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Intro to Ultrasound
Organisation of the Body
| 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 |
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