In‐plane velocity encoding with coherent steady‐state imaging

Abstract

Standard phase-contrast flow quantification (PC-FQ) using radiofrequency (RF) spoiled steady-state (SS) incoherent gradient-echo sequences have a relatively low signal-to-noise ratio (SNR). Unspoiled SS coherent (SSC) gradient-echo sequences have a higher intrinsic SNR and are T 2 /T 1 weighted so that blood has a relatively large signal compared to other tissues. An SSC sequence that was modified to allow in-plane velocity encoding is presented. Velocity encoding was achieved by inverting the readout gradients. This offers the benefit that there is no resultant increase in repetition time (TR), which avoids increased sensitivity to off-resonance artifacts when conventional velocity-encoding methods using separate velocity-encoding gradients are extended to SSC sequences. The results of standard PC-FQ and the new method from in vitro experiments of constant and sinusoidal flow, and in vivo imaging of the carotid artery were compared. Vector field maps and paths obtained from particle-tracking calculations based on the velocity-encoded images were used to visualize the velocity data. The technique has the potential to increase the precision of PC-FQ measurements. Magn Reson Med 54:138 -145, 2005.

In vivo estimation and repeatability of force–length relationship and stiffness of the human achilles tendon using phase contrast MRI

“…Given this constraint, the development of a new PC-MRI sequence that can improve the temporal resolution while maintaining data acquisition time would be desirable. While higher temporal resolution can be achieved by alternate spiral acquisition (16) or the use of steady-state velocity encoding sequences (17), there is typically a compromise on spatial resolution or image quality.…”

Improving contrast to noise ratio of resonance frequency contrast images (phase images) using balanced steady-state free precession

“…Additionally, it provides a unique $\sqrt{{\text{T}}_2/{\text{T}}_1}$ contrast that can be particularly beneficial in certain applications (Hargreaves et al, 2003; Nayak et al, 2005). However, with a few exceptions such as flow imaging (Overall et al, 2002; Markl et al, 2003; Grinstead and Sinha, 2005), neuronal current measurement (Buracas et al, 2008) and bSSFP fMRI (Miller et al, 2003; Scheffler et al, 2001) where strong phase contrast has been demonstrated (Lee et al, 2007), most of the bSSFP studies have utilized only the image magnitude and ignored the image phase.…”

Visualization and Quantification of Flow and Velocity Fields in Intracranial Arteriovenous Malformations Using Phase-Contrast MR Angiography

“…In addition, particle paths can be superimposed instead of vector field maps. These paths were calculated from the phase-contrast flow quan-tification data using simple kinematic equations of motion as described elsewhere [7,8] …”

“…Information in the DICOM header allowed the velocity encoding values, encoding direction, temporal resolution, cine frame number, pixel size, and so on to be imported automatically along with the pixel data. The visualization tools we used and developed were previously described in more detail [6,7]. Briefly, considering an axial slice, the through-plane velocity data (superior-inferior) are plotted as contour maps with isocontour lines separating regions of differing velocity ranges.…”