Ultrasound is a very practical and personal skill, which takes a considerable amount of practice to perfect. The following is a brief description of musculoskeletal ultrasound technique, including a review of basic orientation of some of the controls that can be adjusted to improve the image.
Orientating the Probe
Probably the most important skill that must be learnt is orientation between hand and eye. This is made simpler if the probe and screen are synchronised, i.e. if you move the probe to your left, the anatomy displayed on the screen appears to pass from left to right.
Because for the most common examinations (abdominal and gynae) patients in a radiology department are typically scanned on their backs, facing the sonographer, the convention is that the left side of the screen is right for the patient.
If the positioning of the subject is different then the orientation of the probe may change, so that when the probe is parallel to the display screen the left side of the probe corresponds to the left side of the screen.
It is also convention that when scanning in the sagittal or coronal planes, the left of the screen is superior and the right is inferior.
Positioning the Patient
There is no one best position for the operator or the patient, but if either you or your subject is uncomfortable, you will struggle.
Adjusting the Controls
How much you adjust the machine controls and settings as you scan is very much a matter of taste. Some familiarity and understanding of the controls is essential especially if you are not the only one who uses your scanner.
When you press the freeze button the image displayed at that moment is captured on the screen so that measurements can be taken and a print can be made if required. Most modern machines will also have a Cine Loop function that allows you to scroll back through the preceding several seconds of the scan, frame by frame.
Increasing the depth allows deeper structures to be viewed, but reduces the scale and also slows down the frame rate, as each line of the image takes slightly longer to acquire.
The overall brightness of the image can be adjusted. Either too bright or too dark and it is difficult to see subtle differences in texture. This is the most important adjustment to become accustomed to making.
TGC (Time Gain Compensation)
Gain can also be adjusted selectively at different depths. This can be a simply near or far field adjustment on some portables, up to 10 separate depth adjustments on platform based machines. This is used to compensate for strong attenuation or enhancement by superficial tissue. It is more useful when examining an area. When examining relatively small specific structures, as is the case in the shoulder, adjustment of the overall gain is usually sufficient.
The pulse of ultrasound can be manipulated to be at its narrowest at a particular depth. This means that image quality including lateral resolution is maximised at that level. This can be manually adjusted so that a particular area can be examined in more detail. More than one focus level can be selected, though this can significantly slow down the frame rate.
This takes a portion of the screen and magnifies it. This can be done while scanning or once the image has been frozen. For superficial structures it is normally easier to magnify by just to reducing the depth of the image. For deep structures it is necessary to use the zoom; however orientation is more difficult if zoom is used while scanning.
Cursers are available on all modern machines and are calibrated so that reasonably accurate measurements can be made.
Taking Pictures and Labelling
It is foolhardy to form an opinion based solely on a still ultrasound image and so any conclusions should be drawn while actually scanning the patient. Images are of value as aid memoirs and for demonstration and discussion. To this end it can be useful to label them, if only with left or right.
There are many other functions and parameters that can be applied or adjusted on modern ultrasound machines, but those above represent the basics to carry out an ultrasound examination.
These notes cover some of the basics of scanning, but serve only as an introduction.
Further study of the physics and technology will greatly improve your ability to use and interpret ultrasound scans.
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