The Effectiveness of An Averaged Airway Model in Predicting the Airflow and Particle Transport Through the Airway.

Background: In this study, we proposed an averaged airway model design based on four healthy subjects and numerically evaluated its effectiveness for predicting the airflow and particle transport through an airway. Methods: Direct-averaged models of the conducting airways of four subjects were restored by averaging the three-dimensional (3D) skeletons of four healthy airways, which were calculated using an inverse 3D thinning algorithm. We simulated the airflow and particle transport in the individual and the averaged airway models using computational fluid dynamics. Results: The bifurcation geometry differs even among healthy subjects, but the averaged model retains the typical geometrical characteristics of the airways. The Reynolds number of the averaged model varied within the range found in the individual subject models, and the averaged model had similar inspiratory flow characteristics as the individual subject models. The deposition fractions at almost all individual lobes ranged within the variation observed in the subjects, however, the deposition fraction was higher in only one lobe. The deposition distribution at the main bifurcation point differed among the healthy subjects, but the characteristics of the averaged model fell within the variation observed in the individual subject models. On the contrary, the deposition fraction of the averaged model was higher than that of the average of the individual subject models and deviated from the range observed in the subject models. Conclusion: These results indicate that the direct-averaged model may be useful for predicting the individual airflow and particle transport on a macroscopic scale.

Organic-Gelatin-Free Nanocomposite Fricke Gel Dosimeter.

We report a nanocomposite Fricke gel (NC-FG) dosimeter prepared using only Fe2+ and nanoclay in water, without any organic gelling agents. This dosimeter gels due to its thixotropic properties and exhibits linear energy transfer (LET)-independent radiological properties under carbon ion beam irradiation. The radiation sensitivity of this dosimeter was 1.8 [s-1 kGy-1], which is three times higher than that reported previously (0.6 [s-1 kGy-1]) for a similar dosimeter containing gelatin. The Fe3+ yield was determined to be 0.19 µmol/J by evaluating the difference in spin-lattice relaxivity between Fe3+ and Fe2+. A further increase in the radiation sensitivity was observed upon addition of the hydrated electron scavenger N2O, suggesting the reduction of Fe3+ by a hydrated electron. LET-dependent variations of the contributions of OH radicals and hydrated electrons compensate each other in the oxidation yield of NC-FG. This is the main mechanism of the suppression of LET effects in the Bragg peak compared to conventional Fricke dosimeters. The radiation-induced oxidation yield G(Fe3+) can be described by the stoichiometric equation {G(Fe3+) = G(OH) - G(eaq-) + 2G(H2O2) + G(H)} with the reported LET dependence of the primary yield of water decomposition radicals. The calculated results are in approximate agreement with the absolute value of the experimental oxidation yield of NC-FG. The effects of the addition of small amounts of radical scavengers (nitrate, selenate, or cadmium) are also evaluated. The sensitivity was divided into two types, and influences of intermediate radicals after scavenging reaction are indicated.

Optimum coil insertion speed of various coils in brain aneurysm embolization in vitro.

A coil must comprise material with shape memory to perform optimal coil embolization. To achieve this, the alloy characteristics of the coil (hardness, shape, and thickness) must be understood. In this experiment, a catheter was fixed in the bright position and the movement of the coil was observed under a constant rate of insertion; the optimal insertion rate during clinical use was investigated. The first coil insertion speed was evaluated using simulated aneurysms in an in vivo arterial model. The results showed that the insertion force relates to the deployment shape of the coil, that the feedback through the force indicator using sound is very effective, and that the recorder is useful for analysis of coil embolization. The inserted coils during aneurysm embolization were able to wind uniformly within the aneurysm due to a variety of factors (guiding or micro-catheter position and kick-back phenomenon such as delivery wire). Optimal speed is achieved with proper coil design, which allows the coil to be inserted into the aneurysm. The shape and size of the aneurysm can help determine the necessary size and design of the coil that should be used during the optimal speed range. Aneurysm wall and coil characteristics are considered, along with the friction state of the coil (hardness, shape, and thickness), leading to improvements in safety during the insertion procedure at optimum speed.

Radiological properties of nanocomposite Fricke gel dosimeters for heavy ion beams.

The radiological properties of nanocomposite Fricke gel (NC-FG) dosimeters prepared with different concentrations of nano-clay, perchloric acid and ferrous ions in deaerated conditions were investigated under carbon and argon ion beam irradiation covering a linear-energy-transfer (LET) range of 10 to 3000 eV/nm. We found that NC-FG exhibits radiological properties distinct from those of conventional Fricke gel. The radiation sensitivity of NC-FG is independent of the LET and is nearly constant even at very high LET (3000 eV/nm) values in the Bragg peak region of the argon ion beam. In addition, whereas conventional Fricke gel dosimeters only operate under acidic conditions, NC-FG dosimeters function under both acidic and neutral conditions. The radiation sensitivity decreases with decreasing nano-clay concentration in NC-FG, which indicates that the nano-clay plays a vital role in the radiation-induced oxidation of Fe(2.)

Altered hemodynamics associated with pathogenesis of the vertebral artery dissecting aneurysms.

The etiology of the vertebral dissecting aneurysms is largely unknown, and they frequently occurs in relatively healthy young men. Objectives and Methods. A series of 57 consecutive cases defined by angiography were evaluated with regard to deviation in the course of the affected and contralateral vertebral arteries. Division was into 3 types: Type I without any deviation, Type II with mild-to-moderate deviation but not over the midline; and Type III with marked deviation over to the contralateral side beyond the midline. Results. The most frequent type of VA running was Type III for the affected and Type I nonaffected side, with this being found in all 17 patients except one. All of the Type III dissections occurred just proximal to a tortuous portion, while in cases with Type-I- and Type-II-affected sides, the majority (33 of 39) occurred near the union of the vertebral artery. In 10 of 57, a non-dominant side was affected, all except one being of Type I or II. With 12 recent patients assessed angiographically in detail for hemodynamics, eleven patients showed contrast material retrograde inflowing into the pseudolumen from the distal portion of the dissection site. Turbulent blood flow was recognized in all of these patients with retrograde inflow. Conclusions. Turbulent blood flow is one etiology of vertebral artery dissection aneurysms, with the sites in the majority of the cases being just proximal to a tortuous portion or union of vessels. In cases with dissection proximal to the tortuous course of the vertebral artery, retrograde inflow will occur more frequently than antegrade, which should be taken into account in designing therapeutic strategies.

A computational model study of the influence of the anatomy of the circle of willis on cerebral hyperperfusion following carotid artery surgery.

BACKGROUND: Cerebral hyperperfusion syndrome develops in a small subset of patients following carotid artery surgery (CAS) performed to treat severe carotid artery stenosis. This syndrome has been found to have a close correlation with cerebral hyperperfusion occurring after CAS. The purpose of this study is to investigate whether and how the anatomy of the Circle of Willis (CoW) of the cerebral circulation influences post-CAS cerebral hyperperfusion. METHODS: A computational model of the cerebral circulation coupled with the global cardiovascular system has been developed to investigate hemodynamic events associated with CAS. Nine topological structures of the CoW were investigated in combination with various distribution patterns of stenosis in the feeding arteries of the cerebral circulation. RESULTS: The occurrence of post-CAS cerebral hyperperfusion was predicted for the CoW structures that have poor collateral pathways between the stenosed cerebral feeding arteries and the remaining normal feeding arteries. The risk and the localization of post-CAS hyperperfusion were determined jointly by the anatomy of the CoW and the distribution pattern of stenosis in the cerebral feeding arteries. The presence of basilar artery stenosis or contralateral ICA stenosis increased the risk of post-CAS hyperperfusion and enlarged the cerebral region affected by hyperperfusion. For a certain CoW structure, the diameters of the cerebral communicating arteries and the severity of carotid artery stenosis both had a significant influence on the computed post-CAS cerebral hyperperfusion rates. Moreover, post-CAS cerebral hyperperfusion was predicted to be accompanied with an excessively high capillary transmural pressure. CONCLUSIONS: This study demonstrated the importance of considering the anatomy of the CoW in assessing the risk of post-CAS cerebral hyperperfusion. Particularly, since the anatomy of the CoW and the distribution pattern of stenosis in the cerebral feeding arteries jointly determine the risk and localization of post-CAS cerebral hyperperfusion, a patient-specific hemodynamic analysis aimed to help physicians identify patients at high risk of cerebral hyperperfusion should account for the combined effect of the anatomy of cerebral arteries and cerebral feeding artery stenoses on cerebral hemodynamics.

Development of high-resolution 4D in vivo-CT for visualization of cardiac and respiratory deformations of small animals.

The interest in small animal models of human diseases has generated a need to design a computed tomography (CT) system that operates at a microscopic level. It is particularly important to be able to visualize the dramatic rhythmical motion of organs such as the heart and lungs. In order to evaluate the motion of the heart and lungs of small animals (rats and mice), we developed in the present study a high-resolution 4D in vivo-CT system for small animals that uses synchrotron radiation. To reduce motion artifacts and the radiation dose, the projections were synchronized with airway pressure, the ECG, the x-ray shutter and the CCD shutter. For cardiovascular imaging, a blood pool contrast agent was injected and the data sets were acquired at several ECG points during the end-expiratory phase. For imaging of the lungs, the data sets were acquired at several airway pressures during diastole. The dynamic motion of the cardiovascular system (the ventricles and coronary arteries) and small airways (diameter > 250 microm of rats and 125 microm of mice) was visualized. This high-resolution imaging tool may be very useful for the development of novel drugs in murine models, in addition to its use in the study of cardiovascular and respiratory physiology.