INTRAVASCULAR ULTRASOUND IMAGE SUBTRACTION - A CONTRAST ENHANCING TECHNIQUE TO FACILITATE AUTOMATIC 3-DIMENSIONAL VISUALIZATION OF THE ARTERIAL LUMEN

At 30 MHz, the intravascular ultrasound backscatter of blood confounds the discrimination of the lumen from the arterial wall, This study va lidates a subtraction method which creates a still-frame image with a sharp demarcation of the lumen, The method involves subtraction of con secutive images and 2D ensemble averaging of the absolute pixel values , Subtraction exploits the dynamic properties of flowing red blood cel ls, Three phantom arteries were used, with erythrocytes in their lumen s and wall, For this reason, it was not possible, in one single origin al image, to discriminate the blood in the lumen from the phantom wall , Based on 26 consecutive original images, in the mean subtraction ima ge contrast between lumen and phantom wall grey values increased eight fold from 10.9 (5.3-19.2) (mean and range) in the original image to 87 .7 (73.6-107.0) (P < 0.001). A sufficiently large contrast increase to allow automatic segmentation was obtained by using five original imag es (0.3-s acquisition time) for any single mean subtraction image, Low blood flow velocities (down to 0.5 cm/s) did not alter this result, A utomatic segmentation of the lumen allowed fast 3D reconstruction of t he lumen in all three phantom arteries, In phantom arteries, the intra vascular ultrasound image subtraction technique improved contrast betw een lumen and wall which enabled automated lumen segmentation and fast 3D visualization of both the lumen and defects in the wall.