KEYWORDS: Signal detection, Optical coherence tomography, Optical amplifiers, Tissues, Signal attenuation, Photodetectors, Image quality, Imaging systems, Optical instrument design, Signal to noise ratio
Significance: Optical coherence tomography (OCT) has been widely used in clinical studies. However, the image quality of OCT decreases with increasing imaging depth since the light is rapidly attenuated in biological tissues.
Aim: We present a compensation approach to preserve weak high-frequency signals from deep structures and compress the dynamic range of the detected signal for superior analog-to-digital conversion and image display capability.
Approach: A homemade frequency gain compensation amplifier is designed and fabricated to amplify the electrical signal from a balanced photodetector and compensate for the signal attenuation in swept-source OCT (SSOCT).
Results: It is demonstrated in imaging various objects that this cost-efficient technique effectively enhances the contrast of the deep tissue image.
Conclusions: A frequency gain compensation amplifier is designed and used to compress the dynamic range of the electrical signal detected by the photodetector of an SSOCT system, which enables weak signals from deep structures to be acquired by the ADC and displayed with enhanced local contrast.
Optical coherence tomography (OCT) has been widely used in clinic studies due to the capability to provide high resolution cross sectional images in biological tissue. To achieve real-time imaging display, Graphics Processing Unit (GPU) acceleration is usually used in data processing including Fast Fourier Transform, linearization in k space, and logarithm scaling, however, with additional cost and requirement of complex coding tools such as CUDA. In this paper,a hash table method is used to accelerate the computing speed of logarithm scaling without GPU. For original logarithm scaling in C library, the procession time for an A-line with 2048 points is approximately 10 times longer than this optimized method. A swept source OCT was employed to test this method and the results demonstrated that a high speed real-time OCT imaging display can be achieved with this low cost method.
Saturation artifacts that are commonly observed in endoscopic swept-source optical coherence tomography (SSOCT) images cause image degradation and loss of image information. We present work on the correction of saturation effects in endoscopic SSOCT imaging. This method utilizes a broadband power divider with excellent pick-off flatness to divide the detected interference signal into the two channels of an analog-to-digital converter. Based on the precise calibration of the splitting ratio between the two channels, the maximum measurable signal power of the system was drastically increased by using the low level signal in one channel to correct the saturated signal in the other channel. The experimental results demonstrated that this technique can efficiently correct the saturation artifacts in endoscopic two- and three-dimensional SSOCT images in an accurate and cost-effective manner.
Swept source optical coherence tomography (SSOCT) is an attractive biological imaging technology due to its
advantages of simple setup and high imaging speed. As the light intensity attenuated rapidly in high scattering biological
tissues, the contrast of OCT image will drop with depth. In this paper a new method was introduced to compensate the
attenuation of imaging contrast in SSOCT. The interference signal was divided into two channels of analog to digital
converter (ADC) with a splitting ratio of 1:5. The higher level signal in one channel was used to reconstruct deeper
structure of tissue and the lower level signal in the other channel was used to reconstruct surface structure of tissue. Lowfrequency
signals in one channel were filtered by a high pass filter and then combined with the signal in the other
channel to obtain a high contrast image in both surface and deep area of tissue. Human finger and porcine airway
imaging obtained with the system show that the contrast of SSOCT images can be improved in deeper region of tissue.
A technique to suppress saturation artifacts in swept source optical
coherence tomography (SSOCT) system was presented. The detected signal
was split into two channels of a high speed data acquisition card with two
levels by a power divider. The signal in one channel with higher level was
used to reconstruct OCT images and the signal in the other channel with
lower level was used to compensate the saturated signal in the first channel by
calibrating the splitting ratio between the two channels. Based on dual
channel detection, this technique can enhance the dynamic range of SSOCT
system and remove saturation artifacts in OCT imaging with simple and cost
effective design. Imaging of human finger with the system demonstrated that
this method can achieve high dynamic range without saturation artifacts in
SSOCT.
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