Three-dimensional densitometric reconstruction and visualization of stenosed coronary artery segments.

In this paper we report results from an ongoing study about the diagnostic benefits of three-dimensional (3D) visualization and quantification of stenosed coronary artery segments. Biplane angiographic images do not provide enough information for the exact reconstruction of the coronary arteries. Therefore, a priori information about the 3D shape to be reconstructed must be incorporated into the reconstruction algorithm. One approach is to assume a circular cross-section of the coronary artery. Hence, the diameter is estimated from the contours of the vessel in both projections. Another approach is based on densitometry and searches for a solution of the reconstruction problem close to the previously reconstructed adjacent slice. In this paper we apply contour information as well as the densitometrical profiles of the two orthogonal vessel projections. We present a new probabilistic densitometric reconstruction algorithm, which extends the correct handling of the stochastic properties of the density profiles into the network flow based reconstruction algorithm. The reconstructed coronary segment is visualized in three dimensions. In order to assess the accuracy of the reconstruction, the method is applied to tubes with artificial obstruction of known geometry, modeling coronary artery stenoses. These catheter tubes are filled with normal iodine contrast material. The results of the reconstruction and visualization are discussed with respect to clinical usefulness.

Comparative trial of Omnipaque 350 (iohexol) and Telebrix 350 (sodium-meglumine-ioxithalamate) in left ventriculography and coronary arteriography.

In a double-blind randomized trial, the hemodynamic and electrophysiologic effects of the low-osmolar nonionic contrast medium iohexol (Omnipaque) and the standard high-osmolar ionic monomer sodium-meglumine-ioxithalamate (Telebrix) at left ventricular angiography and selective coronary arteriography were evaluated. Sixty patients were divided into two groups of 30 patients; one group received Omnipaque in a dosage of 350 mgI/ml and the other group received Telebrix in a dosage of 350 mgI/ml. The Omnipaque showed significantly less effects on heart rate and myocardial contractility, and induced less electrophysiological changes than did Telebrix. However, there was a significant increase of 10% in the diameter of the left coronary artery following selective coronary injection with Telebrix, while Omnipaque induced practically no change in vessel diameter. All hemodynamic and electrophysiologic effects proved to be short-lasting. We conclude that ionic and nonionic agents are similarly efficacious in providing adequate images with minimal risk to the patient. However, the nonionic agents exert slightly more alterations in cardiac hemodynamics and in electrocardiographic intervals. The vasodilatory effect on coronary artery diameter by Telebrix may entail a more rapid clearance of contrast medium from the coronary circulation, which might be of some advantage over nonionic contrast media.

Arteriographic evaluation of small coronary arteries.

The purpose of this study was to determine the accuracy of imaging small coronary arteries with current radiographic equipment. Phantom assessments were performed using a phantom that comprises a large array of circular objects of varying diameter and contrast density. More objects could be identified in the moving cinearteriogram than in single cine frames. Using the largest object as the calibration standard, diameters less than 1 mm were markedly overestimated. A simple morphometric method showed that arteriographic visualization of small vessels was better by digital processing than by cine recording. However, there was no statistically significant difference in the average size of the smallest identifiable vessel by either method (0.5 versus 0.51 mm). After correcting for overestimation and the inaccurate imaging of the smallest detectable vessels, the practical arteriographic threshold is approximately 0.5 mm. Parametric imaging holds promise, but its significance for evaluating small vessel disease has yet to be determined.

Pulsatile coronary flow determination by digital angiography.

A new angiographic method to calculate absolute coronary arterial blood flow and its cyclic variations as a function of time, has been designed and evaluated. The method combines densitometric analysis of spatial and temporal aspects concerning the contrast propagation through the arterial system from digital images, and is based on applying the concept of conservation of contrast material in successive images. It requires a standard arteriographic procedure. In simulations with both constant as well as pulsatile flow through a coronary arterial phantom, an excellent agreement with electromagnetic flow measurements was demonstrated (r = 0.993 and r = 0.982, respectively). Preliminary clinical results show, that the method yields reproducible assessment of coronary flow patterns after repeated injections in a patient. In a coronary artery bypass graft, coronary flow patterns in a baseline and a drug-induced hyperemic state were obtained. A consistent coronary flow reserve value was determined after repeated examinations. The method has been shown to be feasible in clinical applications, uncomplicated and fast, but requires further animal and clinical validation in order to determine the possible applications, limitations and accuracy.