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Tactile Imaging

Anna Galea, Parris Wellman, and Robert Howe

Tactile Imaging is a way of non-invasively imaging palpable features. The Tactile Imager consists of a pressure-sensitive array and a position tracker, which is pressed gently into the tissue of interest and run along the surface. Underlying structures will push back on the scanhead according to their stiffness, with stiffer structures generating a higher pressure on the scanhead. The pressures and the position are recorded and compiled into a tactile map, which is an image of the combined effects of underlying stiffness and the geometry in which it is distributed.

One focus of the Tactile Imaging work at the Harvard Biorobotics Laboratory has been on non-invasively monitoring breast health. An understanding of the relationship between the absolute stiffness of an imaged lump and the resultant tactile map is also being pursued.

[Tactile Imaging]
Construction of a Tactile Image.
The individual pressure frames are assembled in space and onto a best-fit plane for visualizing on a computer screen.

[Breast Cancer]
Cross-section of a human breast, showing the normal fat and glandular tissue, and a tumor growing from the glandular tissue.

Breast Cancer, and in fact many breast pathologies, tends to manifest as a discrete hard lump in the softer breast tissue. This is most remarkable in post-menopausal women, whose breasts are mostly soft fat tissue.

It is recommended that every woman over the age of 20 obtains a Clinical Breast Exam (CBE) every year. In a CBE, a clinician pushes into the breast with his or her fingers to feel for lumps. When properly performed, CBEs are a valuable tool in assesing breast health and detecting breast cancer. How well a CBE is performed, however, depends on the clinician, and varies greatly with technique and experience. Tactile Imaging is a way of quantifying CBE to generate an accurate, reproducible map of the palpable extent of breast tissue.

Determining lump parameters

The stiffness of a lump in the breast is correlated with its pathology. Its size is a measure of the extent of disease. Extracting these quantities from a tactile image is a fundamental concern of tactile imaging, and will provide greater insight into a patient's condition.

A method for extracting these values from a tactile image is under current investigation. Finite element methods are used to model a stiff lump embedded in soft tissue, and indented by the scanhead. The interfacial pressure at each position is recorded and collected into a pressure vector. A least squares fit is performed to map the model parameters to the resultant pressure frames. Example movies of some of our FEM data: tumor.mpg and tumor2.mpg

Finite Element model of a hard lump embedded in a soft tissue, indented by a tactile imaging scanhead. The pressure frame at each location is recorded in a pressure vector, which is then mapped to the underlying parameters.

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