Description
Aging is quite enigmatic in human physiology. The loss of muscle mass and function as we age is called sarcopenia. The mechanisms leading to sarcopenia are not completely known. In routine MRI, the T2 values for collagen are so low that it precludes observation. However, the collagens or other macromolecules can be indirectly observed by selectively saturating the bound proton pool by an off-resonance RF pulse and observing the effect on the free proton water signal. This effect is called the magnetization transfer (MT). The MT effect can be quantified by a semi-quantitative index, MTsat which is a fast acquisition or by the quantitative index, the pool size ratio, F or the macromolecular fraction, f from a longer acquisition followed by fitting to the two-pool model (quantitative magnetization transfer, qMT). While a few studies have reported qMT studies on skeletal muscle, there are no reports on age related changes in f. The objective of this thesis is: (i) implementation of a qMT protocol to study age related differences in the pool size ratio, F, and (ii) perform a correlation analysis of MTsat to F. A cohort of 10 healthy young subjects and 6 healthy senior subjects were imaged in a 3T scanner (Siemens Prisma). The qMT protocol consisted of 7 offset RF frequencies at two MT flip angles, T1, B1 and B0 mapping. F, derived from qMT was not significantly different between young and old subjects and showed age related increases in the plantarflexors and decreases in the dorsiflexors. MTsat was significantly reduced with age, consistent with our earlier findings. The hypothesis that collagen is the macromolecule responsible for the MT effect is not consistent with the age-related decrease in MTsat (collagen increases with age). Further, F did not correlate with MTsat when the data was pooled together. This lack of correlation shows that F and MTsat may not be measuring the same quantity. The correlation to the histopathological analysis of biopsied muscle tissue from the same cohort may allow one to identify the macromolecules that correlate with F and with MTsat.
