Abstract
Blood carries oxygen and nutrients to the trillions of cells in our body to sustain vital life processes. Lack of blood perfusion can cause irreversible cell damage. Therefore, blood perfusion measurement has widespread clinical applications. In this paper, we develop PulseCam — a new camera-based, motion-robust, and highly sensitive blood perfusion imaging modality with 1 mm spatial resolution and 1 frame-per-second temporal resolution. Existing camera-only blood perfusion imaging modality suffers from two core challenges: (i) motion artifact, and (ii) small signal recovery in the presence of large surface reflection and measurement noise. PulseCam addresses these challenges by robustly combining the video recording from the camera with a pulse waveform measured using a conventional pulse oximeter to obtain reliable blood perfusion maps in the presence of motion artifacts and outliers in the video recordings. For video stabilization, we adopt a novel brightness-invariant optical flow algorithm that helps us reduce error in blood perfusion estimate below 10% in different motion scenarios compared to 20–30% error when using current approaches. PulseCam can detect subtle changes in blood perfusion below the skin with at least two times better sensitivity, three times better response time, and is significantly cheaper compared to infrared thermography. PulseCam can also detect venous or partial blood flow occlusion that is difficult to identify using existing modalities such as the perfusion index measured using a pulse oximeter. With the help of a pilot clinical study, we also demonstrate that PulseCam is robust and reliable in an operationally challenging surgery room setting. We anticipate that PulseCam will be used both at the bedside as well as a point-of-care blood perfusion imaging device to visualize and analyze blood perfusion in an easy-to-use and cost-effective manner.
Highlights
Blood carries oxygen and nutrients to the trillions of cells in our body to sustain vital life processes
In a clinical context, we compare PulseCam against a commercial pulse oximeter (PulseOx) derived perfusion index in an operationally challenging setting to monitor changes in peripheral perfusion of patients during surgery performed under general anesthesia
We find that PulseCam-derived perfusion estimate is much more sensitive in detecting perfusion changes associated with partial blood flow occlusion induced by Blood Occlusion Pressure (BOP) between 10–70 mmHg
Summary
Blood carries oxygen and nutrients to the trillions of cells in our body to sustain vital life processes. Laser Doppler Flowmetry (LDF) is another popular modality used to measure micro-circulatory blood flow in tissue, especially to assess wound healing and for skin disease research[19]. All of these contact-based optical modalities can only measure blood perfusion at a specific location on the skin surface, i.e., the point-of-contact, and their measurements are sensitive to the exact placement of the probe. We develop a novel camera-based, multi-sensor, motion-robust blood perfusion imaging modality, named PulseCam, that can reliably measure spatial maps and temporal trends of peripheral blood perfusion over the skin surface or internal tissue. PulseCam can be implemented both as a bedside patient monitoring system, e.g., in an ICU or the operating room (see Fig. 1(b)), as well as a hand-held imaging tool to visualize blood perfusion at surgical sites, wounds, and ulcers (see Fig. 1(c))
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