Tactile imaging

Tactile imaging, also called "mechanical imaging", "stress imaging" or "computerized palpation", is a medical imaging modality that translates the sense of touch into a digital image. The tactile image is a function of P(x,y,z), where P is the pressure on soft tissue surface under applied deformation and x,y,z are coordinates where pressure P was measured. The tactile image is a pressure map on which the direction of tissue deformation must be specified. Tactile imaging closely mimics manual palpation, since the probe of the device with a pressure sensor array mounted on its face acts similar to human fingers during clinical examination, deforming soft tissue by the probe and detecting resulting changes in the pressure pattern.

Interpretation: Inverse problem solution for P(x,y,z) would allow reconstruction of the tissue elasticity distribution (E) as function of the same coordinates E(x,y,z). The tissue elasticity image brings valuable information about the tissue or organ because the tissue elasticity modulus is highly sensitive to tissue structural changes accompanying various physiological and pathological processes. Unfortunately, the inverse problem solution is hardly possible for most real objects because it is non-linear and ill posed problem. However, it appeared that the tactile image per se, P(x,y,z), closely reflects the information content of the elasticity image and reveals tissue or organ anatomy and elasticity structure. The tissue elasticity at specified location can be estimated on the basis of spatial gradients within P(x,y,z). Figure 1 presents an experiment on a composite tissue phantom examined by a tactile imaging probe illustrating the ability to visualize the structure of the object.

Historically, the human sense of touch has been the most prevalent and successful medical diagnostic technique. A great variety of diseases were diagnosed through tactile sensing. We find in Kahun Gynecological Papyrus dated 1825 B.C.: "Discernere eam quae concepit ... like that finger upon her menaa." Hippocrates in 400 B.C. wrote: "Such swellings as are soft, free from pain, and yield to the finger, ... and are less dangerous than the others. ... then, as are painful, hard, and large, indicate danger of speedy death; but such as are soft, free of pain, and yield when pressed with the finger, are more chronic than these...".

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