Development of noncontacting mechanical measurement system for instruments in laparo-endoscopic single-site surgery with digital image correlation technology

XU An-an，ZHU Jiang-fan，SU Jin，ZHANG Dong-sheng，WANG Qiang

1.Department of General Surgery，East Hospital of Tongji University，Shanghai，200120，China;

2.Department of Mechanics Shanghai University，Shanghai200444，China

Development of noncontacting mechanical measurement system for instruments in laparo-endoscopic single-site surgery with digital image correlation technology

XU An-an1，ZHU Jiang-fan1，SU Jin1，ZHANG Dong-sheng2，WANG Qiang2

1.Department of General Surgery，East Hospital of Tongji University，Shanghai，200120，China;

2.Department of Mechanics Shanghai University，Shanghai200444，China

ObjectiveAnalysis of mechanical measurements in laparo-endoscopic single-site surgery(LESS)is an important instrument design and surgical simulator.Aims of this study was to set up and evaluate the reliability and stability of noncontacting mechanical measurement system for instrument of LESS in company with digital image correlation technology.MethodsThe noncontacting mechanical measurement system was connected to a digital image correlation devices and a LESS manipulation platform(set up with a SILS Port and an inanimate laparoscopic trainer box).The correlation between the changes of deformation measurements(displacement and strain calculated by digital image correlation technology)and the change of workload(workout by the universal material testing machine)were evaluated.The experiment was repeated 8 times.ResultsA strong correlation was noticed between the changes of deformation measurements and the change of workload.The correlation coefficient was statistical significant(P ＜0.001).A high stability was well shown in all repetitions.Conclusions A noncontacting mechanical measurement system has been developed for LESS.Comprehensive mechanical parameters of SILS port can be obtained precisely by the digital image correlation technology.It is reliable and stable for the evaluation of instruments and manipulations in laparo-endoscopic single-site surgery by this system.

Laparo-endoscopic single-site surgery;Noncontacting measurement system;Digital image correlation technology

Since the introduction oflaparo-endoscopic single-sitesurgery(LESS)in 2007，it has rapidly gained popularity with surgeonsaswellasthe industry.Almost all traditional laparoscopic surgeries can be performed by the LESS approach，including surgeries for morbid obesity，liver，spleen，and gastrointestinal diseases［1］.However，the procedure is more difficult than traditional laparoscopic surgeries due to associated technicalchallenges including laparoscope and instruments crowding around the umbilicus，lossoftriangulation between the two instruments in the operative field and the required ambidexterity ofthe surgeons to adopt relatively difficult maneuvers［2］.To overcome these problems in LESS，new instruments and manipulations have been developed［3－4］.Although these instrumentations may seem beneficial，they leave one vital question:Do these concepts really benefit laparo-endoscopic singlesite surgery?The aim of our study was to try to set up and evaluate the reliability and stability ofthe noncontacting mechanical evaluation system based on digital image correlation technology for an objective assessment of instrumentations in laparo-endoscopic single-site surgery.

Materials and Methods

The noncontacting mechanical measurement system was composed ofthe LESS manipulation platform，a charge-coupled device camera(type:JAI CV-A1)，and a straight grasper(YIDA Medical DeviceCo.，Ltd.，Hangzhou，Zhejiangprovince，China).The LESS manipulation platform was set up by a box trainer(Model 200，RUIHONG laboratory equipment Co.，Ltd.，Shanghai，China)and a SILS PortTM(Covidien， Mansfield， MA， USA). A microcomputer-controlled electronic universal testing machine was used to measure the forces trailing the grasper(BZ2.5/TSIS，ZWICK Co.，Ltd.，German.)

MechanicalTest by the Universal Material Testing Machine

The grasper，which was inserted in the SILS Port，was connected with the universal testing machine by a fishing wire，and was trailed 50mm with a constant speed of 0.33 mm/s.The traction forces per second were obtained and saved by the attached software.

Noncontacting Mechanical Test based on Digital Image Correlation Technology.

The noncontacting mechanical test contained the following steps:

1.Formation of speckle on the SILS port(Fig.1).

2.Selection of dominant-points(the right point and the left point，Fig.2).

3.The grasper was trailed by the universal testing machine(the forces exerted followed the displacement control algorithm).Meanwhile，the transformation of the port was captured by the CCD camera.

Fig.1 Mechanical test by theuniversal testing machine and the digital image correlation(A:Universal material testing machine，B:grasper，C:box trainer，D:fishing wire，E:SILS port，F:fiber optic lights，G:camera)圖1 萬能材料試驗機水平牽引實驗與數字圖像相關技術測試實驗(A:萬能材料試驗機，B:抓鉗C訓練箱 D 牽引線，E:SILS port，F:光源，G:攝像機)

Fig.2 Formation of speckle and selection of dominant-points in the SILS port圖2 散斑制作和紅點選取

As the grasperwas trailed by the universal testing machine，transformation of the SILS Port’s surface was captured by the CCD camera with the frequency of 1 Hz.Then，the commercialsoftware (the MATFOLT CO Ltd，Shanghai)was used to store a series of images acquired by the camera in digital form and perform image analysis to extract full-field shape and deformation measurements(vertical and horizontaldisplacement and strain data).This experiment was repeated for 8 times.

Statistical analysis

Although different vertical and horizontal displacements were obtained for the left and right dominant-points，the changing trends were the same as the dominant-points in the SILS port.Due to this，statistical analyses were conducted only for the left dominant-point.As allthe measurements were continuous variables，The Pearson correlation analysis was conducted to investigate the relationship between the changes of deformation measurements(displacement and strain calculated by digital image correlation technology)and the change of workload(workout by the universal material testing machine).

All statistical analyses were conducted by using SPSS statistical software(version 15.0;SPSS，Inc.，Chicago，IL，USA).Statistical significance was set，and p-value was defined as＜0.05.

Results

Table1 shows the results of the experiments which were repeated for8 times.The Pearson correlation coefficients between the changes of deformation measurements(displacement and strain)and the change of workload were very high(│r│ ＞0.8，P ＜ 0.01).Extremely similar stability results appeared in all repetitions of the procedure as shown in table 1.Due to the high similarity of the results，we chose one of the repetitions(the fifth one)to visualize it in scatterdiagrams as seen in Fig.3 －5.

Table.1 The Pearson correlation analysis(correlation coefficient:r)between the changes of displacement andstrain and the change of workload in all repetitions of the experiment表1 8次重復實驗載荷與應變及位移的Pearson相關分析

Fig.3 Scatterdiagram of the fifth experiment showing the linear correlation between load and strain圖3 載荷與應變的散點圖

Fig.4 Scatterdiagram of the fifth experiment showing the linear correlation between load and horizontal displacement(Hdisplacement)圖4 載荷與水平位移的散點圖

Fig.5 Scatterdiagram of the fifth experiment showing the linear correlation between load and vertical displacement(Vdisplacement)圖5 載荷與垂直位移的散點圖

Discussion

As with most new surgical techniques，the early development oflaparo-endoscopic single-site surgery(LESS)was fraught withproblems:alossof triangulation，clashing of instruments and the instruments with the telescope and camera head，and a lack of maneuverability.New instruments and manipulations were developed by the pioneers to enable surgeons to overcome these difficulties.However，whether these improvements benefit LESS was lacking of objective evaluation.There have been several researches attempted to assess the benefit［5－6］，as the measurements were subjective indexes included the operation success rates，errors，and so on，lacking of definite and objective assessment criteria.We set up a contacting mechanical evaluation platform to compare the articulating instruments and the crosshanded manipulation with conventional instruments.Study indicates that more force and time are needed by using cross-handed manipulation in LESS［7］.However，contacting mechanicalcomponentslike sensor or gauge used in aforementioned researches were vulnerable to external environmental interference during measurement.Therefore，as a whole they can’t reflect more comprehensive Mechanics changes.

Digital image correlation(DIC)，an advanced noncontacting measurement system，has seen explosive growth in the past two decades.In recent years，the method has been modified and extended to encompass a breathtaking number of novel measurement systems.The term digital image correlation refers to the class of noncontacting methods that acquire images of an object，store images in digital form，and perform image analysis to extract full-field shape and deformation measurements.Within the broad field of image analysis，digital image correlation is generally considered a sub-set of digital image registration techniques.The technique can be used to measure and observe the local mechanical behavior(displacement and strain)in natural and semi-natural texture of different materials like metals，ceramics and polymers［8－9］.In biomechanics，DIC are widely used in evaluation for dental restorations and prosthesis，bone repair materials［8－9］.

In this study，basing on the DIC technology，we aimed to set up a reliable noncontacting mechanical measurement system to evaluate instruments in LESS.According to the repeated experimental results of currentstudy，two importantconclusionscan be drawn. First， the noncontacting mechanical measurement system based on DIC technology system is proven to be reliable，as the measurement results almost show a perfect linear correlation with the objective criteria (the universalmaterialtesting machine).Second，an extreme similarity of the results appeared in all repetitions of the experiment demonstrating the high stability of the measurement system.

Due to the high reliability and stability，there are several applications for the newly developed noncontacting mechanical measurement system.The objective and comprehensive measurements will provide a good feedback tool for evaluation of new instruments and manipulations in LESS.In addition，the system’s use in experimental practice would help to refine movement and tissue handling in LESS teaching and training purposes.Moreover，it can also be used to define force patterns incurred during certain surgical postures and the effect of muscle fatigue.The combination of force pattern and parameters of mental workload can be used to indicate the levelof psychological stress during surgical procedures.

With the reliable and stablenoncontacting mechanicalmeasurementsystem，LESS willbe spurred on by rapid advances in technology and better instrumentation.

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經臍入路腹腔鏡手術操作非接觸式力學評估平臺的建立*

徐安安1，朱江帆1，蘇 金1，張東升2，王 強21同濟大學附屬東方醫院微創外科，上海 200120;2上海大學力學系，上海 200444

目的 本研究旨在建立基于數字圖像相關技術的非接觸式力學測試評估平臺，明確其在經臍入路腹腔鏡手術操作評估中的可靠性。方法 用腹腔鏡模擬訓練箱和SILS Port組建經臍入路腹腔鏡手術操作平臺。分析基于數字圖像相關技術評估平臺得到的位移與應變分量改變與客觀標準——萬能材料試驗機水平牽引載荷改變的相關性。結果 本實驗中8次重復實驗的研究結果均顯示，由數字圖像相關技術得到的位移與應變分量改變與萬能材料試驗機牽引實驗載荷改變呈強相關，且相關系數有統計學意義(P＜0.001)。結論 基于三維數字圖像相關技術的非接觸式力學測試方法反映了器械進行操作時SILS port發生的綜合性力學參數改變，方法可靠，適用于經臍入路腹腔鏡手術器械與操作方法評估。

經臍入路腹腔鏡手術;力學評估平臺;數字圖像相關技術

R 656

A

2095-378x(2013)02-0090-04

浦東新區重點發展學科項目資助(PWZxk2010－07)

徐安安(1982－)，男，主治醫師，碩士研究生，主要從事普外科常見疾病的微創治療研究。

作者簡介:朱江帆(1955－)，男，河北人，教授博士生導師，研究腹腔鏡外科的臨床與實驗研究。E-mail:zhujiangfan@hotmail.com