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Analysis of temperature dependence of background phase errors in phase-contrast cardiovascular magnetic resonance.

Busch J, Vannesjo SJ, Barmet C, Pruessmann KP, Kozerke S - J Cardiovasc Magn Reson (2014)

Bottom Line: The temperature of the gradient mount was found to increase by 20-30 K during PC-CMR measurements of 6-12 min duration.It is concluded that changes in gradient mount temperature significantly modify background phase errors during PC-CMR with high gradient duty cycle.Since temperature increases significantly during the first minutes of scanning the results presented are also of relevance for single-slice or multi-slice PC-CMR scans.

View Article: PubMed Central - PubMed

Affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland. kozerke@biomed.ee.ethz.ch.

ABSTRACT

Background: The accuracy of phase-contrast cardiovascular magnetic resonance (PC-CMR) can be compromised by background phase errors. It is the objective of the present work to provide an analysis of the temperature dependence of background phase errors in PC-CMR by means of gradient mount temperature sensing and magnetic field monitoring.

Methods: Background phase errors were measured for various temperatures of the gradient mount using magnetic field monitoring and validated in a static phantom. The effect of thermal changes during k-space acquisition was simulated and confirmed with measurements in a stationary phantom.

Results: The temperature of the gradient mount was found to increase by 20-30 K during PC-CMR measurements of 6-12 min duration. Associated changes in background phase errors of up to 11% or 0.35 radian were measured at 10 cm from the magnet's iso-center as a result of first order offsets. Zeroth order phase errors exhibited little thermal dependence.

Conclusions: It is concluded that changes in gradient mount temperature significantly modify background phase errors during PC-CMR with high gradient duty cycle. Since temperature increases significantly during the first minutes of scanning the results presented are also of relevance for single-slice or multi-slice PC-CMR scans. The findings prompt for further studies to investigate advanced correction methods taking into account gradient temperature and/or the use of concurrent field-monitoring to map gradient-induced fields throughout the scan.

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Echo-time dependence of phase offsets. Comparison of temperature dependent changes of first and zeroth order background phase errors (A) at two echo times (1.8 ms and 2.2 ms) (B,C). Corresponding difference maps of phase images acquired at 0 and 9 min (D,E).
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Fig7: Echo-time dependence of phase offsets. Comparison of temperature dependent changes of first and zeroth order background phase errors (A) at two echo times (1.8 ms and 2.2 ms) (B,C). Corresponding difference maps of phase images acquired at 0 and 9 min (D,E).

Mentions: The amount of thermal fluctuation of the background phase error is dependent on the echo time point and can hence be reduced with a suitable choice of echo time. In FigureĀ 7 the thermal changes are compared for an echo time point of 1.8 ms vs. 2.2 ms in a non-angulated transverse slice through the iso-center for flow encoding along RL (venc 150 cm/s). TR was extended to 4.5 ms to allow for prolonged echo times. For the shift in echo time only the read-out gradient was shifted, all other gradients were kept the same.Figure 7


Analysis of temperature dependence of background phase errors in phase-contrast cardiovascular magnetic resonance.

Busch J, Vannesjo SJ, Barmet C, Pruessmann KP, Kozerke S - J Cardiovasc Magn Reson (2014)

Echo-time dependence of phase offsets. Comparison of temperature dependent changes of first and zeroth order background phase errors (A) at two echo times (1.8 ms and 2.2 ms) (B,C). Corresponding difference maps of phase images acquired at 0 and 9 min (D,E).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4263200&req=5

Fig7: Echo-time dependence of phase offsets. Comparison of temperature dependent changes of first and zeroth order background phase errors (A) at two echo times (1.8 ms and 2.2 ms) (B,C). Corresponding difference maps of phase images acquired at 0 and 9 min (D,E).
Mentions: The amount of thermal fluctuation of the background phase error is dependent on the echo time point and can hence be reduced with a suitable choice of echo time. In FigureĀ 7 the thermal changes are compared for an echo time point of 1.8 ms vs. 2.2 ms in a non-angulated transverse slice through the iso-center for flow encoding along RL (venc 150 cm/s). TR was extended to 4.5 ms to allow for prolonged echo times. For the shift in echo time only the read-out gradient was shifted, all other gradients were kept the same.Figure 7

Bottom Line: The temperature of the gradient mount was found to increase by 20-30 K during PC-CMR measurements of 6-12 min duration.It is concluded that changes in gradient mount temperature significantly modify background phase errors during PC-CMR with high gradient duty cycle.Since temperature increases significantly during the first minutes of scanning the results presented are also of relevance for single-slice or multi-slice PC-CMR scans.

View Article: PubMed Central - PubMed

Affiliation: Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland. kozerke@biomed.ee.ethz.ch.

ABSTRACT

Background: The accuracy of phase-contrast cardiovascular magnetic resonance (PC-CMR) can be compromised by background phase errors. It is the objective of the present work to provide an analysis of the temperature dependence of background phase errors in PC-CMR by means of gradient mount temperature sensing and magnetic field monitoring.

Methods: Background phase errors were measured for various temperatures of the gradient mount using magnetic field monitoring and validated in a static phantom. The effect of thermal changes during k-space acquisition was simulated and confirmed with measurements in a stationary phantom.

Results: The temperature of the gradient mount was found to increase by 20-30 K during PC-CMR measurements of 6-12 min duration. Associated changes in background phase errors of up to 11% or 0.35 radian were measured at 10 cm from the magnet's iso-center as a result of first order offsets. Zeroth order phase errors exhibited little thermal dependence.

Conclusions: It is concluded that changes in gradient mount temperature significantly modify background phase errors during PC-CMR with high gradient duty cycle. Since temperature increases significantly during the first minutes of scanning the results presented are also of relevance for single-slice or multi-slice PC-CMR scans. The findings prompt for further studies to investigate advanced correction methods taking into account gradient temperature and/or the use of concurrent field-monitoring to map gradient-induced fields throughout the scan.

Show MeSH
Related in: MedlinePlus