title: Longitudinal T1 relaxation rate (R1) captures changes in short-term Mn exposure in welders.
abstract: We demonstrated recently that the T1 relaxation rate (R1) captured short-term Mn exposure in welders with chronic, relatively low exposure levels in a cross-sectional study. In the current study, we used a longitudinal design to examine whether R1 values reflect the short-term dynamics of Mn exposure.
  
  
  
  Twenty-nine welders were evaluated at baseline and 12 months. Occupational questionnaires estimated short-term welding exposure using welding hours in the 90days prior to each study visit (HrsW90). In addition, blood Mn levels, the pallidal index (PI; globus pallidus T1-weighted intensity (T1WI)/frontal white matter T1WI), and R1 values in brain regions of interest (ROIs) were determined as Mn biomarkers at each visit. Associations between changes in estimated welding exposure and changes in purported Mn biomarkers were assessed by Spearman's correlations with adjustment for age and baseline R1, HrsW90, and blood Mn values.
  
  
  
  Changes in welding hours (HrsW90: the short-term welding exposure estimate), was associated significantly with changes in R1 values in the putamen (r=0.541, p=0.005), caudate (R=0.453, p=0.023), globus pallidus (R=0.430, p=0.032), amygdala (R=0.461, p=0.020), and hippocampus (R=0.447, p=0.025), but not with changes in blood Mn levels or the PI.
  
  
  
  Changes in R1 values correlated with changes in the short-term welding exposure estimate, but not with more traditional measures of Mn exposure (blood Mn levels or PI). These results suggest that R1 may serve as a useful marker to capture the short-term dynamics in Mn brain accumulation related to welding exposure.
authors: Department of Neurology, Pennsylvania State University College of Medicine-Milton S. Hershey Medical Center, Hershey, PA, USA; Department of Pharmacology, Pennsylvania State University College of Medicine-Milton S. Hershey Medical Center, Hershey, PA, USA.
authors: Mechelle M
authors: MM
authors: Lewis
authors: Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, NC, USA.
authors: Michael R
authors: MR
authors: Flynn
authors: Department of Neurology, Pennsylvania State University College of Medicine-Milton S. Hershey Medical Center, Hershey, PA, USA.
authors: Eun-Young
authors: EY
authors: Lee
authors: Department of Biostatistics, School of Public Health, University of North Carolina, Chapel Hill, NC, USA.
authors: Scott
authors: S
authors: Van Buren
authors: Department of Biostatistics, School of Public Health, University of North Carolina, Chapel Hill, NC, USA.
authors: Eric
authors: E
authors: Van Buren
authors: Department of Neurology, Pennsylvania State University College of Medicine-Milton S. Hershey Medical Center, Hershey, PA, USA.
authors: Guangwei
authors: G
authors: Du
authors: Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, NC, USA.
authors: Rebecca C
authors: RC
authors: Fry
authors: Department of Biostatistics, School of Public Health, University of North Carolina, Chapel Hill, NC, USA.
authors: Amy H
authors: AH
authors: Herring
authors: Department of Public Health Sciences, Pennsylvania State University, Hershey, PA, USA.
authors: Lan
authors: L
authors: Kong
authors: Department of Neurology, Pennsylvania State University College of Medicine-Milton S. Hershey Medical Center, Hershey, PA, USA; Department of Pharmacology, Pennsylvania State University College of Medicine-Milton S. Hershey Medical Center, Hershey, PA, USA.
authors: Richard B
authors: RB
authors: Mailman
authors: Department of Neurology, Pennsylvania State University College of Medicine-Milton S. Hershey Medical Center, Hershey, PA, USA; Department of Pharmacology, Pennsylvania State University College of Medicine-Milton S. Hershey Medical Center, Hershey, PA, USA; Departments of Radiology, Pennsylvania State University College of Medicine-Milton S. Hershey Medical Center, Hershey, PA, USA; Department of Kinesiology, Pennsylvania State University, University Park, PA, USA. Electronic address: Xuemei@psu.edu.
authors: Xuemei
authors: X
authors: Huang
mesh_terms: D000328:Adult; D000395:Air Pollutants, Occupational / Q000097:blood; D001921:Brain / Q000000981:diagnostic imaging*; D003430:Cross-Sectional Studies; D006801:Humans; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging; D008297:Male; D008345:Manganese / Q000097:blood / Q000494:pharmacology*; D008875:Middle Aged; D018709:Statistics, Nonparametric; D013997:Time Factors; D014896:Welding
chemical_list: D000395:Air Pollutants, Occupational; D008345:Manganese
keywords: Longitudinal; MRI; Manganese; R1; Welders