PROBECRAFT

PROBE SELECTION

Typically in POCUS we use three different probe types, the linear array, curvilinear array, and phased array probes.

Each probe has a variety of applications and also pros and cons. The choice of probe type will depend on the nature of the scan undertaken, in particular the required penetration (depth), resolution, and the available acoustic window.

POCUS probe applications:

• The linear probe is typically used for vascular access including procedural guidance, pleural assessment for sliding, and superficial scanning

• The curvilinear probe for eFAST, AAA, subcostal cardiac/IVC, lung, abdominal, some procedures, and early pregnancy.

• The phased probe (also known as sector or cardiac) is predominately used for echo/cardiac scanning. It can also be used in lung scanning (poor pleural image), eFAST, and AAA.

Probe Comparison

PROBE MANIPULATION

To obtain good images it is important to hold the probe and manipulate it in a comfortable and structured manner. Probe position and manipulation are critical to getting adequate image windows and to optimise the image position and orientation.

Holding the probe

Holding the probe in the correct manner is important for a number of reasons:

• Reducing user fatigue

• Stabilising the probe position and allowing subtle movements

• Improved image optimisation and transition between views and different axes

In general correct positioning of the hand is with a hold close to the base of the probe (image below). This position enables the use of the lower aspect of the hand (medial border)to stablise against the patients body. As well the grip means we can manipulate the probes movements more readily (discussed further on) to attain appropriate views and improve the image.

The position of the hand may need to change depending on the location of scanning, the required scan plane and direction, and proximity of the probe to the bed surface. Usually this means positioning to a over hand or underhand grip, utilising the same method to stabilise against the patients body.

pROBE MOVEMENTS

There are four main movements that are utilised in ultrasound to obtain and optimise our images. Generally each movement is done individually in different sequences to attain and improve the required image.

• Sliding is moving the probe along the skin surface, generally maintaining the probe in a certain orientation to the patient

• Rotating maintains the probe central axis at the same position, and rotating it around to change the image orientation (e.g. transverse to long plane view of the aorta)

• Tilting (also termed sweeping or fanning) the probe face is maintained in the same position and the probe is tilted from side to side in the dimension of probe width

• Rocking is similar to tilting but the movement is rocking in the dimension of the probes length

TRANSDUCERS AND PROBE MOVEMENTS (CORE ULTRASOUND)

ORIENTATION AND SCAN PLANES

PROBE MARKER

It is important to be aware of the location of the probe orientation marker so that your ultrasound image has the correct orientation. The marker on the probe side will be denoted clearly by a raised dot or ridge.

SCREEN MARKER

Always check the screen marker location on the screen to understand your image orientation. You need to be aware that the screen marker can be reversed by the user.

• At standard machine settings the screen marker will be at the top left of the screen when using the linear or curvilinear probes in most presets.

• When using the phased array probe in a cardiac preset generally the screen marker will be at the top right of the screen.

Probe and screen marker orientation

• For general scanning and procedures the screen marker should be at the top left corner:

  • In the transverse plane the probe orientation marker is placed towards the patients right side.

  • In the long plane (coronal/sagittal) the probe orientation marker is placed towards the patients head (cephalad).

• For cardiac scanning the cardiology convention should be used, the screen marker is at the top right of the screen (see below):

  • In the transverse plane the probe orientation marker is placed towards the patients left.

  • In the long plane the probe orientation marker is placed towards the patients head (cephalad).

ULTRASOUND SCAN PLANES

• Radiologic scan planes are relative to the anatomical position as shown in the image above:

  • Long planes - Coronal (frontal) and Sagittal

  • Short plane - Transverse or Horizontal

  • Oblique - Combination between planes

• Organ structures are generally not aligned with the above anatomical planes, and are usually imaged in relation to their long and short axes:

  • Long axis - parallel to the structures maximal length

  • Short axis - plane perpendicular to the long axis