1st ultrasound practical Flashcards
What is gain on U/S machines?
Used frequently.
Changes the overall brightness of the real-time (B-mode) ultrasound image.
Overall gain will increase or decrease ALL returned echoes.
Too much overall gain typically introduces noise into the image, sometimes making it appear washed out or over-penetrated.
How do you set your gain?
Find fluid and make it black.
Whats TGC?
(Time Gain Compensation) - selectively adjusts the gain at different depths (near-, mid-, and far-field).
Most sonographers adjust these to left-of-center for the near field (top), and slowly move to right-of-center as image quality decreases deeper in the image.
The idea is to have lower gain in the near field and higher gain deeper in the image where image quality is weaker.
Adjusting the transducer frequency allows you to…
You should use the highest frequency available when…
You should use the lowest frequency available when…
improve the image resolution at the level of the object being evaluated.
You should use the highest frequency available when scanning a superficial object (in the near field).
You should use the lowest frequency available when scanning a deeper object (in the far field, deeper than 5-6 cm).
Remember that the higher the frequency, the better the resolution but poorer penetration. This relates to the wavelength of the frequency.
Remember that the higher the frequency, the
better the resolution but poorer penetration. This relates to the wavelength of the frequency.
Imaging depth does exactly what it sounds like - it describes…
how far into the body you can look with your ultrasound machine.
Measured in centimeters and starts at the surface of the transducer, which is usually resting on the patient’s skin.
Increasing the depth reduces the
image resolution.
At a higher depth, the transducer needs to cover a longer distance (remember to lower your frequency if needed), therefore the frame rate and the resolution are both lower.
The depth should set at the minimum required to visualize all structures of interest!
What does “target plus one” refer to?
Setting your U/S depth.
What you want to do is, turn your depth up or down until you see everything you want to see (e.g., the whole organ), and add one centimeter to the bottom of the screen.
This ensures that you really see the entire area of interest and can also make out its borders, but do not waste computing power (your own and your machine’s).
Seeing surrounding structures is often important but you don’t need to see a load of useless stuff at the same time.
What is focus on U/S machines?
The pulse of ultrasound can be manipulated to be at its narrowest at a particular depth, the focal position (red arrow on image).
This means that image quality including lateral resolution is maximized at that level.
Most modern scanners automatically set the focus point and usually do a good job.
The focus should lie…where?
at or just below (deep to) the structure you want to investigate, and is traditionally marked by a small triangle at the edge of the image, right next to the depth scale.
The focus tells your scanner where the essential part of the image lies and which area you want the best resolution in.
In clinical practice, this mostly plays a role when imaging really small structures, like nerves and vessels, especially vessel walls.
You will hardly think to adjust the focus when looking at the liver or kidney.
More than one Focal zone can be selected; however, this can significantly slow down the image frame rate.
