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Published on: February 10, 2012
Factors influencing flow-induced signal loss in MR angiography: an in vitro study
1Institute of Diagnostic Radiology, Heinrich Heine University, Düsseldorf, Germany.
Objective:
Signal loss due to poststenotic turbulence is one remaining limitation in the clinical use of MRA. The objective of this study was to determine the factors influencing poststenotic signal loss (PSL) in a stenotic tube system.
Materials And Methods:
With use of a two-dimensional gradient echo sequence (FLASH), the influence of (a) the degree of stenosis (50, 75, and 91% cross-sectional area reduction), (b) flow velocity (12, 47, 71, and 94 cm/s), (c) TE (3, 6, 13, and 20 ms), and (d) flip angle (5, 10, 20, ... , 90 degrees) on the length of PSL was measured in a nonpulsatile stenotic tube system. To quantify the effect of first-order gradient motion refocusing (GMR), the signal intensity ratio from flow-compensated and -uncompensated images was calculated. For statistical analysis, multiple regression analysis and unpaired Student t test were used.
Results:
In the flow model used, the length of PSL increased significantly with the degree of stenosis (beta ST' = 0.483 mm/%, beta ST" = 0.447 mm/%, p < 0.0001), flow velocity (beta v' = 0.297 s, beta v" = 0.213 s, p < 0.0001), and TE (beta TE = 1.88 mm/ms, p < 0.0001), respectively, whereas no correlation emerged for varying flip angles (beta alpha = 0.0214, p = 0.29). First-order GMR reduced significantly PSL in through-plane measurements (p < 0.0001). Maximal signal-enhancing effects of first-order GMR were observed 1-3 cm distal to the stenosis.
Conclusion:
Flow model parameters (i.e., degree of stenosis, flow velocity) markedly influenced the length of PSL that could be compensate for by use orf shortened TEs and first-order GMR. Varying flip angles had no significant influence on PSL.
Insights
Poststenotic signal loss in MRA is reduced by higher stenosis degree and flow velocity, but can be compensated by shorter echo times (TE) and gradient motion refocusing (GMR). Varying flip angles did not significantly impact signal loss.
Area of Science:
- Medical Imaging
- Biophysics
- Fluid Dynamics
Background:
- Signal loss in Magnetic Resonance Angiography (MRA) due to poststenotic turbulence limits clinical utility.
- Understanding factors influencing poststenotic signal loss (PSL) is crucial for improving MRA techniques.
Purpose of the Study:
- To investigate the key factors affecting poststenotic signal loss (PSL) in a stenotic tube system.
- To evaluate the impact of stenosis severity, flow velocity, echo time (TE), and flip angle on PSL.
Main Methods:
- Utilized a two-dimensional gradient echo sequence (FLASH) in a nonpulsatile stenotic tube model.
- Measured PSL length across varying degrees of stenosis (50-91%), flow velocities (12-94 cm/s), and TEs (3-20 ms).
- Assessed the effect of first-order gradient motion refocusing (GMR) on signal intensity and PSL.
Main Results:
- PSL length significantly increased with greater stenosis degree, higher flow velocity, and longer TE (p < 0.0001).
- Flip angle variations showed no significant correlation with PSL length (p = 0.29).
- First-order GMR significantly reduced PSL, with maximal effects observed 1-3 cm distal to the stenosis (p < 0.0001).
Conclusions:
- Flow parameters like stenosis degree and velocity significantly influence PSL in MRA.
- Shortened TEs and first-order GMR effectively compensate for PSL.
- Flip angle is not a significant factor in mitigating PSL in this model.
