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

PET/MR Attenuation Correction in Brain Imaging Using a Continuous Bone Signal Derived from UTE

19 May 2015, 16:00
1h 30m
Room Elena

Room Elena

Poster 3 - Advances in MR-PET and MR-SPECT software and quantification Session 8 - Poster Session I

Speaker

Claes Ladefoged (Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet Copenhagen, DK)

Description

In the absence of transmission sources in combined clinical PET/MR systems, MR images are used for MR-based attenuation correction (MRAC). The main challenge in MR-AC is to separate the bone and air, as neither have a signal in the MR images. In the attenuation maps supplied by the vendor, a single value is assigned to bone using an ultra-short echo time (UTE) MR sequence. The purpose of this study was to develop a new multi-class segmentation-based MR-AC method, employing Continuous-Bone-using-R2* (MRAC_CBuR2*), and evaluate it on a large patient cohort. METHODS. 53 [18F]-FDG PET/MR brain patients were included in this study. MRAC was based on an aligned CT (MRAC_CT, used as reference), standard MRAC_UTE and MRAC_CBuR2*. Our method segments the air, brain, CSF and soft tissue voxels on the UTE images, and uses a mapping of R2* values to HU to measure the density in bone voxels. Aligned anatomical masks are used to improve accuracy in noisy regions. Region-based analysis was performed using ICBM 2009a brain atlas with anatomical labels pre-defined. RESULTS. Using CBuR2*, 82% of the voxels in the brain are within ±5% of PET_CT, compared to 27% when using UTE. Using our method, there are clear improvements over UTE. The average error over the full brain is 0.8% (±1.7%), compared to -7.1% (±2.4%) in UTE. Of note, the maximum error in the cerebellum is -15% and 7% in UTE and CBuR2*, respectively. CONCLUSIONS. The proposed method uses the available UTE images to segment tissue classes, and uses the R2* map to measure a continuous bone signal. The improvement over the vendor provided UTE reduces both the global and local error on the reconstructed PET images.

Primary author

Claes Ladefoged (Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet Copenhagen, DK)

Co-authors

Mr Adam Espe Hansen (Department of Clinical Physiology, Nuclear Medicine and PET; Rigshospitalet; Denmark) Dr Didier BENOIT (Rigshospitalet) Dr Flemming Littrup Andersen (Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet Copenhagen, DK) Prof. Ian Law (Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet Copenhagen, DK) Prof. Liselotte Højgaard (Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet Copenhagen, DK) Dr Søren Holm (Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet Copenhagen, DK)

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