Seiichiro Ohno

Development of MRI phantom equivalent to human tissues for 3.0‐T MRI

PURPOSE A 3.0-T MRI phantom (called the CAGN-3.0T phantom) having human-equivalent relaxation times and human-equivalent conductivity was developed. METHODS The ingredients of the phantom are carrageenan (as a gelatinizer), agarose (as a T2-relaxation modifier), GdCl3 (as a T1-relaxation modifier), NaCl (as a conductivity modifier), and NaN3 (as an antiseptic). Numerous samples with varying concentrations of agarose, GdCl3, and NaCl were prepared, and T1 and T2 values were measured using 3.0-T MRI. RESULTS The T1 values of the CAGN-3.0T phantom were unaffected by NaCl, while the T2 values were only slightly affected. Based on the measured data, empirical formulae were devised to express the relationships between the concentrations of agarose, GdCl3, and NaCl and the relaxation times. The formula for expressing the conductivity of the CAGN-3.0T phantom was obtained. CONCLUSIONS By adjustments to the concentrations of agarose, GdCl3, and NaCl, the relaxation times and conductivity of almost all types of human tissues can be simulated by CAGN-3.0T phantoms. The phantoms have T1 values of 395-2601 ms, T2 values of 29-334 ms, and conductivity of 0.27-1.26 S/m when concentrations of agarose, GdCl3, and NaCl are varied from 0 to 2.0 w/w%, 0 to 180 μmol/kg, and 0 to 0.7 w/w%, respectively. The CAGN-3.0T phantom has sufficient strength to replicate the torso without using reinforcing agents, and can be cut with a knife into any shape.

Regional neural response differences in the determination of faces or houses positioned in a wide visual field.

In human visual cortex, the primary visual cortex (V1) is considered to be essential for visual information processing; the fusiform face area (FFA) and parahippocampal place area (PPA) are considered as face-selective region and places-selective region, respectively. Recently, a functional magnetic resonance imaging (fMRI) study showed that the neural activity ratios between V1 and FFA were constant as eccentricities increasing in central visual field. However, in wide visual field, the neural activity relationships between V1 and FFA or V1 and PPA are still unclear. In this work, using fMRI and wide-view present system, we tried to address this issue by measuring neural activities in V1, FFA and PPA for the images of faces and houses aligning in 4 eccentricities and 4 meridians. Then, we further calculated ratio relative to V1 (RRV1) as comparing the neural responses amplitudes in FFA or PPA with those in V1. We found V1, FFA, and PPA showed significant different neural activities to faces and houses in 3 dimensions of eccentricity, meridian, and region. Most importantly, the RRV1s in FFA and PPA also exhibited significant differences in 3 dimensions. In the dimension of eccentricity, both FFA and PPA showed smaller RRV1s at central position than those at peripheral positions. In meridian dimension, both FFA and PPA showed larger RRV1s at upper vertical positions than those at lower vertical positions. In the dimension of region, FFA had larger RRV1s than PPA. We proposed that these differential RRV1s indicated FFA and PPA might have different processing strategies for encoding the wide field visual information from V1. These different processing strategies might depend on the retinal position at which faces or houses are typically observed in daily life. We posited a role of experience in shaping the information processing strategies in the ventral visual cortex.

Development of a human-tissue-like phantom for 3.0-T MRI.

PURPOSE A 3.0-T MRI phantom having human-tissue-equivalent relaxation times was developed. METHODS The ingredients of the phantom are carrageenan (for gelatinization), GdCl(3) (as a T(1)-relaxation modifier), agarose (as a T(2)-relaxation modifier), and NaN(3) (as an antiseptic agent). Numerous samples with varying concentrations of GdCl(3) and agarose were prepared, and T(1) and T(2) were measured using 3.0-T MRI. RESULTS Relaxation times of the phantom samples ranged from 395 to 2601 ms for T(1) values and 29 to 334 ms for T(2) values. Based on the measured results, empirical formulae were devised to express the relationships between the concentrations of relaxation modifiers and relaxation times. CONCLUSIONS Adjustment of GdCl(3) and agarose concentrations allows arbitrary setting of relaxation times, and the creation of a phantom that can mimic relaxation times of human-tissue. Carrageenan is considered the most suitable as a gelling agent for an MRI phantom, as it permits the relatively easy and inexpensive production of a large phantom such as for the human torso, and which can be easily shaped with a knife.

Decreased resting-state connections within the visuospatial attention-related network in advanced aging.

Advanced aging is accompanied by a decline in visuospatial attention. Previous neuroimaging and electrophysiological studies have demonstrated dysfunction in specific brain areas related to visuospatial attention. However, it is still unclear how the functional connectivity between brain regions causes the decline of visuospatial attention. Here, we combined task and rest functional magnetic resonance imaging (fMRI) to investigate the age-dependent alterations of resting-state functional connectivity within the task-related network. Twenty-three young subjects and nineteen elderly subjects participated in this study, and a modified Posner paradigm was used to define the region of interest (ROI). Our results showed that a marked reduction in the number of connections occurred with age, but this effect was not uniform throughout the brain: while there was a significant loss of communication in the anterior portion of the brain and between the anterior and posterior cerebral cortices, communication in the posterior portion of the brain was preserved. Moreover, the older adults exhibited weakened resting-state functional connectivity between the supplementary motor area and left anterior insular cortex. These findings suggest that, the disrupted functional connectivity of the brain network for visuospatial attention that occurs during normal aging may underlie the decline in cognitive performance.

A new phantom and empirical formula for apparent diffusion coefficient measurement by a 3 Tesla magnetic resonance imaging scanner

The aim of this study was to create a new phantom for a 3 Tesla (3T) magnetic resonance imaging (MRI) device for the calculation of the apparent diffusion coefficient (ADC) using diffusion-weighted imaging (DWI), and to mimic the ADC values of normal and tumor tissues at various temperatures, including the physiological body temperature of 37°C. The phantom was produced using several concentrations of sucrose from 0 to 1.2 M, and the DWI was performed using various phantom temperatures. The accurate ADC values were calculated using the DWIs of the phantoms, and an empirical formula was developed to calculate the ADC values of the phantoms from an arbitrary sucrose concentration and arbitrary phantom temperature. The empirical formula was able to produce ADC values ranging between 0.33 and 3.02×10−3 mm2/sec, which covered the range of ADC values of the human body that have been measured clinically by 3T MRI in previous studies. The phantom and empirical formula developed in this study may be available to mimic the ADC values of the clinical human lesion by 3T MRI.

Neural Responses to Central and Peripheral Objects in the Lateral Occipital Cortex.

Human object recognition and classification depend on the retinal location where the object is presented and decrease as eccentricity increases. The lateral occipital complex (LOC) is thought to be preferentially involved in the processing of objects, and its neural responses exhibit category biases to objects presented in the central visual field. However, the nature of LOC neural responses to central and peripheral objects remains largely unclear. In the present study, we used functional magnetic resonance imaging (fMRI) and a wide-view presentation system to investigate neural responses to four categories of objects (faces, houses, animals, and cars) in the primary visual cortex (V1) and the lateral visual cortex, including the LOC and the retinotopic areas LO-1 and LO-2. In these regions, the neural responses to objects decreased as the distance between the location of presentation and center fixation increased, which is consistent with the diminished perceptual ability that was found for peripherally presented images. The LOC and LO-2 exhibited significantly positive neural responses to all eccentricities (0–55°), but LO-1 exhibited significantly positive responses only to central eccentricities (0–22°). By measuring the ratio relative to V1 (RRV1), we further demonstrated that eccentricity, category and the interaction between them significantly affected neural processing in these regions. LOC, LO-1, and LO-2 exhibited larger RRV1s when stimuli were presented at an eccentricity of 0° compared to when they were presented at the greater eccentricities. In LOC and LO-2, the RRV1s for images of faces, animals and cars showed an increasing trend when the images were presented at eccentricities of 11 to 33°. However, the RRV1s for houses showed a decreasing trend in LO-1 and no difference in the LOC and LO-2. We hypothesize, that when houses and the images in the other categories were presented in the peripheral visual field, they were processed via different strategies in the lateral visual cortex.

A basic study for improving the predictability of amber traffic lights: Comparing the brief and long interval rhythm prediction

Defective and faulty traffic lights are the major cause of traffic accidents. Insufficient prediction for the appearance of the amber light will lead to a rear-end collision if the lead driver take a severe brake. In order to make the amber light predictable, we provided an improvement tentative plan for the green traffic light, in which a rhythm flashing pattern was inserted in the latter presentation part of the green light. In this case, drivers can take advantage of temporal information given by the rhythm to predict the upcoming umber light. However the most appropriate duration and the frequency of the flashing part is still unclear. We used a rhythm prediction task to identify and compare the brief (500ms) and long (1700ms) interval prediction in fMRI. We observed left Insula and right middle frontal gyrus (MFG) showed significantly activated during brief interval prediction. Bilateral middle temporal gyrus (MTG), Superior frontal gyrus (SFG), and the right inferior temporal gyrus (ITG), caudate were more active in the long interval prediction. Overall, this research showed that reaction times for brief interval was shorter than long inter prediction, also suggested a distinct mechanisms recruited for the brief and long interval rhythm prediction.

The Neural Activation in Fusiform Face Area for Object Perception in Wide Visual Field.

The fusiform face area (FFA) is thought to be preferentially involved in the processing of faces, and its neural responses exhibit category biases to objects presented in the central visual field. Differences neural activities in FFA for objects categories aligning in the central and peripheral visual field were measured. We using a wide-view (about 120°) visual presentation system developed for vision research and functional magnetic resonance imaging (fMRI), the subject were presented with objects, which were presented at a range of viewpoints in 6 level of eccentricity degree. We investigated the BLOD response to stimuli in the FFA. The result suggests face had much bigger neural activation than other objects in the FFA areas and exhibited significant differences in the neural responses to object categories at eccentricity positions of 0° and 11°, but we not find this the neural response character in the peripheral visual field.

Different neural network for exogenous temporal expectations under sub-second and supra-second in fMRI

Timing is required for both estimating the duration of a presently unfolding event, and forecasting when a future event will occur. When participants used a dynamic visual spatio-temporal trajectory stimulus to predict the final position, exogenous temporal expectations are engaged. However, it is still not clear whether different neural networks are used to measure sub-second and supra-second temporal durations. Here, we used fMRI to find out the differences between brain activity which measure 600ms and 1800ms in an exogenous temporal expectation task. We observe bilateral anterior cingulate cortex (ACC) show significantly activated during sub-second, bilateral MT+ [suggested to contain both middle temporal (MT) and medial superior temporal (MST)], right superior parietal lobule (SPL), and left inferior parietal cortex (IPC) are more active in the 1800ms condition. Overall, this research shows that maybe different components are used for sub-second and supra-second in exogenous temporal expectation.

The DTI study on visual cortex V6 of human brain

The connectivity between functionally distinct areas in the human brain is unknown because of the limitations posed by current postmortem anatomical labeling techniques. Diffusion tensor imaging (DTI) has previously been used to define large white matter tracts based on well-known anatomical landmarks in the living human brain. In the present study, we used DTI coupled with functional magnetic resonance imaging (fMRI) to assess neuronal connections between human striate and functionally defined human V6 areas. Functional areas were identified with conventional fMRI mapping procedures and then used as seeding points in a DTI analysis to ascertain connectivity patterns between cortical areas, thus yielding the pattern of connections.