Calibration of sonographic gel probe covers for in-vivo mechanical testing

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (leaf 29).Cervical insufficiency is a condition in pregnancy in which the cervix asymptomatically dilates in the absence of uterine contractions, resulting in a spontaneous preterm delivery. The condition is often misdiagnosed and presents a significant challenge for the clinical community. In order to establish better diagnostic criteria for cervical insufficiency and to improve assessment of preterm delivery risk for the individual patient, a non-invasive medical imaging tool, which uses ultrasound elastography to test the mechanical properties of cervical tissue, has been developed. The hand-held ultrasound indentation system will enable in vivo collection of stress-strain data from patients that will provide researchers with the necessary information to be used in material modeling and improve diagnosis of cervical insufficiency. The device consists of an ultrasound probe, enclosed by a gel-filled cover. The mechanical properties of the covers vary with each cap as well as with time and temperature. Therefore, in order to ensure accurate measurement, the probe covers must be calibrated prior to use. An experimental study was carried out to examine the effects of various testing conditions on the mechanical behavior of the probe covers. Different freezing and thawing techniques were explored in order to determine favorable conditions in order to preserve the integrity of the probes between the time of manufacture and actual use. From the results of the research, the appropriate combination of testing conditions for probe calibration was determined, as well as freezing and thawing techniques for probe preservation.by Panasaya Charenkavanich.S.B