Michael Wendt

MRI of the thorax during whole-body MRI: evaluation of different MR sequences and comparison to thoracic multidetector computed tomography (MDCT).

To evaluate the accuracy of four MR sequences used as part of a whole‐body MRI protocol to detect pulmonary lesions in cancer patients.

Intraoperative MRI with a rotating, tiltable surgical table: A time-use study and clinical results in 122 patients

OBJECTIVE The objective of our study was to evaluate intraoperative low-field MRI for the frequency and duration of imaging sessions needed during surgery, the direct additional procedure time attributable to imaging, and the proportion of cases in which information provided by intraoperative MRI led to a change in the procedure or otherwise was deemed valuable by operating surgeons. MATERIALS AND METHODS One hundred twenty-two patients (65 males, 57 females; age range, 6-77 years; mean age, 43.8 years) underwent 130 neurosurgical and ENT procedures (106 craniotomies, 17 transsphenoidal pituitary resections, three biopsies, three intracranial cyst aspirations or injections, and one skull base resection) in a specially designed surgical MRI suite equipped with a 0.2-T imager and a prototype rotating, tiltable surgical table. The intraoperative MR sequences included free induction with steady-state precession (fast imaging with steady-state precession [FISP]), steady-state free precession T2-weighted, reverse fast imaging with steady-state free precession (PSIF), FLASH, spin-echo T1-weighted, turbo spin-echo (TSE) T2-weighted, and TSE FLAIR. Each case was analyzed for the number of imaging sessions, duration of each session, total imaging time during surgery, and impact of imaging information on procedure. RESULTS Each patient underwent between one and five intraor postoperative imaging sessions. Imaging times were 1.7 seconds-8 minutes 31 seconds per sequence. The mean total imaging time was 35 minutes 17 seconds per surgical procedure. Imaging was continuous during biopsy and cyst aspiration procedures and averaged 200.67 and 54.66 minutes, respectively. Additional surgical resection based on intraoperative imaging findings was performed in 72.8% of the cases. CONCLUSION Intraoperative low-field MRI provides valuable information for surgical decision making that is predominantly related to detection of residual tumor and the exclusion of complications. The benefits of this technology surpass the time cost associated with its implementation when using proper imaging strategies.

An Augmented Reality system for MRI-guided needle biopsies.

A navigation system can increase the speed and accuracy of MR guided interventions that make use of scanners with high-field closed magnets. We report on first needle placement experiments performed with an Augmented Reality (AR) navigation system. AR visualization provides very intuitive guidance, resulting in a faster procedure. The accuracy of the needle placement depends on the registration accuracy of the system. In the present trials, the needle was placed as good as 1mm close to the target center, however in a small number of cases substantially larger errors occurred and were most likely caused by needle bending.

Use of a blood-pool contrast agent for MR-guided vascular procedures: feasibility of ultrasmall superparamagnetic iron oxide particles.

RATIONALE AND OBJECTIVES The purpose of this study was to examine the dose dependency of the intravascular signal intensity after injection of ultrasmall superparamagnetic iron oxide (USPIO) particles (SH U 555 C) in a rabbit model studied with a low-field-strength magnetic resonance (MR) imaging system. The results were used to facilitate MR-guided vascular procedures in a pig. MATERIALS AND METHODS All experiments were performed at 0.2 T. To determine the optimum USPIO (or SH U 555 C) dose for intravascular interventions, the authors acquired coronal three-dimensional MR angiographic images in 12 rabbits after injection of four dose levels (10, 20, 30, and 40 micromol of iron per kilogram body weight). The intraaortic signal intensities were measured in user-defined regions of interest. For numerical analysis, signal intensity enhancement was computed. Subsequently MR image-guided procedures were performed in USPIO-enhanced vessels in one pig. RESULTS The signal intensity evaluation shows a clear-cut dose dependence in both early and late phases after administration of SH U 555 C. A high-spatial-resolution MR angiogram acquired 20 minutes after injection yielded the best results with the highest dose (40 micromol of iron per kilogram); at that dose, intravascular enhancement was sufficient for vascular procedures for 60 minutes after injection. CONCLUSION SH U 555 C is a promising contrast agent for MR angiography and MR-guided vascular procedures in an open low-field-strength MR imager.

Local Integration of Commercially Available Intra-operative MR-scanner and Neurosurgical Guidance for Metalloporphyrin-Guided Tumor Resection and Photodynamic Therapy

We have locally integrated a commercial intra-operative MR-scanner and neurosurgical guidance system in order to conduct a clinical trial testing for improvement in glioma resection following administration of either of two metalloporphyrin drugs, XcytrinTM or LutrinTM (Pharmacyclics Inc., Sunnyvale, CA). Like other porphyrins, these two drugs have been shown to bind preferentially to tumor. The metal in Xcytrin is gadolinium. It should enhance intra-operative MR-scans taken during tumor resection. This would overcome problems of non-specific MR-enhancement caused by intra-operative contrast leakage from the vascular compartment. Both drugs provide fluorescence contrast in the presence of 450 nm wavelength light. Intra-operative fluorescence contrast should facilitate Lutrin photodynamic therapy administration to otherwise invisible glioma residual in the walls of the resection cavity. The metal in Lutrin is Lutetium. When illuminated with 732nm wavelength light, Lutrin causes tumor death via release of singlet oxygen (i.e., photodynamic therapy).