光学相干层析多普勒成像功能拓展研究

光学多普勒成像(Optical Doppler tomography,ODT)是一种结合了光学相干层析成像技术(Opticalcoherence tomography,OCT)和多普勒流速仪的非侵入、非接触的成像技术,能够实现对高散介质组织内部的血管分布和血液流速的探测。阐述了基于数字希尔伯特变换的相位分离多普勒光学相干层析成像技术的工作原理,并且通过对玻璃毛细管和生物芯片微通道管中聚苯乙烯溶液流速的实验测量,准确测量管内微粒缓慢移动时的多普勒频移量,获得了玻璃管内和生物芯片微通道管中流速分布曲线,证实了所提方法的可行性。获取的多普勒图像具有较高的空间分辨力和速度分辨力,在未来的临床应用中有潜在的应用价值。     

Noninvasive imaging of in vivo blood flow velocity using optical Doppler tomography

We report the development of an optical technique for noninvasive imaging of in vivo blood flow dynamics and tissue structures with high spatial resolution (2-10 microm) in biological systems. The technique is based on optical Doppler tomography (ODT), which combines Doppler velocimetry with optical coherence tomography to measure blood flow velocity at discrete spatial locations. The exceptionally high resolution of ODT permits noninvasive in vivo imaging of both blood microcirculation and tissue structures surrounding the vessel, which has significance for biomedical research and clinical applications. Tomographic imaging of in vivo blood flow velocity in the chick chorioallantoic membrane and in rodent skin is demonstrated.     

Phase-resolved optical coherence tomography and optical Doppler tomography for imaging blood flow in human skin with fast scanning speed and high velocity sensitivity

We have developed a novel phase-resolved optical coherence tomography (OCT) and optical Doppler tomography (ODT) system that uses phase information derived from a Hilbert transformation to image blood flow in human skin with fast scanning speed and high velocity sensitivity. Using the phase change between sequential scans to construct flow-velocity imaging, this technique decouples spatial resolution and velocity sensitivity in flow images and increases imaging speed by more than 2 orders of magnitude without compromising spatial resolution or velocity sensitivity. The minimum flow velocity that can be detected with an axial-line scanning speed of 400 Hz and an average phase change over eight sequential scans is as low as 10 microm/s, while a spatial resolution of 10 microm is maintained. Using this technique, we present what are to our knowledge the first phase-resolved OCT/ODT images of blood flow in human skin.     

Doppler standard deviation imaging for clinical monitoring of in vivo human skin blood flow

We used a novel phase-resolved optical Doppler tomographic (ODT) technique with very high flow-velocity sensitivity (10microm/s) and high spatial resolution (10microm) to image blood flow in port-wine stain (PWS) birthmarks in human skin. In addition to the regular ODT velocity and structural images, we use the variance of blood flow velocity to map the PWS vessels. Our device combines ODT and therapeutic systems such that PWS blood flow can be monitored in situ before and after laser treatment. To the authors' knowledge this is the first clinical application of ODT to provide a fast semiquantitative evaluation of the efficacy of PWS laser therapy in situ and in real time.     

光学多普勒层析三维矢量测速方法研究

光学多普勒层析术(ODT)是一种高分辨、非侵入的生物医学成像手段,能同时得到组织的结构信息和组织内血管的流速信息.提出了一种新型的基于相位分辨技术的ODT三维矢量测速方法.在ODT系统样品臂的准直镜和聚焦透镜之间加入窄带相位片,形成三个不同的相位延迟,通过计算多普勒频移和不同相位延迟下的多普勒展宽,可得到毛细管内的三维矢量流场分布.对已知浓度的聚苯乙烯溶液进行了一系列不同角度和不同流速的实验,结果证明这种新型的ODT矢量测速方法可以较精确的实现三维矢量流速的测量.     

In vivo bidirectional color Doppler flow imaging of picoliter blood volumes using optical coherence tomography

We describe a novel optical system for bidirectional color Doppler imaging of flow in biological tissues with micrometer-scale resolution and demonstrate its use for in vivo imaging of blood flow in an animal model. Our technique, color Doppler optical coherence tomography (CDOCT), performs spatially localized optical Doppler velocimetry by use of scanning low-coherence interferometry. CDOCT is an extension of optical coherence tomography (OCT), employing coherent signal-acquisition electronics and joint time-frequency analysis algorithms to perform flow imaging simultaneous with conventional OCT imaging. Cross-sectional maps of blood flow velocity with <50-microm spatial resolution and <0.6-mm/s velocity precision were obtained through intact skin in living hamster subdermal tissue. This technology has several potential medical applications.     

Study on cerebral microcirculation by Optical Doppler Tomography

Optical Doppler Tomography (ODT) provides a novel method to measure the blood flow velocity in vessels with the diameter at micrometer scale. Rats with cranial window are used as a model, and the changes in the blood flow velocity of cerebral arterioles in sensory cortex are measured in real time with an established ODT system, under electrical stimulation and drug administration. The results show significant differences in the blood flow velocity between experimental groups and control groups, demonstrating the feasibility of ODT in the cerebral microcirculation study. Compared with the conventional Doppler ultrasound, ODT provides much higher spatial resolution, and thus holds a promising future in the application of the cerebral microcirculation study, especially in the observation of the blood flow velocity in micrometer scale vessels. Supported by the National Hi-Tech Research and Development Program of China (863 Program)(Grant No. 2006AA02Z4E0), the National Natural Science Foundation of China (Grant Nos. 60378041, 60478040, 60878057 and 30770685), the Program for New Century Excellent Talents in University (Grant No. NCET-04-0528), and the Opening Project of MOE Key Laboratory of Laser Life Science, South China Normal University     

Doppler-based lateral motion tracking for optical coherence tomography

Nonuniform lateral scanning of the probe beam in optical coherence tomography produces imaging artifacts and leads to a morphologically inaccurate representation of the sample. Here, we demonstrate a solution to this problem, which is based on the Doppler shift carried by the complex-valued depth-resolved scattering amplitude. Furthermore, we demonstrate the feasibility of Doppler flow velocity measurements in underlying flow channels while laterally scanning the imaging probe over large surfaces with arbitrary and varying velocity. Finally, we performed centimeters-long hand-held B-mode imaging of skin in vivo.     

Cerebral blood flow imaged with ultrahigh-resolution optical coherence angiography and Doppler tomography

Speckle contrast based optical coherence angiography (OCA) and optical coherence Doppler tomography (ODT) have been applied to image cerebral blood flow previously. However, the contrast mechanisms of these two methods are not fully studied. Here, we present both flow phantom and in vivo animal experiments using ultrahigh-resolution OCA (μOCA) and ODT (μODT) to investigate the flow sensitivity differences between these two methods. Our results show that the high sensitivity of μOCA for visualizing minute vasculature (e.g., slow capillary beds) is due to the enhancement by random Brownian motion of scatterers (e.g., red and white blood cells) within the vessels; whereas, μODT permits detection of directional flow below the Brownian motion regime (e.g., laser-induced microischemia) and is, therefore, more suitable for brain functional imaging.     

Hemoglobin contrast in magnetomotive optical Doppler tomography

We introduce a novel contrast mechanism for imaging blood flow by use of magnetomotive optical Doppler tomography (MM-ODT), which combines an externally applied temporally oscillating high-strength magnetic field with ODT to detect erythrocytes moving according to the field gradient. Hemoglobin contrast was demonstrated in a capillary tube filled with moving blood by imaging the Doppler frequency shift, which was observed independently of blood flow rate and direction. Results suggest that MM-ODT may be a promising technique with which to image blood flow.     

Self-referenced Doppler optical coherence tomography

Doppler optical coherence tomography (DOCT) allows simultaneous micrometer-scale resolution cross-sectional imaging of tissue structure and blood flow. We demonstrate a fiber-optic polarization-diversity-based differential phase contrast DOCT system as a method to perform self-referenced velocimetry in highly scattering media. Using this strategy, we reduced common-mode interferometer noise to <1 Hz and improved Doppler estimates in a scattering flow phantom by a factor of 5.     

Determination of flow velocity vector based on Doppler shift and spectrum broadening with optical coherence tomography

We describe a technique that uses Doppler optical coherence tomography to estimate accurately the scattering fluid-flow velocity without a priori knowledge of the Doppler angle. Our technique is based on the combined use of the Doppler shift on the interference signal and the Doppler spectrum broadening caused by the particles moving across the probe beam. It is shown that the estimated values of the Doppler angle and average fluid velocity from the experiments agree well with the preset values.     

Doppler-angle measurement in highly scattering media

We describe a dual-channel optical low-coherence reflectometer for accurate measurement of Doppler angles in highly scattering media. Accurate fluid-flow velocity estimation requires measurement of the Doppler shift and angle. Estimated values of the Doppler angle and average fluid-flow velocity from experimental data are in good agreement with preset values.     

Real-time flow imaging by removing texture pattern artifacts in spectral-domain optical Doppler tomography

We present a new, simple method to suppress texture pattern artifacts induced by the optical heterogeneity of tissues to improve the performance of flow imaging for real-time phase-resolved optical Doppler tomography. The method performs transverse scanning of the probe beam in the forward and then reverse directions, and it takes average of the spatial phase changes between them to obtain the final velocity image. It relies on the fact that the phase changes between successive axial scans due to the optical heterogeneity of the sample are time independent, while those due to the moving particles are time dependent. We experimentally demonstrate this method by real-time imaging of a flow phantom.     

Experimental study of the multiple scattering effect on the flow velocity profiles measured in Intralipid phantoms by DOCT

Time domain Doppler Optical Coherence Tomography (DOCT) technique was applied to measure flow velocity profiles in highly scattering media. We analyzed the distortions of the measured velocity profiles of the 1% Intralipid solution flow embedded into the scattering medium at different embedding depths. For this purpose a tissue phantom consisting of a plain glass capillary (inner diameter 0.3 mm) embedded into a slab of Intralipid solution mimicking human skin was designed. The measured flow velocity profiles and behavior of distortions caused by multiple scattering are shown.     

Intraluminal fiber-optic Doppler imaging catheter for structural and functional optical coherence tomography

We describe a miniature fiber-optic Doppler imaging catheter for integrated functional and structural optical coherence tomography (OCT) imaging. The Doppler catheter can map blood flow within a vessel as well as image vessel wall structures. A prototype Doppler catheter has been developed and demonstrated for measuring the intraluminal velocity profile in a vessel phantom (conduit). A simple mathematical model is demonstrated to estimate the total flow rate. This estimation technique also enables the spatial range of flow measurements to be extended by approximately two times the normal OCT image-penetration depth. The Doppler OCT catheter could be a powerful device for cardiovascular imaging.     

Scattering of sound waves by a turbulent wake

In this investigation, the Doppler shifted power spectrum of the scattering cross-section is obtained for plane acoustic waves scattered by fluid flow fluctuations appropriate to a turbulent wake. The wake considered in this paper is assumed almost homogeneous and isotropic and of low Reynolds number.It is shown that the evaluation of the Doppler scattering cross-section essentially reduces to the calculation of the wave number converted and frequency shifted energy spectrum function of the turbulent flow fluctuations. In prescribing the low Reynolds number turbulence spectrum, inertial forces are assumed negligible. Convective effects of the macro-eddies, which cause a Doppler shift in the scattered waves, are considered using a Lagrangian-type of space-time velocity correlation.After finding the spectrum of turbulent fluctuations, the Doppler shifted power spectrum of the scattering cross-section, which characterizes the scattered waves, is obtained explicitly for the far field approximation.     

Measurement of pulsatile flow using MRI and a Bayesian technique of probability analysis

This work shows that complete spatial information of periodic pulsatile fluid flows can be rapidly obtained by Bayesian probability analysis of flow encoded magnetic resonance imaging data. These data were acquired as a set of two-dimensional images (complete two-dimensional sampling of k-space or reciprocal position space) but with a sparse (six point) and nonuniform sampling of q-space or reciprocal displacement space. This approach enables more precise calculation of fluid velocity to be achieved than by conventional two q-sample phase encoding of velocities, without the significant time disadvantage associated with the complete flow measurement required for Fourier velocity imaging. For experimental comparison with the Bayesian analysis applied to nonuniformly sampled q-space data, a Fourier velocity imaging technique was used with one-dimensional spatial encoding within a selected slice and a uniform sampling of q-space using 64 values of the pulsed gradients to encode fluid flow. Because the pulsatile flows were axially symmetric within the resolution of the experiment, the radial variation of fluid velocity, in the direction of the pulsed gradients, was reconstructed from one-dimensional spatial projections of the velocity by exploiting the central slice theorem. Data were analysed for internal consistency using linearised flow theories. The results show that nonuniform q-space sampling followed by Bayesian probability analysis is at least as accurate as the combined uniform q-space sampling with Fourier velocity imaging and projection reconstruction method. Both techniques give smaller errors than a two-point sampling of q-space (the conventional flow encoding experiment).     

Measurements of velocity distributions with a laser doppler imaging system

A laser Doppler imaging system with a TV camera has been constructed and velocity distributions of fluid flow in cross sections of a rectangular channel have been measured. Consequently, it has been found that the system has some advantages in comparison with usual laser Doppler velocimeters, for example, the visualization of flow can be easily achieved.     

Effect of wall scattering on SNR in off-axis differential-type laser Doppler velocimetry

Though various properties and applications of laser Doppler velocimetry have been extensively studied in the past decade, there is little discussion on the effect of light scattering from the surface of a cell on Doppler beat signals or on methods of reducing it. In this paper, the effect of light scattering from the surface of the cell is treated as a background noise and is studied theoretically and experimentally on the detecting process of Doppler beat signals in off-axis differential-type laser Doppler velocimetry. Laser Doppler velocimetry of an off-axis type is verified to be effective for measurement of the flow velocity in the vicinity of a scattering wall. The effect of the light scattered from the wall surface on the signal-to-noise ratio (SNR) of Doppler beat signals is discussed in detail. The minimum distance, which is close to the wall and at which good Doppler beat signals can be obtained, is defined and determined quantitatively. This minimum distance is found to be strongly affected by the off-axis angle of the detecting optical system.