ULTRASOUND IMAGING & EQUIPMENTS - SRIRAM pptx

Ultrasound imaging , Interaction with matter, Working principles, Equipments & Modes.

1. ULTRASONOGRAPHY K.SRIRAM B .SC RADIOGRAPHY & IMAGING TECHNOL OGY

2. TABLE OF CONTENT INTRODUTION BASICS OF ULTRASOUND INTERACTION WITH MATTER. ULTRASOUND TRANSDUCER TYPES OF PROBE COMPONENTS OF USG MACHINE

3. INTRODUCTION Ultrasound is acoustic energy having a frequency of (20KHz) beyond the range of human hearing. The sound travel in the form of wave. Thus ultrasound requires a medium to travel Ultrasound has a shorter wavelength so it can reflect from small surface easily.

4. In diagnostic ultrasound uses 1-20 MHz frequency and velocity depends on the nature of medium through which it travel and independent of frequency. It is not an electro magnetic radiation ,but undergoes reflection and refraction at interfaces. The reflection from tissue is called echo which form the images.

5. BASIC OF ULTRASOUND Ultrasound is produced by a transducer . A transducer converts electrical energy into mechanical energy to produce the ultrasound. The transducer contains piezoelectric crystals that produce the ultrasound . When alternating electric field (AC voltage ) is applied across the piezoelectric crystals ,these crystals contracts or expand and also in the reverse phase of AC ,the crystals again contracts and expands.

6. So rapidly changing of electric field cause the crystals to vibrate which cause the production of sound waves. These sound waves are then sent In the body where it interacts with tissues. Some of the sound waves get reflected back to the transducer . These reflected sound waves interact with the piezoelectric crystals and produces an electrical current

7. So the piezoelectric crystals of the transducer converts electrical energy into mechanical energy to produce . Ultrasound and converts electrical energy into mechanical energy to produce ultrasound and convert reflected sound waves into an electrical signal . These electrical signals are then transmitted to the CPU , where special software process the data and calculates the distance and the time of each echo. Then the CPU form and displays the 2 D images on a monitor.

8. BASIC OF ULTRASOUND

9. INTERACTION WITH MATTER Ultrasound undergoes reflection, refraction, scattering and absorption in matter, depends upon the acoustic properties of matter. Reflection occurs at tissue boundary, where there is a difference in acoustic impedance. Reflection may be a boundary reflection or tissue reflection and tissue reflection mostly gives scattering.

10. Refraction refers the change in direction of the transmitted ultrasound energy. Scattering occurs by both reflection and refraction (small particles). Absorption refers the conversion of acoustic energy into thermal energy in the medium. The acoustic impedance (Z) is the product of density and speed of sound It depends on density and elasticity of the interface and independent of frequency.

11. ULTRASOUND TRANSDUCER Transducer is a device which converts energy from one from to another . Us transducer converts electrical energy into sound energy and vise versa. It works on the principle of piezoelectric effect. When a crystal is subjected to mechanical pressure ,electrical voltage is created and vise versa.

12. PIEZOELECTR IC EFFECT Piezoelectric means pressure electricity . Piezoelectric material have molecular dipoles ,containing + and – electric charges and net the charge is zero . If electric voltage is applied across the crystals ,the dipole orientation changes ,resulting in variation of crystals thickness. The crystal undergoes compression and expansion .

13. If mechanical pressure is applied to the crystal, molecular dipoles change their orientation, altering the electric field, produce voltage signal. The created potential difference is proportional to the pressure applied to the crystal. Natural piezoelectric material is quartz crystal and synthetic ceramic material is most commonly used as crystal, e.g. lead zirconate titanate (PZT, PbZrTiO4).

14. PZT in its natural state has no piezoelectric properties. It is heated over its curie temperature (328–365°C) and external voltage is applied, that causes the diploes to align in the ceramic. The voltage is maintained, until the ceramic is cooled below its curie temperature. Once it is cooled, the diploes retain their alignment.

15. TRANSDUCER Ultrasound transducer consists of : Matching layer Piezoelectric crystals Electrodes Backing back (damping back) Acoustic impendence Acoustic lens Metal shield Signal cable

16. MATCHING LAYER It is placed on the face of the transducer . It minimize the acoustic impedance difference between the transducer and the patient. The thickness of the matching layer is ¼ of the ultrasound wave length, which gives maximum transmission.

17. PIEZOELECTRIC CRYSTALS The piezoelectric crystals of the transducer convert the reflected energy into mechanical energy to produce ultrasound and converts the reflected sound waves into electrical signal. The most commonly used substance is lead zirconate titanate . The thickness of the piezoelectric crystal is generally ½ the wavelength of the ultrasound produced . The thickness of the crystal determines the frequency .

18. The frequency also affects the quality of the ultrasound image. If the frequency is higher the resolution will be better. Thicker crystal –lower frequency. Thinner crystal-higher frequency. These electrical signals are then transmitted to the CPU , where special software process the data and calculates the distance and the time of each echo. Then the CPU form and displays the 2 D images on a monitor.

19. Electrodes The electrodes act as capacitors when the voltage is applied between the electrodes ,the electric field is produced ,which causes a change in crystal shape . Thus the crystals become vibrates ,and the ultrasound waves are produced.

20. BACKING BACK (DAMPING BACK) The backing material is located behind the piezoelectric crystals . It absorbs the backwards ultrasound ,which cause piezoelectric crystals to vibrate and generates a shorter pulse ultrasound ,which reduces the axial resolution of image .

21. ACOUSTIC LENS It is attached at the tip of the probe . It prevents the spreading of ultrasound waves and focuses the ultrasonic waves in the desired direction :thus the image resolutions improved

22. ACOUSTIC IMPENDENCE It is the resistance that uktrasound faces when it passes through a tissue . It depends upon the density of the tissue (D) and the speed of the wave (V). If the difference in impendance is higher then more sound will be reflected rather then transmitted. So the coupling agent

23. TRANSUDCER PROBES The transducer probe comes in different shapes . The shape determines the field of view ,frequency ,penetration power ,and resolution of the image . Low frequency probe typically range from 1-5 MHz High frequency probes are in the5-6 MHz range .

24. TYPES OF PROBE Linear probes Curvilinear probes Phased array Endo cavitary probe .

25. LINEAR PROBES They are high frequency probes in which the crystals are aligned in a linear manner and produce sound waves in a straight line . Linear probes are in better for imaging superficial structures and vessels because they provide better resolution of near tissue but lesser penetration for deeper tissues.

26. CURVILINEAR PROBE Curvilinear probes are also called convex probe which has a widened curved surface. Curvilinear probe are better for trans abdominal imaging . These probes have a lower frequency greater penetration and less resolution .

27. PHASED ARRAY In the phased array probes ,the crystals are assembled closely ,so the sound waves are produced from a single point Generally ,it is used for cardiac and lung imaging . These probes have a lower frequency and greater penetration .

28. ENDOCAVITARY PROBE Endocavitary probes are elongated in shape . They are inserted in specific organs like the trans veginal and trans rectal . These probe have high frequency and better resolution.

29. COMPONENTS OF USG MACHINE Ultra sound machine contains of : Transducer probe . The central processing unit. Transducer pulse controls . Display screen. Keyboard and trackball.

30. TRANSDUCER PROBE .

31. THE CENTRAL PROCESSING UNIT. CPU -contains a microprocessor that calculate and processes the data . CPU sends electrical signals from the transducer .then the CPU forms and displays the 2 –D image on a monitor . The CPU also contains storage devices like hard disk and CD ROM

32. TRANSDUCER PULSE CONTROLS . Transducer pulse controls allow the operator to change the frequency ,duration ,amplitude and scan mode of ultrasounds.

33. DISPLAY SCREEN. The data which will be processed by the CPU will display on the computer screen

34. KEYBOARD AND TRACKBALL. A trackball is a ball shaped computer cursor. It is used to point a cursor on an image . A keyboard contains keys. It is used to enter data and for the measurement during the process.

35. Reference THE PHYSICS OF RADIOLOGY AND IMAGING – K .THAYALAN CONCISE TEXT BOOK ON IMAGING MODALITIES &RECENT ADVANCES IN DIAGNOSTIC RADIOLOGY -by  DR.K.B.GEHLOT ,LALITH AGARWAL. Internet –radiopedia.