Laser speckle contrast imaging
Recently, there has been great interest in using laser speckle contrast imaging (LSCI) as a tool for imaging flow in preclinical research and clinical applications. LSCI utilizes intrinsic tissue contrast from dynamic light scattering and provides a relatively simple technique for visualizing detailed spatiotemporal dynamics of blood flow changes in real-time. Laser speckle is a random interference pattern produced when coherent light scatters from a random medium and can be imaged onto a detector. Motion from scattering particles, such as red blood cells in the vasculature, leads to spatial and temporal variations in the speckle pattern. Speckle contrast analysis quantifies the local spatial variance, or blurring, of the speckle pattern that results from blood flow. Areas with greater motion have more rapid intensity fluctuations and therefore have more blurring of the speckles during the camera exposure time. LSCI can be used to quantify relative changes in blood flow, and has been studied both in animal models and in the clinic.
In our lab, we focus on functional brain imaging and use LSCI to image cerebral blood flow dynamics. Cerebral blood flow (CBF) is an important parameter in the brain, and can be used to study neurological events, including stroke, cortical spreading depression, and functional activation. In animal models, we can use LSCI as a tool to better understand the neurophysiological mechanisms behind each of these events, which can impact future development of therapeutics. In the clinic, LSCI can be used as a monitoring tool during neurosurgery, alerting surgeons of a reduction in cerebral blood flow in a timely manner to reduce the risk of post-operative deficits.
Recent research projects:
- Development of a low-cost LSCI system that can image microcirculatory blood flow
- Assessment of LSCI as an intraoperative blood flow monitoring tool during brain tumor resection procedures
Publications Related to this Research Area
Low-cost laser speckle contrast imaging of blood flow using a webcam
L. M. Richards, S. M. Shams Kazmi, J. L. Davis, K. E. Olin, A. K. Dunn,
Biomedical Optics Express
Laser speckle contrast imaging has become a widely used tool for dynamic imaging of blood flow, both in animal models and in the clinic. Typically, laser speckle contrast imaging is performed using scientific- grade instrumentation. However, due to recent advances in camera technology, these expensive components may not be necessary to produce accurate images. In this paper, we demonstrate that a consumer-grade webcam can be used to visualize changes in flow, both in a microfluidic flow phantom and in vivo in a mouse model. A two-camera setup was used to simultaneously image with a high performance monochrome CCD camera and the webcam for direct comparison. The webcam was also tested with inexpensive aspheric lenses and a laser pointer for a complete low- cost, compact setup ($90, 5.6 cm length, 25 g). The CCD and webcam showed excellent agreement with the two-camera setup, and the inexpensive setup was used to image dynamic blood flow changes before and after a targeted cerebral occlusion.view on publisher's web-site
Comparison of indocyanine green angiography and laser speckle contrast imaging for the assessment of vasculature perfusion.
E. L. Towle, L. M. Richards, S. Kazmi, D. J. Fox, A. K. Dunn,
BACKGROUND: Assessment of the vasculature is critical for overall success in cranial vascular neurological surgery procedures. Although several methods of monitoring cortical perfusion intraoperatively are available, not all are appropriate or convenient in a surgical environment. Recently, 2 optical methods of care have emerged that are able to obtain high spatial resolution images with easily implemented instrumentation: indocyanine green (ICG) angiography and laser speckle contrast imaging (LSCI). OBJECTIVE: To evaluate the usefulness of ICG and LSCI in measuring vessel perfusion. METHODS: An experimental setup was developed that simultaneously collects measurements of ICG fluorescence and LSCI in a rodent model. A 785-nm laser diode was used for both excitation of the ICG dye and the LSCI illumination. A photothrombotic clot model was used to occlude specific vessels within the field of view to enable comparison of the 2 methods for monitoring vessel perfusion. RESULTS: The induced blood flow change demonstrated that ICG is an excellent method for visualizing the volume and type of vessel at a single point in time; however, it is not always an accurate representation of blood flow. In contrast, LSCI provides a continuous and accurate measurement of blood flow changes without the need of an external contrast agent. CONCLUSION: These 2 methods should be used together to obtain a complete understanding of tissue perfusion.view on publisher's web-site
Laser speckle contrast imaging of cerebral blood flow in humans during neurosurgery: a pilot clinical study
A. B. Parthasarathy, E. L. Weber, L. M. Richards, D. J. Fox, A. K. Dunn,
Journal of Biomedical Optics
Monitoring cerebral blood flow (CBF) during neurosurgery can provide important physiological information for a variety of surgical procedures. CBF measurements are important for assessing whether blood flow has returned to presurgical baseline levels and for assessing postsurgical tissue viability. Existing techniques for intraoperative monitoring of CBF based on magnetic resonance imaging are expensive and often impractical, while techniques such as indocyanine green angiography cannot produce quantitative measures of blood flow. Laser speckle contrast imaging (LSCI) is an optical technique that has been widely used to quantitatively image relative CBF in animal models in vivo. In a pilot clinical study, we adapted an existing neurosurgical operating microscope to obtain LSCI images in humans in real time during neurosurgery under baseline conditions and after bipolar cautery. Simultaneously recorded ECG waveforms from the patient were used to develop a filter that helped reduce measurement variabilities due to motion artifacts. Results from this study demonstrate the feasibility of using LSCI to obtain blood flow images during neurosurgeries and its capability to produce full field CBF image maps with excellent spatial resolution in real-time with minimal disruption to the surgical procedure.view on publisher's web-site