Equipment

The Probes:

These are the true workhorses of the ultrasound machine. Each probe contains piezoelectric crystals which vibrate under electric current. When these crystals vibrate, they produce sound that penetrates into tissues. The probe also acts as a receiver for returning echo, which in turn, cause vibration of the crystals that the probe converts to current, that is later interpreted as data by the ultrasound machine.

While there are many types of probes available for POC (point-of-care) ultrasound, there are 4 that are encountered most commonly.

 

Curvilinear or Curved Array Probe: often referred to as the ‘abdominal probe’. Also low frequency (2-5MHz). Functions very similarly to phased array probe except with a larger footprint, which allows for better lateral resolution.

 
 

Endocavitary Probe: Moderate frequency (8-15MHz). Curved array. Ideal for Intraoral or trans -vaginal use.

 

Phased array: often referred to as the ‘cardiac probe’ this is a low frequency (1-5MHz) probe which is scanning the abdomen, retroperitoneal and even soft tissue structures. Given the low frequency, you can expect this to have good penetration, at the expense of resolution. Not great for visualizing small superficial structures. The phased array probe also has a small footprint (area of probe surface) which makes it ideal for getting between the ribs in cardiac studies.

 
 

Linear array probe: High frequency probe (5-15MHz). Unlike the above probes, the array is parallel, allowing for high lateral resolution, as well as maintaining resolution with depth. Due to this, will only see structures directly below probe. Ideal for superficial soft tissue evaluation, evaluation of neurovascular structures, and procedural use.

 

 

The Machines/ ‘Knob-ology’

Know thy Machine!

Never: 

-Run over probe cords 

-Drop probes 

-Hang probes from non-designated holders

Always:

-Clean the probes and keypad before and after each use

-Put machines where they belong in the department

-Plug in machines following use

 

The University Hospital ED currently employs 2 different machines

It is important to care for the machines and their components!

 

Sonosite EDGE

 

 

 


 

 

Philips SparQ

 

The Modes

A-mode: Rarely used. Plots echo as function of depth where x-axis is depth and y-axis is amplitude. Primarily useful in ophthalmologic/retinal ultrasound and for use of ultrasound beam therapy

2D or B-mode: Standard scanning mode. Spatially oriented- Structures are seen as function of brighness (echoic vs anechoic), depth, and width. Provides a cross sectional view of underlying structures. Able to see structures in real time.

 

B-mode used as guidance for attempted vessel cannulation

 

M-mode: takes a small section of horizontal beam (as would be seen in B-mode) and displays it over time. Useful to track motion/dynamic changes in a specific point of an image over a period of time. Vertical axis remains depth, while horizontal axis is time. (used in cardiac valve imaging and fetal heart rate measurements)

 

M-mode used to calculate TAPSE (tricuspid annular plane systolic excursion)

 

Color Doppler: Uses ‘doppler shift’, an induced change in frequency of returning echo to determine movement. Superimposes color to image to show flow either toward or away from probe, as indicated by a color key. By convention, movement towards probe is displayed red, and movement away as blue.

 

Color doppler used to show flow across mitral valve

 

Power Doppler:  Similar to color doppler, but without assigning color to direction. Instead utilizes shades of color to represent level of flow. Useful for low flow states.

 

Power doppler used to show low flow state in IVC/hepatic vein

 

Spectral doppler: Either via pulse-wave (alternating) or continuous (simultaneous transmission and reception). Allows for assessment of flow velocity at a specific point in the image which is then displayed as a function of time. Useful for echocardiography.

 

Spectral doppler used to quantify flow velocity across mitral valve

 

 

Getting ready to scan

Orientation:

Scanning Planes: Ultrasound images are a 2-D representation of the underlying structure. Just as in other imaging modalities such as CT scanning or MRI, the image is displayed as a cross section in a particular plane. However, ultrasound can be more complicated in that the plane of section is determined by the sonographer. Just as one can obtain axial images, one can also obtain images in oblique planes.

By Connexions [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0) or CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons

Transverse plane- AKA axial plane. Perpendicular to the long axis of the body. Separates top from bottom.

 

Sagittal plane- Parallel to the long axis of the body, separating left from right. Midsagittal plane refers to the plane in the midline as opposed to parasagittal which is either left or right from midline

 

Coronal plane- Parallel to long-axis of the body, perpendicular to sagittal plane. Separates anterior from posterior.

 

Oblique plane- Not at right angles to any of the above. 

 

 

When an object or organ of interest does not lie in a standard plane, we often refer to it in terms of its axis.

        Long Axis: the plane which extends parallel to the maximum length dimension of an object

         Short Axis: the plane which is perpendicular to the long axis of an object

     

Probe indicator: There is always a dot, ridge or groove on one side of the probe which functions to assist with orientation. This allows one to determine which side of the probe corresponds to which side of the screen. By convention the indicator on the screen is a blue dot located on the top left of the screen image. By convention, the probe indicator has a specific position based on the imaging plane:

Transverse plane: Probe indicator towards the patient’s right side

 

Sagittal and Coronal planes: Probe indicator towards the patient’s head

 

Handling the probe:

It is important to have stable grasp on the probe, as the acquisition of a good image is often dependent on minute adjustments. In order to be able to make fine adjustments with the probe hand, it is best to hold the probe in the dominant hand with the thumb and index finger, using the other 3 fingers and ulnar aspect of the palm as a sort of ‘tripod’  to brace against the patient’s body.

 

Making adjustments:

Sliding: performed by sliding the entire probe in direction of its long axis over the surface of the body with a 90 degree angle of insonation- generally used to find a good imaging window

 


Sweep: performed by sliding the entire probe in direction of its short axis over the surface of the body with a 90 degree angle of insonation-generally used to find a good imaging window

 

 

Fanning: performed by adjusting the angle of the probe body to the skin in anterior-posterior dimension (short axis) of the probe. This allows the ultrasonographer to scan through different planes of an organ from one imaging window

 

 

Rock: similar to fanning, but in the left-right dimension (long axis) of the probe. Allows sonographer to extend imaging area to desired target not immediately below probe

 

 

Rotation: performed by turning the probe on its long axis. This can allow the provider to obtain an image in an area with small imaging window (i.e ribs), or to obtain appropriate plane of section given variances in anatomy (i.e cardiac views)

 

 

Pressure/Compression: Pressure/Compressive Force on the probe into the body- used to manipulate vessels/tissues in areas of interest

 

 

Knobology:

Definitions

Modes: Machines often preloaded with imaging modes for particular organs/indications which optimize settings for study of interest (e.g cardiac, vascular, abdominal, etc.) 

Depth: Adjust depth of field presented on screen

Focus: Improve resolution at a particular depth in image (not available on all machines)

Gain: Adjusts the strength of the signal returning to the probe- visualized on screen as contrast

Time gain compensation: Adjusts the gain for a specific depth in the image

AutoGain: allows the machine to calculate optimal gain settings

Calipers: used for measurement of distance


Sonosite EDGE

 

Philips SparQ


Written by: Aalap Shah, MD

Peer Reviewed by: Lori Stolz, MD, RDMS

All images obtained by Pattie Smith, RDMS and Aalap Shah, MD except as otherwise noted