New way to correct data distortions benefits PET/MR

Jun 18, 2009

Researchers from Philips Healthcare of Andover, MA, offered new details on the company's development of a hybrid PET/MRI scanner at this week's annual SNM meeting in Toronto.

A research team led by André Salomon from Philips Research division in Aachen, Germany, discussed the development of an attenuation map for a PET/MRI scanner that uses anatomic reference data from MRI and gamma attenuation from PET emission data.

Besides the unique benefits of this new hybrid modality, MRI, unfortunately, does not provide a direct measurement of attenuation coefficients for 511 keV photons as does CT, which is one of the key prerequisites for quantitative PET. Thus, several research groups are addressing this topic with segmentation, atlas-based registration, and computer learning techniques using databases with MR and corresponding CT images.

Salomon and colleagues propose a new iterative reconstruction approach to simultaneously compute the activity and attenuation distribution using a segmented MR image as geometrical reference. The main advantage over other approaches is the use of the true physical attenuation of the 511 keV photons provided by the PET list mode data.

The approach uses what the researchers describe as "a discrete consistency condition from which a maximum likelihood estimation of the activity and attenuation is derived."

First results from simulated and measured clinical data, compared to reference data achieved using CT attenuation maps, indicate "an excellent agreement between both correction techniques," the study noted.

Researchers also observed that performing time-of-flight (TOF) reconstruction and previous region segmentation minimized inherent "crosstalk" between the activity and attenuation estimation.

Their conclusion is that the proposed hybrid method using PET and MRI data leads to "more robust and accurate attenuation correction, which is a significant step toward quantitative PET/MR."

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