Percutaneous MR-guided interventions using an optical Moiré Phase tracking system: Initial results

Abstract

The aim of this study was the development and evaluation of a real-time guidance support using optical Moiré Phase Tracking (MPT) for magnetic resonance (MR) guided percutaneous interventions. A gradient echo sequence, capable of real-time position updates by the MPT system, was modified to enable needle guidance based on four rigidly attached MPT markers at the back of a needle. Two perpendicular imaging planes were automatically aligned along the calibrated needle and centered at its tip. For user guidance, additional information about the needle trajectory and the tip to target distance were added as image overlay. Both, images and guiding information were displayed on the in-room monitor to facilitate MR guided interventions. The guidance support was evaluated by four experienced interventional radiologists and four novices targeting rubber O-rings embedded in a custom-made phantom on a 3T wide-bore MRI system (80 punctures). The skin to target time, user error, system error and total error were analyzed. The mean skin to target time was 146s±68s with no statistically significant difference between experts and novices. A low mean user error (0.91mm±0.43mm), system error (0.53mm±0.27mm) and total error (0.99mm±0.47mm) was reached in all directions. No statistically significant difference in user error, system error and total error could be found between experts and novices. The presented tracking and image guidance system combined with the user interface offers continuous and interactive control of the imaging plane while puncturing in the magnet enabling accurate real-time feedback for both, experienced and non-experienced users.

Modeling of active shimming of metallic needles for interventional MRI

“…Demand in CN0 changes from −0.716 A to −0.723 A in the 0, 0, 0 orientation and CN90 demand remains unchanged. For real time tracking and adaptive shimming, a setup using optical or inductively coupled fiducials attached to base of the needle could be used to provide fast updates of device position and adaptive current updates 57,58 …”

“…For real time tracking and adaptive shimming, a setup using optical or inductively coupled fiducials attached to base of the needle could be used to provide fast updates of device position and adaptive current updates. 57,58 This work does not address potential effects such as radiofrequency (RF)/gradient induced eddy current related B 1 effects 59 and shielding of the shim field. In practice, all shim coils will incorporate broadband chokes to suppress RF and gradient induced currents.…”

Integration and evaluation of a gradient-based needle navigation system for percutaneous MR-guided interventions

“…This is especially problematic when targeting lesions in soft, mobile organs such as the liver that suffer from both respiratory motion and tissue deformation. Nevertheless, comparing the mean total error in all directions to other publications (mean error of 0.99mm±0.47mm to 3.9mm ±2.4mm) the presented gradient based technique shows a slightly lower accuracy [11,13,15,32,33]. This is compensated for because the integrated system uses MRI gradients rather than…”

Minimal artifact actively shimmed metallic needles in MRI

“…[47][48][49] For real time tracking of needle orientation and adaptive needle shimming, optical, or RF based needle tracking techniques can be integrated. 50,51 One design challenge in this technique is the space inside a needle and whether shim conductors might be incorporated with minimal compromise on the core function of the device. For probes with working central channels, shim inserts with flexible printed coils mounted on thin wall hollow tubes F I G U R E 3 Results of active shimming in 1 × 1 × 2 mm 3 balanced SSFP, 1 × 1 × 1 mm 3 FSE, and 2 × 2 × 2 mm 3 3 shot EPI images.…”