Quantitative contrast-enhanced ultrasound imaging: a review of sources of variability

Abstract

Ultrasound provides a valuable tool for medical diagnosis offering real-time imaging with excellent spatial resolution and low cost. The advent of microbubble contrast agents has provided the additional ability to obtain essential quantitative information relating to tissue vascularity, tissue perfusion and even endothelial wall function. This technique has shown great promise for diagnosis and monitoring in a wide range of clinical conditions such as cardiovascular diseases and cancer, with considerable potential benefits in terms of patient care. A key challenge of this technique, however, is the existence of significant variations in the imaging results, and the lack of understanding regarding their origin. The aim of this paper is to review the potential sources of variability in the quantification of tissue perfusion based on microbubble contrast-enhanced ultrasound images. These are divided into the following three categories: (i) factors relating to the scanner setting, which include transmission power, transmission focal depth, dynamic range, signal gain and transmission frequency, (ii) factors relating to the patient, which include body physical differences, physiological interaction of body with bubbles, propagation and attenuation through tissue, and tissue motion, and (iii) factors relating to the microbubbles, which include the type of bubbles and their stability, preparation and injection and dosage. It has been shown that the factors in all the three categories can significantly affect the imaging results and contribute to the variations observed. How these factors influence quantitative imaging is explained and possible methods for reducing such variations are discussed.

Effects of encapsulation damping on the excitation threshold for subharmonic generation from contrast microbubbles

“…Micron-size encapsulated bubbles (radius < 10 lm) are used in diagnostic ultrasound imaging as contrast enhancing agents (de Jong, 1996;Ferrara et al, 2007;Goldberg et al, 2001;Tang et al, 2011). They generate subharmonic signals that are utilized for subharmonic imaging-imaging at frequencies half that of the excitation (Forsberg et al, 2000;Shankar et al, 1998;Shankar et al, 1999).…”

Attenuation Correction and Normalisation for Quantification of Contrast Enhancement in Ultrasound Images of Carotid Arteries

“…Recently, contrast-enhanced ultrasound (CEUS) has made it possible to image and quantify neovascularisation in plaques as well as adventitial VV (Feinstein 2006). However, current quantification of contrast enhancement is significantly limited by spatially heterogeneous and patient-specific attenuation (Tang et al 2008(Tang et al , 2011. During a US scan, ultrasound echo from a target is affected by attenuation between the US transducer and the target.…”

Acoustic Estimation of Resonance Frequency and Sonodestruction of SonoVue Microbubbles

“…Burns and Becher (2000) showed that at low PNP the echo from MB is proportional to transmitted US signal, while at larger PNP values the echo exhibits some additional frequency components. These additional frequency components are usually whole or fractional multiples (harmonics) of the excitation US frequency (Tang et al, 2011). It was also shown that attenuation depends on excitation US frequency (Goertz et al, 2007;Emmer et al, 2009;Tang, Eckersley, 2007;.…”