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Modulating Nonlinear Acoustic Response of Phospholipid-Coated Microbubbles with pH for Ultrasound Imaging. | LitMetric

AI Article Synopsis

  • Activatable microbubble contrast agents can be used in ultrasound imaging to evaluate physiological and pathological conditions, such as tumor acidity.
  • A novel study found that phosphatidylcholine microbubbles show increased harmonic oscillation at lower pH levels, resulting in a threefold increase in signal intensity when pH is lowered from 7.4 to 5.5.
  • This pH-dependent activation relies on the chemical structure of the microbubble shell and could lead to improved ultrasound contrast agents for better tumor imaging, but more research is needed to understand the effects of pH in clinical settings.

Article Abstract

Activatable microbubble contrast agents for contrast-enhanced ultrasound have a potential role for measuring physiologic and pathologic states in deep tissues, including tumor acidosis. In this study, we describe a novel observation of increased harmonic oscillation of phosphatidylcholine microbubbles (PC-MBs) in response to lower ambient pH using a clinical ultrasound scanner. MB echogenicity and nonlinear echoes were monitored at neutral and acidic pH using B-mode and Cadence contrast pulse sequencing (CPS), a harmonic imaging technique at 7.0 and 1.5 MHz. A 3-fold increase in harmonic signal intensity was observed when the pH of PC-MB suspensions was decreased from 7.4 to 5.5 to mimic normal and pathophysiological levels that can be encountered . This pH-mediated activation is tunable based on the chemical structure and length of phospholipids composing the MB shell. It is also reliant on the presence of phosphate groups, as the use of lipids without phosphate instead of phospholipids completely abrogated this phenomenon. The increased harmonic signal likely is the result of increased MB oscillation caused by a decrease of the interfacial tension induced at a lower pH, altering the lipid conformation. While relative signal changes are interpreted clinically as mostly related to blood flow, pH effects could be significant contributors, particularly when imaging tumors. While our observation can be used clinically, it requires further research to isolate the effect of pH from other variables. These findings could pave the way toward for the development of new smart ultrasound contrast agents that expand the clinical utility of contrast-enhanced ultrasound.

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Source
http://dx.doi.org/10.1021/acssensors.3c02382DOI Listing

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