Rowland de Roode

Feasibility of multi-spectral imaging system to provide enhanced demarcation for skin tumor resection

Invading tumors like basal cell carcinoma have usually no distinct demarcation for the human eye. Therefore, during resection, an additional rim around the tumor is removed. However, extending sprouts can be missed since most lesions are not uniform. To improve the visualization of the tumor demarcation, we developed a multi-spectral imaging system especially adapted for dermatological applications based on tunable liquid crystal spectral tunable filter technology and LED illumination. Enhanced visualization of skin tumor demarcation was achieved using three strategies. The first strategy is based on creating false color images by combining narrow band spectral filtered images by placing them into the red, green and blue image components of a color image at three specific wavelengths. These specific wavelengths were determined using a trial on error tool to achieve the highest contrast between malignant and healthy tissue. The second strategy is to make ratio images of narrow band spectral filtered images at specific wavelengths. A trail on error tool was created which enables the user to try multiple wavelengths to obtain optimal contrast. This method could be applied in realtime. For the third strategy, on pixel spectral segmentation is applied by selecting the pixel spectra in the center of a tumor, surrounding tissue and healthy tissue far away from the tumor. The correlation between these specific spectra and all image pixels is calculated using a fast algorithm. The degree is correlation is graded by color coding and presented in a false color images showing a detailed demarcation of suspicious regions in the tissue. Although this strategy is expected to provide a higher specificity, it takes more time to calculate than the first strategy.

Compact multi-spectral imaging system for dermatology and neurosurgery

A compact multi-spectral imaging system is presented as diagnostic tool in dermatology and neurosurgery. Using an electronically tunable filter, a sensitive high resolution digital camera, 140 spectral images from 400 nm up to 720 nm are acquired in 40 s. Advanced image processing algorithms are used to enable interactive acquisition, viewing, image registration and image analysis. Experiments in the department of dermatology and neurosurgery show that multispectral imaging reveals much more detail than conventional medical photography or a surgical microscope, as images can be reprocessed to enhance the view on e.g. tumor boundaries. Using a hardware-based interactive registration algorithm, multi-spectral images can be aligned to correct for motion occurred during image acquisition or to compare acquisitions from different moments in time. The system shows to be a powerful diagnostics tool for medical imaging in the visual and near IR range.

Hyperspectral imaging system for imaging O2Hb and HHb concentration changes in tissue for various clinical applications

To observe local variations in temperature, oxygenation and blood perfusion over time, four imaging systems were developed and compared: Two systems consisting of white broadband light source and a CCD camera in combination with a Liquid Crystal Tunable Filter, one in the visual domain, 420-730 nm, and one in the infrared domain, 650-1100 nm. Thirdly, a CCD camera in combination with a software controlled hyper-spectral light source consisting of a panel with 600 LEDs divided in 17 spectral groups in the range from 370 to 880 nm so that specific spectral distributions can be generated at high repetition rate (>1000 Hz) and, fourthly a standard IR thermal camera for comparison. From the acquired images at the selected wavelengths chromophores concentration images of oxy and deoxy hemoglobin can be calculated applying different algorithms. These imaging techniques were applied and compared for various clinical applications: Tumor demarcation, early inflammation, effectiveness of peripheral nerve block anesthesia, and localization of epileptic seizure. The relative changes in oxygenation and temperature could be clearly observed in good correlation with the physiological condition. The algorithms and data collection/processing can be optimized to enable a real-time diagnostic technique.

Non-invasive skin oxygenation imaging using a multi-spectral camera system: effectiveness of various concentration algorithms applied on human skin

This study describes noninvasive noncontact methods to acquire and analyze functional information from the skin. Multispectral images at several selected wavelengths in the visible and near infrared region are collected and used in mathematical methods to calculate concentrations of different chromophores in the epidermis and dermis of the skin. This is based on the continuous wave Near Infrared Spectroscopy method, which is a well known non-invasive technique for measuring oxygenation changes in the brain and in muscle tissue. Concentration changes of hemoglobin (dO2Hb, dHHb and dtHb) can be calculated from light attenuations using the modified Lambert Beer equation. We applied this technique on multi-spectral images taken from the skin surface using different algorithms for calculating changes in O2Hb, HHb and tHb. In clinical settings, the imaging of local oxygenation variations and/or blood perfusion in the skin can be useful for e.g. detection of skin cancer, detection of early inflammation, checking the level of peripheral nerve block anesthesia, study of wound healing and tissue viability by skin flap transplantations. Images from the skin are obtained with a multi-spectral imaging system consisting of a 12-bit CCD camera in combination with a Liquid Crystal Tunable Filter. The skin is illuminated with either a broad band light source or a tunable multi wavelength LED light source. A polarization filter is used to block the direct reflected light. The collected multi-spectral imaging data are images of the skin surface radiance; each pixel contains either the full spectrum (420 - 730 nm) or a set of selected wavelengths. These images were converted to reflectance spectra. The algorithms were validated during skin oxygen saturation changes induced by temporary arm clamping and applied to some clinical examples. The initial results with the multi-spectral skin imaging system show good results for detecting dynamic changes in oxygen concentration. However, the optimal algorithm needs to be determined. Multi-spectral skin imaging shows to be a promising technique for various clinical applications were the local distribution of oxygenation is of major importance.

Dynamic change of characteristics of (modified) fiber tips used with microsecond pulsed lasers in a liquid environment influencing the effectiveness and safety of treatment

Microsecond pulsed laser systems, like the Thulium, Holmium and Erbium laser are being used for a broad range of medical applications in a liquid environment. Usually, the tissue ablation mechanism of these lasers is based on the instant formation of water vapor. When used with fiber delivery systems, the refraction of the beam coming out of the fiber will change the moment the liquid boundary turns to vapor. This dynamic change can be used in a controlled way but can also have adverse effects if not appreciated. In this study, the effect of the vapor phase change was investigated for various fiber shapes regarding optical and mechanical properties using high speed imaging and ray-trace simulation. Fiber tips of various shapes (bare, angled, tapered, ball shaped) were imaged with high-resolution using 1 &mgr;s light flashes in a video sequence of delay times from 1 to 2000 &mgr;s during exposure with pulsed 2.1 &mgr;m Holmium and pulsed 2.9 &mgr;m Erbium laser pulses. The tip was position in water or near a tissue surface. The dynamics of the explosive vapor bubble changed due to angle of refraction at the silica/vapor interface depending of the shape of the fiber tip. Ball shaped fibers form focused and highly divergent beams, angled fibers become side firing and tapered tips more concentrated. The observations are supported by ray-trace simulation. Clinically this mechanism can be used e.g. to create tiny side firing fibers in root channels of teeth. However, a damaged fiber tip may become unexpectedly side-firing resulting in adverse effects e.g. during lithotripsy. Ball-shaped fibers may be more resistant for damage due to impact with tissue. Using microsecond pulsed laser systems, the change in optical action of the fiber tip in liquid can influence the effectiveness and safety of the procedure.

Development of a multi-spectral imaging system for optical diagnosis of malignant tissues

A multi-spectral imaging system is presented consisting of a spatially and spectrally uniform light source, an electronically tuneable bandpass filter and a sensitive digital camera. When properly calibrated with a white reference, it can reproducibly grab the reflection spectrum of any accessible tissue surface. After a description of technical challenges, some examples are given for the application in dermatology.

Objective methods for achieving an early prediction of the effectiveness of regional block anesthesia using thermography and hyper-spectral imaging

An objective method to measure the effectiveness of regional anesthesia can reduce time and unintended pain inflicted to the patient. A prospective observational study was performed on 22 patients during a local anesthesia before undergoing hand surgery. Two non-invasive techniques thermal and oxygenation imaging were applied to observe the region affected by the peripheral block and the results were compared to the standard cold sensation test. The supraclavicular block was placed under ultrasound guidance around the brachial plexus by injecting 20 cc Ropivacaine. The sedation causes a relaxation of the muscles around the blood vessels resulting in dilatation and hence an increase of blood perfusion, skin temperature and skin oxygenation in the lower arm and hand. Temperatures were acquired with an IR thermal camera (FLIR ThermoCam SC640). The data were recorded and analyzed with the ThermaCamTMResearcher and Matlab software. Narrow band spectral images were acquired at selected wavelengths with a CCD camera either combined with a Liquid Crystal Tunable Filter (420-730 nm) or a tunable hyper-wavelength LED light source (450-880nm). Concentration changes of oxygenated and deoxygenated hemoglobin in the dermis of the skin were calculated using the modified Lambert Beer equation. Both imaging methods showed distinct oxygenation and temperature differences at the surface of the skin of the hand with a good correlation to the anesthetized areas. A temperature response was visible within 5 minutes compared to the standard of 30 minutes. Both non-contact methods show to be more objective and can have an earlier prediction for the effectiveness of the anesthetic block.

Registration and analysis of in vivo multispectral images for correction of motion and comparison in time

In-vivo image-based multi-spectral images have typical problems in image acquisition, registration, visualization and analysis. As its spatial and spectral axes do not have the same unit, standard image algorithms often do not apply. The image size is often so large that it is hard to analyze them interactively. In a clinical setting, image motion will always occur during the acquisition times up to 30 seconds, since most (elderly) patients often have difficulty to retain their poses. In this paper, we discuss how the acquisition, registration, display and analysis can be optimized for in-vivo multi-spectral images.

A modified algorithm for continuous wave Near Infrared Spectroscopy applied to in-vivo animal experiments and on human skin

Continuous wave Near Infrared Spectroscopy is a well known non invasive technique for measuring changes in tissue oxygenation. Absorption changes (&Dgr;O2Hb and &Dgr;HHb) are calculated from the light attenuations using the modified Lambert Beer equation. Generally, the concentration changes are calculated relative to the concentration at a starting point in time (delta time method). It is also possible, under certain assumptions, to calculate the concentrations by subtracting the equations at different wavelengths (delta wavelength method). We derived a new algorithm and will show the possibilities and limitations. In the delta wavelength method, the assumption is that the oxygen independent attenuation term will be eliminated from the formula even if its value changes in time, we verified the results with the classical delta time method using extinction coefficients from different literature sources for the wavelengths 767nm, 850nm and 905nm. The different methods of calculating concentration changes were applied to the data collected from animal experiments. The animals (lambs) were in a stable normoxic condition; stepwise they were made hypoxic and thereafter they returned to normoxic condition. The two algorithms were also applied for measuring two dimensional blood oxygen saturation changes in human skin tissue. The different oxygen saturation levels were induced by alterations in the respiration and by temporary arm clamping. The new delta wavelength method yielded in a steady state measurement the same changes in oxy and deoxy hemoglobin as the classical delta time method. The advantage of the new method is the independence of eventual variation of the oxygen independent attenuations in time.

Reproducible multispectral imaging in dermatology for diagnostics and treatment evaluation

Port wine stained patients need multiple laser treatments which each are paused for 3 months per treatment. For clinical evaluation and better understanding of the laser settings used during these treatments, a special developed multispectral dermatoscope is used to quantify the micro vascularization within the port wine stains. The multispectral dermatoscope captures high resolution images of skin tissue with a surface of approximately one square centimeter. For more accurate treatment evaluation of the port wine stain, recapturing of the exact same location is desired. For multispectral image-analyses an elastic match can be performed so that per pixel spectral analyses can be performed.