This article reviews the fundamental techniques to quantify the physiological severity of (coronary) stenoses. Although a wide survey of different techniques and applications is provided, the focus of this review is on: 1) the assessment of the immediate effect of the stenoses on blood flow (i.e., the hemodynamic severity), and not on the assessment of the pathology of the vessel itself; 2) the flow reserve methods to defining the physiological severity of stenoses; and 3) the determination of blood flow and tissue perfusion by X-ray angiography (a short survey of other imaging modalities is provided as well). Although the practical implementation of the techniques is illustrated by applying them to coronary stenoses, most of the issues involved are of interest in other application areas (using other imaging modalities) as well. This review consists of four parts. The first part deals with the definition of stenoses severity; the second part with tracer kinetic theory necessary to determine flows by imaging; the third part focusses on (cardiac) imaging modalities, with an emphasis on X-ray angiography; and the last part illustrates the practical implementation of the techniques in cardiology.
The long term goal of this research is to determine the clinical relevance of stenosis. Where most QCA algorithms calculate the decrease in lumen from one angiocardiogram, we seek to determine directly the influence of the stenosis on the blood flow. The method uses only a slightly different clinical approach as compared to 'traditional' noninterventional catheterizations. Instead of injecting a steady flow of contrast agent, we propose to inject a string of small droplets. The resulting string of droplets will enable us to estimate the relative blood flow by measuring their time of arrival in some designated regions. Repeating the same procedure after administering a vasodilative drug, we obtain a relative decrease (or less increase) in blood flow in one of the two distal branches of the bifurcation due to the presence of stenosis. From the resulting X-ray image sequence multiple frames are selected, and the information is combined to find the relative blood velocity. The conclusion is that it is possible to use sequences of images instead of just one image to calculate quantitative results. Major problems to overcome are the respiratoryand heart-motions, and differences in acquisition parameters between runs. The usefulness of the new method in real clinical applications and the coherence with other measures are currently under trial.
In clinical cardiology, stenosis in a coronary artery is measured on the basis of visual assessment. The reading of coronary arteriograms leads, however, to large inter- and intra-observer variability. Image analysis and computer assistance result in a more consistent assessment, but this approach is mainly based upon static geometric parameters, such as diameter reduction of a segment of the stenosed artery. A more functional, physiological measurement is thus desirable. This can be realised by measuring the difference between the normal coronary blood flow and the increased flow under hyperaemic conditions, yielding the so-called coronary flow reserve (CFR). In clinical practice, however, this method is difficult and time-consuming. A less demanding approach is reported, in which relative flow distributions are determined densitometrically from digital angiograms acquired under basal and hyperaemic conditions. The proposition is that, if the relative flow distribution in hyperaemic state differs from that during rest, the functional severity of a stenosis downstream from the bifurcation can be indicated. The new approach is validated by comparing the results of a theoretical model for steady flow with a flow phantom experiment for steady and pulsatile flow. The obtained flow ratios correlate very well, both in steady and pulsatile flow, with correlation coefficients exceeding 0.95.
Adaptive filtering of temporally varying X-ray image sequences acquired during endovascular interventions can improve the visual tracking of catheters by radiologists. Existing techniques blur the important parts of image sequences, such as catheter tips, anatomical structures and organs; and they may introduce trailing artifacts. To address this concern, an adaptive filtering process is presented to apply temporal filtering in regions without motion and spatial filtering in regions with motion. The adaptive filtering process is a multi-step procedure. First a normalized motion mask that describes the differences between two successive frames is generated. Secondly each frame is spatially filtered using the specific motion mask to specify different types of filtering in each region. Third an IIR filter is then used to combine the spatially filtered image with the previous output image; the motion mask thus serves as a weighted input mask to determine how much spatial and temporal filtering should be applied. This method results in improving both the stationary and moving fields. The visibility of static anatomical structures and organs increases, while the motion of the catheter tip and motion of anatomical structures and organs remain unblurred and visible during interventional procedures.
Two cases of endobronchial localised non-Hodgkin lymphoma are presented. Pathogenesis, clinical history, diagnosis and treatment of this unusual localisation of non-Hodgkin lymphoma are reviewed
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