ABSTRACT
We describe a contactless optical technique selectively enhancing superficial blood vessels below variously pigmented intact human skin by combining images in different spectral bands. Two CMOS-cameras, with apochromatic lenses and dual-band LED-arrays, simultaneously streamed Left (L) and Right (R) image data to a dual-processor PC. Both cameras captured color images within the visible range (VIS, 400-780 nm) and grey-scale images within the near infrared range (NIR, 910-920 nm) by sequentially switching between LED-array emission bands. Image-size-settings of 1280 x 1024 for VIS & 640 x 512 for NIR produced 12 cycles/s (1 cycle = 1 VIS L&R-pair + 1 NIR L&R-pair). Decreasing image-size-settings (640 x 512 for VIS and 320 x 256 for NIR) increased camera-speed to 25 cycles/s. Contrasts from below the tissue surface were algorithmically distinguished from surface shadows, reflections, etc. Thus blood vessels were selectively enhanced and back-projected into the stereoscopic VIS-color-image using either a 3D-display or conventional shutter glasses. As a first usability reconnaissance we applied this custom-built mobile stereoscopic camera for several clinical settings:* blood withdrawal;* vein inspection in dark skin;* vein detection through iodide;* varicose vein and nevi pigmentosum inspection. Our technique improves blood vessel visualization compared to the naked eye, and supports depth perception.
Subject(s)
Blood Vessels , Forearm/blood supply , Imaging, Three-Dimensional , Blood Vessels/anatomy & histology , Humans , Imaging, Three-Dimensional/instrumentation , Imaging, Three-Dimensional/methodsABSTRACT
OBJECTIVE: During open heart surgery, the myocardium usually provides sufficient visual contrast with both epicardial veins and arteries. However, visibility of coronary arteries may occasionally be impaired due to, e.g., intra-myocardial course of coronary arteries, increased epicardial fat, epicardial post-surgical adhesions, or pericarditis. Seen within the near infra-red range, coronary arteries show higher contrasts in relation to the myocardium than coronary veins. Hence, we developed a non-contact stereo-optical camera to selectively enhance coronary arteries by combining visible and near infra-red images. In this paper we present our first results on porcine and human hearts. MATERIALS AND METHODS: Two CMOS-cameras, with apochromatic lenses and dual-band LED-arrays, -captured visible colour (visible range, or VIS, 400-780nm) and near infra-red grey-scale (near infra-red range, or NIR, 910-920nm) images by sequentially switching between LED-array emission bands. Data was recorded by computer and processed off-line. Arterial NIR contrasts were algorithmically distinguished from shadows and specular reflections. Detected arteries were selectively enhanced and back-projected into the stereoscopic VIS-colour-image using either a 3D-display or conventional shutter glasses. RESULTS: Our technique visualised coronary vasculature and allowed to identify concealed parts of coronary arteries using off-line processing. Raw VIS & NIR images were real-time, processing took < 15s after filming. CONCLUSION: The applied principle works, but needs further development.
ABSTRACT
We describe a route toward contactless imaging of arterial oxygen saturation (SpO2) distribution within tissue, based upon detection of a two-dimensional matrix of spatially resolved optical plethysmographic signals at different wavelengths. As a first step toward SpO2-imaging we built a monochrome CMOS-camera with apochromatic lens and 3lambda-LED-ringlight (lambda1 = 660 nm, lambda2 = 810 nm, lambda3 = 940 nm; 100 LEDs lambda(-1)). We acquired movies at three wavelengths while simultaneously recording ECG and respiration for seven volunteers. We repeated this experiment for one volunteer at increased frame rate, additionally recording the pulse wave of a pulse oximeter. Movies were processed by dividing each image frame into discrete Regions of Interest (ROIs), averaging 10 x 10 raw pixels each. For each ROI, pulsatile variation over time was assigned to a matrix of ROI-pixel time traces with individual Fourier spectra. Photoplethysmograms correlated well with respiration reference traces at three wavelengths. Increased frame rates revealed weaker pulsations (main frequency components 0.95 and 1.9 Hz) superimposed upon respiration-correlated photoplethysmograms, which were heartbeat-related at three wavelengths. We acquired spatially resolved heartbeat-related photoplethysmograms at multiple wavelengths using a remote camera. This feasibility study shows potential for non-contact 2-D imaging reflection-mode pulse oximetry. Clinical devices, however, require further development.
