|ECR 2015 / C-1005|
|Sonoelastography on diabetic heel pads: a feasibility study|
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Aims and objectives
The aim of this study is to investigate whether it is possible to differentiate between diabetic and healthy heel pads by means of real-time sonoelastography (ElaXto). To date, sonoelastography has not been not used for clinical investigations of the heel pad elasticity. Eight diabetic (4M-4F, 55-80 years) and 8 healthy subjects (5F-3M, 60-76 years) underwent B-Mode ultrasound (for heel pad thickness measurement) and sonoelastography (for soft tissue investigation) on both heel pads. Findings showed that there was no statistically significant difference in UHPT between diabetics and healthy subjects (P-value=0.70). However, diabetics tended to have lower UHPT than healthy subjects. Moreover, no statistically significant difference was found between the two groups in the soft layer (P-value=0.76), but diabetics tended to have higher soft tissue than healthy subjects.
The interest in quantifying the mechanical properties of human soft tissues is an important aspect in diagnosing diseased tissues. Knowledge of the mechanical properties of heel pad tissue could be used in tools for screening patients for the purpose of preventing further complications in the foot (e.g. ulcerations in diabetics ) as well as of obtaining validated examination methods for medico-legal purposes (e.g. falanga torture ).
Sonoelastography is a non-invasive method to support the physician in assessing tissue elasticity. This technology provides additional information to standard B-Mode, a better definition of the lesion area, and it is suitable for diagnosis and follow-up. Moreover, it gives information on tissue elasticity by associating different chromatic patterns. Real-time Esaote (Esaote S.p.A., IT) sonoelastography (ElaXto) is based on the concept of elastic strain: an object, subject to stress, distorts proportionally to the intensity of the applied stress and depending on the material. It is known that tissue elasticity, in different districts, is correlated to pathologies . Palpation, which is routinely used in clinical exams, is based on this assumption. In order to perform the sonoelastographic exam, the user has to apply a perpendicular pressure through rhythmic movements on the tissue under exam. Thanks to the pressure given by that action, it is possible to evaluate the modification of the echo signal and thus to compute how the different tissues distort (if they are soft) or move (if they are hard) compared to the probe position. The result of this calculation, computed in real-time, is shown by a color image overlapped to the B-Mode image. The deformability degree is given by a chromatic scale . ElaXto is a qualitative analysis where the estimation of strain information is computed in relation to the surrounding tissue. The computed strain information is dependent on the tissue of the Region of Interest (ROI) . To date, sonoelastography has not been applied on in vivo heel pad for tissue elasticity investigations. The human heel pad is a portion of the plantar foot tissue located between the heel skin and the tuberosity of the calcaneus bone. Anatomically it consists of a very complex structure made of neuronal, vascular, fibrous and elastic components which are intertwined with fat cells . It acts as an efficient shock absorber, smoothing the effects of impact forces during gait. The heel pad exhibits non-linear visco-elastic behavior as characteristic of soft biological tissues. Due to the visco-elastic nature, when a loading/unloading cycle is applied, a load-deformation curve is obtained showing a hysteretic behavior.
In some pathological conditions (e.g. diabetic foot) the damage of the intricate septation may imply the loss of its shock absorbing, causing great pain for the subject, when trying to stand and walk. Specifically, collagen septa in diabetic heel fat pads are found to be thicker and adipose cells smaller than in normal heel fat pads [3, 4]. It is also known that diabetes is associated with an increase of fragmentation . These changes indicate that diabetes may affect the microscopic and macroscopic composition of the plantar soft tissues, making them more vulnerable to mechanical stresses which would lead to ulcerations . Indeed, the diabetic fat pad is reported to be less elastic and less able to distribute pressure, leading to an impaired cushioning effect .
The aim of this study is to investigate whether it is possible to differentiate between diabetic and healthy heel pads in terms of elasticity by means of ElaXto.
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