Sound In Medicine

Sound waves Sound is a mechanical waves travel in air as longitudinal waves in which vibrations in air causes increases (compressions) and decreases in pressure (rarefaction) relative to atmospheric pressure. Where: v is the sound velocity (m/sec) λ is the wavelength (m) F is the frequency of vibrations (Hz) T is the periodic time (sec) v = λ f =λ/T

Sound frequencies classified into: 1.Infrasound: frequency below normal hearing range (f<20 Hz). Produced by natural phenomena e.g. Earthquake. They can not be heard but causes headaches and physiological disturbances. 2. Audible sound: 20-20kHz. 3. Ultrasound: f>20kHz.

Intensity I Energy passing through unit area in unit time. I = Energy / area. Time = Power / area The Decibel Scale Special logarithmic unit for comparing the intensity of two sound waves. Number of dbels = log 10 (I / I o ) Decibel is one tenth of bel 1bel = 10 dbel = 10 log 10 (I / I o )

Interaction of sound waves with matter Reflection Absorption Refraction Scattering

WHAT IS ULTRA SOUND ?

 SONAR (Sound Navigation and Ranging): method of locating underwater objects with ultrasound.  Bats uses the sonar principle for finding food.  Principle of Sonar: sound waves are sent out and reflected from the object. From the time required for receiving Echo and the velocity of sound in the medium the distance to the object can be determined.  MEDICAL DIGNOSTIC ULTRASOUND IS THE USE OF HIGH FREQUENCY SOUND TO AID IN DIGNOSIS AND TREATMENT OF PATIENT.  FREQUENCY RANGES USED IN MEDICAL ULTRASOUND ARE 2-15 MHZ.

Piezoelectric Effect  Definition: alternating voltage passes across quartz crystal (of thickness “d”) will produce similar vibrations of the crystal which results in generation of sound waves.

Transducer A device converts electrical energy (alternating voltage) into mechanical energy (sound waves) in the production of Ultrasound. It serves as a detector by receiving Echo which will vibrate the crystal generating a voltage across it.

Piezoelectric effect Ultrasound Transducers

Piezoelectric effect of Ultrasound Transducers The received weak signals (Echo) are amplified and displayed. To transmit the ultrasound to the body, the vibrating crystal should be in close contact with the skin to eliminate the air by using “Jelly paste” between the crystal and the skin.

Ultrasound production Transducer contains piezoelectric elements/crystals which produce the ultrasound pulses. These elements convert electrical energy into a mechanical ultrasound wave and vice-versa.

Pulse Pulse of sounds is send to soft tissues. Sound interaction with soft tissues= bio effect. Pulsing is determined by transducer or probe crystal and is not operated or controlled.

Echo  Eco is produced by soft tissues.  Tissue interaction with sound = Acoustic propagation properties.  Echoes are received by the transducer crystal.  Echoes are interpreted and processed by ultrasound machine.

 Transducer probe.  CPU(central processing unit).  Transducer pulse control.  Display.  Keyboard /cursor.  Disk storage device.  Printer. 10/ ULTRASOUND MACHINE COMPONENT 16

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Sound is attenuated by tissue. More tissue to penetrate = more attenuation of signal. Compensate by adjusting gain based on depth. near field / far field. AKA: TGC. 18

Gain controls receiver gain only does NOT change power output ☺ think: stereo volume Increase gain = brighter image Decrease gain = darker image 19

The ultimate goal of any ultrasound system is to make like tissues look the same and unlike tissues look different. 20

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 1. Abdomen Pelvis (liver, GB, Pancreas, Spleen, Kidneys, UB & Prostate gland). 2. Doppler. 3. Musculoskeletal. 4. Obgyn. 5. Small parts (Thyroid, Breast, Testicles, Cranial ultrasound & Ophthalmic). 21

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 6/ Ultrasound guide needle biopsy. 7/ ECHO (echocardiography). 8/ Therapeutic Ultrasound (HIFU = High Intensity Focal Ultrasound). 9/ Ultrasound Bone Density Test. 22

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 2. Doppler. 23

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 3. Musculoskeletal. 24

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 4. Obgyn. 25

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 4. Obgyn. 26

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 5. Small parts (Thyroid, Breast, Testicles, Cranial ultrasound & Ophthalmic). 27

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 6/ Ultrasound guide needle biopsy. 28

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 7/ ECHO (echocardiography). 29

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 8/ Therapeutic Ultrasound (HIFU = High Intensity Focal Ultrasound). 30

Ultrasound Applications Ultrasound used in medical field for the following ultrasonic applications: 9/ Ultrasound Bone Density Test. 31

Summary Ultrasound is an oscillating sound pressure wave with a frequency greater than the upper limit of the human hearing range. Ultrasound is an diagnostic medical imaging technique used to visualize all internal organs, to capture their size, structure and any pathological lesions with real time tomographic images. There has been no evidence to date to suggest adverse effects of ultrasonography applications in medical field. 32