Quantifying perception of nonlinear elastic tissue models using multidimensional scaling

Simplified soft tissue models used in surgical simulations cannot perfectly reproduce all material behaviors. In particular, many tissues exhibit the Poynting effect, which results in normal forces during shearing of tissue and is only observed in nonlinear elastic material models. In order to investigate and quantify the role of the Poynting effect on material discrimination, we performed a multidimensional scaling (MDS) study. Participants were presented with several pairs of shear and normal forces generated by a haptic device during interaction with virtual soft objects. Participants were asked to rate the similarity between the forces felt. The selection of the material parameters – and thus the magnitude of the shear\ud and normal forces – was based on a pre-study prior to the MDS experiment. It was observed that for nonlinear elastic tissue models exhibiting the Poynting effect, MDS analysis indicated that both shear and normal forces affect user perception

Design of a Low-cost Tactile Robotic Sleeve for Autonomous Endoscopes and Catheters

Recent developments in medical robotics have been significant, supporting the minimally invasive operation requirements, such as smaller devices and more feedback available to surgeons. Nevertheless, the tactile feedback from a catheter or endoscopic type robotic device has been restricted mostly on the tip of the device and was not aimed to support the autonomous movement of the medical device during operation. In this work, we design a robotic sheath/sleeve with a novel and more comprehensive approach, which can function for whole-body or segment-based feedback control as well as diagnostic purposes. The robotic sleeve has several types of piezo-resistive pressure and extension sensors, which are embedded at several latitudes and depths of the silicone substrate. The sleeve takes the human skin as a biological model for its structure. It has a better tactile sensation of the inner tissues in the torturous narrow channels such as cardiovascular or endo-luminal tracts in human body thus can be used to diagnose abnormalities. In addition to this capability, using the stretch sensors distributed alongside its body, the robotic sheath/sleeve can perceive the ego-motion of the robotic backbone of the catheter and can act as a position feedback device. Because of the silicone substrate, the sleeve contributes toward safety of the medical device passively by providing a compliant interface. As an active safety measure, the robotic sheath can sense blood-clots or sudden turns inside a channel and by modifying the local trajectory, and can prevent embolisms or tissue rupture. In the future, advanced manufacturing techniques will increase the capabilities of the tactile robotic sleeve

A Stepwise Compression-Relaxation Testing Method for Tissue Characterization and Tumor Detection Via a Two-Dimensional Tactile Sensor

This dissertation presents a stepwise compression-relaxation (SCR) testing method built upon a two-dimensional (2D) tactile sensor for mechanical characterization of soft tissues and tumor detection. The core of the 2D sensor entails one whole polydimethylsiloxane (PDMS) microstructure embedded with a 3×3 sensing-plate/transducer array. A soft sample was compressed by the 2D sensor with a step incremental depth at a ramp speed, and then relaxed for certain hold time. When a soft sample was compressed by the 2D sensor, the sensing-plates translated the sample response at different tissue sites to the sensor deflections, which were registered as resistance changes by the transducer array. Instant elasticity (Einstant) and loss factor (tan δ) extracted from the measured data were used to quantify the sample elasticity and viscoelasticity, respectively. First, a three-way ANOVA analysis was conducted on the data of soft materials (PDMS/silicone rubbers) to evaluate the influence of testing parameters (incremental depth, hold time, and ramp speed) on the measured results. The results revealed that both Einstant and tan δ were significantly dependent on testing parameters. Next, the measured results on the soft tissues showed different elasticity and viscoelasticity between muscle tissues and fat/skin tissues. The measured results on the tumor tissues indicated different elasticity and viscoelasticity among the five breast tumor (BT) tissues, and between the two pancreatic tumor (PT) tissues before and after treatment. Due to the larger sample size of the BT tissues, the elasticity distribution among the measure BT tissue sites was used to determine the location, shape and size of the tumor in a BT tissue. The correlation of stress drop (Δσ) (obtained from the difference between the instant and relaxed sensor deflections at each step incremental depth) with the applied strain (ε) was used for tumor detection. Pearson correlation analysis was conducted to quantitatively analyze the measured Δσ-ε relation as slope of stress drop versus applied strain (m=Δσ/ε) and coefficient of determination (R2) as a measure of the goodness of fit of the linear regression for distinguishing tumor tissue from normal tissue. The measured results on soft materials showed that m was significantly dependent on testing parameters, but R2 showed no significant dependency on testing parameters. The measured results on the tumor tissues indicated R2 was significantly varied among the center, edge and outside sites of the BT tissues. However, no difference was found between the BT outside sites and the normal tissues. R2 also revealed significant difference between before and after treatment of the PT tissues, while no difference between the PT tissues after treatment and the normal tissues. R2 of the PT tissues before treatment was significantly different from that of the BT center sites, but m failed to capture their difference. Furthermore, dummy tumors made of silicone rubbers were found to behave differently from the native tumors. In summary, the feasibility of the SCR testing method for tissue characterization and tumor detection was experimentally validated on the measured soft samples, including PDMS, silicone rubbers, porcine and bovine normal tissues, mouse BT and PT tissues. Future work will investigate the feasibility of the SCR testing method for differentiation between benign tumors and malignant tumors

Cost-Effective Screening for Breast Cancer Worldwide: Current State and Future Directions

Affordability of healthcare is highly limited by its skyrocketing cost. Access to screening and diagnostic medical equipment and medicine in developing countries is inadequate for the majority of the population. There is a tremendous worldwide need to detect breast cancer at its earliest stage. These needs must be balanced by the ability of countries to provide breast cancer screening technology to their populations. We reviewed the diagnostic accuracy, procedure cost and cost-effectiveness of currently available technique for breast screening and diagnosis including clinical breast examination, mammography, ultrasound, magnetic resonance imaging, biopsy and a new modality for cancer diagnostics termed elasticity imaging that has emerged in the last decade. Clinical results demonstrate that elasticity imaging even in its simplest and least sophisticated versions, like tactile imaging, has significant diagnostic potential comparable and exceeding that of conventional imaging techniques. In view of many countries with limited resources, effective yet less expensive modes of screening must be considered worldwide. The tactile imaging is one method that has the potential to provide cost-effective breast cancer screening and diagnostics

Tooth Mobility Measurement of Dental Implants

The use of dental implants has increased together with increases in the human life span and it has become an imperative subject for dentists to familiarize themselves with this treatment modality. Unfortunately, there has been no practical and quantitative method for in vivo evaluation of the stability of dental implants. In the tooth mobility examination, the tactile sense of natural teeth is different from that of dental implants. The authors have developed an automatic diagnosis system of tooth mobility for clinical use. The biomechanical mobility of peri-implantium is measured with a pseudo-random vibration, from which the viscoelasticity c1, c2, k of peri-implantium is obtained. The diagnosis system has been applied to the quantitative evaluation of the stability of implants : endodontics endosseous implants (titanium pin), endosseous implants (Bioceram). It has also been applied to the evaluation of the long-term prognoses of dental implantation (Bioceram) and the examination of Intramobile implant (IMZ), and the satisfactory results have been obtained

Palpation force modulation strategies to identify hard regions in soft tissue organs

This work was supported by EPSRC MOTION grant (grant number EP/N03211X/1), National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy’s and St Thomas’ NHS Foundation Trust and King’s College London and Vattikuti Foundation

Understanding the Mechanical Behavior of Costal Cartilage at Their Curved Exterior Surface Via a Tactile Sensor with a Built-In Probe for Distributed-Deflection Detection

This dissertation is aimed to determine the mechanical properties at the exterior surface of costal cartilages (CC) and examine how they vary with the cartilage length and the anatomical sites of CC in the ribcage via conformal indentation testing which is built upon a tactile sensor for distributed-deflection detection. The sensor entails a rectangular Polydimethylsiloxane (PDMS) microstructure sensing-plate integrated with a 5 ×1 transducer array with 0.75mm spatial resolution underneath and a built-in probe of 0.5mm×5mm×3mm above. By pressing the sensor against the exterior surface of a CC tissue with a pre-defined indentation pattern, the sensor conforms to the curved tissue surface via the built-in probe first, and then the mechanical properties of the tissue translate to the spatially distributed deflection in the sensor and register as resistance changes by the transducer array. As a load-bearing and non-stop deforming tissue from respiration, the mechanical properties of CC are critical for maintaining their structural health and delivering their function. CC have been used as a viable source of graft tissue for many autologous therapies and as a cell source for engineered articular cartilage (AC) due to its abundance and surgical accessibility. However, the mechanical properties of CC are not well understood yet. Chest wall deformities, such as Pectus Carinatum (PC), are known to arise from the disorder of CC, but their pathogenesis remains unknown and their surgical outcomes are unpredictable. The mechanical properties of the CC exterior surface influence diffusion of oxygen and nutrients and thus are intrinsic to maintaining their structural characteristics. However, very limited knowledge exists on the mechanical properties of peripheral CC due to their highly irregular geometries. In this dissertation, a novel testing method, conformal indentation, was used to measure the mechanical properties at the CC curved exterior surface, where the structural integrity of CC is retained. Conformal indentation was conducted at the anterior/posterior surfaces of whole porcine 5th -12th CC segments and the anterior/posterior surfaces and the superior/inferior borders of five human PC CC segments from the 7th ~10th ribs along the cartilage length to record their time-dependent response to a multi-step indentation-relaxation testing protocol. The instant indentation modulus and normalized relaxation of the CC segments were derived from the recorded data to quantify their elasticity and viscosity, respectively. The instant indentation modulus at the porcine CC and PC CC exterior surface are in the range of 130kPa ~500kPa and 98kPa~1173kPa, respectively, which are well below their counterpart at the CC transverse cross-sections. The normalized relaxation at the CC exterior surface is relatively high with low applied stress but becomes constant with high applied stress. The constant normalized relaxation at the porcine and PC CC exterior surfaces are in the range of 25%~40% and 5%~25%, respectively. The human CC have higher elasticity and lower viscosity than the porcine CC. Overall, the measured mechanical properties of CC vary with their anatomical sites and thus indicate the adaptation of CC to their local biomechanical environment in the ribcage