Proton spectroscopy and diffusion imaging on the first day of life after perinatal asphyxia: preliminary report

Abstract

Background and purpose: MR techniques have proved useful in assessing brain injury from perinatal asphyxia when the injury is subacute or chronic. Recent advances in understanding the molecular mechanisms of brain injury have made medical intervention plausible, creating a need for assessment of the brain within the first few hours of life. We report the results of early (first 24 hours after birth) MR imaging in seven patients, including proton MR spectroscopy in six.

Methods: MR studies were performed within the first 24 hours of life in seven consecutive patients who were encephalopathic after complicated deliveries. Standard T1-, T2-, and diffusion-weighted sequences were performed in all patients; single-voxel MR spectroscopy was performed in two locations in six of the seven patients. Follow-up MR studies were performed in four patients at ages 7, 8, 9, and 15 days, respectively.

Results: T1-weighted images were normal in all seven patients. T2-weighted images were normal in three patients and showed T2 prolongation in the basal ganglia or white matter in the other four. Diffusion images showed small abnormalities in the lateral thalami or internal capsules in all seven patients. Comparison with clinical course in all seven patients and with follow-up MR studies in four showed that the diffusion images underestimated the extent of brain injury. Proton MR spectroscopy showed substantial lactate elevation in all six of the patients studied. Two patients died in the neonatal period and the other five were left with clinically significant neurologic impairment.

Conclusion: MR spectroscopy performed in the first 24 hours after birth is sensitive to the presence of hypoxic-ischemic brain injury, whereas diffusion imaging may help identify but underestimate the extent of the injury. Further studies are ongoing in an attempt to expand upon this observation.

fig 1.

Patient 5. A, Diffusion-weighted image (b = 700 s/mm²) at age 16 hours. Small areas of reduced diffusion (arrows) are seen in posterior limbs of internal capsules. B, Proton MR spectrum (2000/288) at age 16 hours from single voxel in thalamus/lentiform nucleus. Lactate peak (doublet at 1.33 ppm, indicated by solid arrow) is markedly elevated and NAA peak (singlet at 2.01 ppm, indicated by open arrow) is reduced. C and D, Follow-up SE (517/8) images at age 15 days. Despite some motion degradation, globular T1 shortening (arrows) is seen in lateral putamen and posteromedial lentiform nucleus bilaterally and at the depths of the posterior sylvian cortex. Diffusion images were negative at this study. E, Follow-up proton spectrum (2000/288) from the thalami/lentiform nuclei at age 15 days shows further diminution in the size of the NAA peak and almost complete disappearance of the lactate peak.

fig 2.

Patient 7. A and B, Diffusion-weighted images (b = 700 s/mm²) at age 18 hours shows reduced diffusion, manifest as high signal intensity (arrows), in the lateral thalami and possibly in the posterior limbs of the internal capsules. No significant reduction in diffusion is seen in the centra semiovale (in B). C and D, Follow-up diffusion-weighted images (b = 700, s/mm²) at age 7 days at the same levels show reduced diffusion (hyperintensity, arrows) within a much larger area, including the lentiform nuclei and thalami (in C) and along the corticospinal tracts (in D). E, Axial SE (516/8) image through the basal ganglia shows T1 shortening in the lateral thalami (open arrows) and lentiform nuclei (solid arrows), confirming the injury seen in C.

fig 3.

Patient 2. A, Diffusion-weighted image (b = 700 s/mm²) at the level of the basal ganglia performed at age 16 hours shows diffusely reduced diffusion in cortex and deep gray nuclei. On initial evaluation, this image was thought to be normal; however, subsequent analysis revealed a reduction in the ADC of about 15% throughout the brain. The distortion and hyperintensity of the back of the head results from chemical blankets used to keep the body temperature at 37°C. B, Proton MR spectrum (2000/288) from the thalami and basal ganglia at age 16 hours shows marked reduction of NAA (singlet at 2.01 ppm, indicated by open arrow) and marked elevation of lactate (doublet at 1.33 ppm, indicated by solid arrow). C, Axial SE (3000/120) image at age 18 hours shows some mildly diffuse T2 prolongation.