In vivo detection of nanoparticles in mouse cancer using an integrated photoacoustic micro-ultrasound system

John Sun, Andrew Heinmiller, Dave Bates, Andrew Needles, Catherine Theodoropoulos

VisualSonics Inc., Toronto, ON, Canada

Introduction:•Photoacoustics is a rapidly-emerging imaging

modality that combines the sensitivity of optical and resolution of ultrasound imaging

•A state-of-the-art photoacoustic system was recently developed that co-registers high-resolution micro-ultrasound and high sensitivity photoacoustic images

•Nano-sized agents present an enormous potential in many research fields and can be imaged with photoacoustics

Objectives:•To assess the utility of various nano-sized agents as

photoacoustic contrast agents•To assess gold nanorod imaging in mouse tumor•To compare tumor ultrasound contrast flow and

photoacoustic gold nanorod accumulation

Methods:

Photoacoustics (Vevo® LAZR System, VisualSonics, Toronto, Canada): •Tuneable laser (680-970 nm)• Integrated fibre optics linear array (Fc = 21 MHz)

photoacoustic transducer (LZ250, VisualSonics)

Vessel Phantom Study •Nanoparticle agents filled PE20 tubing and were

imaged in water•Nanoparticles used were:

» Gold nanoparticles: Gold nanorod (Nanopartz, Loveland, California), gold nanoshell (Nanospectra, Houston, Texas)

» Fluorescent agents: Angiosense 680 and 750 (PerkinElmer, Waltham, MA), IRDye800 (Li-Cor, Lincoln, Nebraska)

•Concentrations used for gold nanoparticles were 1.5 mgAu/mL and for fluorescent agents were 20 nmol/mL

•Laser fluence was kept under 4 mJ/cm2 to avoid deformation of the nanoparticles

•Each nanoparticle’s respective peak absorption wavelength was used for photoacoustic imaging

Mouse Study: •Female hairless SCID mice with subcutaneous

tumors were imaged•150 µL of 1.5 mgAu/mL of gold nanorods (Ntracker,

Nanopartz) were injected intravenously through the tail vein

•Tumor photoacoustic intensity was measured up to 3 hours post injection

•50 µL of ultrasound contrast (Vevo MicroMarker® Contrast Agent, VisualSonics) was injected intravenously to assess tumor perfusion

•Tumor perfusion was correlated to gold nanorod accumulation in the tumor

•Gold nanorod accumulations in the tumor and mammary fat pad were compared

Results:• In the vessel phantom study, gold nanorods showed

the greatest photoacoustic intensity (Figure 1a). Though fluorescent agents yield lower intensities, however they were significantly greater than that observed in saline

•Following intravenous injection of gold nanorods, photoacoustic intensity showed a greater increase in the tumor relative to the mammary fat pad (Figure 2)

•Amount of gold nanorod accumulation in the tumor showed an inverse correlation to tumor perfusion measured by ultrasound contrast imaging (Figure 1B)

Summary:•The Vevo LAZR photoacoustic imaging system can

detect and quantify gold nanorod accumulation in mouse tumors.

•Preferential accumulation of gold nanorods was observed in the tumor, likely due to its leaky vasculature

•Perfusion assessed by ultrasound contrast imaging appeared to be inversely correlated to the amount of gold nanorod accumulation in the tumor

•Florescent agents can be detected with photoacoustic imaging, hence they may be viable photoacoustic contrast agents

http://www.visualsonics.com/photoacoustic-technology

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Figure 2. Much higher amount of gold nanorod accumulation in the tumor was observed than compared to the mammary fat pad.

Figure 3. A) Tumor with high amount gold nanorod accumulation and low ultrasound contrast perfusion B) Tumor with low amount of gold nanorod accumulation and high ultrasound contrast perfusion.

Figure 1. A) Photoacoustic intensity of various contrast agents. B) Correlation between ultrasound contrast perfusion and gold nanorod accumulation in mouse tumor.

A) B)

• Tumor • Mammary fat pad

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PA intensity∆ = 9.8

PE = 19.6

PA intensity∆ = 1.1

PE = 82.3