Doyoung Chang

Geometric evaluation of systematic transrectal ultrasound guided prostate biopsy.

PURPOSE Transrectal ultrasound guided prostate biopsy results rely on physician ability to target the gland according to the biopsy schema. However, to our knowledge it is unknown how accurately the freehand, transrectal ultrasound guided biopsy cores are placed in the prostate and how the geometric distribution of biopsy cores may affect the prostate cancer detection rate. MATERIALS AND METHODS To determine the geometric distribution of cores, we developed a biopsy simulation system with pelvic mock-ups and an optical tracking system. Mock-ups were biopsied in a freehand manner by 5 urologists and by our transrectal ultrasound robot, which can support and move the transrectal ultrasound probe. We compared 1) targeting errors, 2) the accuracy and precision of repeat biopsies, and 3) the estimated significant prostate cancer (0.5 cm(3) or greater) detection rate using a probability based model. RESULTS Urologists biopsied cores in clustered patterns and under sampled a significant portion of the prostate. The robot closely followed the predefined biopsy schema. The mean targeting error of the urologists and the robot was 9.0 and 1.0 mm, respectively. Robotic assistance significantly decreased repeat biopsy errors with improved accuracy and precision. The mean significant prostate cancer detection rate of the urologists and the robot was 36% and 43%, respectively (p <0.0001). CONCLUSIONS Systematic biopsy with freehand transrectal ultrasound guidance does not closely follow the sextant schema and may result in suboptimal sampling and cancer detection. Repeat freehand biopsy of the same target is challenging. Robotic assistance with optimized biopsy schemas can potentially improve targeting, precision and accuracy. A clinical trial is needed to confirm the additional benefits of robotic assistance.

Gait planning based on kinematics for a quadruped gecko model with redundancy

Recent research on mobile robots has focused on locomotion in various environments. In this paper, a gait-generation algorithm for a mobile robot that can travel from the ground to a wall and climb vertical surfaces is proposed. The algorithm was inspired by a gecko lizard. Our gait planning was based on inverse kinematics using the Jacobian of the whole body, where the redundancy was solved by defining an object function for the gecko posture to avoid collisions with the surface. The optimal scalar factor for these two objects was obtained by defining a superior object function to minimize the angular acceleration of joints. The algorithm was verified through simulation of the gecko model travelling on given task paths and avoiding abnormal joint movements and collisions.

Ultrasound Probe and Needle-Guide Calibration for Robotic Ultrasound Scanning and Needle Targeting

Image-to-robot registration is a typical step for robotic image-guided interventions. If the imaging device uses a portable imaging probe that is held by a robot, this registration is constant and has been commonly named probe calibration. The same applies to probes tracked by a position measurement device. We report a calibration method for 2-D ultrasound probes using robotic manipulation and a planar calibration rig. Moreover, a needle guide that is attached to the probe is also calibrated for ultrasound-guided needle targeting. The method is applied to a transrectal ultrasound (TRUS) probe for robot-assisted prostate biopsy. Validation experiments include TRUS-guided needle targeting accuracy tests. This paper outlines the entire process from the calibration to image-guided targeting. Freehand TRUS-guided prostate biopsy is the primary method of diagnosing prostate cancer, with over 1.2 million procedures performed annually in the U.S. alone. However, freehand biopsy is a highly challenging procedure with subjective quality control. As such, biopsy devices are emerging to assist the physician. Here, we present a method that uses robotic TRUS manipulation. A 2-D TRUS probe is supported by a 4-degree-of-freedom robot. The robot performs ultrasound scanning, enabling 3-D reconstructions. Based on the images, the robot orients a needle guide on target for biopsy. The biopsy is acquired manually through the guide. In vitro tests showed that the 3-D images were geometrically accurate, and an image-based needle targeting accuracy was 1.55 mm. These validate the probe calibration presented and the overall robotic system for needle targeting. Targeting accuracy is sufficient for targeting small, clinically significant prostatic cancer lesions, but actual in vivo targeting will include additional error components that will have to be determined.

Design and Application of a Wire-Driven Bidirectional Telescopic Mechanism for Workspace Expansion with a Focus on Shipbuilding Tasks

Various products and patents have been established with regard to telescopic mechanisms over a long period of time. However, to the best of our knowledge, with reference to motional characteristics, few studies have been reported on a telescopic mechanism that is capable of bidirectional extension. Moreover, as we wish to point out here, such a kind of mechanism has received little attention due to the absence of practical applications. However, in the case of blast-cleaning and painting in double-hulled structures in shipbuilding, the bidirectional-extension mechanism seems to be a worthwhile subject for investigation since it will be of great help in the execution of suggested tasks for the entire transverse web floor with a range of 2–3 m. Since the self-traveling robotic platform is located on longitudinal stiffeners whose heights range from 400 to 800 mm, the manipulator to be installed on the robotic platform should have a bidirectional stroke to continuously approach the upper and lower sections of the transverse web floor. Further, with the rapid progress of the shipbuilding industry in South Korea, the importance of the bidirectional-extension mechanism in the automation of double-hulled structures has been increasingly recognized. Thus, for the design of a new mechanism, this paper describes a new type of telescopic mechanism that is capable of bidirectional strokes; the paper focuses on the mechanical design, analysis, manufacture and experimentation. Further, a customized pulley with a cylindrical-helix groove is designed to prevent the problem of overlapping steel wires since it leads to inaccurate position control with respect to the motors rotation. In particular, experiments have been conducted in terms of the positional repeatability of the manufactured telescopic manipulator and the quality of blast-cleaning of an upper section of a transverse web floor in a double-hulled structure. Throughout the experiments, the manufactured mechanism has demonstrated an amazing bidirectional translating stroke that has ranged from –500 to +2000 mm in field testing. Further, the repeatability of the manufactured bidirectional manipulator with the suggested motor–pulley system has been clearly identified as ±0.84 mm in the descending direction and ±0.63 mm in the ascending direction.

Robot for ultrasound-guided prostate imaging and intervention

The paper presents a new robot for manipulating a transrectal ultrasound probe for image-guided intervention of the prostate, the TRUS robot. The robot positions and orients the probe for image scanning and needle targeting of the prostate. Image slices and their respective position are mapped three-dimensionally to render volumetric images. The robot is designed to accommodate the constraints of the clinical prostate intervention. The robot includes all 4 degrees-of-freedom that are available in manual handling of the probe. In-vitro studies on pelvic mockups verify 3D imaging capabilities. The robot is clinically used in robot-assisted laparoscopic radical prostatectomy for providing intraoperative ultrasound-based navigation for the surgeon.

Geometric systematic prostate biopsy.

Abstract Objective: The common sextant prostate biopsy schema lacks a three-dimensional (3D) geometric definition. The study objective was to determine the influence of the geometric distribution of the cores on the detection probability of prostate cancer (PCa). Methods: The detection probability of significant (>0.5 cm3) and insignificant (<0.2 cm3) tumors was quantified based on a novel 3D capsule model of the biopsy sample. The geometric distribution of the cores was optimized to maximize the probability of detecting significant cancer for various prostate sizes (20–100cm3), number of biopsy cores (6–40 cores) and biopsy core lengths (14–40 mm) for transrectal and transperineal biopsies. Results: The detection of significant cancer can be improved by geometric optimization. With the current sextant biopsy, up to 20% of tumors may be missed at biopsy in a 20 cm3 prostate due to the schema. Higher number and longer biopsy cores are required to sample with an equal detection probability in larger prostates. Higher number of cores increases both significant and insignificant tumor detection probability, but predominantly increases the detection of insignificant tumors. Conclusion: The study demonstrates mathematically that the geometric biopsy schema plays an important clinical role, and that increasing the number of biopsy cores is not necessarily helpful.

Development of a characteristic point detecting seam tracking algorithm for portable welding robots

A double-hulled structure is a typical hazardous environment found in the shipbuilding areas. Therefore many efforts have been made for automation, especially for the welding tasks. However, constraints such as size and weight limits of the robot and the randomness of the tasks have made automation very difficult. Therefore simple and robust algorithms are preferable in this typical field. In this paper a seam tracking algorithm for weaving weld path planning using a laser displacement sensor is developed. It is designed to enable portable robots detect the seam of very irregular single butt welding profiles. The algorithm consists of four steps; Scan, Filtering, Generation of reference points, Path planning. In the scan process depth data of a cross section of the profile is obtained. Next, Gaussian filter is used to remove noise from the raw data. A differential characteristic point detection algorithm is applied to the filtered data to detect the reference points which represent the shape and location of the gap of the profile to be welded. Finally path planning for single-V butt multi-pass welding is done based on these reference points. The algorithm is validated through welding experiments.

Kinematics-based gait planning of a quadruped gecko-like model

Recent research on mobile robots is focused on locomotion in various environments. In this paper gait generation algorithm for a mobile robot that can locomote from ground to wall and climb vertical surfaces is proposed bio-inspired by a gecko lizard. The gait planning is based on the inverse-kinematics with the Jacobian of whole body, where the redundancy is solved by defining an object function to follow the real gecko posture and avoid collisions with the surface. The optimal scalar factor for these two objects is obtained by defining a superior object function that is to minimize the angular acceleration. The algorithm was verified through simulation of the gecko model locomoting given task paths avoiding abnormal joint movements and collisions.