Laser Doppler imaging of burn scars: A comparison of wavelength and scanning methods
ABSTRACT Laser Doppler perfusion imaging (LDI) is a useful tool for the early clinical assessment of burn depth and prognostic evaluation of injuries that may require skin grafting. We have evaluated two commercially available laser Doppler imagers for the perfusion measurement of normal and burn scar tissue.
A single wavelength (635 nm), step-wise scanning LDI and a dual wavelength (633 and 780 nm), continuous scanning LDI were used. Twenty patients with hypertrophic burn scars (time since injury: 1 month-8 years) were recruited and the color and elevation of the scar was clinically assessed using a modified Vancouver Burn Scar Scale. Perfusion of each scar region was measured using both imagers. A symmetric contralateral region of unburned skin was also imaged to record baseline perfusion.
Comparisons of wavelength and scanning technique were made using perfusion values obtained from 22 burn scars. Highly significant positive correlation was observed in all comparisons. In addition, output from both instruments was strongly and significantly correlated with the clinical grading of the scar.
Both LDI scanners perform similar perfusion measurements. The results also indicate that red and near-infrared (NIR) wavelength photons provide similar blood flow information. The faster, continuous scanning method provides a clinical advantage without a significant loss of blood flow information. However, a critical evaluation of both instruments suggests that caution must be exercised when using these optical diagnostic techniques and that some knowledge of light-tissue interaction is required for the proper analysis and interpretation of clinical data.
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- "This enhancement of local blood flow, the stimulation of microcirculation, and possibly neovascularization, may be beneficial for the treatment of diseases that are caused by excessive fibrosis, as well as influence fibroblast growth in vitro. However, fresh hypertrophic scars display a pattern of 100–150% increase in perfusion, as has been shown in trunk and extremity scars using Laser Doppler measurements   . We believe the use of PTF in vivo in fresh HS might therefore cause an increase in inflammation and excessive formation of HS rather than a decrease. "
ABSTRACT: Fibroblasts are thought to be partially responsible for the persisting contractile forces that result in burn contractures. Using a monolayer cell culture and fibroblast populated collagen lattice (FPCL) three-dimensional model we subjected hypertrophic scar and non-cicatricial fibroblasts to the antifibrogenic agent pentoxifylline (PTF – 1 mg/mL) in order to reduce proliferation, collagen types I and III synthesis and model contraction. Fibroblasts were isolated from post-burn hypertrophic scars (HSHF) and non-scarred skin (NHF). Cells were grown in monolayers or incorporated into FPCL's and exposed to PTF. In monolayer, cell number proliferation was reduced (46.35% in HSHF group and 37.73% in NHF group, p < 0.0001). PTF selectively inhibited collagen III synthesis in the HSHF group while inhibition was more evident to type I collagen synthesis in the NHF group. PTF also reduced contraction in both (HSHF and NHF) FPCL.Burns: journal of the International Society for Burn Injuries 08/2009; 35(5-35):701-706. DOI:10.1016/j.burns.2008.11.017 · 1.84 Impact Factor
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- "Thus, as tissue absorption increases, the LSPI perfusion index will decrease for a given flow rate and the slope of the LSPI output across a specified flow range has an inverse relation with the tissue absorption coefficient. Our previous work using LDI with burn patients demonstrated the problems of specular reflection artifact  "
ABSTRACT: Laser Doppler imaging (LDI) has become a standard method for optical measurement of tissue perfusion, but is limited by low resolution and long measurement times. We have developed an analysis technique based on a laser speckle imaging method that generates rapid, high-resolution perfusion images. We have called it laser speckle perfusion imaging (LSPI). This paper investigates LSPI output and compares it to LDI using blood flow models designed to simulate human skin at various levels of pigmentation. Results show that LSPI parameters can be chosen such that the instrumentation exhibits a similar response to changes in red blood cell concentration (0.1%-5%, 200 microL/min) and velocity (0-800 microL/min, 1% concentration) and, given its higher resolution and quicker response time, could provide a significant advantage over LDI for some applications. Differences were observed in the LDI and LSPI response to tissue optical properties. LDI perfusion values increased with increasing tissue absorption, while LSPI perfusion values showed a slight decrease. This dependence is predictable, owing to the perfusion algorithms specific to each instrument, and, if properly compensated for, should not influence each instrument's ability to measure relative changes in tissue perfusion.IEEE Transactions on Biomedical Engineering 11/2004; 51(11):2074-84. DOI:10.1109/TBME.2004.834259 · 2.23 Impact Factor
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ABSTRACT: Collecting microlymphatics play a vital role in promoting lymph flow from the initial lymphatics in the interstitial spaces to the large transport lymph ducts. In most tissues, the primary mechanism for producing this flow is the spontaneous contractions of the lymphatic wall. Individual units, known as lymphangion, are separated by valves that help prevent backflow when the vessel contracts, thus promoting flow through the lymphatic network. Lymphatic contractile activity is inhibited by flow in isolated lymphatics, however there are virtually no in situ measurements of lymph flow in these vessels. Initially, a high speed imaging system was set up to image in situ preparations at 500 fps. These images were then manually processed to extract information regarding lymphocyte velocity (-4 to 10 mm/sec), vessel diameter (25 to 165 um), and particle location. Fluid modeling was performed to obtain reasonable estimates of wall shear stress (-8 to 17 dynes/cm2). One of the difficulties encountered was the time consuming methods of manual particle tracking. Using previously captured images, an image correlation method was developed to automate lymphatic flow measurements and to track wall movements as the vessel contracts. Using this method the standard error of prediction for velocity measurements was 0.4 mm/sec and for diameter measurements it was 7.0 Âµm. It was found that the actual physical quantity being measured through this approach is somewhere between the spatially averaged velocity and the maximum velocity of a Poiseuille flow model.