Magnetic resonance velocity imaging using a fast spiral phase contrast sequence

Abstract

Time-resolved velocity imaging using the magnetic resonance phase contrast technique can provide clinically important quantitative flow measurements in vivo but suffers from long scan times when based on conventional spin-warp sequences. This can be particularly problematic when imaging regions of the abdomen and thorax because of respiratory motion. We present a rapid phase contrast sequence based on an interleaved spiral k-space data acquisition that permits time-resolved, three-direction velocity imaging within a breath-hold. Results of steady and pulsatile flow phantom experiments are presented, which indicate excellent agreement between our technique and through plane flow measurements made with an in-line ultrasound probe. Also shown are results of normal volunteer studies of the carotids, renal arteries, and heart.

Fast phase‐contrast velocity measurement in the steady state

“…Using this with Eq. [5] above, PNR for SSPC can be derived: Thus, velocity-image quality in SSPC is directly proportional to magnitude SNR, and also increases with increasing m 1 . The PNR of standard PC can be similarly calculated:…”

“…Standard PC also does not require the slope-1/2 approximation used in Eq. [5]. The amount of flow encoding generated by SSPC is directly controlled by the bipolar gradient waveform through m 1 , its first moment.…”

“…To ensure that the slope-1/2 approximation in Eq. [5] is valid, m 1 should be chosen such that ͉␥m 1 v͉ ϩ ͉ F ͉ Ͻ . While F is an unknown quantity, a reasonable maximum F,max can be substituted.…”

Phase-sensitive black-blood coronary vessel wall imaging

“…Third, cardiac and respiratory motion may lead to additional blurring that adversely affects the identification of the polarity of the signal. Finally, problems related to additional phase errors due to flowing blood have not been addressed in detail in previous PS-IR techniques since these were designed to differentiate between stationary tissue, e.g., in the brain (25)(26)(27)(31)(32)(33)(34)(35)(36)(37), or between infarcted and noninfarcted myocardium tissues (29,38,39).…”

Rapid mapping of flow velocity using a new PARSE method

“…Pelc et al (6) and Hausmann et al (7) applied the four-point method to reduce the image acquisition time in 3D. Later an interleaved spiral PC technique was implemented to speed up flow quantification in both 2D and 3D with a much shorter readout time (8). Recently, it was demonstrated that using undersampling in conjunction with radial acquisition can significantly reduce the total measurement time (9).…”