INTRODUCTION : INTRODUCTION Ultrasonography is the second most commonly used imaging format Important part of specialty areas in clinical veterinary medicine – internal medicine – gynaecology and obstretics – surgery – cardiology – gastro – enterology – orthopaedics and – ophthalmology Insights into basic anatomy and physiological processes Almost all organs and tissues are now accessible Minimally invasive imaging method Least hazards
WHAT IS ULTRASOUND? : WHAT IS ULTRASOUND? Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes.
Ultrasound : Ultrasound Ultrasound is defined as sound waves of frequencies greater than 20,000 Hz. Frequency range of 1-10MHz (max.20MHz) used in medical and veterinary diagnostics No disturbance to animals at employed diagnostic frequencies A sound wave travels in a pulse and when it is reflected back it becomes and echo. It is the pulse echo principle, which is used for ultrasound imaging. No propagation in vacuum and poor transmission in gases Generated by piezoelectric materials.
Principle : Principle A pulse is generated by one or more piezoelectric crystals in an ultrasound transducer. When these crystals are stimulated electrically it changes its shape and produces sound waves of particular frequencies. The frequency of a transducer is determined by the times the crystals expands and contracts per second. In an ultrasound scanner the crystal is shocked by a short pulse of electricity to vibrate.
Basic Ultrasound Machine : Basic Ultrasound Machine Components – Central Processing Unit (CPU) – Transducer probe – Transducer Pulse Controls: – Display – Keyboard/Cursor – Disk Storage – Printers
As the transducer is placed in close contact with the body surface through a coupling medium, it undergoes continuous modification that occurs through three processes Absorption, Reflection And scattering.
Absorption: : Absorption: It occurs when the energy in the sound beam is absorbed by the tissues thereby converting it into heat. Absorption process forms the basis of therapeutic ultrasound.
Reflection : Reflection It is the redirection of a portion of the ultrasound beam back towards the source. The reflection gives rise to echo and forms the basis of diagnostic ultrasound. These echoes are converted by piezoelectric effect into electric signals that are displayed onto on oscilloscope screen.
Scattering : Scattering It occurs when the beam encounters an interface that is irregular and smaller than the sound beam. The portion of the beam that interacts with this interface is scattered in all the directions. Two closely related phenomenons occur, refraction and diffraction of which refraction is a common cause of artifacts.
Echo quantification : Echo quantification For displaying this echo amplitude information, different modes are used.
Display Modes : A-mode (amplitude) : Display Modes : A-mode (amplitude) Reflective surfaces are displayed as vertical spikes with different amplitudes along baseline Application: Echo-encephalography Echo-ophthalmography Pregnancy diagnosis (previously).
B-mode (brightness) : B-mode (brightness) Returning echoes are displayed as dots with varying brightness on the monitor Brightness or grey scale.
2-D Brightness mode: – Assembles numerous 1-D scan in to 2-D US image – Echoes traced along vertical line.
Interfaces that are stationary- are seen in straight line Interfaces that re in motion –are seen as wiggly line.
Real Time Mode : Real Time Mode Static organs: Slow frame rate & high scan line density Cardiological scans: Higher frame rate.
3-D ultrasound – ultrasound waves are directed from multiple angles – waves are reflected back and captured, providing very detailed 3-dimensional images of the baby 4-D ultrasound – the process of streaming 3-D images into live, real-time video of the baby. This allows viewers to see real-time motion.
Triangular or pie shaped (Sector) Use: Echocardiography,Sonography of intra pelvic & intra thoracic organs, brain, eyes, testes & joints.
Rectangular linear (Linear) Use: Sonography of abdominal organs (extra thoracic) Sonography of superficial structure (skin, mammary gland, joints and tendons).
Trapezoid convex (Curved array) Use: Abdominal ultrasonography Pregnancy diagnosis.
Endorectal Transducer : Endorectal Transducer Transducer with attached biopsy guide system and inserted needle Provide advantage of US beam offset by 45 degree.
Scanning procedure: : Scanning procedure: Ultrasonography involves considerable cooperation between the patient and the sonologist. The transducer must be in close contact with the patients skin to have minimum attenuation of the sound beam. In Vety. Patients it requires clipping of hair and cleaning of skin. There should not be any air between the transducer and skin, as it will completely block the beam. So good contact is provided by application of mineral oil or an aqueous gel between the transducer and contact surface. Any coupling medium should be applied liberally. Both gas and bone acts as a barrier to ultrasound beam as these reflect the beam. Therefore, a proper acoustic window should be formed to visualize the organ.
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