31P-MRSI of the brain with B1-shimmed NOE enhancement

B.L. van de Bank, S. Orzada, F. Smits, M.W. Lagemaat, A.K. Bitz and T.W.J. Scheenen

31P-MRSI of the brain with B1-shimmed NOE enhancement

Why spectroscopy (31P)• Understanding metabolic processes

• Energy metabolism and/or phospholipid metabolism

• Advantages of 31P over 1H• Comprehensible spectrum

• No overlapping resonances• Direct insight in forementioned processes• Lower Larmor frequency

• Longer wavelengths, less destructive interferences• Homogeneous excitation patterns

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0.511.522.533.54

31P-MRSI of the brain with B1-shimmed NOE enhancement

Our previous work

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Tacq: 16 minVoxel: 6.3cc

Wijnen et al. ISMRM 18 (2010) 377

31P-MRSI of the brain with B1-shimmed NOE enhancement

How did we do it at that time?

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Wijnen et al. ISMRM 18 (2010) 377

31P• Surface coil

• Big transceive element• Quadrature driven

•Inhomogeneous B1

• Spatially dependent field• Adiabatic pulses• SAR demanding

• High SNR

1H• Birdcage coil

• Inhomogeneous field distribution (cp mode)

• No optimization possible

31P-MRSI of the brain with B1-shimmed NOE enhancement

What do we want?

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31P• Surface coil

• Big transceive element• Quadrature driven

•Inhomogeneous B1

• Spatially dependent field• Adiabatic pulses• SAR demanding

• High SNR

1H• Birdcage coil

• Inhomogeneous field distribution (cp mode)

• No optimization possible

31P• Volume Tx coil, quadrature driven

• Array of receive coils• Phased signal addition

•Homogeneous B1

• Spatially independent field• Short Hard pulses• Lower SAR constraints

• High SNR

1H• Volume coil

• Independent acting channels

• Field optimization1

• B1-shimming

Metzger et al. MRM. 59:396-409 (2008)

31P-MRSI of the brain with B1-shimmed NOE enhancement

Aim• To design, develop and contruct a coil setup:

• Signal handling: 120.3MHz & 297.2MHz

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1H• Anatomical background imaging• B0- & B1-shimming• NOE Signal enhancement

31P• Homogeneous excitation• Spectroscopic imaging• Local receive SNR Boost

31P-MRSI of the brain with B1-shimmed NOE enhancement

Coil design – 1H

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1H

• Adapted existing design1

• 8 individual channels• Transceive elements• With meander

• Octogonal shaped• Ø |26cm (/28cm)

1Orzada et al. Proc. ISMRM 17 (2009) # 3010

31P-MRSI of the brain with B1-shimmed NOE enhancement

Coil design – 31P

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31P• Birdcage coil• Insert for 8CH headcoil• TXRX & TX-only • Quadrature driven• Plexiglass tube:

• Øout = 25cm, length = 18cm

• thk = 0,5cm, #legs = 8, HP

• Local receive array• 7 Channels• Receive only

• Ø = 5cm

• decoupled by overlap & pre-amp

31P-MRSI of the brain with B1-shimmed NOE enhancement

Coil design – 1H & 31P

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1H 31P

31P-MRSI of the brain with B1-shimmed NOE enhancement

Coil design – 1H & 31P

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31P-MRSI of the brain with B1-shimmed NOE enhancement

Coil design – 1H & 31P

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31P-MRSI of the brain with B1-shimmed NOE enhancement

Safety check – |E|- & |H|-fields

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|E|-field|H|-field

8CH

8CH + BC8CH + BC + RX

2

• Robot measurement• Probes1:

• H3DV7 - |H|

• ES3DV2 - |E|

• Tissue simulating Fluid:• 120MHz: ε = 76,5 & σ = 0,78 S/m

• 296MHz: ε = 56,3 & σ = 0,98 S/m

1Schmid & Partner Engineering AG (SPEAG), Zürich, Switzerland2Bitz et al. Proc. ISMRM 19 (2011) #490

31P-MRSI of the brain with B1-shimmed NOE enhancement

Transceive vs. Separate TX & RX

Boost SNR locally > 600%

SNR Birdcage

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31P-MRSI of the brain with B1-shimmed NOE enhancement

Enhancement?no NOE NOE

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31P-MRSI of the brain with B1-shimmed NOE enhancement

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Whole brain• 3D MRSI

• Pulse acquire

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B1-map

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TR/TE: 1500/0.10ms

FA: 45°Block pulse: 0.3ms

FOV: 240x240x240mm3

Matrix: 12x12x8

Actual voxel size: 35cc

Tacq: 7:48

31P-MRSI of the brain with B1-shimmed NOE enhancement

All together• 3D MRSI

• NOE-enhancement• Receive array

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TR/TE: 1500/0.10ms

FA: 45°Block pulse: 0.3ms

FOV: 160x160x140

Matrix: 12x12x10

Actual voxel size: 7.3cc

TA: 15:55

31P-MRSI of the brain with B1-shimmed NOE enhancement

Summary• Development and functionality 7T coil setup

• 1H B1-shimming• Separating TX&RX

• SNR boost (up to 700%)• Signal enhancement

• ~30% • Nuclear Overhauser Effect

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Start exploiting all exciting features

Thank you very much for your attention

31P-MRSI of the brain with B1-shimmed NOE enhancement

Noise correlation

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• Check decoupling between individual coil elements

• Average noise correlation: 10 ± 7%• Maximum: 23% (CH 3&6)

31P-MRSI of the brain with B1-shimmed NOE enhancement

Field distribution altered?

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• Assess 1H field distribution• Is it altered by birdcage?

• Simulated1 & measured• With & without birdcage

+BC-BC

1CST Studio Suite, CST, Darmstadt, Germany