COMBINED DIFFUSE OPTICAL SPECTROSCOPY – MAGNETIC RESONANCE IMAGING OF HUMAN CALF MUSCLES

A magnetic resonance imaging (MRI) compatible near infrared spectrometer (NIRS) system was developed and evaluated for continuous-wave diffuse optical spectroscopy (DOS) and concurrent functional MRI measurements of human muscle. Phantom and in-vivo experiments using the system’s fiber bundle suggested that an isolation distance greater than 8 mm needs to exist between adjacent illumination-detection channels. Using single and probe-pair arrangements (inter-fiber separations of 80 µm and 5 mm, respectively), in-vivo DOS point-measurements (total=20 images) were performed on 1) the antecubital vein and a reference tissue area and 2) the lower leg at the medial (MG) and lateral gastrocnemius (LG) under isokinetic exercise. Mean spectral morphological differences and relative mean intensity changes at Hemoglobin key wavelengths were found, namely reduced mean pixel intensity (~30%) for the vessel-area and a signal change of ~1-4% between the rest and the recovery condition at both muscle locations for the single-probe configuration. Subsequent work is necessary to evaluate the oxygenation assessment capabilities of this system. Lastly, experiments were performed in which two volunteers had concurrent measurement of optical and blood oxygen level dependent (BOLD) MRI, before and following exercise. The same probe arrangement was used for DOS measurements for this experiment. The BOLD signal was studied for manually-derived ROIs. BOLD recovery curves corresponding to the LG followed routine temporal progression where immediate post-exercise signal is hypointense, followed with a sigmoidal-shaped recovery. A decrease ranging between ~0.1-20% was found in the normalized mean spectral signal (20 images) for recovery with reference to the rest condition at both muscle locations for single-probe measurements and for one probe-pair measurement (for 800,808 and 850 nm). The specific trend of the measured decrease in the mean spectral curves during recovery was not consistent among these trials. Future steps include repeatable phantom experiments, increased optical power delivery, enhanced skin contact and improved reflectance measurements Thesis Master of Applied Science (MASc)