WITH effect Doppler we we meet on a daily basis, not realizing of this . Imagine to myself passing through by you car with siren . Tone sirens more tall at approaching car ( morehigh frequency ) than at him removal ( more than low frequency ). Change niya frequencies ( Doppler shift frequency ) depends from speeds the car and original frequencies sirens .Analysis ultrasound waves reflected from boundaries tissue, gives information about the depth and reflective abilities tissues . Classic Doppler is following uses ultrasound waves ,reflected ny from moving red blood cells . Effect Doppler is used for receiving information about speeds blood flow . Speed blood flow determined by by change to frequencies sentand accepted ultrasound momentum . Shift frequencies ( Doppler shift ) about portional respect speeds blood flow to speeds sound and original frequency.
is he computed by the next formula :
where F d – Doppler shift ; F0 – initial frequency ; V – speed blood flow ; WITH – with scab sound .
Therefore , the speed blood flow equals :
F xC V = – ——-.
F0 V more strict the form formula It has following
Fd x With V = ——————- •
2 F0 x Cos0
Original frequency multiplied by 2 so as dopple rovsky shift arises twice : when transfer momentum and at reflection .
Cosine theta (Cose) is introduced at formula for accounting corner between ultrasound by beam and bloodstream .
Cose = 1 if ultrasonic Ray parallel blood current . With this registered maximum speed. Cose = 0 when direction ultrasound ray perpen dicularly bloodstream . With this registeredzero speed. For correct measurements angle between ultra sound by beam and blood flow should be less than 20 ° .
Important consider that at doppler – echocardiography maximum speed succeeds to register at direction ultrasound ray parallel isle dummy bloodstream . AT otherwise casemaximum speed and , accordingly , the gradient Pressure (cm. below) will be undervalued . With this at standard Echocardiography the best quality Images is achieved at directionultrasound ray perpendicular investigated structure .
Insofar as value original frequency (2F0) is at denominator formula, the maximum values soon STI are recorded at using low frequency sensors (2.5 MHz ). Than above maximumspeed blood flow through stenotic valve , the above gradient pressure . It is obvious that at decreasing from version valve for ensure permanent shock
volume required increase speed . Increase speeds can be measured at using Doppler – echocardiography .
Gradient pressure through valve can be calculated with using simplified the equations Bernoulli :
D P = 4 V2,
Where R – gradient pressure ( in mm Hg. Art .); V – maxi little speed blood flow ( in m / s ).
This the equation often is used at doppler – echocardiographic research stenosis and untill fatigue valves as well also intracardiac discharges . High speed indicators blood flowcomplement anatomy chesky information by according to M – mode and two-dimensional Echocardiography . Analysis doppler signal provides information not only about speed, butand direction blood flow . Speed, direction to sensor , from are fighting above isolines ( positive values ), and speed, designed from sensor , – below isolines ( negative values ).
Reflected Doppler signal presents with the battle spectrum speeds by of time . Square under crooked spectrum denoted by as integral speeds blood flow . Value integral speedsblood flow depends on from maximum speeds and of time exile . The indicator can be calculated on most echo cardiographic devices .
Careful analysis spectrum speeds gives infor mation about density flow . Density depends on from numbers red blood cells, moving with certain by speed . With uniform or laminarcharacter blood current most red blood cells moving with the same speed, at the same time speeding up and slowing down . With this spectrum speeds It has narrow the borderand only a little number red blood cells moving with other sko rosty . This phenomenon is described as low variability speed . With turbulent character blood flow through stenoticvalve is observed wide scatter values speeds red blood cells . With this Doppler spectrum you looking ” Filled . “ This phenomenon is described as high variability speeds or “Expansion spectrum . “
Should have at mind that turbulent character blood flow and expansion spectrum often associate, but not are identical high speeds signal . Inten sivness doppler signal on grayishimage is presented different shades gray . Maximum number erythrocytes, driving camping with certain speed, forms dark part spectrum . Few red blood cells, moving with highspeed, form light part spectrum . The best way this it is seen at doppler research ste – nozirovannogo valve . The greatest density spectrum celebrated at contour lines, so as mostred blood cells moving with low by speed directly above or under valve . Small part erythrocy com , speeding up through stenotic the valve moves with high by speed .
AT clinical practice are used modes constantly – wave and pulsed Doppler research . With constantly – wave doppler research are used two piezoelectric crystal . One constantlytransmits as well other constantly takes signal without delays by of time . it allow ate measure high speeds without clear localization the source signal by throughout the lengthUltrasound kovogo ray .
With pulsed doppler research one piezoelectric crystal is used as for re cottages pulse, so and for reception reflected signal through preset time.
Impulse Doppler research allows exactly define a source speed signal . For localization the source ” Control volume ” , about meaningful small rectangle or circle, set at regioninterest , focusing by two-dimensional image . Control volume can shift up and way down by go ultrasound ray for receiving maximum speed .
AT connections with by the presence of delays by of time at at eat reflected ultrasound signal pulsed Doppler study correctly defines speeds only up to 2 m / s .
but pulsed Doppler study allows receive spectrum more high qualities by by comparison with constantly – wave .
With pulsed research frequency repetitions pulses must not less than at two times exceed measurable speed. Frequency repetitions pulses going down with an increase depthsresearch . Maxi little Doppler shift the frequency of which can correctly measure at given frequency repetitions momentum , called the limit Nyquist .
With exceeding limit Nyquist is observed Effect distortions spectrum (aliasing effect ), which leads to artificial change polarity sko rosti and deformations reflected signal .
Effect distortions spectrum can to avoid behind account :
• high frequencies repetitions pulses ;
• multiple control volumes ;
• decrease depths doppler research ;
• offsets isolines spectral scales .
AT clinical practice are used various re presses Echocardiography .
Seroshkalnaya EchoCG : • two-dimensional Echocardiography ; • M – mode EchoCG ( M – motion, English , movement ).
Doppler – echocardiography : • constantly – wave Doppler research ; • imp ulsnoe Doppler research . Various modes Echocardiography not compete as well dopol
ny friend other. how Generally, they use at combining nii . Everything modes Echocardiography use ultrasound, however, differ by way reception and analysis reflected soundwaves .