PET and MRI are two powerful imaging technologies that are characterized by high sensitivity and the ability to provide superior anatomic detail, respectively, which might make them ideal for evaluating the upper abdomen. However, PET requires long acquisition times, including the acquisition of data from moving organs, which may result in image blurring. On the other hand, MRI, especially standard DCE-MRI, can scan the chosen field of view in a shorter time, but requires the patient’s cooperation with the respiratory instructions and the ability to suspend respiration for the acquisition time of breath-hold sequences, usually in the range 14–20 s. Moreover, even in patients with an adequate respiratory breath-hold ability, the quality and the diagnostic information of DCE-MRI are also dependent on the hemodynamics of the patient and the timing of contrast agent injection and data acquisition. These variables explain the occurrence of respiratory artifacts and erroneous phases of contrast enhancement imaging in DCE-MRI.
After developing a novel self-navigated method that simultaneously corrects both PET data and DCE-MRI data for respiratory motion without increasing acquisition times, we focused on investigating its clinical performance and to compare the motion-corrected (MoCo) and uncorrected (non-MoCo) PET, MRI and fused PET/MRI data (Catalano 2018).
In this study, the quality of MoCo PET images was found to be higher than that of non-MoCo PET images. The improved quantitation allowed by MoCo PET might be clinically relevant. In fact, besides the contribution of PET quantitation to discriminating benign from malignant lesions, assessment of treatment response relies on measured differences in SUVmax and MTV along with possible complete visual disappearance of metabolically active lesions.
Furthermore, MoCo DCE-MRI might improve the overall quality of the data in patients unable to follow breathing instructions (deaf patients, patients with a different first language, or patients unable to hear the voice of the technologist while gradients are on), and in those with hemodynamic compromise in whom timing of arterial and portal venous phase imaging is challenging. The higher quality provided by fused PET/MRI data after MoCo has important clinical implications, as in the case of small but metabolically active lesions whose anatomic correlate might be difficult to identify. This is especially true when metabolic PET data are improperly fused over the MR anatomic overlay.