Sound presents by myself mechanical fluctuations ha zoobrazny , liquid or dense environment . Each sound characterized by certain frequency, speed and in intensity . Frequencysound presents by myself number cycles dilution and compression at second. Unit measure of frequencies sound is an Hertz ( Hz ) and him derivatives . 1 Hz corresponds to 1cycle at second. Also are used concepts kHz (1 kHz = 103 Hz ) and MHz (1 MHz = 106 Hz ). Often that sound perceived human ear as height sound . Length the waves – thisdistance that passes sound behind one cycle dilution and compression that corresponds to distance between in two consecutive peaks . Frequency and length the wavesinterconnected . Insofar as sound overcomes certain distance behind second than more cycles sound hesitation at second ( more frequency), the in short length the waves . SpeedSound = Frequency Length the waves .
Speed sound is measured at meters at second ( m / s ) and determined by properties environment in which sound spreads . AT soft tissues speed sound with puts 1540 m / s .Intensity or volume sound is measured at decibels. Than above intensity sound , the more distance at which he heard . Sound with by frequency higher than perceived humanchesky ear ( over 20 kHz ), called ultrasound . A technique that uses ultrasound for heart research , got title echocardiography ( echocardiography ). Ultrasound formed thanks toproperty of some crystals perform mechanical fluctuations under WHO by action electricity . The Effect received on rank piezoelectric ( pressure – electricity ). If a to file electricvoltage on piezoelectric crystal, it starts vibrate .
Ultrasonic sensor contains some crystals, which pass on formed ultrasound the waves through body the patient .
Large part ultrasound waves dissipates or absorbed tissues, and only small their part reflected and caught sensor . Reflected the waves deform piezoelectric crystals with image by knowledge electric fields . Reflected signal carries information about the depth and character investigated tissue . AT the greatest degrees reflection ultrasound happened walks onthe border tissue with different density . Veli rank electric field formed reflected ultrasound waves determines intensity and brightness Images on the screen device .
Structures with high reflective capacity (e.g., bones) in grayish image boo are blowing white colors , structures with low reflective ability ( for example , muscle ) – gray color, notreflecting ultrasound structure (e.g., WHO spirit ) – black colors .
Location on the screen structure, which reflected ultrasound depends from delays between transmitted and accepted ultrasound momentum . More deep located structures are displayed at bottom parts picture, then as superficial structures – at top parts screen . So , the image on the screen It has view triangle with top vertex formed ultrasound sensor .
With spreading ultrasound at homogeneous environment happens gradual dissipation and damping signal at the original direction . With passing nii ultrasound through Wednesdaywith different density on the border mediums part ultrasound waves reflected at the reverse direction .
Exactly reflected ultrasound the waves perceived disappear sensor and analyzed ultrasound device . Length ultrasonic the waves connected with by speed and by frequency as follows ratio ( Length Waves = Speed / Frequency ). Insofar as length the waves back proportional to rate than above frequency ultrasound, the in short length the waves .
Than in short length wavelength, the more permitting and less penetrating ability to . So , you sokochastotnye sensors (5.0 to 7.5 MHz) provide the good resolution at researchsuperficial structures and at children ( table . 1.1).
Than below frequency ultrasound, the more length the waves . Than more length wavelength, the less permit walking and more penetrating ability to . So , the low-frequencysensors (2.5 to 3.5 MHz) provide a good penetrating ability at research more deep structures and at adults patients .