European journal of radiology
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Review
Pulmonary hyperpolarized noble gas MRI: recent advances and perspectives in clinical application.
The invention of hyperpolarized (HP) noble gas MRI using helium-3 ((3)He) or xenon-129 ((129)Xe) has provided a new method to evaluate lung function. Using HP (3)He or (129)Xe for inhalation into the lung air spaces as an MRI contrast agent significantly increases MR signal and makes pulmonary ventilation imaging feasible. This review focuses on important aspects of pulmonary HP noble gas MRI, including the following: (1) functional imaging types, (2) applications for major pulmonary diseases, (3) safety considerations, and (4) future directions. Although it is still challenging to use pulmonary HP noble gas MRI clinically, the technology offers promise for the investigation of the microstructure and function of the lungs.
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In combined PET/MRI standard PET attenuation correction (AC) is based on tissue segmentation following dedicated MR sequencing and, typically, bone tissue is not represented. We evaluate PET quantification in whole-body (WB)-PET/MRI following MR-AC without considering bone attenuation and then investigate different strategies to account for bone tissue in clinical PET/MR imaging. To this purpose, bone tissue representation was extracted from separate CT images, and different bone representations were simulated from hypothetically derived MR-based bone classifications. ⋯ In PET/MR imaging using standard MR-AC PET uptake values in soft lesions and bone lesions are underestimated by about 10%. In individual patients this bias can be as high as 22%, which is significant during clinical follow-up exams. If bone segmentation is available, then assigning a fixed attenuation value of spongious bone to all bone structures appears reasonable and results in only a minor bias of 5%, or less in uptake values of soft tissue and bone lesions.