Basic Principle of Ultra Sound Scan.pptx

Basic principles of USS

1. BASIC PRINCIPLES OF ULTRASOUND

2. OUTLINE INTRODUCTION CLASSIFICATION OF SOUND PROPERTIES OF SOUND PRINCIPLES OF DIAGNOSTIC ULTRASOUND ULTRASOUND IMAGING TERMINOLOGIES PARTS OF THE ULTRASOUND MACHINE MODES OF ULTRASOUND APPLICATIONS OF ULTRASOUND BIOEFFECT OF ULTRASOUND CONCLUSION REFRENCES

3. INTRODUCTION Sound is mechanical energy travelling through a medium (solid or liquid). That is, it requires molecules to transmit it from one molecule to the othe r Sound propagates in a longitudinal (straight line) fashion as pressure waves . A typical sound wave consist of areas of compression (squeeze) and rarefaction (stretch) creating a wave pattern Ultrasound doesn’t use ionizing radiations and so it is safe especially for use in pregnant women and children

4. CLASSIFICATION OF SOUND Sound is classified based on the ability of the human ear to hear it Infrasound : <20Hz Audible sound: 20Hz – 20,000Hz Ultrasound: >20,000Hz (20kHz) Diagnostic Ultrasound: 2-15MHz

5. PROPERTIES OF SOUND Wave-length is the distance covered by one cycle of compression and rarefaction Period is the duration of one cycle of compression and rarefaction Amplitude is the difference between the peak (maximum) and the trough (minimum) of the wave and the mean value F requency is the number of cycles in a second . The higher the frequency, the better the image quality (resolution), but the lower the depth of penetration Propagation Speed is distance travelled by a sound wave through a specified medium in 1 second. It i s a function of the medium only

6. Propagation speed of sound in soft tissues is at 1,540m/s Power is the rate of energy transfer through a sound wave Intensity is concentration of energy in a sound wave and thus dependent on power and cross sectional area of the sound beam . Amplitude, power and intensity define the strength of a sound wave

7. PRINCIPLE OF DIAGNOSTIC ULTRASOUND Ultrasound waves are generated from tiny crystals packed within a transducer (probe). When ELECTRIC ENERGY (A/C) is applied, the crystals contract and expand (MECHANICAL ENERGY) at the same frequency at which the current changes polarity generating sound energy (waves). Conversely, as the returning ultrasound beam (echoes) reach the transducer, the crystals generate electric current. This is analysed and amplified by the ultrasound machine to generate images that are displayed on the monitor. This is because of the PIEZOELECTRIC property of the crystals.

8. Any material capable of transforming energy from one form to the other is said to have piezo-electric property, and its effect as Piezoelectric effect The behaviour of Ultrasound at an acoustic interface could be reflection, refraction, transmission or absorption An Acoustic interface (AI) is the boundary between adjacent tissues with different impedance Acoustic Impedance is the resistance of a medium to ultrasound transmission

9. When an incident ultrasound beam (IB) encounters AI at a perpendicular angle, the sounds will be either reflected (echoes) back to the transducer or transmitted (TB ) The strength of the echo is variable and depends on the difference between the impedance of the background and the obstacle material. The wider the difference i n impedance, the stronger the echoes. Air scatters ultrasound beam. Therefore, a coupling material ( couplants ) is required between the transducer and skin to displace the air. When scanning pelvic structures, pockets of bowel gas can make it difficult to visualize anatomy lying posteriorly to them. Therefore, a full bladder is usually required to displace the bowels and equally serves as an acoustic window.

10. Acoustic Impedance is the product of the density of the medium and the velocity of ultrasound in the medium The amount of echoes produced depend on the acoustic impedance of the medium While air absorbed all sound waves, water transmits all, and bone reflects all Attenuation is the reduction in the energy intensity of sound beam as it encounters a medium. It is dependent on acoustic impedance and depth of tissue

11. ULTRASOUND IMAGING TERMINOLOGIES Isoechoic Hyerechoic (hyperechogenic) Hypoechoic (Hypoechogenic) Anechoic(Echo free, echoluscent, sonoluscent) Mixed echogenicity

12. PARTS OF THE ULTRASOUND MACHINE HARDWARE Probe (Transducer) Control Panel Monitor Measuring facilities Storing device SOFTWARE: 2D, Doppler, 3D/4D e.t.c

13. MODES OF ULTRASOUND Diagnostic ultrasound is available in several modes depending on the fundamental technology, image acquisition, and display: A-Mode (amplitude mode)-no longer used but the basis of modern uss (1st used for BPD B-Mode (brightness- 2 dimensional (2D) uss , real-time)-Real time means that any real movement in tissue is immediately associated with a corresponding movement in the displayed image. M-Mode (motion)- for evaluating cardiac activity, chambers, valves using high pulse repetitive frequency. Time on the x-axis and depth on the y-axis Doppler Ultrasound and 3D and 4D modes

14. Doppler ultrasound is used primarily to evaluate vascular flow by detecting frequency shifts in the reflected beam, utilizing a principle termed the Doppler effect This effect occur when a sound emitter or reflector is moving relative to the stationary receiver of sound. Objects moving toward the detector appear to have a higher frequency and shorter wavelength, whereas objects moving away from the detector appear to have a lower frequency and longer wavelength Examples include Colour Doppler, Power Doppler, Spectral Doppler

15. APPLICATIONS OF ULTRASOUND DIAGNOSTIC/MONITORING I maging of the abdomen (liver, gallbladder , pancreas , kidneys) P elvis (female reproductive organ s) F etus (routine fetal surveys for detection of anomalies , Feral surveillance ) V ascular system (aneurysms, arterial-venous communications, deep venous thrombosis) Testicles (tumor, torsion, Infection)

16. Breasts P ediatric brain (hemorrhage, congenita l Malformation s) Chest (size and location of pleural flui d collections ) Heart/Echocardiography(Congenital or acquired heart defects) THERAPEUTIC U ltrasound -guided interventions are routinely used to facilitate L esion biopsy A bscess drainage radiofrequency ablation

17. BIOEFFECTS OF ULTRASOUND SCAN Currently, there are at least three ways in which ultrasound can produce biological effects: 1. Cavitation- is the growth of small gas bubbles 2. Microstreaming- It is an inevitable consequence of the fact the ultrasound is a mechanical wave that will always exert some mechanical forces on the medium through which it travels 3. Heating-Absorption. It is defined as the direct conversion of the sound energy into heat and it is always present to some extent. All scanning generate some tissue heating. However, no injurious effects have been identified from ultrasound scanning of the fetus

18. CONCLUSION Understanding the basic principles of Ultrasound and having the basic skills of Ultrasound is inevitable for the medical student who would some day become a Medical Doctor

19. REFRENCES Lecture Notes (Dr Nyango D.D, Dr Angba H.A) LANGE medical book B asic Radiology 2nd edition