Composite attenuation correction method using a Ge-transmission multi-atlas for quantitative brain PET/MR.

In positron emission tomography (PET), Ge-transmission scanning is considered the gold standard in attenuation correction (AC) though not available in current dual imaging systems. In this experimental study we evaluated a novel AC method for PET/magnetic resonance (MR) imaging which is essentially based on a composite database of multiple Ge-transmission maps and T1-weighted (T1w) MR image-pairs (composite transmission, CTR-AC). This proof-of-concept study used retrospectively a database with 125 pairs of co-registered Ge-AC maps and T1w MR images from anatomical normal subjects and a validation dataset comprising dynamic [C]PE2I PET data from nine patients with Parkinsonism. CTR-AC maps were generated by non-rigid image registration of all database T1w MRI to each subject's T1w, applying the same transformation to every Ge-AC map, and averaging the resulting Ge-AC maps. [C]PE2I PET images were reconstructed using CTR-AC and a patient-specific Ge-AC map as the reference standard. Standardized uptake values (SUV) and quantitative parameters of kinetic analysis were compared, i.e., relative delivery (R) and non-displaceable binding potential (BP). CTR-AC showed high accuracy for whole-brain SUV (mean %bias ± SD: 0.5 ± 3.5%), whole-brain R (-0.1 ± 3.2%), and putamen BP (3.7 ± 8.1%). SUV and R precision (SD of %bias) were modest and lowest in the anterior cortex, with an R %bias of -1.1 ± 6.4%). The prototype CTR-AC is capable of providing accurate MRAC-maps with continuous linear attenuation coefficients though still experimental. The method's accuracy is comparable to the best MRAC methods published so far, both in SUV and as found for ZTE-AC in quantitative parameters of kinetic modelling.