MR Spectroscopy Sensitivity and Specificity
MR spectroscopy demonstrates high diagnostic accuracy for distinguishing neoplastic from nonneoplastic brain lesions, with sensitivity of 91% and specificity of 95% in posttreatment surveillance of brain tumor patients, representing the highest performance among advanced MRI modalities. 1
Performance in Brain Tumor Evaluation
Posttreatment Surveillance (Highest Quality Evidence)
- MRS achieves 91% sensitivity (95% CI, 79%-97%) and 95% specificity (95% CI, 65%-99%) for detecting tumor recurrence versus treatment-related changes in patients with known brain tumor history 1
- This represents superior performance compared to other advanced MRI techniques in the same clinical context 1
- The combination of post-contrast T1 and post-contrast FLAIR sequences are most sensitive for detecting leptomeningeal metastases, with MRI sensitivity of 66-98% and specificity of 77-97.5% 2
Tumor Characterization and Grading
- For distinguishing neoplastic from nonneoplastic lesions, logistic regression models using MRS data achieve 85% sensitivity and 87% specificity with ROC area of 0.96 3
- MRS increases diagnostic accuracy for indeterminate brain lesions from 55% (based on conventional MRI alone) to 71% when spectroscopy is added 4
- For high-grade versus low-grade glioma differentiation, MRS demonstrates high accuracy, though specific sensitivity/specificity values vary by study 4
Key Metabolite Ratios and Diagnostic Thresholds
Choline/NAA Ratio
- A Cho/NAA amplitude ratio >1 provides 79% sensitivity and 77% specificity for tumor detection, with ROC area of 0.84 3
- This quantitative threshold performs reasonably well but is inferior to multivariate logistic regression models 3
NAA/Cr Ratio for Primary vs. Metastatic Tumors
- NAA/Cr ratio >0.4 predicts metastatic tumors with 73.8% accuracy, 73.3% sensitivity, and 74.2% specificity 5
- Mean NAA/Cr and Cho/Cr ratios are significantly higher in secondary (metastatic) tumors compared to primary brain tumors 5
- Strong correlation exists between NAA/Cr and Cho/Cr ratios (r = 0.61) 5
Clinical Context Matters
Comparison with Other Modalities
- MRS outperforms qualitative blinded interpretation by individual readers, which averages 82% sensitivity and 74% specificity 3
- Unblinded group interpretation by experienced neuroradiologists achieves 89% sensitivity and 92% specificity 3
- FDG-PET/CT shows pooled sensitivity of 77% and specificity of 78% for brain tumor surveillance, inferior to MRS 1
Limitations and Pitfalls
- Interpretation accuracy depends heavily on proper technique, adequate voxel placement, and experienced analysis 3, 4
- Methodologic quality varies across studies; most use histopathology as reference standard but don't always specify blinded interpretation 4
- Small sample sizes in many studies limit generalizability, particularly for distinguishing radiation necrosis from recurrent tumor 4
Practical Algorithm for MRS Interpretation
For Suspected Tumor Recurrence
- Obtain MRS with single-voxel technique positioned in enhancing portion of lesion 3, 5
- Calculate Cho/NAA ratio: values >1 suggest tumor (79% sensitivity, 77% specificity) 3
- Apply multivariate analysis if available: improves accuracy to 85% sensitivity, 87% specificity 3
- Combine with perfusion MRI (DSC-MRI: 87% sensitivity, 86% specificity) for optimal diagnostic confidence 1
For Primary vs. Metastatic Differentiation
- Measure NAA/Cr and Cho/Cr ratios at short TE 5
- NAA/Cr >0.4 favors metastasis (73.3% sensitivity, 74.2% specificity) 5
- Consider patient age: metastases occur at mean age 55.9 years vs. 43.9 years for primary tumors 5
- Higher Cho/Cr ratios also favor metastatic disease 5