Spectroscopic photoacoustic imaging of lipid-rich plaques in the human aorta in the 740 to 1400 nm wavelength range

Abstract

Spectroscopic photoacoustic imaging has the potential to discriminate between normal and lipid-rich atheromatous areas of arterial tissue by exploiting the differences in the absorption spectra of lipids and normal arterial tissue in the 740 to 1400 nm wavelength range. Identification of regions of high lipid concentration would be useful to identify plaques that are likely to rupture (vulnerable plaques). To demonstrate the feasibility of visualizing lipid-rich plaques, samples of human aortas were imaged in forward mode, at wavelengths of 970 and 1210 nm. It was shown that the structure of the arterial wall and the boundaries of lipid-rich plaques obtained from the photoacoustic images were in good agreement with histology. The presence of lipids was also confirmed by comparing the photoacoustic spectra (740 to 1400 nm) obtained in a region within the plaque to the spectral signature of lipids. Furthermore, a lipid-rich plaque was successfully imaged while illuminating the sample through 2.8 mm of blood demonstrating the possibility of implementing the photoacoustic technique in vivo.

Characterizing Phantom Arteries with Multi-channel Laser Ultrasonics and Photo-acoustics

“…However, true calcification has higher impedance. Using the acoustic velocity of calcification [∼ 2000 m/s 14] and the density of the primary component of calcification, hydroxyapatite [∼ 3.0 g/cm 3 10], a rough estimate for the acoustic impedance is ∼ 6 N·s/cm 3 . Acrylic has an acoustic velocity ∼ 2700 m/s and density ∼ 1.2 g/cm 3 [1], resulting in an impedance of 3.2 N·s/cm 3 .…”

“…For example, lipids are imaged with high resolution and contrast [3]. PA imaging is absorption based.…”

“…Recently, the optical spectrum of lipids was exploited to visualize lipid pools within the wall of a human aorta using PA imaging [3]. Additional advances include characterization of atheroscle-2 rotic plaques using intravascular ultrasound and photoacoustic techniques [32,51,54], and PA detection of the inflammatory response of atherosclerotic lesions using gold nanorods as a targeting agent [22,29,60].…”

The Laser Technology: New Trends in Biology and Medicine

“…Photo-acoustic imaging uses the intrinsic chromophore, which has an optical absorption signature, as long as appropriate irradiation wavelengths are applied. It is used for example for haemoglobin [66], melanin [67], water [68] or lipid [69].…”

Feasibility ofin vivointravascular photoacoustic imaging using integrated ultrasound and photoacoustic imaging catheter

“…To overcome this limitation, a photoacoustic characterization of arterial tissues has been investigated. [2][3][4][5] In photoacoustic imaging, which is being explored for a wide range of biomedical applications, 6 the contrast is based on differences of light absorption of various tissues. Short laser pulses are absorbed by tissues and converted into heat due to fast nonradiative relaxation.…”