Vibroacoustographic System for Tumor Identification

Abstract

Oral and head and neck squamous cell carcinoma (OSCC) is the sixth most common cancer worldwide. The primary management of OSCC relies on complete surgical resection of the tumor. Margin-free resection, however, is difficult given the devastating effects of aggressive surgery. Currently, surgeons determine where cuts are made by palpating edges of the tumor. Accuracy varies based on the surgeon's experience, the location and type of tumor, and the risk of damage to adjacent structures limiting resection margins. To fulfill this surgical need, we contrast tissue regions by identifying disparities in viscoelasticity by mixing two ultrasonic beams to produce a beat frequency, a technique termed vibroacoustography (VA). In our system, an extended focal length of the acoustic stress field yields surgeons' high resolution to detect focal lesions in deep tissue. VA offers 3D imaging by focusing its imaging plane at multiple axial cross-sections within tissue. Our efforts culminate in production of a mobile VA system generating image contrast between normal and abnormal tissue in minutes. We model the spatial direction of the generated acoustic field and generate images from tissue-mimicking phantoms and ex vivo specimens with squamous cell carcinoma of the tongue to qualitatively demonstrate the functionality of our system. These preliminary results warrant additional validation as we continue clinical trials of ex vivo tissue. This tool may prove especially useful for finding tumors that are deep within tissue and often missed by surgeons. The complete primary resection of tumors may reduce recurrence and ultimately improve patient outcomes.

Keywords: head and neck cancer; intraoperative imaging; tumor imaging.

Figure 1

Vibroacoustography system schematic and design. A) System transceiver with labeled components, B) The system possesses function generators (f₁ and f₂) for creating the ultrasonic tones of difference frequency (Δf), 3dB splitters to divide the signals, mixer to mix the two split signals for a reference in the Lock-in amplifier, power amplifiers (PAs) to augment the input signals to the transducer, low noise amplifier (LNA), among other designated components.

Figure 2

Multiphysics simulation of system. Electric potential profiles of the inner and outer PZT elements (bottom) that emit two acoustic beams into the control volume that focus at a common focal point. The intensity of the acoustic field is given by the rightmost colorbar in Pascals, whereas the PZT electric potential is given by the leftmost colorbarin Volts. The acoustic beams from the elements are directed towards the focal point in the Z (vertical) and X (horizontal) directions.

Figure 3

System validation with phantoms. A) VA scan of rectangular PVA phantom; pixel color is based on the amplitude of the acoustic emission at the given spatial position within the sample, B) VA image of circular PVA phantoms, C) High resolution photograph of rectangular PVA phantom in orientation from which the VA image was generated, D) High resolution photograph of circular PVA phantoms.

Figure 4

Ex vivo image of human tongue with squamous cell carcinoma; first sample. A) Histological section of the specimen, B) Graphical representation of the specimen, C) High resolution visible image of the sample, D) VA image of the power of acoustic emission from the sample at 38 kHz represented by colored pixels.

Figure 5

Ex vivo image of human tongue with squamous cell carcinoma; second sample. A) Histological section of the resected tissue, B) Diagram of resected ex vivo tissue dimensions, C) High resolution photograph of resected ex vivo tissue, D) VA scan of ex vivo tongue reconstructed into a 2D image with VA amplitude measurement.