Laser speckle imaging (LSI) has been gaining popularity for the past few years. Like other optical imaging modalities such
as optical coherence tomography (OCT), orthogonal polarization spectroscopy (OPS), and laser Doppler imaging (LDI), LSI
utilizes nonionizing radiation. In LSI, blood flow velocity is obtained by analyzing, temporally or spatially, laser speckle (LS)
patterns generated when an expanded laser beam illuminates the tissue. The advantages of LSI are that it is fast, does not
require scanning, and provides full-field LS images to extract realtime, quantitative hemodynamic information of subtle
changes in the tissue vasculature. For medical applications, LSI has been used for obtaining blood velocities in human retina,
skin flaps, wounds, and cerebral and sublingual areas. When coupled with optical fibers, LSI can be used for endoscopic
measurements for a variety of applications. This paper describes the application of LSI in retinal, sublingual, and skin flap
measurements. Evaluation of retinal hemodynamics provides very important diagnostic information, since the human retina
offers direct optical access to both the central nervous system (CNS) and afferent and efferent CNS vasculature. The
performance of an LSI-based fundus imager for measuring retinal hemodynamics is presented. Sublingual microcirculation
may have utility for sepsis indication, since inherent in organ injury caused by sepsis is a profound change in microvascular
hemodynamics. Sublingual measurement results using an LSI scope are reported. A wound imager for imaging LS patterns
of wounds and skin flaps is described, and results are presented.
A fundus camera was modified to illuminate the retina of a rabbit model with low power laser light in order to obtain laser speckle images. A fast-exposure charge-coupled device (CCD) camera was used to capture laser speckle images of the retina. Image acquisition was synchronized with the arterial pulses of the rabbit to ensure that all images are obtained at the same point in the cardiac cycle. The rabbits were sedated and a speculum was inserted to prevent the eyelid from closing. Both albino (New Zealand) and pigmented (Dutch belted) rabbits were used in the study. The rabbit retina is almost avascular. The measurements are obtained for choroidal tissue as well as retinal tissue. Because the retina is in a region of high metabolism, blood velocity is strongly affected by blood oxygen saturation. Measurements of blood velocity obtained over a wide range of O<sub>2</sub> saturations (58%-100%) showed that blood velocity increases with decreasing O<sub>2</sub> saturation. For most experiments, the left eye of the rabbit was used for laser measurements whereas the right eye served as a control. No observable difference between pre- and post-experimented eye was noted. Histological examinations of retinal tissue subjected to repeated laser measurements showed no indication of tissue damage.
Infiltration of medications during infusion therapy results in complications ranging from erythema and pain to tissue necrosis requiring amputation. Infiltration occurs from improper insertion of the cannula, separation of the cannula from the vein, penetration of the vein by the cannula during movement, and response of the vein to the medication. At present, visual inspection by the clinical staff is the primary means for detecting intravenous (IV) infiltration. An optical sensor was developed to monitor the needle insertion site for signs of IV infiltration. Initial studies on simulated and induced infiltrations on a swine model validated the feasibility of the methodology. The presence of IV infiltration was confirmed by visual inspection of the infusion site and/or absence of blood return in the IV line. Potential sources of error due to illumination changes, motion artifacts, and edema were also investigated. A comparison of the performance of the optical device and blinded expert observers showed that the optical sensor has higher sensitivity and specificity, and shorter detection time than the expert observers. An improved model of the infiltration monitoring device was developed and evaluated in a clinical study on induced infiltrations of healthy adult volunteers. The performance of the device was compared with the observation of a blinded expert observer. The results show that the rates of detection of infiltrations are 98% and 82% for the optical sensor and the observer, respectively. The sensitivity and specificity of the optical sensor are 0.97 and 0.98, respectively.
Blood velocity information can be extracted by analyzing, either temporally or spatially, laser speckle (LS) patterns generated when a laser source illuminates the tissue. While a temporal analysis, such as that used for laser Doppler velocimetry (LDV), provides high spatial resolution, the time required to obtain flow data in vivo on large areas of tissue limits its utility. The LS imaging (LSI) technique combines the nonscanning, full-field, LS method and the modified multiple scattering algorithms developed for LDV analysis to retrieve blood velocity parameters. It provides a noninvasive means for realtime, quantitative measurements of subtle changes in the tissue vasculature. This paper describes the use of the LSI technique on free flap measurements of a swine model and compares the results with those obtained using an LDV probe. Both the LSI and the LDV measurements showed similar results - blood velocity and flow decreased about 10%-33% from the tip to the caudal base of the flap, respectively. The difference between the tip and the caudal base is a measure of flap ischemia. However, tissue pigmentation affects the blood flow parameters retrieved from the LDV measurements, it does not affect the blood velocity parameters retrieved from the LSI measurements. Both techniques were also used during free tissue transfer procedures in patients to demonstrate the utility of the LSI for monitoring the status of the graft.