Applicability of composite materials for space radiation shielding of spacecraft.

Energetic ion beam experiments with major space radiation elements, 1H, 4He, 16O, 28Si and 56Fe, have been conducted to investigate the radiation shielding properties of composite materials. These materials are expected to be used for parts and fixtures of space vehicles due to both their mechanical strength and their space radiation shielding capabilities. Low Z materials containing hydrogen are effective for shielding protons and heavy ions due to their high stopping power and large fragmentation cross section per unit mass. The stopping power of the composite materials used in this work is intermediate between that of aluminum and polyethylene, which are typical structural and shielding materials used in space. The total charge-changing cross sections per unit mass, σUM, of the composite materials are 1.3-1.8 times larger than that of aluminum. By replacing conventional aluminum used for spacecraft with commercially available composite (carbon fiber / polyether ether ketone), it is expected that the shielding effect is increased by ∼17%. The utilization of composite materials will help mitigate the space radiation hazard on future deep space missions.

Investigation of shielding material properties for effective space radiation protection.

Geant4 Monte Carlo simulations were carried out to investigate the possible shielding materials of aluminum, polyethylene, hydrides, complex hydrides and composite materials for radiation protection in spacecraft by considering two physical parameters, stopping power and fragmentation cross section. The dose reduction with shielding materials was investigated for Fe ions with energies of 500 MeV/n, 1 GeV/n and 2 GeV/n which are around the peak of the GCR energy spectrum. Fe ions easily stop in materials such as polyethylene and hydrides as opposed to materials such as aluminum and complex hydrides including high Z metals with contain little or no hydrogen. Attenuation of the primary particles in the shielding and fragmentation into more lightly charged and therefore more penetrating secondary particles are competing factors: attenuation acts to reduce the dose behind shielding while fragmentation increases it. Among hydrogenous materials, 6Li10BH4 was one of the more effective shielding materials as a function of mass providing a 20% greater dose reduction compared to polyethylene. Composite materials such as carbon fiber reinforced plastic and SiC composite plastic offer 1.9 times the dose reduction compared to aluminum as well as high mechanical strength. Composite materials have been found to be promising for spacecraft shielding, where both mass and volume are constrained.

Evaluation of coronary artery disease and cardiac morphology and function in patients with hypertrophic cardiomyopathy, using cardiac computed tomography.

Coronary artery disease and cardiac morphology and function were evaluated in 51 patients with hypertrophic cardiomyopathy (HCM), without typical chest pain, using cardiac computed tomography (CT). This study investigated the prevalence of coronary artery disease, the indicators of obstructive coronary stenosis, and the magnitude of left ventricular (LV) hypertrophy. The patients' mean coronary artery calcium score was 198.8 ± 312.0 and was positively correlated with the number of coronary risk factors (r = 0.32; P < 0.05). Of the 51 patients with HCM, 42 (82.4 %) had some degree of stenosis and 8 (15.7 %) had obstructive stenosis. Noncalcified and mixed plaques were detected in 14 (27.5 %) and 11 (21.6 %) patients, respectively. Multivariate logistic regression revealed that diabetes was an independent indicator of the presence of obstructive stenosis in HCM patients. Multivariate linear regression revealed that low estimated glomerular filtration rates and high triglyceride concentrations were independent indicators of higher LV mass indexes. In conclusion, cardiac CT revealed that coronary artery disease was common among patients with HCM. The presence of obstructive coronary stenosis and the magnitude of LV hypertrophy were related to the presence of diabetes, triglyceride levels, and estimated glomerular filtration rate.

A randomized intervention trial of 24-wk dairy consumption on waist circumference, blood pressure, and fasting blood sugar and lipids in Japanese men with metabolic syndrome.

UNLABELLED: Dairy foods are postulated to have beneficial effects on blood pressure, body fat, serum lipids, and the incidence of type 2 diabetes. To evaluate the effects of the consumption of milk and dairy products, we performed a randomized dietary intervention trial for 24 wk in Japanese men, aged 20 to 60 y, with 2 or more components of the metabolic syndrome ( CLINICAL TRIAL REGISTRATION: UMIN000006353). Subjects were randomized to a control group (n=98) that received dietary intervention focused on weight control supervised by registered dietitians, and a dairy-consumption group (n=102) that received both dietary intervention and regular home dairy delivery of 400 g/d for 24 wk. Co-primary endpoints included waist circumference, blood pressure, fasting blood sugar (FBS), and serum lipids. The dietary intervention decreased energy intake from 2,150 to 1,850 kcal/d in both groups (p<0.01). Mean rates of compliance with the dairy-consumption intervention were over 90%, resulting in increased calcium intake in the dairy-consumption group from 329 to 667 mg/d (p<0.01). Co-primary endpoints improved in both groups, but the degree of improvement was smaller in the dairy-consumption group (one-sided p=0.99). Subgroup analyses specified in the study protocol identified weight and leisure-time physical activity (LTPA) as significant effect modifiers. Differences in changes in systolic blood pressure compared with the control group were 28.0 mmHg (95% CI, 214.0 to 21.9, interaction; p<0.01) in the normal weight group and 25.8 mmHg (211.4 to 20.2, interaction; p=0.02) in the moderate-to-high LTPA group, indicating lower systolic blood pressure in the dairy-consumption group among participants in these subgroups. In conclusion, although effects on the co-primary endpoints of dairy consumption were not shown, dairy consumption lowered systolic blood pressure in the subgroups with normal weight and moderate-to-high LTPA and lowered FBS in the subgroup with normal weight.

The influence of effective energy on computed tomography number depends on tissue characteristics in monoenergetic cardiac imaging.

Purpose. To evaluate the influence of effective energy on computed tomography (CT) number in monoenergetic images (MEIs). Methods. Three bottle phantoms filled with water, oil, and a contrast agent were scanned at 100 and 140 kVp tube energy with a dual-source CT scanner. Cardiac dual-energy CT data was collected from 17 patients. CT numbers were measured in the 3 phantom materials and in the left ventricular cavity, myocardium, pericardial fat, and vertebral bone in MEIs from 40 to 190 keV. Results. In the phantoms, the mean CT number increased in oil whereas it decreased in the contrast agent as the energy level increased (P < 0.001). In clinical subjects, the mean CT numbers for the left ventricular cavity, myocardium, and vertebral bone were highest in the 40 keV images (P < 0.001) and decreased as the energy level increased. In contrast, the CT number for pericardial fat was lowest in the 40 keV images (P < 0.001) and increased with increasing energy. Conclusions. The influence of effective energy on CT number varies with material and tissue type in monoenergetic cardiac imaging, which could evaluate tissue characteristics through assessment of the changes in CT number associated with effective energies.

Optimization of energy level for coronary angiography with dual-energy and dual-source computed tomography.

Dual-energy computed tomography (DE-CT) uses polyenergetic X-rays at 100- and 140-kVp tube energy, and generates 120-kVp composite images that are referred to as polyenergetic images (PEIs). Moreover, DE-CT can produce monoenergetic images (MEIs) at any effective energy level. We evaluated whether the image quality of coronary angiography is improved by optimizing the energy levels of DE-CT. We retrospectively evaluated data sets obtained from 24 consecutive patients using cardiac DE-CT at 100- and 140-kVp tube energy with a dual-source scanner. Signal-to-noise ratios (SNRs) were evaluated in the left ascending coronary artery in PEIs, and in MEIs reconstructed at 40, 50, 60, 70, 80, 90, 100, 130, 160 and 190 keV. Energy levels of 100, 120 and 140 kVp generated the highest SNRs in PEIs from 10, 12 and 2 patients, respectively, at 60, 70 and 80 keV in MEIs from 2, 10 and 10 patients, respectively, and at 90 and 100 keV in those from one patient each. Optimization of the energy level for each patient increased the SNR by 16.6% in PEIs (P < 0.0001) and by 18.2% in MEIs (P < 0.05), compared with 120-kVp composite images. The image quality of coronary angiography using DE-CT can be improved by optimizing the energy level for individual patients.

Myocardial hypoperfusion detected by cardiac computed tomography in an adult patient with heart failure after classic repair for corrected transposition of the great arteries.

A 69-year-old male with a history of classic repair for corrected transposition of the great arteries (TGA) arrived at our hospital with dyspnoea upon exertion. Echocardiography revealed severe dilation and diffuse hypokinesis of the systemic ventricle without obvious valvular dysfunction. Cardiac computed tomography (CT) revealed no significant stenosis. However, the morphological right coronary artery (CA) on the left side was unequally distributed to the large systemic ventricle and was mostly obscured, especially on the anterior wall. A low attenuation area in the anterior wall of the systemic ventricle and prominent trabeculations suggested ischaemia or infarction. We considered that chronic myocardial hypoperfusion due to an inadequate coronary arterial supply was one cause of the exacerbated heart failure long after the classic repair. Cardiac CT is useful for evaluating the distribution of the CA and to predict blood supply to the myocardium in corrected TGA.

[Coronary ectasia resulting in thrombotic coronary occlusion after warfarin interruption: a case report].

A 68-year-old man taking aspirin and warfarin for ectatic right coronary artery complained of chest pain and was admitted to our hospital with acute myocardial infarction. He had discontinued taking warfarin due to nail bleeding for a month. Coronary angiography revealed total occlusion at segment 3 of the ectatic right coronary artery with massive thrombus. Because of unsuccessful reperfusion by an aspiration device, a 5F straight catheter was inserted into the ectatic right coronary artery to aspirate the massive thrombus, and Thrombolysis in Myocardial Infarction grade 3 flow reperfusion was obtained. Intravascular ultrasonography showed "moyamoya" vessels in the ectatic right coronary artery, suggesting an abnormal coronary flow pattern, but there was no evidence of unstable plaque. Warfarization should be considered to treat ectatic coronary artery.

[Coronary artery embolism from ruptured plaque in the left main trunks with difficulty in detection of culprit lesion: a case report].

A 60-year-old man complained of severe chest pain and was emergently admitted to our hospital with a dignosis of anterior acute myocardial infarction. Emergent coronary angiography revealed significant stenosis in segment 7 and filling defect in segment 11 without flow delay. Haziness was observed in segment 5. Coronary thromboembolism was suspected, but the embolic source or culprit lesion was hard to detect. Intravascular ultrasonography detected ruptured plaque with lipid pooling in segment 5. Stent implantation for segment 5 was performed successfully and the patient had an excellent clinical course. Coronary thromboembolism is rare and intravascular ultrasonography may be useful to detect the culprit lesion.