Phase‐contrast single‐point imaging with synchronized encoding: a more reliable technique for in vitro flow quantification

Abstract

Purpose The purpose of this study is to provide a standard method for flow velocity measurements with phase‐contrast (PC) MRI. This method can be used for in vitro studies that place high demands on measurement accuracy. Clinically relevant PC MRI techniques can be validated using this method before being applied in vivo. Methods Many motion‐related errors in PC MRI, particularly flow misregistration, depend on the timing of the encoding gradients in the pulse sequence. By synchronizing all encoding gradients and shortening the overall encoding interval, these errors can be significantly reduced. Based on this concept, a single‐point PC MRI method is proposed. Results Flow experiments were conducted in vitro. No considerable errors were found in the velocity data of the proposed method. For comparison, a conventional PC MRI technique showed up to 100% local velocity deviation and up to 35% flow rate deviation in the same experiments. Conclusions With the proposed method, the overall measurement accuracy is significantly increased compared to conventional PC MRI techniques. Due to long acquisition times and high specific absorption rates, this method can only be applied in vitro.

The impact of 4D flow displacement artifacts on wall shear stress estimation

“…First, a SYNC SPI 18 as illustrated in Figure 1A was applied. This sequence minimizes any flow‐related displacement artifacts by synchronizing all 6 encoding time points (), which is achieved by replacing the frequency encoding by a third phase‐encoding axis.…”

“…This can only be achieved by exclusively using phase encoding for all directions, known as single‐point imaging (SPI). Based on this concept, Bruschewski et al 18 proposed a new PC MRI sequence, termed synchronized PC single‐point imaging sequence (SYNC SPI), which allows for highly accurate velocity measurements. Due to its nature as an SPI sequence, the total acquisition time of several hours renders the sequence unfeasible for in vivo applications.…”

“…First, a SYNC SPI 18 as illustrated in Figure 1A was applied. This sequence minimizes any flow-related displacement artifacts by synchronizing all 6 encoding time points (t RO 0 ,…”

Towards Analyzing the Influence of Measurement Errors in Magnetic Resonance Imaging of Fluid Flows

“…50. However, even the latter increase is by far less than considering multiple evaluations of the conjugate gradient approach with random disturbances of the k-space data, where even m × n = 4096 evaluations for the extremal values of the data set do not provide any guarantee of 4 Note, the two interval models presented in this section for an uncertainty representation are basically chosen as a starting point for the analysis of the sensitivity and reliability of a velocity reconstruction on the basis of variable sampling percentages. These intervals do not necessarily capture the complete ranges of random disturbances and measurement outliers occurring during the experiment.…”

“…Conventional methods, for example, are notably prone to flowinduced errors. An approach to overcome these errors and to enable measurements in strongly turbulent flows at high flow velocities was presented in [4]. However, the main disadvantage of this method is the long acquisition time.…”