Quantification and visualization of cardiovascular 4D velocity mapping accelerated with parallel imaging or k-t BLAST: head to head comparison and validation at 1.5 T and 3 T

Abstract

Background: Three-dimensional time-resolved (4D) phase-contrast (PC) CMR can visualize and quantify cardiovascular flow but is hampered by long acquisition times. Acceleration with SENSE or k-t BLAST are two possibilities but results on validation are lacking, especially at 3 T. The aim of this study was therefore to validate quantitative in vivo cardiac 4D-acquisitions accelerated with parallel imaging and k-t BLAST at 1.5 T and 3 T with 2D-flow as the reference and to investigate if field strengths and type of acceleration have major effects on intracardiac flow visualization.

Methods: The local ethical committee approved the study. 13 healthy volunteers were scanned at both 1.5 T and 3 T in random order with 2D-flow of the aorta and main pulmonary artery and two 4D-flow sequences of the heart accelerated with SENSE and k-t BLAST respectively. 2D-image planes were reconstructed at the aortic and pulmonary outflow. Flow curves were calculated and peak flows and stroke volumes (SV) compared to the results from 2D-flow acquisitions. Intra-cardiac flow was visualized using particle tracing and image quality based on the flow patterns of the particles was graded using a four-point scale.

Results: Good accuracy of SV quantification was found using 3 T 4D-SENSE (r2 = 0.86, -0.7 ± 7.6%) and although a larger bias was found on 1.5 T (r2 = 0.71, -3.6 ± 14.8%), the difference was not significant (p = 0.46). Accuracy of 4D k-t BLAST for SV was lower (p < 0.01) on 1.5 T (r2 = 0.65, -15.6 ± 13.7%) compared to 3 T (r2 = 0.64, -4.6 ± 10.0%). Peak flow was lower with 4D-SENSE at both 3 T and 1.5 T compared to 2D-flow (p < 0.01) and even lower with 4D k-t BLAST at both scanners (p < 0.01). Intracardiac flow visualization did not differ between 1.5 T and 3 T (p = 0.09) or between 4D-SENSE or 4D k-t BLAST (p = 0.85).

Conclusions: The present study showed that quantitative 4D flow accelerated with SENSE has good accuracy at 3 T and compares favourably to 1.5 T. 4D flow accelerated with k-t BLAST underestimate flow velocities and thereby yield too high bias for intra-cardiac quantitative in vivo use at the present time. For intra-cardiac 4D-flow visualization, however, 1.5 T and 3 T as well as SENSE or k-t BLAST can be used with similar quality.

Figure 1

There was a strong correlation between stroke volumes (SV) of the aorta and main pulmonary artery (MPA) with 2D-flow (left, solid line represents line of identity). Bias was low (1.7 ± 6.3%, right).

Figure 2

Typical flow graphs over the cardiac cycle in one subject at 1.5 T (top row) and 3 T (bottom row) for the aorta (left column) and main pulmonary artery (MPA, right column). Remaining subjects are shown in the Additional files.

Figure 3

The correlation of stroke volumes (SV) with 4D-SENSE flow acquisitions and 2D flow (left panels) was higher for acquisitions on 3 T (bottom) compared to 1.5 T (top). The correlations for k-t BLAST (right panels) on 3 T and 1.5 T were similar. Solid line represents line of identity. Results from k-t SENSE are shown as white circles.

Figure 4

Bland-Altman analysis of stroke volume (SV) quantified on 4D flow acquisitions and 2D flow acquisitions on both 1.5 T (top row) and 3 T (bottom row) accelerated with SENSE (left panels) and k-t BLAST (right panels). Results from k-t SENSE are shown as white circles.

Figure 5

Visualization of intra-cardiac 4D-flow using particle tracing with four-chamber cine images for anatomical reference, in the same subject as Figure 6. Flow is coloured blue on the right side and red on the left side of the heart. Only a small amount of particles exhibit a non-physiological flow, which was read as good image quality. No major differences were seen between 1.5 T or 3 T nor between k-t BLAST or SENSE.

Figure 6

Visualization of intra-cardiac 4D-flow using particle tracing with short-axis cine images for anatomical reference in the same subject as Figure 5. Flow is coloured blue on the right side and red on the left side of the heart. Only a small amount of particles exhibit a non-physiological flow, which was read as good image quality. No major differences were seen between 1.5 T or 3 T nor between k-t BLAST or SENSE.