Shinya Onogi

Production and validation of acoustic field to enhance trapping efficiency of microbubbles by using a matrix array transducer

We have developed a new matrix array transducer for controlling the behavior of microbubbles, which is different from that for high-intensity focused ultrasound (HIFU) therapy, in order to emit continuous wave by designing an acoustic field including multiple focal points. In the experiment using a thin-channel model, a wider acoustic field has an advantage for trapping microbubbles. In the experiment using a straight-path model, we have confirmed that a higher concentration of acoustic energy does not result in more aggregates. The dispersion of acoustic energy is important because the trapping performance is affected by the relationship between the shape of the acoustic field and the concentration of the suspension.

Development of the needle insertion robot for percutaneous vertebroplasty

Percutaneous Vertebroplasty (PVP) is an effective and less invasive medical treatment for vertebral osteoporotic compression fractures. However, this operative procedure is quite difficult because an arcus vertebra, which is narrow, is needled with accuracy, and an operators hand is exposed to X-ray continuously. We have developed a needle insertion robot for Percutaneous Vertebroplasty. Its experimental evaluation on the basic performance of the system and needle insertion accuracy are presented. A needle insertion robot is developed for PVP. This robot can puncture with accuracy and an operator does not need to be exposed to X-ray. The mechanism of the robot is compact in size (350 mm x D 400 mm x H270 mm, weight: 15 kg) so that the robot system can be inserted in the space between C-arm and the patient on the operating table. The robot system is controlled by the surgical navigation system where the appropriate needle trajectory is planned based on pre-operative three-dimensional CT images. The needle holding part of the robot is X-ray lucent so that the needle insertion process can be monitored by fluoroscopy. The position of the needle during insertion process can be continuously monitored. In vitro evaluation of the system showed that average position and orientation errors were less than 1.0 mm and 1.0 degree respectively. Experimental results showed that the safety mechanism called mechanical fuse released the needle holding disk properly when excessive force was applied to the needle. These experimental results demonstrated that the developed system has the satisfactory basic performance as needle insertion robot for PVP.

An accurate calibration method of ultrasound images by center positions of a metal ball

This paper provides a novel method for three-dimensional tracking of ultrasound images. One of the issues to determine the position of a ultrasound image plane is the thickness of the image plane. The proposed methodology address the issue by the calibration phantom using a fiducial sphere with the diameter of 5.5 mm because comet-trail artifact can be observed in the image plane through the center of the sphere. Meanwhile, to measure the sphere center accurately by a tracking device, a pointer tool with the same sphere at the tip is also proposed. To validate the feasibility of the method, simulation and phantom tests were conducted. From the results of the phantom test, the accuracy of the calibration was 0.65, 0.40, and 0.42 mm in 10, 50, 100 points calibration. The results demonstrate that the proposed method has a great potential for accurate US probe calibration.

Improving the strength of sutureless laser-assisted vessel repair using preloaded longitudinal compression on tissue edge

Little is known about the approximation of coapted edges in sutureless laser‐assisted vessel welding. Tissue shrinkage by laser irradiation may cause coapted edges to separate, reducing strength of welding. This may be avoided by preloaded longitudinal compression on the tissue edges to be welded. This study compared welding strength with and without preloaded compression in ex vivo animal experiments.

Forming acoustic attraction force to concentrate microbubbles in flow using a matrix array transducer

We have reported our attempts for active path selection of microbubbles by acoustic radiation forces, where we have investigated to control microbubbles by forming multiple focal points of continuous wave using a matrix array transducer. However, because those focal points were located to sweep microbubbles along the slope of sound pressure, it was difficult to concentrate microbubbles against the direction of flow. To produce attractive force to concentrate microbubbles in flow, we formed time-shared acoustic field of two focal points with phase variation. We have succeeded to concentrate microbubbles in water flow utilizing two focal points with opposite phase, where streamline of microbubbles was clearly confirmed in a thin channel. Also we confirmed induction performance using an artificial blood vessel with Y-form bifurcation, where induction rate to a desired path was calculated and varied according to the emission pattern of the focal points in time-shared acoustic fields.

Robotic ultrasound probe handling auxiliary by active compliance control

This paper describes a support system for ultrasound (US) probe scanning by a robotic probe holding system to support manual handling of an US probe. The system, consisting of an US probe manipulator with parallel link mechanism and a 6-axis force sensor, is able to hold and manipulate an US probe according to force applied to the probe by a technician. To enable the smooth coordinated control, compliance control is used. Moreover, we have proposed velocity-depended viscosity depending on the velocity of the robot. In this study, the appropriate viscosity corresponding to operational velocity was measured experimentally and the feasibility of the coordinated motion control was validated. The results of the viscosity measurement showed a clear inverse correlation between the viscosity and the operational velocity. In the coordinated motion control evaluation, the relation between the applied force and the robot velocity in the viscosity of high, low, and dynamic velocity-depended coefficient was measured. The result showed the dynamic velocity-depended viscosity provides well-coordinated motion in any operational velocities. The results demonstrated the system has a great potential for support of US diagnosis as an auxiliary medical robot.

Production of acoustic field with multiple focal points to control high amount of microbubbles in flow using a 2D array transducer

We have newly developed a 2D array transducer to control the behavior of microbubbles, which is different from that for HIFU therapy, to emit continuous wave by designing acoustic field including multiple focal points. In the experiment using a straight path model, we have confirmed that higher concentration of acoustic energy does not result more aggregation. We also have confirmed the trapped areas of microbubbles are located not in the peak of the distribution of sound pressure, but in the middle range. The dispersion of acoustic energy is important because there was a relation in the trapping performance of microbubbles and the shape of acoustic field.

Image plane positioning by pneumatic actuators for ultrasound guidance

Image guided procedures such as percutaneous needle insertion or high intensity focused ultrasound, have become quite widespread. In images acquisition, ultrasound (US) is convenient to use in a conventional operating room, and inexpensive compared to CT and MRI. However, US requires to handle an US probe and do not have the base coordinate system. Therefore, intraoperative image position is unclear and cannot position to interested area. To address the issues, we have developed a robotic system based on US calibration and a probe scanning robot. In this study, to validate the implement system, positioning accuracy of an image plane was evaluated. Moreover, we developed an automated US guidance system with a conventional US probe. The system enables image plane positioning to visualize a therapeutic tool automatically. From the results, positioning accuracy of the image plane was 1.6 mm and 1.5 deg, maximally. In the phantom test, the error between the positions of the image plane and the mock needle was 2.5 mm and 0.9 deg. We have confirmed that the proposed system is greatly applicable for an intraoperative US guidance.

Control of fracture reduction robot using force/torque measurement

We have developed a surgical robotic system for femoral fracture reduction employing indirect traction. Indirect traction in fracture reduction is a generally used surgical method for preventing complications such as bone splits caused by high stress on bones. For traction, a patients foot is gripped by a jig and pulled to the distal side. Indirect traction has the advantage of distributing bone stress by utilizing a strong traction force; however, this procedure does not accurately control the proper positioning of fractured fragments when a surgical robot is used. The human leg has knee and an ankle joints, and thus robotic motion presents problems in not being able to directly propagate reduction motion to a fractured femoral fragment, rendering control of bone position difficult. We propose a control method for fracture reduction robots using external force/torque measurements of the human leg to achieve precise fracture reduction. Results showed that the proposed method reduced repositioning error from 6.8 mm and 15.9 degrees to 0.7 mm and 5.3 degrees, respectively.

Registration using 3D-printed rigid templates outperforms manually scanned surface matching in image-guided temporal bone surgery.

PurposeImage-guided surgery (IGS) for otological procedures requires minimal invasiveness and a high degree of accuracy. We have recently developed a noninvasive registration method, the Surface Template-Assisted Marker Positioning (STAMP) method, which uses a rigid template of the surface of the temporal bone. However, the STAMP method is not applicable when the bony surface is not exposed, such as in endoscopic surgery. Thus, we extended our research to apply the STAMP method onto the skin and tested its feasibility in this study.MethodsWe designed a phantom made of a rigid box and soft material for the study. The target registration error (TRE) was measured at preset measuring points in the phantom. We modified the STAMP method to be applicable for use on the skin around the ears (S-STAMP). The same phantom was also registered using the conventional, manually scanned surface matching method. We compared the TRE after the different registration methods.ResultsThe TRE after the S-STAMP registration method was significantly smaller than that of the conventional surface matching method at all error measurement points in the phantom. However, the TRE after the S-STAMP registration method was significantly larger than that of paired point registration using invasive fiducial markers.ConclusionsThe S-STAMP method using a rigid template on the soft surface yields a significantly smaller TRE than that of conventional, manually scanned surface matching registration. This strategy provides an alternative option to improve the accuracy of IGS without loading patients with additional invasive procedures.