The sector angle is important as it affects the frame rate dramatically

A narrow sector angle (width) allows either (1) a higher frame rate (the time required to build the image is reduced by reducing the number of beams for a whole sector) or (2) a better lateral resolution (the line density can be increased)

A higher frame rate increases temporal resolution

A higher line density increases lateral resolution

By using a sector just wide enough to include all relevant details, the ultrasound system is utilised in the best way

This user control is similar to the brightness control of a television set

Some of the emitted echo signal is reflected back to the probe when the emitted beam hits a reflective interface in the tissue

The echo signal returning from the tissue is converted to an electronic signal by the probe

This signal is very weak and has to be amplified before it is processed into a greyscale image. The signal amplification is called “gain”

Undergain: If the user sets the gain control too low, the amplification of the electrical signals is too small, and the 2D greyscale image on the screen becomes too dark

Overgain:If the gain control is set too high, the 2D greyscale image becomes too bright

The ultrasound image can be optimised by adjusting different user controls

The most important user controls are:
– Gain
– Depth
– Sector angle
– Time Gain Compensation

These user controls will be explained in greater detail on the next slides

It is important that you become familiar with these user controls on your own ultrasound system allowing you to optimise the ultrasound image in order to improve the added diagnostic value of the images

The ultrasound image on the screen can be turned upside/down or left/right with user controls

In FATE and adult cardiac ultrasound the ultrasound image displays the sector with the two radii diverting from the top of the screen. The OM is on the right side of the screen, and the arc of the sector is displayed towards the bottom of the screen

The orientation indicator (OI) on the monitor is placed in the upper left corner of the screen by convention (Except for cardiac ultrasound where the OI is placed in the upper right corner of the screen)

Whenever possible keep alignment of the orientation marker (OM) on the probe and the OI as shown on the image

Whether the orientation of the probe is appropriate can be checked by tapping a finger on one end of the gel covered foot print of the probe and watch the movement on the monitor – the “finger-test”

There are two ways to hold the probe properly during the FATE examination

The screw driver grip: With either the back or the palm of the operator hand placed on the patient during scanning

The pencil or lipstick grip: The grip on the probe is made with the thumb and index finger. The third digit may strengthen the stability of the grip on probe

The image is generated by the transducer and the ultrasound system and then displayed on the screen. For example, cardiac ultrasound employs phased array probes that display the image as a sector on the screen. The sector is demarcated by the two radii and the arc. In the figure the two radii of the sector are red and blue

The red and the blue radii diverge from the probe at the top of the monitor (the skin surface)
The orientation indicator (OI) is at the right side of the screen by convention in cardiac ultrasound (contrary to all other clinical ultrasound applications where the OI is placed on the left side of the screen)
The blue and red radii on the probe sector always correspond to the radii on the screen
The probe can be moved in three dimensions, but the orientation on the screen remains the same

The image of a blood vessel on the ultrasound monitor represents a thin slice of tissue

The size of the slice is determined by the profile of the ultrasound beam and can be described by height, width and thickness

The ultrasound beam is approximately 1 mm in thickness in the focus zone for all probes

Width is determined by the width of the foot print of the transducer

Height can be changed by adjusting the image depth on the ultrasound system

Parallel shifting of the probe back and forth and from side to side and rotating and tilting the probe allows you to capture the best possible cross sectional view of your target structure in the best possible position

A high frequency linear probe is most appropriate for peripheral vascular access and peripheral nerve blocks

The high frequency generates good image resolution allowing visualization of small structures

However, the depth of tissue penetration is curtailed to 2-6 cm

The probe is fitted with an orientation marker (OM)

On the image the OM is indicated by a green arrow. The OM facilitates the correct orientation of the probe on the patient