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PET/MR imaging of bone lesions – implications for PET quantification from imperfect attenuation correction

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

Abstract

Purpose

Accurate attenuation correction (AC) is essential for quantitative analysis of PET tracer distribution. In MR, the lack of cortical bone signal makes bone segmentation difficult and may require implementation of special sequences. The purpose of this study was to evaluate the need for accurate bone segmentation in MR-based AC for whole-body PET/MR imaging.

Methods

In 22 patients undergoing sequential PET/CT and 3-T MR imaging, modified CT AC maps were produced by replacing pixels with values of >100 HU, representing mostly bone structures, by pixels with a constant value of 36 HU corresponding to soft tissue, thereby simulating current MR-derived AC maps. A total of 141 FDG-positive osseous lesions and 50 soft-tissue lesions adjacent to bones were evaluated. The mean standardized uptake value (SUVmean) was measured in each lesion in PET images reconstructed once using the standard AC maps and once using the modified AC maps. Subsequently, the errors in lesion tracer uptake for the modified PET images were calculated using the standard PET image as a reference.

Results

Substitution of bone by soft tissue values in AC maps resulted in an underestimation of tracer uptake in osseous and soft tissue lesions adjacent to bones of 11.2 ± 5.4 % (range 1.5–30.8 %) and 3.2 ± 1.7 % (range 0.2–4 %), respectively. Analysis of the spine and pelvic osseous lesions revealed a substantial dependence of the error on lesion composition. For predominantly sclerotic spine lesions, the mean underestimation was 15.9 ± 3.4 % (range 9.9–23.5 %) and for osteolytic spine lesions, 7.2 ± 1.7 % (range 4.9–9.3 %), respectively.

Conclusion

CT data simulating treating bone as soft tissue as is currently done in MR maps for PET AC leads to a substantial underestimation of tracer uptake in bone lesions and depends on lesion composition, the largest error being seen in sclerotic lesions. Therefore, depiction of cortical bone and other calcified areas in MR AC maps is necessary for accurate quantification of tracer uptake values in PET/MR imaging.

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Acknowledgments

The authors thank Albert Lonn for useful discussions.

Research support

This work was supported in part by a research grant from GE Healthcare, Waukesha, WI, USA.

Conflicts of interest

One of the authors (S.W.) is an employee of GE HealthCare, Waukesha WI, USA.

The research group receives research support from GE Healthcare.

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Authors and Affiliations

  1. Department of Medical Radiology, University Hospital of Zurich, Zurich, Switzerland

    Andrei Samarin, Cyrill Burger, David W. Crook, Irene A. Burger, Daniel T. Schmid, Gustav K. von Schulthess & Felix P. Kuhn

  2. GE Healthcare, Waukesha, WI, USA

    Scott D. Wollenweber

  3. Nuclear Medicine, University Hospital Zurich, Rämistrasse 100, 8091, Zurich, Switzerland

    Andrei Samarin

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  1. Andrei Samarin
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  2. Cyrill Burger
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  5. Irene A. Burger
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  7. Gustav K. von Schulthess
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Correspondence to Andrei Samarin.

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Samarin, A., Burger, C., Wollenweber, S.D. et al. PET/MR imaging of bone lesions – implications for PET quantification from imperfect attenuation correction. Eur J Nucl Med Mol Imaging 39, 1154–1160 (2012). https://doi.org/10.1007/s00259-012-2113-0

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  • DOI: https://doi.org/10.1007/s00259-012-2113-0

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