Sattam S' Lingawi, MD, FRCPC, ABR

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MR
SPECTROSCOPY
Histopathological Radiology

• Sattam S. Lingawi, MD, FRCP(C), ABR
• Assistant Professor of Radiology
• King Abdulaziz University

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MRS

• Purpose
• Provide an over view of the clinical capabilities
  of MRS in neuroimaging.
• Answer the often asked question
• How can MRS help me in my clinical practice?

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What is MRS?

• It is an MRI technique whereby the echo that is
  obtained from the body is analyzed into its
  various radio-frequency components rather than
  making an image.

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Echo Analysis
MRI
MRS
ECHO
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Chemical Shift Imaging

• Different substances spin at different
  frequencies, because they have different atomic
  numbers and side chains.
• This allows the differentiation of various
  structures.

Frequency
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Chemical Shift Imaging

• CSI is measured in Particle Per Million (p.p.m).
• Why not measured in Hertz?
• Hz has large numbers.
• Hz values vary with magnet strength.
• P.P.M are always fixed.

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MRS Is A Histopathological Exam

• Distinguish abnormalities with same radiological
  appearance
• Tumor vs. Radiation Necrosis.
• Tumor vs. Infection.
• Lymphoma vs. Toxoplasmosis.

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MRS Is A Histopathological Exam

• Abnormalities without anatomic change
• Tumor infiltration.
• Diffuse axonal injury.
• Hepatic encephalopathy.
• Herpes encephalitis.
• Ischemia.

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Suppression Techniques
Water

• Water is 100,000 X than metabolites.
• Fat is 10,000 X than metabolites.
• need suppression.

Metabolites
CHESS Chemical Shift Suppression. WEFT Water
Elimination Fourier Transform Tech.
I.R Pulses to null water signal prior to
spectroscopy
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Techniques

• Two Techniques
• Stimulated Echo Acquisition Mode (STEAM). TE
  35 msec
• Minor Metabolite
• Low SNR
• Point Resolved Spectroscopy (PRESS). TE135
• Major Metabolites
• High SNR
• Inverted Lipid/Lactate peak.

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Requirements

• High Field.
• 1.5 T 3T.
• High Homogeneity
• Less than 0.2 p.p.m
• Assessed by measuring the water peak width.

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Chemical Shift
1.5 T
0
0.5 T
ppm
The degree of shift is directly proportional to
the field strength
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Normal H-MRS

• 0 - TMS
• .8-1.5 Lipid
• 1.3 Lactate
• 2.02 NAA1
• 2.05-2.5 Glx
• 2.5 NAA3
• 2.6 NAA2
• 3.03 Cr.

• 3.22 Choline
• 3.36 SI
• 3.43 glu1
• 3.56 MI
• 3.8 glu2
• 3.65-3. 8 Glx
• 3.9 Cr2
• 4.06 MI

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Metabolites

• NAA Neuronal marker. (2.0 ppm)
• Neuronal marker
• Any neuronal loss.decrease NAA.
• Choline Cell membrane. (3.2 ppm)
• High cellularity membrane turn-
• overincrease Choline.
• CreatineGlial tissue marker. (3.0 ppm)
• Decreases in tumors esp. malignant.

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Metabolites

• Lactate Cell death. (1.3 ppm)
• Necrosis hypoxia (anaerobic glycolysis)
  increase Lact.
• Normal in CSF.
• Lipid (1.3-1.5 ppm)
• Seen in tumors necrotic tissue.
• Myo-Inositol (3.5 ppm)
• Decreases in High grade malignancy
• Increases in Alzheimers dementia and metastases.

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How About Contrast?

• No definite answer.
• Some literature reports no effect.
• Other literature reports 15-40 reduction in
  metabolites peak.

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Single vs. Multi-Voxel Spectroscopy
Single Voxel
Multi Voxel

• 2X2X2 cm cube
• Short TE (STEAM)
• TE30-35 msec
• All Metabolites
• Lesion 60-80

• 2X2X2 cm cube
• 2-3mm inner cubes
• Long TE (PRESS)
• TE135-260 msec
• Major Metabolites
• Margin outline

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MRS
Infant
Adult
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MRS for 6 days
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Tumour

• Increased Choline
• Variable Creatine (incr./decr.)
• Increased ChoCr

Choline
NAA
Cr
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alanin
Meningiomas have elevated Alanin
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Single voxel demand repeated sampling
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Repeated single voxel is time consuming.
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• Multi-voxel outlines lesion extent.
• Voxel 10 MRINormal MRS Abnormal

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Multi-voxel allows comparison with normal tissue.
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Radiotherapy
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Tumor Grading

• Tumors
• Cho, Cr NAA
• The higher the grade the more accentuated these
  figures.
• Necrosis Increased Lactate and Lipid.
• NAA may remain normal in
• Low grade Glioma
• Gliomatosis cerebri
• Brainstem Glioma

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Tumor Mimics

• Acute infarction.
• TB
• Encephalitis
• Hamartoma

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Infarction
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Lipid Peak
Long TE (PRESS)
Short TE (STEAM)
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Lipid Peak

• Doublet narrow peak
• Tumor
• Infection
• Infarction

• Broad featureless peak
• Post Rad. Necrosis
• Sampling error

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GBM vs Radiation Necrosis
Lipid
Death Peak
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Tumor vs Radiation Necrosis

• Tumor
• Increased Choline Creatine.
• Radiation Necrosis
• Decreased Choline.
• Increased Lipid.

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Radiation

• Pre-Radiation
• Malig. transformation.
• Mapping extent.
• Determine biopsy site.
• Tumor staging.

• Post-Radiation
• Radiation necrosis.
• Edge recurrence.
• Lesion stability.

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• Abscess
• Better imaged with short TE (STEAM) , to reveal
  minor metabolites. (0.9-2.0 ppm)
• Increased amino acids.
• Succinate
• Acetate
• Puruvate
• Lactate (Also seen in tumors)
• In vitro studies revealed fatty acids in T.B.

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TOXO VS LYMPHOMA
Toxoplasmosis
Lymphoma
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Toxo vs Lymphoma

• Lymphoma Cho, Lip, Lact.
• Toxo Cho, Lip, Lact.

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TUMOR VS INFECTION VS NECROSIS
Tumor
Cho
NAA
Lipid
Lipid
Infection
Necrosis
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MRS

• Apart from Tumors, Necrosis and Infections
• ARE THERE ANY OTHER APPLICATIONS FOR MRS?

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TLE
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TLE

• Lateralization
• Decrease NAA
• Increased Choline (15)

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Dementia

• Applications
• Detection of Dementia (Decrease NAA).
• Differentiation between Alzheimer and other types
  of dementia.
• Alzheimer is associated with increased
  Myo-inositol (specific).
• Predict patients at risk while clinically silent.

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AlzheimersDementia
NAA
Early
Myo-Inositol
Intermediate
Late
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MRS In Aids

• Lymphoma Cho, lac/lipid, NAA,
• Toxo lipid/lac, NAA, Cho.
• PML NAA, Cho, lac/lipid
• HIV NAA, MI

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ACUTE MULTIPLE SCLEROSIS

• Cho, lipid, lact, MI Increased
• NAA Normal
• NAA May increase on follow-up

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Conclusion

• New MR technology.
• The main applications are
• Differentiating Tumor, Necrosis and Infection.
• Determining the extent of radiation fields.
• High potential in epilepsy and dementia.
• Other applications need to be carefully
  interpreted.

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THANK YOU
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Neonatal Hypoxia
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CANAVAN
Increased NAA
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Reference
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Normal Pit MRS for 6 days
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Encephalitis