Ultrasounds Flashcards
Properties of ultrasounds
High frequency
Real-time imaging
Non-ionising
Cost effective
Difference between ultrasound B mode, M mode and Doppler mode
B mode:
Brightness mode
Displays anatomy of internal organs, tissues & structures
M mode:
Motion mode
Displays motion of tissue or organ over time
Doppler mode:
Detects velocity & direction of blood flow in vessels
Explain ultrasound reflection
Occurs when sound waves encounter boundary between tissues with different densities
Some sound waves are reflected back to transducer to create image
Amount of reflection depends on angle of incidence & difference in acoustic impedance between tissues
Explain ultrasound refraction
Occurs when sound waves pass through tissues with different acoustic properties causing them to change direction
Occurs when sound waves pass through tissues at oblique angle or when they encounter regions of different tissue density
Causes waves to be deflected away from transducer which decreases image quality
Explain ultrasound scatter
Occurs when sound waves encounter small structures within tissues (e.g. blood cells or cell membranes)
Amount of scatter depends on size & density of structures
Contributes to contrast of ultrasound image
How does frequency of an ultrasound affect the image
Low frequency (e.g. 3.5 MHz) - good depth of penetration but poor resolution
High frequency (e.g. 10 MHz) - poor depth of penetration but good resolution
How is an ultrasound image formed
- Transducer emits high-frequency sounds
- Sound waves reflected back as they encounter different tissues
- Reflected sound waves processed by computer
- Brightness & contrast of image adjusted
What is gain in ultrasounds
Gain is amplification applied to returning echo
Usually several gain controls (near-far field)
The further sound has to travel the quieter returning echo (gain adjusted to compensate)
Gain turned up for deeper tissues
What transducer is this and what is it used for
Sector transducer
Echocardiography, intrathoracic & intraabdominal organs, regions with small contact areas (brain, eye, joints)
What transducer is this and what is it used for
Phased array
Sector scanner with electronic steering of crystal emission
Mainly echocardiography
What transducer is this and what is it used for
Linear array
Multiple crystals arranged in line & sequentially triggered
Abdominal organs, muscles, joints & tendons
What transducer is this and what is it used for
Curvilinear
Multiple crystals arranged in arc
Abdominal organs & pregnancy diagnosis
What do homogenous and heterogenous mean in ultrasounds
Homogenous (uniform) - regular pattern throughout (most normal tissues)
Heterogenous (non-uniform) - irregular pattern (disease tissue)
What does anechoic mean
Structures produce no echo (all sound passes through)
Fluid (blood, urine, bile)
Appear black
What does hypoechoic mean
Structures produce little echo (most sound passes through)
Tissues with high water content (cartilage, muscle, renal medulla)
Dark grey appearance
