presentation ismrm 2011
TRANSCRIPT
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
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.
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!
What happens?
Movement of diaphragm & ribs
• Expansion of lungs intake of oxygen
• Including movement in abdominal region
• Increase in air volume
• Change in O2/CO2
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
Dynamic B0 Mapping of the Breast 3
3 Luttje et al. poster 1035
Me
an
B0-f
ield
dis
trib
utio
n [H
z]
50 100 150Time [s]0
150
160
170
180
140
130
Dynamic B0 Mapping of the Breast 3
3 Luttje et al. poster 1035
Me
an
B0-f
ield
dis
trib
utio
n [H
z]
Re
sp
ira
tory
se
nso
r [a
.u.]
50 100 150
50 100 150
Time [s]
Time [s]
0
0
150
160
170
180
140
130
0
-4000
4000
8000
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, …
Tim
e
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
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
Results: Correction for free breathing
• Frequency offset during breathing cycle:
• ~100 – 150 Hz (~0.3 – 0.5 ppm)
Squares: STEAM, Line: Field probe
Results: B0 deviation during breath hold
• During breath-hold oxygen is used: (02/C02)
• B0 deviation
• Cardiac activity also influences B0
0 5 10 15 20-10
-5
0
5
time [s]
Off-r
eso
na
nce fre
qu
ency [H
z]
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)
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
Thank you for your attention