In Vivo Proton Spectroscopy. Experimental Aspects and Potential

Brain metabolites in definite amyotrophic lateral sclerosis

Biomarkers beyond clinical assessment are needed in patients who suffer from amyotrophic lateral sclerosis (ALS). Here, single-voxel proton magnetic resonance spectroscopy ((1)H MRS) of the gray matter of the motor cortex and the white matter including the pyramidal tracts was used to investigate concentrations of N-acetylaspartate (NAA), creatine (Cr), choline (Cho), myoinositol, glutamate, and glutamine in patients with definite ALS in a longitudinal design (three measurements at study inclusion, after 3 and 6 months). A volume-corrected analysis of gray and white matter fractions within the volumes of interest (VOI) was performed for the identification of the absolute metabolite concentrations. The patient group showed a significant decline of the compound NAA over time in the motor cortex areas both of the clinically more and less affected hemisphere between first measurement and month 6 and for the less affected side additionally between first measurement and month 3. For the NAA/(Cr + Cho) ratio, significant decline in the less affected hemisphere was observed from the first measurement to month 3 and to month 6 as well as from month 3 to month 6. In contrast, neither NAA nor the NAA/(Cr + Cho) ratios in the white matter areas showed any significant alterations. All other compounds showed no significant changes over time. In summary, the longitudinal changes of cortical metabolite concentrations in the course of ALS could be assessed by optimized (1)H MRS techniques at group level, so that (1)H MRS parameters, in particular volume-corrected values of NAA in the clinically less affected hemisphere, seem to have the potential to serve as a surrogate marker for monitoring ALS disease progression.

A proton magnetic resonance spectroscopic study in ALS: correlation with clinical findings

OBJECTIVE

To evaluate neuronal dysfunction in the motor region subcortical white matter in ALS using volumetric localized proton magnetic resonance spectroscopy (1H-MRS).

METHODS

Sixteen patients with E1 Escorial definite, probable, or possible ALS and eight healthy age-matched control subjects were studied. The ALS patients were divided into those with limb onset (n = 8) and those with bulbar onset (n = 8). Measurements of the metabolic ratios N-acetylaspartate (NAA)/creatine and phosphocreatine (Cr+PCr), NAA/choline (Cho), and Cho/(Cr+PCr) were correlated with clinical assessments.

RESULTS

We found no differences in the metabolic peak area ratios in the motor region when comparing the total ALS group and the control subjects. However, correlations were found between the NAA/(Cr+PCr) ratio and the E1 Escorial category (p = 0.03), the ALS severity scale (p = 0.01), and the Medical Research Council score (p = 0.06). No correlations were found between the NAA/(Cr+PCr) ratio and the Ashworth Spasticity Scale, reflex score, or disease duration (p > 0.16). Bulbar-onset patients had a lower NAA/(Cr+PCr) ratio in the motor region compared with limb-onset patients (p = 0.03).

CONCLUSION

In vivo 1H-MRS of the subcortical white matter in the motor region is unlikely to be sensitive enough to detect early disease changes in ALS because there is considerable overlap between the metabolic peak area ratios from patients with ALS and normal control subjects. However, changes in the NAA/(Cr+PCr) metabolic peak area ratios correlate with clinical measures of disease severity, and this measure may be useful in monitoring disease progression.

Transient metabolic changes observed with proton MR spectroscopy in normal human brain after radiation therapy

PURPOSE

To observe the time course of the proton magnetic resonance spectroscopy (1H-MRS) variations due to radiation therapy on normal human brain.

METHODS AND MATERIALS

We followed 11 patients receiving an exclusive external radiation therapy for brain tumor for 8 months. They underwent proton MRS scans before any radiation exposure and 1, 4, and 8 months after they began the radiation therapy. The patients received 60 Gy in tumoral area fractionated over 6 weeks. The contralateral normal brain hemisphere received a radiation dose from 20 to 50 Gy. The main metabolite concentrations (N-acetylaspartate (NAA), choline compounds (Cho), creatine (Cr), and lactate (Lac) were evaluated by the areas of the peaks after peak fitting. Normalized values (NV) were obtained by processing the ratio of the peak area of a given metabolite to the sum of all the spectrum peak areas; ratios (NAA/Cho, NAA/Cr, and Cho/Cr) were processed. One patient, who received panencephalic radiotherapy (30 Gy) after metastasectomy from a primary kidney adenocarcinoma, has been monitored with 1H-MRS eight times for 6 months to observe the onset of the metabolic changes.

RESULTS

Changes were observed in irradiated normal brain tissue 4 months after radiation therapy began: the NAA/Cho and NAA/Cr ratios and the NAA (NV) decreased while the Choline (NV) increased. Four months later, normal values were recovered.

CONCLUSION

1H-MRS has the potentiality to detect and to evaluate in vivo early adverse metabolic effects of radiation therapy in the normal human brain. These changes are significant 4 months after the radiation therapy began and appear to resolve over time.