May 17 – 20, 2015
La Biodola, Isola d'Elba
Europe/Rome timezone

PET/MR: Improvement of the UTE μ-Maps Using Modified MLAA

May 19, 2015, 11:00 AM
Room Maria Luisa

Room Maria Luisa

Talk 6 - Whole-body and dedicated organ MR-PET Session 6 - Whole-body and dedicated organ MR-PET


Didier Benoit (Rigshospitalet)


For a quantitative analysis in positron emission tomography (PET) or single-photon emission computed tomography (SPECT), attenuation correction (AC) is mandatory. CT-scans or transmission scans are common tools for determination of the attenuation μ-map, but in the case of a PET/MR hybrid system it is difficult to associate one of these scans. Many techniques have been developed in order to improve AC for PET/MR. Some methods are based on template- or atlas techniques, other methods apply a segmentation technique based on Dixon or UTE (Ultrashort Echo Time) MR to create the μ-map, followed by a standard OSEM reconstruction (OSEM/DIXON and OSEM/UTE). A different approach for AC has been developed by employing the emission sinogram data in the μ-map derivation. In this context, we modified the iterative MLAA (Maximum-Likelihood reconstruction of Attenuation and Activity) algorithm to improve the resulting emission image from the PET/MR system. We constrained the attenuation map update using the UTE μ-map and the T1-weighted (T1w) MR image in order to improve convergence towards a solution. Results show that the modified MLAA algorithm improved the estimated emission image compared to standard OSEM/UTE and OSEM/DIXON. In certain regions of the brain, in particular close to the skull and the air cavities, the modified MLAA algorithm generated less error than OSEM/UTE and OSEM/Dixon. The modified MLAA algorithm is able to compute an attenuation μ-map that is slightly more similar to the aligned CT μ-map than the UTE μ-map.

Primary author

Didier Benoit (Rigshospitalet)


Mr Adam Espe Hansen (Department of Clinical Physiology, Nuclear Medicine and PET; Rigshospitalet; Denmark) Mr Ahmadreza Rezaei (University of Leuven) Mr Claes Ladefoged (Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet Copenhagen, DK) Dr Flemming Andersen (Rigshospitalet, University of Copenhagen) Dr Johan Nuyts (University of Leuven) Dr Liselotte Højgaard (Rigshospitalet, University of Copenhagen) Mr Sune Keller (Rigshospitalet, University of Copenhagen) Dr Søren Holm (Rigshospitalet, University of Copenhagen)

Presentation materials