Proton MR Spectroscopy (MRS)
Proton MR Spectroscopy (MRS)
Proton MR spectroscopy is a non-invasive diagnostic technique that measures metabolite concentrations in brain tissue. It provides biochemical information about cellular metabolism and tissue composition.
Key Principles
- Uses magnetic properties of hydrogen nuclei
- Measures concentrations of brain metabolites
- Can be single-voxel or multi-voxel
- Complements conventional MRI findings
Major Metabolites Detected
- N-Acetylaspartate (NAA)
- Neuronal marker
- Peak at 2.02 ppm
- Indicates neuronal integrity
- Choline (Cho)
- Cell membrane marker
- Peak at 3.2 ppm
- Elevated in high cellular turnover
- Creatine (Cr)
- Energy metabolism marker
- Peak at 3.0 ppm
- Used as internal reference
- Lactate
- Anaerobic metabolism marker
- Double peak at 1.33 ppm
- Indicates hypoxia/ischemia
Pediatric Applications
- Brain Tumors
- Tumor characterization
- Treatment response monitoring
- Differentiation from radiation necrosis
- Tumor recurrence detection
- Metabolic Disorders
- Mitochondrial diseases
- Leukodystrophies
- Amino acid disorders
- Organic acidemias
- Developmental Disorders
- Hypoxic-ischemic injury
- Autism spectrum disorders
- Cerebral palsy
- Infectious Diseases
- Brain abscess
- Encephalitis
- Progressive multifocal leukoencephalopathy
Acquisition Parameters
- Single-Voxel Techniques
- PRESS (Point-Resolved Spectroscopy)
- STEAM (Stimulated Echo Acquisition Mode)
- Typical voxel size: 2-8 cm³
- Multi-Voxel Techniques
- Chemical Shift Imaging (CSI)
- Spectroscopic Imaging
- Better spatial coverage
- Echo Times
- Short TE (20-35ms): More metabolites visible
- Long TE (135-144ms): Better baseline, fewer peaks
- Choice based on clinical question
Quality Control Measures
- Shimming optimization
- Water suppression
- Motion correction
- Signal-to-noise ratio assessment
Analysis Guidelines
- Quantitative Analysis
- Absolute quantification
- Metabolite ratios
- Age-specific normal values
- Pattern Recognition
- Disease-specific patterns
- Regional variations
- Developmental changes
- Common Ratios
- NAA/Cr: Neuronal integrity
- Cho/Cr: Membrane turnover
- NAA/Cho: Tumor evaluation
Pediatric Considerations
- Age-dependent changes in metabolite levels
- Myelination effects on spectra
- Regional variations in developing brain
- Need for age-matched controls
