How patient-specific do internal carotid artery inflow rates need to be for computational fluid dynamics of cerebral aneurysms?

BACKGROUND: Computational fluid dynamics (CFD) has become a popular tool for studying 'patient-specific' blood flow dynamics in cerebral aneurysms; however, rarely are the inflow boundary conditions patient-specific. We aimed to test the impact of widespread reliance on generalized inflow rates. METHODS: Internal carotid artery (ICA) flow rates were measured via 2D cine phase-contrast MRI for 24 patients scheduled for endovascular therapy of an ICA aneurysm. CFD models were constructed from 3D rotational angiography, and pulsatile inflow rates imposed as measured by MRI or estimated using an average older-adult ICA flow waveform shape scaled by a cycle-average flow rate (Qavg) derived from the patient's ICA cross-sectional area via an assumed inlet velocity. RESULTS: There was good overall qualitative agreement in the magnitudes and spatial distributions of time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and spectral power index (SPI) using generalized versus patient-specific inflows. Sac-averaged quantities showed moderate to good correlations: R2=0.54 (TAWSS), 0.80 (OSI), and 0.68 (SPI). Using patient-specific Qavg to scale the generalized waveform shape resulted in near-perfect agreement for TAWSS, and reduced bias, but not scatter, for SPI. Patient-specific waveform had an impact only on OSI correlations, which improved to R2=0.93. CONCLUSIONS: Aneurysm CFD demonstrates the ability to stratify cases by nominal hemodynamic 'risk' factors when employing an age- and vascular-territory-specific recipe for generalized inflow rates. Qavg has a greater influence than waveform shape, suggesting some improvement could be achieved by including measurement of patient-specific Qavg into aneurysm imaging protocols.

Feasibility of synthetic MRI in knee imaging in routine practice.

BACKGROUND: Synthetic magnetic resonance (MR) is a method allowing reduction of examination time and access to quantitative imaging. PURPOSE: This study sought to assess the image quality and diagnostic accuracy of synthetic magnetic resonance imaging (MRI) compared to standard MRI in patients with knee pain. MATERIAL AND METHODS: In total, 22 patients underwent standard 1.5 knee MRI with an added synthetic sequence. Quantitative T1, T2, and proton density (PD) images were generated synthetically; T1, PD, and short tau inversion recovery (STIR) weighted images were created with chosen echo time (TE), repetition time (TR), and inversion time (TI). Two blinded musculoskeletal radiologists evaluated the overall sequence quality, visualization of anatomic structures, and presence of artifacts using a 3-point score. RESULTS: The synthetic sequence was acquired in 39% less time than the conventional MRI. Synthetic PD, T1, and STIR images were rated fair (2%, 5%, and 2%, respectively) or good quality (98%, 95%, and 98%, respectively), despite the presence of popliteal artery artifacts. Cartilage and meniscus were well visualized in all cases. Anterior cruciate ligament visualization was rated poor in 7%, 14%, and 30% of PD, STIR, and T1 images, respectively. CONCLUSION: Our pilot study confirmed the feasibility of synthetic MRI in knee examinations, proving faster and achieving appropriate quality and good diagnostic confidence.