Noncontact blood perfusion mapping in clinical applications

Abstract

Non-contact imaging photoplethysmography (iPPG) to detect pulsatile blood microcirculation in tissue has been selected as a successor to low spatial resolution and slow scanning blood perfusion techniques currently employed by clinicians. The proposed iPPG system employs a novel illumination source constructed of multiple high power LEDs with narrow spectral emission, which are temporally modulated and synchronised with a high performance sCMOS sensor. To ensure spectrum stability and prevent thermal wavelength drift due to junction temperature variations, each LED features a custom-designed thermal management system to effectively dissipate generated heat and auto-adjust current flow. The use of a multi-wavelength approach has resulted in simultaneous microvascular perfusion monitoring at various tissue depths, which is an added benefit for specific clinical applications. A synchronous detection algorithm to extract weak photoplethysmographic pulse-waveforms demonstrated robustness and high efficiency when applied to even small regions of 5 mm 2 . The experimental results showed evidences that the proposed system could achieve noticeable accuracy in blood perfusion monitoring by creating complex amplitude and phase maps for the tissue under examination.

Smart Garment Fabrics to Enable Non-Contact Opto-Physiological Monitoring

“…The individual pixels within the ROI could potentially preserve this notch, but the relevant phase and amplitude differences in the individual PPG signals across those pixels made the averaged signal appear “smoothed”, effectively masking the notch. The size of the kernel used to average pixels within the ROI directly influenced the iPPG signal morphology, which was confirmed by the observation made earlier in [ 4 ].…”

“…A camera-based method, also known as imaging (iPPG) or remote (rPPG) photoplethysmography, has been used to demonstrate the possibility of remote pulse rate extraction, where tissue surface is illuminated by ambient [ 2 ] or artificial light [ 3 ], and modulated backscattered light is captured by an image sensor, e.g., a digital camera. The significant downside of iPPG, compared to the traditional contact PPG, is the need of a powerful light source to spotlight the region of interest (ROI) [ 4 ]. The quality of an iPPG signal is also susceptible to the directionality and uniformity of such illumination [ 5 ].…”

Frame Registration for Motion Compensation in Imaging Photoplethysmography

“…In order to create a stabilized light flux, an illuminator comprised of individual high-power LEDs was constructed based on the principles and results reported in previous work [36]. In short, three high-power light emitting diodes (LEDs) (LXML Series, Philips, Andover, MA, USA) emitting at 530 nm with a typical half-power bandwidth of 20 nm were mounted on an aluminum substrate of high thermal conductivity to divert excess heat generated by the semiconductors (see Figure 4a).…”

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“…For example, highpower quartz-halogen illumination is used for the multispectral 96 and for the long-range 74 , 75 setups, 3kw in the former and 2kW in the latter case. Iakovlev et al introduced a custom light source based on narrow-band-width high power LEDs for PPGI applications 97 . Moreover, Moco et al demonstrated that homogenous and orthogonal illumination can reduce ballistocardiographic artifacts in PPGI measurements 26 , while Trumpp et al found a significant improvement when in addition perpendicular polarization is used 98 .…”