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Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation 

Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation  November 14, 2005, CMRR : Djaudat Idiyatullin. Mike’s crazy idea is working . Interleaved excitation and sampling during a frequency-swept pulse. …. …. BIR4. Steady state

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Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation 

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  1. Magnetic Resonance Imaging of Fast Relaxing Spins: Acquisition during Adiabatic Excitation  November 14, 2005, CMRR : Djaudat Idiyatullin

  2. Mike’s crazy idea is working 

  3. Interleaved excitation and sampling during a frequency-swept pulse … … BIR4 • Steady state • Sensitive to spins with a very short T2 • It is not FID but the signal predictable by Bloch simulation.

  4. How to extract information from this weird sampling during swept excitation? Least square method Monte Carlo simulation Wavelet transform

  5. How to extract information from this weird sampling during swept excitation?Solution: • Away from adiabatic condition 2. Linear system- Correlation method

  6. Linear system System h(t) Output r(t) Input x(t) • A system is linear if: • Linearity : Output = C * Input • Shift invariant : delaying of Input → same delaying of Output Convolution x(τ) → x(τ)h(t- τ) Fourier theorem: 0 τ t

  7. Evolution of the isochromats during HS8 pulse (dw=10mks, (~ 30 degree), R2=500Hz)

  8. Evolution of the isochromats during HS8 pulse (dw=10mks, (~ 30 degree), R2=500Hz) Linear system

  9. Correlation method for linear system FT Spin system h(t) Excitation x(t) Response r(t) * System spectrum FT

  10. Simulated data HS4 pulse 100 isochromats from -12.5kHz step 250Hz dw=10mks R1=500Hz

  11. SWeep Imaging with Fourier Transform (SWIFT) HSn pulses Flip angle < 90 degree Tr ~ Tp Bw=sw=2πN/Tp Back-projection reconstruction

  12. SWIFT, characteristics Signal intensity depends only on T1 and spin density (M0) : Maximum signal intensity Ernst angle: Maximum T1 contrast: Spin density contrast: Sensitive to short T2 :

  13. SWIFT, hardware problems “Dead time” after pulse 4.7T , 7T : ~ 3μs : sw < 130kHz 4T : ~ 20μs : sw < 40kHz FIFO underflow happens if: Tr < 5ms for 128 sampling Tr < 10ms for 256 sampling sw ~ 25-35 kHz

  14. Empty “16”-element TEM head coil MIP of 3D image sw=32kHz128x128 x 644T

  15. Sensitivity to short T2 3D image of thermoplastic T2~0.3ms sw=100kHz128x128 x 1284.7T

  16. Sensitivity to short T2 MIP of 3D image plastic toy in breast coil sw=39kHz128x128 x 128D=25cm4T

  17. First in vivo SWIFT 3D images Slices of 3D image of feet sw=20kHz4T

  18. Sensitivity to raspberry Slices of 3D image raspberryin vivosw=100kHz128x128x128D=3cm4.7T

  19. Another Mike’s crazy idea 

  20. Breast MR scanner

  21. Thanks to:Ivan Tkac Gregor Adriany Peter Andersen Tommy Vaughan Xiaoliang ZhangCarl SnyderBrian Hanna John StruppJanis Zeltins Patrick BolanLance DelaBarreUte Goerke all CMMR Fast & Quiet MRI by Sweeping Radiofrequency Djaudat Idiyatullin, Curt Corum, Jang-Yeon Park, Michael Garwood Macros, C programmingHardware Software Yellow pages of CMRR Discussion

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