Fast retrospectively triggered local pulse-wave velocity measurements in mice with CMR-microscopy using a radial trajectory

Abstract

BackgroundThe aortic pulse-wave velocity (PWV) is an important indicator of cardiovascular risk. In recent studies MRI methods have been developed to measure this parameter noninvasively in mice. Present techniques require additional hardware for cardiac and respiratory gating. In this work a robust self-gated measurement of the local PWV in mice without the need of triggering probes is proposed.MethodsThe local PWV of 6-months-old wild-type C57BL/6J mice (n=6) was measured in the abdominal aorta with a retrospectively triggered radial Phase Contrast (PC) MR sequence using the flow-area (QA) method. A navigator signal was extracted from the CMR data of highly asymmetric radial projections with short repetition time (TR=3 ms) and post-processed with high-pass and low-pass filters for retrospective cardiac and respiratory gating. The self-gating signal was used for a reconstruction of high-resolution Cine frames of the aortic motion. To assess the local PWV the volume flow Q and the cross-sectional area A of the aorta were determined. The results were compared with the values measured with a triggered Cartesian and an undersampled triggered radial PC-Cine sequence.ResultsIn all examined animals a self-gating signal could be extracted and used for retrospective breath-gating and PC-Cine reconstruction. With the non-triggered measurement PWV values of 2.3±0.2 m/s were determined. These values are in agreement with those measured with the triggered Cartesian (2.4±0.2 m/s) and the triggered radial (2.3±0.2 m/s) measurement. Due to the strong robustness of the radial trajectory against undersampling an acceleration of more than two relative to the prospectively triggered Cartesian sampling could be achieved with the retrospective method.ConclusionWith the radial flow-encoding sequence the extraction of a self-gating signal is feasible. The retrospective method enables a robust and fast measurement of the local PWV without the need of additional trigger hardware.

Cardiac 4D phase-contrast CMR at 9.4 T using self-gated ultra-short echo time (UTE) imaging

“…As has been already demonstrated in the literature [34, 48, 49], precise trajectory measurements are crucial and of utmost importance to obtain good image quality with radial imaging techniques. Since trajectory errors might also influence the calculated flow velocities, we used a vendor supplied calibration [42], which measures the trajectory through k -space in all three spatial dimensions based on the actually applied imaging gradients.…”

“…Nevertheless, shortening the acquisition time further or increasing spatial resolution the presented 4D PC UTE technique might benefit from applying Compressed Sensing [51], 3D Radial GRAPPA [52] or even a combination of these techniques [53] in order to compensate for larger under-sampling factors. However, it has to be pointed out that it is currently not clear to what extent the application of acceleration techniques in combination with a center-out radial 3D sampling will influence the reliability of the calculated flow maps [49]. …”

“…However, as shown with a recently proposed self-gated 2D PC radial FLASH sequence [49] using golden-angle based rotation angles [54] or the extension to 3D center-out radial sampling [55, 56], k -space homogeneity after self-gating can be further increased which consequently allows for further shortening of the total acquisition time.…”

Review of Journal of Cardiovascular Magnetic Resonance 2013

“…Previous techniques for measurement of PWV in mice required cardiac and respiratory gating. The authors developed a robust self-gated method to measure PWV without the need for triggering [ 24 ]. This method will be useful for the study of transgenic mice with altered vascular function.…”

Velocity mapping of the aortic flow at 9.4 T in healthy mice and mice with induced heart failure using time-resolved three-dimensional phase-contrast MRI (4D PC MRI)

“…While slice-selective PC MRI is a standard tool for preclinical studies [ 22 – 26 ], the application of 4D PC MRI on small-animal MRI systems is still challenging. As high technical requirements are necessary, the approaches that have been developed thus far for three-dimensional PC MRI in small animals are all based on multi-slice acquisition techniques [ 27 , 28 ].…”