Estimation of PSD Shifts for High-Resolution Metrology of Thickness Micro-Changes with Possible Applications in Vessel Walls and Biological Membrane Characterization

Abstract

Achieving accurate measurements of inflammation levels in tissues or thickness changes in biological membranes (e.g., amniotic sac, parietal pleura) and thin biological walls (e.g., blood vessels) from outside the human body, is a promising research line in the medical area. It would provide a technical basis to study the options for early diagnosis of some serious diseases such as hypertension, atherosclerosis or tuberculosis. Nevertheless, achieving the aim of non-invasive measurement of those scarcely-accessible parameters on patient internal tissues, currently presents many difficulties. The use of high-frequency ultrasonic transducer systems appears to offer a possible solution. Previous studies using conventional ultrasonic imaging have shown this, but the spatial resolution was not sufficient so as to permit a thickness evaluation with clinical significance, which requires an accuracy of a few microns. In this paper a broadband ultrasonic technique, that was recently developed by the authors to address other non-invasive medical detection problems (by integrating a piezoelectric transducer into a spectral measuring system), is extended to our new objective; the aim is its application to the thickness measurement of sub-millimeter membranes or layers made of materials similar to some biological tissues (phantoms). The modeling and design rules of such a transducer system are described, and various methods of estimating overtones location in the power spectral density (PSD) are quantitatively assessed with transducer signals acquired using piezoelectric systems and also generated from a multi-echo model. Their effects on the potential resolution of the proposed thickness measuring tool, and their capability to provide accuracies around the micron are studied in detail. Comparisons are made with typical tools for extracting spatial parameters in laminar samples from echo-waveforms acquired with ultrasonic transducers. Results of this advanced measurement spectral tool are found to improve the performance of typical cross-correlation methods and provide reliable and high-resolution estimations.

A New High-Resolution Spectral Approach to Noninvasively Evaluate Wall Deformations in Arteries

“…Nevertheless, there is a clear limit in attempting any possible ulterior improvement in resolution, which is always related to the signal-to-noise ratio (SNR) encountered in real medical applications. In this sense, the paper authors already have analyzed, previously [ 30 , 32 – 34 ], the influence of possible poor SNR levels in ultrasonic echoes on the induction of errors in results of our spectral estimation technique (AR-PSD). Simulation results during these computational analyses indicate that the AR-PSD processing option presents an inherent good performance with noisy echo-signals, as it was proved in the practice by applications of our calculation algorithms to other spectral evaluations also into tissues.…”

“…First results show a very high potential spatial resolution (increasing with the selected overtone order). It must be noted that the applied particular autoregressive PSD technique presents an inherent good performance with noisy echo-signals, as it was reported for applications of a similar calculation algorithm to other type of spectral evaluations also into biological tissues [ 30 – 34 ].…”

“…The operator TCC was chosen as a reference in the analysis of our approach for its simple implementation to have results independent of the actual center frequency value [ 9 ] and besides because it was proved by us that this option provides a reasonable spatial resolution just in this type of biomedical applications [ 26 , 30 ].…”