Background

The clinical translation of MRI-guided cardiovascular catheterization has been limited by the unavailability of devices that are both visible and safe under MRI. In par-ticular, rigid metallic guidewires are essential for most catheterization procedures and are at risk of heating during MR imaging [1]. Here we present an MRI method that simultaneously improves the visualization of commercially available nitinol guidewires and mini-mizes RF induced heating. Methods RF-efficient gradient echo spiral imaging was chosen to minimize heating (8 interleaves, TE/TR = 0.86/10ms, flip angle = 10°). Through-slice dephasing generated a positive contrast “device image ” [2], exploiting local field inhomo-geneity such that the metallic guidewire appears hyperin-tense with background signal suppressed. An anatomical image and a device image were interleaved in alternating frames. Image processing (signal thresholding and selec-tion of elongated structures) was performed on the device image to isolate the guidewire signal from other sources of field inhomogeneity. Imaging was performed on a 1.5T MRI scanner (Aera, Siemens, Erlangen, Germany). MRI-guided left heart catheterization was performed in a pig using a 0.035 ” com-mercially available nitinol guidewire (Nitrex, Covidien, Ply-mouth, MN). The RF induced temperature rise at the tip of an insulated nitinol rod during MR imaging was mea-sured in the ASTM 2182 gel phantom using a fiberoptic temperature probe (OpSense, Quebec, Canada). Results A pair of anatomical and device images were generated with a temporal resolution of 160ms (80ms per image), or 6.25 frames/s. Image processing occurred in real-time and a color overlay of the device on the anatomy was dis-played to the operator for guidance during catheterizatio