1. Frequency correction for MR
Spectroscopy in the human breast at
7T with external field monitoring
B.L. van de Bank, V.O. Boer, M.P. Luttje, J.P. Wijnen, G. van Vliet,
J.M. Hoogduin, P.R. Luijten and D.W.J. Klomp
Department of Radiology, University Medical Center Utrecht, Utrecht, the Netherlands
2. Declaration of Relevant Financial Interests
or Relationships
Speaker Name: Bart van de Bank
I have no relevant financial interest or relationship to disclose with regard
to the subject matter of this presentation.
3. 3B.L.vandeBank-2@umcutrecht.nl
Take a deep breath!
Breathing is an essential part of our life.
We breath all day long and automatically as well,
even during an MR examination.
and do not forget to exhale!
5. 5B.L.vandeBank-2@umcutrecht.nl
How does this relate to MR?
• Breathing induces B0 variations
• Brain1,2
• Breast 3
• Breast: worst case region
• Lungs
• Heart
1 van Gelderen et al. MRM (2007)
2 Versluis et al. NeuroImage (2011)
3 Bolan et al. MRM (2004)
ΔB0 [Hz]Dynamic B0-Map
7. 7B.L.vandeBank-2@umcutrecht.nl
Dynamic B0 Mapping of the Breast 3
3 Luttje et al. poster 1035
MeanB0-fielddistribution[Hz]Respiratorysensor[a.u.]
50 100 150
50 100 150
Time [s]
Time [s]
0
0
150
160
170
180
140
130
0
-4000
4000
8000
8. 8B.L.vandeBank-2@umcutrecht.nl
Aim & challenges to overcome
B0 fluctuation is not periodical
• Motional component
• Susceptibility changes
• Eddy currents
• Drift
• Results in:
• Line broadening
• Blurring
• Affects: MRS, SWI, EPI, …
Time
9. 9B.L.vandeBank-2@umcutrecht.nl
External field measurement equipment
Field probe 4
• Cylinder filled with
trifluoroethanol (TFE)
• Transceive loop for 19F @ 7T
• Interfaced via independent
NMR spectrometer
• Integrated in dedicated
breast RF coil setup 5
4 Barmet et al. MRM 62:269–276 (2009)
5 Klomp et al. NMR Biomed. (2011)
The Load&GoTM Real Time Shims
(RTS), Resonance Research
10. 10B.L.vandeBank-2@umcutrecht.nl
Experiments
MRS water
• STEAM
• (TR/TE 1500/5.6ms)
• Dynamic series
Breath-hold & regular breathing
• Retrospective correction
• Repeated pulse acquire
• (TR 100 ms)
• Setup
• Phantom study, male volunteer
• Exclude tissue motion in voxel
Real-time
• Triggered single pulse acquire
• prior to excitation
• Female volunteer
14. 14B.L.vandeBank-2@umcutrecht.nl
Discussion
• B0 correction can be performed for breast spectroscopy at 7T
• Breathing, cardiac, drift, Eddy currents
• Allows for real-time B0 updating
Further optimization:
• Frequency deviation is location dependent
• For correction extend to multiple field probes
• Real-time shim updating is feasible with this setup (Z2, XY, …)
• Eddy current characterization and compensation on high
order shims 6
6 Juchem et al Concepts Magn Reson Part B (2010)
15. 15B.L.vandeBank-2@umcutrecht.nl
Conclusion
• Field probe can be positioned in close proximity of tissue of
interest
• Direct observation of temporal frequency variations is possible
• Accurate detection allows for real-time B0 correction
• Reduces B0 induced artifacts and improves SNR as shown here
for breast spectroscopy at 7T
• Also applicable for other locations and sequences