Automated Correlation of Intravascular Ultrasound Images with Angiography

Abstract

One limitation of intravascular ultrasound (IVUS) is the restriction to viewing one cross‐sectional image at a time. Computerized three‐dimensional reconstructions of IVUS images have been developed in an attempt to overcome this limitation. These algorithms, however, are limited by artifacts from catheter movements and rotation within large vessels. Consequently, this technique has been applied only to straight segments of small caliber vessels. Contrast angiography has long been the standard for vascular imaging. In order to take advantage of both contrast angiography and IVUS, we developed a computer procedure to automatically correlate IVUS images with their corresponding locations on contrast angiograms, and to display both images in a side by side format. Models of the aortic arch and aorto‐ileo‐femoral system were constructed with artificial plaques located at various sites. The models were filled with iodinated contrast media and radiographic images were obtained. Timed pull‐backs were performed in both models in order to obtain sets of serial cross‐sectional images. For each data set, a digitized set of 75 serial IVUS images and model angiographic images were loaded in the computer procedure. We then correlated at least one IVUS image containing a known landmark with its position on the model angiogram. The procedure then automatically displayed sequential ultrasound images along with their corresponding positions on the reference angiogram. We analyzed the error of this algorithm as a function of the number of correlation points used. The maximum error was 4 mm over a total pullback distance of 130 mm (relative error of 3%). This algorithm was subsequently used to correlate IVUS images obtained from the aortic arch of a patient with their corresponding positions on an aortogram. Our results demonstrate that computer‐based correlation of IVUS images with their corresponding positions on angiograms is accurate, may enhance the use of IVUS to assess vascular pathology, and provides an alternative to three‐dimensional reconstructions.