Resolution and material assessment capability of a vibroacoustographic imaging system

Abstract

There has been significant growth in non-invasive screening techniques for evaluating abnormal tissue. Vibroacoustography (VA), an imaging modality based on ultrasound-stimulated acoustic emission and non-linear scattering characteristics of the target, has previously been used to generate relative real-time, pathology-specific image contrast between abnormal tissue and normal surrounding tissue; however, an in-depth tissue assessment has yet to be completed. VA utilizes two non-destructive low MHz ultrasound tones to produce an acoustic beat frequency in the low kHz range. The acoustic radiation force perturbs the target as a function of its mechanical and acoustic properties and the emissive acoustic waves are detected by a nearby hydrophone to form an image based on the viscoelastic characteristics of the target. We have previously reported that our VA imaging system can distinguish suspect tissue from normal tissue in tissue-mimicking phantoms (TMPs) and ex vivo models with high image contrast; however, the goal of this work is to assess the measurement performance and resolution capabilities of this system in pre-clinical models, specifically TMPs in tissue assessment. Lateral and axial resolution, as well as material characterization, studies were performed on isotropic two-layered and multiple-layered TMP targets. The resolution studies resulted in ∼1 mm lateral and ∼12 mm axial, which were confirmed and validated for a confocal transducer geometry. The system showed sufficient measurement performance to detect regions with elastic moduli difference of at least 10 kPa and lateral width of at least 4 mm. This result, coupled with high imaging contrast, supports the utilization of VA for potential applications in in vivo medical imaging and tissue assessment for intraoperative applications.