High speed intravascular photoacoustic imaging with fast optical parametric oscillator laser at 1.7 μm

Abstract

Intravascular photoacoustic imaging at 1.7 lm spectral band has shown promising capabilities for lipid-rich vulnerable atherosclerotic plaque detection. In this work, we report a high speed catheterbased integrated intravascular photoacoustic/intravascular ultrasound (IVPA/IVUS) imaging system with a 500 Hz optical parametric oscillator laser at 1725 nm. A lipid-mimicking phantom and atherosclerotic rabbit abdominal aorta were imaged at 1 frame per second, which is two orders of magnitude faster than previously reported in IVPA imaging with the same wavelength. Clear photoacoustic signals by the absorption of lipid rich deposition demonstrated the ability of the system for high speed vulnerable atherosclerotic plaques detection. V C 2015 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4929584] Acute cardiovascular events are mostly due to blood clots or thrombus induced by the sudden rupture of vulnerable atherosclerotic plaques within the coronary artery wall. 1,2Thin-cap fibroatheroma (TCFA) has a large, lipid-rich, necrotic core, which has been demonstrated as a primary type of vulnerable atherosclerotic plaque with a high risk to ruptures.3-5 Accurate quantification of both the morphology and composition of a plaque are essential for early detection and optimal treatment in clinics. Several catheter-based intravascular imaging techniques have been investigated. Intravascular ultrasound (IVUS) has been widely used in clinics 4-6 and provides structural information of the atherosclerotic plaque with good penetration depth and axial resolutions of approximately 70 lm. However, the contrast between the lipid-rich region and other soft tissues is limited.6-8 Optical coherence tomography (OCT) has a higher axial resolution of $10 lm, which is ideal for thin fibrous cap thickness measurements, but the penetration depth is less than 2 mm and generally requires blood to be flushed from the imaging area.9,10 Intravascular near-infrared reflection spectroscopy (NIRS) identifies the presence of lipid-rich plaque by detection of the reflection spectrum of the vascular wall, but lacks depth resolution. 11,12Photoacoustic (PA) imaging is a hybrid imaging technique that detects the ultrasound signals generated by the absorption of short pulsed laser inside tissue.13-15 Based on the optical absorption contrast of the tissues within the vessel wall, intravascular photoacoustic (IVPA) imaging for characterizing plaque compositions has been studied. [16][17][18][19][20][21][22][23][24][25][26][27] Recently, due to the high optical absorption by first overtone of C-H bonds around 1720 nm, IVPA imaging of lipid-rich atherosclerotic plaque at 1.7 lm spectral band has been attracting great attention. 21,28 However, current IVPA imaging speed is limited by the repetition rate of commercial nanosecond lasers at 1.7 lm. Using a laser with 10 Hz repetition rate, one cross-sectional image requires tens of seconds to finish, which limits the translation of the technology for in vivo application. 16,18,21,23,24 In this letter, we report o...

Real-time volumetric lipid imaging in vivo by intravascular photoacoustics at 20 frames per second

“…Partially due to ineffective coupling and scattering at the catheter tip, the optical exposure is less than 0.4 J/cm 2 at 1.7 µm, which is below the 1 J/cm 2 threshold specified by the ANSI laser safety standard [22]. Despite using a pulse energy which is one order of magnitude lower than that used previously in IVPA/US systems working at 1.7 µm, the PA SNR achieved in our imaging system was 20 dB, comparable to earlier reports [22,23]. We used pork lard as a lipid target for in vivo imaging, which has a different lipid composition, and thus a slightly different absorption spectrum, compared to lipid-rich plaque [20].…”

“…It is the first in vivo IVPA/US imaging in a coronary artery reported to date, acquiring images of coronary lipid in this highly mobile, challenging environment. Our IVPA/US imaging system significantly increased the imaging speed from 1 fps (the fastest imaging speed reported so far for a lipidimaging IVPA system) to 20 fps [21][22][23]31]. The operating parameters of our implementation of this technology match those desired of a clinical imaging system in terms of acquisition speed, operating wavelength, and scan method.…”

“…An intensive research effort is ongoing towards the further development of IVPA/US imaging systems. Imaging speed is primarily limited by laser pulse rate: with the introduction of 500 Hz to 2 kHz repetition rate laser systems, operating at the wavelengths of lipid absorption peaks near 1.2 µm or 1.7 µm, the IVPA/US lipid imaging speed has recently increased to about 1 frame per second (fps) [21][22][23]. Use of a more conventional laser wavelength facilitates speed but offers limited biological image contrast [24].…”

Fully integrated optical coherence tomography, ultrasound, and indocyanine green-based fluorescence tri-modality system for intravascular imaging

“…For intravascular imaging, near-infrared fluorescence (NIRF) imaging can be used to identify inflammatory reaction, which is one of the main characteristics of vulnerable plaques [8]. However, most imaging systems focus on one or dual-modality imaging [9][10][11][12][13]18,19], which are not enough for an accurate characterization of these characteristics (large lipid pool, thin fibrous cap, and major inflammatory reaction). For example, it is difficult to identify whether there is a thin fibrous cap or not by using a combined NIRF and IVUS system.…”

Q-switched Erbium-doped fiber laser at 1600 nm for photoacoustic imaging application

“…10,11 Traditionally, a dye laser or an optical parametric oscillator (OPO) is used to generate the laser at the specified wavelength in the NIR region. 9,12 However, the PRR of these lasers is usually in the 10 Hz to kHz level, which is too slow for real-time imaging. On the other hand, intensity modulated laser diodes (LDs) with several kHz PRR have been demonstrated as an alternative source for PAI.…”