Synthesis of Patient-Specific Transmission Data for PET Attenuation Correction for PET/MRI Neuroimaging Using a Convolutional Neural Network

Attenuation correction is a notable challenge associated with simultaneous PET/MRI, particularly in neuroimaging, where sharp boundaries between air and bone volumes exist. This challenge leads to concerns about the visual and, more specifically, quantitative accuracy of PET reconstructions for data obtained with PET/MRI. Recently developed techniques can synthesize attenuation maps using only MRI data and are likely adequate for clinical use; however, little work has been conducted to assess their suitability for the dynamic PET studies frequently used in research to derive physiologic information such as the binding potential of neuroreceptors in a region. At the same time, existing PET/MRI attenuation correction methods are predicated on synthesizing CT data, which is not ideal, as CT data are acquired with much lower-energy photons than PET data and thus do not optimally reflect the PET attenuation map. Methods: We trained a convolutional neural network to generate patient-specific transmission data from T1-weighted MRI. Using the trained network, we generated transmission data for a testing set comprising 11 subjects scanned with C-11-labeled N-[2-]4-(2-methoxyphenyl)-1-piperazinyl]ethyl]N-( 2-pyridinyl)cyclohexanecarboxamide) (C-11-WAY-100635) and 10 subjects scanned with C-11-labeled 3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)benzonitrile (C-11-DASB). We assessed both static and dynamic reconstructions. For dynamic PET data, we report differences in both the nondisplaceable and the free binding potential for C-11-WAY-100635 and distribution volume for C-11-DASB. Results: The mean bias for generated transmission data was -1.06% +/- 0.81%. Global biases in static PET uptake were -0.49% +/- 1.7%, and -1.52% +/- 0.73% for C-11-WAY-100635 and C-11-DASB, respectively. Conclusion: Our neural network approach is capable of synthesizing patient-specific transmission data with sufficient accuracy for both static and dynamic PET studies.