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  • 1
    Keywords: Germany ; IN-VIVO ; VIVO ; IMAGES ; imaging ; SIGNAL ; PARAMETERS ; UNCERTAINTY ; DIFFUSION TENSOR ; ARTIFACTS ; DIFFUSION ; radiology ; FRAMEWORK ; human brain ; USA ; Diffusion Tensor Imaging ; PHANTOMS ; phantom ; DTI ; Overestimation ; NOISE ; Artefacts ; ANISOTROPY ; SAMPLING SCHEMES ; Background noise ; DIFFUSION-TENSOR MRI ; Eigenvalues ; Eigenvector shift ; High b value ; LOW SNR ; RICIAN NOISE
    Abstract: The signal-to-noise ratio of in vivo diffusion tensor imaging (DTI) is usually very limited, especially if high resolution data is acquired. In a variety of settings, the signal of diffusion weighted images can drop below the background noise level yielding an underestimated diffusion constant. In this work, we report two new artefacts in DTI that are important in this regime. Both artifacts are described analytically and numerically and are demonstrated in DTI phantoms and in subjects in vivo. First, eigenvectors are systematically shifted towards distinct 'attractive' orientations of the gradient scheme. Second, certain eigenvalues can be overestimated due to the underestimation of the measured diffusion, which can result in the misordering of eigenvalues We show that these effects are relevant for current clinical settings of DTI
    Type of Publication: Journal article published
    PubMed ID: 19067007
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  • 2
    Keywords: IMAGES ; SYSTEM ; REGISTRATION ; POSE ESTIMATION
    Abstract: PURPOSE : Percutaneous nephrolithotomy (PCNL) plays an integral role in treatment of renal stones. Creating percutaneous renal access is the most important and challenging step in the procedure. To facilitate this step, we evaluated our novel mobile augmented reality (AR) system for its feasibility of use for PCNL. METHODS : A tablet computer, such as an iPad[Formula: see text], is positioned above the patient with its camera pointing toward the field of intervention. The images of the tablet camera are registered with the CT image by means of fiducial markers. Structures of interest can be superimposed semi-transparently on the video images. We present a systematic evaluation by means of a phantom study. An urological trainee and two experts conducted 53 punctures on kidney phantoms. RESULTS : The trainee performed best with the proposed AR system in terms of puncturing time (mean: 99 s), whereas the experts performed best with fluoroscopy (mean: 59 s). iPad assistance lowered radiation exposure by a factor of 3 for the inexperienced physician and by a factor of 1.8 for the experts in comparison with fluoroscopy usage. We achieve a mean visualization accuracy of 2.5 mm. CONCLUSIONS : The proposed tablet computer-based AR system has proven helpful in assisting percutaneous interventions such as PCNL and shows benefits compared to other state-of-the-art assistance systems. A drawback of the system in its current state is the lack of depth information. Despite that, the simple integration into the clinical workflow highlights the potential impact of this approach to such interventions.
    Type of Publication: Journal article published
    PubMed ID: 23526436
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