The images of Laser Doppler like other Doppler based modalities, such as Doppler ultrasound, provide information about moving objects. A He-Ne laser is used for illumination of the skin and the backscattered and reflected light is collected by a detector. Containing an optically ideal chromophore, the flowing red blood cells are an outstanding target for Laser Doppler Imaging (LDI) to assess the subsurface extent of vascular lesions Blood flow can be calculated based on the Doppler shift of moving red blood cells. 2D Laser Doppler images provide a sub-surface map of perfusion of the skin as a metabolic indicator of angiogenesis underlying malignancies or other diseases processes.
Response to therapy
LDI has been used in research setting to monitor response to treatment for HIV associated Kaposi’s sarcoma with high accuracy and precision with histological correlation. As patients respond to treatment, the sub-surface blood flow map decreases on following Laser Doppler images. Vise versa, as patients develop resistance to treatment on in case of non-compliance, the blood flow in Kaposi’s sarcoma lesions increases even is the size of the lesions at the surface of the skin remains stable.
The limitations of this technique lie in the difficulties of obtaining quantitative flow measures, making intra and inter subject comparisons of flow difficult if not impossible, as well as not being able to obtain depth information. In the future, additional mathematical algorithms to semi-quantify the sub-surface blood flow map would decrease subjectivity. In addition, potential hybrid combination with other Doppler modalities, such as ultrasound with 3D capabilities, would result in added information about the depth of increased vascular bed.
Tumor angiogenesis plays in vital role in growth and metastasis in many tumors, including melanoma. Therefore, LDI can be used to assess the efficacy of anti-angiogenic treatments.