Eva Rothgang

In vivo 31P MR spectroscopic imaging of the human prostate at 7 T: Safety and feasibility

31P MR spectroscopic imaging of the human prostate provides information about phosphorylated metabolites that could be used for prostate cancer characterization. The sensitivity of a magnetic field strength of 7 T might enable 3D 31P MR spectroscopic imaging with relevant spatial resolution in a clinically acceptable measurement time. To this end, a 31P endorectal coil was developed and combined with an eight‐channel 1H body‐array coil to relate metabolic information to anatomical location. An extensive safety validation was performed to evaluate the specific absorption rate, the radiofrequency field distribution, and the temperature distribution of both coils. This validation consisted of detailed Finite Integration Technique simulations, confirmed by MR thermometry and B  1+ measurements in a phantom and in vivo temperature measurements. The safety studies demonstrated that the presence of the 31P endorectal coil had no influence on the specific absorption rate levels and temperature distribution of the external eight‐channel 1H array coil. To stay within a 10 g averaged local specific absorption rate of 10 W/kg, a maximum time‐averaged input power of 33 W for the 1H array coil was allowed. For transmitting with the 31P endorectal coil, our safety limit of less than 1°C temperature increase in vivo during a 15‐min MR spectroscopic imaging experiment was reached at a time‐averaged input power of 1.9 W. With this power setting, a second in vivo measurement was performed on a healthy volunteer. Using adiabatic excitation, 3D 31P MR spectroscopic imaging produced spectra from the entire prostate in 18 min with a spatial resolution of 4 cm3. The spectral resolution enabled the separate detection of phosphocholine, phosphoethanolamine, inorganic phosphate, and other metabolites that could play an important role in the characterization of prostate cancer. Magn Reson Med, 2012.

Rapid freehand MR-guided percutaneous needle interventions: an image-based approach to improve workflow and feasibility.

To develop and evaluate software‐based methods for improving the workflow of magnetic resonance (MR)‐guided percutaneous interventions.

Diffusion-weighted imaging during MR-guided radiofrequency ablation of hepatic malignancies: analysis of immediate pre- and post-ablative diffusion characteristics.

Background Previous studies have shown a benefit of magnetic resonance (MR)-diffusion-weighted imaging (DWI) for follow-up after liver radiofrequency (RF) ablation. However, no data are available concerning acute changes of DWI characteristics immediately after RF ablation. Purpose To analyze and compare the MR-diffusion characteristics of pre-interventional hepatic malignancies and the ablation zone during successful MR-guided RF ablation. Material and Methods This retrospective study was conducted in accordance with the guidelines of the local institutional review board. Forty-seven patients with 29 HCC (24 patients) and 30 hepatic metastases (23 patients) underwent MR-guided radiofrequency ablation including DWI before and immediately after ablation (b = 50, 400, 800 s/mm2). Two reviewers (A and B) analyzed DWI with focus on detectability of the tumor before ablation and characteristics of the coagulative area after treatment. Mean apparent diffusion coefficient (ADC) was compared between liver, untreated tumor, and hyperintense areas in post-ablative DWI (b = 800 s/mm2) with the paired Student’s t-test. Results Pre-ablative: the reviewers classified 19/29 (A) and 23/29 (B) HCC and 25/30 (A and B) metastases as detectable in DWI. Post-ablative: a hyperintense rim surrounding the ablation zone was observed in 28/29 treated HCC and 30/30 treated metastases (A and B). A homogenous hypointense central ablation zone was found in 18/29 (A) and 20/29 (B) treated HCC and 17/30 (A & B) treated metastases in DWI. ADC of the rim was significantly lower than ADC of the liver (P < 0.001). Conclusion DWI enables visualization of the target tumor in MR-guided liver radiofrequency ablation in most cases. A common post-ablative DWI finding is a hyperintense rim with decreased ADC surrounding the ablation zone.

Liver lesion conspicuity during real‐time MR‐guided radiofrequency applicator placement using spoiled gradient echo and balanced steady‐state free precession imaging

To retrospectively evaluate the conspicuity of liver lesions in a fluoroscopic spoiled gradient echo (GRE) and a balanced steady‐state free precession (SSFP) magnetic resonance imaging (MRI) sequence.

Interventional MR-imaging for thermal ablation therapy

Magnetic Resonance Imaging (MRI) has several unique advantages for guiding thermal ablation therapies. It not only provides excellent soft-tissue contrast and multiplanar capabilities, but also is sensitive to thermal effects. To make full use of these advantages for thermal ablation procedures, we present an integrated solution for a thermal therapy workflow that combines dedicated MRI pulse sequences and visualization/analysis tools for trajectory planning, automatic slice positioning for image-guided needle placement, and advanced MR thermal mapping. The paper highlights a novel approach to detect the needle in real-time MR images and to automatically realign the scan planes. In addition, a global approach to correct for B0 field shift during online MR thermometry is introduced. The application has been implemented using the open-source eXtensible Imaging Platform (XIP).

Fast 3-T MR-guided transrectal prostate biopsy using an in-room tablet device for needle guide alignment: a feasibility study

ObjectivesTo assess the feasibility of adding a tablet device inside the scanner room to assist needle-guide alignment during magnetic resonance (MR)-guided transrectal prostate biopsy.MethodsTwenty patients with one cancer-suspicious region (CSR) with PI-RADS score ≥ 4 on diagnostic multiparametric MRI were prospectively enrolled. Two orthogonal scan planes of an MR fluoroscopy sequence (~3 images/s) were aligned to the CSR and needle-guide pivoting point. Targeting was achieved by manipulating the needle-guide under MR fluoroscopy feedback on the in-room tablet device. Technical feasibility and targeting success were assessed. Complications and biopsy procedure times were also recorded.ResultsNeedle-guide alignment with the in-room tablet device was technically successful in all patients and allowed sampling after a single alignment step in 19/20 (95%) CSRs (median size 14 mm, range: 4-45). Biopsy cores contained cancer in 18/20 patients. There were no per-procedural or post-biopsy complications. Using the tablet device, the mean time to first biopsy was 5.8 ± 1.0 min and the mean total procedure time was 23.7 ± 4.1 min.ConclusionsUse of an in-room tablet device to assist needle-guide alignment was feasible and safe during MR-guided transrectal prostate biopsy. Initial experience indicates potential for procedure time reduction.Key Points• Performing MR-guided prostate biopsy using an in-room tablet device is feasible.• CSRs could be sampled after a single alignment step in 19/20 patients.• The mean procedure time for biopsy with the tablet device was 23.7 min.

A system for advanced real-time visualization and monitoring of MR-guided thermal ablations

In modern oncology, thermal ablations are increasingly used as a regional treatment option to supplement systemic treatment strategies such as chemotherapy and immunotherapy. The goal of all thermal ablation procedures is to cause cell death of disease tissue while sparing adjacent healthy tissue. Real-time assessment of thermal damage is the key to therapeutic efficiency and safety of such procedures. Magnetic resonance thermometry is capable of monitoring the spatial distribution and temporal evolution of temperature changes during thermal ablations. In this work, we present an advanced monitoring system for MR-guided thermal ablations that includes multiplanar visualization, specialized overlay visualization methods, and additional methods for correcting errors resulting from magnetic field shifts and motion. To ensure the reliability of the displayed thermal data, systematic quality control of thermal maps is carried out on-line. The primary purpose of this work is to provide clinicians with an intuitive tool for accurately visualizing the progress of thermal treatment at the time of the procedure. Importantly, the system is designed to be independent of the heating source. The presented system is expected to be of great value not only to guide thermal procedures but also to further explore the relationship between temperature-time exposure and tissue damage. The software application was implemented within the eXtensible Imaging Platform (XIP) and has been validated with clinical data.