Parametric array for tissue harmonic imaging

Abstract

More than 50% of abdominal scans are performed on technically difficult patients due to worldwide increase of obesity. Tissue harmonic imaging has shown some improvements on obese patients but the problem remains unsolved. The use of dual frequency pulses allows the generation of sum and difference frequencies in tissue. We hypothesize that the difference frequency (Δf, parametric array) can survive larger penetration depths and increase SNR while maintaining the spatial characteristics of the primary wave. Our objective was to optimize the parameters for efficient generation of the parametric array and study its spatial characteristics for imaging obese patients. Numerical simulations using KZK equation and measurements in tissue-like media were performed to study parametric arrays. Pulses with two frequencies (f1, f2) were considered where 0.1f1≤Δf≤f1. Pulse inversion was utilized to isolate even harmonics, including Δf. The amplitude of Δf was maximized at Δf = f1. The axial resolution is not seriously compromised by the lower frequency of Δf when using PI. For 0.5 dB/cm attenuation difference between Δf and 2f1, Δf echoes from 20 cm deep were greater by 10 dB. Application of the parametric array on larger technically difficult patients would offer similar benefits as those in sonar applications.