CN103211588B - Blood flow velocity imaging method based on transverse velocity model - Google Patents
Blood flow velocity imaging method based on transverse velocity model Download PDFInfo
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- CN103211588B CN103211588B CN201310161275.9A CN201310161275A CN103211588B CN 103211588 B CN103211588 B CN 103211588B CN 201310161275 A CN201310161275 A CN 201310161275A CN 103211588 B CN103211588 B CN 103211588B
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Abstract
The invention provides a blood flow velocity imaging method based on a transverse velocity model. The method includes the steps that laser which is subjected to beam expansion is used for irradiating the body surface, and a CMOS camera is used for carrying out continuous imaging on irradiated areas; motion of red cells in shallow blood vessels of the body surface causes fluctuation of backscattering light intensity; an overall pixel matrix is used as a paralleled detector array, and each pixel in the CMOS camera is used as an independent detector; light intensity signals recorded by each pixel form an independent signal sequence, a normalized autocorrelation function of each signal sequence is calculated after continuous imaging; and the gradient of a linear area before a first zero point of the normalized autocorrelation function is the crossing time tau0 of the red cells transversely penetrating through detecting focal spots, and the transverse speed of the red cells is Vtransverse=w/tau0, and w is the transverse width of the detecting light focal spots.
Description
Technical field
The present invention relates to blood flow imaging technical field, particularly a kind of blood flow velocity formation method based on transverse flow speed model.
Background technology
The fast imaging that body surface shallow-layer microcirculqtory system blood flow velocity distributes, be widely used clinically, at present, the blood flow imaging technology of Noninvasive comprises: Speckles Technique, acoustic doppler velocimeter, Doppler laser velocimeter, doppler optical coherence chromatography, the laser Doppler perfusion imaging technology based on high-speed cmos camera.Speckles Technique can not carry out quantitative measurement, is not also suitable for flow velocity faster, and acoustic doppler velocimeter can only be for trunk, cannot be for microcirculqtory system.Doppler optical coherence chromatography and Doppler laser velocimeter are all spot measurements, need mechanical scanning to realize larger area imaging, and image taking speed is slow.Laser Doppler perfusion imaging technology based on high-speed cmos camera is the improvement to Doppler laser velocimeter, the same with Doppler laser velocimeter is all based on Doppler effect, use frame rate for the high-speed cmos camera of 20KHZ left and right, replace mechanical scanning, realize fast imaging.But this high-speed cmos camera and needed googol, according to transmission and processing speed, make the cost of this imaging technique very high, it is larger that while blood flow velocity result is affected by doppler angle uncertainty.
Summary of the invention
The object of the invention is to provide a kind of blood flow velocity formation method based on transverse flow speed model, it can intermittently pass in and out the low frequency fluctuation of surveying the backscattering light intensity signal that light focal spot causes by erythrocyte and remove to calculate blood flow velocity, with the method for the high frequency Fluctuation Calculation blood flow velocity being caused by Doppler effect that replaces using at present.
Technical solution proposed by the invention is such:
A kind of blood flow velocity formation method based on transverse flow speed model, this formation method comprises the steps: to use the laser 5 through expanding to irradiate body surface 6, with 7 pairs of area to be illuminated territory continuous imagings of CMOS camera, the light intensity signal of CMOS camera 7 each pixel record forms independently signal sequence, calculate the normalized autocorrelation functions of each signal sequence, before first zero point of normalized autocorrelation functions, the slope in partial linear region is that erythrocyte 1 is horizontally through the transition time of surveying light focal spot 2
, erythrocytic lateral velocity is
, wherein,
for surveying the transverse width of light focal spot.
Principle of the present invention is as follows: the laser 5 through expanding is to irradiate body surface 6 with the subvertical direction of body surface 6, with 7 pairs of area to be illuminated territories of CMOS camera, carry out continuous imaging, the whole picture element matrix of CMOS camera 7 is equivalent to parallel detector array, each pixel is an independently detector, records corresponding focus place time dependent backscattering light intensity signal.Suppose that the blood circumstance at the focal spot place that certain pixel is corresponding is as shown in Fig. 1 (a), in figure, stain represents mobile erythrocyte, dotted rectangle frame table shows the focal spot 2 of surveying light, when erythrocyte does not enter detection light focal spot 2, the signal reflecting back is very weak, when erythrocyte 1 enters detection light focal spot 2, have stronger reflected signal, therefore be subject to the interrupted turnover of mobile erythrocyte 1 to survey the modulation of light focal spot 2, backscattering light intensity signal forms pulse one by one in time, when erythrocyte 1 translational speed is when slower, time through detection light focal spot 2 is longer, the pulse width producing is larger, when erythrocyte 1 translational speed is when very fast, time through detection light focal spot 2 is shorter, the pulse width producing is narrower, the corresponding erythrocyte 1 of time width of pulse is through the time of surveying light focal spot 2, it is the transition time
.In Fig. 1 (a), in non-focusing region, through the erythrocyte 3,4 of detecting light beam, because these erythrocyte 3,4 are outside focal spot 2, less on the impact of backscattering light intensity signal, therefore, the erythrocytic impact outside focal spot 2 can be ignored.In Fig. 1 (b), rectangle frame represents the focal spot 2 amplifying, and erythrocyte is with speed
flow through focal spot 2, survey light vertically, doppler angle is
,
longitudinal component
cause Doppler frequency shift, be assumed to
; Erythrocyte is with lateral velocity
through surveying light focal spot 2, back-scattering light can be expressed as
, suppose blood vessel around the back-scattering light of stationary tissue be
, this two parts light all enters detector and interferes (being heterodyne method), and the light detecting is
, because
much smaller than
, the light intensity signal detecting can be reduced to
, as shown in Figure 2 (a) shows, the higher-order of oscillation wherein derives from Doppler effect,
so,, the blood flow imaging method based on Doppler effect is all that analysis of high frequency vibration signal calculates flow velocity, higher to the frame frequency requirement of camera, generally at 20KHZ.Low frequency envelope in Fig. 2 (a) (as shown in Fig. 2 (b)) corresponding to
, the pulse in Fig. 2 (b) is exactly that erythrocyte forms through surveying light focal spot, so width average time of pulse is exactly, and erythrocyte is through the time of surveying light focal spot, i.e. transition time
, suppose that the transverse width of surveying light focal spot is
, erythrocytic lateral velocity
.Because the frequency of the low-frequency pulse in Fig. 2 (b) is lower, therefore the frame frequency of camera is required to be not less than 500HZ.When the time of exposure of camera is greater than several cycle of the higher-order of oscillation that Doppler effect causes, the higher-order of oscillation that Doppler effect causes, just by average, only has erythrocyte intermittently to pass in and out and surveys the low-frequency pulse that light focal spot causes, as shown in Fig. 2 (b) in signal.
Although transverse flow speed model can only obtain the cross stream component of flow velocity,
,
for actual flow velocity,
for doppler angle, because body surface shallow-layer blood vessel major part is all to approach parallel distribution with body surface, when imaging system and irradiating laser and body surface approach when vertical, doppler angle
scope between 90 °～80 °, the scope of flow velocity cross stream component exists
between, approach very much actual flow velocity
so, with transverse flow speed, can represent actual flow velocity, need not consider the impact of unknown doppler angle, and the current blood flow imaging method based on Doppler effect obtains, be the longitudinal component of flow velocity,
, work as doppler angle
scope exist
in the time of between degree, result is
, and actual flow velocity
differ larger, can not reflect true flow velocity.
For the signal as shown in Fig. 2 (b), by normalized autocorrelation functions, calculated the mean breadth of pulse, i.e. the transition time
,
（1）
In above formula
the auto-correlation function of the light intensity signal that expression detects.
Fig. 3 (a) and (b), (c) represent respectively the low frequency envelope signal that flow velocity ratio detects while being 4:2:1, although under same speed, width and the amplitude of the backscattering light pulse that erythrocyte produces while passing detection light focal spot are variant, but the width of flow velocity and pulse has obvious dependency.The normalized autocorrelation functions of Fig. 3 (a) and (b), (c) is as shown in Fig. 3 (d), cross hairs, solid line and the dotted line result that corresponding flow velocity ratio is 4:2:1 respectively, choose that between two horizontal dotted lines, the reasonable region of the linearity is as slope computer capacity (being that ordinate value is the scope between 0.2～0.8), the inverse of the slope that three is corresponding (is the transition time
) ratio be 19:10:6, the ratio of transverse flow speed is 1:1.9:3.2, and flow velocity is substantially identical.
Compared with prior art, the present invention has following remarkable result:
(1) the present invention proposes a kind of computation model of flow velocity cross stream component, by erythrocyte, intermittently pass in and out the low frequency fluctuation of surveying the backscattering light intensity signal that light focal spot causes and calculate flow velocity, replace the method for the high frequency Fluctuation Calculation flow velocity being caused by Doppler effect of use at present, make the minimum requirements of CMOS camera frame frequency be reduced to 500HZ by existing 20KHZ, thereby reduced the requirement to CMOS camera and data transmission and processing speed.
(2) what this method was measured is flow velocity cross stream component, and doppler Method is measured, be flow velocity longitudinal component, body surface shallow-layer blood vessel major part is all to approach parallel distribution with body surface, flow velocity cross stream component be subject to doppler angle probabilistic affect less, thereby, more approach real blood flow rate.
Accompanying drawing explanation
Fig. 1 (a) is the blood flow velocity imaging schematic diagram based on transverse flow speed model, represents that erythrocyte is flowed through to survey the schematic diagram of light focal spot 2 in figure.
Fig. 1 (b) is the enlarged drawing of the detection light focal spot shown in Fig. 1 (a).
Fig. 2 (a) represents the light intensity signal that CMOS camera detects.
The light intensity signal that Fig. 2 (b) expression detects is removed the envelope of the higher-order of oscillation.
Fig. 3 (a) represents that flow velocity ratio is the envelope that the light intensity signal that detects is removed the higher-order of oscillation at 4 o'clock.
Fig. 3 (b) represents that flow velocity ratio is the envelope that the light intensity signal that detects is removed the higher-order of oscillation at 2 o'clock.
Fig. 3 (c) represents that flow velocity ratio is the envelope that the light intensity signal that detects is removed the higher-order of oscillation at 1 o'clock.
The normalized autocorrelation functions of the low frequency envelope that Fig. 3 (d) expression detects according to Fig. 3 (a), Fig. 3 (b), Fig. 3 (c).
Fig. 4 is the structural representation of the blood flow velocity imaging device based on transverse flow speed model.
The specific embodiment
By embodiment below, the present invention is further elaborated.
Shown in Figure 4, a kind of blood flow velocity imaging device based on transverse flow speed model is comprised of laser instrument 10, beam expanding lens 9, imaging system 8, CMOS camera 7 and computer 11.The blood flow that object 6 to be measured is palm top layer is body surface, the laser that laser instrument 10 sends irradiates body surface 6 after beam expanding lens 9 expands, the laser 5 expanding approaches vertical with body surface 6, imaging system 8 makes irradiated area image in CMOS camera 7, computer 11 is controlled the image of CMOS camera 7 continuous acquisition imaging regions, each pixel of CMOS camera 7, as detector independently, records corresponding focus place time dependent backscattering light intensity signal.The focus point of supposing pixel 12 correspondences is 13, and the signal that pixel 12 collects is
, calculate
normalized autocorrelation functions, the slope in partial linear region is that erythrocyte 1 is horizontally through the transition time of surveying light focal spot 2 before first zero point of normalized autocorrelation functions
, with formula (1), calculate erythrocyte through the transition time of 13 focal spots 2
, transverse flow speed is
, here
to survey light focal spot 2 transverse widths.
Survey light focal spot 2 transverse widths
by following methods, measured: by a known flow rate, be
in vitro blood flow as sample, regulate light beam and blood flow flow direction to approach vertical, according to above-mentioned same method, measure the time that erythrocyte passes detection light focal spot 2
, can obtain
.
Therefore, transverse flow speed is
.
Signal sequence to CMOS camera 7 each pixel record is processed according to above method, can obtain the blood flow rate distributed image of whole imaging region.
Parameter for the blood flow velocity imaging device critical piece based on transverse flow speed model of this method is as follows: the frame frequency of CMOS camera 7 is 500HZ; The time of exposure of selecting CMOS camera 7 is that second 100 is delicate.
Claims (1)
1. the blood flow velocity formation method based on transverse flow speed model, it is characterized in that: be provided with by laser instrument (10), beam expanding lens (9), imaging system (8), the blood flow velocity imaging device based on transverse flow speed model that CMOS camera (7) and computer (11) form, adopt this device to carry out laser irradiation body surface (6) after beam expanding lens (9) expands that blood flow velocity formation method comprises the steps: that laser instrument (10) sends, the laser expanding (5) approaches vertical with body surface (6), imaging system (8) makes irradiated area image in CMOS camera (7), computer (11) is controlled the image of CMOS camera (7) continuous acquisition imaging region, each pixel of CMOS camera (7) is as detector independently, record corresponding focus place time dependent backscattering light intensity signal, calculate the normalized autocorrelation functions of the time dependent light intensity signal of each pixel record, before first zero point of normalized autocorrelation functions, the slope of the range of linearity is that erythrocyte (1) is horizontally through the transition time of surveying light focal spot (2)
, erythrocytic lateral velocity is
, wherein,
for surveying the transverse width of light focal spot.
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| CN109924969A (en) * | 2019-04-19 | 2019-06-25 | 优谱激光科技(南京)有限公司 | A kind of laser imaging blood perfusion detection device with light probe |
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