Fast measurement of intracardiac pressure differences with 2D breath‐hold phase‐contrast MRI

Abstract

Intracardiovascular blood pressure differences can be derived from velocity images acquired with phase-contrast (PC) MRI by evaluating the Navier-Stokes equations. Pressure differences within a slice of interest can be calculated using only the inplane velocity components from that slice. This rapid exam is proposed as an alternative to the lengthy 3D velocity imaging exams. Despite their good spatial coverage, the 3D exams are prone to artifacts and errors from respiratory motion and insufficient temporal resolution, and are unattractive in the clinical setting due to their excessive scan times (>10 min of free breathing). The proposed single-slice approach requires only one or two breath-holds of acquisition time, and the velocity data can be processed for the calculation of pressure differences online with immediate feedback. The impact of reducing the pressure difference calculation to two dimensions is quantified by comparison with 3D data sets for the case of blood flow within the cardiac chambers. The calculated pressure differences are validated using high-fidelity pressure transducers both in a pulsatile flow phantom and in vivo in a dog model. There was excellent agreement between the transducer and PC-MRI results in all of the studies.

Improving computation of cardiovascular relative pressure fields from velocity MRI

“…Also in vivo comparisons with invasive catheter measurements have been performed. A study performed in the heart, a predominantly convex geometry, resulted in good agreement (17), whereas results obtained in the aorta showed an underestimation by pressure differences computed from velocity MRI (20). The authors argue that this difference was mainly caused by temporal smoothing due to an insufficient temporal resolution, as well as an averaging effect originating from the segmented data acquisition over many heart cycles.…”

“…Use of an iterative approach with a quasirectangular domain has become popular for the computation of relative pressure fields from velocity MRI due to its simplicity (13,(17)(18)(19)(20). The computational intensity required has often been mentioned as the main drawback of this method (14).…”

“…A popular workaround has been to use a modified, quasirectangular domain by solving the problem iteratively on the rectangular bounding box of the domain using different variants of the Jacobian method and repeatedly modifying the pressure gradients outside the domain to match the concurrent pressure solution. Using this method, relative pressure fields in the left ventricular (14,17,18) and aortic cavities (19,20) have been described.…”

“…The accuracy of the pressure field computation from velocity MRI using this method has been validated extensively using both phantom studies and in vivo comparisons with catheter measurements (17,18,20,21), but mainly for structures of interest with simple geometries, such as the approximately spherical cardiac chambers. The obtained pressure field may be less accurate for structures with more complex external or internal configurations.…”

Noninvasive Measurement of Intra-Aneurysmal Pressure and Flow Pattern Using Phase Contrast with Vastly Undersampled Isotropic Projection Imaging

“…Numerous investigators have explored the impact of flow in relationship to aneurysm morphology by using techniques such as digital subtraction angiography (DSA) [5][6][7][8][9][10][11][12][13][14] and computational flow dynamics (CFD). [15][16][17][18][19][20] However, these methods require an invasive procedure.…”