2012.10.30. 1 COURSE FAQ Forthcoming lectures: 16. October – „IGT lecture” 23. October – NO LECTURE, holiday 30. October – MR Spectroscopy 6. November – PET + Final Test Test: - Basic imaging techniques, what are they - 5-10 easy, simple choice questions - If November 6. is not good for everyone, I will organize extra time for getting the short test done Study material: | Lecture material will be distributed in PDF 2 wks before the test. In vivo MR spectroscopy Ervin Berényi András Jakab Diagnostic neuroimaging modalities CT – Computed Tomography Brain anatomy Stereotactic reference frame Structural MRI Fine brain anatomy Vascular structure Diffusion, perfusion MRI Fine pathological information Intra-operative imaging modalities, open MRI, low- field Positron Emission Tomography PET Brain metabolism Brain function Functional MR imaging fMRI Brain function Electro encephalography, LORETTA, Magnetoencephalography MR Spectroscopy Brain metabolism Biochemical mapping Take home message about MR spectroscopy • Performing NMR experiments for an image pixel • Spectrum of brain chemicals, i.e. metabolites Diagnose their alterations metabolites. Diagnose their alterations. • Display, measure: – Choline – Creatine – N-acetyl-aspartate – Lactate – Lipids
15
Embed
Week 5. Basics and clinical uses of MR spectroscopy.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
2012.10.30.
1
COURSE FAQ
Forthcoming lectures:16. October – „IGT lecture”23. October – NO LECTURE, holiday30. October – MR Spectroscopy6. November – PET + Final Test
Test:- Basic imaging techniques, what are they- 5-10 easy, simple choice questions- If November 6. is not good for everyone, I will organize extra
time for getting the short test done
Study material:Lecture material will be distributed in PDF 2 wks before thetest.
• 1944 – “developing a method to examine themagnetic properties of
b l
• Otto Stern (1988-1969)• 1943 – “proton magnetic
spin discovery”
protons by nuclearresonance”
The Birth of NMR
• 1952 – Felix Bloch & Edward Mills Purcell• “for the precision measurements on nuclear magnetic resonance”
(1905-1983) (1912-1997)Stanford Harvard
The The firstfirst 11H NMR H NMR spectrumspectrum of of waterwater
Bloch, F.; Hansen, W. W.; Packard, M. Bloch, F.; Hansen, W. W.; Packard, M. The nuclear induction experiment.The nuclear induction experiment. Physical Review (1946), 70 474Physical Review (1946), 70 474--85. 85.
NMR spectroscopy
• Richard Ernst • 1991 – “developing high
resolution NRM spectroscopy”
Magnetic resonance imaging(MRI !)
• 2003 – Paul Lauterbur & Sir Peter Mansfield
(1929-2007) (1933-)
2012.10.30.
3
Damadian’s pattern from 1972 Lauterbur’s 1973 Nature paper
Indomitable1977.0,05-0,1 TSzupravezető54,43 kg
Damadian, Minkoff, Goldsmith
Damadian and the coil
The first MR image of a human
1977. Július 3. 4:45, Minkoff
The first pathological case
Physiol. Chem. & Phys., 10:285-87, 1978.
2012.10.30.
4
First pathological case – lungcancer
Physiol. Chem. & Phys, 10:285-87, 1978.
Basics of MR spectroscopy
• Nuclei of atoms bear a physical propertycalled a spin.
• All moving charged bodies create aAll moving, charged bodies create a magnetic field around themselves
• Nuclei with spins act as small magnets
Basics of MR spectroscopy
• In the presence of a strong externalmagnetic field, nuclei spins are orientedand show precession with a well-defined frequencydefined frequency
• This is the Larmor frequency which isproportional to the strength of theexternal field
• This is the resonance frequency of thegiven nucleus
Basics of MR spectroscopy• If a nuclei is in a different
microenvironment, its resonantfrequency is altered
This means that atomic bonds and• This means that atomic bonds and neighbouring atoms determine theresonance frequencies (Chemical Shift)
• One can depict it using a spectrum, where each peak represents a specificatom is a specific bond
EthanolEthanol 11H NMR H NMR spectrumspectrum
Chemical shift1951
Modern ethanol spectrModern ethanol spectrumum
Arnold, J.T., S.S. Dharmatti, and M.E. Packard, J. Chem. Phys., 1951. Arnold, J.T., S.S. Dharmatti, and M.E. Packard, J. Chem. Phys., 1951. 1919: p. 507. : p. 507.
2012.10.30.
5
Free Induction Decay
FT
FT
Processing for MRS
Where can MRS be used?
• Proton MRS– Brain– Prostate– Liver
• Phosphorus MRS– Liver– Heart– Muscles
Different types of MRS• Volume selective MRS• MRS Imaging (MRSI) - metabolite mapping
Localized spectra is obtained from a single volume of interest (VOI)Localization is achieved by
RF
Gy
RF
Gz
ysequential selection of three orthogonal slicesThe size and location of VOI can be easily controlledAnatomic 1H images are used for localizing the VOI
Image selected in vivo spectroscopy, ISIS
Point resolved
Single Volume Localization
Po nt resolved spectroscopy, PRESS
Stimulated echo acquisition mode, STEAM
2012.10.30.
6
RF
GxGyGz
90°180° 180°
Point Resolved Spectroscopy, PRESS
(TE1+TE2)/2TE1/2Gz
TE2/2
A slice-selective 90o pulse is followed by two slice-selective 180o refocusing pulsesAchieves localization within a single acquisitionSuitable for signals with long T2 – 1H MRS
90° 90° 90°
RF
Gx
Gy
Gz
Stimulated Echo Acquisition Mode, STEAM
TE/2 TE/2TM
Gz
Three slice-selective 90o pulses form a stimulated echo from a single voxel.Achieves localization within a single acquisitionOnly half of the available signal is obtainedCan achieve shorter TE than PRESS
Effects of MR Parameters on PRESS spectra
Repetition Time, TRNumber of Signal AveragesEcho Time, TEVoxel Size
Single Voxel Spectroscopy: Overview
Simplicity
Flexibility in voxel size and position
Accurate definition of VOI
Excellent shim and spectral resolution
Many voxels within the same dataset
RF
90°
Chemical Shift Imaging
Multiple localized spectra are obtained simultaneously from a set of voxels spanning the region of interest
Gslice
G y
G z
Uses same phase-encoding principles as imaging
No gradient is applied during data collection, so spectral information is preserved
Display of all spectra
Underlying reference image shows voxel position
CSI Spectral Map
Individual spectra can be displayed enlarged
Spectral map can be archived together with the reference image and the CSI grid
[Mg2+], kinetics of creatine kinase and ATP hydrolysis.
2012.10.30.
8
1H MR Spectroscopy
Brain 1-H MRS
CholineCreatine
N-acetyl aspartatewater
5.0 4.0 3.0 2.0 1.0ppm
Choline (lactate/lipid)
•NAA is a neuronal marker and indicates density and viability of neurons. •It is decreased in glioma, ischemia and degenerative diseases.
N-Acetyl aspartate (NAA)
CH3-C-NH-CH-CH2-COOHO
CH2-COOH
2.02, CH32.52, CH22.70, CH24.40, CH
Important 1H Signals
Creatine (Cr), phosphocreatine (PCr)
NH2-C-N-CH2-COOHCH3
NH3.04, CH33.93, CH2
•Cr is a marker of aerobic energy metabolism•Cr signal is constant even with pathologic changes and may be used as a control value• However, isolated cases of Cr deficiency may occur in children
•Cho compounds are involved in phospholipidmetabolism of cell membrane.•Increase Cho mark tumor tissue or multiple sclerosis plaques
Choline (Cho), choline compounds
3.24, CH33.56, CH24.07, CH2
CH3-N-CH2-CH2-OH
CH3
CH3
Important 1H Signals
plaquesGlutamate (Glu), glutamine (Gln)
2.1, CH22.4, CH23.7, CH
•Glu is a neurotransmitter, Gln a regulator of Glumetabolism•It is hardly possible to detect their signals sepratly. The signals are jointly designated “Glx”.
HOOC-CH2-CH2-CH-COOH
NH2
NH2-CH2-CH2-CH-COOH
NH2
•Lactate is the final product of glycolysis•It can be detected in ischemic/hypoxic tissue and tumors indicating lack of oxygen
Lactate (Lac)
1.33, CH34.12, CH
Taurine (Tau)•Cells examination indicates
CH3-CH-COOH
OH
Important 1H Signals
3.27, NCH23.44, SCH2
•Cells examination indicates taurine synthesis in astrocytes
NH2-CH2-CH2-S-OH
PO4-
PO4-
PO4- PO4
-
PO4-
PO4-
Myo-inositol (Ins)
3.56, CH
•Ins marks glia cells in brain •It is decreased in hepatic encephalopathy and elevated in Alzheimer’s disease.
Neurochemical pathways & neuro-MRS
2012.10.30.
9
A normal brain MR spectrum The effect of echo time on the spectra
Mitochondrial myopathy
TE 144 ms TE 288 ms
Quantitative MRS
• Metabolit ratios• Cr is stable, we compare metabolites to
this• Contralateral – CSI• Water as reference signal (proton cc ≈ 77-
88 M)• Water content• External reference (not so practical)
• No contraindicationsNo contraindications• Lactate is elevated, NAA & Cr reduced• Sensitivity: high• Specificity: lower, developmental disorders
affect it as well
Neonatal hypoxia
Shaken Baby Syndrome MRS in infants - indications• Normal UH, CT, MRI, SPECT, PET• No contraindications• Lactat elevated, NAA and Cr reduced• Specificity is extremely high in a few