Ultrasound Flashcards
How is an ultrasound image produced?
- Sound waves are transmitted into the body
- Some tissues reflect waves and some transmit them into deeper levels
- Reflected waves are used to make an image using the piezoelectric effect
What is attenuation?
- Transmitted waves will lose energy as they pass deeper into tissues and eventually become too weak to form an image
What are the two tissue types regarding echogenicity?
- Hyperechoic = causes increased reflection, so whiter image e.g., diaphragm
- Hypoechoic = causes decreased reflection, so darker image e.g., kidney, spleen and liver
- Anechoic = no reflection, so black e.g., bladder
Describe a linear array transducer
- Produces a rectangular image using piezoelectric crystals that are arranged in a line
- Good resolution of superficial tissues
- Used for large animals
Describe a convex array transducer
- Triangular, fain-shaped image produced using piezoelectric crytals that are clustered together
- Good resolution of deeper tissues
Describe a phased array transducer
- Triangular, fan-shaped image produced using piezoelectric crystals that are closely grouped together and fire in sequence
- Useful for small spaces and cardiac imaging
Describe a small-footprint linear transducer (hockey stick)
- Uses high frequency to produce very clear images of small superficial structures such as nerves
Describe a endocavity transducer
- Used inside the body directly on the surface of organs to produce a wide field of internal structural view
What are the potential risks to the patient when performing ultrasonography
- Mechanical injury due to tissue vibration and formation of bubbles in gases
- Thermal injury, as bone absorbs US heat and the probe can also overheat
What are the potential risks to the sonographer when performing ultrasonography?
- Patient aggression
- Eye strain
- Arm or neck strain
- Slips and trips
How should the patient be prepared for ultrasonography?
- May need to fast
- Sedation may be required
- Clip to remove hair, apply surgical spirit to degrease site and use ultrasound gel; this will remove the space for air to fill so better contact
What are the 2 basic modes?
- B mode (brightness): 2D cross sectional view
- M mode (movement): single scan line
What are the doppler modes?
- Detects movement of fluids such as blood
- Colour doppler: shows direction of fluid in colour
- Spectral doppler: shows direction and velocity of fluid flow
What is contrast-enhanced ultrasonography?
- Used to image blood flow in organs
- Gas filled microbubbles given IV
- Microbubbles reflect most waves giving good contrast
- Contrast media quickly cleared, as gas breathed out
What are the uses of ultrasonography?
- Anatomy/physiology
- Point of care
- US guided biopsy/needle aspirate
- Pregnancy diagnosis
What are ultrasound not useful for?
- Fractures and nervous tissue, as waves get reflected or absorbed by bone and none passes through
- Air filled structures, as all waves reflected at surface
Name 5 comparison between an ultrasound and a X-ray
- US detect tissues/structures not visible on a X-ray
- US is dynamic
- US performed with minimal patient preparation
- US has no ionising radiation
- X-ray useful for bone, US reflected by bone
What are some advantages of using ultrasound over radiography in pregnancy diagnosis?
- No radiation risk
- Earlier visualisation (10-22 days after mating)
- Heartbeats used to evaluate viability
- Estimate number of foetuses
