Spectroscopy (January, 2010)

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Spectroscopy (January, 2010)

  1. 1. Magnetic ResonanceMagnetic Resonance SpectroscopySpectroscopy (MRS)(MRS) Basic PrinciplesBasic Principles Single Voxel TechniquesSingle Voxel Techniques Chemical Shift Imaging (CSI)Chemical Shift Imaging (CSI) Water SuppressionWater Suppression Clinical ApplicationsClinical Applications
  2. 2. MR SpectroscopyMR Spectroscopy • Magnetic Resonance Spectroscopy (MRS)Magnetic Resonance Spectroscopy (MRS) provides a non-invasive method of studyingprovides a non-invasive method of studying metabolism in vivo.metabolism in vivo. • The tissue’s chemical environmentThe tissue’s chemical environment determines the frequency of a “metabolitedetermines the frequency of a “metabolite peak” in an MRS “spectrum”.peak” in an MRS “spectrum”. 2
  3. 3. 3 Spectrum: graph of amount ofSpectrum: graph of amount of metabolites versus frequencymetabolites versus frequency NAA Peak Choline Peak Creatine Peak
  4. 4. MR SpectroscopyMR Spectroscopy • Candidates for MRS include:Candidates for MRS include: • 11 H,H, 3131 P,P, 1313 C,C, 2323 Na,Na, 77 Li,Li, 1919 F,F, 1414 N,N, 1515 N,N, 1717 O,O, 3939 KK • The most commonly studied nuclei areThe most commonly studied nuclei are 11 HH andand 3131 PP • This lecture is focused on Proton (This lecture is focused on Proton (11 H)H) SpectroscopySpectroscopy 4
  5. 5. MR SpectroscopyMR Spectroscopy • Imaging Voxel:Imaging Voxel: – 1 – 5 mm1 – 5 mm33 – Signal from water (and fat)Signal from water (and fat) – 111 Molar concentrations111 Molar concentrations • Spectro Voxel:Spectro Voxel: – 1 – 8 cm1 – 8 cm33 – Signal from metabolitesSignal from metabolites – 1 – 10 milliMolar concentrations1 – 10 milliMolar concentrations 5
  6. 6. Proton SpectroscopyProton Spectroscopy • Electrons have HUGE magnetic momentsElectrons have HUGE magnetic moments – ~700 times the proton magnetic moment~700 times the proton magnetic moment • The static magnetic BThe static magnetic B00 field “seen” by a nucleusfield “seen” by a nucleus in a molecule is shielded by the covalent electronin a molecule is shielded by the covalent electron structure surrounding the nucleus.structure surrounding the nucleus. • The electron cloud produces a small change inThe electron cloud produces a small change in the magnetic field around nuclei in molecules.the magnetic field around nuclei in molecules. 6
  7. 7. Proton SpectroscopyProton Spectroscopy • Electrons in water molecules (HElectrons in water molecules (H22O) create aO) create a different local magnetic field than electrons in fatdifferent local magnetic field than electrons in fat molecules (CHmolecules (CH22)) • This is “Chemical Shift” which we see in clinicalThis is “Chemical Shift” which we see in clinical images.images. 7
  8. 8. 8
  9. 9. 9http://www.steve.gb.com/science/spectroscopy.htmlhttp://www.steve.gb.com/science/spectroscopy.html Ethanol spectrumEthanol spectrum OHOH CHCH22 CHCH33
  10. 10. Proton SpectroscopyProton Spectroscopy • Chemical shiftsChemical shifts inin HzHz areare dependentdependent onon the strength of the applied field Bthe strength of the applied field B00 – Chemical shift between water and fat:Chemical shift between water and fat: • 220 Hz at 1.5T220 Hz at 1.5T • 440 Hz at 3T440 Hz at 3T • Chemical shiftsChemical shifts inin ppmppm areare independentindependent of the strength of the applied field Bof the strength of the applied field B00 – Chemical shift between water and fat:Chemical shift between water and fat: • 3.44 ppm at 1.5T3.44 ppm at 1.5T • 3.44 pm at 3T3.44 pm at 3T 10
  11. 11. Proton SpectroscopyProton Spectroscopy 11 Single voxel spectroscopy (Single voxel spectroscopy (SVSSVS)) •Point-RESolved Spectroscopy (Point-RESolved Spectroscopy (PRESSPRESS)) •Stimulated echo acquisition method (Stimulated echo acquisition method (STEAMSTEAM)) Chemical shift imaging (Chemical shift imaging (CSICSI).). •2D-CSI2D-CSI •3D-CSI3D-CSI Essential: suppress the water signal, CHEmical-Shift-Essential: suppress the water signal, CHEmical-Shift- Selective (Selective (CHESSCHESS) pulses) pulses
  12. 12. Proton SpectroscopyProton Spectroscopy 12 •The concentration of pure water is 55.6 M forThe concentration of pure water is 55.6 M for HH22O or 111 M forO or 111 M for 11 H.H. •The water concentration in the brain is aboutThe water concentration in the brain is about 70% or 36 M.70% or 36 M. •In vivoIn vivo 11 H spectroscopy requires waterH spectroscopy requires water suppression because the 36 M water signalsuppression because the 36 M water signal overpowers the 1-10 mM signal of theoverpowers the 1-10 mM signal of the metabolites.metabolites.
  13. 13. Proton SpectroscopyProton Spectroscopy 13 This figure demonstrates the importance of suppressing theThis figure demonstrates the importance of suppressing the water signal. The metabolites of interest have a signalwater signal. The metabolites of interest have a signal one hundred times smaller than that of the water peak,one hundred times smaller than that of the water peak, and without water suppression would be poorly resolvedand without water suppression would be poorly resolved © Scott & White 2004© Scott & White 2004 10001000 800800 600600 400400 200200 00 00 55 1010 1515 2020 2525
  14. 14. Proton Spectroscopy (SVS with PRESS)Proton Spectroscopy (SVS with PRESS) Basic diagram of SVS with spin echo (ref #1)Basic diagram of SVS with spin echo (ref #1) • Water-suppressionWater-suppression • The 90° pulse excites a slice.The 90° pulse excites a slice. • The first 180° pulse refocuses the transverseThe first 180° pulse refocuses the transverse magnetization in a row of tissue within themagnetization in a row of tissue within the slice.slice. • The second 180° pulse refocuses theThe second 180° pulse refocuses the magnetization within a column of the row,magnetization within a column of the row, leaving a single voxel.leaving a single voxel. • Then, the signal represents a combination ofThen, the signal represents a combination of spins in that voxel precessing at slightlyspins in that voxel precessing at slightly different frequencies (function of time).different frequencies (function of time). • Fourier transform of signalFourier transform of signal  number ofnumber of spins at a given frequency in a voxelspins at a given frequency in a voxel (function of frequency).(function of frequency). © Scott & White 2004© Scott & White 2004 14 For one acquisition scheme– Point RESolved SpectroscopyFor one acquisition scheme– Point RESolved Spectroscopy (PRESS)(PRESS)
  15. 15. Proton SpectroscopyProton Spectroscopy (SVS with PRESS)(SVS with PRESS) The effect of echo time in SE single voxel spectroscopy (SVS).The effect of echo time in SE single voxel spectroscopy (SVS). Left: TE=30ms; Right: TE=144 ms. Glx (glutamine) and myoinositol (mI) haveLeft: TE=30ms; Right: TE=144 ms. Glx (glutamine) and myoinositol (mI) have short Tshort T22 values and are not visible on long TE spectra.values and are not visible on long TE spectra. 15 © Scott & White 2004© Scott & White 2004
  16. 16. Proton SpectroscopyProton Spectroscopy (SVS with PRESS)(SVS with PRESS) 16 Major healthy brain metabolite peaks:Major healthy brain metabolite peaks: short TE spectra (add’l peaks): 4) myoinositol (mI) at 3.56 ppm, 5) glutamineshort TE spectra (add’l peaks): 4) myoinositol (mI) at 3.56 ppm, 5) glutamine and glutamate (Glx) between 2.05-2.5 ppm and 3.65-3.8 ppm, and 6)and glutamate (Glx) between 2.05-2.5 ppm and 3.65-3.8 ppm, and 6) glucose at 3.43 ppm.glucose at 3.43 ppm. long TE spectra: 1) N-acetylaspartate (NAA) at 2.02 ppm, 2) choline (Cho) atlong TE spectra: 1) N-acetylaspartate (NAA) at 2.02 ppm, 2) choline (Cho) at 3.20 ppm, and 3) creatine (Cr) at 3.02 ppm and 3.9 ppm.3.20 ppm, and 3) creatine (Cr) at 3.02 ppm and 3.9 ppm. © Scott & White 2004© Scott & White 2004
  17. 17. Proton SpectroscopyProton Spectroscopy (SVS with STEAM)(SVS with STEAM) Basic diagram of SVS with STEAM:Basic diagram of SVS with STEAM: •Water-suppressionWater-suppression •The 90° pulse excites a slice.The 90° pulse excites a slice. •A second 90° pulse refocuses the transverseA second 90° pulse refocuses the transverse magnetization in a row of tissue within themagnetization in a row of tissue within the slice.slice. •A third 90° pulse refocuses the magnetizationA third 90° pulse refocuses the magnetization within a column of the row, leaving a singlewithin a column of the row, leaving a single voxel.voxel. Negative to STEAM: rephasing only aboutNegative to STEAM: rephasing only about 50% of the original generated transverse50% of the original generated transverse magnetization (low SNR).magnetization (low SNR). ~ (sort of ) Positive to STEAM: shorter echo~ (sort of ) Positive to STEAM: shorter echo times than PRESS sequence.times than PRESS sequence. 17 © Scott & White 2004© Scott & White 2004
  18. 18. Multivoxel SpectroscopyMultivoxel Spectroscopy (Chemical Shift Imaging)(Chemical Shift Imaging) Phase encoding gradients can be utilized, as inPhase encoding gradients can be utilized, as in imaging, in order to encode spatial information.imaging, in order to encode spatial information. Figure 4 illustrates a simple 2D chemical shiftFigure 4 illustrates a simple 2D chemical shift imaging (CSI) acquisition scheme.imaging (CSI) acquisition scheme. 18
  19. 19. Figure 4Figure 4 19 © Scott & White 2004© Scott & White 2004
  20. 20. Multivoxel SpectroscopyMultivoxel Spectroscopy (Chemical Shift Imaging)(Chemical Shift Imaging) Figure 5 illustrates the imaging setup for a 2D CSIFigure 5 illustrates the imaging setup for a 2D CSI acquisition.acquisition. A single slice is defined through the area ofA single slice is defined through the area of interest, and then a box is specified within thisinterest, and then a box is specified within this (white lines).(white lines). Spectra will then be generated for all voxels withinSpectra will then be generated for all voxels within the box.the box. 20
  21. 21. Figure 5Figure 5 21 This figure presents the spectra for a low grade brainstem glioma.This figure presents the spectra for a low grade brainstem glioma. SE CSI acquisition: two spectra (TE=30 ms--second column, andSE CSI acquisition: two spectra (TE=30 ms--second column, and 144 ms--third column). The first column shows the voxel144 ms--third column). The first column shows the voxel corresponding to the spectra on the same row. Rows: 1st=lesioncorresponding to the spectra on the same row. Rows: 1st=lesion spectra, 2nd= normal brain spectra.spectra, 2nd= normal brain spectra. © Scott & White 2004© Scott & White 2004
  22. 22. 22 The lesion spectra demonstrate decreasedThe lesion spectra demonstrate decreased NAANAA (a marker of(a marker of neuronal integrity) and increasedneuronal integrity) and increased cholinecholine (a marker of myelin(a marker of myelin breakdown). The short TE spectrum demonstrates elevatedbreakdown). The short TE spectrum demonstrates elevated myo-myo- inositolinositol (a marker of glial cells).(a marker of glial cells). Figure 6 (next slide) presents a color-coded choline metaboliteFigure 6 (next slide) presents a color-coded choline metabolite map.map. © Scott & White 2004© Scott & White 2004 Figure 5Figure 5
  23. 23. Figure 6Figure 6 23 Multivoxel SpectroscopyMultivoxel Spectroscopy © Scott & White 2004© Scott & White 2004 Choline Map
  24. 24. • The clinical utility of the brain spectrum restsThe clinical utility of the brain spectrum rests upon 2 important properties:upon 2 important properties: – The nature and concentration of brain chemicalsThe nature and concentration of brain chemicals identified is remarkably constant—identified is remarkably constant— • A “normal” brain spectrum is readily recognizedA “normal” brain spectrum is readily recognized – The particular neurochemicals concerned are ofThe particular neurochemicals concerned are of clinical relevance in healthy and diseased brain.clinical relevance in healthy and diseased brain. 24 Brain SpectroscopyBrain Spectroscopy
  25. 25. 25 © 2007 by© 2007 by ProScanProScan ImagingImaging
  26. 26. 26 Single Voxel Prescription/positioningSingle Voxel Prescription/positioning
  27. 27. 27 Single Voxel Spectra from PhantomSingle Voxel Spectra from Phantom On Left: STEAM 35 TE On Right: PRESS 35 TEOn Left: STEAM 35 TE On Right: PRESS 35 TE
  28. 28. 28 Single Voxel Spectra PRESS TE 144Single Voxel Spectra PRESS TE 144
  29. 29. 29 Single Voxel Spectra PRESS TE 288Single Voxel Spectra PRESS TE 288
  30. 30. Brain SpectroscopyBrain Spectroscopy • Voxel placementVoxel placement 30 • SpectrumSpectrum
  31. 31. Brain SpectroscopyBrain Spectroscopy • Voxel placementVoxel placement • With saturation bandsWith saturation bands 31 • Spectrum from GBMSpectrum from GBM • Elevated choline, lactateElevated choline, lactate • decreased NAAdecreased NAA
  32. 32. 32 2D CSI of phantom --processed result2D CSI of phantom --processed result Mutlivoxel spectroscopyMutlivoxel spectroscopy
  33. 33. 33 3D CSI from3D CSI from phantom—phantom— processed resultprocessed result with compositewith composite metabolite mapmetabolite map
  34. 34. Spectroscopy of the ProstateSpectroscopy of the Prostate • Prostate cancer is associated withProstate cancer is associated with proportionatelyproportionately lowerlower levels oflevels of citratecitrate andand higher levels of choline and creatine thanhigher levels of choline and creatine than are seen in benign prostatic hyperplasiaare seen in benign prostatic hyperplasia (BPH) or in normal prostate tissue.(BPH) or in normal prostate tissue. 34
  35. 35. 35 Spectroscopy of the ProstateSpectroscopy of the Prostate © Reviews in Urology 2006© Reviews in Urology 2006
  36. 36. 36 Spectroscopy of the ProstateSpectroscopy of the Prostate greatly reduced citrategreatly reduced citrate, elevated choline, elevated choline  prostate cancerprostate cancer
  37. 37. 37 The diagnostic value of MRThe diagnostic value of MR spectroscopy is typically based on thespectroscopy is typically based on the detection of elevated levels of cholinedetection of elevated levels of choline compounds, which are a marker ofcompounds, which are a marker of active tumors.active tumors. Spectroscopy of the BreastSpectroscopy of the Breast © Radiology 2007© Radiology 2007
  38. 38. 38 Spectroscopy of the BreastSpectroscopy of the Breast © Radiology 2007© Radiology 2007
  39. 39. 39 (From previous slide)(From previous slide) Palpable mammographically detected andPalpable mammographically detected and biopsy-proved invasive lobular carcinomabiopsy-proved invasive lobular carcinoma in left breast of 56-year-old woman.in left breast of 56-year-old woman. This is a true-positive finding.This is a true-positive finding. Spectroscopy of the BreastSpectroscopy of the Breast © Radiology 2007© Radiology 2007
  40. 40. 40 Spectroscopy of the BreastSpectroscopy of the Breast © Radiology 2007© Radiology 2007
  41. 41. 41 Suspicious nonmass lesion detected atSuspicious nonmass lesion detected at screening MR imaging in 38-year-oldscreening MR imaging in 38-year-old woman withwoman with BRCA-1BRCA-1 gene who was imaged at day 11 ofgene who was imaged at day 11 of her menstrual cycle.her menstrual cycle. This is a true-negative finding.This is a true-negative finding. Spectroscopy of the BreastSpectroscopy of the Breast © Radiology 2007© Radiology 2007
  42. 42. 42 elevatedelevated levels oflevels of cholinecholine compoundscompounds  markermarker of active tumors.of active tumors. Spectroscopy of the BreastSpectroscopy of the Breast
  43. 43. 43 Spectroscopy at 3T vs 1.5TSpectroscopy at 3T vs 1.5T 1.5T1.5T3T3T
  44. 44. 44 References:References: • Proton magnetic resonance spectroscopy inProton magnetic resonance spectroscopy in the brain: Report of AAPM MR Task groupthe brain: Report of AAPM MR Task group #9.#9. Drost, D.J., et al., Med Phys 29(9)Drost, D.J., et al., Med Phys 29(9) Sept 2002.Sept 2002. • Questions and Answers in MagneticQuestions and Answers in Magnetic Resonance ImagingResonance Imaging (2(2ndnd Edition). Elster,Edition). Elster, A.D. and Burdette, J. H. Mosby, St. LouisA.D. and Burdette, J. H. Mosby, St. Louis 20012001
  45. 45. 45 References:References: • Medical Magnetic Resonance Imaging andMedical Magnetic Resonance Imaging and Spectroscopy.Spectroscopy. Edited by BudingerEdited by Budinger &Margulis. Society of Magnetic&Margulis. Society of Magnetic Resonance in Medicine 1986Resonance in Medicine 1986 • Clinical Applications of MR SpectroscopyClinical Applications of MR Spectroscopy Edited by Mukherji Wiley & Sons, NewEdited by Mukherji Wiley & Sons, New York 1998York 1998
  46. 46. 46 References:References: • MRI from Picture to ProtonMRI from Picture to Proton D.W.D.W. McRobbie et al. Cambridge UniversityMcRobbie et al. Cambridge University Press 2003Press 2003 • Magnetic Resonance Spectroscopy ofMagnetic Resonance Spectroscopy of Neurological DiseasesNeurological Diseases E. R. DanielsenE. R. Danielsen Marcel Dekker, Inc. New York 1998.Marcel Dekker, Inc. New York 1998.
  47. 47. 47 • ©© Reviews in Urology 2006Reviews in Urology 2006 Carroll, et. al.,Carroll, et. al., Magnetic ResonanceMagnetic Resonance Imaging andImaging and Spectroscopy of Prostate CancerSpectroscopy of Prostate Cancer;; REVIEWS INREVIEWS IN UROLOGY Vol. 8 Suppl. 1 2006UROLOGY Vol. 8 Suppl. 1 2006 • ©© Scott & White 2004Scott & White 2004 Runge,VM, Nitz,WR, et al.Runge,VM, Nitz,WR, et al. The Physics of Clinical MR, forThe Physics of Clinical MR, for Neuroradiology, Taught Through Images.Neuroradiology, Taught Through Images. • ©© Radiology 2007Radiology 2007 Bartella, et al.,Bartella, et al., Enhancing Nonmass Lesions in the Breast:Enhancing Nonmass Lesions in the Breast: Evaluation with Proton (1H) MR SpectroscopyEvaluation with Proton (1H) MR Spectroscopy RadiologyRadiology Volume 245 (1) October 2007Volume 245 (1) October 2007 • © 2007 by ProScan Imaging© 2007 by ProScan Imaging THE MRI MENTOR, Volume 1, Number 10 – October 8,THE MRI MENTOR, Volume 1, Number 10 – October 8, 20072007 References:References:

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