Hybrid Two-Dimensional Proton Spectroscopic Imaging of Pediatric Brain: Clinical Application

PURPOSE: To introduce and demonstrate the advantages of the new hybrid two-dimensional (2D) proton spectroscopic imaging (Sl) over the single voxel spectroscopy (SVS) and conventional 2D Sl in the clinical application of spectroscopy for pediatric cerebral disease. MATERIALS AND METHODS: Eighty-one hybrid 2D proton spectroscopic imaging was performed in 79 children (36 normal infants and children, 10 with hypoxic-ischemic injury, 20 with toxic metabolic encephalopathy, seven with brain tumor, three with meningoencephalitis, one with neurofibromatosis, one with Sturge-Weber syndrome and one with lissencephaly) ranging in age from the third day of life to 15 years. In adult volunteers (n = 5), all three techniques including hybrid 2D proton Sl, SVS using PRESS sequence, and conventional 2D proton Sl were performed. Both hybrid 2D proton Sl and SVS using PRESS sequence were performed in clinical cases(n= 12). All measurements were peformed with a 1.5-T scanner using standard head quadrature coil. The 16 x 16 phase encoding steps were set on variable field of view (FOV) depending on the size of the brain. The hybrid volume of interest inside FOV was set as 75 x 75 x 15 mm3 or smaller to get rid of unwanted fat signal. Point-resolved spectroscopy (TR/TE = 1,500 msec/135 or 270 msec) was employed with standard chemical shift selective saturation (CHESS) pulses for water suppression. The acquisition time and spectral quality of hybrid 2D proton Sl were compared with those of SVS and conventional 2D proton Sl. RESULTS: The hybrid 2D proton Sl was successfully conducted upon all patients. The 2D spectral data acquisition time was less than 6 minutes, while the data acquisition time of SVS was 4.3 minutes. This was short enough for pediatric application. The spectra acquired with hybrid 2D proton Sl showed nearly the same sensitivity and spectral resolution with SVS. The spectral quality of hybrid 2D proton Sl was, on the other hand, far better than that of conventional 2D proton Sl. The other advantage of hybrid 2D proton Sl was that the extent of metabolic abnormalities could be evaluated through the characteristics of the relative levels of the three metabolites, i.e., N-acetylaspartate, choline, and creatine. CONCLUSION: The hybrid 2D proton Sl can be successfully employed for the evaluation of the metabolic abnormalities in the various pathologic conditions of pediatric brain without penalty in acquisition time and spectral quality when compared to SVS. The extent of metabolic abnormalities, which cannot be obtained with SVS technique, also can be evaluated with hybrid 2D proton Sl.

Leukoencephalopathy Following CNS Prophylaxis Therapy in Pediatric Leukemia: MR Imaging Findings

PURPOSE: To evaluate the MR imaging findings and the usefulness of MR imaging in the diagnosis and followup of leukoencephalopathy following CNS prophylaxis therapy in pediatric leukemia. MATERIALS AND METHODS: We retrospectively evaluated the MR imaging findings of eight children with white matter abnormalities on MR out of seventeen acute leukemic patients with various neuropsychiatric symptoms who received intrathecal methotrexate administration, with or without cranial irradiation. In all cases, initial MR was performed within a week of the onset of neuropsychiatric symptoms. Follow-up MR was performed one to sixteen months after initial study, and the MR imaging findings were compared with the initial findings. RESULTS: The initial MR imaging findings were classified into three categories: focal or multifocal white matter abnormalities (3/8), and diffuse white matter abnormalities without enhancement (3/8), and diffuse white matter abnormalities with enhancement (2/8). At follow-up MR, diffuse or focal atrophic changes were noted in all children. White matter abnormalities improved in two out of three patients with focal or multifocal white matter abnormalities. In five with diffuse white matter abnormalities, the extent of these showed no significant change, but contrast enhancement was markedly reduced in two children in whom diffuse white matter abnormalities with enhancement had been demonstrated. CONCLUSION: In pediatric leukemia, the MR imaging findings of leukoencephalopathy following CNS prophylaxis therapy are variable, but are specific with the clinical history of neuropsychiatric symptoms after intrathecal methotrexate administration, with or without cranial irradiation. The MR imaging is valuable in the diagnosis and follow-up of leukoencephalopathy following CNS prophylaxis therapy in pediatric leukemia.