UC Irvine

Quantitative characterization of blood flow is important to assess acute physiological health and hemodynamic effects of clinical interventions. A critical need exists for a robust device designed to assess blood flow in biomedical applications. Laser Speckle Imaging (LSI) is a wide-field non-invasive optical technique that enables superficial blood flow quantification. A few potential clinical applications of LSI include assessing blood flow during burn patient triaging, quantifying tissue perfusion in a neonatal intensive care unit, and real-time blood flow mapping during surgery. The blood flow information that LSI provides can be helpful for bedside care. However, since LSI systems are highly sensitive to motion, most LSI studies are typically performed using mounted systems. Widespread use of LSI in the clinic has not occurred, in part, due to the bulky form factor and lack of mobility of these systems.

Our proposed solution to address the limitations of these mounted systems is a handheld LSI device. Handheld LSI would provide clinicians with objective blood flow measurements in a convenient form factor. However, motion artifact during handheld data acquisition can lead to unreliable and inaccurate blood flow values. Attempts have been made to account for motion artifact noise, but they lack an approach to align (co-register) images. Co-registration is a necessary step prior to the common practice of image averaging to improve the signal-to-noise ratio in producing blood flow maps. Our approach to address both motion artifact and image co-registration for handheld LSI was adding a fiducial marker (FM) into our imaging protocol.

We developed a portable, handheld LSI device and a protocol that integrated a FM into the imaging workflow. We automated the processes of sorting frames based on motion artifact and co-registering misaligned images. We compared the performance of the mounted and handheld setups using in vitro flow phantom experiments as a proof-of-concept study. We then demonstrated translation of our imaging protocol into an ongoing in vivo study with a porcine burn wound model.

We attempted to further reduce motion artifact by making additional modifications to the handheld LSI device. The modified LSI device was also validated with in vitro flow phantom experiments and in vivo imaging of vessels within a dorsal skinfold window chamber model.

In addition to the concerns of motion artifacts for clinical imaging, optical property changes in dynamic wounds or developing tissues may cause inaccuracies in the measured blood flow. We addressed this issue by combining LSI and Spatial Frequency Domain Imaging (SFDI), a non-contact imaging modality used to quantify tissue optical properties, to obtain corrected blood flow values. We then showed the potential errors in blood flow values when optical properties are not properly accounted for in the dynamic wounds of a porcine burn wound model.

Collectively, these works demonstrate our attempts at providing a viable alternative for clinical blood flow imaging with our handheld LSI device and imaging protocol and accounting for motion artifact and optical property changes in LSI.