. The user, in turn, can correct, supplement, and/or confirm the results of image-processing agents. This is done at a very high level of abstraction such that no knowledge of the underlying segmentation methods, parameters or agent functioning is needed. High-level interaction thereby replaces more traditional contour correction methods like inserting points and/or (re)drawing contours. This makes it easier for the user to obtain good results, while inter- and intra-observer variability are kept minimal, since the image segmentation itself remains under control of image-processing agents. The system has been applied to intravascular ultrasound (IVUS) images. Experiments show that with an average of 2-3 high-level user interactions per correction, segmentation results substantially improve while the variation is greatly reduced. The achieved level of accuracy and repeatability is equivalent to that of manual drawing by an expert. Index Terms--Cooperative systems, image segmentation, knowledge based systems.

The behavior of the center of gravity estimate, as a function of additive noise present in gray value images, is examined and reported.

This paper describes a multimodality framework for computer-aided myocardial viability assessment based on neuro-fuzzy techniques. The proposed approach distinguishes two main levels: the modality-independent inference level and the modality-dependent application level. This two-level distinction releases the hard constraint of multimodality image registration. An abstract description template is used to describe the different myocardial functions (contractile function, perfusion, metabolism). Parameters extracted from different image modalities are combined to derive a diagnostic image. The neuro-fuzzy techniques make our system transparent, adaptive and easily extendable. Its effectiveness and robustness are demonstrated in a positronn emission tomography/magnetic resonance imaging data fusion application. Index Terms--Computer-aided diagnosis, data fusion, myocardial viability, neuro-fuzzy systems.

Many segmentation methods for thoracic volume data require manual input in the form of a seed point, initial contour, volume of interest etc. The aim of the work presented here is to further automate this segmentation initialization step. In this paper an anatomical modeling and matching method is proposed to coarsely segment thoracic volume data into anatomically labeled regions. An anatomical model of the thorax is constructed in two steps: 1) individual organs are modeled with blended fuzzy implicit surfaces and 2) the single organ models are grouped into a tree structure with a solid modeling technique named constructive solid geometry (CSG). The combination of CSG with fuzzy implicit surfaces allows a hierarchical scene description by means of a boundary model, which characterizes the scene volume as a boundary potential function. From this boundary potential, an energy function is defined which is minimal when the model is registered to the tissue-air transitions in thoracic magnetic resonance imaging (MRI) data. This allows automatic registration in three steps: feature detection, initial positioning and energy minimization. The model matching has been validated in phantom simulations and on 15 clinical thoracic volume scans from different subjects. In 13 of these sets the matching method accurately partitioned the image volumes into a set of volumes of interest for the heart, lungs, cardiac ventricles, and thorax outlines. The method is applicable to segmentation of various types of thoracic MR-images, provided that a large part of the thorax is contained in the image volume. Index Terms - Anatomical model matching, cardiac MRI, inexact shape modeling, model driven segmentation.

Abnormalities of peripheral arterial compliance are clinically useful markers of atherosclerosis and risk of vascular events. Local peripheral arterial compliance can be easily and accurately assessed in the clinic by computer-controlled pulse volume recordings (air plethysmography). The purpose of this study was to investigate the relationship between clinical cardiovascular risk factors, a surrogate of atherosclerotic burden, and peripheral arterial compliance in the thigh and calf determined by quantification of local pulse volume recordings in patients undergoing coronary angiography. Peripheral arterial compliance in the thigh and calf was measured in 346 patients undergoing diagnostic cardiac catheterization at 4 centers. Demographic and cardiovascular risk factor data were collected, and their relationship to local arterial compliance examined using a new device that assesses maximal local arterial volume change in an extremity segment. Pulse volume recordings detected decreased local arterial compliance in the thigh associated with a history of hypertension (p < 0.0001), diabetes mellitus (p = 0.0001), and hyperlipidemia (p = 0.0007). In the calf, this arterial compliance measure was associated with a history of hypertension (p < 0.0001 ) and diabetes mellitus (p = 0.002). Females had lower arterial compliance than males in the thigh (p = 0.003) and calf (p < 0.0001). Limited evidence of lower arterial compliance in the thigh was found for those with obesity (p=0.07). This procedure also demonstrated that subjects with multiple cardiovascular risk factors had lower arterial compliance in the thigh than subjects with no or I risk factor (p = 0.0001). Peripheral arterial compliance determined by air plethysmography is strongly associated with standard cardiovascular risk factors. The noninvasive measurement of local arterial compliance by regional pulse volume recording may be a useful adjunct for cardiovascular risk stratification early in the course of... [ABSTRACT FROM AUTHOR]

A widely used subpixel precision estimate of an object center is the weighted center of gravity (COG). We derive three maximum-likelihood estimators for the variance of the two-dimensional (2-D) COG as a function of the noise in the image. We assume that the noise is additive, Gaussian distributed and independent between neighboring pixels. Repeated experiments using 2500 generated 2-D bell-shaped markers superimposed with an increasing amount of Gaussian noise were performed, to compare the three approximations. The error of the most exact approximative variance estimate with respect to true variance was always less than 5% of the latter. This deviation decreases with increasing signal-to-noise ratio. Our second approximation to the variance estimate performed better than the third approximation, which was originally presented by Oron et al. [1] by up to a factor ≈10. The difference in performance between these two approximations increased with an increasing misplacement of the window in which the COG was calculated with respect to the real COG. [ABSTRACT FROM AUTHOR]

Objectives This report describes whether lossy Joint Photographic Experts Group (JPEG) image compression/decompression has an effect on the quantitative assessment of vessel sizes by state-of-the-art quantitative coronary arteriography (QCA).Background The Digital Imaging and Communications in Medicine (DICOM) digital exchange standard for angiocardiography prescribes that images must be stored loss free, thereby limiting JPEG compression to a maximum ratio of 2:1. For practical purposes it would be desirable to increase the compression ratio (CR), which would lead to lossy image compression.Methods A series of 48 obstructed coronary segments were compressed/decompressed at CR 1:1 (uncompressed), 6:1, 10:1 and 16:1 and analyzed blindly and in random order using the QCA-CMS analytical software. Similar catheter and vessel start- and end-points were used within each image quartet, respectively. All measurements were repeated after several weeks using newly selected start- and end-points. Three different sub-analyses were carried out: the intra-observer, fixed inter-compression and variable inter-compression analyses, with increasing potential error sources, respectively.Results The intra-observer analysis showed significant systematic and random errors in the calibration factor at JPEG CR 10:1. The fixed inter-compression analysis demonstrated systematic errors in the calibration factor and recalculated vessel parameter results at CR 16:1 and for the random errors at CR 10:1 and 16:1. The variable inter-compression analysis presented systematic and random errors in the calibration factor and recalculated parameter results at CR 10:1 and 16:1. Any negative effect at CR 6:1 was found only for the calibration factor of the variable inter-compression analysis, which did not show up in the final vessel measurements.Conclusions Compression ratios of 10:1 and 16:1 affected the QCA results negatively and therefore should not be used in clinical research studies. [ABSTRACT FROM PUBLISHER]

In order to assess the changes in the number and severity of transient and persistent myocardial perfusion defects before and after coronary artery bypass grafting (CABG), early and late post-exercise thallium-201 (tl-201) tomography was performed in 25 patients, on average 10 days before and 2.5 months after CABG. Six patients had a previous Q wave myocardial infarction. Comparing the pre- and post-CABG exercise test data (symptom limited bicycle ergometry) showed an improvement in working capacity (from 129±34 to 145 ±35 W, P<0.05) and a reduction in exercise induced angina from 77 to 9% of the patients(P<0.001). From the tomographic data, six short axis and three sagittal cross-sections of the left ventricular myocardium were reconstructed. In each patient study, a total of 51 myocardial segments were defined and analysed in a semi-quantitative manner by means of a five point scoring method indicative of the severity of a defect (from 0 = normal tl-201 uptake to 4 = absence of tl-201 activity). In this patient population the total number of segements with transient tl-201 perfusion defects decreased from 11.0±7 segments per patient (mean±SD; before surgery to 4.9±4 after surgery (p<0.01); the number of segments with ‘persistent’ tl-201 defects decreased as well from 7.5±6 to 3.9±4 segments per patient (P<0.03). On average, the severity score of transient perfusion defects decreased from 17.7±12 to 7.1±6 per patient (mean±SD.P<0.01) and that of ‘ persistent ’ defects from 17.4±15 to 8.4 ± 9 (p<0.03). From these data it may be concluded, that the apparent reversibility of certain tl-201 defects are compatible not only with scar tissue, but also with a reversibly ischaemic myocardium. [ABSTRACT FROM PUBLISHER]

In this paper we report the sequelae of a patient with an anomalous right coronary artery (RCA)originating from the pulmonary artery (PA) in association with a normal heart, operated upon at the age of 13 years. Three years after the end-to-side reimplantation of the RCA, with a rim of thePA, into the aorta, the surgical result has been evaluated by cineangiography. Before operation both coronary arteries were tortuous and increased in size. Afterwards the left coronary artery showed a normalized calibre, although the RCA remained tortuous with no decrease of the internal diameter. The notable postoperative changes in shape and size of the LCA may be due to the disappearanceof the steal phenomenon. The lack of involutive changes in the RCA could be explained by its thinner wall. Left ventricular wall motion, evaluated under resting conditions and during an atrial pacing stress test, was found to be normal. [ABSTRACT FROM PUBLISHER]

In this study it is argued that the clinical manifestations of unstable angina pectoris, with at its extreme end impending myocardial infarction, may be due to increased coronary arterial vasomotion superimposed on a pre-existing obstruction in a coronary artery.As nifedipine, a powerful calcium antagonist, has initially proven its efficacy in relieving the symptoms of Prinzmetal's angina, a condition in which severe spasm of the coronary artery is now proven to be the main cause, the drug was given to two groups of patients in whom abnormal vasomotion was suspected and its effects scrutinized.Twelve patients with symptoms of coronary artery disease (CAD) were studied with repeated arteriograms after injection of 0.15 mg nifedipine in the left coronary artery. Two control cine-angiograms were made prior to drug administration and two cinefilms were repeated 30 s and 5 min after administration of nifedipine. The mean diameter of the normal, stenotic and poststenotic segments showed a statistically significant increase after drug administration. Vasodilalion persisted after coronary O2 saturation, and presumably coronary flow, had returned to normal.In 52 other patients, who were seen in the coronary care unit for impending myocardial infarction and who had been treated with maximal beta-adrenergic blockade, nitrates and bedrest, but who remained symptomatic, nifedipine 60 mg orally for 24 h was added to the treatment. Within 2 h after administration 42 of the 52 became asymptomatic. In the 10 non-responders, all with extensive multi-vessel disease, two sustained a myocardial infarction and eight received urgent coronary artery bypass grafting in an effort to alleviate their symptoms. All had severe 3 vessel disease in contrast to the responders in whom 1 or 2 vessel disease was predominant.These data show that increased coronary artery vasomotion can be influenced by nifedipine. The excellent clinical response to the drug in this group of patients with unstable angina pectoris indicates that nifedipine may become the preferred agent to be used particularly when the cause of the angina pectoris is suspected to be the result of abnormal coronary vasomotor tone. [ABSTRACT FROM PUBLISHER]