Compatibility of interventional x-ray and magnetic resonance imaging: feasibility of a closed bore XMR (CBXMR) system.

A next-generation interventional guidance system is proposed that will enable intraprocedural access to both x-ray and magnetic resonance imaging (MRI) modalities. This closed bore XMR (CBXMR) system is comprised of a conventional radiographic rotating anode x-ray tube and a direct conversion flat panel detector on a rotating gantry positioned adjacent to the bore of a 1.5 T MRI. To assess the feasibility of such a system, we have investigated the degree of compatibility between the x-ray components and the MRI. For /-->B(ext)/ < 200 G the effect on the radiographic tube motor was negligible regardless of the orientation of -->B(ext) with respect to the motor axis of rotation--the frequency of anode rotation remained within 6% of the 3400 rpm frequency measured at 0 G. For /-->B(ext)/ >2400 G the anode slowed down to below 2400 rpm at all orientations. At intermediate B(ext), the frequency of rotation varied between 2400 and 3200 rpm, showing a strong dependence on orientation, with -->B(ext) perpendicular to the tube axis having a much stronger effect on the rotation frequency than -->B(ext) parallel to the tube axis. In contrast to the effect of -->B(ext) on the induction motor, parallel -->B(ext) had a stronger detrimental effect on the cathode-anode electron beam, whose path was at 16 degrees to the tube axis, than the perpendicular -->B(ext). Parallel -->B(ext) of several hundred Gauss had a defocusing effect on the x-ray focal spot. -->B(ext) perpendicular to the electron beam shifted the beam without significant defocusing. We have determined that the direct conversion flat panel detector (FPD) technology is not intrinsically sensitive to -->B(ext), and that the modifications required to make the proposed FPDs MRI compatible are minimal. The homogeneity of the MRI signal in the normal field of view was not significantly degraded by the presence of these x-ray components in the vicinity of the MRI bore entrance.