“An ultrasound surface wave elastography technique for noninvasive measurement of scar tissue”

Boran Zhou – zhou.boran@mayo.edu
Xiaoming Zhang – zhang.xiaoming@mayo.edu
Department of Radiology, Mayo Clinic,
Rochester, MN 55905 

Saranya P. Wyles – Wyles.Saranya@mayo.edu
Alexander Meves – Meves.Alexander@mayo.edu
Department of Dermatology, Mayo Clinic,
Rochester, MN 55905 

Steven Moran – Moran.Steven@mayo.edu
Department of Plastic Surgery, Mayo Clinic,
Rochester, MN 55905

Popular version of paper 1pBA11
Presented Monday afternoon, May 13, 2019
177th ASA Meeting, Louisville, KY

Hypertrophic scars and keloids are characterized by excessive fibrosis and can be functionally problematic. Indeed, hypertrophic scarring is characterized by wide, raised scars that remain within the original borders of injury and have a rapid growth phase. We have developed an ultrasound elastography technique to assess the skin elasticity for patients with scleroderma (1). Currently, no clinical technique is available to noninvasively quantify and assess the progression and development of scar restoration. There is a need for quantitative scar measurement modalities to effectively evaluate and monitor treatments.

We aim to assess the role of ultrasound surface wave elastography (USWE) in accurately evaluating scar metrics. 3 Patients were enrolled in this research based on their clinical diagnoses. For the patients with scar on the forearm, they were tested in a sitting position with their left or right forearm or upper arm placed horizontally on a pillow in a relaxed state. The indenter of the handheld shaker was placed on the tissue at control and scar sites. A 0.1-s harmonic vibration was generated by the indenter on the tissue (2). The vibration was generated at 3 frequencies: 100, 150 and 200 Hz. An ultrasound system with an ultrasound probe with a central frequency of 6.4 MHz was positioned about 5 mm away from the indenter and used for detecting the surface wave motion of the tissue (3).

The wave motions on the 8 selected locations on the tissue surface were noninvasively measured using our ultrasound-based method (Fig. 1a)(4). The phase change with distance of the harmonic wave propagation on the tissue surface was used to measure the surface wave speed.
The measurement of wave speed can be improved by using multiple phase change measurements over distances (5). The regression of the phase change with distance can be obtained by “best fitting” a linear relationship between them (Fig. 1b). Using the tissue motion at the first location as a reference, the wave phase delay of the tissue motions at the remaining locations, relative to the first location, was used to measure surface wave speed (6).

Wave speeds of forearm or upper arm control and scar sites of the 3 patients at 100, 150, and 200 Hz before and after treatment were compared in Figure 2. The p values for the t-tests of the differences between before and after treatment were less than 0.05 for scar sites at 3 frequencies. The higher wave speed indicates the stiffer tissue. The obtained results suggest that scar portion was softener after treatment. USWE provides an objective assessment of the reaction of the scar to injury and treatment response.

Figure 1. (a) Representative B-mode image of skin, (b) Blue circles represent the selected dots for wave speed measurement.

Figure 2. Comparison of wave speeds at 3 frequencies between forearm control and scar sites.

References

1. Zhang X, Zhou B, Kalra S, Bartholmai B, Greenleaf J, Osborn T. An Ultrasound Surface Wave Technique for Assessing Skin and Lung Diseases. Ultrasound in Medicine & Biology. 2018;44(2):321-31.
2. Zhang X, Osborn T, Zhou B, et al. Lung ultrasound surface wave elastography: a pilot clinical study. IEEE transactions on ultrasonics, ferroelectrics, and frequency control. 2017;64(9):1298-304.
3. Clay R, Bartholmai BJ, Zhou B, et al. Assessment of Interstitial Lung Disease Using Lung Ultrasound Surface Wave Elastography: A Novel Technique With Clinicoradiologic Correlates. J Thorac Imaging. 2018.
4. Zhang X, Zhou B, Miranda AF, Trost LW. A Novel Noninvasive Ultrasound Vibro-elastography Technique for Assessing Patients With Erectile Dysfunction and Peyronie Disease. Urology. 2018;116:99-105.
5. Zhou B, Zhang X. The effect of pleural fluid layers on lung surface wave speed measurement: Experimental and numerical studies on a sponge lung phantom. Journal of the Mechanical Behavior of Biomedical Materials. 2019;89:13-8.
6. Zhang X, Zhou B, Osborn T, Bartholmai B, Kalra S. Lung ultrasound surface wave elastography for assessing interstitial lung disease. IEEE Transactions on Biomedical Engineering. 2018:1-.

Share This