Quantitative DTI assessment in human lumbar stabilization muscles at 3 T.

OBJECTIVES: To characterize diffusion tensor imaging (DTI) tensor eigenvalues (λ1, λ2, λ3), fractional anisotropy, mean diffusivity, and radial diffusivity in healthy lumbar musculature. METHODS: Seventeen healthy subjects (10 men, 7 women; mean age, 28 ± 7 years) were scanned using a 3.0-T magnetic resonance imaging. Axial DTI was performed using 15 diffusion directions (b = 400 mm/s) at the L4 level. Oswestry Low Back Pain and Godin Physical Activity questionnaires were administered to rule out underlying lower back problems. RESULTS: Skeletal muscle DTI metrics were similar to those previously published. All measurements showed low coefficients of variation, except for quadratus lumborum. Laterality was not significant. Significant sex differences were observed in the quadratus lumborum (P < 0.05). Significant correlations were found between subjects' weight and body mass index with fractional anisotropy and λ1 of the multifidus muscles. CONCLUSIONS: The DTI metrics in paraspinal muscles can be reliably measured and are influenced by body mass index and weight but not by age or physical activity.

Effect of trans-bullar gentamicin treatment on guinea pig angular and linear vestibulo-ocular reflexes.

This study provides the first systematic examination of the effects of intratympanic gentamicin instillation on vestibulo-ocular responses of guinea pigs during both Earth-vertical yaw axis and off-vertical axis rotation. A scleral search coil was sutured to the right eye of pigmented female guinea pigs prior to trans-bullar instillation of a 0.2-ml bolus of either 20 mg/ml or 40 mg/ml of gentamicin (1) into the right middle ear (unilateral treatment groups) or (2) into both ears (bilateral treatment groups). Two weeks later, eye movement responses were tested during yaw axis sinusoidal rotation at 7 frequencies (0.02, 0.05, 0.1, 0.2, 0.5, 1 and 2 Hz, 40 deg/s peak velocity) and during off-vertical axis rotation at five constant velocities (20, 40, 60, 80 and 100 deg/s), tilted 30 deg relative to the earth-vertical axis. The main result was that unilateral trans-bullar gentamicin instillation produced almost exclusively unidirectional deficits in horizontal angular vestibulocular reflex (HVOR) responses and modulation and bias responses to off-vertical axis rotation (OVAR). The HVOR gain was reduced during rotation toward the injected ear in a dose-dependent manner for frequencies of 1 Hz and lower, but there was no effect on responses during rotation toward the intact ear. Further, the modulation and bias responses to OVAR were reduced profoundly in a dose-dependent manner during rotation toward the treated ear. It is suggested that these effects indicate selective cytotoxic and/or physiologic effects of gentamicin intoxication in the inner ear or, possibly, the vestibular nerve and central nervous system.