From Dogbones to Organs: Applying Digital Image Correlation in the Context of Minimally Invasive Surgery
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Although minimally invasive surgery (MIS) reduces post-surgery recovery time, it drastically reduces haptic feedback to the surgeon, leading to increased risk in tissue damage and higher training requirements[1]. To date the only solution commercially available is a force measurement system provided by the instruments in the DaVinci robot (Intuitive Surgical Operations Inc, Sunnyville, California)[2]. We aim to provide a full-field solution by calculating a strain map of the tissues and overlap it on the surgical footage to provide information on underlying structural morphology. Calculation of the strain maps was achieved using a stereo-DIC setup, utilising NCorr[3] as the DIC solver and an in-house post-processing code to translate the 2D results into 3D strain by the principles of simple stereo and virtual strain gauges[4]. Ex-Vivo tests were conducted using a stereoscopic surgical camera provided by CMR Surgical (Cambridge, UK). Silicon phantoms were made with a Young’s modulus of 14kPa to match material properties of the liver[5] and featured an embedded nodule mimicking a lesion. Phantom geometry included dogbones alongside samples featuring a curved surface geometry to evaluate factors such as sample thickness, nodule depth, and nodule stiffness on the strain map. Strain was applied in a tensile testing machine at a rate of 2%/s up to 35% strain to keep below liver rupture strain[5]. Finally, a liver phantom created from a patient CT scan[6], scaled to 50% of original geometry was tested in a laparoscopic trainer. We found that a lesion could be detected in the strain map when embedded down to 80% of its diameter independent of sample thickness. The main factor affecting the detection was the image quality. With limitations including geometry and image quality, the method demonstrates promising results that strain maps of tissue surfaces can be used to assess tissue morphology and detect abnormalities during surgery.
