Changes in skin circulation after insertion of a microdialysis probe visualized by laser Doppler perfusion imaging

Microdialysis makes possible in vivo estimation of endogenous and exogenous substances in the dermal extracellular space. Insertion of the microdialysis probe and its subsequent presence in the skin may affect both the reactivity of the skin test site and the measurement of target substances. Laser Doppler flowmetry is a non-invasive method for estimating cutaneous blood flow. A further development of this technique, laser Doppler perfusion imaging, has been used to study the time course of the circulatory changes caused in the area of microdialysis probe insertion. Laser Doppler perfusion imaging was performed prior to, during, and after microdialysis probe insertion in the skin of the ventral forearm in three subjects. Probe insertion caused an increase in skin blood perfusion in the whole test area. About 15 min after probe insertion, the flare, which is presumed to be of chiefly axon reflex origin, began to subside and the circulatory response could be seen to center around the site of insertion and the tip of the probe. Skin perfusion levels had returned to near normal levels within 60 min. Local anesthesia of the point of guide insertion inhibited the flare, but did not affect circulatory reactivity in the skin nearby. Both microdialysis and laser Doppler perfusion imaging seem to be promising new methods in dermatologic research.

Blood flow rate in the microvasculature of the optic nerve head in primary open angle glaucoma. A new approach

In order to evaluate the optic nerve head perfusion in patients with primary open-angle glaucoma (POAG), we measured the velocity of the red blood cells (RBCs) in the capillaries of the optic nerve head with a laser-Doppler velocimeter and evaluated the blood viscosity by determining the capacity of the RBCs to disaggregate with an erythroaggregameter. Our results showed that in POAG patients optic nerve blood velocity was reduced and that the aggregability of the RBCs was increased. The two parameters were not significantly correlated, possibly because of local papillary autoregulation and anatomical variability in the papilla vessels. These two factors could explain why the same rheological anomaly in two subjects could lead to different responses in blood velocity. The RBC hyperaggregability cannot be explained by quantitative modifications of the plasma proteins. Modifications in the membrane of the RBCs could indeed be responsible for hyperaggregability, since our data suggest that deformability of the RBCs is impaired in glaucoma.

Development of a new laser-Doppler microvelocimetering and its application in patients with coronary artery stenosis

A new Laser-Doppler microvelocimetering (LDMV) was developed to study blood flow in individual vessels in patients with coronary artery stenosis. The LDMV measures steady blood flow velocity, diameter of vessels and pulsation flow. In addition, the effects of China's traditional herbs--Salvia Mitiorrhyza and other drugs--on the blood flow in the patients were investigated. LDMV constitutes a new quantitative procedure and is a promising tool for rapid monitoring of tissue perfusion in cardiovascular disease and estimating the action of drugs on microcirculation.

Guidelines for measurement of cutaneous blood flow by laser Doppler flowmetry. A report from the Standardization Group of the European Society of Contact Dermatitis

The report reviews individual-related variables (age, sex, race, anatomical site), intra- and inter-individual variation (temporal, physical and mental activity, food and drugs), and environment-related variables (air convection, temperature). Technical variation, instrument validation including a standard reactive hyperemia experiment, and a standard operating procedure are discussed and included in the guidelines.

Local choroidal blood flow in the cat by laser Doppler flowmetry

PURPOSE

To develop a procedure using a noninvasive technique that will allow the investigation of choroidal blood flow (ChBF) regulation in discrete regions of the cat eye. Validation of this procedure will provide a method to study intrinsic, neural, and pharmacologic factors that regulate regional ChBF.

METHODS

The technique to measure ChBF is based on laser Doppler flowmetry. However, in contrast to conventional laser Doppler flowmetry, which uses fiber-optic probes in direct contact with the tissue to deliver the laser beam and detect the scattered light, with this technique the beam is delivered through a fundus camera and the scattered light is detected in the retinal image plane of the camera. Measurements were made in 34 anesthetized cats under conditions that would ensure that the flow measured represented ChBF in the choriocapillaris: the laser beam was aimed at retinal intervascular sites in the tapetal region of the fundus; the Doppler shift power spectrum of the light scattered by the red blood cells had the shape and frequency range typical for a microvascular bed; and the recorded flow did not decrease by more than 5% when the cat was given 100% O2 to breathe for 4 minutes. The responses to various physiologic and pharmacologic stimuli were tested and compared with those obtained from retinal vessels.

RESULTS

Intravenous infusions of acetylcholine increased ChBF in a dose-response fashion, whereas sympathetic nerve stimulation at various frequencies decreased ChBF as predicted by previous studies. By comparison, retinal blood flow was negligibly affected by these two stimuli. In contrast to retinal blood flow, ChBF was unaffected by diffuse luminance flicker. ChBF was found to be pulsatile. The mean of the pulsatile component of ChBF represented approximately 34% of mean ChBF, a value similar to those derived from ChBF measurements in minipigs and retinal blood flow in the cat.

CONCLUSIONS

This study demonstrates that laser Doppler flowmetry is a valid technique for obtaining local, noninvasive, and continuous recordings of relative ChBF. Tested under steady-state conditions for blood pressure, heart rate, and acid-base balance, ChBF is stable for long periods of time, allowing the investigation of the effect of various physiologic stimuli and pharmacologic agents on this flow.

Capillary blood flow velocity measurements in cystoid macular edema with the scanning laser ophthalmoscope

Using a scanning laser ophthalmoscope, we calculated the velocity of retinal blood flow in a juxta-foveolar capillary during the course of cystoid macular edema after partial central retinal vein occlusion in a 53-year-old woman. The mean velocity of the fluorescent dots in the macular capillary of the right eye with cystoid macular edema was 1.59 +/- 0.08 mm/sec at the initial examination. Despite the systemic administration of indomethacin (75 mg/day for three weeks), best-corrected visual acuity decreased from 20/30 to 20/70, and the velocity became 0.82 +/- 0.13 mm/sec. Prednisolone (30 mg/day orally for one week) improved the cystoid macular edema, and the velocity was 0.96 +/- 0.06 mm/sec 12 days after initiation of the drug. The velocity gradually improved; one year later it was 1.65 +/- 0.17 mm/sec and visual acuity was 20/22. Velocity in the left eye, which did not have cystoid macular edema, was 2.16 +/- 0.16 mm/sec. Thus, scanning laser ophthalmoscopy proved useful for measuring the velocity of retinal blood flow.

Spectral analysis of laser Doppler signals in real time using digital processing

A versatile spectrum analyser was developed to generate and display laser Doppler shift signals, and derived parameters, continuously in real time using a digital signal processing chip. A major attraction of the system is that it is entirely programmable, so that both the algorithms and the attributes of the system, such as window function and frame overlap, can be easily altered. It was used to investigate the relative merits of a variety of algorithms using a blood-flow phantom. An index based on the first moment of the Doppler power spectrum was found to be the most reliable flow indicator, with linearity extending towards a velocity of 5 mm s-1 for a blood haematocrit of 5%. The system is not limited to analysis based on the fast Fourier transform (FFT), and is suitable for non-linear techniques such as maximum entropy spectral estimation (MESE).

Ion velocity distributions in gramicidin channels determined with laser Doppler velocimetry

Laser Doppler scattering from Tl(I) ions moving synchronously through an ensemble of gramicidin channels in a bilayer membrane gives their intrachannel velocity distribution. The observed velocity distributions are unimodal indicating that ion flow through some region or regions of the channels is relatively steady. Average intrachannel velocities range from 3.75 x 10(-2) m/s to 2.38 x 10(-1) m/s for transmembrane potentials between 10 mV and 150 mV, respectively.

Effects of adjacent surfaces of different shapes on regurgitant jet sizes: an in vitro study using color Doppler imaging and laser-illuminated dye visualization

OBJECTIVES

The present study was designed to estimate the influence of different-shaped adjacent surfaces on regurgitant jets as assessed by color Doppler imaging and laser-illuminated dye optical visualization.

BACKGROUND

Because color Doppler techniques provide real-time two-dimensional imaging of flow, the evaluation of valvular regurgitation by analysis of variance-encoded regurgitant jets by this method has been widely used in clinical studies. However, recent studies have demonstrated that color Doppler jet sizes are affected not only by several hemodynamic factors and instrument settings but also by the interaction between jets and adjacent wall surfaces. In clinical conditions, jets may interact with adjacent walls of variable shapes that might have different effects on the jet size.

METHODS

An in vitro model was constructed consisting of a rigid, optically clear receiving chamber that had no outlet resistance and had a pulsatile pump ejecting through 1.5, 2.3 and 3.1 mm2 inflow orifices into the chamber. The surfaces were flat or smoothly and equally curved, convex and concave aluminum positioned at 0, 2 and 4 mm from and to the side of the inflow orifices. The pump was run with stroke volumes from 0.5 to 3.0 ml and with a pulse frequency of 70 beats/min. The echocardiographic and laser beams were aimed at the inflow orifice imaging jets perpendicular to the surfaces (vertical view) through the central plane of the jet flows. Maximal jet areas were measured by both color Doppler techniques and laser-illuminated dye visualization.

RESULTS

Color Doppler study showed fair correlation between the jet areas and the stroke volumes (r = 0.83 to 0.99), but the jet sizes under different surface conditions were variable. All the surface jet areas at a jet-surface distance of 0 and 2 mm were smaller than free jet areas at the same stroke volume for both flat and convex surfaces (p < 0.001). Flow constraint by the concave surface resulted in the smallest jet areas (p < 0.001). The color Doppler jet areas on the curved surfaces were significantly smaller than the laser-illuminated dye visualization jet areas (p < 0.01 to 0.0001). However, at intermediate jet-surface distances (4 mm and sometimes 2 mm with higher velocity flows), jet interaction with the flat and especially with the convex surface resulted in larger jets. This effect was most pronounced on dye fluorescence studies because flow around these jets consisted mainly of low velocity vortical events with only partial surface adherence and these low velocity swirling flows were not well imaged by color Doppler technique.

CONCLUSIONS

Our study suggests that the different-shaped adjacent surfaces with different degrees of flow alterations resulted in variable decreases in jet size and that color Doppler imaging could not encode and image the angled and low velocity swirling events well when jets flowed along the curved surfaces. These effects need to be taken into account when interpreting color Doppler images.

Myocardial ischemia is not a prerequisite for the stimulation of coronary collateral development

To understand better the temporal sequence of coronary collateral development and the factors that may govern that development, dogs were chronically instrumented with left circumflex (LCf) Doppler flow probe, ameroid constrictor, balloon occluder, and left atrial and aortic catheters. Collateral blood flow was measured at least weekly or when the coronary artery occluded. The reactive hyperemic response (RH) to a 15-second LCf occlusion was recorded three times per week. Most LCf arteries occluded during the 4th week after surgery. Two patterns of coronary collateral development were observed. In 11 animals collateral flow did not change for 2 or 3 weeks; peak RH and flow debt repayment, indexes of coronary vascular reserve, changed little. The next week there was an abrupt increase in collateral flow from approximately 15% of normal to 100%. This increase was coincident with a sudden loss of coronary vascular reserve and therefore suggests myocardial ischemia was the principal stimulus. However, in 11 dogs collateral flow increased gradually over 3 to 4 weeks as indexes of RH slowly decreased. The greatest increase in collateral flow occurred while peak RH was still approximately twice baseline flow, representing 80% of peak flow measured 1 week after surgery. Therefore in these animals ischemia is less likely to have been the major stimulus of coronary collateral development.

A comparison of cocaine vs. lidocaine with oxymetazoline for use in nasal procedures

This study compared the degree of vasoconstriction and anesthesia obtained with cocaine vs. that obtained with a mixture of lidocaine and oxymetazoline (lido/oxy) in healthy, male volunteers. Blood flow was evaluated by laser Doppler flowmetry. Anesthesia was measured with Semmes-Weinstein monofilaments, testing both sensation threshold and pain perception. A greater decrease in blood flow was seen after the administration of lido/oxy than after the administration of cocaine. Pain perception change was not significantly different between treatment groups at 10 minutes after removal of the medication-soaked pledget, but lido/oxy caused a greater decrease in pain perception than cocaine after 50 minutes. No significant difference in sensation threshold change was seen between treatment groups. Lidocaine with oxymetazoline is, therefore, believed to be an effective alternative to cocaine for nasal procedures.

Abnormal cutaneous vasomotion and reduced cutaneous blood mass remain in congestive heart failure even with normalized cardiovascular hemodynamics

To elucidate the pathophysiologic role of cutaneous microcirculation in congestive heart failure, finger cutaneous microcirculation was analyzed in 17 patients with acute heart failure (AHF) and 12 patients with hemodynamically compensated heart failure (c-HF) by using laser Doppler spectroscopy; the results were correlated with simultaneously obtained cardiovascular hemodynamics. Mean finger cutaneous blood flow in AHF was significantly lower compared with c-HF (p < 0.01) and control (n = 20, p < 0.001). Mean finger cutaneous blood mass was significantly reduced in both AHF (p < 0.01) and c-HF (p < 0.01) compared with control. Frequency of characteristic giant concave waves indicating sudden occurrence of flow reduction (B wave) was significantly higher in AHF (p < 0.01) and c-HF (p < 0.05) than that in control. Frequency of B waves correlated significantly with pulmonary capillary wedge pressure (PCWP) (r = 0.73, p < 0.01) and pulmonary artery systolic pressure (r = 0.54, p < 0.05). When changes after medical treatments were compared there were significant correlations between changes in B-wave frequency and changes in PCWP (r = 0.89, p < 0.01) and changes in finger cutaneous blood flow and changes in total systemic peripheral resistance (r = -0.75, p < 0.05). Cutaneous microcirculation in AHF was characterized by decreased finger cutaneous blood flow and finger cutaneous blood mass and prominent B waves, which reflected abnormal vasomotion activity. B-wave prominence and reduced finger cutaneous blood mass remained in c-HF even with normalized cardiovascular hemodynamics.

Acute effect of cigarette smoking on the coronary circulation: constriction of epicardial and resistance vessels

OBJECTIVES

This study was performed to determine the acute effect of cigarette smoking on proximal and distal epicardial conduit and coronary resistance vessels.

BACKGROUND

Cigarette smoking causes constriction of epicardial arteries and a decrease in coronary blood flow in patients with coronary artery disease, despite an increase in myocardial oxygen demand. The role of changes in resistance vessel tone in the acute coronary hemodynamic effect of smoking has not been examined.

METHODS

Twenty-four long-term smokers were studied during cardiac catheterization after vasoactive medications had been discontinued. The effect of smoking one cigarette 10 to 15 mm long on proximal and distal conduit vessel segments was assessed before and immediately after smoking and at 5, 15 and 30 min after smoking (n = 8). To determine the effect of smoking on resistance vessels, coronary flow velocity was measured in a nonobstructed artery with a 3F intracoronary Doppler catheter before and for 5 min after smoking (n = 8). Eight patients were studied without smoking to control for spontaneous changes in conduit arterial diameter (n = 5) and resistance vessel tone (n = 3).

RESULTS

The average diameter of proximal coronary artery segments decreased from 2.56 +/- 0.12 mm (mean +/- SEM) before smoking to 2.41 +/- 0.09 mm 5 min after smoking (-5 +/- 2%, p < 0.05). Distal coronary diameter decreased from 1.51 +/- 0.07 to 1.39 +/- 0.06 mm (-8 +/- 2%, p < 0.01). Marked focal vasoconstriction after smoking was observed in two patients. Coronary diameter returned to baseline by 30 min after smoking. There was no change in vessel diameter in control patients. Despite a significant increase in the heart rate-mean arterial pressure product, coronary flow velocity decreased by 7 +/- 4% (p < 0.05) and coronary vascular resistance increased by 21 +/- 4% (p < 0.01) 5 min after smoking. There was no change in these variables in the control subjects.

CONCLUSIONS

Smoking causes immediate constriction of proximal and distal epicardial coronary arteries and an increase in coronary resistance vessel tone, despite an increase in myocardial oxygen demand. These acute coronary hemodynamic effects may contribute to the adverse cardiovascular consequences of cigarette smoking.

Laser anemometry measurements of steady flow past aortic valve prostheses

An experimental investigation was conducted in steady flow to examine the fluid dynamics performance of three prosthetic heart valves of 27 mm diameter: Starr-Edwards caged ball valve, Bjork-Shiley convexo-concave tilting disk valve, and St. Vincent tilting disk valve. It was found that the pressure loss across the St. Vincent valve is the least and is, in general, about 70 percent of that of the Starr-Edwards valve. The pressure recovery is completed about 4 diameters downstream. The velocity profiles for the ball valve reveal a large single reversed flow region behind the occluder while those for the tilting disks valves reveal two reversed flow regions immediately behind the occluders. Small regions of stasis are also found near the wall in the minor opening of Bjork-Shiley valve and in the major opening of St. Vincent valve. The maximum wall shear stresses of the three valves at a flow rate of 30 l/min are in the range 30-50 dyn/cm2 which can cause hemolysis of attached red blood cells. The corresponding maximum Reynolds normal stresses are in the range of 1600-3100 dyn/cm2. The Reynolds normal stresses decay quickly and return approximately to the upstream undisturbed level at about 4 diameters downstream while the wall shear stresses decay at a slower rate. The maximum Reynolds normal stresses occur at about 1 diameter downstream while the maximum wall shear stress is at about 2 diameters downstream. In general, the St. Vincent valve has better performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Microcirculation in experimental brain oedema assessed by laser-Doppler flowmetry

Continuous measurement of CBV and CBF by means of laser-Doppler flowmetry was performed to analyse the cerebrovascular response to water accumulation during brain infusion oedema in cats. The presence of an oedema generator elicits a continuous reduction of CBV and a transient reduction of CBF. With cessation of this mechanical force of oedema production, CBV and CBF returned to control levels. These results indicate that excess accumulation of water in brain tissue by itself does not decrease CBF even when the driving pressure of oedema fluid is present, but that brain oedema attenuates CBV only when a pressure gradient exists. These results suggest that there are microcirculatory changes in brain oedema before and after removal of the oedema generating focus. The laser-Doppler flow method is a useful technique for the continuous assessment of tissue perfusion.

Dopaminergic control of gastric mucosal blood flow in humans. A study with endoscopic laser Doppler flowmetry coupled with gastric submucosal drug injection

We studied the dopaminergic regulation of the gastric mucosal blood flow (GMBF) measured with an endoscopic laser Doppler flowmetry in 27 healthy volunteers. They were randomly assigned to receive an endoscopic gastric submucosal injection (0.5 ml) of physiological saline (control group, N = 10), 50 micrograms of dopamine (DA) hydrochloride (N = 8), and 500 micrograms of a DA antagonist, metoclopramide (MCP) (N = 9). The drugs were dissolved in the same saline volume (0.5 ml) as used in control group and were injected via the mucosal area where the baseline GMBF was measured and the postdose GMBF was monitored until 5 min postdose. There was no significant difference in the mean (+/- SEM) baseline laser Doppler signals among the control, DA, and MCP groups (92.6 +/- 9.3, 81.8 +/- 9.0 and 96.9 +/- 13.3 mV, respectively). In the control group, no significant postdose changes in the laser Doppler signals occurred until 5 min postinjection. In contrast, the DA group exhibited a significant (P < 0.05 or 0.01) increase in the laser Doppler signals at 2, 3, 4, and 5 min postdose (118.9 +/- 18.8, 128.5 +/- 16.9, 146.6 +/- 18.6, and 131.2 +/- 14.2 mV, respectively), whereas the MCP group exhibited a significant (P < 0.05 or 0.01) decrease in the signals at 4 and 5 min postdose (67.9 +/- 5.3 and 64.8 +/- 3.5 mV, respectively), as compared not only with the respective baseline values but also with those obtained from other two groups at the corresponding postinjection periods.(ABSTRACT TRUNCATED AT 250 WORDS)

[Cutaneous microcirculation and diabetic disease. A functional and flowmetry study in subjects with diabetes mellitus type 2]

Laser-Doppler single fingertip skin blood flow has been evaluated in 41 euglycemic type II diabetic patients under basal conditions and after dynamic testing (both ischemia and thermal stress). The same subjects have also undergone tests for the assessment of the degree of autonomic nervous system (ANS) dysfunction. The results have been compared to those obtained in 38 age-matched healthy subjects. In diabetic patients: baseline flow levels were much higher; the post-ischemic flow increase was less evident; a shorter hyperemic phase followed ischemia; a longer latency period was noticed, during thermal stress, together with a lower and slower hyperemic peak level. According to the results of ANS dynamic tests, diabetic subjects were divided into 3 groups: Group 1 (subjects with negative results); Group 2 (subjects with only one positive result); Group 3 (subjects with more than one positive test). Microcirculation disturbances were more often found in Group 3. These results show that a correlation exists between diabetic microangiopathy and ANS dysfunction. They also support the hypothesis, already pointed out by other research groups, of a similar mechanism causing diabetic neurologic and vascular complications.

Experiments on extracted teeth into the validity of using laser Doppler techniques for recording pulpal blood flow

The performances of two laser Doppler flow meters (Periflux model PF3 and Moor Blood Flow Monitor model MBF3D) were investigated. Recordings were made while diluted blood was pumped at different rates through the pulp cavities of extracted human or pig teeth. The probe of each instrument was fixed to the enamel surface 2 mm from the original position of the gingival margin. Both instruments performed similarly, although the Moor gave the better signal/noise ratios. Both were capable of detecting flow in the core of the pulp as well as the superficial part closest to the probe tip. With either instrument, and with any one dilution of blood (range 0.5-45% v/v red cells), there was a near-linear relationship between the blood-flow signal and the flow rate of blood through the tooth. However, when data obtained with different red-cell concentrations were compared, a good correlation between the blood-flow signal and red-cell flux (product of concentration and mean velocity) was obtained only with red-cell concentrations up to 1% v/v. Therefore these instruments would give an accurate indication of blood flow changes only under conditions in which either this value was not exceeded or if the red-cell volume fraction remained constant; neither of which can be assumed to apply when recording from teeth in situ. The signals representing the concentration of moving blood cells were unreliable in both instruments. It is concluded that the information provided by these laser Doppler flow meters can be ambiguous and must be interpreted with care.

Prediction of sampling depth and photon pathlength in laser Doppler flowmetry

Monte Carlo simulation of photon migration in tissue was used to assess the sampling depth, measuring depth and photon pathlength in laser Doppler flowmetry. The median sampling depth and photon pathlength in skin, liver and brain tissue were calculated for different probe geometries. The shallowest median sampling depth found was 68 microns for a 120 microns diameter single fibre probe applied to a one-layered skin tissue model. By using separate transmitting and receiving fibres, the median sampling depth, which amounted to 146 microns for a 250 microns fibre centre separation, can be successively increased to 233 microns when the fibres' centres are separated by 700 microns. Total photon pathlength and thereby the number of multiple Doppler shifts increase with fibre separation, thus favouring the choice of a probe with a small fibre separation when linearity is more important than a large sampling depth. Owing mainly to differences in the tissue g-value and scattering coefficient, the median sampling depth is shallower for liver and deeper for brain, in comparison with skin tissue. For skin tissue, the influence on the sampling depth of a homogeneously distributed blood volume was found to be limited to about 1 per cent per percentage increase in tissue blood content, and may, therefore, be disregarded in most practical situations. Simulations show that the median measuring depth is strongly dependent on the perfusion profile.

[An apparatus using laser speckle phenomenon for noninvasive 2-dimensional analysis of choroidal microcirculation]

A new instrument using the laser speckle phenomenon for noninvasive 2-dimensional analysis of the choroidal microcirculation was developed. The fundus was illuminated with a diode laser spot and its image speckle was detected with an area sensor. The difference between the average of the output data (I-mean) and the output data from successive scannings of the image speckles at the sensor plane was calculated and integrated to give as D-mean, and I-mean/D-mean was defined as normalized blur (NB), which is a quantitative index of blood flow velocity. The results were displayed in color graphics showing the 2-dimensional variation of the NB level in the area of interest. The NB had good correlation with the speed measured on ground glass in the range between 2 and 130mm/sec. Using this instrument, the effect of intraocular pressure on the chroidal circulation of the rabbit was studied. The coefficient of reproducibility was 6.9% when measured in the same area twice at 5-minute intervals. A stepwise reduction in the ocular perfusion pressure was introduced by elevating the intraocular pressure manometrically. A linear correlation was found between the NB and the ocular perfusion pressure.

Laser Doppler perfusion imaging by dynamic light scattering

Imaging of tissue perfusion is important in assessing the influence of peripheral vascular disease on microcirculation. This paper reports on a laser Doppler perfusion imaging technique based on dynamic light scattering in tissue. When a laser beam sequentially scans the tissue (maximal area approximately 12 cm *12 cm), moving blood cells generate Doppler components in the back-scattered light. A fraction of this light is detected by a remote photodiode and converted into an electrical signal. In the signal processor, a signal proportional to the tissue perfusion at each measurement point is calculated and stored. When the scanning procedure is completed, the system generates a color-coded perfusion image on a monitor. A perfusion image is typically built up of data from 4,096 measurement sites, recorded during a time period of 4 min. This image has a spatial resolution of about 2 mm * 2 mm. A theory for the system inherent amplification factor dependence on the distance between individual measurement points and detector is proposed and correction measures are presented. The performance of the laser Doppler perfusion imager was evaluated using a flow simulator. The correlation coefficient between the estimated flow parameter and the perfusion through a mechanical flow simulator was calculated to r = 0.996. To assess the sampling depth of the laser beam, light scattering in tissue was simulated by a Monte Carlo technique. The average sampling depth for skin tissue was calculated to 200-240 microns, depending on the blood content.(ABSTRACT TRUNCATED AT 250 WORDS)