Ryutaro Himeno

Extraction from biological volume data of a region of interest with non-uniform intensity

A method is proposed for extracting the region of interest from biological volume data when non-uniform intensity is involved. Binary coded processing, using thresholding and active contour models, is often used for extracting the region of interest from biological images, but this method suffers from two defects: no allowance is made for the three-dimensional structure of the region of interest and preprocessing of the data is required. On the other hand, the region growing method can extract a complex 3-D structure and requires no preprocessing, although it is difficult to apply to biological volume data that contain a lot of noise and have non- uniform intensity in the region of interest. This paper reports improvements to the conventional region growing method to provide more robustness against non-uniform intensity and noise. This is achieved by only paying attention to the local area, using information inside and outside the region of interest, and by using a median value. This method can be easily applied as the number of parameters is less than that by conventional techniques and no prior knowledge of the original data is needed.

Three‐dimensional Reconstruction of the Equine Ovary

The equine ovary has a very unique structure in terms of its extreme large size, the presence of the ovulation fossa and the inverted location of its cortex and medulla. In the previous study, it was recognized that the application of three‐dimensional internal structure microscopy (3D‐ISM) to observe the mare ovary is very effective. Three‐dimensional reconstruction of serially sliced images made by 3D‐ISM was successful in this study with the aid of the sophisticated image processing technique. The rotation of the reconstructed ovary has been carried out with and without the application of the transparency technique in the ovarian stromal region. The spatial localization of follicles and corpus luteum was clearly visualized by rotating the reconstructed image of the ovary. The extraction of the images of follicles and corpus luteum was also available and gave a quantifiable understanding of their structure.

Blood Flow Simulator using Medical Images without Mesh Generation

Conventional blood flow simulators needed to generate meshes, which had to have fine resolution at the segments where significant flow pattern changes occurred. So, to generate ideal meshes, excellent ability in mesh generation itself was essential, at the same time, detailed knowledge in flow analysis was important. These had been reasons why the flow simulation was not widely used in medical field. We developed a new blood flow simulator without mesh generation. Our system used voxel model as simulation. The voxel models were directly made from grey scale medical modalities such as CT-Angiography, MR-Imaging or 3D-Angiography. We applied our system to two models, one was the model of coil embolization for brain aneurysm, the other was protection for carotid artery stenting. In coil embolization model, flow pattern change in aneurysm sac were calculated giving various amount of coils. Increasing volume embolization ratio, flow velocity in the sac was decreased. If protrusion of coil crossing flow in the parent artery, flow in the sac possibly increase. In case of carotid artery stenting, protective balloon occlusion of distal internal carotid artery could not prevent migration of debris from the site of balloon angioplasty to external carotid artery. In coil embolization, our simulator successfully showed decrease of flow velocity in aneurysm sac depending on increasing amount of coil(s). The result was significant alert that the crossing protrusion of coils possibly increase flow in the aneurysm sac. At carotid artery stenting, debris to the ECA might cause brain ischemia because of possible ECA ICA anastomosis. Our simulator can work stably even extremely complex structure such as “coils in aneurysm” model without detailed knowledge on the computational fluid dynamics nor mesh generation. Moreover, voxel models were directly built from medical modalities without special knowledge. Here, our simulator can work well in practical medical field.

Population of follicles and luteal structures during the oestrous cycle of mares detected by three-dimensional internal structure microscopy.

The structure of the equine ovary is different from that of other mammals in its extremely large size, the presence of ovarian fossa and the inverted location of its cortex and medulla. A three‐dimensional internal structure microscopy (3D‐ISM), which consists of a computer‐controlled slicer, a CCD camera, a laser disc recorder and a PC, is very useful for the observation of the internal structures in equine ovaries. In addition, the three‐dimensional images of follicles and corpus luteum (CL) reconstructed by the segmentation technique can clarify the spatial arrangement in the equine ovary. In this study, to understand the changes in the ovarian internal structures of the mare during the oestrous cycle, the size and numbers of follicles and luteal structures were analysed by 3D‐ISM in addition to the concentrations of progesterone (P4) and oestradiol‐17β. As a result, many small follicles (<10 mm in diameter) were detected. It was recognized that the luteal structures were distinguished into three types, such as the corpus haemorragicum (CH), which is formed by blood elements at the cavity after ovulation, CL and corpus albican (CA). There were some CHs and CL in the group, which had the concentration of P4 > 1 ng/ml. CHs were also observed in the group, which had low level of P4 (P4 < 1 ng/ml). CAs were found regardless of the P4 level. In conclusion, 3D‐ISM enabled the internal observation of the ovarian structures in detail, and estimation of the stage of the ovarian cycle with complementary physiological information. The findings by 3D‐ISM provide basic information for clinical applications.

Decision algorithm for 3D blood vessel loop based on a route edit distance

This paper reports on a method to distinguish true from false of the loop in the blood vessel graph. Most conventional studies have used a graph to represent 3D blood vessels structure. Blood vessels graph sometimes has a false loop and this exerts a harmful influence to the graph analysis. Conventional study simply cut them but this is not suitable for the graph include real loop. For this reason, we try to distinguish true from false of the loop in the graph. Our method uses the loop inside and the outside main blood vessel shape to distinguish the similar loop. This main blood vessel we called route is long, thick, and not shares to other route as much as possible. Even if a graph includes false loop, this main route will avoid the false connection and detect the same main blood vessel. Our method detects such a main route in each loop branch point and stores it as the outside feature for comparing. Inside feature is measured by converting the inside blood vessels as one route. Each loop is compared by the graph edit distance. Graph edit distance is easily able to deal with the route adding, deleting and replacing. Our method was tested by the cerebral blood vessels image in MRI. Our method tried to detect the arterial cycles of Willis from the graph including false loops. As a result, our method detected it correctly in four data from five.

A Computational Cardiovascular Model for Characterizing Arterial pulses under Various Physiopathological Conditions

Arterial pulse is one of the most important biosignals monitored in clinics for diagnosing cardiovascular disease. Despite the many past efforts attempted to correlate characteristics of arterial pulse with cardiovascular diseases, the precise characteristics of arterial pulse that best predict the risk of cardiovascular disease yet remain a subject of considerable debate. This is due to the fact that arterial pulse is sensitive to a variety of factors, including both physical ones and physiopathological ones. Given a measured arterial pulse, the best way to uncover potential pathological factors is to isolate the respective effects of different factors, which is, however, difficult to realize in practice. In this context, we develop a computational cardiovascular model, aiming to provide a mathematical platform for quantitatively studying the respective contributions of various factors to characteristics of arterial pulse. Such a model is obtained by adopting a multi-scale modeling method, where the arterial tree is described by a wave propagation model coupled with a lumped parameter description of the remainder. In this study, the model is examined by simulating arterial pulse changes associated with arterial stenoses and aging, and hemodynamics in the left brachial artery as the artery is subjected to a varying cuff pressure during oscillometric blood pressure measurement. Simulated results demonstrate that the model can reasonably capture the main characteristics of arterial pulses under the conditions studied. Particularly, the cuff simulations reveal that the accuracy of oscillometric pressure measurement is affected not only by the local arterial properties but also by hemodynamic conditions in the rest of the cardiovascular system.

3-D analysis of microvascular architecture of the spleen with ultra-high-resolution for partial splenic embolization

The purpose of this study is to clarify embolic effects of embolic agents for partial splenic embolization. Partial splenic embolization is a minimally invasive technique for splenomegaly. However, embolic agents have been empirically chosen because embolic effects have never been studied quantitatively. We have constructed a quantitative 3-D analysis system of microvascular architecture. The system has consisted of data acquisition, segmentation, and measurement of diameters of end arterioles. 3-D volumetric data of samples with ultra-high resolution was acquired using a synchrotron radiation CT constructed in SPring-8. Segmented microvascular architecture was obtained applying an adaptive region growing method. This method is a kind of dynamic thresholding to cope with nonuniformity of the voxel intensity. To recognize end of arterioles, distance map from initial point placed at the root of the major trunk have been generated applying single-seeded coding. Diameters of vasculature are measured using single-seeded clusters which are formed from the same single-seeded code in the distance map and Euclidean distance transform which measures the minimum distances between each voxel and vascular boundary. Diameters of end arterioles are obtained choosing the maximum value in the result of Euclidian distance transform in the most distant cluster. In this study, we found diameters of embolized end arterioles were ranging from 48 to 72 micrometers with the analysis system. We have concluded that a quantitative 3-D analysis system have been successfully developed for microvascular architecture. A new approach to establish theoretical basis of embolization therapy with microspheres have been provide owing to the system.

The effect of mechanical property change of the viscoelastic tube on the characteristic of the arterial stiffness indexes. – Consideration based on numerical simulation –

Recently, Arterial Stiffness has attracted a great deal of attention as the predictor of the circulatory system condition. The Arterial Stiffness indexes (Pulse Wave Velocity: PWV, pulse wave shape index (AIx: Augmentation Index), Pulse Pressure: PP, Mean Arterial Pressure: MAP, etc.), seem to show the change of the static stiffness. However, the pulse wave has the periodic beating in vivo, it is considered that Arterial Stiffness index is influenced not only the static stiffness but also dynamic viscoelastic modulus or peripheral resistance. Accordingly, the analysis was carried out by using numerical simulation, to understand the effect of the difference of such mechanical property on the pulse wave propagation and the Arterial Stiffness indexes. A single cylindrical tube was constructed by the model of the systemic artery from central aorta to common iliac artery bifurcation. When the ideal beating of periodic pressure pulse wave were given at the input, pulse pressure conditions were calculated. The vascular elastic modulus, the viscoelastic modulus and peripheral resistance were changed independently. Following results were obtained. 1) By the increase in the vascular elastic and the viscoelastic modulus, the wave reflection from peripheral was increased, and then the PP and PWV increase. 2) By the increase in the peripheral resistance, the AIx and MAP increase although the PP does not change. From these results, following conclusions were obtained. 3) The change of PWV shows the change of vascular elasticity and viscoelasticity of the thick artery, and it similarly changes by the aging with the PP. 4) The AIx value gradually increase by the aging, similarly with the MAP.