Visualization of Human Aortic Valve Dynamics Using Magnetic Resonance Imaging with Sub-Millisecond Temporal Resolution

Abstract

Background: Visualization of aortic valve dynamics is important in diagnosing valvular diseases but is challenging to perform with magnetic resonance imaging (MRI) due to the limited temporal resolution.

Purpose: To develop an MRI technique with sub-millisecond temporal resolution and demonstrate its application in visualizing rapid aortic valve opening and closing in human subjects in comparison with echocardiography and conventional MRI techniques.

Study type: Prospective.

Population: Twelve healthy subjects.

Field strength/sequence: 3 T; gradient-echo-train-based sub-millisecond periodic event encoded imaging (get-SPEEDI) and balanced steady-state free precession (bSSFP).

Assessment: Images were acquired using get-SPEEDI with a temporal resolution of 0.6 msec. get-SPEEDI was triggered by an electrocardiogram so that each echo in the gradient echo train corresponded to an image at a specific time point, providing a time-resolved characterization of aortic valve dynamics. For comparison, bSSFP was also employed with 12 msec and 24 msec temporal resolutions, respectively. The durations of the aortic valve rapid opening (T_ro ), rapid closing (T_rc ), and the maximal aortic valve area (AVA) normalized to height were measured with all three temporal resolutions. M-mode echocardiograms with a temporal resolution of 0.8 msec were obtained for further comparison.

Statistical test: Parameters were compared between the three sequences, together with the echocardiography results, with a Mann-Whitney U test.

Results: Significantly shorter T_ro (mean ± SD: 27.5 ± 6.7 msec) and T_rc (43.8 ± 11.6 msec) and larger maximal AVA/height (2.01 ± 0.29 cm² /m) were measured with get-SPEEDI compared to either bSSFP sequence (T_ro of 56.3 ± 18.8 and 63.8 ± 20.2 msec; T_rc of 68.2 ± 16.6 and 72.8 ± 18.2 msec; maximal AVA/height of 1.63 ± 0.28 and 1.65 ± 0.32 cm² /m for 12 msec and 24 msec temporal resolutions, respectively, P < 0.05). In addition, the get-SPEEDI results were more consistent with those measured using echocardiography, especially for T_ro (29.0 ± 4.1 msec, P = 0.79) and T_rc (41.6 ± 4.3 msec, P = 0.16). DATA CONCLUSION: get-SPEEDI allows for visualization of human aortic valve dynamics and provided values closer to those measured using echocardiography than the bSSFP sequences.

Level of evidence: 1 TECHNICAL EFFICACY STAGE: 1.

Keywords: aortic valve; aortic valve area; cardiovascular magnetic resonance imaging; sub-millisecond; temporal resolution; ultra-fast MRI.