Harald Busse

Non-Invasive Assessment of Hepatic Steatosis in Patients with NAFLD Using Controlled Attenuation Parameter and 1H-MR Spectroscopy

Introduction Non-invasive assessment of steatosis and fibrosis is of growing relevance in non-alcoholic fatty liver disease (NAFLD). 1H-Magnetic resonance spectroscopy (1H-MRS) and the ultrasound-based controlled attenuation parameter (CAP) correlate with biopsy proven steatosis, but have not been correlated with each other so far. We therefore performed a head-to-head comparison between both methods. Methods Fifty patients with biopsy-proven NAFLD and 15 healthy volunteers were evaluated with 1H-MRS and transient elastography (TE) including CAP. Steatosis was defined according to the percentage of affected hepatocytes: S1 5-33%, S2 34–66%, S3 ≥67%. Results Steatosis grade in patients with NAFLD was S1 36%, S2 40% and S3 24%. CAP and 1H-MRS significantly correlated with histopathology and showed comparable accuracy for the detection of hepatic steatosis: areas under the receiver-operating characteristics curves were 0.93 vs. 0.88 for steatosis ≥S1 and 0.94 vs. 0.88 for ≥S2, respectively. Boot-strapping analysis revealed a CAP cut-off of 300 dB/m for detection of S2-3 steatosis, while retaining the lower cut-off of 215 dB/m for the definition of healthy individuals. Direct comparison between CAP and 1H-MRS revealed only modest correlation (total cohort: r = 0.63 [0.44, 0.76]; NAFLD cases: r = 0.56 [0.32, 0.74]). For detection of F2–4 fibrosis TE had sensitivity and specificity of 100% and 98.1% at a cut-off value of 8.85 kPa. Conclusion Our data suggest a comparable diagnostic value of CAP and 1H-MRS for hepatic steatosis quantification. Combined with the simultaneous TE fibrosis assessment, CAP represents an efficient method for non-invasive characterization of NAFLD. Limited correlation between CAP and 1H-MRS may be explained by different technical aspects, anthropometry, and presence of advanced liver fibrosis.

Navigation concepts for MR image-guided interventions.

The ongoing development of powerful magnetic resonance imaging techniques also allows for advanced possibilities to guide and control minimally invasive interventions. Various navigation concepts have been described for practically all regions of the body. The specific advantages and limitations of these concepts largely depend on the magnet design of the MR scanner and the interventional environment. Open MR scanners involve minimal patient transfer, which improves the interventional workflow and reduces the need for coregistration, ie, the mapping of spatial coordinates between imaging and intervention position. Most diagnostic scanners, in contrast, do not allow the physician to guide his instrument inside the magnet and, consequently, the patient needs to be moved out of the bore. Although adequate coregistration and navigation concepts for closed‐bore scanners are technically more challenging, many developments are driven by the well‐known capabilities of high‐field systems and their better economic value. Advanced concepts such as multimodal overlays, augmented reality displays, and robotic assistance devices are still in their infancy but might propel the use of intraoperative navigation. The goal of this work is to give an update on MRI‐based navigation and related techniques and to briefly discuss the clinical experience and limitations of some selected systems. J. Magn. Reson. Imaging 2008;27:276–291.

Simulations of thermal tissue coagulation and their value for the planning and monitoring of laser-induced interstitial thermotherapy (LITT).

MRI information is widely used for the monitoring of thermal therapies, such as laser‐induced interstitial thermotherapy (LITT). However, a detailed knowledge about the relationship between time/temperature exposure and resulting tissue thermal damage is needed to estimate the lesion extent. The aims of this work were to model the thermal response of laser‐irradiated tissue and to assess the value of Monte Carlo simulation (MCS) for tumor therapy planning and monitoring. MCS yielded true 3D distributions of laser‐induced temperature and thermal damage. These results were compared with 2D MR thermometry data from in vitro experiments performed on animal liver tissue over an ordinary range of laser powers (10–25 W) and irradiation times (5–25 min). Clinical reference data were available from MR‐guided liver LITT procedures. MCS correctly predicted the shape of temperature and damage distributions. The quantitative agreement between simulated and measured lesion diameters was within 10% and 15% for the in vitro and in vivo cases, respectively. The simulated 53°C isotherm best estimated the boundary of the final thermal damage (6% variance). This study shows that MCS of interstitial laser coagulation provides unique information that can be of use in the empirical correlation of temperature with thermal damage, and can assist greatly in thermal treatment planning and monitoring. Magn Reson Med 49:351–362, 2003.

MRI‐guided procedures in various regions of the body using a robotic assistance system in a closed‐bore scanner: Preliminary clinical experience and limitations

To present the clinical setup and workflow of a robotic assistance system for image‐guided interventions in a conventional magnetic resonance imaging (MRI) environment and to report our preliminary clinical experience with percutaneous biopsies in various body regions.

Advanced approach for intraoperative MRI guidance and potential benefit for neurosurgical applications.

To present an advanced approach for intraoperative image guidance in an open 0.5 T MRI and to evaluate its effectiveness for neurosurgical interventions by comparison with a dynamic scan‐guided localization technique.

Software for automated MRI‐based quantification of abdominal fat and preliminary evaluation in morbidly obese patients

To present software for supervised automatic quantification of visceral and subcutaneous adipose tissue (VAT, SAT) and evaluates its performance in terms of reliability, interobserver variation, and processing time, since fully automatic segmentation of fat‐fraction magnetic resonance imaging (MRI) is fast but susceptible to anatomical variations and artifacts, particularly for advanced stages of obesity.

Flexible add‐on solution for MR image‐guided interventions in a closed‐bore scanner environment

MRI is of great clinical utility for the guidance of various diagnostic and therapeutic procedures. In a standard closed‐bore scanner, the simplest approach is to manipulate the instrument outside the bore and move the patient into the bore for reference and control imaging only. Without navigational assistance, however, such an approach can be difficult, inaccurate, and time consuming. Therefore, an add‐on navigation solution is described that addresses these limitations. Patient registration is established by an automatic, robust, and fast (<30 sec) localization of table‐mounted MR reference markers and the instrument is tracked optically. Good hand‐eye coordination is provided by following the virtual instrument on MR images that are reconstructed in real time from the reference data. Needle displacements of 2.2 ± 0.6 mm and 3.9 ± 2.4 mm were determined in a phantom (P < 0.05), depending on whether the reference markers were placed at smaller (98‐139 mm) or larger (147‐188 mm) distances from the isocenter. Clinical functionality of the navigation concept is demonstrated by a double oblique, subscapular hook‐wire insertion in a patient with a body mass index of 30.1 kg/m2. Ease of use, compactness, and flexibility of this technique suggest that it can be used for many other procedures in different body regions. More patient cases are needed to evaluate clinical performance and workflow. Magn Reson Med, 2010.

Fusion von MRT-, fMRT- und intraoperativen MRT-Daten Methode und klinische Bedeutung am Beispiel neurochirurgischer Interventionen

ZusammenfassungZiel dieser Arbeit waren die Realisierung und klinische Bewertung einer Bildfusion präoperativer MRT- und fMRT-Bilder mit intraoperativen Datensätzen eines interventionellen MRT-Systems am Beispiel neurochirurgischer Eingriffe.Ein vertikal offenes 0,5-T-MRT-System wurde mit einem erweiterten Navigationssystem ausgestattet, welches eine Integration zusätzlicher Bildinformationen (Hochfeld-MRT, fMRT, CT) in die intraoperativ akquirierten Datensätze erlaubt. Diese fusionierten Bilddaten wurden zur Interventionsplanung und multimodalen Navigation verwendet.Bisher wurde das System bei insgesamt 70 neurochirurgischen Eingriffen eingesetzt, davon 13 mit Bilddatenfusion (rund 15-minütiger Zusatzaufwand). Das erweiterte Navigationssystem zeichnet sich im Vergleich zur systemeigenen Navigation auf der Basis kontinuierlich akquirierbarer Real-time-Bilder durch eine schnellere Bildwiederholung und eine höhere Bildqualität aus. Der Vergleich beider Navigationsbilder erlaubt das frühzeitige Erkennen von Patienten- bzw. Gewebeverlagerungen.Die multimodale Bildfusion erlaubte eine differenziertere Navigationsplanung, insbesondere bei der Resektion tief liegender Hirntumoren oder bei Läsionen in enger Nachbarschaft zu eloquenten Arealen. Die erweiterte intraoperative Orientierung bzw. Instrumentenführung erhöht die Sicherheit und Genauigkeit neurochirurgischer Interventionen.AbstractThe aim of this work was to realize and clinically evaluate an image fusion platform for the integration of preoperative MRI and fMRI data into the intraoperative images of an interventional MRI system with a focus on neurosurgical procedures.A vertically open 0.5 T MRI scanner was equipped with a dedicated navigation system enabling the registration of additional imaging modalities (MRI, fMRI, CT) with the intraoperatively acquired data sets. These merged image data served as the basis for interventional planning and multimodal navigation.So far, the system has been used in 70 neurosurgical interventions (13 of which involved image data fusion – requiring 15 minutes extra time). The augmented navigation system is characterized by a higher frame rate and a higher image quality as compared to the system-integrated navigation based on continuously acquired (near) real time images. Patient movement and tissue shifts can be immediately detected by monitoring the morphological differences between both navigation scenes.The multimodal image fusion allowed a refined navigation planning especially for the resection of deeply seated brain lesions or pathologies close to eloquent areas. Augmented intraoperative orientation and instrument guidance improve the safety and accuracy of neurosurgical interventions.

Non-invasive estimation of prostate cancer aggressiveness using diffusion-weighted MRI and 3D proton MR spectroscopy at 3.0 T

Background Clinical management of prostate cancer increasingly aims to distinguish aggressive types that require immediate and radical treatment from indolent tumors that are candidates for watchful waiting. This requires reliable and reproducible parameters to effectively control potential cancer progression. Magnetic resonance imaging (MRI) may provide a non-invasive means for this purpose. Purpose To assess the value of diffusion-weighted imaging and proton MR spectroscopy for the prediction of prostate cancer (PCa) aggressiveness. Material and Methods In 39 of 64 consecutive patients who underwent endorectal 3-T MRI prior to radical prostatectomy, prostate specimens were analyzed as whole-mount step sections. Apparent diffusion coefficient (ADC), normalized ADC (nADC: tumor/healthy tissue), choline/citrate (CC), and (choline + creatine)/citrate (CCC) ratios were correlated with Gleason scores (GS) from histopathological results. The power to discriminate low (GS ≤ 6) from higher-risk (GS ≥ 7) tumors was assessed with receiver operating characteristics (area under the curve [AUC]). Resulting threshold values were used by a blinded reader to distinguish between aggressive and indolent tumors. Results Ninety lesions (1 × GS = 5, 41 × GS = 6, 36 × GS = 7, 12 × GS = 8) were considered. nADC (AUC = 0.90) showed a higher discriminatory power than ADC (AUC = 0.79). AUC for CC and CCC were 0.73 and 0.82, respectively. Using either nADC < 0.46 or CCC > 1.3, as well as both criteria for aggressive PCa, the reader correctly identified aggressive and indolent tumors in 31 (79%), 28 (72%), and 33 of 39 patients (85%), respectively. Predictions of tumor aggressiveness from TRUS-guided biopsies were correct in 27 of 36 patients (75%). Conclusion The combination of a highly sensitive normalized ADC with a highly specific CCC was found to be well suited to prospectively estimate PCa aggressiveness with a similar diagnostic accuracy as biopsy results.

Method for automatic localization of MR-visible markers using morphological image processing and conventional pulse sequences: Feasibility for image-guided procedures

To evaluate the feasibility and accuracy of an automated method to determine the 3D position of MR‐visible markers.