Salient Features of Soft Tissue Examination Velocity during Manual Palpation Jelizaveta Konstantinova1, Kaspar Althoefer1, Prokar Dasgupta2, Thrishantha Nanayakkara1 1Centre for Robotics Research (CoRe), Dept. of Informatics, King’s College London 2MRC Centre for Transplantation, DTIMB and NIHR BRC, King’s College London

Outline Motivation Studies of Manual Palpation Experimental setup Results Finite Element Simulations Conclusions and Next Steps

Motivation To detect tissue abnormalities and provide haptic feedback during robot-assisted minimally invasive surgery (RMIS) in real time; Artificial probing or palpation should be introduced Liu et al., 2010 Zbyszewski et al.,2011

Motivation But: Non-linear and non-homogeneous environment leads to high variability of tactile information; The influence of probing behaviour on abnormality detection should be studied Palpation velocity could be one of the parameters, defining the effectiveness of results during tactile examination

Manual Palpation Studies To study the effect of velocity during manual palpation Ten participants with at least five years of surgical experience Silicone Phantom or Porcine Kidney sample with embedded hard nodules Unidirectional movement Three types of velocity: slow, natural and fast

Experimental Setup To understand the impact of velocity during manual palpation of soft tissue Computer to record and synchronise data Force and torque sensor to record applied pressure Microsoft Kinect camera to track position of the hand – 1 - 2 mm accuracy for an average palpation velocity Subject performs unidirectional palpation

Experiments on Manual Palpation

Results of manual palpation studies Factors, which might influence the detection rate of hard nodules: - Applied force - Applied velocity - Palpation material

Results of manual palpation studies Factors, which might influence the detection rate of hard nodules: - Applied force - Applied velocity - Palpation material (p<0.0001) Porcine kidney or silicone organ Palpation behaviour should be studied in conjunction with the given viscoelastic properties of environment

Results of manual palpation studies Silicone phantom: - Applied velocity (p<0.0001) 256 – 300 mm/s 69 % detection rate Velocity, mm/s 300 200 100 144 – 220 mm/s 82 % detection rate 85 – 123 mm/s 87 % detection rate Slow Natural Fast Clusters of velocity magnitude across all experiments

Finite Element Simulations To understand stress sensed by human finger Slow velocity Stress, Pa 5 mm deep 3 mm deep Distance, mm Slow: 100 mm/s Hyperelastic Arruda-Boyce model Hard nodules (r = 5mm): 3 and 5 mm deep Velocity according to experiments Natural: 180 mm/s Fast: 280 mm/s

Conclusions and Next Steps The impact of palpation velocity on the detection rate has been demonstrated The detection rate of hard formations can be improved by using corresponding velocity startegy What is the optimal tactile examination strategy to detect tumours in soft tissue?

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