Digital subtraction angiography following an injection of iodinated contrast material can regularly produce good quality images. In addition to the conventional anatomical information, the timed sequence of digital images also contains useful temporal information which hitherto has been largely ignored. A simple method of image processing is described which utilises this timing information and presents it as a colour-coded set of functional images. Three parameters MAX, T-MAX and T-1/2 MAX are extracted from time-density curves, analogous to the time-activity curves of Nuclear Medicine, on a pixel-by-pixel basis. These parameters are used as a measure of overall organ perfusion, blood transit time between different vascular compartments, and as an indication of the initial delivery of contrast material to an organ. They have found use in the analysis of myocardial perfusion, before and after pharmacological intervention, and in the examination of the cerebral and renal circulations. The potential advantages of this technique derive from its superior spatial, temporal and contrast resolution.
Application of electrocardiogram gated digital subtraction angiography to the assessment of coronary artery bypass graft function was studied one week to eight years after bypass operation in ten unselected patients with recurrent chest pain. For the digital method, contrast was injected into the ascending aorta via a 4 or 5 French gauge catheter. The results of this technique were compared with those of selective graft and coronary angiography in the same patients by two independent observers. Of twenty six grafts in the series, patency was confirmed in twenty one by both selective and digital angiography. The quality of graft run off, graded by each observer using a simple scoring system, demonstrated six points of inter observer disagreement when standard cineangiograms were used, compared with nine points of disagreement when digital images were used. Digital subtraction angiography provided useful graft visualisation, but was less good than conventional angiography at defining the native coronary circulation. The role of this promising new technique has yet to be established.
The effects of nifedipine on myocardial perfusion abnormalities were investigated in 6 patients with left coronary artery disease using a digital angiographic method. Selective left coronary angiograms were digitized on-line into a 256 x 256 pixel matrix, approximately 20 ECG-gated end-diastolic frames being acquired during each coronary injection. After background subtraction, parametric analysis was undertaken, measuring sequential changes in contrast opacification against time. Isochrone maps were derived showing the distribution of times to attainment of peak contrast density throughout the left ventricle (the Tmax image) reflecting myocardial perfusion, and of times to arrival of half peak opacification (the T1/2max image) as an index of coronary flow. At basal heart rate (fixed by pacing) mean Tmax was attained in well supplied myocardium at the 7th cardiac cycle, and at the 9th cardiac cycle in the least perfused territory. Overdrive pacing reduced arrival times by 2-3 cycles, but inhomogeneity persisted. After sublingual nifedipine, contrast arrival was significantly accelerated by a mean of two cardiac cycles in poorly perfused regions, and by one cardiac cycle elsewhere. After nifedipine, overdrive pacing shortened Tmax and T1/2max most markedly in the least supplied territory. Results with this new technique indicate that nifedipine has beneficial effects on regional malperfusion in coronary disease.
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