Adaptive subtraction as an aid in MR-guided placement of catheters and guidewires

Purpose: To demonstrate the utility of mask subtraction optimization in magnetic resonance (MR)-guided placement of catheters and guidewires.

Materials and methods: MR-guided positioning of magnetically prepared catheters and guidewires was done by dynamically imaging a single thick slab at two frames per second. Selective visualization of the prepared parts of the devices was achieved by the use of a conventional baseline subtraction technique and by the use of an adaptive subtraction technique. In the latter, the best reference image is automatically selected from a fixed or a sliding subset of hitherto acquired dynamic images. The efficacy of both approaches was compared by tracking experiments in a flow phantom and in the aortoiliac arteries of a pig.

Results: Baseline subtraction produced adequate visualization of paramagnetic markers in the absence of subject motion and for fixed scan conditions. The sensitivity to subject motion and interactive modification of the scan parameters was greatly reduced by using adaptive subtraction. Adaptive subtraction images, other than conventional subtraction images, appeared to be insensitive to slow periodic motion, e.g., respiratory motion, and were only transiently affected by gross subject motion and interactive alterations of the scan parameters.

Conclusion: Adaptive subtraction is superior to baseline subtraction for guiding the manipulation of catheters and guidewires in the presence of gross and periodic subject motion and whenever scan parameters are modified in the course of a procedure.