Validation of non-contrast multiple overlapping thin-slab 4D-flow cardiac magnetic resonance imaging

Abstract

Background: Cardiac magnetic resonance (CMR) flow quantification is typically performed using 2D phase-contrast (PC) imaging of a plane perpendicular to flow. 3D-PC imaging (4D-flow) allows offline quantification anywhere in a thick slab, but is often limited by suboptimal signal, potentially alleviated by contrast enhancement. We developed a non-contrast 4D-flow sequence, which acquires multiple overlapping thin slabs (MOTS) to minimize signal loss, and hypothesized that it could improve image quality, diagnostic accuracy, and aortic flow measurements compared to non-contrast single-slab approach.

Methods: We prospectively studied 20 patients referred for transesophageal echocardiography (TEE), who underwent CMR (GE, 3 T). 2D-PC images of the aortic valve and three 4D-flow datasets covering the heart were acquired, including single-slab, pre- and post-contrast, and non-contrast MOTS. Each 4D-flow dataset was interpreted blindly for ≥moderate valve disease and compared to TEE. Flow visualization through each valve was scored (0 to 4), and aortic-valve flow measured on each 4D-flow dataset and compared to 2D-PC reference.

Results: Diagnostic quality visualization was achieved with the pre- and post-contrast 4D-flow acquisitions in 25% and 100% valves, respectively (scores 0.9 ± 1.1 and 3.8 ± 0.5), and in 58% with the non-contrast MOTS (1.6 ± 1.1). Accuracy of detection of valve disease was 75%, 92% and 82%, respectively. Aortic flow measurements were possible in 53%, 95% and in 89% patients, respectively. The correlation between pre-contrast single-slab measurements and 2D-PC reference was weak (r = 0.21), but improved with both contrast enhancement (r = 0.71) and with MOTS (r = 0.67).

Conclusions: Although non-contrast MOTS 4D-flow improves valve function visualization and diagnostic accuracy, a significant proportion of valves cannot be accurately assessed. However, aortic flow measurements using non-contrast MOTS is feasible and reaches similar accuracy to that of contrast-enhanced 4D-flow.

Keywords: Aortic flow; Contrast enhancement; Offline analysis; Phase contrast.

Fig. 1.

Examples of multiple thin-slab 4D-flow images of varying quality of valve visualization, graded as shown in parentheses.

Fig. 2.

Example of aortic flow measurements made in one patient using the 2D-PC imaging (top) and the three different 4D-flow techniques (below). See text for details.

Fig. 3.

Example of visualization of mitral regurgitation (MR, white arrow) as shown in TEE (A), single slab non-contrast 4D-flow (B), single slab post-contrast 4D-flow (C), and non-contrast MOTS 4D-flow (D). The signal intensity of the MR jet and aortic flow is worst in the single slab non-contrast, best in the single slab post-contrast, and intermediate in the non-contrast MOTS.

Fig. 4.

Example of visualization of tricuspid regurgitation (TR, white arrow) as shown in TEE (A), single slab non-contrast 4D-flow (B), single slab post-contrast 4D-flow (C), and non-contrast MOTS 4D-flow (D). The signal intensity of the TR jet is worst in the single slab non-contrast, best in the single slab post-contrast, and intermediate in the non-contrast MOTS.

Fig. 5.

Comparison between the 4D-flow measurements of the aortic valve flow and the 2D phase-contrast reference values: linear regression (left) and Bland-Altman analyses for pre-contrast single-slab (top), post-contrast single-slab (middle) and non-contrast multi-slice (bottom) techniques. LOA – limits of agreement.