Non-contrast-enhanced MRA using Velocity-sensitised, Acceleration-sensitised and Combined Sensitisation with Fast-Spin-Echo Readout
Andrew Nicholas Priest1, Ian G Murphy1, and David John Lomas1

1Radiology, Addenbrookes Hospital and Cambridge University, Cambridge, United Kingdom


This work develops an NCE-MRA technique based on the flow-sensitised dephasing (FSD) method but using a fast-spin echo (FSE) readout to avoid off-resonance artifacts and allow a larger field of view. The flow-preparation module may be velocity-sensitised, acceleration-sensitised or mixed velocity-and-acceleration-sensitised. The FSE readout allows these approaches to be combined with additional flow sensitisation by ‘adaptive refocus’ which reduces the refocusing flip angle in systole. These approaches performed well in healthy volunteers, in particular the velocity-sensitisation and mixed-sensitisation approaches. Adding adaptive refocus increased venous contamination and thus reduced the arterial image quality. Future work will evaluate these methods in patients.


The flow-sensitised dephasing (FSD) approach to Non-Contrast-Enhanced MRA (NCE-MRA) generates 3D subtraction angiograms, suppressing flowing blood by sensitising the signal to either velocity1–2 or acceleration3. Acceleration sensitisation allows improved discrimination between arteries and veins3 but can be sub-optimal in some patients with insufficiently pulsatile arterial flow4.

Previous FSD work has mostly used a balanced SSFP (bSSFP) readout, but this causes off-resonance artifacts that reduce the usable field of view (FoV) and the vessel homogeneity. An alternative approach using a fast-spin echo (FSE) readout which should eliminate these problems. An FSE readout may optionally incorporate additional flow-related signal dephasing, e.g. by using an ‘adaptive refocus’ approach which reduces the refocusing flip angle5 during the systolic ‘dark-blood’ acquisition.

The aim of this work is to develop an NCE-MRA technique using an FSE readout and a flow-sensitised dephasing approach that can combine both velocity and acceleration sensitisation.


Following ethical approval and informed consent, the lower legs of 10 healthy volunteers were imaged at 1.5 T (Discovery MR450, GE Healthcare, Waukesha, WI). NCE-MRA images were acquired for each subject, using the three different preparation modules shown in Figure 1. These acquisitions have a large first gradient moment m1 for velocity sensitisation, a large second gradient moment m2 for acceleration sensitisation, and large m1 and m2 for mixed velocity/acceleration-sensitisation. In each case, bright-blood (diastolic) and dark-blood (systolic) acquisitions were interleaved.

Additionally, in 8 subjects the three NCE-MRA sequences were repeated using adaptive refocus for added flow suppression in the systolic phase. Also, a product NCE-MRA sequence, which uses only adaptive refocus, was acquired for comparison.

The acquisitions used a 3D FSE readout (TE=60, TR=3RR, FoV=40cm, acquisition matrix=320x224x40, slice thickness=2.4mm, ETL=64, ARC acceleration factor=2, 0.5 Nex, refocus flip angle=180°, flow compensation, radial view order, total scan time=207 heartbeats). Fat and other background signals were suppressed using non-spectrally-selective dual inversion recovery6. However, the product sequence instead used ASSET parallel imaging and single inversion recovery. The refocusing flip angle was 180° except for the systolic phase of adaptive refocus acquisitions, which used 105° (steady state). The velocity- and acceleration-sensitisation gradients were optimised for each subject using prior 2D multi-phase acquisitions as scout sequences (parameters as above but 1 slice, thickness 4–6cm, 8 phases, m1 range 46–154 nTs2/m, m2 range 2.8–9.2 nTs3/m) in a similar fashion to ref 7. The systolic trigger delay was determined from a 2D cine phase-contrast acquisition through the popliteal arteries (TE/TR=3.3/6.6 ms; flip angle=30°; matrix 256×128; FoV=40x20 cm2; slice thickness=7 mm; venc=80 cm/s, 1 vps), while the diastolic delay was determined using a 2D multi-phase single-shot FSE scout sequence (TE=78ms, TR=4RR, ASSET factor 2, slice thickness 150 mm, 16 phases covering 80% of cardiac cycle).

MIP images were assessed by an experienced radiologist (blinded to sequence type and randomised within each subject) who used 5-point Likert scales (0–4) to score arterial image quality, deep vein signal contamination and background levels.

For demonstration purposes, example velocity-sensitised images were acquired using both FSE and bSSFP readouts in one volunteer.


The chosen flow sensitisation parameters ranged from 62–108 nTs2/m (m1) and 3.7–6.4 nTs3/m (m2). Example images from one subject are shown in Fig. 2.

Boxplots of the radiologist scores are shown in Figure 3. All images were graded as being of diagnostic quality, with the velocity-sensitised images the best and the mixed velocity/acceleration-sensitisation also graded highly. For all three sequence types, the addition of adaptive refocus increased the venous contamination levels and consequently reduced the quality of arterial depiction.

Figure 4 compares example images acquired using FSE and bSSFP readouts, showing the greater coverage and vessel homogeneity for FSE.


The use of FSE for the readout offers good or excellent arterial image quality over a larger field of view than previous FSD studies using bSSFP, and without off-resonance artifacts. We have also demonstrated (for the first time to our knowledge) the feasibility of combining velocity- and acceleration-sensitisation in a single flow preparation module, and of combining both with adaptive refocus for further potential improvements to the flow suppression. In healthy volunteers with normal arterial flow profiles, the separate approaches work well so (as expected) these combinations added little benefit. We now plan to assess these combined approaches in patients with peripheral vascular disease and less predictable arterial flow profiles where they may prove more effective than the separate strategies4.


A 3D FSE-based flow-sensitised NCE-MRA technique has been developed and demonstrated, with good results, in healthy volunteers. This approach can optionally combine acceleration sensitisation and velocity sensitisation. Future work will evaluate these approaches in patients.


We thank the Addenbrooke's Charitable Trust and the Cambridge NIHR Biomedical Research Centre for funding; and the MRIS staff for assistance with this study.


1. Fan Z, Sheehan J, Bi X, Liu X, Carr J, Li D. Evaluation of Non Contrast Enhanced MRA in patients with PVD. Magn Reson Med. 2009;62(6):1523-32.

2. Priest AN, Graves MJ, Lomas DJ. Non-contrast-enhanced vascular magnetic resonance imaging using flow-dependent preparation with subtraction. Magn Reson Med. 2012;67(3):628–637.

3. Priest AN, Taviani V, Graves MJ, Lomas DJ. Improved Artery–Vein Separation with Acceleration-Dependent Preparation for Non–Contrast-Enhanced Magnetic Resonance Angiography. Magn Reson Med. 2014;72(3):699–706.

4. N Shaida, AN Priest, TC See, AP Winterbottom, MJ Graves, DJ Lomas. Evaluation of Non Contrast Enhanced MRA in patients with PVD. Proc Intl Soc Mag Reson Med. 2014; 22: 3865.

5. Storey P, Atanasova IP, Lim RP, Xu J, Kim D, Chen Q, Lee VS. Tailoring the flow sensitivity of fast spin-echo sequences for noncontrast peripheral MR angiography. Magn Reson Med. 2010;64(4):1098-108.

6. Priest AN, Low G, Graves MJ, Lomas DJ. Non-contrast-enhanced MR angiography of the thoracic central veins. Proc Intl Soc Mag Reson Med. 2014; 22: 2513.

7. Fan Z, Zhou X, Bi X, Dharmakumar R, Carr JC, Li D. Determination of the optimal first-order gradient moment for flow-sensitive dephasing magnetization-prepared 3D noncontrast MR angiography. Magn Reson Med. 2011 Apr;65(4):964–972.


Figure 1: Preparation modules for: (a) velocity-sensitisation; (b) acceleration-sensitisation; and (c) mixed velocity- and acceleration-sensitisation. The blue motion-sensitisation gradient (MSG) waveforms in (c) are the sum of those in (a) and (b). In this work, the effective echo time was 20 ms and MSG duration was 3 ms.

Figure 2: MIPs of subtraction NCE-MRA acquired with: velocity, acceleration and mixed sensitisation (left, from top); the same methods combined with adaptive refocus (right, from top); and the manufacturer’s product sequence using adaptive refocus only (bottom image). Images are from the lower legs of a healthy volunteer, and use m1 = 62 nTs2/m and m2 = 6.4 nTs3/m.

Figure 3: Box plots showing the median (red), inter-quartile range (blue box), maximum and minimum scores for the 7 different methods: velocity, acceleration and mixed sensitisation both with and without adaptive refocus (aR) and product sequence with adaptive refocus only (adRef). For arterial image quality, score 4 was the best with 0/1 being non-diagnostic. For venous contamination and background, score 0 was the best with 3/4 potentially affecting diagnosis.

Figure 4: Comparison of FSE (left) and bSSFP (right) velocity-selective NCE-MRA methods for an example volunteer with m1 = 99.6 and 98.2 nTs2/m respectively. The FSE method shows improved arterial homogeneity and improved coverage, which in this case was limited primarily by the sensitive volume of the receiver coil.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)