PRINCIPLE AND APPLICATION OF ULTRASOUND IN VETERINARY PRACTICE : PRINCIPLE AND APPLICATION OF ULTRASOUND IN VETERINARY PRACTICE Adarsh Kumar 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
- gastro - enterology
- orthopaedics and
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:
- Disk Storage
- Printers Slide 7: 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
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:
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 Slide 14: 2-D Brightness mode:
- Assembles numerous 1-D scan in to 2-D US image
- Echoes traced along vertical line Slide 15: 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 Slide 17: 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 Slide 18: Triangular or pie shaped (Sector) Use: Echocardiography,Sonography of intra pelvic & intra thoracic organs, brain, eyes, testes & joints Slide 19: Rectangular linear (Linear) Use:
Sonography of abdominal organs (extra thoracic)
Sonography of superficial structure (skin, mammary gland, joints and tendons) Slide 20: Trapezoid convex (Curved array) Use:
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. Echogenicity : Echogenicity Anechoic (echo free)
-Tissues without acoustic interfaces appear as black area (fine or coarse) -Tissues with medium echogenicity appear light to medium grey Hypoechoic (echo poor)
- Tissues with low echogenicity appear medium to dark grey Hyperechoic (echo rich)
Echo rich tissues, calcification and gas filled organs appear as white or light grey Slide 24: Anechoic
(echo free) Medium echogenicity Hypoechoic
(echo poor) low echogenicity Hyperechoic (echo rich) Image interpretation Acoustic Shadowing of Sound Wave : Acoustic Shadowing of Sound Wave Total reflection of sound waves at interfaces of bone, calcification & gas-filled structures
No imaging of area distal to reflective interface
Shadowing is displayed as a uniform black area distal to reflector
Incomplete shadowing may appear distal to stones & calculi Acoustic enhancement : Acoustic enhancement Clinical applications of Ultrasound : Clinical applications of Ultrasound Pregnancy diagnosis - as early as 14 days conceptual fluid is seen in equine. In canines….20 days.
Twin pregnancies, pregnancy losses, pseudopregnancy, Ovarian cysts and haematoma, ovarian tumours and infection.
The organs which can be scanned usefully are liver, kidney, urinary bladder, spleen, uterus, ovaries, teat and udder.
Merit of ultrasound is its ability to characterize internal parenchymal organ architecture which was previously impossible without contrast radiography, angiography or exploratomy laparotomy. Clinical applications of Ultrasound : Clinical applications of Ultrasound In ruminants, the use of a rectal linear scan head could be quite versatile for diagnosis of ovarian and uterine disorders
Used for assessment of intra and periabdominal diseases in
Characterize internal architecture
Extent of involvement
Access the extent of involvement of adjacent organs.
Emerging tool for contact less separation, concentration and manipulation of micro particles and biological cells Clinical applications of Ultrasound : Clinical applications of Ultrasound Guidance of biopsy instruments and catheters (liver and kidney biopsies, pericardium and chest drainage)
Bone heal monitoring
Assessment of blood flow and supply