Biophotonics: Acousto-optic Elastography

Oregon Health & Science University, Portland OR

Investigators

Abstract

0086719 Kirkpatrick It is well known that the mechanical properties of pathological tissues vary from that of healthy tissue. For example, many disease processes such as tumors of the breast and prostate manifest themselves as stiff, hard nodules relative to the surrounding tissue. Subsurface skin tumors present themselves as objects with distinct mechanical properties relative to the surrounding normal tissue. The displacement of fibrillar papillary dermis by the softer, cellular mass of a growing melanoma is one such example of this. This feature frequently allows their detection through manual palpation. However, standard soft tissue palpation is not only qualitative, but also highly subjective. Furthermore, it provides information on a rather large spatial scale, thus the ability to detect small tumors by palpation is limited. Acousto-optic elastrography (AOE) offers the potential for increased spatial resolution (i.e. smaller lesions may be detected) and better strain resolution (low-contrast elastic modulus distributions may be visualized) than other elastographic methods. However, this increased spatial and strain resolution is gained a the cost of decreased probing depth, as optical methods are limited to the outer few millimeters of tissue. Furthermore, optical elastography is limited in that only relatively small areas or volumes of tissues may be probed at any one time. Never the less, optical methods can still be useful in the early detection of neoplastic changes because many of these early changes occur in the mucosa and submucosa of the affected organs. In this proposal, the investigators aim to implement a novel, acousto-optical method for evaluation tissue mechanical properties. The method, incorporating a novel fiber-coupled laser speckle strain gauge, provides high resolution strain and strain rate measurements in tissues undergoing loading or undergoing creep recovery following loading. These data can be used to quantify tissue regions with differential stiffness for both diagnostic purposes and for basic tissue mechanics research. Using image and signal processing techniques, tissue regions which display differential tissue stiffnesses can be delineated from these images. The end goal is that these images can provide the clinician direct information regarding the pathological state of the tissue under examination.