Linghua Kong

Single sensor that outputs narrowband multispectral images.

We report the work of developing a hand-held (or miniaturized), low-cost, stand-alone, real-time-operation, narrow bandwidth multispectral imaging device for the detection of early stage pressure ulcers.

Real-Time Multispectral Imager for Home-Based Health Care

Multispectral imaging (MSI) is becoming a powerful tool for tissue abnormality detection. Conventional MSI systems, however, are not readily suitable for challenges of routine clinical uses due to the fact that they are expensive, bulky, and time consuming to acquire the data. In this letter we report a novel approach to instrument MSI technology into a handheld, low-cost, standing-alone, real-time operational device that is suitable for home-based health care. It covers techniques used to produce multiple images at discrete signature wavelengths of tissues with a single shot.

Developing handheld real time multispectral imager to clinically detect erythema in darkly pigmented skin

Pressure ulcers have been identified as a public health concern by the US government through the Healthy People 2010 initiative and the National Quality Forum (NQF). Currently, no tools are available to assist clinicians in erythema, i.e. the early stage pressure ulcer detection. The results from our previous research (supported by NIH grant) indicate that erythema in different skin tones can be identified using a set of wavelengths 540, 577, 650 and 970nm. This paper will report our recent work which is developing a handheld, point-of-care, clinicallyviable and affordable, real time multispectral imager to detect erythema in persons with darkly pigmented skin. Instead of using traditional filters, e.g. filter wheels, generalized Lyot filter, electrical tunable filter or the methods of dispersing light, e.g. optic-acoustic crystal, a novel custom filter mosaic has been successfully designed and fabricated using lithography and vacuum multi layer film technologies. The filter has been integrated with CMOS and CCD sensors. The filter incorporates four or more different wavelengths within the visual to nearinfrared range each having a narrow bandwidth of 30nm or less. Single wavelength area is chosen as 20.8μx 20.8μ. The filter can be deposited on regular optical glass as substrate or directly on a CMOS and CCD imaging sensor. This design permits a multi-spectral image to be acquired in a single exposure, thereby providing overwhelming convenience in multi spectral imaging acquisition.

Handheld erythema and bruise detector

Visual inspection of intact skin is commonly used when assessing persons for pressure ulcers and bruises. Melanin masks skin discoloration hindering visual inspection in people with darkly pigmented skin. The objective of the project is to develop a point of care technology capable of detecting erythema and bruises in persons with darkly pigmented skin. Two significant hardware components, a color filter array and illumination system have been developed and tested. The color filter array targets four defined wavelengths and has been designed to fit onto a CMOS sensor. The crafting process generates a multilayer film on a glass substrate using vacuum ion beam splitter and lithographic techniques. The illumination system is based upon LEDs and targets these same pre-defined wavelengths. Together, these components are being used to create a small, handheld multispectral imaging device. Compared to other multi spectral technologies (multi prisms, optical-acoustic crystal and others), the design provides simple, low cost instrumentation that has many potential multi spectral imaging applications which require a handheld detector.

Portable Gage for Pressure Ulcer Detection

Pressure ulcers are widely considered to be a critical problem in rehabilitation since they result in severe discomfort and high healthcare cost. The prevention of pressure ulcers is a constant preoccupation for every nursing team. This paper introduces a novel handheld instrument that can detect subtle changes in the skin biomechanical properties by measuring its biomechanical response. This could be used to detect stage-I pressure ulcers and deep tissue injury. Its high bandwidth makes it possible to load the skin under wide range of conditions. The instrument is portable, inexpensive, and intrinsically precise. Several experiments were conducted to validate the function of the device. Preliminary results show that the device could effectively measure the difference in the viscoelasticity between human skin of different sites, hence paving the way for the development of clinical protocols and trials

A Hand-held Mosaicked Multispectral Imaging Device for Early Stage Pressure Ulcer Detection

The use of a custom filter mosaic overlaying a CMOS/CCD sensor represents a novel idea to multispectral imaging. The innovation provides simple, miniaturized, low cost instrumentation that has many potential biological applications which require a hand-held detector. This makes it extremely adaptable and can serve as an integrated component to distributed diagnosis and home healthcare (D2H2). A mosaicked sensor is a monolithic array of many sensors, arranged in a geometric pattern with each sensor covered by an optical filter sensitive to a specified wavelength. In this way, only one spectral component is sensed at each pixel and the other spectral components must be estimated from neighbors. Although with great potential, one challenge faced by this device, however, is the reconstruction of the high-resolution full-spectral image from the low-resolution input. Due to the physical limitations in fabrication and the usage of the multispectral filter mosaic, two types of degradations exist, including filter misalignment and the missing spectral components, that must be corrected using intelligent algorithms to take full advantage of the hardware capability of the device. In this paper, we first describe a custom geometric correction method to restore the image from the misalignment distortion. We then present a binary tree-based generic demosaicking algorithm to efficiently estimate the missing special components and reconstruct a high-resolution full-spectral image. We choose early detection of pressure ulcer as a targeting area as early stage pressure ulcers and other subcutaneous lesions are nearly invisible in clinical settings, particularly so for dark pigmented skin. We show how the geometric correction and demosaicking algorithms successfully reconstruct a full-spectral image from which apparent contrast enhancement between damaged skin and the normal skin is observed.

Fabrication of multispectral imaging technology driven MEMS-based micro-arrayed multichannel optical filter mosaic

Multispectral imaging is becoming a new powerful tool in a wide range of biological studies by adding spectral, spatial and temporal dimensions to tissue abnormity and the underlying biological processes. A standard spectral imaging setup includes two major components, a band pass selection device (such as liquid crystal tunable filter and diffraction grating) and a scientific-grade monochrome camera. Contemporary multispectral imaging technologies typically use traditional optical filters e.g., filter wheels, a generalized Lyot filter, an electrically tunable filter, multiple-band pass filters or the methods of dispersing light, e.g., optic-acoustic crystals. The instrumented systems are bulky, expensive, require multiple exposures or extensive post-processing to align up multiple images of pure spectral components. Recently a break-through technology has emerged to instrument multispectral imaging technology into handheld real-time devices using miniaturized filter mosaic containing micro-arrayed multiple channel band-pass optical filters. The filter mosaic can be directly placed near the focal plane immediately in front of the imaging sensor of an off-shelf CCD/CMOS camera, with potentially one such micro-filter covers one pixel of the imaging sensor. This paper reveals the technical details of how such a micro-arrayed multi channel optical filter is fabricated using traditional multi-film vacuum deposition and the modern micro-lithography technologies. The selection of different coating materials, their structures and effects to the adhesive forces between film and substrate, the spatial resolution, width of passing band, and the transmittance of the resulting miniaturized optical filter is discussed.

Multispectral image analysis of bruise age

The detection and aging of bruises is important within clinical and forensic environments. Traditionally, visual and photographic assessment of bruise color is used to determine age, but this substantially subjective technique has been shown to be inaccurate and unreliable. The purpose of this study was to develop a technique to spectrally-age bruises using a reflective multi-spectral imaging system that minimizes the filtering and hardware requirements while achieving acceptable accuracy. This approach will then be incorporated into a handheld, point-of-care technology that is clinically-viable and affordable. Sixteen bruises from elder residents of a long term care facility were imaged over time. A multi-spectral system collected images through eleven narrow band (~10 nm FWHM) filters having center wavelengths ranging between 370-970 nm corresponding to specific skin and blood chromophores. Normalized bruise reflectance (NBR)- defined as the ratio of optical reflectance coefficient of bruised skin over that of normal skin- was calculated for all bruises at all wavelengths. The smallest mean NBR, regardless of bruise age, was found at wavelength between 555 & 577nm suggesting that contrast in bruises are from the hemoglobin, and that they linger for a long duration. A contrast metric, based on the NBR at 460nm and 650nm, was found to be sensitive to age and requires further investigation. Overall, the study identified four key wavelengths that have promise to characterize bruise age. However, the high variability across the bruises imaged in this study complicates the development of a handheld detection system until additional data is available.

Instrument an Off-Shelf CCD Imaging Sensor Into a Handheld Multispectral Video Camera

In this letter, we report the feasibility study of converting an ordinary off-shelf charge-coupled device (CCD) imaging sensor into a multispectral imaging instrument, using the multispectral bruises detection as an example. The resulting handheld device is capable of producing in real-time multiple pixel-registered images centered at different wavelengths in a single exposure, thereby providing overwhelming operational convenience. The results are advantageous for the development of a handheld narrowband multispectral imaging video camera for image guided medical surgery.

Bruise chromophore concentrations over time

During investigations of potential child and elder abuse, clinicians and forensic practitioners are often asked to offer opinions about the age of a bruise. A commonality between existing methods of bruise aging is analysis of bruise color or estimation of chromophore concentration. Relative chromophore concentration is an underlying factor that determines bruise color. We investigate a method of chromophore concentration estimation that can be employed in a handheld imaging spectrometer with a small number of wavelengths. The method, based on absorbance properties defined by Beer-Lamberts law, allows estimation of differential chromophore concentration between bruised and normal skin. Absorption coefficient data for each chromophore are required to make the estimation. Two different sources of this data are used in the analysis- generated using Independent Component Analysis and taken from published values. Differential concentration values over time, generated using both sources, show correlation to published models of bruise color change over time and total chromophore concentration over time.