Despite its many advantages, thermography as a medical diagnostic tool has two basic limitations: 1 its images are indirect manifestations of interior thermal structure and hence do not yield explicit spatial information; 2 it is fundamentally two-dimensional. It is shown in the present paper that the three-dimensional variations of the temperature-dependent volume heat source, often called the blood perfusion term in the bio-heat equation, can be extracted from time dependent thermographic observations. On the other hand, spatial variations of the metabolic healing term cannot be determined from a similar procedure. Numerical experiments are performed to explore the sensitivity of the technique in determining the magnitude and location of a hypothetical lesion. Limitations of the technique in terms of the thermal penetration depth and signal-to-noise ratio are also examined.