Getting started in clinical ultrasound: taking a probe in hand, mastering the gesture and the orientation of the probe in relation to the image

Clinical ultrasound is revolutionizing medical practice, offering healthcare professionals an invaluable tool for improving patient care. This fast, non-invasive imaging technique enhances the physical examination. Learn the basics of ultrasound, basic gestures and the essentials of interpretation by comparing the clinical picture with the images.

There are many advantages to taking up clinical ultrasound. First and foremost, this skill improves the quality and speed of diagnosis, by providing complementary information to the physical examination. What's more, clinical ultrasound can be performed quickly and at the patient's bedside, saving you time and optimizing patient care. Last but not least, this non-invasive, patient-safe technique can be repeated as often as required, enabling personalized, tailored follow-up.

However, it is important not to confuse clinical ultrasound with specialty ultrasound. While the latter is generally performed by radiologists, clinical ultrasound can be performed by health professionals from different specialties (general practitioners, emergency physicians, specialists, midwives, nurses, etc.) directly at the patient's bedside, by a caregiver who is immersed in the overall clinical context. The objective of clinical ultrasound is to complete the clinical examination by visualizing the internal organs, answer one or more clear diagnostic questions, usually in binary form (presence or absence), in order to facilitate a more adequate and accurate decision-making regarding the patient's management.

It is important to emphasize that the detection of a specific sign can significantly enrich the syndromic summary and refine the diagnostic orientation.  On the other hand, the absence of this sign, or its non-detection by the practitioner, may often require the use of additional imaging investigations to obtain an accurate diagnosis.

To train you in clinical ultrasound, a certain investment of time and energy is necessary. The learning path usually consists of several stages, ranging from theoretical training to supervised practice, including the acquisition of technical skills and image interpretation. Once trained in clinical ultrasound, the benefits in the medium and long term are numerous. You will be able to improve your daily practice, by being able to make more accurate and faster orientation diagnoses. In addition, clinical ultrasound will allow you to strengthen collaboration with the various actors in your network, facilitating the sharing of information and the coordination of care.

The basics of clinical ultrasound

To get started with clinical ultrasound, you will first need to understand the fundamentals of ultrasound imaging. This article is intended to be an introduction to the fundamental notions of ultrasound imaging, how to handle an ultrasound machine and how to understand an ultrasound image.

The skills you will have acquired after finishing this article:

• Understand the basic operation of an ultrasound imaging probe;
• Understand the behavior of ultrasonic waves on tissues and structures with different compositions;
• Understand the importance of patient positioning and active participation in the examination;
• Learn to situate yourself in relation to the image transmitted by the probe on the screen;
• Finding your way around basic controls ;
• Select the correct transducer frequency ;
• Practice and master the gesture and movements involved in handling the probe;
• Maintain and disinfect your probe at the beginning and end of the examination.

Understanding ultrasound theory

An ultrasound scanner, whether on a cart or ultraportable, is a relatively simple machine, consisting of a probe that embeds a transducer that generates and receives ultrasound waves, a computer, phone or tablet that processes the signals, and a screen that shows the images generated in real time.

The part of the probe that comes into contact with the patient's skin is called the probe nose. All probes have an indicator to help the user locate and distinguish between the left and right sides of the probe. Techniques for scanning the probe to locate and obtain clear images will be covered later in this article.

The ultrasound machine therefore emits ultrasound ; sound waves in a frequency range too high to be detected by the human ear. The mechanical sound waves generated by the ultrasound machine transducer propagate through the tissues and create a local, ephemeral, non-irradiating mechanical disturbance due to the acoustic impedance of the tissues. Impedance is the property of tissues that represents their resistance to the propagation of sound probes.

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How different tissues respond to sound waves

Low impedance (very dark gray or black)

Structures with a low acoustic impedance allow the complete passage of sound probes → they thus generate a very dark or anechoic image.

Examples: various fluids, blood, urine...

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High impedance (gray)

Structures with high acoustic impedance partially reflect sound waves → they thus generate a gray image.

Examples: solid organ, liver, spleen

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Very high impedance (white)

Structures with a very high acoustic impedance fully reflect sound waves → thus generate a white image. Structures such as bones do not allow the passage of sound waves, which means that they reflect anechoic (very dark) shadows.

Examples: pleura, bone, metal implants, diaphragm...

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Gas (cloudy gray, artifact image)

The gases spread the sound waves, producing a cloudy greyish image.

Example: lung

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Understanding the choice of frequency in relation to the organ

Different sound frequencies produce images at different depths. So, depending on the organ or tissue depth you're looking at, you need to set your probe to the right frequency. On a trolley-mounted ultrasound scanner, you need to choose the right probe for the job, whereas on a portable or ultraportable ultrasound scanner, all frequencies are present on a single probe nose (as is the case withechOpen O1) or on two probe noses (convex and linear).

To determine which frequency to use, remember this basic rule of ultrasound:

• The more superficial the structures, the higher the frequency.
  • Example: superficial blood vessels → 7.5 MHz to 10 MHz
• The deeper the structures, the lower the frequency.
  • Example: liver → 3.5 MHz

The convex probe, also known as an abdominal probe, is the most versatile probe because it allows you to visualize most of the (numerous) structures in the abdomen, often deep. Its frequency, which is often between 2 and 5 MHz, as well as its wide field of view, makes it possible to capture several organs in the same image and to note the presence of effusions. However, it can be difficult to handle if you have to look through intercostal windows.

The phased array probe, sometimes called a cardiac probe, is designed, among other things, for echocardiography. With variable frequencies between 1 and 5 MHz, it makes it easier to look at the heart through intercostal windows.

The linear probe offers a higher frequency (from 7.5 MHz), and allows you to look at surface structures such as vessels or the superficial pleura. Its linear nose makes it easy to look at the pleura through the intercostal windows. Given its frequency range, it does not allow the visualization of deep organs.

Ultraportable ultrasound scanners, on the other hand, integrate a range of frequencies in a single probe nose, making them suitable for most applications. echOpen The O1, for example, features 3 frequencies: 3.5, 5 and 7.5 MHz. Versatile, the shape of the ultraportable probe nose is also suitable for exploring different parts of the human body.

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Find your bearings in relation to the image

One of the aspects you'll need to master is understanding the orientation of the image on the screen - although this is not necessarily intuitive if you're a beginner.

Start by locating your probe's indicator:

• In cross-section, the probe indicator should point to the right of the patient (because the patient is lying in the anatomical reference position, and is seen from below, as in a CT scan).
• In both longitudinal and coronal sections, the marker should point towards the patient's head.

For your first cuts, we recommend that you go through the orientation exercise again and again until it becomes intuitive.

The image below shows an example of an ultrasound scan of the patient's right kidney. The probe is placed on the patient's skin in a longitudinal position, with the indicator pointing towards the patient's head.

• The top of the cone corresponds to the surface on which the probe is placed (patient's skin);
• The bottom of the cone shows the deeper structures. If you have placed the probe on your patient's abdomen (as in the example below), at the bottom of the cone you will see the structures closer to his spine;
• On the right side of your cone you will see the structures closest to your patient's lower body;
• On the left side of your cone you will see the structures closest to your patient's head.

Mastering the gesture

Depending on the case, you can make different gestures to move the probe and get a clear and centered image of what you want to observe. You can also apply some pressure against your patient's skin to check the compressibility of a vessel or clear pockets of gas that obstruct the view of an organ.

Before the gesture becomes intuitive, we advise you to practice on yourself on several body dials. As you do so, you'll notice that the ultrasound gel wears off quickly: it's important to apply it often to get a clear image.

Using your ultrasound software

Whether you're training on a conventional, portable or ultraportable ultrasound scanner, you need to get used to using the different buttons, options and controls or knobs on your machine. They will be slightly different on each ultrasound machine, and the more advanced ones may feature a variety of options.

To get started, however, you just need to understand the basic controls:

• Frequency (or depth) adjustment according to organ or body part.
• Adjust gain (or image brightness).
  • A poorly calibrated image will be too bright or too dark, and you could miss out on important details.
• Capture images or video loops.
  • This function lets you save slices of interest. On some classic ultrasound scanners, you can also print them out. On more recent ultrasound scanners, as well as on most ultraportables, you can save your images in a dedicated gallery, where you can also insert notes or create a patient file.

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Disinfecting your ultrasound machine

Once the examination has been completed, you should clean and disinfect your probe according to the manufacturer's instructions. In most cases, the recommendation is to wipe the probe with absorbent paper. Then disinfect the device with a disinfectant wipe.

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The next steps in your initiation

You now have the basic theoretical knowledge you need to perform your very first test ultrasound scans!

The next stage of your training will involve interpreting and annotating images and loops, both physiological and pathological. This step will enable you to develop your expertise, refine your clinical judgment and your understanding of anatomy. Once you've acquired the basics, we'll invite you to perform ultrasound scans on yourself. After an average of thirty sections per organ, you will have sufficiently mastered probe positioning and the gesture that will enable you to acquire quality images.

After this self-study phase, you will start performing ultrasound scans on your patients in test mode, for a recommended period of several weeks. This stage will enable you to put your new skills into practice in a real-life context, while benefiting from guidance and constructive feedback from your peers and trainers.

Finally, you will fully integrate clinical ultrasound into your daily medical practice. This new skill will allow you to make faster and more accurate diagnoses, optimize patient care, and strengthen collaboration with your peers. In short, clinical ultrasound training is a sustainable and beneficial investment for your professional career and the health of your patients. Don't hesitate any longer and embark on this promising and exciting path!

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