Ultrasound backscatter microscope for In vivo imaging of human fingertip

This thesis concerns the development of an Ultrasound Backscatter Microscope (UBM), and its application to imaging human fingertip skin under in vivo conditions. UBM is similar to B-mode diagnostic ultrasound imaging, but uses higher frequency acoustic waves (50 MHz) to achieve resolutions of the order of tens of microns. In UBM, contrast depends on the mechanical properties of tissues, a feature which complements techniques such as optical microscopy, CT and MRI that rely on other tissue properties. UBM is less expensive than most imaging techniques, and is also non-invasive. However, because of increased attenuation of the acoustic waves at higher frequencies, tissues being imaged must be located within a few millimeters of the surface. A UBM system was designed and built using a high frequency PVDF transducer (nominal frequency of 75 MHz), a pulser, a digitizing oscilloscope, a scanning system and the IEEE488 interface. The axial and lateral resolutions were experimentally determined to be about 20 m and 150 pm respectively. The device was used to image human fingertip skin under in vivo conditions so as to obtain information about the internal structure of the finger to aid biomechanical studies of human tactile sensing. Since phased-array transducers are not available at high frequencies, echoes from tissues at different lateral locations were obtained by mechanically scanning the transducer across the finger. Signal processing was done on the reflected echoes to obtain 2-D images. Images of fingerpad skin of six human subjects showed three distinct layers up to a depth of about 1.2 mm. Comparison images of fingertip skin on the dorsal side also showed a layered structure with lesser thicknesses for the first two layers, which is consistent with known anatomical information. The thesis concludes with a discussion of possible improvements and other applications of UBM. Thesis supervisor: Dr. Mandayam A. Srinivasan Title: Principal Research Scientist Thesis supervisor: Prof. Dennis M. Freeman Title: Assistant Professor