Simulation study on practical choices for B / A measurement by the generalized finite amplitude insert-substitution method

The measurement of the parameter of nonlinearity B/A of tissues and liquids has potential to aid medical diagnosis. Therefore, accurate B/A measurement stays a relevant task. The finite amplitude insert-substitution (FAIS) method estimates B/A of biological tissues based on the measured 2nd harmonic in two configurations, (1) when only the reference medium is between the acoustic source and receiver, and (2) when the studied sample is inserted in the acoustic path with the reference medium. The generalised FAIS (gFAIS) has been previously proposed with the advantage of measuring B/A of liquids as well as ex-vivo tissues and allowing freedom in sample positioning. This simulations study validates the gFAIS method and provides insight into the practical choices for the setup that allow for an accurate measurement. Source and receiver size, distance between the source and the receiver and sample positioning have been studied on the subject of their effect on the measurement error for a homogeneous (modelling liquid) and a heterogeneous (modelling tissue) sample. Since B/A estimation also requires the measurement of the attenuation coefficients at the fundamental and 2nd harmonic frequnecy, practical choices for these measurements have also been studied

A fixed-distance plane wave method for estimating the ultrasound coefficient of nonlinearity

A practical method is proposed to assess the ultrasound coefficient of nonlinearity of a medium by measuring the fundamental and 2nd harmonic in the near field of a plane piston source for varying source pressure. The method uses the Fubini solution to extract the slope of the linear dependency of the ratio harmonic/fundamental on the fundamental pressure measured at the same location. It eliminates the need for a motion stage, required by methods observing harmonic growth with source distance. It also excludes the need to measure the pressure at the source, since, in the current experiment, conducted in distilled water, it neglects depletion of the fundamental due to attenuation and energy transfer to higher harmonics. The variability of the estimated beta was evaluated with 9 measurements for which the setup was mounted anew. This was performed for 4 different distances from the source. The estimated beta slightly decreased with increasing distance from the source, possibly due to focusing effects. The average beta estimated over all measurements was 3.48+-0.43, showing good agreement with previously reported values. The reproducibility and accuracy of the proposed method is relevant for its adoption aimed at beta measurements in tissue samples for clinical diagnostic research

A review on B/A measurement methods with a clinical perspective

The nonlinear parameter of ultrasound B/A has shown to be a useful diagnostic parameter, reflecting medium content, structure, and temperature. Despite its recognized values, B/A is not yet used as a diagnostic tool in the clinic due to the limitations of current measurement and imaging techniques. This review presents an extensive and comprehensive overview of the techniques developed for B/A measurement of liquid and liquid-like media (e.g., tissue), identifying the methods that are most promising from a clinical perspective. This work summarizes the progress made in the field and the typical challenges on the way to B/A estimation. Limitations and problems with the current techniques are identified, suggesting directions that may lead to further improvement. Since the basic theory of the physics behind the measurement strategies is presented, it is also suited for a reader who is new to nonlinear ultrasound

The generalized finite amplitude insert-substitution method for B/A measurement of tissues and liquids

B/A holds promise as a biomarker for tissue characterization. Moreover, measuring B/A enables identifying isomer types in biological liquids, potentially aiding diagnosis of some diseases. The standard finite amplitude insert-substitution method of measuring B/A has several limitations. It assumes a linear dependency of the attenuation coefficient on frequency, limiting it to tissue applications, and necessitates sample positioning close to the receiver. Here we propose the generalized finite amplitude insert-substitution method, which allows for B/A measurement of tissues and liquids, and gives freedom in sample positioning. In this work, we present the derived formula and validate the experimental procedure. For this purpose, B/A measurements of corn oil, porcine fat and porcine liver were conducted. For each substance, several conditions were tested, including various distances between the source and the receiver, various sample positions and amplitudes of the transmitted pulses. A better agreement with literature data was found for lower source pressure amplitudes and distances within the near field of the source transducer. In these conditions, the measurement error was confined to 8% and 25% of the literature values of corn oil and the considered tissues, respectively. No clear indication of the influence of sample position on the measurement accuracy was found

A fixed-distance plane wave method for estimating the ultrasound coefficient of nonlinearity

\u3cp\u3eA practical method is proposed to assess the ultrasound coefficient of nonlinearity of a medium by measuring the fundamental and 2nd harmonic in the near field of a plane piston source for varying source pressure. The method uses the Fubini solution to extract the slope of the linear dependency of the ratio harmonic/fundamental on the fundamental pressure measured at the same location. It eliminates the need for a motion stage, required by methods observing harmonic growth with source distance. It also excludes the need to measure the pressure at the source, since, in the current experiment, conducted in distilled water, it neglects depletion of the fundamental due to attenuation and energy transfer to higher harmonics. The variability of the estimated beta was evaluated with 9 measurements for which the setup was mounted anew. This was performed for 4 different distances from the source. The estimated beta slightly decreased with increasing distance from the source, possibly due to focusing effects. The average beta estimated over all measurements was 3.48+-0.43, showing good agreement with previously reported values. The reproducibility and accuracy of the proposed method is relevant for its adoption aimed at beta measurements in tissue samples for clinical diagnostic research.\u3c/p\u3