Remotely-Controlled Approach for Stereotactic Neurobiopsy

Characterization and reduction of saturation banding in multiplanar coherent and incoherent steady-state imaging

Hypointense band artifacts occur at intersections of nonparallel imaging planes in rapidly acquired MR images; quantitative or numerical analysis of these bands and strategies to mitigate their appearance have largely gone unexplored. The magnetization evolution in the different regions of multiplanar images was simulated for three common rapid steady-state techniques (spoiled gradient echo, steady state free precession, balanced steady state free precession). Saturation banding was found to be highly dependent on the pulse sequence, acquisition time, and phase-encoding order. Encoding the center of k-space at the end of the acquisition of each slice (i.e., reverse centric phase encoding) is demonstrated to be a simple and robust method for significantly reducing the relative saturation in all imaging planes. View ordering and resolution dependence were confirmed in multiplanar abdominal images. The added importance of reducing the artifact in accelerated acquisition techniques (e.g., parallel imaging) is particularly notable in multiplanar balanced steady state free precession images in the brain.

Minimally invasive precision brain access using prospective stereotaxy and a trajectory guide

PURPOSE

To evaluate the capabilities of MR-guided "prospective stereotaxy" methods for accessing brain structures for biopsy or electrode implantation.

MATERIALS AND METHODS

MR-guided biopsy and deep brain stimulator (DBS) electrode implantations were performed with a trajectory guide and real-time MR guidance. Imaging methods were used to plan the selected path through the brain, appropriately orient the trajectory guide, and monitor the device insertion to assure technical success and screen for hemorrhage. Assessments of technical success rate, targeting accuracy, and complications associated with this technique were performed.

RESULTS

A total of 187 biopsy procedures were performed with guidance via prospective stereotaxy methods. All brain biopsies were diagnostic and two patients sustained superficial wound infections that were treated successfully with antibiotics. One patient died postoperatively of a myocardial infarction despite preoperative medical clearance. A total of 42 DBS electrode insertions were performed in patients with Parkinson's disease or dystonia. The difference between planned and actual electrode position averaged 1.2 mm +/- 0.7 mm on the first pass and only a single brain penetration was required in 90% of electrode insertions. Complications included a single asymptomatic hemorrhage and two early infections, with the latter addressed by an adjustment to sterile practice.

CONCLUSION

Prospective stereotaxy, in combination with a trajectory guide, has been proven capable of efficiently and accurately targeting structures throughout the brain.

1.5 T: spectroscopy-supported brain biopsy

The technique for performing brain biopsy has evolved significantly over the last three decades. Intraoperative MRI guidance has enhanced the diagnostic rate for brain biopsy by now allowing neurosurgeons to compensate for brain shift while performing the procedure in near-real time. The development of a trajectory guide enables the neurosurgeon to determine a safe and accurate path for intraoperative MRI-guided brain biopsy and to secure the position of the needle within the target tissue. Magnetic resonance spectroscopy (MRS) has been used to help distinguish recurrent brain tumor from the effect of previous treatments by measuring specific metabolites within the area of concern. Combining the use of a trajectory guide with MRS should enhance the diagnostic yield for MRI-guided brain biopsy.