Contact-less, Multi-Spectral Imaging of Dermal Perfusion

Photoplethysmography Revisited: From Contact to Noncontact, From Point to Imaging

Abstract: Photoplethysmography (PPG) is a noninvasive optical technique for detecting microvascular blood volume changes in tissues. Its ease of use, low cost and convenience make it an attractive area of research in the biomedical and clinical communities. Nevertheless, its single spot monitoring and the need to apply a PPG sensor directly to the skin limit its practicality in situations such as perfusion mapping and healing assessments or when free movement is required. The introduction of fast digital cameras into clinical imaging monitoring and diagnosis systems, the desire to reduce the physical restrictions, and the possible new insights that might come from perfusion imaging and mapping inspired the evolution of the conventional PPG technology to imaging PPG (IPPG). IPPG is a noncontact method that can detect heart-generated pulse waves by means of peripheral blood perfusion measurements. Since its inception, IPPG has attracted significant public interest and provided opportunities to improve personal healthcare. This study presents an overview of the wide range of IPPG systems currently being introduced along with examples of their application in various physiological assessments. We believe that the widespread acceptance of IPPG is happening, and it will dramatically accelerate the promotion of this healthcare model in the near future.

Processing images of at least one living being

Abstract: A method of processing images of at least one living being, includes obtaining a sequence (19) of digital images taken at consecutive points in time. At least one measurement zone (26) comprising a plurality of image points is selected. For each measurement zone (26), a signal (28,30) representative of at least variations in a time- varying value of a combination of pixel values at at least a number of the image points for use in determining at least one of a presence and a frequency value of at least one peak in a spectrum of the signal (28,30) corresponding to a frequency of a periodic physiological phenomenon is obtained. The step (25) of selecting at least one measurement zone (26) includes analyzing information based on pixel data of a plurality of image parts in at least one of the images (19), each image part including at least one image point, and selecting each measurement zone (26) from contiguous parts determined to have similar characteristics.

Method and system for obtaining a first signal for analysis to characterize at least one periodic component thereof

Abstract: A method of facilitating obtaining a first signal, for analysis to characterize at least one periodic component, includes obtaining two second signals representative of intensities of electromagnetic radiation. The first signal is at least derivable from an output signal obtainable by applying a transformation to the second signals such that any value of the output signal is based on values from each respective second signal at corresponding points in time. The method further includes obtaining a value of a variable determining influences of components of respective second signals on the output signal when the signals corresponding to the second signals are captured and the transformation is applied, by (i) analyzing the first, second and/or the output signals to select a value of a parameter corresponding to a respective one of the variables; or (ii) calculating values of at least one time-varying factor corresponding to a respective one of the variables.

Method and system for image analysis

Abstract: A method of image analysis, includes: obtaining a sequence (37;51) of images, each represented by pixel data; performing a vision-based analysis on at least one of the sequence (37;51) of images to obtain data for classifying a state of a subject represented in the images; - determining at least one value of a physiological parameter of a living being represented in at least some of the sequence (37;51) of images; and classifying a state of the subject using the data obtained with the vision-based analysis and the at least one value of the physiological parameter. The at least one value of the physiological parameter is determined through analysis of image data from the same sequence (37;51) of images from which the at least one image on which the vision-based analysis is performed is taken. A method of enabling remote photoplethysmographic analysis includes: obtaining a sequence (37;51) of images from at least one camera (3), each represented by pixel data representative of reflected ambient light in at least a limited range of wavelengths; and, for at least one measurement zone (41), providing a signal representative of at least variations in a time-varying value of a combination of pixel values at at least a number of image points in the measurement zone (41) for use in determining at least one value of a physiological parameter. At least part of a selected subject represented in the sequence (37;51) of images is tracked, and a directable light source (4) illuminating at least part of the selected subject is controlled.

Method of controlling a function of a device and system for detecting the presence of a living being

Abstract: A method of controlling a function of a device, includes obtaining a sequence (19;34;48) of digital images taken at consecutive points in time. At least one measurement zone (25) including a plurality of image points is selected. For at least one measurement zone (25), a signal (30;41;55) representative of at least variations in a time- varying value of a combination of pixel values at at least a number of the image points is obtained and at least one characteristic of the signal (30;41;55) within at least a range of interest of its spectrum relative to comparison data is determined. The determination comprises at least one of: (i) determining whether the signal (30;41;55) has a spectrum with a local maximum at a frequency matching a comparison frequency to a certain accuracy; and (ii) determining whether at least a certain frequency component of the signal (30;41;55) is in phase with a comparison signal to a certain accuracy. The function is controlled in dependence on whether the determination is positive.

Motion Artifact Reduction in Photoplethysmographic Signals using Singular Value Decomposition

Abstract: Artifact free photoplethysmographic (PPG) signals, obtained with red and infrared (IR) optical sources and detectors are necessary for non-invasive estimation of oxygen saturation (SpO2) in arterial blood. Movement of a patient corrupts the PPGs with motion artifacts, resulting in large errors in the computation of SpO2. This paper presents a novel singular value decomposition (SVD) based method to reduce motion artifacts from corrupted PPG signals. Test results on a prototype incorporating the proposed SVD technique show that stable and reliable SpO2 measurement is achieved even when PPGs are distorted by motion artifacts, thus establishing the efficacy of the proposed method.

Virtual Instrument for the Measurement of Haemo-dynamic Parameters Using Photoplethysmograph

Abstract: This paper presents the design and development of a virtual instrument for the measurement of haemo-dynamic parameters namely, pulse rate and oxygen saturation in arterial blood based on the popular photoplethysmographic (PPG) principle. A clip-on sensor, housing red and infrared (IR) light emitting diodes and suitable photo detectors is developed. The sensor is interfaced to a PC utilizing the audio channel of the sound card, thus dispensing with expensive analog to digital converter hardware. Since the frequency response of the audio channel is not suitable for the PPG waveforms of red and IR, FM modulation and demodulation are employed. An empirical relationship is developed for the computation of the oxygen saturation in arterial blood using the red and IR PPG data and the well-known and well-established extinction coefficients of haemoglobin with and without oxygen. Data acquisition and processing are accomplished under LabVIEW virtual environment.

A non-invasive spectral reflectance method for mapping blood oxygen saturation in wounds

Abstract: Reflectance spectroscopy is a common technique used to analyze blood oxygen saturation in biological tissues. This study describes a non-invasive method for mapping blood oxygen saturation in wounds using reflectance measurements obtained from a hyperspectral imaging system. The maps illustrate changes in blood oxygen saturation with high spatial resolution. This allows observation into local blood oxygen supplies of tissue as opposed to common point measurement techniques such as pulse oximetry and optical fiber probing. To demonstrate this, an algorithm designed to calculate the blood oxygen saturation from narrow band reflectance images at 760 and 800 nm was used. The algorithm incorporates the contributions of absorption by oxy-(HbO/sub 2/) and deoxy-hemoglobin (Hb) at the oxygen (O/sub 2/) sensitive and O/sub 2/ insensitive wavelength. Results of the algorithms performance are presented to demonstrate that reflectance measurements can be used to determine the amount of blood O/sub 2/ saturation of a wound.