Kerstin Jungnickel

Magnetic resonance-guided freehand radiofrequency ablation of malignant liver lesions: a new simplified and time-efficient approach using an interactive open magnetic resonance scan platform and hepatocyte-specific contrast agent.

ObjectivesThe aims of this study were to develop magnetic resonance (MR)–guided freehand radiofrequency ablation (RFA) using a near-real-time interactive MR platform in an open 1.0-T MR scanner and to determine the feasibility and safety of this new approach in the clinical setting. MethodsThe study was performed using an open 1.0-T MR system and a low-pass filter to prevent interaction between the RFA generator and the scanner. Artifact size of the radiofrequency needle was measured in 2 perpendicular views (transversal [tra] and coronal [cor]) in vitro and in the tra orientation in vivo for diagnostic (T1 high resolution isotropic volume excitation [THRIVE]/T2 turbo spin-echo [TSE]) and near-real-time (T1 fast-field-echo [FFE]) imaging. A liver-specific contrast medium (gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid) was administered 20 minutes before the intervention to enhance lesion visibility. Visibility was rated and compared for both interventional and diagnostic imaging sequences using a 10-point grading scale. Intervention time and complications were recorded. ResultsThe mean diameter of needle artifact size for interventional T1 FFE was 17.4 ± 0.7 mm (tra) and 17.1 ± 1.1 mm (cor) in vitro and 15.2 ± 1.5 mm (tra) in vivo. Artifact size for diagnostic imaging was 12.5 ± 1.8 mm (tra) and 11.2 ± 1.4 mm (cor) in vitro and 10.5 ± 1.7 mm in vivo using THRIVE and 8.1 ± 2.4 mm (tra) and 10.8 ± 1.8 mm (cor) in vitro and 9.7 ± 2.0 mm (tra) in vivo using T2 TSE.A total of 57 patients with liver malignancies (mean tumor size, 17 ± 7 mm) underwent freehand MR-guided RFA. In all patients, the ablative procedure was technically successful. Lesion visibility of the diagnostic T2 TSE sequence (4 ± 2) was significantly decreased compared with both the diagnostic (THRIVE, 7 ± 2) and interventional (T1 FFE, 8 ± 1) T1-weighted sequences. Mean time to position the applicator was 7.5 ± 2 minutes. Procedure times ranged from 30 to 60 minutes. The mean in-room time was 57 ± 22 minutes. No major complications were recorded. ConclusionsMagnetic resonance–guided freehand RFA using a near-real-time interactive MR platform in an open 1.0-T MR scanner is feasible, safe, and applicable in clinical routine. The administration of a hepatocyte-specific contrast agent enhances lesion visualization and therefore improves targeting. Without the need for additional sophisticated devices, this new approach simplifies and shortens the RFA procedure compared with previously published methods.

MR-compatible RF ablation system for online treatment monitoring using MR thermometry

RF ablation (RFA) is used for thermal ablation of tumors in which the RF electrode is placed in the tissue under image-guidance. Because of the good tumor visibility and the lack of ionizing radiation, MR-guided RFA is the method of choice. Additionally, with the help of MR thermometry the RF ablation can be monitored during the intervention. Unfortunately, the imaging of an MR scanner is highly sensitive to interferences caused by external electrical signals. In this paper the high-power RF ablation signal of a commercially available medical therapy device is made MR-compatible. A design of a low-pass filter with high-power compatibility is presented. The filter performance is demonstrated by means of simulations and measurements.

Separating the uncorrelated noise from the correlated detector noise of flat panel systems in order to quantify flat panel noise easily

One big advantage in terms of image quality of modern flat panel detector systems compared to CR systems beside the better DQE of these systems is the possibility to correct for inhomogeneities of the X-ray beam and the detector (flat field correction) as well as for bad pixels. However, the used correction methods are taking a lot of time or do not cover all possible combinations of radiation quality and exposure used for patient imaging. A method is presented to achieve these correction images very easily by using a proposed method for comparing two images. This method, which has so far been used for certain noise measurements and in some cases noise reduction, can also be used for separating correlated from uncorrelated noise by correlating in frequency sub-bands the information of two images. In this study it is proven, that the uncorrelated noise image of two expositions is very similar to the correction image gained just before the two exposures. That allows to calibrate a detector quite more often and for much more beam qualities/exposures than before to achieve a better correction and another possibility of constancy testing for flat panel detectors, because the proposed method is so sensitive that it will detect single pixel changes within the detector.

Heating of conductive wires in an open high field MRI environment: Effect of different wire positions in the MR scanner room

The measurements are performed inside a high-field open 1 T MR-scanner (Philips Panorama) using sequences with high SAR according to the ASTM recommendations. A phantom filled with hydroxyethyl cellulose is placed in the MR scanner’s center. The wire under investigation is partly immersed (20cm) in the phantom to reconstruct a typical clinical situation. Temperature at the wire’s tip and inside the phantom is measured using fibre optic probes. Different wire lengths and positions are investigated concerning their contribution to the heating of the wire’s tip inside the phantom.

MRI-Guided Brachytherapy in the Liver

Percutaneous brachytherapy, an ablative therapy achieving substantial tumor kill by directly applying ionizing radiation to solid tumors in the liver, is introduced. An interventional magnetic resonance environment, using a modified 1.0 T open MRI system and commercially available as well as custom-made components, is presented. The interventional procedure, from premedication to the MRI-guided therapeutic process to final process control is explained in detail. Subsequent irradiation therapy, follow-up, and tumor control are illustrated.