INTRODUCTION

Quantitative susceptibility mapping (QSM) is able to provide high contrast for iron-rich deep-brain nucleus. This is attributed to the sensitivity of magnetic susceptibility to the spatial variations of molecular or cellular components that exhibit different magnetic susceptibility properties, especially for brain iron and myelin. Although there have been atlases proposed for certain age groups¹, a longitudinal statistical atlas construction from general healthy population based on QSM is still lacking. In this work, we constructed longitudinal QSM atlases over the whole lifespan (from 1 to 83 years-old), aiming to achieve an improved characterization of normative human brain development and aging related to susceptibility changes. One common QSM atlas is built for every 10-years interval to demonstrate the unique age-specific morphology and appearance of human brains. This 4D longitudinal atlas provides an efficient tool for studying and analyzing iron deposition in deep-brain nucleus for different age intervals, as well as brain myelination and demyelination process for normal aging.

METHOD

A total of 152 subjects (83 F/69 M) within age 1-83 years old were included. The 8 infant subjects (age 1-2) were scanned at the Brain Imaging & Analysis Center of Duke University on a MR750 3T scanner. The 14 toddlers (age 5-10) and 13 teenagers (age 10-20) subjects are collected at the Medical University of Graz, Austria using a Siemens TimTrio 3T scanner. The 45 younger (age 22-53) subjects and the 72 older (age 46-83) subjects were scanned at Department of Radiology, Ren Ji Hospital, Shanghai, China using a GE HDx 3T scanner. All the images were resampled to the same spatial resolution 1×1×1 mm3 through operation in k-space. Except for the infant subjects, the rest 144 subjects are separated into 8 age groups, for each group the age interval is 10 years (i.e., 10-20 years old, … 70-80 years old). A group-wise registration algorithm was conducted for each age interval to produce an age-specific anatomical template (Fig. 1). Then, a longitudinal registration is performed across different age intervals to generate the longitudinal common atlas space.

RESULTS

Fig.2 shows the susceptibility evolution in white matter bundles, e.g., internal capsule (IC) and splenium of corpus callosum (SCC). For the youngest brain template (1 year), the susceptibility contrast between white matter and gray matter are apparently lower than that of the middle-age brain template (30-40 years), susceptibility in both IC and SCC becomes more diamagnetic as shown by the fitted curves in the bottom row of Fig. 2. Both white matter bundles of the old-age template (60-70 years) become relatively more paramagnetic comparing to those of the 30-40 year-old template. This result indicates that the brain white matter myelinates during brain maturation and then demyelinates with aging which is consistent with previous DTI studies on normal aging². As shown in Fig.3, the susceptibility contrast between deep gray matter (e.g., putamen (PU), globus pallidus (GP) and caudate nucleus (CN)) and surroundings is relatively low in infant brain, which indicates less iron content stored in newborns³. The mean susceptibility value within each region shows an exponential growth with aging, which is supported by the classic histochemical studies⁴. For infants, toddlers and teenagers, the inner and outer GP can be well distinguished based on susceptibility differences. Anatomically, the inner and outer GP is physically separated by medial medullary lamina, which becomes thinner with human brain maturation resulting a blurring delineation between the two. The susceptibility inhomogeneity within PU in adult brains are also revealed by susceptibility images, and this gradient trend become more apparent with aging. This is consistent with previous findings that iron accumulation follows a precise direction from posterior to the anterior in PU.

CONCLUSION

Serial longitudinal QSM atlases were constructed for every 10-years age interval based on group-wise registration across the whole human lifespan. The common susceptibility templates provided a standard coordinate system to conduct group analyses for QSM studies at various ages. These atlases also provided an efficient tool for segmenting brain structures at specific age, benefiting from the dramatic delineation between different brain tissues. The susceptibility templates also indicated common tissue structure variations at each age interval, which is a critical reference for investigating the brain gray and white matter development with aging.

Acknowledgements

No acknowledgement found.

References

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