Laser Doppler imaging

The DMSO induced increased blood flow was measured using the moorLDI laser Doppler imager (Moor Instruments Ltd, Devon, UK). The instrument scans a low power laser beam in a raster pattern over the skin. Moving blood in the microvasculature causes a Doppler shift, which is processed to build up a color-coded image of cutaneous blood flow. The mean and standard deviation of the blood perfusion units in a region of interest was calculated. 

FIGURE 37.2 DMSO response of xerotic leg skin, (a) Dose dependent increase of DMSO induced cutaneous blood flow before on untreated skin, (b) After twice daily application of a water-in-oil emulsion for six weeks the response was markedly reduced. DMSO induced blood flow was measured with a laser Doppler imager. Data expressed as blood perfusion units. Statistical significance was determined using the paired r-test ( p >. 05,... 

Issachar, N., Gall, Y., Borrel, M.T., and Poelman, M.-C., Correlation between percutaneous penetration of methyl nicotinate and sensitive skin, using laser Doppler imaging. 

Brown RFR, Rice P and Bennett NJ (1998). The use of laser Doppler imaging as an aid in clinical decision making in the treatment of vesicant burns. Burns, 24, 692-698. 

HN Mayrovitz, SG Carta. Laser-doppler imaging assessment of skin hyperemia as an indicator of trauma after adhesive strip removal. Adv Wound Care 9(4) 38-42, 1996. 

H N Mayrowitz, J Macdonald, J R Smith, Blood perfusion hypoaemia in re nse to graded loading of human heels assessed by laser Doppler imaging , Clin Physiology, 1999 19 351-359. 

Velocity vectors of the gas flow measured using laser Doppler anemometry inside a closed chamber during the formation of a tulip flame. Images of the flame are also shown, though the velocity measurements required many repeated runs, hence, the image is only representative. The chamber has square cross sections of 38.1mm on the side. The traces in the velocity fields are the flame locations based on velocity data dropout. The vorticity generated as the flame changes shape appears clearly in the velocity vectors. 

There are many nonintrusive experimental tools available that can help scientists to develop a good picture of fluid dynamics and transport in chemical reactors. Laser Doppler velocimetry (LDV), particle image velocimetry (PIV) and sonar Doppler for velocity measurement, planar laser induced fluorescence (PLIF) for mixing studies, and high-speed cameras and tomography are very useful for multiphase studies. These experimental methods combined with computational fluid dynamics (CFDs) provide very good tools to understand what is happening in chemical reactors. 

NMR imaging techniques were applied to the measurements of velocity field in opaque systems such as tomato juice and paper pulp suspensions [58-60]. In both cases, the particle concentrations are sufficiently high that widely applied techniques such as hot film and laser Doppler anemometry could not be used. The velocity profile for a 6 % tomato juice slurry clearly showed a power-law behavior [58, 59]. Row NMR images for a 0.5 % wood pulp suspension provided direct visual of three basic types of shear flow plug flow, mixed flow and turbulent flow as mean flow rate was increased. Detailed analysis of flow NMR image is able to reveal the complex interaction between the microstructure of suspensions and the flow [60]. 

Of particular importance to glucose collection at the site of a microdialysis probe would be changes in localized blood flow. Anderson et al. used laser Doppler perfusion imaging to determine how localized blood flow is altered after microdialysis probes insertion into the forearm of human volunteers and determined that after 60 min blood flows were equivalent to those at 24 h.57 However, Wientjes et al. found for longer term implants that it appeared that 2-3 days were necessary to achieve a stable glucose concentration or baseline.58 The GlucoDay system has been... 

Groth L, Jorgensen A, Serup J. Cutaneous microdialysis in the rat insertion trauma and effect of anaesthesia studied by laser Doppler perfusion imaging and histamine release. Skin Pharmacology and Applied Skin Physiology 1998, 11, 125-132. 

Anderson C, Andersson T, Wardell K. Changes in skin circulation after insertion of a microdialysis probe visualized by laser Doppler perfusion imaging. Journal of Investigative Dermatology 1994, 102, 807-811. 

Fullerton, A., Rode, B., and Serup, J. Skin irritation and grading based on laser Doppler perfusion imaging. Skin Res. Technol. 2002 8 23-31. 

In all covered topics, the advancement of instrumentation and software that has enabled the scientists to perform the research is often ignored. One interesting paper presented by Neil Abbot et al. [161] used laser Doppler perfusion imaging to follow skin blood flow. The work was done in the red and short wave NIR regions of the spectrum. While these wavelengths have been used before, Doppler imaging is a new step in instrumentation for this topic. 

N. C. Abbot et al., Laser Doppler Perfusion Imaging of Skin Blood Flow Using Red and Near-Infrared Sources, J. Invest. Dermatol., 107(6), 2235 (1996). 

From the 1970s, a large number of imaging studies of non-Brownian suspensions flowing in mm- to cm-sized channels have been performed via Laser Doppler Veiocimetry [120-123] and NMRI [124,125], but little information has been obtained at the single-particle level. Optical microscopy experiments on channel flows of colloids have only recently started to appear, often in relation to microfluidics applications [126]. To avoid image distortions, channels witli square or rectangular cross sections are preferred to cylindrical capillaries. 

The conventional approaches to anemometry are laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) [6,37,38]. The former is employed to obtain point-like measurements of one velocity component, whereas a combination of two or three LDV systems allows for the measurement of the vectorial structure of the velocities. The PIV is, instead, conceived for two-dimensional acquisition of velocity fields. One important industrial application of these techniques is in laser diagnostic of gas turbines and engines [9]. For instance, atomization of liquid fuels into droplets is typical of modern IC engines and one can study the fuel-air mixing that is an essential factor in efficient combustion. In... 

Intrusive measurement techniques such as a Pitot static tube and hot-wire anemometer [24-26], and nonintrusive techniques such as laser Doppler velocimeter and particle image velocimetry (PIV) have been used to study the flow field. Goh, Kusadomi, and Gollahalli [13-15] mapped the velocity field in the flame using a Pitot static tube with a pressure transducer (Barocel). Details of the techniques and selection guidelines are presented in books on experimental aspects of fluid mechanics. Interested readers are referred to Holman [27], Goldstein [28], and Miller [29], to name a few. 

---