Ultrasound tip: multi-beam ON / OFF

G’day, here’s a quick tip from one serious ultrasound enthusiast to you all.

I have learned this by hard trial and error, it is one of those simple tricks which I probably should have learned early on in my US training, but missed.  Of course, I had a fool for a teacher! So I am going to share it  with you all and hopefully make your US use more satisfying and efficient.

The multi-beam?  What is that you say, well it isn’t something that you usually fiddle with for the routine type of scanning that ED and GP docs are doing, but you should.

What does it do?  Modern US probes are smart pieces of kit that have all types of built in trickery in order to optimise the images they produce, reduce artefacts and save you time.  “Muli-beam” describes the ability of a probe to throw out all sorts of angled ‘beams’ of sound across the field to try and get around obstacles and echoic interfaces that might interfere with the image most distally.

Awesome – this is a great idea, and I am sure that we all take this technology for granted when we slap on a probe in our FAST or pelvic scans.

BUT – this is one trick that sometimes you can do without, in fact it sometimes defeats your purpose entirely. So you need to know how and when to turn it off.

I am using Sonosite’s M-Turbo machines, so I can tell you how to turn this function on/off there – otherwise call your rep and ask them.

On the M-Turbo, you need to locate the MB On/Off  ‘soft key’, this is usually one of the six buttons in a row just below the screen (it says “MB On” as default usually).  Here is a 6 second tutorial on how to turn ON/OFF MB on the Sonosite from Matt Dawson (Ultrasoundpodcast.com).  Is it just me or is there somebody having sex in the background noise?  Weird, but thanks Matt.

So all you need to do is push the button and the probe toggles between MB On  and  MB Off modes.  Easy as pie.  Now the tough bit – why would you want to do this?

The multi-beam helps the probe “see around corners” and get rid of artefacts from echoic objects in the near field.  However – sometimes that is precisely what we want in order to identify small, echoic objects in the near field – e.g.. needles, foreign bodies, fractures etc.  Turning OFF the MB means the probe puts out purely parallel ‘beams” of sound which behave as straight “line-of-sight” beams – so any obstacle is more obvious – i.e.. creates more artefacts, which you see as shadow behind the bright dot you are looking for.

So if you are using your probe to find a small FB, less than 3 or 4 mm wide (shard of glass, Implanon, palm frond etc) then MB is your worst enemy.  It will fill in the black shadow behind the FB making it look like a dot, rather than a convincing FB with a shadow behind it.  It can make it nigh on impossible to see small FBs in the fat tissue.

The other instance where MB might be doing more harm than good is when you are doing procedures with needles – aspirating pus, collections, nerve blocks, inserting arterial lines and CVCs.  Sure you can still do it, but why not push that little button and make your life easier.

Final tip – don’t forget to return it to “ON” before doing your next search for an aorta in a fat man – it will then make your life easier once more – as I hope this post has done.

As is often the case the really smart people out there on #FOAMed land have delivered some golden tips via twitter.  Mike Stone (@bedsidesono) gives a list of the terminology used by other US manufacturers to describe the same mode – “Distortion correction” I think Laleh Garahbagian (@Sonospot) points out is the proper technical term for what all these moses do.

Thanks to Scott Weingart (emcrit.com) for pointing out that MB OFF is best for lung / chest scans where you are completely relying on artefacts to get your images.  Great tip.  OK, if you have any more tips – hit me on twitter or the comments – happy scanning  .  Casey
MB tweets



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