One of the most common questions is “how can I optimise my image on the [insert your ultrasound machine name here]?” It’s a great question, but it’s also one of the most difficult to answer quickly. This is because:

 

  1. Very few controls on your ultrasound system are completely independent of each other. You cannot adjust one aspect of your image without it changing something else. Everything is a compromise, and prioritisation is key.
  2. Achieving an “optimised image” is completely contextual. For example, big dog or small cat; early pregnancy or late pregnancy; start of the scan (simple pregnancy confirmation) or later on in the examination (a detailed investigation checking viability)?

 

An experienced operator will adjust the settings on their machine throughout their scan as priorities change.

 

DYNAMIC RANGE

On some machines, this is called “compression,” which is perhaps a more explanatory term. By turning this up, you are requiring the ultrasound machine to display a greater range of greys. By reducing it, you “compress” the number of shades of grey, resulting in a more contrasted image.

There is no magic number as to where this should be. It depends partly on personal preference, and partly on the task in hand. At the beginning of a scan, for example, you may wish to reduce your dynamic range to create greater contrast between hyper and hypoechoic regions (i.e. areas which are highly reflective, such as the foetus, and areas which return very few echoes, such as the amniotic fluid), particularly in early pregnancy when gestation sacs may be difficult to spot. Once you’ve found your region of interest, however, you may wish to increase your dynamic range in order to achieve greater detail or ‘texture’ in your image.

As an aside, some people find that a good way to discern difficult to spot pregnancies is to turn on pseudo-colour or “colorize map.” This is because the human eye can pick up subtle colour changes better than it can distinguish between shades of grey.

 

FOCAL POINT

Many people forget to adjust their focal depth, and this is a major cause of sub-optimal image quality. Your focal point is the point at which the ultrasound beam is narrowest, and lateral resolution is highest. Beyond your focal point, however, the beam diverges. Thus, everything beyond your focal point suffers from reduced image quality, which deteriorates with depth. If you’re guilty of scanning with your focal point sitting up the top of your screen which you never adjust, make changing this the first thing you do! If anything, it is better to have your focal point too deep (beyond the area in which you are looking) than too shallow.

 

DEPTH

Many of us start with the depth all the way out, and this is legitimate practice when performing an initial sweep of the area. If you do not reduce your depth once you’ve located your area of interest, however, you are losing out.

Most people starting off with scanning will begin with a collection of pictures of huge long sectors, with a few tiny puppies squashed up at the very top. What will differentiate you from a beginner is to go beyond simply spotting a pregnancy and grabbing some pictures, but adjusting your depth to make individual sacs the focus of your examination, allowing you to see them in greater detail and check for viability.

 

SECTOR WIDTH

Similarly, whilst a wide sector width is useful for an overview, you may wish to consider reducing this for particular areas of interest. This gives an enormous boost to your image resolution in two ways:

  1. More scan lines are able to interrogate the smaller area, providing you with higher lateral resolution. To learn about what lateral resolution is, click here.
  2. There are still fewer scan lines needed to interrogate a narrow sector than a wide one, and so your frame rate is increased.

Hence, reducing your sector width results in a sharper image and a more responsive one – perfect for looking at puppies’ hearts.

 

ZOOM

A similar effect can be achieved by using the zoom function. Again, your scan lines have a smaller area to interrogate, resulting in a higher resolution image. This live zoom is very different to post-processing zoom either on the saved image or on your computer, which is simply a magnification, with no associated increase in image quality.

 

PERSISTENCE

A high persistence averages many frames together, resulting in a smoother image. This is aesthetically pleasing and can help to reduce noise, but can result in a ‘delayed’ feel to the image if looking at fast-moving structures. A very high persistence may prevent you from spotting a foetal heartbeat, so be careful.

 

FREQUENCY

If you have attended one of our training courses, you cannot fail to have left without the importance of ultrasound frequency being drilled into you! Higher frequencies result in better axial and lateral resolution, but attenuate more rapidly with depth. Don’t just assume, however, that because your next scan is a St Bernard that you must drop your frequency and keep it there. Always try the highest frequency that you can, and reduce it only if you are not achieving sufficient penetration.