Akihide Yamamoto

Direct measurement of mammographic x-ray spectra using a CdZnTe detector

Our purpose is to directly measure mammographic x-ray spectra with collimators and a low-efficiency CdZnTe detector developed recently and to find out the best fit response function of CdZnTe detector to correct the measured spectra. Photon spectra (target Mo or Rh) produced by a mammographic x-ray unit at 25-32 kV and 240 mAs (= 3 times of 80 mAs) and transmitted through 0.03 mm Mo or 0.025 mm Rh filter and object (0.1 mm Al to 0.8 mm Al phantoms) have been analyzed. Since detected spectra were distorted by the response of CdZnTe detector and did not present the true photon spectra, the correction was applied by the stripping procedure. The response function of detector used in this procedure has been determined by the evaluation of interactions (K-escape, coherent scattering, and Compton scattering processes) and incomplete charge collection calculated using the Monte Carlo method. We have used Kalpha1, Kalpha2, Kbeta1, Kbeta2 radiations of Cd, Zn, and Te, respectively and have used the weight function for the incomplete charge collection and have considered Compton scattering. The Monte Carlo simulations were continued by changing the important factors (mean path length of hole lambda(h), dead layer of the CZT crystal and weight factor Wq) of incomplete charge collection until the best fit response function was found out. Corrected photon spectra were compared with the mammographic x-ray spectral data of Bureau of Radiological Health (BRH) measured using a Ge detector. Attenuation curves of aluminum for 25-32 kV were calculated from the corrected photon spectra and compared with the attenuation curves measured using an ionization chamber. These results obtained using the CdZnTe detector agreed with the mammographic x-ray spectral data of BRH and attenuation curves obtained by the ionization chamber.

Association between chronic stress-induced structural abnormalities in Ranvier nodes and reduced oligodendrocyte activity in major depression

Repeated stressful events are associated with the onset of major depressive disorder (MDD). We previously showed oligodendrocyte (OL)-specific activation of the serum/glucocorticoid-regulated kinase (SGK)1 cascade, increased expression of axon-myelin adhesion molecules, and elaboration of the oligodendrocytic arbor in the corpus callosum of chronically stressed mice. In the current study, we demonstrate that the nodes and paranodes of Ranvier in the corpus callosum were narrower in these mice. Chronic stress also led to diffuse redistribution of Caspr and Kv 1.1 and decreased the activity in white matter, suggesting a link between morphological changes in OLs and inhibition of axonal activity. OL primary cultures subjected to chronic stress resulted in SGK1 activation and translocation to the nucleus, where it inhibited the transcription of metabotropic glutamate receptors (mGluRs). Furthermore, the cAMP level and membrane potential of OLs were reduced by chronic stress exposure. We showed by diffusion tensor imaging that the corpus callosum of patients with MDD exhibited reduced fractional anisotropy, reflecting compromised white matter integrity possibly caused by axonal damage. Our findings suggest that chronic stress disrupts the organization of the nodes of Ranvier by suppressing mGluR activation in OLs, and that specific white matter abnormalities are closely associated with MDD onset.

High amyloid‐β deposition related to depressive symptoms in older individuals with normal cognition: a pilot study

Previous studies have reported depressive symptoms in the preclinical stages of Alzheimers disease (AD). The objective of this study was to determine whether depressive symptoms are associated with cortical amyloid burden. In order to do this, we measured cortical amyloid via 11C‐labeled Pittsburgh Compound B ([11C]PIB) uptake using positron emission tomography (PET) in cognitively normal subjects.

Validity of using a 3-dimensional PET scanner during inhalation of 15O-labeled oxygen for quantitative assessment of regional metabolic rate of oxygen in man

Use of 15O labeled oxygen (15O2) and positron emission tomography (PET) allows quantitative assessment of the regional metabolic rate of oxygen (CMRO2) in vivo, which is essential to understanding the pathological status of patients with cerebral vascular and neurological disorders. The method has, however, been challenging, when a 3D PET scanner is employed, largely attributed to the presence of gaseous radioactivity in the trachea and the inhalation system, which results in a large amount of scatter and random events in the PET assessment. The present study was intended to evaluate the adequacy of using a recently available commercial 3D PET scanner in the assessment of regional cerebral radioactivity distribution during an inhalation of 15O2. Systematic experiments were carried out on a brain phantom. Experiments were also performed on a healthy volunteer following a recently developed protocol for simultaneous assessment of CMRO2 and cerebral blood flow, which involves sequential administration of 15O2 and C15O2. A particular intention was to evaluate the adequacy of the scatter-correction procedures. The phantom experiment demonstrated that errors were within 3% at the practically maximum radioactivity in the face mask, with the greatest radioactivity in the lung. The volunteer experiment demonstrated that the counting rate was at peak during the 15O gas inhalation period, within a verified range. Tomographic images represented good quality over the entire FOV, including the lower part of the cerebral structures and the carotid artery regions. The scatter-correction procedures appeared to be important, particularly in the process to compensate for the scatter originating outside the FOV. Reconstructed images dramatically changed if the correction was carried out using inappropriate procedures. This study demonstrated that accurate reconstruction could be obtained when the scatter compensation was appropriately carried out. This study also suggested the feasibility of using a state-of-the-art 3D PET scanner in the quantitative PET imaging during inhalation of 15O labeled oxygen.

Visualization of Lenticulostriate Arteries by Flow-Sensitive Black-Blood MR Angiography on a 1.5T MRI System: A Comparative Study between Subjects with and without Stroke

BACKGROUND AND PURPOSE: The branches of the LSA are the main causative arteries for lacunar infarction, though the vascular changes are largely unknown. Herein, we examined the correlation of LSA imaging findings in patients with lacunar infarction compared with controls by using FSBB-MRA. MATERIALS AND METHODS: Fifteen patients (9 men, 6 women; mean age, 73 years) with infarction at the basal ganglia and/or its vicinity were prospectively enrolled, and 12 aged-matched control subjects (6 men, 6 women; mean age, 68 years) were examined by using FSBB-MRA on a 1.5T MR imaging system. Total number and length of visualized LSA branches were compared by a 2-tailed 2-sample t test. Stepwise multiple regression analyses were performed, including hypertension, hyperlipidemia, smoking history, and diabetes mellitus after evaluation of their colinearity. P < .05 after correction for multiple comparisons was considered significant. RESULTS: Patients with stroke had significantly fewer LSA branches (average, 6.3; 95% CI, 5.4–7.1) than controls (8.7; 95% CI, 7.8–9.5) (P = .0003). The total LSA lengths were 117 mm (95% CI, 96–138 mm) for patients with stroke and 162 mm (95% CI, 133–91 mm) for control subjects (P = .01). In stepwise multiple regression analysis, only the LSA branch numbers were significantly related to infarction (P = .0003), while only hypertension was significantly related to total LSA length (P = .0085). CONCLUSIONS: Using FSBB-MRA to visualize LSA branches, we found a significant reduction in the numbers of LSA branches in patients with stroke, and hypertension was inversely related to total LSA length. FSBB is a promising method to investigate the LSA by using 1.5T MR imaging.

Delayed atrophy in posterior cingulate cortex and apathy after stroke

A few studies have been performed on chronic structural changes after stroke. The primary purpose of the present study was to investigate regional cortical volume changes after the onset of stroke and to examine how the cortical volume changes affected neuropsychiatric symptoms.

Low amyloid-β deposition correlates with high education in cognitively normal older adults: a pilot study

Several epidemiological studies have found a lower incidence of Alzheimers disease in highly educated populations, but the protective mechanism of education against the disease is still unclear. Our objective was to investigate the association between education and 11C‐labeled Pittsburgh Compound B (PIB) uptake with positron emission tomography in participants with normal cognitive ability.

3-Tesla magnetic resonance angiographic assessment of a tissue-engineered small-caliber vascular graft implanted in a rat.

In the development of small-caliber vascular grafts (diameter; less than 3 mm), animal implantation studies have been mostly performed by using rat abdominal aortas, and their certain patency must evaluate with sacrificing every observation periods, which is both labor-intensive and time-consuming when performing a large number of experiments. This study is the first to demonstrate the application of 3-Tesla contrast-free time-of-flight magnetic resonance angiography (TOF-MRA) in the continuous assessment of the status of a tissue-engineered vascular graft in rat. As a model graft, a single connective tubular tissue (diameter; 1.5 mm), prepared by embedding the silicone rod (diameter; 1.5 mm) into a subcutaneous pouch of a rat for 2 weeks an in vivo tissue-engineering, was used. The graft was implanted in the abdominal aorta (diameter; 1.3 mm) of the rat by end-to-end anastomosis. Repeated TOF-MRA imaging of the graft obtained over a 3-month follow-up period after implantation made it possible to evaluate the patency of the graft, both simply and noninvasively. It also permitted visualization of the connected abdominal aorta and renal and common iliac arteries having smaller caliber (diameter; less than 1 mm). In addition, the degree of the stenosis or aneurysm could also be detected. 3-Tesla MRA allowed the simplified and noninvasive assessment of the status on the vascular graft, including the formation of a stenosis or aneurysm, in the same rat at different times, which will be contributing to enhance the development of tissue-engineered vascular grafts even with small caliber.

Resting-state synchrony between the retrosplenial cortex and anterior medial cortical structures relates to memory complaints in subjective cognitive impairment

Subjective cognitive impairment (SCI) is a clinical state characterized by subjective cognitive deficits without cognitive impairment. To test the hypothesis that this state might involve dysfunction of self-referential processing mediated by cortical midline structures, we investigated abnormalities of functional connectivity in these structures in individuals with SCI using resting-state functional magnetic resonance imaging. We performed functional connectivity analysis for 23 individuals with SCI and 30 individuals without SCI. To reveal the pathophysiological basis of the functional connectivity change, we performed magnetic resonance-diffusion tensor imaging. Positron emission tomography-amyloid imaging was conducted in 13 SCI and 15 nonSCI subjects. Individuals with SCI showed reduced functional connectivity in cortical midline structures. Reduction in white matter connections was related to reduced functional connectivity, but we found no amyloid deposition in individuals with SCI. The results do not necessarily contradict the possibility that SCI indicates initial cognitive decrements, but imply that reduced functional connectivity in cortical midline structures contributes to overestimation of the experience of forgetfulness.

Use of T1-weighted/T2-weighted magnetic resonance ratio to elucidate changes due to amyloid β accumulation in cognitively normal subjects

The ratio of signal intensity in T1-weighted (T1w) and T2-weighted (T2w) magnetic resonance imaging (MRI) was recently proposed to enhance the sensitivity of detecting changes in disease-related signal intensity. The objective of this study was to test the effectiveness of T1w/T2w image ratios as an easily accessible biomarker for amyloid beta (Aβ) accumulation. We performed the T1w/T2w analysis in cognitively normal elderly individuals. We applied [11C] Pittsburgh Compound B (PiB)-PET to the same individuals, and Aβ deposition was quantified by its binding potential (PiB-BPND). The subjects were divided into low and high PiB-BPND groups, and group differences in regional T1w/T2w values were evaluated. In the regions where we found a significant group difference, we conducted a correlation analysis between regional T1w/T2w values and PiB-BPND. Subjects with high global cortical PiB-BPND showed a significantly higher regional T1w/T2w ratio in the frontal cortex and anterior cingulate cortex. We found a significant positive relationship between the regional T1w/T2w ratio and Aβ accumulation. Moreover, with a T1w/T2w ratio of 0.55 in the medial frontal regions, we correctly discriminated subjects with high PiB-BPND from the entire subject population with a sensitivity of 84.6% and specificity of 80.0%. Our results indicate that early Aβ-induced pathological changes can be detected using the T1w/T2w ratio on MRI. We believe that the T1w/T2w ratio is a prospective stable biological marker of early Aβ accumulation in cognitively normal individuals. The availability of such an accessible marker would improve the efficiency of clinical trials focusing on the initial disease stages by reducing the number of subjects who require screening by Aβ-PET scan or lumbar puncture.