It is currently Fri 17. Nov 2017, 23:18


MRI RF Coil Examples

Use of CST Microwave Studio (MWS)
  • Author
  • Message
Offline

Tim.Herrmann

  • Posts: 33
  • Joined: Wed 17. Nov 2010, 16:19
  • Institut: Department of Biometry and Medical Informatics/OvG University Magdeburg/ www.uhf-mri.ovgu.de

MRI RF Coil Examples

PostFri 1. Nov 2013, 20:08

For forum members two MRI RF coil examples for simulation with Microwave Studio 2013.

In these examples we use the co simulation approach ->> Design Studio in relation with MWS.

We replace some or all Capacitors (lumped elements) by Ports.

Advantage: The RF coil will simulated off resonate --> increase of simulation comfort if you have enough Hardware GPU Power to simulate the additional ports.

1. MRI Surface coil for 7 Tesla
MRI_Surface_coil_7_Tesla_1.zip
(76.7 KiB) Downloaded 2865 times


You need run this simulation by Design Studio.

1. update S-Parameter Task (Design Studio)


2. MRI Birdcage low pass coil for 1.5 Tesla.
MRI_Birdcage_1_5_Tesla.zip
(1.07 MiB) Downloaded 3138 times





You need run this simulation by Design Studio.

1. update S-Parameter Task (Design Studio)
2. update AC, CP+ mode Task (Design Studio)
3. Evaluate the Post-processing Template B1+ in the 3D Area of MWS.
4. update PP1 Task (Design Studio)




Best Tim.
Attachments
BC_coil_b1_field.png
BC_coil_b1_field.png (66.91 KiB) Viewed 34389 times
BC_coil.png
BC_coil.png (49.77 KiB) Viewed 34389 times
SC_coil.png
SC_coil.png (31.49 KiB) Viewed 34389 times
Offline

Tim.Herrmann

  • Posts: 33
  • Joined: Wed 17. Nov 2010, 16:19
  • Institut: Department of Biometry and Medical Informatics/OvG University Magdeburg/ www.uhf-mri.ovgu.de

Re: MRI RF Coil Examples

PostTue 5. Nov 2013, 01:27

Dear Snowthunder, I've modified the Birdcage model now it's working fine at 63 MHz for S11 and S22.

Stick to guideline to get all the results for the 1.5 Tesla MRI Birdcage coil.




Dear,Tim
Thanks for posting the modal in the forum.I have tested them and have some query.
For the surface coil: There is only one loop about the surface coil.Why are there five ports? In my opinion ,port2,port3,port4,port5 should be removed or replaced by appropriate capacitors.Port1 is the port for exciation and received.
For the birdcage coil:I have some query about the simulation results.The designed birdcage should be resonant at 63MHz,but the reflection coefficient (S11 and S22) are too big, the magnitude are almost one.In this case ,all the input power are total refelcted. In my opinion, the magtitude of S11(or S22) shoud be smalll at the resonat frequency.I hope you can give me some suggestions.Thanks very much.


Dear Tim,
I am a phd student from Chines Academy of Scienses.Could you give me some general RF-coil models, so that I can have an easier excess in RF-coil simulation.I am sorry to trouble you and wish your reply.
Best wish to you

snowthunder
Offline

Tim.Herrmann

  • Posts: 33
  • Joined: Wed 17. Nov 2010, 16:19
  • Institut: Department of Biometry and Medical Informatics/OvG University Magdeburg/ www.uhf-mri.ovgu.de

Re: MRI RF Coil Examples

PostFri 23. Oct 2015, 16:51

Dear Alexia, the asymmetry problem is caused by low mesh resolution
for this CST example.

CST want to store examples with results on the Suite DVD 4.7 GB this
caused no realistic mesh adjustments.

I sent you an the BC in higher resolution with good matching and tuning values.

MRI_Birdcage_1_5_Tesla.zip
(1.23 MiB) Downloaded 2345 times



Further more a tutorial for BC hosted by our group.
viewtopic.php?f=8&t=37

Best regards

TH.


Dear Mr Hermann,

I am sorry to bother you but I am trying to understand how to simulate correctly a MRI birdcage and you seem to have taken part in the CST 1.5T model example available with the software.

I have been studying the model and I do not understand a few things. If by any chance you would have time to consider this, it would be helpful but I would understand you have not! You may just have references I could read.

First in my model I tend not to consider that important to match the impedance of the coil to 50 ohm as the only thing I want is the right field distribution meaning the homogeneous resonant mode of the birdcage to be at the larmor frequency. I thought I could always compensate for loss of power by reflection by artificially increasing the input power to scale the magnitude of the field to the experimental one. The only reason for me the matching would be important is that I realised that both 3D ports 90° apart do not see the same impedance for the birdcage so with a 50 ohm reference impedance source the reflection will be different for both ports therefore the power sent by each port into the birdcage different. And I would like both ports to send an equivalent power.

Before CST I used SEMCAD and it seemed to me they solved this problem by using at the two ports an ideal voltage source but I am not completly sure it was not a 50 ohm source. Nevertheless using these voltage sources (ideal or 50 ohm, I am not sure) without any matching I managed to get a 13% error on the B1 field distribution compared to experiment.

So the only thing I tend to look at is the input impedance of the birdcage seen from the 3D ports not considering the complementary matching circuit. And when I look at the input impedance seen from the 3D port from the CST example (cf attached files), I realise that although the field monitors are set at 63MHz, the birdcage seem to resonate more at 64.5MHz. And the quality factor being very high, 63 MHz is actually out of the resonance.

Nevertheless the field distribution at 63MHz is clearly correct compared for example to our experimental B1 map data.

So do the tuning and matching capacitors parallel to the 3D port MT1 and MT2 compensate for that off resonance?
How should I determine their values? Should I just use the tuning tool to minimize the S11 for the input port without the matching capacitances first and then with the matching capacitance?

Thank you in advance for any help you could bring us.

Best regards

Alexia
Offline

GregK

  • Posts: 1
  • Joined: Sat 5. Dec 2015, 16:43
  • Institut: ETH Zurich

Re: MRI RF Coil Examples

PostSat 5. Dec 2015, 22:09

Foremost thank you for such great examples. Is there somewhere a tutorial how to set-up this simulation on one own? (i.e. how to build geometry, add lump elements and set the simulations parameters). This would be a tremendous help for people starting with CST.

Best wishes,
Greg
Offline

Tim.Herrmann

  • Posts: 33
  • Joined: Wed 17. Nov 2010, 16:19
  • Institut: Department of Biometry and Medical Informatics/OvG University Magdeburg/ www.uhf-mri.ovgu.de

Re: MRI RF Coil Examples

PostMon 7. Dec 2015, 02:07

Dear Greg, our group will lunch a Youtube tutorial for MRI RF coils construction with CST MWS 2015 in January 2016.

Best Tim.
Offline

Christian.Bruns

  • Posts: 1
  • Joined: Wed 25. Nov 2015, 11:49
  • Institut: Department of Biometry and Medical Informatics/OvG University Magdeburg/ www.uhf-mri.ovgu.de

Re: MRI RF Coil Examples

PostTue 2. Feb 2016, 13:40

Dear Greg,
here is a youtube Tutorial for building and preparing a surface coil for simulation in CST Microwave Studio. A tutorial with evaluation of the results will follow.


Best wishes,
Christian

Return to CST Microwave Studio (MWS)

Who is online

Users browsing this forum: No registered users and 1 guest

cron