Real-time correction of rigid body motion-induced phase errors for diffusion-weighted steady-state free precession imaging.

Purpose: Diffusion contrast in diffusion-weighted steady-state free precession magnetic resonance imaging (MRI) is generated through the constructive addition of signal from many coherence pathways. Motion-induced phase causes destructive interference which results in loss of signal magnitude and diffusion contrast. In this work, a three-dimensional (3D) navigator-based real-time correction of the rigid body motion-induced phase errors is developed for diffusion-weighted steady-state free precession MRI.

A new design and rationale for 3D orthogonally oversampled k-space trajectories.

A novel center-out 3D trajectory for sampling magnetic resonance data is presented. The trajectory set is based on a single Fermat spiral waveform, which is substantially undersampled in the center of k-space. Multiple trajectories are combined in a "stacked cone" configuration to give very uniform sampling throughout a "hub," which is very efficient in terms of gradient performance and uniform trajectory spacing.

A parallel imaging technique using mutual calibration for split-blade diffusion-weighted PROPELLER.

Split-blade diffusion-weighted periodically rotated overlapping parallel lines with enhanced reconstruction (DW-PROPELLER) was proposed to address the issues associated with diffusion-weighted echo planar imaging such as geometric distortion and difficulty in high-resolution imaging. The major drawbacks with DW-PROPELLER are its high SAR (especially at 3T) and violation of the Carr-Purcell-Meiboom-Gill condition, which leads to a long scan time and narrow blade. Parallel imaging can reduce scan time and increase blade width; however, it is very challenging to apply standard k-space-based techniques such as GeneRalized Autocalibrating Partially Parallel Acquisitions (GRAPPA) to split-blade DW-PROPELLER due to its narrow blade.

Turboprop IDEAL: a motion-resistant fat-water separation technique.

Suppression of the fat signal in MRI is very important for many clinical applications. Multi-point water-fat separation methods, such as IDEAL (Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation), can robustly separate water and fat signal, but inevitably increase scan time, making separated images more easily affected by patient motions. PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) and Turboprop techniques offer an effective approach to correct for motion artifacts.

A computer-assisted protocol for endovascular target interventions using a clinical MRI system for controlling untethered microdevices and future nanorobots.

The possibility of automatically navigating untethered microdevices or future nanorobots to conduct target endovascular interventions has been demonstrated by our group with the computer-controlled displacement of a magnetic sphere along a pre-planned path inside the carotid artery of a living swine. However, although the feasibility of propelling, tracking and performing real-time closed-loop control of an untethered ferromagnetic object inside a living animal model with a relatively close similarity to human anatomical conditions has been validated using a standard clinical Magnetic Resonance Imaging (MRI) system, little information has been published so far concerning the medical and technical protocol used. In fact, such a protocol developed within technological and physiological constraints was a key element in the success of the experiment.

Medical and technical protocol for automatic navigation of a wireless device in the carotid artery of a living swine using a standard clinical MRI system.

A 1.5 mm magnetic sphere was navigated automatically inside the carotid artery of a living swine. The propulsion force, tracking and real-time capabilities of a Magnetic Resonance Imaging (MRI) system were integrated into a closed loop control platform.

Ferromagnetic artifacts in MRI: minimization of motion effects in long TR acquisitions.

A feasibility study is under way for a multiplexed tracking/imaging/propulsion sequence to control a ferromagnetic microdevice in the human vasculature. Ferromagnetic artifact motion can be problematic for the acquired images but we show that when the phase encoding direction is made to match the main direction of motion of the device, the acquisition of planes distant of 3.4 cm of the ferromagnetic bead used show acceptable distortions and signal loss even when the bead incurs significant motion during acquisition.

High-precision absolute positioning of medical instruments in MRI systems.

An absolute positioning technique has been developed for ferromagnetic markers in medical instruments and untethered devices operating in a magnetic resonance imaging (MRI) system. This technique allows high precision 3D readings of the location of the device with respect to the absolute center of the MRI bore. The local magnetic field induced by the device is used as a signature for localization from 3 one-dimensional projections.