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Circular scanning with an off-center planar detector is an acquisi-tion scheme that allows to save detector area while keeping a largefield of view (FOV). Several filtered back-projection (FBP) algorithmshave been proposed earlier. The purpose of this work is to present twonewly developed back-projection filtration (BPF) variants and evaluatethe image quality of these methods compared to the existing state-of-the-art FBP methods.

Purpose: The purpose of this work is to combine two areas of active research in tomographic x-ray imaging. The first one is the use of iterative reconstruction techniques. The second one is differential phase contrast imaging (DPCI). Method: We derive an SPS type maximum likelihood (ML) reconstruction algorithm with regularization for DPCI. Forward and back-projection are implemented using spherically symmetric basis functions (blobs) and differential footprints, thus completely avoiding the need for numerical differentiation throughout the reconstruction process. The method is applied to the problem of reconstruction of an object from sparsely sampled projection. Results: The results show that the proposed method can handle the sparely sampled data efficiently. In particular no streak artifacts are visible which are present images obtained by filtered back-projection (FBP). Conclusion: Iterative reconstruction algorithms have a wide spectrum of proven advantages in the area of conventional computed tomography. The present work describes for the first time, how a matched forward and back-projection can be implemented for DPCI, which is furthermore free of any heuristics. The newly developed ML reconstruction algorithm for DPCI shows that for the case of sparsely sampled projection data, an improvement in image quality is obtained that is qualitatively comparable to a corresponding situation in conventional x-ray imaging. Based on the proposed operators for forward and back-projection, a large variety of iterative reconstruction algorithms is thus made available for DPCI.

Purpose: Treatment of malignant tumors by either hyperthermia induced drug delivery or thermal ablation requires complete coverage of the treatment area and precise control of the thermal dose.Both can be achieved by volumetric ultrasonic heating in combination with simultaneous MR-based temperature mapping. The translation ofthese techniques to the clinic requires thorough preclinical testing in large cohorts. Mouse and rat studies are preferred over largeranimals for ethical reasons as well as the larger variety of available tumor models. Our work aims to develop temperature induced drug delivery and ablation protocols in rats and to subsequently evaluatetreatment outcome using small animal imaging methods. To this end, we adapted a clinical MR-HIFU system for the treatment of rats by utilizing a dedicated small animal setup. Methods: All animals were positioned in a HIFU dedicated small animal 4-channel MR volume coil that was used as add-on to a clinical 3T Philips Sonalleve MR-HIFU system. Hyperthermia was performed for 15 min using binary temperaturecontrol on lateral gastrocnemius muscle (n = 5) and on subcutaneousinoculated tumors on the hind limb of rats (9L rat glioma; n = 5).For thermal ablation, tumors were partly heated to T = 65 °C with continuous wave ultrasound (1.44 MHz) under MR temperature monitoring(n = 5). The treatment effect was assessed with T2-weighted imagingand dynamic contrast enhanced (DCE-) MRI using Gd-DTPA as contrast agent. Excised muscle and tumors were further evaluated with histology. Results: The target temperatures were readily achieved in hyperthermia and ablation treatments while changes in body temperature remained below 1 °C. For hyperthermia treatments, no indication of tissue damage was found on MR images. Analysis of the Gd-DTPA uptake kinetics post ablation indicated a difference in non-perfused volume inthe tumor of 371 ± 123 mm3 (Δ tissue volume with ktrans ≥ 0.04 min-1). NADH-diaphorase staining of ablated tumors showed a sharp demarcation between viable and non-viable cells. Conclusion: These results demonstrate that both controlled hyperthermia and thermal ablation treatment of malignant tumors in small animals can be performed on a clinical MR-HIFU system. This approach provides all theadvantages of clinical MR-HIFU, such as volumetric heating, temperature feedback control and a clinical software interface, while also having many of the advantages of a dedicated small animal system. Theuse of a clinical system facilitates a rapid translation of these protocols into the clinic.

Purpose: Recently, image-based computational fluid dynamic (CFD) simulations have been proposed to investigate the local hemodynamics inside human cerebral aneurysms. It is suggested that the knowledge ofthe computed three-dimensional flow fields can be used to assist clinical risk assessment and treatment decision making. Therefore, itis desired to know the reliability of CFD for cerebral blood flow simulation, and be able to provide clinical feedback. However, the validations are not yet comprehensive as they lack either patient-30 specific boundary conditions (BCs) required for CFD simulations or quantitative comparison methods. Methods: In this work, based on a recently proposed in-vitro quantitative CFD evaluation approach via virtual angiography, the CFD evaluation is extended from phantom to patient studies. In contrast to previous work, patient-specific blood flow rates obtained by transcranial color coded Doppler ultrasound measurements are used to impose CFD BCs. Virtual angiograms (VAs) are constructed which resemble clinically acquired 35 angiograms (AAs). Quantitative measures are defined to thoroughly evaluate the correspondence of the detailed flow features between the AAs and the VAs, and thus, the reliability of CFD simulations. Results: The proposed simulation pipeline provides a comprehensive validation method of CFDsimulation for reproducing cerebral blood flow, with a focus on theaneurysm region. Six patient cases are tested and close similaritiesare found in terms of spatial and temporal variations of CA distribution between AAs and VAs. For 40 patient #1 to #5, discrepancies ofless than 11% are found for the relative root mean square errors intime intensity curve comparisons from characteristic vasculature positions. For patient #6, where the CA concentration curve at vesselinlet cannot be directly extracted from the AAs and given as a BC, deviations about 20% are found. Conclusions: As a conclusion, the reliability of the CFD is well confirmed. Besides, it is shown that the45 accuracy of CFD simulations is closely related to the input BCs.

Purpose: Quantitative assessment of tissue perfusion by imaging methods could improve outcome control during treatment of peripheral vascular disease. Currently, revascularization treatments are assessedby planar angiography which only allows for qualitative inspection of blood flow in vessels. In this paper, we present a method for quantitative estimation of contrast enhancement (i.e., temporal attenuation curves) in skeletal muscles using a C-arm system for effective evaluation during treatment. Methods: The proposed method tackles the loss of spatial depth information which occurs in conventional angiography by combining the acquired angiograms with two additional C-arm rotational soft tissue scans. The area subject to contrast propagation is segmented from the two images that are tomographically reconstructed from the rotational scans and is then used to estimate from the angiograms the spatially averaged contrast attenuation alongthe X-ray directions. A segmentation method which is tailored to theestimation procedure is applied to reduce inaccuracies in the estimation. The accuracy of the method in estimating temporal attenuationcurves in muscular tissue is evaluated in a simulation study usingexperimental data from CT perfusion acquisitions. Results: Resultsshow that the estimation accuracy is limited (16-25% relative error)owing to spatial inhomogeneity of contrast which appears characteristic of the way contrast diffuses in muscular tissue and to the presence of vessels along the X-ray directions. Nonetheless, the methodallows for quantitative differentiation of normal and hypoperfused tissue which is challenging when using conventional angiography. Conclusions: Periprocedural quantification of muscle perfusion as provided with the presented method can be applied to measure differencesoccurring in response to peripheral revascularization; therefore theproposed method represents an improvement with respect to the current methods for immediate post treatment assessment in the angio-room