The catheter-based intravascular photoacoustic (IVPA) imaging for diagnosing atherosclerosis, which can provide optical absorption contrast of the arterial wall besides acoustic scattering contrast from the conventional intravascular ultrasound (IVUS) imaging, has been intensively researched recently. The resolution of IVPA is determined by the frequency bandwidth of an ultrasonic transducer. Higher resolution can be achieved by increasing the transducer's working frequency and bandwidth. We introduce IVPA imaging at 35 and 80 MHz by using newly designed integrated IVUS/IVPA probes. This is the first time IVPA has been achieved as high as 80 MHz. Six-micrometer tungsten wires were imaged to evaluate the probes' spatial resolutions and beam patterns. Healthy rabbit aorta was imaged in vitro. Imaging results show that IVPA has superior contrast over IVUS in identifying the arterial wall, and IVPA at 80 MHz demonstrates extraordinary resolution (35 μm) compared to 35 MHz.
Intravascular ultrasound (IVUS) is mature imaging modality to diagnose blood vessel disease, especially for calcification characterization. Based on the intrinsic optical absorption, intravascular photoacoustic (IVPA) works as a complementary method to IVUS. In this paper, we develop a miniature intravascular probe combined photoacoustic and ultrasound imaging. The optical components and ultrasound transducer were integrated to achieve internal illumination. Atherosclerotic human artery was imaged ex vivo, which demonstrates the imaging ability of the multi-functional probe and illustrate its clinical potential.
Arterial wall is composed of three layers: intima, media and adventitia. Intima-media thickness (IMT) is an important
prognostic indicator of atherosclerotic diseases. Although intravascular ultrasound (IVUS) imaging is a commonly used
method for delineation of the layered structures, it is inferior to the optical absorption contrast offered by intravascular
photoacoustic (IVPA) imaging. We introduce an integrated miniature probe that combines the capabilities of IVUS and
IVPA imaging for the evaluation of arterial wall layered structures. Healthy rabbit aorta was imaged ex vivo. IVPA
results showed superior contrast over IVUS in identifying the layered structures of arterial wall.
For in vivo medical applications, endoscopy shows great potential for its minimally invasive manner,
flexibility and close-up imaging characteristic. A miniaturized imaging probe combining ultrasound and
photoacoustic endoscopy has been developed. The output of a 532-nm pulse laser was coupled into and
delivered to the probe by a 200-micron-core multimode fiber. A 40 MHz ring shape ultrasound transducer
was fabricated to receive pulse echo ultrasound and photoacoustic signals as well. The light-guiding optical
fiber, the ring ultrasound transducer, and a mirror-based reflective material for the coaxial laser beam and
ultrasound signal were integrated into the probe with a final packaged diameter of 2.5 mm. The
performance of the probe was tested by imaging a graphite rod. The imaging ability of this dual-modality
system was demonstrated by imaging the cross section of a rabbit aorta.
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