Quantitative ultrasound for evaluating human cervical microstructure

Abstract

This study uses quantitative ultrasound techniques to investigate the possibility of monitoring changes in cervical microstructure with acoustic backscatter. Standard “general imaging” ultrasound transducers and a novel endocavity transducer were used to detect changes in the power spectrum of the ultrasonic backscattered echo signal as a function of the angle between the acoustic beam and the dominant macrostructure of cervix specimens from hysterectomy. The echo signal power was assessed by integrating the echo signal power spectrum between consistent frequency limits. The echo signal power was found to decrease as a function of steering angle. Normalizing the echo signal power to that found at 0° (acoustic beams normal to the cervical canal) it was found that there was a monotonically increasing loss of power with increasing beam angle, and that power loss was symmetric about 0°. Those data were then compared to identically acquired and processed data from phantoms with spherical scatterers. Data from phantoms with spherical scatterers serve as a normalization for the expected backscatter signal power loss (with increasing steering angle) that would be expected due to the loss of effective aperture and directivity of the transducer. The power loss from the cervix consistently exceeded that from the phantoms, was statistically significant for all angles greater than 50°, and the excess power loss is likely due to the presence of aligned collagen fibers in the cervical microstructure.