共查询到20条相似文献,搜索用时 10 毫秒
1.
Laser Doppler perfusion monitoring and imaging technologies generate time traces and two-dimensional flow maps of the microcirculation.
With the goal of reaching different tissue depths, these technologies are equipped with lassers operating at different wavelengths
λ. The fact that the average scattering angle, at a single scattering event, between a photon and a red blood cell increases
with λ is compensated for by a 1/λ effect in the scattering vector, rendering the average frequency shift virtually independent
of the choice of wavelength. Monte Carlo simulations showed that the corresponding spectral signature of the Doppler signals
for λ=632.8nm and 780nm were close to identical. The theoretical predictions were verified by calculating the centre-of-gravity
(COG) frequency of the laser Doppler power spectral density for the two wavelengths from forearm and finger skin, representing
a low and high perfusion area, respectively (forearm COG=123 against 121Hz, finger COG=220 against 212 Hz). When the wavelength
changes from 632.8nm to 780nm, the heterodyne efficiency of the detector and, thereby, the inherent system amplifcation increase.
For tissues with identical microvascular flow conditions, the output signal therfore tends to increase in magnitude when shifting
to longer wavelengths. 相似文献
2.
Laser Doppler flowmetry (LDF) is a non-invasive method to measure tissue blood flow. During reactive hyperaemia, the LDF signal
increases to a peak and then returns to a resting value. A simplified model is developed to explain these variations. The
emphasis is on simulating the effects occurring rather than on trying to mimic the anatomical structure of the microcirculation.
A single blood vessel is therefore analysed. The increasing value of blood velocity is studied, and vasodilatation as well
as vasoconstriction are taken into account. The model parameters are calculated using wavelets. For a 2-min occlusion on a
healthy subject, the radius of the vessel is initially 15 μm, increasing to 24.6 μm at the peak, reached 14 s after the release
of the occlusion. The model shows that the high value of the LDF signal during the initial phase of reactive hyperaemia is
produced by an increasing number of erythrocytes in a cross-section, due to vasodilatation rather than an increase in moving
blood cell velocities. Moreover, the rapidity of the vasodilatation and vasoconstriction effects determine the rapidity of
the signal variations. The paper aims to give a basic solution to develop a numerical model. 相似文献
3.
Analysis and processing of laser Doppler perfusion monitoring signals recorded from the beating heart 总被引:1,自引:0,他引:1
Karlsson MG Casimir-Ahn H Lönn U Wårdell K 《Medical & biological engineering & computing》2003,41(3):255-262
Laser Doppler perfusion monitoring (LDPM) can be used for monitoring myocardial perfusion in the non-beating heart. However,
the movement of the beating heart generates large artifacts. Therefore the aim of the study was to develop an LDPM system
capable of correlating the laser Doppler signals to the cardiac cycle and to process the signals to reduce the movement artifacts.
Measurements were performed on three calves, both on the normal beating heart and during occlusion of the left anterior descending
coronary artery (LAD). The recorded LDPM signals were digitally processed and correlated to the sampled ECG. Large variations
in the output (perfusion) and DC signals during the cardiac cycle were found, with average coefficients of variation of 0.36
and 0.14 (n-14), respectively. However, sections with a relatively low, stable output signal were found in late diastole,
where the movement of the heart is at a minimum. Occlusion of the LAD showed the importance of recording the laser Doppler
signals at an appropriate point in the cardiac cycle, in this case late systole, to minimise movement artifacts. It is possible
to further reduce movement artifacts by increasing the lower cutoff frequency when calculating the output signal. 相似文献
4.
Melhuish JM Krishnamoorthy L Bethaves T Clark M Williams RJ Harding KG 《Medical & biological engineering & computing》2004,42(2):259-263
The microcirculation under compression bandages has been assessed by numerous methods; however, the measurement techniques
can disrupt the bandage-skin interface, affecting the measurement. In this study, a non-invasive method for measuring cutaneous
blood flow using laser Doppler flowmetry (LDF) is presented. Ten volunteers had their microcirculation assessed by a laser
Doppler probe being placed on their upper forearm with and without a light-transmissive gel and with a compression bandage
plus light-transmissive gel. A circulatory challenge to the bandaged forearm in two of the volunteers was also undertaken.
The median (95% confidence interval) perfusion (p.u.) for the skin surface was 24 (15–33) perfusion units (p.u.), and the
skin plus light-transmissive gel demonstrated a higher perfusion: 66 (50–82) p.u., (p<0.012). The addition of the compression
bandage, with additional gel allowed to permeate through to the underlying skin, decreased the perfusion to 27 (20–34) p.u.
(p<0.007). In both volunteers, the microcirculatory flow responded to the vascular challenge, resulting in flow changes related
to the cuff pressure (45-27 and 14-8 p.u.). This method demonstrated that it may be possible to assess the microcirculation
through intact bandages, without the need to place any sensors at the skin-bandage interface. 相似文献
5.
Dr A. N. Obeid 《Medical & biological engineering & computing》1993,31(1):43-52
The paper reports the results of investigations comparing the relative in vitro responses of different signal processing algorithms
commonly employed in laser Doppler flowmetry (LDF). A versatile laser Doppler system is described which enabled complex signal
processing to be implemented relatively simply using digital analysis. The flexibility of the system allowed a variety of
processing algorithms to be studied by simply characterising the algorithm of interest under software control using a personal
computer. An in vitro physical model is also presented which was used to maintain reproducible fluid flows. Flows of particles
were studied in a physical model using both a near-infra-red (NIR) diode and an He/Ne laser source. The results show that
frequency-weighted algorithms are responsive to both particle velocity and concentration, whereas non-weighted algorithms
respond to concentration only. The linearity of the velocity response is critically dependent on both the dimensions of the
in vitro model and the frequency bandwidth of the signalprocessing algorithm. 相似文献
6.
Comparison of laser speckle and laser Doppler perfusion imaging: Measurement in human skin and rabbit articular tissue 总被引:7,自引:0,他引:7
Forrester KR Stewart C Tulip J Leonard C Bray RC 《Medical & biological engineering & computing》2002,40(6):687-697
Laser Doppler perfusion imaging (LDI) is currently used in a variety of clinical applications, however, LDI instruments produce
images of low resolution and have long scan times. A new optical perfusion imager using a laser speckle measurement technique
and its use for in vivo blood flow measurements are described. Measurements of human skin and surgically exposed rabbit tissue
made using this instrument were compared with a commercial laser Doppler perfusion imaging instrument. Results from blood
flow measurements showed that the laser speckle imager measured an 11–67% decrease in blood flow under arterial occlusion.
Under similar conditions, the laser Doppler imager measured blood flow decreases of 21–63%. In comparison with LDI, it was
observed that the higher temporal resolution of the laser speckle imager was more sensitive to measuring the hyperaemic response
immediately following occlusion. This in vivo study demonstrated some of the several advantages laser speckle imaging has
over conventional LDI, making the new instrument more versatile in a clinical environment. 相似文献
7.
8.
G. E. Nilsson 《Medical & biological engineering & computing》1984,22(4):343-348
Laser Doppler flowmeter for the assessment of tissue blood flow are generally equipped with a signal processor which generates
the first moment of the unnormalised power spectral density as a continuous output signal. This signal is related to blood
flow for low and moderate flow rates. At higher flow rates the interpretation of the output signal becomes ambiguous as a
consequence of the multiple scattering in moving blood cells and the homodyne mixing of waves on the detector surface. The
paper describes a new signal processor which takes these effects into account and establishes a linear relationship between
the flowmeter output signal and blood flow for all flow rates. The performance of the signal processor was evaluated by an
experimental fluid model which optically resembled the blood flow through the microvasculature. The transiently high blood
flow in the initial phase of reactive hyperaemia, recorded from palmar skin, gave peak values which were almost double those
recorded with the original signal processor of the flowmeter. In conjunction with these high peak values a high concentration
of moving blood cells was recorded, indicating that the initially high flow rate is produced by an increased number of moving
blood cells due to vasodulation rather than by a change in average velocity. 相似文献
9.
Low-frequency noise in laser Doppler recordings can be generated because of thermal instabilities in the gas laser cavity.
Mode partition noise can be eliminated by thermal stabilisation of the laser cavity. The paper describes a method for closed
loop temperature control of the laser cavity. The method uses orthogonal properties of longitudinal laser modes for the temperature
control. The signal-to-noise ratio is considerably improved by the procedure. It is recommended that all gas laser equipped
Doppler instruments used for precision blood flow studies shold be equipped with stabilised laser sources. 相似文献
10.
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 μm for a 120 μm 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 μm for a 250 μm fibre centre separation, by be successively increased to 233 μm when the fibres' centres
are separated by 700 μm. 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. 相似文献
11.
12.
H. Ahn K. Johansson O. Lundgren G. E. Nilsson 《Medical & biological engineering & computing》1987,25(2):207-211
The performance of different signal processors for laser Doppler tissue flowmeters was evaluated by the use of a well defined
flow model comprising a segment of the feline intestinal wall. The processor that, apart from being based on the calculation
of the first moment of the power spectral density, also takes into account the effect of multiple scattering in a number of
blood cells gave an output signal that was linearly related to the intestinal wall perfusion as recorded independently by
a drop-counting technique. At a recording bandwidth of 12 kHz, this linear relationship was valid for the entire flow range
0–300 ml min−1 100 g−1 (r=0·98). The processor based on the first moment of the power spectral density alone under-estimated the highest flow rates
by about 35 per cent, while within the flow range 0–100 ml min−1 100 g−1 this processor also gave an output signal linearly related to flow at a recording bandwidth of 12 kHz (r=0·96). When the
bandwidth was limited to 4 kHz, the output signals from both processors were linearly related to flow only within the range
0–100 ml min−1 100 g−1 (r=0·90). The output signals recorded with the 4 kHz systems were, however, generally only about 65 per cent of those recorded
with the 12 kHz systems. 相似文献
13.
14.
Discrimination of capillary and arterio-venular blood flow in skin by laser Doppler flowmetry 总被引:5,自引:0,他引:5
The scattering and absorption of light by tissue and blood is wavelength dependent; the tissue penetration of green light
(λ=543·5nm) is about 60 per cent of that of red light (λ=632·8 nm) but the absorption of green light by blood is about 20
times greater than for red light. The effect of this difference has been studied by observing the responses of skin blood
flow to heat and weal, measured by laser Doppler flowmetry at the two wavelengths. By using time autocorrelation function
analysis (ACF) of the scattered light measured, low and high frequency components have been associated with capillary and
larger vessel flow, respectively. The comparison of ACF from scattered green and red light has shown that measurements cannot
be interpreted by only considering light penetration depth through a homogeneous tissue. Light absorption and multiple scattering
by blood at the individual microvessel level, blood rheology and vessel morphology are parameters which are considered for
greater attention. 相似文献
15.
16.
Integrating probe for tissue laser Doppler flowmeters 总被引:1,自引:0,他引:1
Methods to measure microvascular blood flow usually probe small volumes of tissue. Therefore, spatial differences in skin
blood flow alter the signal, when the sensing element is moved a short distance. To reduce the effects of spatial differences
in skin blood flow, but yet record its temporal variability, a new integrating probe for laser Doppler flowmeters was developed.
The probe receives light from seven different scattering volumes simultaneously, and the instrument processes an integrated
signal which is ultimately taken as the average flow value. Significant spatial integration is found, as spatial variability
is reduced by the square root of the number of scattering volumes. 相似文献
17.
A new method of screening for diabetic neuropathy using laser Doppler and photoplethysmography 总被引:2,自引:0,他引:2
Kim SW Kim SC Nam KC Kang ES Im JJ Kim DW 《Medical & biological engineering & computing》2008,46(1):61-67
The purpose of this study is to suggest a simple, new method of screening for diabetic neuropathy. We measured blood volume
changes by photoplethysmography (PPG) and blood perfusion by laser Doppler (LD) in the index fingers and big toes in 40 control
subjects and in 50 (19 mild, 17 moderate, and 14 severe based on the nerve conduction velocity (NCV) test) and 35 diabetic
patients with and without neuropathy, respectively. According to the results of PPG and LD measurements, the toe to finger
ratios obtained from the neuropathic group were significantly higher than those from the control (p < 0.001) and the non-neuropathic groups (p < 0.001). Based on the NCV, the sensitivity of the LD method (92.0%) was higher than that of the PPG method (84.0%) for both
left and right sides. Although specificity of the LD (92.8%) was also higher than the PPG (84.3%) bilaterally, the PPG showed
better reproducibility (5.5 versus 9.5%) and a significant ratio increase with severity, while the LD did not. Our suggested
PPG method using the toe to finger ratio is reliable, simple, economical, and accurate, and could become an effective new
screening tool for the early detection of diabetic neuropathy. 相似文献
18.
Yu. N. Belenkov I. V. Shatalova V. A. Voronin 《Bulletin of experimental biology and medicine》1996,121(4):434-437
An experimental model is used to reproduce high-speed unsteady turbulent flows of small diameter (3 to 5 mm). The spectra
of the simulated flows were recorded by the continuous Doppler method and their volumes were estimated as the product of the
velocity-time integrals times the cross-sectional area of the tubes. The flow volumes were too high in comparison with the
specified values in all cases, necessitating the use of correction factors. The factors were inversely proportional to the
flow velocities, and thus to the turbulence (as is evident from the Reynolds turbulence equation). For the range of maximum
velocities of turbulent intracardiac flows most frequently occurring in practice (140 to 500 cm/sec) the correction factors
were 0.76–0.87. The method may be very helpful in developing noninvasive criteria of the severity of regurgitations, in differentiating
these, and in determining the prognosis, particularly for borderline states and combined heart defects.
Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 121, No. 4, pp. 477–480, April, 1996
Presented by E. I. Chazov, Member of the Russian Academy of Medical Sciences 相似文献
19.
R. Bray K. Forrester J. J. McDougall A. Damji W. R. Ferrell 《Medical & biological engineering & computing》1996,34(3):227-231
Laser Doppler imaging (LDI) is investigated as a novel method for in vivo ligament tissue blood flow determination. LDI output
signal is obtained from surgically exposed rabbit medial collateral ligaments (MCL). The LDI signal, is compared with simultaneously
determined, coloured microsphere (CM)-derived standardised MCL blood flow. Correlation of LDI output with the CM flow data
and a linear regression of 17 data points in nine rabbits (joint injured to provoke an acute vascular response in the tissues)
indicate that LDI provides a reasonable estimate of MCL blood flow, at least over the ranges assessed. If properly calibrated,
and given enough tissue-specific data points, LDI may have advantages over conventional, but more invasive, techniques. The
potential clinical application of LDI technology to joint injury and arthritis research is discussed. 相似文献
20.
L. A. Mikhailichenko 《Bulletin of experimental biology and medicine》1999,128(2):786-790
The dynamics of fluctuations of capillary blood flow in the cortex of rat kidneys under conditions of transient occlusion
of renal arteries and veins or simultaneous occlusion of afferent and efferent vessels was studied by laser Doppler flowmetry.
The initial variability of blood flow in the right kidney was higher than in the left kidney. The most pronounced changes
in the right kidney were observed during occlusion and subsequent recirculation. In the left kidney, the most pronounced changes
were found during occlusion and after arterial occlusion. Spectral analysis gave similar results. The recovery of renal blood
flow after transient venous occlusion took longer time than after arterial occlusion (especially in the right kidney).
Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 128, No. 8, pp. 148–152, August, 1999 相似文献