Xiumei Liu

Rapid-scanning forward-imaging miniature endoscope for real-time optical coherence tomography.

We developed a miniature endoscope that is capable of rapid lateral scanning and is suitable for real-time forward-imaging optical coherence tomography (OCT). The endoscope has an outer diameter of 2.4 mm, consisting of a miniature tubular lead zirconate titanate (PZT) actuator, a single-mode fiber-optic cantilever, and a graded-index lens. Rapid lateral scanning at 2.8 kHz is achieved when the fiber-optic cantilever is resonated with the PZT actuator. This allows OCT imaging to be performed by fast lateral beam scanning followed by slow depth scanning, which is different from the conventional OCT imaging sequence. Real-time OCT imaging with the endoscope operated in the new image acquisition sequence at 6 frames/s is demonstrated.

Rapid scanning all-reflective optical delay line for real-time optical coherence tomography.

We describe a dispersion-free high-speed scanning optical delay line that is suitable for real-time optical coherence tomography, in particular, when an ultrabroadband light source is used. The delay line is based on all-reflective optics consisting of two flat and one curved mirrors. We achieve optical path-length scanning by oscillating one of the two flat mirrors with a resonant galvanometer. The delay line is compact and easy to implement. A total scanning depth of 1.50 mm with an 89% duty ratio, a maximal scanning speed of approximately 9.1 m/s, and a 4.1-kHz repetition rate has been demonstrated.

Continuous focus tracking for real-time optical coherence tomography

We report an approach to achieving continuous focus tracking and a depth-independent transverse resolution for real-time optical coherence tomography (OCT) imaging. Continuous real-time focus tracking is permitted by use of a lateral-priority image acquisition sequence in which the depth-scanning rate is equivalent to the imaging frame rate. Real-time OCT imaging with continuous focus tracking is performed at 1 frame/s by reciprocal translation of a rapid lateral-scanning miniature imaging probe (e.g., an endoscope). The optical path length in the reference arm is scanned synchronously to ensure that the coherence gate coincides with the imaging beam focus. The image quality improvement is experimentally demonstrated by imaging a tissue phantom embedded with polystyrene microspheres and rabbit esophageal tissues.

Development of a fast scanning miniature probe and methods of dispersion management for high-resolution optical coherence tomography

We present a design of a miniature fiber-optic probe capable of rapid lateral scanning. The miniature probe permits forward-looking optical coherence tomography (OCT) imaging of internal organs in real time. Fast lateral scanning also enables a new real-time image acquisition sequence, potentially permitting real-time focus tracking. To perform sensitive heterodyne detection, a sufficient Doppler frequency is achieved by using an electro-optic (EO) phase modulator. In this paper we describe an effective approach to compensate the dispersion induced by the EO crystal up to the third order. We show that an optimal axial resolution offered by the light source can be recovered through the dispersion management. Preliminary results of real-time OCT imaging of biological tissues with the lateral-priority scanning probe are presented.

Optimization of optical spectral throughput of acousto-optic modulators for high-speed optical coherence tomography

We describe a generic method to optimize the optical spectral throughput of a pair of acousto-optic modulators (AOM) which can be used for introducing a frequency shift in ultrahigh-resolution heterodyne optical coherence tomography. Systematic and quantitative analysis of a pair of AOMs indicates that a configuration with a spectral bandwidth of more than 200 nm at a center wavelength of 825 nm (tunable) can be achieved. Using a pair of AOMs in conjunction with a broadband low coherence light source, real-time imaging of biological tissues with an axial resolution ~3 microm (in air) has been experimentally demonstrated with a high-speed OCT system.

Miniature lateral priority scanning endoscope for real-time forward-imaging optical coherence tomography

We developed a new forward-imaging miniature PZT-actuated endoscope of a 2.4-mm diameter, capable of rapid lateral scanning at 2.4 kHz. Real-time OCT imaging was demonstrated using an image acquisition sequence with lateral priority scanning.

Real-time ultrahigh-resolution lateral-priority OCT imaging with a broad spectrum throughput acousto-optic modulation

We describe a generic method to optimize the optical spectrum throughput of acousto-optic modulators for performing real-time lateral-priority OCT imaging with an axial resolution of /spl sim/2.3 /spl mu/m. Ultrahigh-resolution imaging of biological tissues is demonstrated.