Ultrasonography
- Fundamentals of ultrasound
- High-frequency sound waves produced by a transducer are used to make images
- 2 – 20 MHz
- Higher frequency waves penetrate less deeply into the tissue but has increased resolution
- High-frequency waves used for superficial structures
- Low-frequency waves used for deep structures
- Image is made by sending high-frequency sound into the patient and measuring the magnitude and time of returning echoes
- The echoes depend on the density of tissue
- Different tissues give different echoes
- Cyst -> Hypoechoic/anechoic (because it’s mostly water)
- Homogenous tissues (liver, spleen -> homogenous small echoes
- Calcium, fat, air -> hyperechoic
- Ultrasound interactions with tissues
- Reflection
- Refraction
- Transmission
- Attenuation
- Acoustic shadowing
- Some tissues reflect all sound waves back to the transducer
- This means that tissues distal to these tissues are not exposed to sound waves and will therefore not be visible on ultrasound -> acoustic shadowing
- Examples
- Calcium (stones)
- Air
- Acoustic amplification
- Some tissues refect very few sound waves back to the transducer
- This means that the tissues distal to these tissue are exposed to more sound waves than normal and will be hyperechoic on ultrasound -> acoustic amplification
- Examples
- Cysts
- Fluid
- Advantages
- Produce no ionizing radiation
- Especially usefully in obstetrics
- Quick
- No long-term side effects
- Portable
- Produce no ionizing radiation
- Real-time ultrasound
- Allows images to be seen in sequential frames, just like a movie
- Good for moving structures, like the heart
- Patient preparation
- Abstinence from food before abdominal studies
- Only liquid is allowed
- Types
- A-mode (amplitude)
- One-dimensional
- Used in ophthalmology
- B-mode (brightness)
- Most often used
- Produces a 2D image
- M-mode (motion)
- The motion of a structure is plotted along the x-axis
- Used for movement of cardiac valves
- Colour doppler
- The machine analyses the frequency of the echoes -> blood can be coloured according to which direction it’s moving in
- Blood flowing toward the transducer is red
- Blood flowing away from the transducer is blue
- Good to evaluate stenoses, direction of blood flow, valvular insufficiency
- The machine analyses the frequency of the echoes -> blood can be coloured according to which direction it’s moving in
- A-mode (amplitude)
- Indications
- Examination of heart (echocardiography)
- Examination of biliary system
- Examination of urinary system
- Asymptomatic, pulsatile abdominal masses
- Female pelvic organs
- Abdominal hernia
- Appendicitis
- Ascites
- High-frequency sound waves produced by a transducer are used to make images