V Schulz

Publications (3)4.53 Total impact

• Conference Proceeding: MR-based attenuation correction for whole-body PET/MR system

  Z. Hu, S. Renisch, B. Schweizer, T. Blaffert, N. Ojha, T. Guo, J. Tang, C. Tung, J. Kaste, V. Schulz, I. Torres, L. Shao
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  ABSTRACT: Philips has introduced the world's first whole body sequential PET/MR system. We present the current status of MR-based attenuation correction (MRAC) technique. MRAC consists of MR image acquisition, segmentation, truncation compensation (TC), μ-value assignment, as well as correction for patient table and RF coils. These components have been described last year; this paper focuses on updates of the two most critical steps of MRAC: segmentation and TC. The segmentation algorithm attempts to distinguish 3 biological classes: air, lungs, and soft tissue. It combines an intensity-based region-growing technique with lung-model adaptation. For TC, the following three-step approach to correct for truncation in the MR-based attenuation maps has been developed and investigated: (A) Areas in the attenuation map which are possibly truncated are identified. (B) For these areas, an estimate of the outer patient contour is extracted from a registered PET image which is reconstructed without attenuation correction. (C) Truncation correction areas as extracted from the PET contours are added to attenuation map. The segmentation algorithm was applied to a number of datasets from a large pool of volunteers from multiple MR systems. The algorithm yields expected results except for susceptibility and motion artifacts. While the truncation compensation algorithm works for most cases, the robustness needs to be further improved.
  Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
• Article: Automatic, three-segment, MR-based attenuation correction for whole-body PET/MR data.

  V Schulz, I Torres-Espallardo, S Renisch, Z Hu, N Ojha, P Börnert, M Perkuhn, T Niendorf, W M Schäfer, H Brockmann, T Krohn, A Buhl, R W Günther, F M Mottaghy, G A Krombach
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  ABSTRACT: The combination of positron emission tomography (PET) and magnetic resonance (MR) tomography in a single device is anticipated to be the next step following PET/CT for future molecular imaging application. Compared to CT, the main advantages of MR are versatile soft tissue contrast and its capability to acquire functional information without ionizing radiation. However, MR is not capable of measuring a physical quantity that would allow a direct derivation of the attenuation values for high-energy photons. To overcome this problem, we propose a fully automated approach that uses a dedicated T1-weighted MR sequence in combination with a customized image processing technique to derive attenuation maps for whole-body PET. The algorithm automatically identifies the outer contour of the body and the lungs using region-growing techniques in combination with an intensity analysis for automatic threshold estimation. No user interaction is required to generate the attenuation map. The accuracy of the proposed MR-based attenuation correction (AC) approach was evaluated in a clinical study using whole-body PET/CT and MR images of the same patients (n = 15). The segmentation of the body and lung contour (L-R directions) was evaluated via a four-point scale in comparison to the original MR image (mean values >3.8). PET images were reconstructed using elastically registered MR-based and CT-based (segmented and non-segmented) attenuation maps. The MR-based AC showed similar behaviour as CT-based AC and similar accuracy as offered by segmented CT-based AC. Standardized uptake value (SUV) comparisons with reference to CT-based AC using predefined attenuation coefficients showed the largest difference for bone lesions (mean value ± standard variation of SUV(max): -3.0% ± 3.9% for MR; -6.5% ± 4.1% for segmented CT). A blind comparison of PET images corrected with segmented MR-based, CT-based and segmented CT-based AC afforded identical lesion detectability, but slight differences in image quality were found. Our MR-based attenuation correction method offers similar correction accuracy as offered by segmented CT. According to the specialists involved in the blind study, these differences do not affect the diagnostic value of the PET images.
  European Journal of Nuclear Medicine 10/2010; 38(1):138-52. · 4.53 Impact Factor
• Conference Proceeding: MR-based attenuation correction for a whole-body sequential PET/MR system

  Z. Hu, N. Ojha, S. Renisch, V. Schulz, I. Torres, A. Buhl, D. Pal, G. Muswick, J. Penatzer, T. Guo, P. Bonert, C. Tung, J. Kaste, M. Morich, T. Havens, P. Maniawski, W. Schafer, R.W. Gunther, G.A. Krombach, L. Shao
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  ABSTRACT: In this paper MR-based attenuation method was implemented for a clinical whole-body PET/MR system. While awaiting future clinical evaluation, the algorithm seems promising from preliminary patient data evaluation, from both qualitative PET image quality and quantification accuracy. While the 3-segment MRAC resembles the results from short PET transmission scans, future work will be to implement and validate segmentation of more tissue classes, such as cortical bone. Robustness of MR image truncation compensation and incorporation of flexible coils need to be improved.
  Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009