A quantitative analysis of gait patterns in vestibular neuritis patients using gyroscope sensor and a continuous walking protocol.

BACKGROUND: Locomotion involves an integration of vision, proprioception, and vestibular information. The parieto-insular vestibular cortex is known to affect the supra-spinal rhythm generators, and the vestibular system regulates anti-gravity muscle tone of the lower leg in the same side to maintain an upright posture through the extra-pyramidal track. To demonstrate the relationship between locomotion and vestibular function, we evaluated the differences in gait patterns between vestibular neuritis (VN) patients and normal subjects using a gyroscope sensor and long-way walking protocol. METHODS: Gyroscope sensors were attached to both shanks of healthy controls (n=10) and age-matched VN patients (n = 10). We then asked the participants to walk 88.8 m along a corridor. Through the summation of gait cycle data, we measured gait frequency (Hz), normalized angular velocity (NAV) of each axis for legs, maximum and minimum NAV, up-slope and down-slope of NAV in swing phase, stride-swing-stance time (s), and stance to stride ratio (%). RESULTS: The most dominant walking frequency in the VN group was not different compared to normal control. The NAVs of z-axis (pitch motion) were significantly larger than the others (x-, y-axis) and the values in VN patients tended to decrease in both legs and the difference of NAV between both group was significant in the ipsi-lesion side in the VN group only (p=0.03). Additionally, the gait velocity of these individuals was decreased relatively to controls (1.11 ± 0.120 and 0.84 ± 0.061 m/s in control and VN group respectively, p<0.01), which seems to be related to the significantly increased stance and stride time of the ipsi-lesion side. Moreover, in the VN group, the maximum NAV of the lesion side was less, and the minimum one was higher than control group. Furthermore, the down-slope and up-slope of NAV decreased on the impaired side. CONCLUSION: The walking pattern of VN patients was highly phase-dependent, and NAV of pitch motion was significantly decreased in the ipsi-lesion side. The change of gait rhythm, stance and stride time, and maximum/minimum NAV of the ipsi-lesion side were characteristics of individuals with VN.

Quantitative analysis of the hippocampus using images obtained from 7.0 T MRI.

In-vivo volumetric measurements of hippocampus have proven to be highly informative for studying various neurological diseases such as Alzheimer's disease. The usefulness of volumetric imaging, however, has been limited due to the poor image resolutions obtained by currently available MRI images. In this study, a new result of volumetric image measurement of the hippocampus using 7.0 T MRI images of high contrast and resolution is described. To verify the usefulness of the proposed method, its reliability and sensitivity were examined and compared with existing imaging techniques such as 1.5 T or 3.0 T MRI imaging. The results of our study with 7.0 T MRI clearly demonstrated superior boundary detection for the hippocampal head, body, and tail compared with low field MRIs. In conclusion, robust and reproducible volumetric measurements as well as 3D images of clear contrast obtained with 7.0 T suggest the usefulness of high field MR imaging and its eventual use for the accurate diagnosis of hippocampal diseases and related research.

Observation of glucose metabolism in the thalamic nuclei by fusion PET/MRI.

UNLABELLED: The anatomy of the thalamus and its connectivity with surrounding areas are known. Localized metabolic activities at the thalamic substructural level have not been measured in vivo in human brains because of limited resolution and contrast. METHODS: The energy metabolism and fine anatomic structures of the thalamus were measured simultaneously in 5 healthy subjects using a PET/MRI fusion imaging system. Measured metabolism in individual thalamic nuclei was quantified by corresponding PET/MRI images. RESULTS: Substructures of the thalamus were clearly distinguished in 7.0-T MRI images, and the corresponding metabolic activities measured by PET were integrated by the PET/MRI system. The medial dorsal thalamic nucleus consistently showed the highest glucose uptake among the thalamic nuclei. CONCLUSION: These results demonstrate that substructure-specific metabolic activities in the thalamus can be measured with a PET/MRI system consisting of an ultra-high-resolution PET component and an ultra-high-field MRI component.

Analysis of biased PET images caused by inaccurate attenuation coefficients.

UNLABELLED: PET scanners with an elongated axial field of view intended to increase overall system sensitivity, such as the high-resolution research tomograph (HRRT) scanner, have been reported to produce images with decreased signals in the brain stem and cerebellum. The cause of this negative bias of the images was analyzed, and the effects of an inaccurate linear attenuation coefficient (mu-value) of tissue and bones were separately examined. METHODS: A new phantom was manufactured, and 18 human subjects were recruited for the study. (18)F-FDG PET images were reconstructed using attenuation coefficient maps generated by various algorithms. The algorithms included maximum a posteriori reconstruction for transmission data (MAP-TR) with default priors, MAP-TR with adjusted priors for bone (MAP-TR(adj-b)), MAP-TR with adjusted priors for tissue (MAP-TR(adj-t)), and noise-equivalent count TR and CT-TR. RESULTS: With the CT-TR and MAP-TR(adj-t) algorithms, increased intensity in the brain stem and cerebellum was seen, and negative bias was reduced. With the MAP-TR(adj-t) algorithm, however, positive bias increased in the central region. Inappropriate attenuation coefficients of brain tissue increased the positive or negative bias of reconstructed images, especially for the central regions of the volume. Poor representation of the skull or bone also locally increased the bias in the near regions where bone detection had failed. CONCLUSION: An inaccurate mu-map obtained from the MAP-TR algorithm caused the bias problem for the HRRT system. The CT-TR algorithm provided a relatively more reliable mu-map that demonstrated a small degree of intensity bias. Appropriate priors for mu-values of each tissue compartment and better classification to distinguish bone from tissue are necessary for accurate attenuation correction.

Altered T2* relaxation time of the hippocampus in major depressive disorder: implications of ultra-high field magnetic resonance imaging.

Previous studies with 1.5 T or 3.0 T magnetic resonance imaging (MRI) have produced mixed results regarding the structural changes of the hippocampus in major depressive disorder (MDD). Subtle region-specific hippocampal tissue changes might be more sensitively detected by measuring the T2* relaxation time (T2*-RT) by ultra-high-field (UHF) MRI, as it provides much higher contrast and sensitivity and consequently greater resolution. We assessed the T2*-RTs of hippocampal sub-regions in 16 MDD patients (9 with recurrent MDD) and 16 control subjects using an UHF 7.0 T MRI system. T2*-RTs of CA1, CA2, CA3, CA4, and subiculum were calculated for both left and right hippocampus. MDD patients had significantly longer T2*-RTs in the right CA1 and subiculum than control subjects. Patients with recurrent MDD had significantly longer T2*-RTs in the right subiculum than those experiencing a first depressive episode, and longer T2*-RTs in the right CA1, CA3, and subiculum than control subjects. Values for T2*-RTs of the right CA3 were significantly correlated with illness duration. In conclusion, we report that T2*-RTs in the right subiculum and CA1 were increased in patients with MDD, especially in cases of recurrent MDD. These findings suggest that region-specific hippocampal damage may be occurring in recurrent depression.