Bremer Jonathan BS, Presenter: Nothing to Disclose

Weili Lin PhD, Abstract Co-Author: Nothing to Disclose

Brooke Steele PhD, Abstract Co-Author: Nothing to Disclose

Lucas Carol PhD, Abstract Co-Author: Nothing to Disclose

Qingwei Liu BS, Abstract Co-Author: Nothing to Disclose

Robert Dennis PhD, Abstract Co-Author: Nothing to Disclose

The main purpose of this study is to develop an imaging approach for measuring flow velocity with half of the acquisition time when compared to the conventional phase contrast (PC) approaches

A typical 2D PC velocity measurement method requires at least two interleaved scans with positive and negative velocity encodings. In this study, we propose a new approach where positive and negative velocity encoding gradients (Vg) were applied in the odd and even phase encoding lines, respectively. Consequently, aliasing is expected for flowing spins but not for stationary tissue. The intensity of flowing spins in the magnitude image will be modulated by cosθ where θ is the phase developed due to flow in the presence of Vg. Additionally, an equal corresponding intensity modulated by sinθ is overlaid half a FOV away in the phase encoding direction. θ and ultimately velocity at pixels can be obtained by taking the inverse tangent of the ratio of their corresponding intensities half a FOV way in the phase encoding direction with their intensities. Flow measurements were made in a flow phantom consisting a vinyl tube of 9.53mm internal diameter. The flow rates were varied between 1.67cc/s and 16.67cc/s. A conventional 2D phase contrast was also employed to obtain velocity measurements for comparisons

The proposed approach is capable of obtaining velocity measurements with half of the acquisition time of a typical 2D PC sequence. Mean flow difference between PC–MRI and the proposed approach was 0.36 ± 0.17cc/s and mean peak velocity difference was 0.89 ± 1.3cm/s

The proposed approach is capable of reducing scan time by a factor of approximately two. The agreement between PC–MRI and the proposed approach improves with increased flow. Nevertheless, the proposed method tends to overestimate flow measurements because pixels values outside the object onto which the corresponding intensity modulated by sinθ (described above) is overlaid, are not zero.

This approach offers velocity measurements with a factor 2 of reduction in acquisition time which should minimize patient discomfort and motion artifacts and improve patient throughput.

Jonathan, B, Lin, W, Steele, B, Carol, L, Liu, Q, Dennis, R, MR Velocity Encoded Magnitude Image.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5011231.html