Thrombi are often observed in aneurysms and are considered to play an important role in rupture. It is crucial to scrutinise any correlation between the probability of rupture and the extent of thrombus generation. Numerical techniques such as CFD seem promising for this purpose. However, there are, at present, no models that allow us to evaluate thrombus generation. The authors aim at the proposal of such a model. In the present paper, the process of platelet aggregation is discussed. In blood flow near the entry to an aneurysm, red blood cells are haemolysed due to high pressure. Adenosine diphosphate (ADP) in those haemolysed red blood cells is released into the plasma and induces the aggregation. Making reference to actual aggregation curves of human plasma for various ADP concentrations, the authors modelled the rate at which the density of aggregated platelets continues to increase. Furthermore, the present model was applied to blood flow in an endothelialised glass aneurysm in combination with CFD. As a result, the distribution of platelets clotting in an aneurysm was obtained.

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We have developed a catheter and guidewire simulator for interventional therapy. This system was developed to predict the course of approach to a lesion and to present numerical results and animation for surgical planning, intra-operative assistance, the analysis of the structure of the guidewire and the design of a new guidewire. The model of the guidewire is constructed with viscoelastic springs and segments as the dynamic deformation of a flexible structure. The proximal part of the guidewire is inserted into the catheter model. The vessel is an elastic circular cylinder, whose shape is defined by the centerline and the radii. Collisions between the guidewire and the vessel are calculated and the contact forces are determined according to the stiffness and friction of the vessel wall. In this article, we introduce our simulator and several examples of the simulation results.

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Objective: Nitric oxide (NO), which has a high affinity for oxyhemoglobin (OxyHb), regulates basal vascular tone and cerebral blood flow. We examined serial changes in the concentration of NO end products (NO₂^-/ NO₃^-) in the cerebrospinal fluid (CSF) and plasma from patients who had suffered aneurysmal subarachnoid hemorrhage (SAH), in order to investigate the relationship between NO₂^-/N₃^- concentration and cerebral vasospasm.
Methods: Nineteen patients (13 females and 6 males) with SAH who had undergone cisternal drainage were enrolled for this study. In 17 patients, CSF and plasma samples were taken for analysis of nitrite and nitrate levels after surgery. The Griess procedure was applied to measure nitrite and nitrate in the CSF and serum. Only nitrite and nitrate in the CSF were measured in the cases.
Results: The mean CSF nitrate concentration in the SAH patients was 8.6 ± 0.8 µmol/l, indicating statistically significant elevation compared with that of the control (5.9 ± 0.9 µmol/l). However, CSF nitrate in the SAH patients remained at low levels during days 4-7. The mean plasma nitrate was 16.1 ± 1.7 µmol/l, a significantly lower level than that of the control (41.5 ± 5.62 µmol/l). A positive correlation existed between the mean nitrate in CSF and in plasma, fitting the straight line (y=0.367x+2.653, R²=0.527). Five patients developed a serious vasospasm leading to poor outcome, but we could not detect any elevation of the nitrate level in sequential measurements.
Conclusion: The concentration of CSF nitrate in the patients with SAH decreased to a low level during days 4 to 7 and did not correlate with the onset of cerebral vasospasm. A likely explanation for this result was that the total amount of NO production in the brain decreased after SAH.

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