MR-based attenuation correction for torso-PET/MR imaging: pitfalls in mapping MR to CT data
MR-based attenuation correction (AC) will become an integral part of combined PET/MR systems. Here, we propose a toolbox to validate MR-AC of clinical PET/MRI data sets.
Torso scans of ten patients were acquired on a combined PET/CT and on a 1.5-T MRI system. MR-based attenuation data were derived from the CT following MR–CT image co-registration and subsequent histogram matching. PET images were reconstructed after CT- (PETCT) and MR-based AC (PETMRI). Lesion-to-background (L/B) ratios were estimated on PETCT and PETMRI.
MR–CT histogram matching leads to a mean voxel intensity difference in the CT- and MR-based attenuation images of 12% (max). Mean differences between PETMRI and PETCT were 19% (max). L/B ratios were similar except for the lung where local misregistration and intensity transformation leads to a biased PETMRI.
Our toolbox can be used to study pitfalls in MR-AC. We found that co-registration accuracy and pixel value transformation determine the accuracy of PETMRI.
KeywordsPET/MRI PET/CT Attenuation correction
We thank our technologists from the Department of Radiology and Nuclear Medicine for their support in acquiring the clinical data.
The selection, validation and implementation of the co-registration algorithms were supported by the German Research Foundation (DFG): BE 3169/2-2.
- 3.Schlemmer H, Pichler B, Wienhard K, Schmand M, Nahmias C, Townsend D, et al. Simultaneous MR/PET for brain imaging: first patient scans. J Nucl Med. 2007;48(6):45P.Google Scholar
- 5.Hofmann M, Steinke F, Judenhofer M, Claussen C, Schoelkopf B, Pichler B. A machine learning approach for determining the PET attenuation map from magnetic resonance images. In: IEEE Nuclear Science Symposium and Medical Imaging Conference; 2006; San Diego, CA: IEEE; 2006.Google Scholar
- 8.Weigert M, Beyer T, Quick HH, Pietrzyk U, Palm C, Müller SP. Generation of a MRI reference data set for the validation of automatic, non-rigid image co-registration algorithms. Nuklearmedizin. 2007;46(2):A116.Google Scholar
- 10.Martínez-Möller A, Souvatzoglou M, Botnar R, Navab N, Ziegler S, Schwaiger M, et al. An approach for MR-based attenuation correction for combined MR/PET: effects of ignoring bones. J Nucl Med. 2007;48(suppl 2):156.Google Scholar