UCSF

Stroke and cardiovascular disease are major health threats in the United States. Treatment is typically done under X-ray fluoroscopy but MR imaging could provide physiological information and does not have ionizing radiation. An issue with MR is that tools have to be compatible in a magnetic field environment. Hence, the aim is to build an RC with satisfactory tip visualization at various orientations. It will be utilized in a stroke model involving swine where the catheter will be inserted in the femoral artery up to the carotid. There will also be testing the accuracy of the electromagnetic simulation software XFdtd.

A unique material, pyralux (by Dupont), was processed with photolithography to etch the design. The resonators were wrapped around catheters and tuning was done to achieve the proper resonant frequency for 3.0 T and 1.5 T MR scanners. Scans were made with vascular phantoms and mainly MRA (TOF GRE) protocols. Catheters were oriented perpendicular or parallel to the B0 magnetic field. OsiriX and MS excel were used to calculate the SNR of the catheter relative to the background.

Increasing flip angle, starting from 5 degrees and ending at 90 degrees, decreases the SNR and stronger signal is achieved at 1.5T than 3.0T with these parameters. There is not a significant different between SNR with the perpendicular and parallel orientations in the 3.0T. XFdtd successfully demonstrated the relationship between frequency, capacitance, and inductance with a single coil model but not with the double helix. A clot was successfully induced in the femoral artery of a pig and temperature mapping shows insignificant heating hazards.

The goal of the resonator is to visualize the tip, so wider bandwidth would be useful to account for frequency shifts caused by magnetic field disturbances. While choosing the ROI for analysis, selection was based off covering the catheter width and choosing the background such that any artifacts can be accounted for. Although the same TOF GRE sequence in previous successful cases were used, the new sequences tested this year were variable so they were not included in analysis.

From this study, it is shown that the resonator has similar SNR regardless of orientation in the GE 3.0 T scanner. It would be most beneficial to use low flip angles and currently the 1.5 T scanner.