Quantifying mechanical and morphological properties of plantar foot soft tissues: a systematic review of techniques, methods and their clinimetric properties

Optical/acoustic radiation imaging (OARI) is a novel imaging modality being developed to interrogate the optical and mechanical properties of soft tissues. OARI uses acoustic radiation force to generate displacement in soft tissue. Optical images before and after the application of the force are used to generate displacement maps that provide information about the mechanical properties of the tissue under interrogation. Since the images are optical images, they also represent the optical properties of the tissue as well. In this paper, the authors present the first imaging probe that uses acoustic radiation force in conjunction with optical coherence tomography (OCT) to provide information about the optical and mechanical properties of tissues to assist in the diagnosis and staging of epithelial cancers, and in particular bladder cancer. The OARI prototype probe consisted of an OCT probe encased in a plastic sheath, a miniaturized transducer glued to a plastic holder, both of which were encased in a 10 cm stainless steel tube with an inner diameter of 10 mm. The transducer delivered an acoustic intensity of 18 W/cm(2) and the OCT probe had a spatial resolution of approximately 10-20 μm. The tube was filled with deionized water for acoustic coupling and covered by a low density polyethylene cap. The OARI probe was characterized and tested on bladder wall phantoms. The phantoms possessed Young's moduli ranging from 10.2 to 12 kPa, mass density of 1.05 g/cm(3), acoustic attenuation coefficient of 0.66 dB/cm MHz, speed of sound of 1591 m/s, and optical scattering coefficient of 1.80 mm(-1). Finite element model (FEM) theoretical simulations were performed to assess the performance of the OARI probe. The authors obtained displacements of 9.4, 8.7, and 3.4 μm for the 3%, 4%, and 5% bladder wall phantoms, respectively. This shows that the probe is capable of generating optical images, and also has the ability to generate and track displacements in tissue. This will provide information about the optical and mechanical properties of the tissue to assist in epithelial cancer detection. The corresponding theoretical FEM displacement was 5.8, 5.4, and 5.0 μm for the 3%, 4%, and 5% phantoms, respectively. Deviation between OARI displacement and FEM displacement is due to the resolution of the crosscorrelation algorithm used to track the displacement. To the authors' knowledge, this is the first probe that successfully combines OCT with a source of acoustic radiation force. The OARI probe has the ability to provide information about the mechanical and optical properties of phantoms and soft tissue. This could prove useful in early epithelial cancer detection. Because the probe is 10 mm in diameter, it is currently only useful for skin and oral applications. The probe would have to be reduced in size to make it applicable for cancer detection in other internal sites. Future work will focus on utilizing phase-sensitive optical coherence elastography to obtain the resulting OARI displacements, improving the resolution of the probe, and enable physicians to better evaluate the mechanical properties of soft tissues.

Background Foot abnormality has become a public health concern. Early detection of pathological soft tissue is hence an important preventive measure, especially to the elderly who generally have a higher risk of foot pathology (i.e. ulceration) [1]. Accumulated changes over time diminish the mechanical properties of plantar soft tissue, causing easy breakdown of tissue and instability of foot during walking. Non invasive in-vivo assessment on plantar soft tissue mechanical responses is hence needed. This is to identify abnormal soft tissue such that early precaution measures can be taken to avoid foot pathology that requires long healing period. The purpose of this study is to assess ageing effect on plantar tissue using an improved version of instrumented in vivo tissue tester [2]. It also aims to provide a useful parameter to identify tissue with high ulceration risk. This is done by varying metatarsophalangeal (MTP) joint configurations and imposing large tissue deformation to the soft tissue.

The mechanical properties of soft tissues play a key role in studying human injuries and their mitigation strategies. While such properties are indispensable for computational modelling of biological systems, they serve as important references in loading and failure experiments, and also for the development of tissue simulants. To date, experimental studies have measured the mechanical properties of peripheral tissues (e.g. skin) in-vivo and limited internal tissues ex-vivo in cadavers (e.g. brain and the heart). The lack of knowledge on a majority of human tissues inhibit their study for applications ranging from surgical planning, ballistic testing, implantable medical device development, and the assessment of traumatic injuries. The purpose of this work is to overcome such challenges through an extensive review of the literature reporting the mechanical properties of whole-body soft tissues from head to toe. Specifically, the available linear mechanical properties of all human tissues were compiled. Non-linear biomechanical models were also introduced, and the soft human tissues characterized using such models were summarized. The literature gaps identified from this work will help future biomechanical studies on soft human tissue characterization and the development of accurate medical models for the study and mitigation of injuries.

Guided wave elastography of layered soft tissues

Digital image correlation and finite element modelling as a method to determine mechanical properties of human soft tissue in vivo

One of the long-term complications of diabetes is peripheral neuropathy, where insensitive nerves can lead to serious foot ulceration. Studies have shown that the mechanical properties of plantar soft tissues change with diabetes. Ultrasound methods could be used to measure plantar tissue thickness and mechanical properties, as a quantitative assessment tool. Diabetic shoes or orthoses are often custom-designed for each person to prevent foot injury during daily activities. This study developed an ultrasonic method and sensors that can be use between the foot and a custom insole to continuously monitor the mechanical properties of plantar soft tissue during physical activities. In the proposed sensor design, the protection layer on the sensing side (bottom electrode) was eliminated and the top side was electrically shielded to reduce environmental noises. A developed wearable ultrasonic sensor was used in a preliminary experiment to measure plantar tissue thickness. Plantar heel tissue thickness was successfully measured, decreasing from 16.2 mm to 10.1 mm with pressure changes from 0 to 190 kPa. Stress-strain pressure application and release curves and the heel tissue hysteresis parameter were also successfully calculated.

The shear mechanical properties of diabetic and non-diabetic plantar soft tissue

Integration of plantar soft tissue stiffness measurements in routine MRI of the diabetic foot

Micromechanical poroelastic and viscoelastic properties of ex-vivo soft tissues

Biomechanical properties of the forefoot plantar soft tissue as measured by an optical coherence tomography-based air-jet indentation system and tissue ultrasound palpation system

The most frequent clinical complication is diabetes. Diabetes is characterized by elevated blood glucose levels resulting in sensory nerve damage or lesions. Diabetic foot wounds are often slow to heal and require medical attention and monitoring. This study evaluates the effect of far-infrared radiation on the microcirculation and plantar pressure in the diabetic foot. Ten diabetics and 4 nondiabetics were recruited in this study. The diabetic group was examined before and after the intervention in each month for 3 consecutive months. Four nondiabetic groups were also measured before and after the intervention for 2 weeks in each month. The surface temperature and blood flow in the diabetic foot was significantly improved (temperature: 32.1 ± 2.3°C vs 33.5 ± 2.2°C, P < .05; blood flow image: 118.3 ± 58.1 PU [perfusion unit] vs 50.4 ± 4.3 PU, P < .05). The sympathetic nerve activity index LF also increased from 40.8 ± 18.6% to 61.8 ± 13.5% (P = .07) in the second month. Plantar pressure tended to increase in the third month. This might indicate that far-infrared radiation could affect the mechanical properties of the plantar foot soft tissue. These results indicated that the effects of far-infrared radiation would improve blood circulation and change the soft tissue properties in the diabetic foot.

This article provides an overview of the development history and advantages and disadvantages of measurement methods for soft tissue properties of the plantar foot. The measurement of soft tissue properties is essential for understanding the biomechanical characteristics and function of the foot, as well as for designing and evaluating orthotic devices and footwear. Various methods have been developed to measure the properties of plantar soft tissues, including ultrasound imaging, indentation testing, magnetic resonance elastography, and shear wave elastography. Each method has its own strengths and limitations, and choosing the most appropriate method depends on the specific research or clinical objectives. This review aims to assist researchers and clinicians in selecting the most suitable measurement method for their specific needs.

An understanding of the mechanical properties of skin and other soft tissues is valuable for many applications, for example in planning surgical procedures or in designing equipment that must interface with the body such as orthopaedic implants, seating or razors. Similarly, the ability to characterise the properties of soft tissues is valuable in many areas of medicine and biology, for example in evaluating the effects of drug treatments or the progression of a disease. However, the properties of soft tissues, and particularly those of skin, are complex and not amenable to conventional engineering analysis. The properties are highly dependent on the environment and should ideally be measured in situ in a living subject. Because of these two problems, conventional test methods are rarely appropriate or adequate in testing soft tissues, and new techniques are required.

Development of a foot scanner for assessing the mechanical properties of plantar soft tissues under different bodyweight loading in standing

Shear wave elastography is a new noninvasive tool for the analysis of the biomechanical properties of the muscles in healthy and pathological conditions. Shear wave elastography is currently considered as a promising real-time visualization tool for quantifying explicitly the mechanical properties of soft tissues in sports medicine including muscle strain injury (MSI). This chapter shows utilizing diagnostic tools of magnetic resonance imaging, B mode ultrasound (US), and shear wave elastography in both acute and chronic phases. Also, the proposal for this chapter is to indicate the possibility of utilizing shear wave elastography for musculoskeletal injury, not only properties of the muscle but also fascial tissues. It introduces the relationship between previous muscle strain injury and local soft tissue stiffness, and we assessed the mechanical properties of soft tissues from a clinical perspective.