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In this study we test the feasibility of using low-cost LEDs to selectivity heat blood for enhanced thermal imaging of vascular structures. Applications of this new imaging technique include mapping blood vessels during surgeries such as tumor removal and vascular repair. In addition, this technique could potentially be used to determine the location of increased vascular density, and thus breast cancer tumors. Porcine blood, skeletal muscle, skin and fat were illuminated with LEDs that emit at 405 nm and 530 nm (near the blood absorption peaks) and the increase in temperature as a function of time was recorded using a thermal camera. In the studies with the 530 nm LED, blood heated more than other tissue types and the heating rate for the blood was significantly faster than other tissues. Illumination of blood with the 530 nm LED at low powers (tissue irradiance <500 mW/cm2) will selectively heat blood with no damage to surrounding tissue. Illumination with the 405 nm LED produced large temperature changes (up to 15°C) at low LED powers (tissue irradiance <500 mW/cm2). The heating and heating rates measured with this LED were higher than those measured for the 530nm LED. However, blood, skin and fat showed comparable amounts of heating and heating rates. The amount of heating in muscle tissue was dependent on the skeletal muscle type, but most samples showed heating comparable to or larger than blood. This LED was not effective at selectively heating blood relative to the other tissue types. The results of the preliminary studies suggest that the best contrast can be achieved with pulsed 530 nm LED illumination and an image analysis method that highlights rapid changes in temperature.
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