Inter-study reproducibility of interleaved spiral phase velocity mapping of renal artery haemodynamics

Abstract

Background: Qualitative and quantitative assessment of renal blood flow is valuable in the evaluation of patients with renal and renovascular diseases as well as in patients with heart failure. The temporal pattern of renal flow velocity through the cardiac cycle provides important information about renal haemodynamics. High temporal resolution interleaved spiral phase velocity mapping could potentially be used to study temporal patterns of flow and measure resistive and pulsatility indices which are measures of downstream resistance.

Methods: A retrospectively gated breath-hold spiral phase velocity mapping sequence (TR 19 ms) was developed at 3 Tesla. Phase velocity maps were acquired in the proximal right and left arteries of 10 healthy subjects in each of two separate scanning sessions. Each acquisition was analysed by two independent observers who calculated the resistive index (RI), the pulsatility index (PI), the mean flow velocity and the renal artery blood flow (RABF). Inter-study and inter-observer reproducibility of each variable was determined as the mean +/- standard deviation of the differences between paired values. The effect of background phase errors on each parameter was investigated.

Results: RI, PI, mean velocity and RABF per kidney were 0.71+/- 0.06, 1.47 +/- 0.29, 253.5 +/- 65.2 mm/s and 413 +/- 122 ml/min respectively. The inter-study reproducibilities were: RI -0.00 +/- 0.04 , PI -0.03 +/- 0.17, mean velocity -6.7 +/- 31.1 mm/s and RABF per kidney 17.9 +/- 44.8 ml/min. The effect of background phase errors was negligible (<2% for each parameter).

Conclusions: High temporal resolution breath-hold spiral phase velocity mapping allows reproducible assessment of renal pulsatility indices and RABF.

Figure 1

Oblique coronal (top) and oblique transverse (bottom) pilot images showing the proximal paths of the left and right renal arteries in an example subject (a) together with through-plane systolic magnitude images and velocity maps from both scanning sessions (initial (b) and repeat (c)). The renal artery regions of interest are shown in inserts images to the bottom left of the magnitude images. (open arrow = left renal artery, solid arrow = right renal artery).

Figure 2

Bland Altman plots showing inter-observer reproducibility of measurements of cross-sectional area, RABF, mean flow velocity, PI and RI (initial scanning session) (a). Corresponding plots for the inter-study reproducibility (observer 1) are shown in (b).

Figure 3

Velocity-time curves in the initial (blue) and repeat (red) scanning sessions in all 10 subjects, as determined by observer 1. In the repeat left acquisition in subject 4, a much reduced RR interval (895 ms vs 1095 ms) and ECG mis-triggering (open arrow) resulted in velocity-time curve errors and this acquisition was omitted from all further analyses. (For all graphs, x-axis: time after R-wave (ms), y-axis: mean velocity (mm/s)).