title: Nonlinear ultrasound imaging of nanoscale acoustic biomolecules.
abstract: Ultrasound imaging is widely used to probe the mechanical structure of tissues and visualize blood flow. However, the ability of ultrasound to observe specific molecular and cellular signals is limited. Recently, a unique class of gas-filled protein nanostructures called gas vesicles (GVs) was introduced as nanoscale (∼250 nm) contrast agents for ultrasound, accompanied by the possibilities of genetic engineering, imaging of targets outside the vasculature and monitoring of cellular signals such as gene expression. These possibilities would be aided by methods to discriminate GV-generated ultrasound signals from anatomical background. Here, we show that the nonlinear response of engineered GVs to acoustic pressure enables selective imaging of these nanostructures using a tailored amplitude modulation strategy. Finite element modeling predicted a strongly nonlinear mechanical deformation and acoustic response to ultrasound in engineered GVs. This response was confirmed with ultrasound measurements in the range of 10 to 25 MHz. An amplitude modulation pulse sequence based on this nonlinear response allows engineered GVs to be distinguished from linear scatterers and other GV types with a contrast ratio greater than 11.5 dB. We demonstrate the effectiveness of this nonlinear imaging strategyin vitro,in cellulo, andin vivo.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, USA.
authors.forename: David
authors.identifier: 0000-0002-4921-6406
authors.initials: D
authors.lastname: Maresca
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology , Pasadena, California 91125, USA.
authors.forename: Anupama
authors.initials: A
authors.lastname: Lakshmanan
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, USA.
authors.forename: Audrey
authors.initials: A
authors.lastname: Lee-Gosselin
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology , Pasadena, California 91125, USA.
authors.forename: Johan M
authors.initials: JM
authors.lastname: Melis
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, USA.
authors.forename: Yu-Li
authors.initials: YL
authors.lastname: Ni
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, USA.
authors.forename: Raymond W
authors.identifier: 0000-0003-2202-1980
authors.initials: RW
authors.lastname: Bourdeau
authors.affiliation: Division of Engineering and Applied Science, California Institute of Technology , Pasadena, California 91125, USA.
authors.forename: Dennis M
authors.initials: DM
authors.lastname: Kochmann
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, USA.
authors.forename: Mikhail G
authors.identifier: 0000-0002-0291-4215
authors.initials: MG
authors.lastname: Shapiro