CT-SUBTRACTION ANGIOGRAPHY (CTSA) - RESUL TS WITH AN AUTOMATED ELASTIC SUBTRACTION ALGORITHM

Purpose: To develop and implement a method to obtain digital subtracti on (DS) spiral computed tomography angiograms (SCTA) in order to avoid superimposition of bony structures and vascular calcifications on SCT A maximum intensity projections (MIPs) and shaded surface display (SSD ). Method: Two SCTA data sets, one before and one during the injection of a contrast agent bolus, were obtained with identical scan paramete rs. Since ordinary subtraction of the two data sets fairs to reliably separate bones and calcifications from the vascular lumen because of m otion, a so-called elastic subtraction procedure was designed to corre ct 3D misregistration between the two data sets. It automatically acco mmodates for local position changes between baseline and contrast imag es, including regionally inconsistent non-linear displacements and arb itrary rotations. This method was tested in seven patients and evaluat ed against ordinary DS in terms of image quality and artifacts. Result s: In all patients ''elastic'' CTSA proved superior to ordinary DS. It provides automated and reliable separation of vessels from bones and calcifications. This improves the delineation of vessels in the neck a nd the skull base and of intracranial vessels. DS-SCTA facilitates MIP s and SSD without artifacts introduced by thresholding. Conclusion: El astic DS-SCTA is a robust method for automated un-masking of vessels f rom bones and warrants clinical trials and comparison with MR- and con ventional angiography.