MRI AT HIGH MAGNETIC FIELDS. Kâmil Uğurbil. University of Minnesota

Transcription

1 MRI AT HIGH MAGNETIC FIELDS Kâmil Uğurbil University of Minnesota

2 CENTER for MAGNETIC RESONANCE RESEARCH (CMRR)

3 Blood Vessel Distribution in Rat Brain brain slice (ink injection) Venous structure: T 2 *-weighted GE EPI (150 x 150 x 1000 µm 3 ) Ogawa S, Lee T-M, Kay AR, Tank DW.. Proc Natl Acad Sci USA 1990;87:

4 MAGNETIC FIELD AROUND BLOOD VESSELS 0% deoxy-hb 10% deoxy-hb 30% (Arteries)

5 BLOOD OXYGEN LEVEL DEPENDENT CONTRAST (BOL One VOXEL in the IMAGE DEOXY-Hemoglobin (Paramagnetic)

6 INCREASED NEURONAL ACTIVITY INCREASE in REGIONAL BLOOD FLOW (& Volume) LOWER DEOXYHEMOGLOBIN CONTENT per unit volume in the BRAIN if Cerebral Oxygen Consumption (CMRO 2 ) does not increase commensurately

7 MAGNETIC FIELD AROUND BLOOD VESSELS Increased Neuronal Activity: deoxy-hb 30% deoxy-hb 10%

8 From Ogawa et al 1992 PNAS paper From Ogawa et al 1992 PNAS Paper. From Kwong et al 1992 PNAS paper Title Ogawa et al PNAS 1992: Figure 2 images superimposed

9 Opaque anatomical Image In Grey scale SILENT WORD GENERATION

10 STATE-of-the-ART in 1990 PET Difference Images Raichle, M. Trends in Neurosciences, (2): p

11 Scales of the Brain

12 Ocular Dominance Columns OPTICAL IMAGING, MONKEY V2 V1 Ts o et al., Science 1990

13 Ogawa S, Menon RS, Tank DW, Kim SG, Merkle H, Ellermann JM, Ugurbil K. Biophys J 1993;64(3): B 0 B 0 B

14 EXTRAVASCULAR BOLD R 2 * (1/s) Gradient Echo T RATIO of Capillary vs. Venule/Vein 60 & 100 µ 12 7T contribution 10 to FUNCTIONAL 5 µ SIGNAL 8 CHANGES in GE BOLD 1.5T R* 2 (1/s) Vessel diameter ν vw = κ B 0 f dhb κ = constant f dhb = fraction of dhb in blood Deoxyhemoglobin Change ΔS S O e TE R 2 * ( R 2 * / ν vw ) (κ B 0 TE) Δf dhb Frequency Frequency ν Difference, on the vessel Hz wall, (Hz) vw B o Functional Signal Change Slope CONSTANT Green lines mark expected values for 30% deoxyhb in all vessels K. Uludağ, B. Müller-Bierl, K. Uğurbil Neuroimage (2009) 48(1): p

15 EXTRAVASCULAR BOLD (GRADIENT ECHO) RATIO of Functional Signal contribution from the two different vessel types RATIO RATIO ΔS Capillary/Venule of SLOPES T 7T 10.5T 5 µ vs. 60 or 100 µ Vessel diameter B o f dexyhb Frequency ν on the vessel wall, (Hz) vw B o ΔS S O e TE R 2 * ( R 2 * / ν vw ) (κ B 0 TE) Δf dhb Functional Signal Change Slope Deoxyhemoglobin Change CONSTANT Green lines mark expected values for 30% deoxyhb in all vessels K. Uludağ, B. Müller-Bierl, K. Uğurbil Neuroimage (2009) 48(1): p

16 EXTRAVASCULAR BOLD (GRADIENT ECHO) RATIO of Functional Signal contribution from the two different vessel types RATIO RATIO ΔS Capillary/Venule of SLOPES T 7T 10.5T 5 µ vs. 60 or 100 µ Vessel diameter B o f dexyhb Frequency ν on the vessel wall, (Hz) vw B o Green lines mark expected values for 30% deoxyhb in all vessels K. Uludağ, B. Müller-Bierl, K. Uğurbil Neuroimage (2009) 48(1): p

17 EXTRAVASCULAR BOLD GRADIENT Echo (GE) SPIN Echo (SE) R 2 * (1/s) T 7T 9.4T 16.4T Vessel diameter 60&100 µ 5 µ R 2 2 (1/s) T 7T 9.4T 16.4T Vessel diameter 60 µ Frequency Difference, on the vessel Hz wall, (Hz) Frequency Frequency on the Difference, vessel wall, Hz (Hz) ν vw ν vw 5 µ 100 µ 2% blood volume Green lines mark expected values for 30% deoxyhb K.Uludağ, B. Müller-Bier, K. Uğurbil Neuroimage (2009) 48(1): p

18 MR detected Mapping Signals and Physiologic Changes induced by Neuronal activity ΔS/S 4 SE fmri, TE set to tissue T 2 total fmri signal (micro-vasculature) total fmri signal (macro-vasculature) ΔCBV=0 total fmri signal [%] d) ΔCBV 16% field strength (T) K. Uludağ, B. Müller-Bierl, K. Uğurbil Neuroimage (2009) 48(1): p

19 Ocular Dominance Columns OPTICAL IMAGING, MONKEY HIGH Field SPIN ECHO fmri (when the resolution is High enough) V2 V1 Ts o et al., Science 1990

20 Ocular Dominance Columns OPTICAL IMAGING, MONKEY S B 0 TE X S B 0 TE LOW FIELD HIGH FIELD GE fmri x >1 for B 0 < ~ 10T x 1 as B 0 >> 10T Ts o et al., Science 1990

21 High Res. GE fmri 1.5 T courtesy of Mark Haacke JMRI 9: (1999). 0.4x0.4x2 mm 3 High Res. GE fmri 7T 0.5x0.5x2 mm 3

22 Ocular Dominance (ODC) and Orientation maps in Human V1 (7 Tesla) ODC REPRODUCIBILITY 2 days 3 days Left Right Yacoub, Shmuel, et al. Neuroimage (2007) 37(4):

23 Ocular Dominance (ODC) and Orientation maps in Human V1 (7 Tesla) ODC Orientation Left Phase Right 1 mm 1 mm Yacoub, Shmuel, et al. Neuroimage (2007) 37(4): Yacoub, Harel, Uğurbil PNAS (2008) 105(30):

24 Orientation Domains in the Primary Visual Cortex Monkey Optical Imaging Human fmri (SE, 7 Tesla) ~4 mm ~4 mm Yacoub, Harel, Uğurbil PNAS 2008

25 Challenge: To Acquire High Field Human Data 4 TESLA Barfuss et.al. NMR Biomed:3(1)1990 From SIEMENS CORPORATE RESEARCH

26 INITIAL RESULTS from SIEMENS at 4 TESLA Object dimension L ~ λ for RF Barfuss et.al. NMR Biomed:3(1)1990 (DATA from SIEMENS)

27 4T vs. 7T : B1 NON-UNIFORMITY & SNR T. Vaughan et al MRM 46, (2001) 4T 7T Mean SNR (boxes) from 6 identical comparison studies in approximately fully relaxed Gradient recalled echo images

28 Transmit B 1 Maps with a Volume Coil at 7T 0.06 B 1 (µt/v)

29 Simulation of B 1 + (300 MHz; 7 Tesla) Deionized Water L ~ λ Yang et al. MRM 47 (5), (2002) CMRR / PennState collaboration

30 Simulation of B mm NaCl Yang et al. MRM 47 (5), (2002) CMRR / PennState collaboration

31 Simulation of B mm NaCl Yang et al. MRM 47 (5), (2002) CMRR / PennState collaboration

32 EXCERPT from the ABSTRACT: and in the human head. Temporal progression of the RF field indicates that the standing wave and associated dielectric res- onance occurring in a pure water phantom near 300 MHz is greatly dampened in the human head due to the strong decay of the electromagnetic wave. The characteristic image intensity distribution in the human head is the result of spatial phase distribution and amplitude modulation by the interference of the RF traveling waves determined by a given sample- coil config- uration. The numerical calculation method is validated with

33 7T Body: Head: λ = 12 cm L ~ cm L/λ~1.7 ~ 3.3

34 7 T B 1 Field Contours in a TEM BODY COIL UNLOADED L/λ > ~ 1 Body ~ 3λ x 6λ LOADED Traveling wave regime Vaughan, J.T., et al. MRM, (1): p

35 7 T B 1 + Field Contours in a TEM BODY COIL Body coil Transmit Only Local array Receive only d, cm 60 LOADED d Magnet isocenter Body Coil Tx Local Coil Rx Vaughan, J.T., et al. MRM, (1): 244-8

36 E field B 1 field Simulations by Jinfeng Tian,CMRR, U Minnesota Vaughan, J.T., et al. MRM, (1): p

37 Relative B 1 Phase (experimental) Current carrying element ground plane Van de Moortele et al MRM 2005; 54:

38 Relative B 1 Phase M k + B 1,k Van de Moortele et al MRM 2005; 54(6):

39 Relative Transmit B 1 AMPLITUDE 300 MHz [a.u] M M B + + 1,k B 1,k k k Van de Moortele et al Magn Reson Med 2005; 54(6):

40 Relative Transmit B 1 AMPLITUDE 300 MHz [a.u] M k + B 1,k Van de Moortele et al Magn Reson Med 2005; 54(6):

41 Relative RECEIVE B 1 AMPLITUDE 300 MHz N j B 1, j N j B 1, j 64 MHz Van de Moortele et al Magn Reson Med 2005; 54(6):

42 Transmit B 1 Maps with a Volume Coil at 7T 0.06 B 1 (µt/v)

43 3 Tesla: Actual Flip Angle Map

44 Multichannel TRANSMIT & RECEIVE Adriany Vaughan, et al, J.T., MRM et al. 2005;53(2): MRM, (1): p Van Snyder, Moortele C.J., et et al. al MRM, 2005; (6): 61(3): p Metzger, G.J., et al. MRM, (2): p x T/R Switches up to 32 Low Noise Preamps. Receive Digital Receiver 16 Independent RF Channels 16 x 1 kw amp 16 Channel RF Safety Monitoring

45 Multiband RF Pulse Performance: ptx vs. Circularly Polarized L Curves for RF Energy vs. B1 Homogeneity (RMSE) MB=2, 1 spoke 0.6 RF Energy Same fidelity Same energy ~70% Decrease Root Mean Square Error (RMSE) in Transmit B1 X. Wu, S. Schmitter, E. J. Auerbach, S.Moeller, K. Uğurbil, and P-F Van de Moortele ISMRM 2013, #74; MRM 2013; Magn Reson Med 70: (2013)

46 Parallel Transmit (ptx) with Multiband Pulses, 7 T: Improving B 1 + Homogeneity for MB2 Wu et al. Magn Reson Med 70: (2013) Experimental Flip angle map 16 channel GRE sag view Circularly Pol. ptx, 1 spoke

47 1x16 L curves of peak 10 g SAR vs. excitation error (RMSE) Xu et al 2014 ISMRM 1x8 1x8 1x16 2x8 2x8 2x8, axial 2x8, coronal

48 Parallel Imaging Performance as a Function of Field Strength Geometry Factor in the Center; FOV 25 cm Geometry Factor B o, Tesla 2 R B o, Tesla SNR 4.5 PI = SNR 2 full g R 3 4 R 5 Wiesinger F, Van de Moortele PF, Adriany G, De Zanche N, Ugurbil K, Pruessmann KP. Magn Reson Med 2004;52(5):

49 Higher Fields Favors Parallel Imaging Performance SNR PI = SNR full g R B o, Tesla R (Reduction Factor) Wiesinger et al, NMR Biomed /10/15 JT Vaughan-CMRR-UMN 49

50 7T Cardiac Cine: Parallel Imaging with a local 32-Channel Receive Array R=2 R=5 Snyder, DelaBarre &Vaughan

51 Proc Natl Acad Sci U S A, 74, (1977) PCr P i ATPγ + ADP P i ATPγ

52 HUMAN VISUAL CORTEX 7 Tesla P i PCr ATP Syn. Creatine Kinase P i γ-atp (A-B) SNR Chemical Shift Resolution * * (B) Measurement of Pi + ADP ATP γ-atp H. Lei, et al, PNAS 100, (2003) (A)

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54 Functional MRI Mapping of Hemifield Visual Stimulation [4-13 C] Glu [4-13 C] Glu Slice 1 64 min Slice 2 48 min 32 min 16 min W. Chen, et al. MRM 2001; 45; min

55 J. Budde S. Gunamony R. Pohmann MPI, Tübingen 9.4 T vs. 3T 9.4T, 21 slices, projection thickness 14.3mm 3T, 14 slices, projection thickness 14mm

56 9.4T, 21 slices, projection thickness 14.3mm 3T, 14 slices, projection thickness 14mm 9.4 T vs. 3T MPI, Tübingen

57 TOF angiography at 7 Tesla at 0.4 mm isotropic resolution S. Schmitter, CMRR

58 7 Tesla T2 Weighted ANATOMIC IMAGING in The Brain Three-dimensional Segmentation of the Internal Structures of the Human HIPPOCAMPUS Henry, T.R., M. Chupin, S. Lehericy, J. Strupp, M.A. Sikora, Z.- Y. Sha, K. Ugurbi, and P.- F. Van de Moortele: Radiology, 2011; 261(1): p Image acquisition: University of Minnesota, CMRR; Image Segmentation: CNRS UPR LENA, University Pierre and Marie Curie, Paris, France;Center for NeuroImaging Research, University Pierre and Marie Curie - Paris, France; Neuroradiology, Pitie-Salpetriere Hospital, Paris, France

59 4 Tesla 7 Tesla

60 7 Tesla 60

61 CENTER for MAGNETIC RESONANCE RESEARCH (CMRR)