Background: Cutaneous sclerotic disorders are histologically characterized by increased fibrosis and collagen hyalinization in the dermis and deeper soft tissue. These conditions can be a significant source of morbidity, but there is no reliable measure to quantify disease severity in both the clinical and research setting . Acoustic Radiation Force Impulse (ARFI) and Shear Wave Elasticity Imaging (SWEI) use ultrasound waves to make micron level transient deformation in soft tissue and measure the its dynamics to directly quantify material properties such as elasticity and viscosity . They are sensitive to the functional pathology of sclerosis, making them ideal for assessing fibrotic conditions . Already proven useful in evaluating fibrosis of the liver , this technology can be translated for use in cutaneous sclerosis to answer the clinical gaps in this field.
Aims: This study aims to determine the potential for employing ARFI/SWEI in the clinical evaluation of cutaneous sclerosis, testing the hypothesis that the diseased skin is stiffer than the normal skin.
Methods: Using the 14L5 transducer on the Siemens S2000 scanner with custom designed beam sequences and processing, ARF was generated at a 0.55cm focus using a F/1 7.2MHz pushing excitation and was tracked at the first harmonic frequency of 12.2MHz on and off-axis. We recruited patients with sclerotic disease and imaged them using ARFI/SWEI on lesionous and normal skin in various body sites. Along with standard B-mode, on-axis displacement (averaged over 1.7mm) and off-axis shear wave propagation (ROI size 1.7mm x 7.2mm) was measured using normalized cross-correlation on rf-data. A total of 12 patients have been imaged-to-date but only 2 patient data were analyzed for this abstract.
Results: Computed Shear Wave Speed (SWS) and mean ARFI displacement magnitude were normalized to their controls. Metrics from lesionous skin were normalized by those acquired from normal skin laterally opposite to the affected region, and those of normal skin were normalized by dividing the metrics from the left side of the body to the right side. Normalized SWS and mean ARFI displacement inside the lesionous skin and inside the normal skin for two patients are shown in Figure 1. SWS inside the lesionous skin is significantly greater than that inside the normal skin (p=0.03); mean ARFI displacement inside the lesionous skin is significantly smaller than that inside the normal skin (p=0.007).
Conclusions: As hypothesized, the SWS was greater and mean ARFI displacement smaller in lesionous skin compared to those in normal skin. Although the speed and displacement magnitude are impacted by both the material stiffness and geometry, the results show that there are significant differences in these metrics due to stiffness alone. We are continuing patient accrual and exploring ways for robust analyses.
Acknowledgements: This work has been supported by NIH grants EB002132 and Dermatology Foundation. We thank the Ultrasound Division at Siemens Medical Solutions, USA, Inc. for their technical and in-kind support. We also thank Dr. Veronica Rotemberg for her help with patient imaging.
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Figure 1. Top: comparison of normalized SWS in lesional skin to normal skin; Bottom: comparison of normalized mean ARFI displacement inside lesional skin to normal skin. In both cases, the two populations were significantly different from each other with p<0.05 using Mann-Whitney U test.