| Question | Answer |
| What is POCUS | Point Of Care Ultrasound
Used in emergency medicine to rule in/rule out
Used in procedural guidance, diagnostics e.g. cardiovascular, respiratory, obstetrical, gastrointestinal and vascular as well as in monitoring |
| The reverse piezoelectric effect | Transducer made of several piezoelectric elements that produce sound waves in response to electric current
Frequency of 2-20 MHz |
| Acoustic impedance | The resistance ultrasonic waves encounter as they pass through tissue
Depends on: density of the tissue, speed of sound wave
Large difference between air and body tissue to a liquid medium is used to reduce the difference and increase resolution |
| Direct piezoelectric effect | Any change in AI which causes sound waves to bounce back and be detected by PE elements in the transducer to be converted back to an electric signal
Delay between receiving echo and intensity of echo produces a B-image |
| Image resolution | Proportional to frequency of the beam
Higher frequency does not penetrate as deep so is better for imaging superficial structures - good lateral and axial resolution
Lower frequency can penetrate deeper so are used for abdominal and pelvic scans |
| Focal zone | Narrowest point of the ultrasound beam where lateral resolution is at its optimum |
| Axial resolution | Along the axis of the ultrasound beam
Dependent on transducer frequency |
| Lateral resolution | Differentiating between object perpendicular to the ultrasound beam
Focal zone
Decreases with depth due to scattering and divergence of the beam |
| Elevational resolution | The ability to resolve objects within the height or thickness of the beam
Dependent on the number of PE crystals and their sensitivity |
| Anechoic | Structures that do not reflect sound waves and appear black
e.g. blood vessels, bile tracts and ureters |
| Hypoechoic | Reflect fewer sound waves in comparison to surrounding structures |
| Isoechoic | Structures reflect similar number of soundwaves to surrounding structures |
| Hyperechoic | Reflect most soundwaves and appear bright white
e.g. bone, dense fibrous connective tissue (perimysium) |
| Homogenous | A smooth texture pattern to a structure |
| Heterogenous | An uneven pattern to a structure |
| What are colour dopplers used for | Can be used to measure movement of fluid through a vessel, tissue or the heart
Rely on the doppler shift principle
Red = towards transducer
Blue = away from transducer |
| Doppler shift principle | Object moving away or towards transducer leads to a shift in the frequency of returning sound wave
Towards transducer - increased frequency (positive doppler)
Away from transducer - decreased frequency (negative doppler) |
| What can increase doppler shift | Increase in frequency
Increase in blood flow velocity
Decrease in angle of insonation |
| Angle of insonation | No doppler beam is perpendicular
It must be parallel to direction of flow
45-60 degrees is sufficient |
| Linear-array probes | Higher frequency - 5-18 MHz
Depth - less than 5cm
Uses - vascular, MSK, thyroid and breast imaging |
| Curvilinear probes | Lower frequency - 2-9 MHz
Uses - abdominal, cardiac and obstetric imaging
Provides a wider field of view at deeper depths |
| Phased-array probes | Much smaller
Lower frequency
Uses - cardiac imaging as can fit between the ribs |
