Basic Scanning Techniques: Tips and Tricks
Proper image acquisition requires a sound knowledge of anatomy, machine logistics, patient positioning and probe maneuvers.
- Grip: Grasp the ultrasound probe close to the end (the foot-print of the probe, away from the cord/tail) using a pincer grasp, rest your hand and wrist on the patient or stretcher for stabilization. By convention, the probe indicator should be orientated towards the patient's right side or toward the patient's head. Cardiac exams are different and discussed on the cardiac page.
- Mechanics: Remember that small motor movements correlate to large changes on the screen. An ultrasound beam is just a 1 mm thick slice of displayed anatomy, so using slow and fluid movements will increase your sensitivity and likelihood of detecting abnormal pathology. Click here for a nice review of ultrasound terminology and probe maneuvers.
- Scan: Scan the area/organ of interest in at least 2 planes to verify the anatomy or pathology. Always compare the abnormal/pathologic to the normal (i.e. the painful left eye compared to the non-painful right eye).
- Patient Positioning: Move your patient! What can patient positioning do to improve your images? Movement can displace bowel gas, allow fluid to relocate to a more dependent position, relax abdominal musculature, and allow an organ such as the heart or the gallbladder to fall towards the probe. Adjustments can also be made to make the exam more comfortable for the scanner - neck and back strain are a very high cause for disability in experienced sonographers.
- Just breathe (the patient, that is). Many times a patient's respirations will cause a structure of interest to come in and out of the field, the gallbladder is notorious for this. Rather than chase it with your probe, fix your probe's position and allow the patient's breathing to bring it in/out of view. At the appropriate time, ask the patient to hold his or her breath for a few seconds to obtain the necessary image or clip.
Much like a television remote, there are many models and versions, but the key functionality is the same and easily recognized on various devices. Below are some universal settings and functions that you will need to know.
2D, Basic or B-mode
The B stands for "Brightness": the typical default scanning mode, optimized for resolution.
This mode allows you to visualize flow and its direction relative to the ultrasound probe itself. The common thought is that blue represents venous flow and red represents arterial flow. In actuality, blue is movement or flow away from the probe and red is flow or movement toward the probe.
Power Doppler: most useful in low flow states (i.e. testes, lymph nodes, abscesses) to demonstrate the presence or absence of flow.
Continuous and Pulse Wave Doppler
These Doppler settings measure the velocity (speed and direction) of the flow, and are displayed as waveforms, which can help differentiate between venous and arterial flow.
- Continuous Wave Doppler: useful for high-flow states, such as measuring RVSP.
- Pulse Wave Doppler: useful for measuring flow over a specific region utilizing a "gate", such as across a heart valve to measure cardiac output.
"Motion" mode: this essentially displays a still image representing motion over time. This is useful for calculations such as fetal heart rate, pleural sliding and ejection fraction.
This adjusts the brightness of the image, most machines will allow you to adjust the overall brightness, as well as focused areas (time-gain compensation) to ensure that you are able to visualize the structure of interest, without compromising image quality due to artifacts or "noise".
Depth is displayed in cm on the side of the display, ideally the structure of interest should take up at least 2/3 of the display screen. More shallow depths allow for faster frame rates, which lead to better image resolution.
Pre-sets and exam types
Modern machines have exam presets to optimize imaging, be sure that your exam is appropriately selected. For a musculoskeletal ultrasound, the high-frequency linear transducer will have options such as "venous, small parts, nerve, etc". You may find that changing your exam type will drastically improve or hamper your image quality.