A new simulation method was developed that considered a tumor as a solid body and therapeutic response as deformation of the tumor using mechanical analogy. As radiation exposure to the tumor was related to the external force to the solid body, the geometrical change of the tumor could be estimated from fundamental equations in solid mechanics. A change in tumor volume was calculated using finite element (FE) method. The FE models were constructed from CT images of patients before the radiotherapy. The initial radiotherapeutic parameters of tumor radioresistance and repopulation rate were determined based on a linear-quadratic model and then revised by the comparison with actual tumor volume change. Three patients with uterine cervix carcinoma were applied in this method. Simulation results well showed tendencies of tumor volume changes with radiotherapy. In addition, this method could provide the appropriate value of radiotherapeutic parameters for individual case. In conclusion, our approach could calculate three-dimensional tumor deformation during the course of radiotherapy and will provide useful information for more effective treatment.

Keywords

Mechanical Analogy, Radiotherapy, Linear-Quadratic Model, Tumor Deformation, Finite Element Analysis

Paper information

Seishin TAKAO, Shigeru TADANO, Hiroshi TAGUCHI and Hiroki SHIRATO, “Computer Simulation of Radiotherapy for Malignant Tumor”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 4 (2009), pp.576-588 . doi:10.1299/jbse.4.576

The spinal cord is mainly composed of white matter and gray matter which consist of solid and liquid phases. When the tissue deforms, the liquid phase in the tissue flows out through between the solid phases. The interaction and frictional resistance between the two phases result in the macroscopic visco-elastic behavior. In addition, the solid phase in soft tissue contains a large amount of negatively-charged proteoglycan. This electro chemical behavior affects the visco-elastic properties of the tissue. This study investigated the electro-kinetic behavior of white matter and gray matter under a variety of compressive loadings. Column-shaped specimens, 5 mm diameter and 5 mm height, were made from white matter and gray matter of bovine cervical spinal cord, and the specimens were set in physiological saline. The streaming potential was measured under compressive loading, stress relaxation, and cyclic loading. The results showed the streaming potentials to have a linear relation to tissue stress in compression and relaxation. In cyclic loading tests, the streaming potential changes according to the stress change in the loading.

Keywords

Biomechanics, Spinal Cord, Streaming Potential, Uniaxial Loading, Visco Elastic Property, Stress Relaxation

Paper information

Shigeru TADANO, Kazuhiro FUJISAKI, Masaki KATOH and Ryosuke SATOH, “Streaming Potential of White Matter and Gray Matter in Bovine Spinal Cord under Compressive Loading”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 2 (2009), pp.239-248 . doi:10.1299/jbse.4.239

Bone is often regarded as a composite material consisting of hydroxyapatite (HAp-like) mineral particles, organic matrix (mostly Type I collagen) and water phases in microscopic scale. The mechanical properties of bone at macroscopic scale depend on the structural organization and properties of constituents in the microscopic scale. In the attempts of understanding the effect of microscopic constituent on the mechanical properties of bone, the relationship between mechanical properties and mineral content of intact or completely demineralized samples have been studied. Even a slight alteration in the mineral content would have significant effect on the mechanical properties. In this work, the effect of degree of demineralization to the mechanical properties of bovine cortical bone was examined by gradually removing the mineral content and measuring constituents at every step till almost no traces of minerals were observed. Specimens were demineralized in 10% disodium EDTA solutions for 12, 24, 48, 72 hours and 14 days. The volume fraction of each structural constituent in the demineralized specimens was calculated from their X-ray absorption characteristics and quantifying transmitted X-ray intensity. Tensile tests were performed to measure the elastic modulus and ultimate strength of the demineralized specimens. This work shows the strong dependence of elastic modulus and ultimate strength of cortical bone to the mineral content as microscopic constituent. The degree of dependence with mineral loss has been demonstrated precisely so to provide the importance of mineral content and its role on the mechanical functioning of bone.

Keywords

Biomechanics, Bone, Mineral Content, Mechanical Properties, X-Ray Absorption, Demineralization

Paper information

Masahiro TODOH, Shigeru TADANO, Bijay GIRI and Masahiro NISHIMOTO, “Effect of Gradual Demineralization on the Mineral Fraction and Mechanical Properties of Cortical Bone”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 2 (2009), pp.230-238 . doi:10.1299/jbse.4.230

Precise assessment of therapeutic response in radiotherapy has been an important issue in the field of radiation oncology. This study proposed a methodology to evaluate therapeutic response based on tumor geometries. Three-dimensional (3D) tumor shapes were obtained from follow-up CT scans taken once a week throughout the treatment period. Tumor geometries were represented in two-dimensional (2D) surface geometry maps. These maps indicated the distances from the tumor center to surface at each azimuthal and horizontal angle by colors, in order to represent the characteristics of tumor morphologies. This method was applied to three clinical cases of head and neck cancer. The changes of tumor geometries could be represented visually and quantitatively using surface geometry maps. These maps provided valuable information about tumors for accurate diagnosis of tumor response to radiotherapy.

Keywords

Tumor Geometry, Surface Geometry Map, Radiotherapy, Therapeutic Response

Paper information

Seishin TAKAO, Shigeru TADANO, Hiroshi TAGUCHI and Hiroki SHIRATO, “Analysis of Three-Dimensional Characteristics in Tumor Morphology”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 2 (2009), pp.221-229 . doi:10.1299/jbse.4.221

Surface electromyography (sEMG) is commonly used to measure muscle activity because of easy application. Advantages of sEMG measurements include noninvasiveness and no pain. However, there are also problems with the sEMG technique when the activities of individual muscles are measured. The measurement of activity of individual muscles in the forearm with sEMG must be analyzed further because of superimposition of sEMG signals. In this work, a cylindrical phantom-forearm model filled with ground specimens of muscle was developed containing source and surface electrode pairs. A weak alternating current was applied to a source electrode pair immersed in the model, and the sEMG signals were measured with surface electrodes around the surface of the model. The attenuation characteristics of muscle action potential (MAP) were estimated from the measured sEMG, and the source position of the MAP was reverse-estimated. The reverse-estimated depth was accurate for less than 30mm of source depth. A 10% difference in the power exponent of attenuation caused errors in the reverse-estimation of less than 3mm.

Keywords

Forearm, Surface Electromyography (sEMG), Conductive Model, Reverse-Estimation, Biomechanics

Paper information

Yasuhiro NAKAJIMA, Satoshi YOSHINARI and Shigeru TADANO, “An Experimental Model on the Activity of Forearm Muscles Using Surface Electromyography”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 2 (2009), pp.212-220 . doi:10.1299/jbse.4.212

Keywords

Paper information

Shigeru TADANO, “Preface”, Journal of Biomechanical Science and Engineering, Vol. 4, No. 2 (2009), pp.165-165 . doi:10.1299/jbse.4.165

Naturally occurring holes in bone called foramina are not detected as region of crack initiation or growth. Lumbar vertebrae, which are subjected to complex external loads, have considerable number of such big and small foramina. The mechanical characteristics of bone profoundly depend on the mineral content (HAp crystals) and collagen fibers alignment, where c-crystallographic axis of HAp crystals are preferentially oriented parallel to the long axis of collagen fibers. In the current work, we investigated the crystal orientation and mineral distribution around the foramen using X-rays to explore the reason of foramen not being region of crack initiation or growth to the precise level. Specimens were harvested from bovine lumbar vertebrae. The orientations of HAp crystals were determined from the diffracted intensity profile of X-rays using imaging plate. Mineral fractions were measured from the fraction of X-rays transmitted through the specimen. The tangential orientation of the crystals revealed around the foramen edge was considered as the main reinforcing parameter for the foramen. The minerals were distributed in the specimen without any predictable tendency. Hence, they were not considered as a strengthening parameter. A thicker cortical region was discovered near the surface around the upper edge of the foramen, which was also extended within the cancellous mass as a thin cylindrical cortical shell covering the foramen from inside. Such structures were regarded to result the foramen a damage resistant site.

Keywords

Stress Concentration, Foramen, Bovine Lumbar Vertebra, Cortical Bone, Hydroxyapatite Crystals, X-Ray Diffraction

Paper information

Bijay GIRI, Shigeru TADANO, Kazuhiro FUJISAKI and Masahiro TODOH, “Microstructure of Bone Around Natural Hole in Bovine Lumbar Vertebra”, Journal of Biomechanical Science and Engineering, Vol. 2, No. 1 (2007), pp.1-11 . doi:10.1299/jbse.2.1

Since the cortical bone has higher elastic modulus compared to the cancellous bone, its geometry is very important for stress analysis of bone structure. During finite element modeling of bone structure, cortical bone is generally determined as the region having higher CT values with respect to specific threshold value. However, it is difficult to determine the thin cortical bone regions by considering a specific threshold value. This study proposes a method to select regions of cortical bone from clinical CT images by considering CT value distributions of cortical and cancellous bone. Applying the method to bovine proximal femur, the mean error in cortical thickness compared to the actual bone was found to be less than one pixel (0.39×0.39 mm). Hence, the proposed method could accurately determine the cortical bone regions from clinical CT images. The method was also applied to develop a finite element model with the precise cortical bone structure.

Keywords

Biomechanics, Finite Element Model, Clinical CT Image, Cortical Bone Region, CT Value Distribution

Paper information

Hiroki NAKATSUCHI, Shigeru TADANO, Masahiro TODOH, Yukio NAKATSUCHI, Shinichiro MORI and Masahiro ENDO, “Finite Element Modeling of the Cortical Bone Region Using Clinical CT Images”, Journal of Biomechanical Science and Engineering, Vol. 1, No. 2 (2006), pp.316-326 . doi:10.1299/jbse.1.316