Focality in Febrile Seizures: A Retrospective Assessment Using Arterial Spin Labeling MRI.

PURPOSE: Defining focality of febrile seizures (FS) in clinical practice remains controversial. We investigated focality issues in FS with a postictal arterial spin labeling (ASL) sequence. METHODS: We retrospectively reviewed 77 children (median: 19.0 months, range: 15.0-33.0 months) who consecutively visited our emergency room for FS and underwent brain magnetic resonance imaging (MRI), including the ASL sequence, within 24 hours of seizure onset. ASL data were visually analyzed to assess perfusion changes. Factors related to the perfusion changes were investigated. RESULTS: The mean time to ASL acquisition was 7.0 (interquartile range: 4.0-11.0) hours. The most common seizure classification was unknown-onset seizures (n = 37, 48%), followed by focal-onset (n = 26, 34%) and generalized-onset seizures (n = 14, 18%). Perfusion changes were observed in 43 (57%) patients: most were hypoperfusion (n = 35, 83%). The temporal regions were the most common location of perfusion changes (n = 26, 60%); the majority of these were distributed in the unilateral hemisphere. Perfusion changes were independently associated with seizure classification (focal-onset seizures, adjusted odds ratio [aOR]: 9.6, p = 0.01; unknown-onset seizures aOR: 10.4, p < 0.01), and prolonged seizures (aOR: 3.1, p = 0.04), but not with other factors (age, sex, time to MRI acquisition, previous FS, repeated FS within 24 hour, family history of FS, structural abnormality on MRI, and developmental delay). The focality scale of seizure semiology positively correlated with perfusion changes (R = 0.334, p < 0.01). CONCLUSION: Focality in FS may be common, and its primary origin might be the temporal regions. ASL can be useful for assessing focality in FS, particularly when seizure onset is unknown.

Evaluation of MR signal index for the assessment of occupational manganese exposure of welders by measurement of local proton T1 relaxation time.

Magnetic resonance (MR) imaging has become a useful tool for the estimation of occupational exposure to manganese (Mn). However, validity of signal indices on T1-weighted imaging, a proxy measurement of T1 relaxation time shortening due to Mn deposition, needs to be evaluated in an occupationally exposed population. We performed MR imaging on 20 male welders and 10 age- and gender-matched, non-office workers in a shipyard. We measured the relative signal intensity ratio of the globus pallidus (GP) to the frontal white matter on T1-weighted MR images (pallidal index, PI). We also assessed the visual scale for the relative signal intensity of the GP, which was graded as 0-2 by a radiologist. We evaluated both signal index and visual scale in relation to the T1 relaxation time measured at the GP. Both PI and T1 relaxation time were significantly increased in the welders compared to the non-welders. T1 relaxation time began to decrease from visual scale 2, while PI began to increase from visual scale 1. Environmental Mn exposure indices correlated well with both T1 relaxation time and PI. However, blood Mn level correlated only with T1 relaxation time, and not with PI. T1 relaxation time correlated with PI only at the higher level of PI. These results indicate the possible inaccuracy of visual scoring and the discrepancy between T1 relaxation time and PI, especially at the lower level of signal intensity. Although both T1 and PI are good biomarkers for the environmental Mn exposure, non-linearity of the relationship between T1 and PI must be considered in the assessment of Mn exposure using MRI.

Quantitative assessment of bone marrow cellularity by magnetic resonance imaging in workers with long-term exposure to solvents.

This study was conducted to develop a noninvasive method of bone marrow cellularity evaluation in solvent-exposed painters. Six painters with hypocellular marrow and 132 referents were examined using magnetic resonance imaging (MRI). Full examination of the peripheral blood and bone marrow biopsy was done on each patient. Signal indices were calculated from the signal intensities measured at the vertebral bodies from T12 to S1 and on the paraspinal muscles on both the T1- and the T2-weighted image (T1WI and T2WI). Bone marrow cellularities of the painters were between 20.3% and 33.6%. Signal indices at T1WI were greater in the hypocellular marrow cases compared to those of the referents (p<0.05, p<0.01) and were significantly higher in older women compared with men (p<0.05). After adjusting for age and gender, the signal index of cases at S1 of T1WI was higher than that of the referents by 0.364. Five of the six cases had signal index at S1 of T1WI higher than the mean +1 standard deviation for the same age group and gender. MRI signal indices can be used as a useful indicator of bone marrow cellularity in a high-risk population after adequate adjustment.