MRI-driven PET quantification

 

The combination of PET with MRI raises new challenges in terms of image quantification that need to be addressed to validate the quantitative accuracy achieved on these machines. Two aspects will be carefully investigated: PET attenuation correction and MRI driven motion correction.

 

Attenuation correction is based on the electron density of the tissues, which is provided by the X-ray CT in PET-CT systems. Unlike CT, MRI does not provide such information and cannot be used directly to derive attenuation coefficients. Several new strategies are being developed to deduce attenuation coefficients from MRI scans or from PET data. It is unlikely that a single method alone will be sufficient to address efficiently this problem. We will evaluate the combined use of time-of-flight PET data and specific MR sequences for the estimation of the PET attenuation map for brain and whole-body imaging, and compare its performance against the methods provided by the PET/MR manufacturers.

 

Motion, especially respiratory and cardiac motions, introduces artifacts and quantitative biases in PET images. This issue of patient motion is more severe in high spatial and temporal resolution imaging, such as provided by PET-MRI. Simultaneous PET-MRI is very appealing for motion compensation, since techniques such as multiple navigator echoes or MR tagging can be used to measure 3-dimensional motion fields, which can then be incorporated into the iterative PET reconstruction to obtain motion-corrected PET images. Yet, corresponding PET-MRI acquisition protocols remain to be optimized as the duration of the MRI tagged acquisition prevents from acquiring other relevant MRI data simultaneously with the PET scan. Motion correction strategies will be implemented and/or validated on our PET-MRI machine, for protocols significantly penalized by organ motions.

 

 

Partners:

 

 

 

 

 

Project Leader : Claude Comtat (CEA SHFJ)