Guy Lamouche

Review of tissue simulating phantoms with controllable optical, mechanical and structural properties for use in optical coherence tomography

We review the development of phantoms for optical coherence tomography (OCT) designed to replicate the optical, mechanical and structural properties of a range of tissues. Such phantoms are a key requirement for the continued development of OCT techniques and applications. We focus on phantoms based on silicone, fibrin and poly(vinyl alcohol) cryogels (PVA-C), as we believe these materials hold the most promise for durable and accurate replication of tissue properties.

Experimental validation of an optimized signal processing method to handle non-linearity in swept-source optical coherence tomography.

We evaluate various signal processing methods to handle the non-linearity in wavenumber space exhibited by most laser sources for swept-source optical coherence tomography. The following methods are compared for the same set of experimental data: non-uniform discrete Fourier transforms with Vandermonde matrix or with Lomb periodogram, resampling with linear interpolation or spline interpolation prior to fast-Fourier transform (FFT), and resampling with convolution prior to FFT. By selecting an optimized Kaiser-Bessel window to perform the convolution, we show that convolution followed by FFT is the most efficient method. It allows small fractional oversampling factor between 1 and 2, thus a minimal computational time, while retaining an excellent image quality.

Deformable and durable phantoms with controlled density of scatterers.

We have developed deformable and durable optical tissue phantoms with a simple and well-defined microstructure including a novel combination of scatterers and a matrix material. These were developed for speckle and elastography investigations in optical coherence tomography, but should prove useful in many other fields. We present in detail the fabrication process which involves embedding silica microspheres in a silicone matrix. We also characterize the resulting phantoms with scanning electron microscopy and optical measurements. To our knowledge, no such phantoms were proposed in the literature before. Our technique has a wide range of applicability and could also be adapted to fabricate phantoms with various optical and mechanical properties.

Artifact removal in Fourier-domain optical coherence tomography with a piezoelectric fiber stretcher

We describe an artifact removal setup swept-source optical coherence tomography (OCT) system that enables high-speed full-range imaging. We implement a piezoelectric fiber stretcher to generate a periodic phase shift between successive A-scans, thus introducing a transverse modulation. The depth ambiguity is then resolved by performing a Fourier filtering in the transverse direction before processing the data in the axial direction. The dc artifact is also removed. The key factor is that the piezoelectric fiber stretcher can be used to generate discrete phase shifts with a high repetition rate. The proposed experimental setup is a much improved version of the previously reported B-M mode scanning for spectral-domain OCT in that it does not generate additional artifacts. It is a simple and low-cost solution for artifact removal that can easily be applied.

Common path swept-source OCT interferometer with artifact removal

We present here the implementation of a fiber-based common-path interferometer for Swept Source Optical Coherence Tomography (SS-OCT). A common path configuration is often a suitable approach for increasing the stability of the measurements. Optical fibers are sensitive to temperature and some other mechanical perturbations which compromise absolute accuracy measurements. A common-path configuration provides a mean to define a reference at the probe location and, thereby, to compensate for the optical path length perturbations. Additionally, in SS-OCT, we have to deal with autocorrelation noise and the mirror image artifact due to the computation of the Fourier transform. Thus, our common-path implementation also includes acousto-optics modulators to remove the depth degeneracy as it has already been done when using a traditional interferometer configuration. The efficiency of our system is validated by comparing images acquired with a traditional SS-OCT configuration and with our common path SS-OCT configuration.

Optical delay line using rotating rhombic prisms

We propose a robust and efficient delay line using an ensemble of rotating rhombic prisms. Delay lines relying on rotating elements provide fast and stable operation. Optical systems using rhombic prisms are quite easy to align since these prisms are efficient even when slightly misaligned. Optical delay lines with a single rotating element usually have a poor duty cycle and show large nonlinearity in the variation of the optical path lengh with the angular position. Our delay line improves over existing technology by using off-centroid rotation and reinjection. Off-centroid rotation allows the use of multiple prisms and, by optimizing the conditions of operation, the duty cycle is increased and the nonlinearity is decreased. The duty cycle and repetition rate are further increased by reinjecting the incoming ray towards the delay line when it is not first intercepted by the prism ensemble. We have designed and built such a delay line using five prisms. The experimental device was tested at 2000 delay scans per second and provided a duty cycle larger than 80% with about 5% nonlinearity. Higher delay scan rates are easily achievable with this technology. The delay line was introduced in a time-domain optical coherence tomography system and example of imaging of biological tissue is provided.

Artery phantoms for intravascular optical coherence tomography: healthy arteries.

We present a method to make phantoms of coronary arteries for intravascular optical coherence tomography (IV-OCT). The phantoms provide a calibrated OCT response similar to the layered structure of arteries. The optical properties of each layer are achieved with specific concentrations of alumina and carbon black in a silicone matrix. This composition insures high durability and also approximates the elastic properties of arteries. The phantoms are fabricated in a tubular shape by the successive deposition and curing of liquid silicone mixtures on a lathe setup.

Intravascular optical coherence tomography on a beating heart model

The advantages and limitations of using a beating heart model in the development of intravascular optical coherence tomography are discussed. The model fills the gap between bench experiments, performed on phantoms and excised arteries, and whole animal in-vivo preparations. The beating heart model is stable for many hours, allowing for extended measurement times and multiple imaging sessions under in-vivo conditions without the complications of maintaining whole-animal preparation. The perfusate supplying the heart with nutrients can be switched between light scattering blood to a nonscattering perfusate to allow the optical system to be optimized without the need of an efficient blood displacement strategy. Direct access to the coronary vessels means that there is no need for x-ray fluoroscopic guidance of the catheter to the heart, as is the case in whole animal preparation. The model proves to be a valuable asset in the development of our intravascular optical coherence tomography technology.

Surface inspection of hard to reach industrial parts using low-coherence interferometry

Optical inspection tools based on low-coherence interferometry and specialized for hard to reach industrial parts are presented. A common path configuration using optical fiber components is described. Small diameter probes originally developed for biomedical applications have been specialized for industrial inspection. Probes that can be used with a Cartesian surface scanning system or a cylindrical scanning system are presented. The probes include a reference that makes absolute accuracy measurements easier. Characterization of the internal surface of a worn plasma torch electrode has been realized using that technique. Surface profiling of the barrel of a gun was also performed.

Artery phantoms for intravascular optical coherence tomography: diseased arteries

Abstract. We propose and test various strategies for the creation of artery phantoms mimicking different kinds of diseased arteries when imaged by intravascular optical coherence tomography (IVOCT). We first review the method for making healthy artery phantoms. We then describe the procedure to fabricate diseased artery phantoms with intima thickening, lipid pool, thin-capped fibroatheroma, calcification, and restenosis (homogeneous and layered) after stent apposition. For each case, a phantom is fabricated, an IVOCT image is obtained, and the image is compared to that of a real artery.