- Poster presentation
- Open Access
Comparison of two novel methods of measuring the blood velocity in the deep veins of the lower leg using phase contrast MR imaging
© Pierce et al; licensee BioMed Central Ltd. 2009
- Published: 28 January 2009
- Wall Shear Stress
- Wave Input
- Velocity Encode
- Muscle Pump
- Average Velocity Profile
To compare the effectiveness of two novel methods developed to measure the velocity of the blood in the deep veins in the lower leg.
To investigate the causes and treatment of deep vein thrombosis, there is a need for blood flow measurements in the lower limb veins. The work of Downie et al into the effects of compression stockings on geometry  and wall shear stress  concludes that MR imaging should be utilised for continued research of the haemodynamics of the lower limb venous system as it can supply structural and velocity data from the same acquisition. Venous velocity is low and more dependent on the respiratory than cardiac cycle, requiring new methods. Also the muscle pump can cause large spikes in the velocity requiring real-time measurement.
Two sequences have been developed using Phase-Contrast velocity mapping: gated SEGmented GRadient Echo (SEG-GRE) sequence and an Interleaved SPiral (ISPLASH) sequence. Both use VElocity ENCoding (VENC) of 10 cm/s, arterial flow saturation upstream, slice thickness of 7 mm and pixel size of 1 × 1 mm.
Seven normal volunteers were asked to lie prone (1.5 T Siemens Avanto) with left leg raised 10 – 15 cm, resting the ankle on a foam support, with a pair of carotid surface coils (Machnet) placed around the calf. The volunteers were asked to breathe deeply, in time with an LED driven by a 7 second/cycle square wave input . The logfiles for the subject's respiratory belt sensor were recorded for each spiral scan.
triggered by the square wave input with 7 seconds cine acquisition window (23 respiratory-cine frames) covering one respiratory cycle, acquiring 11 rawdata lines per cine frame per cycle. The velocity encoding gradients are applied every other excitation (REF – VENC) within each cine frame. The number of averages was 2, acquisition time 2.5 minutes, time per frame 285 ms.
The ISPLASH sequence uses water excitation and balanced velocity encoding using alternate excitations (VENC (+ve) – VENC (-ve)). It was run with 4 interleaves repeated continuously covering 35 seconds. The spiral data was re-gridded and by sliding reconstruction (In-house Matlab programs) allowed interpolation between repetitions. Time per frame is 320 ms, with interpolation 80 ms between frames.
The peak mean velocity measured from SEG-GRE averaged ISPLASH (4 respiratory cycles) and the full ISPLASH
Peak mean velocity (cm/s)
Two methods for measuring the venous blood velocities in the lower leg have been compared and show good agreement. The first method produces an averaged velocity profile over the respiratory cycle but relies on sustained regular breathing. The second method, ISPLASH, allows for more 'real time' imaging allowing further investigation into areas such as the muscle pump and graduated compression devices.
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This article is published under license to BioMed Central Ltd.