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Automatic, three-segment, MR-based attenuation correction for whole-body PET/MR data

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European Journal of Nuclear Medicine and Molecular Imaging Aims and scope Submit manuscript

Abstract

Purpose

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.

Methods

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.

Results

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 SUVmax: −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.

Conclusion

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.

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Acknowledgment

This work was supported by the EU FP7 project HYPERImage (grant agreement 201651).

Conflicts of interest

The first seven authors are employees of Philips.

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Authors and Affiliations

  1. Department of Molecular Imaging Systems, Philips Research Europe, Weishausstrasse 2, 52066, Aachen, Germany

    V. Schulz

  2. Philips Research Europe, Aachen, Germany

    I. Torres-Espallardo & M. Perkuhn

  3. Department of Diagnostic Radiology, RWTH Aachen University, Aachen, Germany

    I. Torres-Espallardo, M. Perkuhn, T. Niendorf, A. Buhl, R. W. Günther & G. A. Krombach

  4. Institute of Imaging & Computer Vision, RWTH Aachen University, Aachen, Germany

    I. Torres-Espallardo

  5. Philips Research Europe, Hamburg, Germany

    S. Renisch & P. Börnert

  6. Philips Healthcare, Cleveland, OH, USA

    Z. Hu & N. Ojha

  7. Max-Delbrueck Center for Molecular Medicine, Berlin, Germany

    T. Niendorf

  8. Department of Nuclear Medicine, RWTH Aachen University, Aachen, Germany

    W. M. Schäfer, H. Brockmann, T. Krohn & F. M. Mottaghy

  9. Department of Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany

    V. Schulz

Authors
  1. V. Schulz
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  2. I. Torres-Espallardo
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  3. S. Renisch
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  4. Z. Hu
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  13. R. W. Günther
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  15. G. A. Krombach
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Correspondence to V. Schulz.

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Schulz, V., Torres-Espallardo, I., Renisch, S. et al. Automatic, three-segment, MR-based attenuation correction for whole-body PET/MR data. Eur J Nucl Med Mol Imaging 38, 138–152 (2011). https://doi.org/10.1007/s00259-010-1603-1

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  • DOI: https://doi.org/10.1007/s00259-010-1603-1

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