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The optical penetration depth has been measured in human intracranial tumors. The penetration depth in highly malignant gliomas is typically twice as large as the penetration depth in the surrounding normal brain tissue. Typical values for different wavelengths are: 1 mm for blue/green, 2.5 mm for red and 6 mm for near infrared. The penetration depth in a metastasis (from lung) is about the same as in the surrounding tissue.
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Svaasand et al. (1985) studied this question.
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