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Inter-study reproducibility of interleaved spiral phase velocity mapping of renal artery haemodynamics
© Keegan et al; licensee BioMed Central Ltd. 2015
- Published: 3 February 2015
- Resistive Index
- Pulsatility Index
- Renal Resistive Index
- Background Phase
- Phase Velocity Mapping
Renal resistive index (RI) and pulsatility index (PI) are reliable measures of downstream renal resistance which correlate with the severity of renal disease. To date, MR phase velocity mapping studies have lacked the temporal resolution required to determine these pulsatility parameters. Our aim is to develop a high temporal resolution breath-hold spiral phase velocity mapping technique for assessment of the temporal flow patterns in renal arteries and to determine inter-study reproducibility.
An interleaved spiral phase velocity mapping sequence was developed on a 3T Skyra scanner (Siemens) using 1-1 water excitation and with full k-space coverage in 8 spiral interleaves of 12 ms duration. Phase map subtraction of datasets with symmetric bi-polar velocity encoding gradients resulted in velocity maps with a through-plane phase sensitivity of +/- 150cm/s. Retrospectively ECG gated data were acquired in a 17 cardiac cycle breath-hold (includes 1 dummy cycle) with a spatial resolution of 1.4 x 1.4 mm (reconstructed to 0.7 x 0.7 mm) and a repeat time of 19 ms. Renal artery velocity maps were acquired in 10 healthy volunteers (10 left and 10 right arteries). Data were acquired in each of two separate scanning sessions with the volunteer leaving the scanner between sessions. For each acquisition (40 in total), RI and PI were calculated by 2 observers as follows:
RI = (PSV - MDV) / PSV
PI = (PSV - MDV) / MV
where PSV = peak systolic velocity, MDV = minimum diastolic velocity and MV = mean velocity through the cardiac cycle
Background phase errors were determined from (i) a large stationary phantom acquisition and (ii) by fitting a background phase map to user defined stationary points in the inter-vertebral disks. Inter-observer and inter-study reproducibility of RI, PI and renal artery blood flow (RABF) per kidney were determined as the mean (+/- standard deviation) of the paired differences between observers and between scanning sessions and by the intraclass correlation coefficient (ICC).
High temporal resolution breath-hold spiral phase velocity mapping allows reproducible assessment of renal pulsatility indices and RABF. We conclude that this technique is suitable for studying temporal flow velocity patterns in the renal arteries.
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.