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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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Related in: MedlinePlus

Change in phase errors for different geometries and encoding velocities. Linear and zeroth order background phase errors measured at different temperatures for the x, y and z gradient coils in sagittal, transverse and coronal slices with velocity encodings of 50, 100 and 150 cm/s. Velocity was encoded along AP (A), RL (B) and FH (C).
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Fig3: Change in phase errors for different geometries and encoding velocities. Linear and zeroth order background phase errors measured at different temperatures for the x, y and z gradient coils in sagittal, transverse and coronal slices with velocity encodings of 50, 100 and 150 cm/s. Velocity was encoded along AP (A), RL (B) and FH (C).

Mentions: In Figure 3 the resultant change in background offset at the echo times extracted from the data acquired with field monitoring is summarized for all nine measurements. Changes in 1st and 0th order offsets are depicted for flow encoding along the x, y and z gradient coils. At 10 cm distance from the iso-center changes in phase error of up to 11% of the encoding velocity can occur over the duration of the scan (Figure 3C). Apart from coronal orientation with venc 150 cm/s changes in 0th order offsets are below 2.5% of the encoding velocity. Accordingly, assuming standard phantom calibration at room temperature of the gradients vs. measurements at 20 K above room temperature, errors of more than 10% of the encoding velocity can occur in a 20 cm FOV over a measurement time of 12 minutes. Already after 4 minutes errors of up to 7.5% of the encoding velocity occur.Figure 3


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)

Change in phase errors for different geometries and encoding velocities. Linear and zeroth order background phase errors measured at different temperatures for the x, y and z gradient coils in sagittal, transverse and coronal slices with velocity encodings of 50, 100 and 150 cm/s. Velocity was encoded along AP (A), RL (B) and FH (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig3: Change in phase errors for different geometries and encoding velocities. Linear and zeroth order background phase errors measured at different temperatures for the x, y and z gradient coils in sagittal, transverse and coronal slices with velocity encodings of 50, 100 and 150 cm/s. Velocity was encoded along AP (A), RL (B) and FH (C).
Mentions: In Figure 3 the resultant change in background offset at the echo times extracted from the data acquired with field monitoring is summarized for all nine measurements. Changes in 1st and 0th order offsets are depicted for flow encoding along the x, y and z gradient coils. At 10 cm distance from the iso-center changes in phase error of up to 11% of the encoding velocity can occur over the duration of the scan (Figure 3C). Apart from coronal orientation with venc 150 cm/s changes in 0th order offsets are below 2.5% of the encoding velocity. Accordingly, assuming standard phantom calibration at room temperature of the gradients vs. measurements at 20 K above room temperature, errors of more than 10% of the encoding velocity can occur in a 20 cm FOV over a measurement time of 12 minutes. Already after 4 minutes errors of up to 7.5% of the encoding velocity occur.Figure 3

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