A method for correcting X-ray scattering to improve the CT-number accuracy of dental cone-beam CT images is proposed. The proposed method is based on an approximate function; that is, X-ray scatter components are approximately calculated by using the mean pixel value of a measured transmittance image and a scatter parameter. The scatter parameter is defined as the ratio of scatter-generation and attenuation coefficients. When the correction method was applied to an inhomogeneous head phantom, the CT numbers were almost completely corrected and the artifacts in the corrected axial and sagittal reconstructed images were reduced. The absolute error from the true CT number for the mandible was reduced from 549 to 30 HU by the correction method. Volume-rendering images with few artifacts were also acquired using the corrected reconstructed images. These results demonstrate that the proposed method is effective for improving the accuracy of hardness and shape measurements of a mandible in cone-beam CT images. The method enables the use of a model based on such corrected cone-beam CT images for diagnostic support and surgical planning.
It is required to collapse a lung in VATS (video-assisted thoracic surgery). The tumor position is displaced corresponding to ling collapse. Then, navigation system, which presents the tumor position for a surgeon without any palpation process, may be effective for VATS. The purpose of this study is to develop the navigation system using the collapse simulation of lung. This paper shows a collapse simulation with a loaf lung, which has no lobatum, as a first step of this study. First, we obtained and modeled the material properties of hog lung from the data obtained by rheometer. The Zener's model was used to represent the viscoelastic properties of lung from the analysis of the data. Next, the biomechanical model of lung was developed based on Finite Element Method. The collapse simulation was carried out using the model. The analysis result shows the lung model was collapsing and the deformation had the similar tendency to real lung.
We have developed novel three-dimensional finite element brain model (previously reported whole model) with material property of hyper elastic feature, which successfully demonstrated the intraoperative deformation simulation. However, shortening of computation time was essential for the real-time simulation. In this study, a parametric study to evaluate the difference of constitutive models affects both deformation results and computational time of simulation. Hyper and linear elastic models performed both gravity induced brain shift after fronto-temporal craniotomy and cerebellar hemispheric retraction by spatula for the posterior fossa surgery. The gravity induced brain shift simulation using the linear elastic material model successfully achieved up to 51% reduction of computation time compared with hyper elastic one within acceptable displacement error. Cerebellar retraction simulation also showed acceptable deformation results in both models, while in pressure analysis, an obvious underestimation in liner elastic one. Our results showed the usefulness of linear elastic model in gravity induced simulation for the reduction of computation time. On the other hand, careful attention was needed in the evaluation of pressure analysis by surgical maneuver when using linear elastic model.
Capsule endoscope and double-balloon endoscope are representative enteroscopes. However, it is difficult to use these endoscopes in patients with intestinal obstruction and adhesion. We developed a new enteroscope that can be used in patients with intestinal obstruction and adhesion; this instrument consists of an ileus tube and an optical fiberscope (diameter, 1.1 mm). When this enteroscope removed from the body, one can observe the small intestine by controlling the internal pressure of a balloon of the ileus tube as maintaining a bowel adequately. We devised a control unit to sufficiently control the internal pressure of the balloon for enabling observation of the whole area of the small intestine, and performed a basic experiment. The experimental results revealed that in a step response, the control accuracy was 0.05-0.15 kPa without an overshoot. Further, in a disturbance response, in comparison with a case without control, a one-20th was able to decrease pressure fluctuation. In addition, we performed a pulling test using an ileus tube and a small intestine model, and confirmed that we might pull out an ileus tube at constant speed by controlling the fluctuations in the internal pressure of the balloon.