Detecting pulmonary nodules by using ultrasound multiple scattering

Abstract

Although X-Ray Computed Tomography (CT) is widely used for detecting pulmonary nodules inside the parenchyma, it cannot be used during video-assisted surgical procedures. Real-time, non-ionizing, ultrasound-based techniques are an attractive alternative for nodule localization to ensure safe resection margins during surgery. Conventional ultrasound B-mode imaging of the lung is challenging due to multiple scattering. However, the multiple scattering contribution can be exploited to detect regions inside the lung containing no scatterers. Pulmonary nodules are homogeneous regions in contrast to the highly scattering parenchyma containing millions of air-filled alveoli. We developed a method relying on mapping the multiple scattering contribution inside the highly scattering lung to detect and localize pulmonary nodules. Impulse response matrices were acquired in ex-vivo pig and dog lungs using a linear array transducer to semi-locally investigate the backscattered field. Extracting the multiple-scattering contribution using singular-value decomposition and combining it with a depression detection algorithm allowed us to detect and localize regions with less multiple scattering, associated with the nodules. The feasibility of this method was demonstrated in five ex-vivo lungs containing a total of 20 artificial nodules. Ninety-five percent of the nodules were detected. Nodule depth and diameter significantly correlated with their ex-vivo CT-estimated counterparts (R = 0.960, 0.563, respectively).

State of the Art in Lung Ultrasound, Shifting from Qualitative to Quantitative Analyses

“…Indeed, when the quantity of fluid increases, the mean distance between scatterers increases, thus increasing L* (Mohanty et al 2017). In the following years, similar techniques were experimentally tested to differentiate rat lungs with pulmonary fibrosis (PF) from healthy lungs (Mohanty et al 2020), detect pulmonary nodules (regions inside lungs containing no scatterers) (Roshankhah et al 2021a) and differentiate rat lungs affected by PF (or edema) from healthy lungs of control rats (Lye et al 2021).…”

Design Optimization and Tradeoff Analysis of an Actuated Continuum Probe for Pulmonary Nodule Localization and Resection

“…Furthermore, ultrasound is not considered a viable method for lung imaging as the lung's air-filled alveoli introduce air-liquid interfaces that cause the significant multiple scattering (MS) of ultrasound waves. MS occurs when a wave experiences multiple reflections before returning to the transducer, as opposed to single reflection events, defined as single scattering (SS) [14]. MS introduces nonlinearity to the relationship between propagation time and the distance from the transducer due to wave distortion and absorption.…”

“…For these reasons, research by Roshankhah, et al [14] introduced a modified ultrasound imaging approach to pulmonary nodule localization that utilizes both multiple scattering (MS) and single scattering (SS) to enhance the effectiveness of margin delineation via real-time imaging. Because alveoli do not exist in pulmonary nodules, MS is reduced significantly in comparison to adjacent lung tissue.…”

“…Such a device, deployed through intercostal ports, would enable the intraoperative imaging and precise mapping of nodules for improved margins and improved patient outcomes. Reproduced from [14], with the permission of the Acoustical Society of America. Such a device, deployed through intercostal ports, would enable the intraoperative imaging and precise mapping of nodules for improved margins and improved patient outcomes.…”

“…(Right) rendered map using depression detection algorithm to quantify the standard deviation of SS intensity, showcasing nodule location in white. Reproduced from[14], with the permission of the Acoustical Society of America.…”