Characterization of tissue in the pulley system using high-frequency ultrasonic basckscatter signals

Trigger finger is a common disease that is usually diagnosed by palpating the A1 pulley region of the hand. The accuracy of palpation examination certainly is largely depending on physician's clinical experience. Recently, ultrasound images have been explored in an attempt to provide an objective means for assessing trigger finger. However, with an average thickness of around 0.5 mm, the resolution of ultrasound scanners commonly applied in clinics is inadequate to sensitively discern the complexity of tissues in the pulley. To jump over this hurdle, high-frequency ultrasound images incorporated with ultrasonic parameters were implemented to further characterize the A1 pulley and surrounding tissues in the hand. In vitro experiments were performed to respectively measure the subcutaneous fat, A1 pulleys, and superficial flexor tendons (FDS) of the A1 pulley region from 8 cadavers. The excised tissues were immersed in a saline tank and were measured by a 31 MHz high-frequency ultrasound system. In addition to acquiring B-mode images, ultrasonic parameters, including integrated backscatter (IB) and Nakagami parameter (m), were subsequently calculated from backscattering signals of the corresponding regions. High-frequency ultrasound images have shown to provide a sufficient resolution able to differentiate variation among each tissue structure. The IB of subcutaneous fat, A1 pulleys, FDS was respectively measured to be −95.48±1.25 dB, −92.82±0.86 dB, and −92.40±0.95 dB; while the corresponding m was 0.75±0.07, 0.71±0.07, and 0.38±0.14. Specifically, the IB of the A1 pulley was much larger than that of the subcutaneous fat (p<0.01). A significant difference of m between the A1 pulley and FDS (p<0.01) also can be found. This study has demonstrated that high-frequency ultrasound image in conjunction with ultrasonic parameters are able to characterize the A1 pulley and surrounding tissues for further diagnosis on the syndrome of trigger finger.