Although manganese (Mn) is a trace metal essential for humans, chronic exposure to Mn can cause accumulation of this metal ion in the brain leading to an increased risk of neurological and neurobehavioral health effects. This is a concern for welders exposed to Mn through welding fumes. While brain Mn accumulation in occupational settings has mostly been reported in the basal ganglia, several imaging studies also revealed elevated Mn in other brain areas. Since Mn functions as a magnetic resonance imaging (MRI) T1 contrast agent, we developed a whole-brain MRI approach to map in vivo Mn deposition differences in the brains of non-exposed factory controls and exposed welders. This is a cross-sectional analysis of 23 non-exposed factory controls and 36 exposed full-time welders from the same truck manufacturer. We collected high-resolution 3D MRIs of brain anatomy and R1 relaxation maps to identify regional differences using voxel-based quantification (VBQ) and statistical parametric mapping. Furthermore, we investigated the associations between excess Mn deposition and neuropsychological and motor test performance. Our results indicate that: (1) Using whole-brain MRI relaxometry methods we can generate excess Mn deposition maps in vivo, (2) excess Mn accumulation due to occupational exposure occurs beyond the basal ganglia in cortical areas associated with motor and cognitive functions, (3) Mn likely diffuses along white matter tracts in the brain, and (4) Mn deposition in specific brain regions is associated with exposure (cerebellum and frontal cortex) and motor metrics (cerebellum and hippocampus).

Background: Since the introduction of whole‐body photon‐counting detector CT (PCD‐CT) into clinical practice, extensive physics assessments have been conducted to elucidate its image quality advantages over energy‐integrating detector CT (EID‐CT) and to support its clinical adoption. However, evaluations of its three‐dimensional (3D) noise power spectrum (NPS), which simultaneously quantifies in‐plane and through‐plane noise texture and magnitude, remain limited. Purpose: To experimentally evaluate the 3D NPS of an NAEOTOM Alpha PCD‐CT system and its dependence on scan mode, reconstruction image type, quantum iterative reconstruction (QIR) strength, mono‐energy (keV) level, spiral pitch, and radiation dose. Methods: Repeated scans of a 20 cm water phantom and a 30 cm PMMA phantom were conducted under the clinical Standard mode, clinical Ultra‐High‐Resolution (UHR) mode, and an Expert Service mode. Reconstructed image types include T3D, virtual monoenergetic image (VMI), and T1 (a linear reconstruction of total‐energy bin available via the Expert Service mode). Data were collected at seven dose levels (0.4–24 mGy) and four spiral pitch levels (0.35–1.5). T3D and VMI images were reconstructed with varying QIR strengths, and VMIs were reconstructed at energies ranging from 40 to 190 keV. The 3D NPS, , was calculated from each ensemble of 3D image volumes. Axial was obtained by integrating NPS _3D along , while was obtained by integrating NPS _3D over and . Results: of T1 images were flat, indicating no noise correlation across PCD rows. In contrast, all clinical‐mode reconstructions exhibited through‐plane noise correlation, as reflected in the shape of their . For clinical‐mode reconstructions, the shape of their 3D NPS showed a mild to moderate dependence on dose, with lower doses producing NPS profiles shifted towards lower frequencies in both axial and z directions. With a matched post‐object radiation exposure, the larger phantom resulted in higher noise and stronger noise correlation compared to the smaller phantom. QIR only mildly enhanced noise correlation. For a given CTDI _vol , spiral pitch has a negligible impact on 3D NPS. Due to through‐plane noise correlation, the variance of T3D and VMI decreases with slice thickness () approximately as , in contrast to the scaling observed in T1 images. The shape of the 3D NPS of VMI showed only weak dependence on the keV level along the axial frequency direction. Compared to the Standard mode, the UHR mode reduced image variance by 26% when using a soft‐tissue (Br44) kernel and by 77% with a sharp (Br76) kernel. However, 3D NPS analysis revealed stronger through‐plane noise correlation in UHR images. Conclusion: The 3D NPS provides new insight into the noise characteristics of PCD‐CT: Noise in the native PCD‐CT projection data is uncorrelated across detector rows, but clinical reconstruction processes introduce noise spatial correlation along both axial and z directions, particularly at higher QIR strengths, lower radiation doses, or with larger image objects that increase the percentage of scattered photons. Compared to the Standard mode, UHR mode reconstruction exhibits stronger noise correlation due to its superior detector spatial resolution, allowing for more aggressive spatial smoothing to achieve the desired spatial resolution in the final image.

Chronic overexposure to manganese (Mn) can occur in occupational settings, such as welding, leading to increased Mn levels in the brain. Excess brain Mn accumulation may result in neurotoxicity, which is characterized by Parkinsonian-like symptoms including motor and cognitive dysfunctions. In this work, we demonstrate a novel methodology for personalized diagnosis and spatial characterization of abnormal Magnetic Resonance Imaging R1 (R1 = 1/T1) relaxation rates arising from excessive Mn accumulation in welders’ brains. Utilizing voxel-wise population-derived norms based on a frequency age-matched non-exposed group (n = 25), we demonstrate the ability to conduct subject-specific assessments and mapping of Mn exposure using MRI relaxometry. Our results show elevated R1 in multiple brain regions in individual welders, but also extreme between-subject variability in Mn accumulation, debasing the concept that high exposures correlate with uniformly high Mn deposition in the brain. Consequently, the presented personalized methodology serves as a counterpart to group-based comparison, which allows for understanding the level of individual exposure and the toxicokinetics of Mn accumulation. This work lays a foundation for improved occupational health assessments and preventive measures against neurotoxic metal exposure.

In this work we demonstrate a novel methodology for personalized diagnosis and spatial characterization of abnormal Magnetic Resonance Imaging R1 (R1 = 1/T1) relaxation rates arising from excessive manganese (Mn) accumulation in welders’ brains. Utilizing voxel-wise population-derived norms based on a frequency age-matched non-exposed group (n = 25), we demonstrate the ability to conduct subject-specific assessments and mapping of Mn exposure using MRI relaxometry. Our results show elevated R1 in multiple brain regions in individual welders, but also extreme between-subject variability in Mn accumulation, debasing the concept that high exposures correlate with uniformly high Mn deposition in the brain. Consequently, the presented personalized methodology serves as a counterpart to group-based comparison, which allows for understanding the level of individual exposure and the toxicokinetics of Mn accumulation. This work lays a foundation for improved occupational health assessments and preventive measures against neurotoxic metal exposure.