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Motion artifacts often spoil the radiological interpretation of MR images, and in the most severe cases the scan needs be repeated, with additional costs for the provider. We discuss the application of a novel 3D retrospective rigid motion correction and reconstruction scheme for MRI, which leverages multiple scans contained in a MR session. Typically, in a multi-contrast MR session, motion does not equally affect all the scans, and some motion-free scans are generally available, so that we can exploit their anatomic similarity. The uncorrupted scan is used as a reference in a generalized rigid-motion registration problem to remove the motion artifacts affecting the corrupted scans. We discuss the potential of the proposed algorithm with a prospective in-vivo study and clinical 3D brain protocols. This framework can be easily incorporated into the existing clinical practice with no disruption to the conventional workflow.

In radiotherapy treatments of head and neck cancer, ionizing radiation is used to destroy malignant tumor tissue, while sparing the surrounding healthy tissue. For successful delivery of radiotherapy treatments, an accurate definition of the target is essential. This target is defined using threedimensional imaging techniques such as computed tomography (CT), positron emission tomography (PET) and magnetic resonance imaging (MRI). MRI can visualize, amongst others, local differences in the diffusion of water: diffusion weighted MRI (DW-MRI). Tumors have different diffusion characteristics than normal tissue. With DW-MRI these differences can be visualized and used in target volume delineation. In order to use DW-MRI in a radiotherapy setting, geometric accuracy is vital. The most common method to acquire DW-MRI, DW-EPI, is known for its sensitivity to geometric distortions, especially in areas with large magnetic field inhomogeneities. The geometric accuracy of DW-EPI was evaluated in patients with a retrospective analysis of magnetic field maps. It was found that severe geometric distortions are present when using DW-EPI in the head and neck region. Therefore, the use of an alternative acquisition method, DW-SPLICE, was proposed. This method is based on a turbo spin echo sequence, which is used for standard anatomical imaging and has comparable, high geometric accuracy. The method was implemented and demonstrated in patients. Using DW-SPLICE, diffusion weighted images with excellent geometric accuracy were acquired in head and neck cancer patients. Additionally, the DW-SPLICE technique was extended in order to improve fat suppression. Additional images were acquired in order to yield a dataset which was suitable for water fat separation. The results from the water fat separation were applied in order to provide a more robust and homogeneous fat suppression. The diffusion weighted images acquired with DW-SPLICE were used to generate target volume delineations. Using an intensity threshold, an initial volume was segmented on diffusion weighted images. Subsequently these were manually adjusted based on the diffusion coefficients. These delineations were compared with those based on PET. Pathology validation of PET delineations has shown these to be quite accurate. The (semi-)automatic target volume delineations on DW-SPLICE show good correspondence with target volume delineations based on PET, indicating that, for a large part, both techniques indicate the same target for treatment. Using surgical specimens, obtained after total laryngectomy, pathological validation of DW-MRI can be performed. Patients received an MRI exam with DW-MRI prior to surgery. The surgical specimen of the larynx was processed, resulting in a digitally reconstructed threedimensional volume which was matched to the imaging prior to surgery. The initial results from the first patient show that the target volume delineation based on DW-MRI has very good agreement with the tumor defined on pathology. When diffusion weighted images are acquired with good geometrical accuracy, these images can be a valuable addition for target volume delineation in head and neck radiotherapy.

PURPOSE: Diffusion weighted (DW) MRI, showing high contrast between tumor and background tissue, is a promising technique in radiotherapy for tumor delineation. However, its use for head-and-neck patients is hampered by poor geometric accuracy in conventional echo planar imaging (EPI) DW-MRI. An alternative turbo spin echo sequence, DW-SPLICE, is implemented and demonstrated in patients. METHODS: The DW-SPLICE sequence was implemented on a 3.0T system and evaluated in 10 patients. The patients were scanned in treatment position, using a customized head support and immobilization mask. Image distortions were quantified at the gross tumor volume (GTV) using field map analysis. The apparent diffusion coefficient (ADC) was evaluated using an ice water phantom. RESULTS: The DW images acquired by DW-SPLICE showed no image distortions. Field map analysis at the gross tumor volumes resulted in a median distortion of 0.2 mm for DW-SPLICE, whereas for the conventional method this was 7.2 mm. ADC values, measured using an ice water phantom were in accordance with literature values. CONCLUSIONS: The implementation of DW-SPLICE allows for diffusion weighted imaging of patients in treatment position with excellent geometrical accuracy. The images can be used to facilitate target volume delineation in RT treatment planning. This article is protected by copyright. All rights reserved.

Background: Validation of magnetic resonance imaging (MRI) and development of guidelines for the delineation of the gross tumor volume (GTV) is of utmost importance to benefit from the visibility of anatomical details on MR images and to achieve an accurate GTV delineation. In the ideal situation, the GTV delineation corresponds to the histopathologically determined ‘true tumor volume’. Consequently, we developed guidelines for GTV delineation of laryngeal and hypopharyngeal tumors on MRI and determined the accuracy of the resulting delineation of the tumor outline on histopathology as gold standard. Material and methods: Twenty-seven patients with T3 or T4 laryngeal/hypopharyngeal cancer underwent a MRI scan before laryngectomy. Hematoxylin and eosin sections were obtained from surgical specimens and tumor was delineated by one pathologist. GTV was delineated on MR images by three independent observers in two sessions. The first session (del1) was performed according to clinical practice. In the second session (del2) guidelines were used. The reconstructed specimen was registered to the MR images for comparison of the delineated GTVs to the tumor on histopathology. Volumes and overlap parameters were analyzed. A target margin needed to assure tumor coverage was determined. Results: The median GTVs (del1: 19.4 cm3, del2: 15.8 cm3) were larger than the tumor volume on pathology (10.5 cm3). Comparable target margins were needed for both delineation sessions to assure tumor coverage. By adding these margins to the GTVs, the target volumes for del1 (median: 81.3 cm3) were significantly larger than for del2 (median: 64.2 cm3) (p ≤ 0.0001) with similar tumor coverage. Conclusions: In clinical radiotherapy practice, the delineated GTV on MRI is twice as large as the tumor volume. Validated delineation guidelines lead to a significant decrease in the overestimation of the tumor volume.

Bone metastasis occurs for men with advanced prostate cancer which promotes osseous growth and destruction driven by alterations in osteoblast and osteoclast homeostasis. Patients can experience pain, spontaneous fractures and morbidity eroding overall quality of life. The complex and dynamic cellular interactions within the bone microenvironment limit current treatment options thus prostate to bone metastases remains incurable. This study uses voxel-based analysis of diffusion-weighted MRI and CT scans to simultaneously evaluate temporal changes in normal bone homeostasis along with prostate bone metatastsis to deliver an improved understanding of the spatiotemporal local microenvironment. Dynamic tumor-stromal interactions were assessed during treatment in mouse models along with a pilot prospective clinical trial with metastatic hormone sensitive and castration resistant prostate cancer patients with bone metastases. Longitudinal changes in tumor and bone imaging metrics during delivery of therapy were quantified. Studies revealed that voxel-based parametric response maps (PRM) of DW-MRI and CT scans could be used to quantify and spatially visualize dynamic changes during prostate tumor growth and in response to treatment thereby distinguishing patients with stable disease from those with progressive disease (p