Angelos Echiadis

Remote simultaneous dual wavelength imaging photoplethysmography: a further step towards 3-D mapping of skin blood microcirculation

This paper presents a camera-based imaging photoplethysmographic (PPG) system in the remote detection of PPG signals, which can contribute to construct a 3-D blood pulsation mapping for the assessment of skin blood microcirculation at various vascular depths. Spot measurement and contact sensor have been currently addressed as the primary limitations in the utilization of conventional PPG system. The introduction of the fast digital camera inspires the development of the imaging PPG system to allow ideally non-contact monitoring from a larger field of view and different tissue depths by applying multi-wavelength illumination sources. In the present research, the imaging PPG system has the capability of capturing the PPG waveform at dual wavelengths simultaneously: 660 and 880nm. A selected region of tissue is remotely illuminated by a ring illumination source (RIS) with dual-wavelength resonant cavity light emitting diodes (RCLEDs), and the backscattered photons are captured by a 10-bit CMOS camera at a speed of 21 frames/second for each wavelength. The waveforms from the imaging system exhibit comparable functionality characters with those from the conventional contact PPG sensor in both time domain and frequency domain. The mean amplitude of PPG pulsatile component is extracted from the PPG waveforms for the mapping of blood pulsation in a 3-D format. These results strongly demonstrate the capability of the imaging PPG system in displaying the waveform and the potential in 3-D mapping of blood microcirculation by a non-contact means.

Non-invasive measurement of peripheral venous oxygen saturation using a new venous oximetry method: evaluation during bypass in heart surgery.

Monitoring of mixed venous oxygen saturation (SvO(2)) is currently performed using invasive fibre-optic catheters. This procedure is not without risk as complications may arise from catheterization. This paper describes an alternative, non-invasive method of monitoring peripheral venous oxygen saturation (SxvO(2)) which, although it cannot replace pulmonary artery catheters, can serve as an adjunct/early warning indicator of when there is an imbalance in oxygen supply and demand. The technique requires the generation of an artificial venous pulse at the finger, thereby causing modulation of the venous blood volume within the digit. The blood volume changes are monitored using an optical sensor. Just as pulse oximetry utilizes the natural arterial pulse to perform a spectrophotometric analysis of the peripheral blood in order to estimate the arterial blood oxygen saturation, the proposed venous oximetry technique uses the artificially generated venous pulse to estimate SxvO(2). A prototype device was tested in a pilot study with patients undergoing heart surgery. Data from this study support the notion that the method is capable of tracking haemodynamic changes and suggests the technique is worthy of further development and evaluation.

Development of effective photoplethysmographic measurement techniques: From contact to non-contact and from point to imaging

This paper provides an overview of the most recent developments in photoplethysmography (PPG). Existing contact point measurement techniques, i.e. pulse oximetry probes, are contrasted with the next generation non-contact and imaging implementations, i.e. non-contact reflection and camera-based PPG. The development of effective PPG monitoring techniques relies on novel approaches to opto-physiological modeling.

A remote approach to measure blood perfusion from the human face

A CMOS camera-based imaging photoplethysmography (PPG) system has been previously demonstrated for the contactless measurement of skin blood perfusion over a wide tissue area. An improved system with a more sensitive CCD camera and a multi-wavelength RCLED ring light source was developed to measure blood perfusion from the human face. The signals acquired by the PPG imaging system were compared to signals captured concurrently from a conventional PPG finger probe. Experimental results from eight subjects demonstrate that the camera-based PPG imaging technique is able to measure pulse rate and blood perfusion.

BioThreads: A Novel VLIW-Based Chip Multiprocessor for Accelerating Biomedical Image Processing Applications

We discuss BioThreads, a novel, configurable, extensible system-on-chip multiprocessor and its use in accelerating biomedical signal processing applications such as imaging photoplethysmography (IPPG). BioThreads is derived from the LE1 open-source VLIW chip multiprocessor and efficiently handles instruction, data and thread-level parallelism. In addition, it supports a novel mechanism for the dynamic creation, and allocation of software threads to uncommitted processor cores by implementing key POSIX Threads primitives directly in hardware, as custom instructions. In this study, the BioThreads core is used to accelerate the calculation of the oxygen saturation map of living tissue in an experimental setup consisting of a high speed image acquisition system, connected to an FPGA board and to a host system. Results demonstrate near-linear acceleration of the core kernels of the target blood perfusion assessment with increasing number of hardware threads. The BioThreads processor was implemented on both standard-cell and FPGA technologies; in the first case and for an issue width of two, full real-time performance is achieved with 4 cores whereas on a mid-range Xilinx Virtex6 device this is achieved with 10 dual-issue cores. An 8-core LE1 VLIW FPGA prototype of the system achieved 240 times faster execution time than the scalar Microblaze processor demonstrating the scalability of the proposed solution to a state-of-the-art FPGA vendor provided soft CPU core.

Development of a remote photoplethysmographic technique for human biometrics

Non-contact reflection photoplethysmography (NRPPG) is being developed to trace pulse features for comparison with contact photoplethysmography (CPPG). Simultaneous recordings of CPPG and NRPPG signals from 22 healthy subjects were studied. The power spectrum of PPG signals were analysed and compared between NRPPG and CPPG. The recurrence plot (RP) was used as a graphical tool to visualize the time dependent behaviour of the dynamics of the pulse signals. The agreement between NRPPG and CPPG for physiological monitoring, i.e. HRV parameters, was determined by means of the Bland-Altman plot and Pearsons correlation coefficient. The results indicated that NRPPG could be used for the assessment of cardio-physiological signals.

Prospective Venox Feasibility Study

Venox is a propriety venous oximetry system, capable of measuring peripheral venous oximetry. In this ongoing study, Venox is being compared against mixed central venous oximetry during human cardiac surgery, with fibre optic reflectance spectrophotometry being used as the gold standard, placed in the pulmonary artery. A background review of the pulse oximetry, current venous oximetry techniques and the potential advantage of the Venox system are discussed. Lessons learnt, preliminary results, and future plans are included in discussion

Innovation for personalization: A healthcare case study

This paper describes a research and innovation platform for the development of ideas relating to the investigation of blood perfusion in peripheral tissue. The Loughborough Innovation Platform for Health Technologies (LIPHT) can be used to demonstrate the use of the research and innovation pipe-line in more than one dimension. For this paper the first dimension considered is that of ‘blue sky’ idea through to their exploitation for the benefit of users and at the same time creating a wealth stream; the second dimension is the changing market as the ideas develop – from a hospital-based instrument operated by clinicians through to a point and click device for the use by the knowledgeable layman in the community. The starting point for these developments is a medical device known to many people as the ‘finger clip’ that measures arterial blood oxygen saturation; the end point is an optical device capable of imaging blood perfusion.