Design and simulation of dynamic hip prosthesis based on remote motion center mechanism / 生物医学工程学杂志

The rotation center of traditional hip disarticulation prosthesis is often placed in the front and lower part of the socket, which is asymmetric with the rotation center of the healthy hip joint, resulting in poor symmetry between the prosthesis movement and the healthy lower limb movement. Besides, most of the prosthesis are passive joints, which need to rely on the amputee's compensatory hip lifting movement to realize the prosthesis movement, and the same walking movement needs to consume 2-3 times of energy compared with normal people. This paper presents a dynamic hip disarticulation prosthesis (HDPs) based on remote center of mechanism (RCM). Using the double parallelogram design method, taking the minimum size of the mechanism as the objective, the genetic algorithm was used to optimize the size, and the rotation center of the prosthesis was symmetrical with the rotation center of the healthy lower limb. By analyzing the relationship between the torque and angle of hip joint in the process of human walking, the control system mirrored the motion parameters of the lower on the healthy side, and used the parallel drive system to provide assistance for the prosthesis. Based on the established virtual prototype simulation platform of solid works and Adams, the motion simulation of hip disarticulation prosthesis was carried out and the change curve was obtained. Through quantitative comparison with healthy lower limb and traditional prosthesis, the scientificity of the design scheme was analyzed. The results show that the design can achieve the desired effect, and the design scheme is feasible.

Spinal Kinetic Control Based on a 6-DOF Robotic Manipulator / 医用生物力学

Objective To design and implement a control algorithm in a 6 degree of freedom (DOF) robotic manipulator, so as to simulate the spinal motion and provide stable and efficient testing plan for biomechanical tests on spinal implants. Methods The recognition method of stiffness matrix for L2-5 spinal system was firstly studied for decoupling purpose. Secondly, the direct force control system under each axial motion was established by combining the 6-axis manipulator control system with the incremental proportion integration differentiation (PID) control algorithm. By using the 6-axis direct force control system, pure moment of 7.5 N·m was applied in the direction of main motion axis to simulate flexion-extension (FE), lateral bending (LB) and axial rotation (AR) motion of L2-5 spinal segment. Results The range of motion (ROM) of L2-5 segment in FE, LB and AR direction was 23.01°,27.92°,9.81°, respectively. A 7.5 N·m pure moment could be achieved in the main motion axis, while maintaining zero force/moment in the unconstrained axis with root mean square (RMS) errors being less than 3 N and 0.1 N·m, respectively. Conclusions The proposed algorithm of direct force control using PID controller with predetermined stiffness decoupling matrix was capable of applying pure moment to the spine under FE, LB, AR motion. The research findings have a relatively high value of engineering application for various biomechanical testing of lumbar vertebrae.

Spinal Kinetic Control Based on a 6-DOF Robotic Manipulator / 医用生物力学

Objective To design and implement a control algorithm in a 6 degree of freedom (DOF) robotic manipulator, so as to simulate the spinal motion and provide stable and efficient testing plan for biomechanical tests on spinal implants. Methods The recognition method of stiffness matrix for L2-5 spinal system was firstly studied for decoupling purpose. Secondly, the direct force control system under each axial motion was established by combining the 6-axis manipulator control system with the incremental proportion integration differentiation (PID) control algorithm. By using the 6-axis direct force control system, pure moment of 7.5 N·m was applied in the direction of main motion axis to simulate flexion-extension (FE), lateral bending (LB) and axial rotation (AR) motion of L2-5 spinal segment. Results The range of motion (ROM) of L2-5 segment in FE, LB and AR direction was 23.01°,27.92°,9.81°, respectively. A 7.5 N·m pure moment could be achieved in the main motion axis, while maintaining zero force/moment in the unconstrained axis with root mean square (RMS) errors being less than 3 N and 0.1 N·m, respectively. Conclusions The proposed algorithm of direct force control using PID controller with predetermined stiffness decoupling matrix was capable of applying pure moment to the spine under FE, LB, AR motion. The research findings have a relatively high value of engineering application for various biomechanical testing of lumbar vertebrae.

A bench-top micro-CT capable of simulating head motions

Computational three-dimensional (3D) models of a dental structure generated from 3D dental computed tomography (CT) images are now widely used in digital dentistry. To generate precise 3D models, high-resolution imaging of the dental structure with a dental CT is required. However, a small head motion of the patient during the dental CT scan could degrade the spatial resolution of CT images to the extent that digital dentistry is no longer possible. A bench-top micro-CT has been built to evaluate the head motion effects on the dental CT images. A micro-CT has been built on an optic table with a micro-focus x-ray source and a flat-panel detector. A rotation stage, placed in between the x-ray source and the detector, is mounted on two-directional goniometers that can rotate the rotation stage in two orthogonal directions while the rotation stage is performing the CT scan. The goniometers can make object motions of an arbitrary waveform to simulate head tilting or head nodding. CT images of a phantom have been taken with and without introducing the motions, and the motion effects on the CT images have been evaluated. Object motions parallel to the detector plane have greater effects on the CT images than those against the detector plane. With the bench-top micro-CT, the motion effects have been visually seen at a tiny rotational motion as small as 0.3°. The bench-top micro-CT can be used to evaluate head motion effects on the dental CT images. The projection data, taken with the motion effects, would be used to develop motion artifact correction methods for a high-resolution dental-CT.

Effect of respiratory amplitude on the dose distribution of volumetric modulated arc therapy / 中华放射医学与防护杂志

Objective To study the effect of the respiratory amplitude on the dose distribution of volumetric modulated arc therapy (VMAT).Methods Respiratory motion simulation phantom (QUASAR) was used to simulate the respiratory movement from head to toe,and a two-dimensional ionization chamber matrix was used to collect the dose distribution in isocenter with different respiratory amplitude.Verisoft software and absolute dose analysis were used to analyze dose distribution,percentage errors of absolute dose in isocenter,passing rates of radiation field for the data collected,and results were compared to planned dosage.Results The effect on isocenter target dose of respiratory motion was below dose tolerance 5％ (t =-22.614--10.756,P ＜ 0.05).The respiratory movement made the dose on the edge of the target area higher,with fewer hot spots and more cold spots in the target area.As the respiratory amplitude increased,the effect of respiratory movement on the overall dose distribution in the target area was greater.The difference of the whole beam γ passing rate between 6,8,10 mm and stationary state was significant (t =3.095,8.685,14.096,P ＜ 0.05).The difference of target γ passing rate between 8,10 mm and stationary state was significant (t =6.081,9.841,P ＜0.05).Conclusions The respiratory movement could cause the dose transmission errors of VMAT,the error increased with increased range of motion.The actual radiation dose for normal tissues along the direction of respiratory movement on the target edge was higher than what was planned.