General
- Using different lamour fq of molecule one can detect the relative amounts of molecules in that voxel
- Different protons in different molecules have different magnetic fields across it due to the differences in the amount of electrons around the protons. (the electron will change the magnetic field experienced by the proton)
- Detected elevated 2- hydroxyglutarate (2HG) levels in gliomas with IDH1 mutations compared with wild type
- Useful in
- Malignant vs non-malignant (abscess/inflammatory)
- High vs low grade
- Monitoring of low grade tumour
- Identification of highest grade area to direct biopsy
Normal MRS spectrum
- Choline, Creatine and NAA in normal quantities and there is no lactate or lipid peak
- “Upward sloping”
- Dominant N-acetyl aspartate (NAA) peak at 2.0 ppm
- Creatine (Cr) at 3.0 ppm
- Choline (Cho) at 3.2 ppm
High grade spectrum
- Raised Choline
- Decreased NAA
- Lactate and Lipid peak
- “Downward sloping”
“Good” vs “Bad” spectrum
- Normal choline, creatine, and NAA peaks forms a straight line that distended an of 45° from the x-axis. This is known as Hunter's angle and can be used to determine quickly whether the MRS is most probably normal or not
Pathology on 3 different modal
Differentiating | MRI | MRS | MR perfusion |
Tumefactive demyelination | - 50% show enhancement, usually an open ring with in complete portion facing grey matter - Mildy increased diffusion (unlike abscess) | - Elevation glutamate/glutamine peaks - Reduced NAA - Inc cho, lipis, lactate | - No elevation in rCBV |
High grade glioma | - Peripheral, heterogenous enhancement with nodules and necrosis - Can be ring enhancing - Solid parts diffusion restriction | - Reduce NAA, Myoinositol - Inc. Lipid, choline and lactate | - Marked elevation rCBV |
Primary CNS lymphoma | - Homogenous enhancement common - Ring enhancing in HIV/immunocompromise - Restricted diffusion (lower ADC then metastasis or HGG) | - Large Choline peak - Reversed Cho/Cr Ratio - Markedly reduced NAA - Lactate peak possible | - Modest elevation rCBV |
Look at 5 different molecules (Carbohydrate, Carbonated GIN and Love Letters)
Molecule | Resonance (ppm) | Clinical use | Description | Classic association |
Lipid | 0.5–1.5 | - Cell necrosis - Fat | Slightly overlaps lactate peak at TE ≈ 35 | ↑: Diploic space and subcutaneous fat |
Lactate | 1.3 | - Ischaemia - Infection - Anaerobic activity | A couplet peak. Not present in normal brain. End product of anaerobic glycolysis; a marker of hypoxia. Present in: ischaemia, infection, demyelinating disease, inborn errors of metabolism... At higher TE (e.g. TE = 144), the peak inverts which can help distinguish it from the lipid peak | ↑: Ischemia, infarction, seizures, metabolic disorders, necrotic tumors |
N-acetyl aspartate (NAA) | 2 | Neuronal marker (sign of healthy neuron) -reduced in any disease process | Normally the tallest peak (higher than Cr or Cho). ↓ in ≈ all focal and regional brain abnormalities (tumor, MS, epilepsy, Alzheimer's disease, abscess, brain injury...) | ↓ Leukodystrophy, malignant neoplasm, multiple sclerosis, infarction ↑ Elevated in Canavan disease |
Creatine (Cr) | 3ᵃ | Baseline marker | Useful primarily as a reference for choline. Higher in gray matter than white matter | Assumed to be unchanged and used to calculate ratios (Cho:Cr and NAA:Cr) ↓ Tumors |
Choline (Cho) | 3.2 | Cell turn over marker - increased in tumour Membrane marker | Marker of membrane synthesis. ↑ in neoplasms and some rare conditions of increased cell growth & in the developing brain. ★ Stroke is low in choline | ↑ Increased in tumors, inflammation, infection, multiple sclerosis … |
Glutamate | ㅤ | Neurotransmitter marker | ㅤ | ㅤ |
Inositol | 3.56 | Glial marker | ㅤ | ↑ Gliosis, astrocytosis, Alzheimer’s disease |
- ᵃCr has another less important peak
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