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This white paper summarizes the various ways in which MR may improve cardiac electrophysiology procedures of both types, catheter ablation and cardiac resynchronization therapy. The report gives an overview of how applications do or may benefit from pre-, post- and evenintra-operative MRI, focussing on research in groups affiliated with Philips.

A Simultaneous Non-contrast Angiography and intraPlaque hemorrhage (SNAP) MR imaging technique was proposed to detect both luminal stenosis and hemorrhage in atherosclerosis patients in a single scan. 13patients with diagnosed carotid atherosclerotic plaque were recruited after informed consent. All scans were performed on a 3T MR imaging system with SNAP, 2D time-of-flight (TOF) and magnetization-prepared 3D rapid acquisition gradient echo (MP-RAGE) sequences. The SNAPsequence utilized a phase sensitive acquisition, and was designed toprovide positive signals corresponding to intraplaque hemorrhage (IPH) and negative signals corresponding to lumen. SNAP images were compared to TOF images to validate lumen area measurements using linear mixed models and the intraclass correlation coefficient (ICC). IPHidentification accuracy was evaluated by comparing to MP-RAGE images using Cohen’s Kappa. Diagnostic quality SNAP images were generatedfrom all subjects. Quantitatively, the lumen area measurements by SNAP were strongly correlated (ICC=0.96, p<0.001) with those measuredby TOF. For IPH detection, strong agreement (&#954;=0.82, p<0.001)was also identified between SNAP and MP-RAGE images. The SNAP technique was proposed and validated to reliably detect in a single acquisition both luminal size and intraplaque hemorrhage in the patients with carotid atherosclerosis.

Backgroud: This study was to validate the feasibility of using clinical 3.0T MRI to monitor the migration of autotransplanted bone marrow (BM)-derived stem-progenitor cells (SPC) to the injured arteries of near-human sized swine for potential cell-based arterial repair.Methodology: The study was divided into two phases. For in vitro evaluation, BM cells were extracted from the iliac crests of 13 domestic pigs and then labeled with a T2 contrast agent, Feridex, and/or afluorescent tissue marker, PKH26. The viability, the proliferation efficiency and the efficacies of Feridex and/or PKH26 labeling were determined. For in vivo validation, the 13 pigs underwent endovascular balloon-mediated intimal damages of the iliofemoral arteries. Thelabeled or un-labeled BM cells were autotransplanted back to the same pig from which the BM cells were extracted. Approximately three weeks post-cell transplantation, 3.0T T2-weighted MRI was performed todetect Feridex-created signal voids of the transplanted BM cells inthe injured iliofemoral arteries, which was confirmed by subsequenthistologic correlation. Principal Findings: Of the in vitro study,the viability of dual-labeled BM cells was 95-98%. The proliferation efficiencies of dual-labeled BM cells were not significantly different compared to those of non-labeled cells. The efficacies of Feridex- and PKH26 labeling were 90% and 100%, respectively. Of the in vivo study, 3.0T MRI detected the auto-transplanted BM cells migratedto the injured arteries, which was confirmed by histologic examinations. Conclusion: This study demonstrates the capability of using clinical 3.0T MRI to monitor the auto-transplantation of BM cells thatmigrate to the injured arteries of large animals, which may providea useful MRI technique to monitor cell-based arterial repair.

Angiogensis is playing an important role during fracture healing. The aim of this study was the evaluation of steady-state USPIO enhanced MR blood volume measurements in a longitudinal study of angiogenesis in an experimental fracture model. The MR results estimated an increase of blood volume during fracture healing, which corelated wellwith the histological findings. Quantitative MR is thus expected tobe a helpful tool for the monitoring of neovascularization.

In this paper, we present a novel approach to rigidly register intraoperative electromagnetically tracked ultrasound (US) with preoperative magnetic resonance (MR) images. The clinical rationale for thiswork is to allow accurate needle placement during thermal ablation of liver metastases using multimodal imaging. We adopt a model-basedapproach that rigidly matches segmented liver surface shapes obtained from the multimodal image volumes. Towards this end, a shape-constrained deformable surface model combining the strengths of both deformable and active shape models is used to segment the liver surfacefrom the MR scan. It incorporates a priori shape information while external forces guide the deformation and adapts the model to a target structure. The liver boundary is extracted from US by merging a dynamic region-growing method with a graph-based segmentation framework anchored on adaptive priors of neighboring surface points. Registration is performed with a weighted ICP algorithm with a physiological penalizing term. The MR segmentation model was trained with 30 datasets and validated on a separate cohort of 10 patients with corresponding ground truth. The accuracy and robustness of the method wereassessed by registering four US/MR datasets, yielding accurate landmark registration errors (3.7 +/- 0.69mm) and high robustness, and isthus acceptable for radiofrequency clinical applications.

Fast and robust in vivo B1 mapping is an essential prerequisite forquantitative MRI or multi-element transmit applications like RF-shimming or accelerated multi-dimensional RF pulses. However, especially at higher field strength, the acquisition speed of current B1-mapping approaches is typically limited by SAR constraints, T1 relaxation times, or characteristic sequence properties, which makes a multi-transmit element B1 calibration scan rather time consuming. Moreover, existing B1 mapping approaches are typically prone to motion,since the flip angle is calculated from two or more acquisitions separated in time. In this work, a novel multi-slice B1 mapping approach dubbed DREAM (Dual Refocusing Echo Acquisition Mode) is proposed, which derives a 2D B1 map from a single, ultra-short acquisitionof about 130 ms duration, which is more than an order of magni- tudefaster than most existing B1 mapping techniques. Moreover, the transceive phase and B0 are delivered in addition and for free. The performance of the approach is demonstrated in vivo by B1 mapping experiments in the abdomen at 3T.

Transmit SENSE is typically applied to improve spatially selective RF pulses in two or three dimensions. This study investigates the application of Transmit SENSE to one-dimensional RF pulses. For these RF pulses, Transmit SENSE is applicable in case of large B1 variations across the slice or slab to be excited. Typically, such large B1 variations are found across the slabs excited in 3D volume imaging orin the framework of the REgional Saturation Technique (REST). 1D Transmit SENSE can improve the excitation slab profile, and particularly can result in a significant reduction of RF power and the relatedspecific absorption rate (SAR). Since the involved RF pulses have the same duration as standard slice-selection pulses, they can easilybe incorporated in standard sequences without changing sequence timing. The approach was tested using synthetic and realistic coil sensitivity profiles.

The document consists of a diploma thesis, which describes a completely automated segmentation chain for the bones of the human hip joint from diagnostic MR images including the model-building process for the corresponding anatomical structures. Mainly relying on the well-established model-based segmentation framework, the approach discusses strategies such as the Hough Transform for pre-positioning the involved surface models in the image to enhance robustness of the model-based framework. Furthermore, simple strategies for optimal choice of parameters for the model-based framework are investigated. Theproposed methods have been tested on a set of nine MR images of female patients, all suffering from hip dysplasia.

Cardiac resynchronization therapy (CRT) aims at improving the pumping function of the heart using bi-ventricular pacing. For the lead implantation procedure, knowledge of the heart function, the relevant anatomy (i.e. coro-nary sinus (CS), great cardiac vein (GCV) and its tributaries) and left ventricu-lar (LV) scar formation is of great interest. Previous reports demonstrate feasibility of coronary venous(CV) imaging using magnetic resonance imaging (MRI) mostly in volunteers and coronary artery disease patients. In this report, we evaluate the feasibility of albumin binding contrast (Vasovist and Multi-hance) enhanced cardiac MRI of the CV system in heart failure (HF) patients referred to CRT. These agents remain for a longer time period in the intravascular space, enlarging the MRI window for vascular structures. The images are compared with X-ray (XR) coronary venous angiograms, obtained during the pacer implantation procedure, and with non-contrast magnetization transfer (MTC) MRI images. Furthermore, late enhancement (LE) MRI scar imaging using the same contrast agents is investigated in a limited amount of patients. The CV anatomy can be visualized in HF patients prior to bioventricular pacer implantation using albumin binding contrast agent enhanced cardiac MRI. CS offspring anatomy from the right atrium (RA) and candidate vein branches for LV lead implantation can be indentified pre-operatively, aiding better patient selection for CRT. In ischemic HF patients scheduled for CRT, scar information can be obtained using LE imaging with the Multihance contrast agent further complementing the pre-operative information of the anatomy.

The aging population in the European Union and the US has increased the importance of research in neurodegenerative diseases. Imaging plays an essential role in this endeavor by providing insight to the intricate cellular and inter-cellular processes in living tissues that will otherwise be difficult, or impossible, to gain. Because of the sheer size of the imagery data, the lack of sufficient medical staff, and the inaccuracies resulting from manual processing, automated processing of image-based data to generate quantitative and reproducible results is necessary. To this effect, in this thesis a fully automatic image-processing algorithm for brain tissue segmentation from magnetic resonance (MR) images is proposed. Contrary to the present iterative expectation maximization (EM) based algorithms, it uses online (sample-by-sample) learning to adapt to the intensity inhomogeneity inherent to MR images. Since the proposed method can adapt to the intensity inhomogeneity online, multiple iterations over the data as in the present algorithms are not necessary, and consequently the processing time is decreased dramatically. The used online learning scheme is based on learning vector quantization and is further tailored to the segmentation of MR images by integration of spatial context and the use of a special locality-preserving scanning order of the data. Explorations of various scanning orders and a modification to the learning rule to allow for 3D learning have lead to three variants of the proposed algorithm. These proposed methods are validated by comparing the segmentation masks to basic k-means clustering, and present EM-based methods, namely, FAST and the state-of-the-art EMS, on simulated and real datasets. The proposed methods demonstrated a significant reduction of the processing time (a factor of 20) compared to the EM-based methods. Tests on BrainWeb simulated data showed that segmentation accuracy is comparable to the EM-based methods, however, tests on real data, where the segmentations of EMS were used as ground truth, showed lower accuracy than the EM-based FAST. Moreover, the tests on real data showed that the proposed methods as well as FAST make a significant amount of misclassifications in the so-called deep grey matter areas, which suggests the necessity of a spatial prior atlas as it is used in EMS.

Purpose: To evaluate the effect of different b-values on intravoxelincoherent motion (IVIM) and diffusion parameters for prostate cancer detection. Materials and methods: Thirty three patients (mean age of 61.6 years, mean serum PSA of 10 ng/dl) undergoing endorectal coil MRI of the prostate underwent multiparametric imaging includingdiffusion weighted (DW) imaging with five b-values (0, 188, 375, 563and 750 s/mm2), T2 weighting and dynamic contrast enhanced MRI. Diffusion coefficients were obtained from a simple mono-exponential fitusing different non-zero b-values. A simplified IVIM model was used to generate perfusion fractions, by combining both the measured and the extrapolated diffusion data at a b-value of zero. Correlationswere made with the results of DCE-MRI using an extended Tofts pharmacokinetic model. Pathologic correlation was obtained by precisely targeting the needle via a fused MRI-Transrectal Ultrasound (MR-TRUS)image-guided biopsy system. Results: Diffusion coefficients differentiated tumors from normal tissues in the prostate using all possible combinations of non-zero b-values; however, perfusion fractionsdemonstrated large variations depending on the choice of b-values.Exclusion of the highest b-value of 750 (s/mm2) led to better correlations of perfusion fraction with DCE-MRI and predicted the presenceof cancer independent of diffusion. Conclusions: Estimates of perfusion fraction using IVIM obtained on DW-MRI correlate with DCE-MRIparameters and are predictive for cancer in MRI of the prostate. Perfusion fraction therefore represents another independent parameterto help differentiate prostate cancers from surrounding benign tissue using multiparametric MRI

Recently, it was shown that human dielectric properties can be mapped using MRI. This method, named electrical properties mapping (EPT),relies on measurements of the B1+ amplitude and its phase. This phase, however, cannot be measured directly; therefore, the assumptionthat the transceive phase is twice the B1+ phase is used. This assumption is acceptable at low field strengths, however, leads to significant reconstruction errors with increasing field strength. Here, opposing errors were observed for the permittivity and conductivity mapping, which can be explained by the effect of the transceive phaseerror on the error in the reconstructed conductivity and permittivity. This abstract investigates if the wave-number, combining the conductivity and permittivity, benefits from these opposing errors, andcan be determined more accurately at 7T than the separate dielectricproperties.