Advancements in Positron Emission Tomography/Magnetic Resonance Imaging and Applications to Diagnostic Challenges in Neuroradiology.

Since the clinical adoption of magnetic resonance (MR) in medical imaging, MR has proven to be a workhorse in diagnostic neuroradiology, with the ability to provide superb anatomic detail as well as additional functional and physiologic data, depending on the techniques utilized. Positron emission tomography/computed tomography has also shown irreplaceable diagnostic value in certain disease processes of the central nervous system by providing molecular and metabolic information through the development of numerous disease-specific PET tracers, many of which can be utilized as a diagnostic technique in and of themselves or can provide a valuable adjunct to information derived from MR. Despite these advances, many challenges still remain in neuroradiology, particularly in malignancy, neurodegenerative disease, epilepsy, and cerebrovascular disease. Through improvements in attenuation correction, motion correction, and PET detectors, combining the 2 modalities of PET and MR through simultaneous imaging has proven feasible and allows for improved spatial and temporal resolution without compromising either of the 2 individual modalities. The complementary information offered by both technologies has provided increased diagnostic accuracy in both research and many clinical applications in neuroradiology.

Left and right ventricular kinetic energy using time-resolved versus time-average ventricular volumes.

PURPOSE: To measure the effects of using time-resolved (TR) versus time-averaged (TA) ventricular segmentation on four-dimensional flow-sensitive (4D flow) magnetic resonance imaging (MRI) kinetic energy (KE) calculations. MATERIALS AND METHODS: Right (RV) and left (LV) ventricular KE was calculated from 4D flow MRI data acquired at 3.0T in 10 healthy volunteers and five subjects with cardiac disease using TR and TA segmentation. KE was calculated from the mass of blood within the ventricles multiplied by the velocities squared. Differences in TR and TA KE and interobserver variability were quantified with Bland-Altman analysis. RESULTS: In healthy volunteers, peak systolic RV KE (KERV ) were 4.89 ± 1.49 mJ using TR and 5.53 ± 1.62 mJ using TA segmentation (P = 0.016); peak systolic LV KE (KELV ) were 3.29 ± 0.96 mJ and 4.16 ± 1.26 mJ (P = 0.005). Peak diastolic KERV were 3.33 ± 0.90 mJ (TR) and 3.61 ± 1.12 mJ (TA) (P = 0.082), while peak diastolic KELV were 4.90 ± 1.49 mJ and 5.31 ± 1.59 mJ (P = 0.044). In patient volunteers, peak systolic KERV were 4.34 ± 3.78 mJ using TR and 4.88 ± 3.98 mJ using TA segmentation (P = 0.26); peak systolic KELV were 4.39 ± 4.21 mJ and 4.36 ± 3.84 mJ (P = 0.91). Peak diastolic KERV were 3.34 ± 2.08 mJ (TR) and 4.05 ± 1.12 mJ (TA) (P = 0.08), while peak diastolic KELV were 4.34 ± 5.11 mJ and 4.06 ± 3.47 mJ (P = 0.75). Interobserver differences in KELV were greater for TR than TA calculations; bias ranged from 3 ± 30% for TA peak systolic KELV to 36 ± 30% for TR peak diastolic KELV . CONCLUSION: Although qualitatively similar, KE values calculated through TA segmentation were consistently greater than TR KE, with differences more pronounced during systole and in the LV. LEVEL OF EVIDENCE: 2 J. Magn. Reson. Imaging 2017;45:821-828.