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Portable machines are widely used in Sports medicine. They provide good quality diagnostic information and are easy to set up and transport. Radiologists prefer the highest quality imaging and more advanced functions. Cart-based machines still outperform the portable machines (but at a cost). Rheumatologists will need a good superficial probe and excellent Doppler. Most machines have needle optimisation software for interventional procedures.
Bigger is better?
Generally (but not always), cart-based machines have a higher imaging quality and more advanced functions.
The more expensive the better?
Generally, yes, you get what you pay for. Portable machines start around £12,000 and go up to around £35-40,000. Cart-based machines start around £45,000 and go to over £100,000.
What about second-hand machines?
Probes have not changed much over the past few years. Ultrasound machines themselves keep improving in function and picture quality by software updates. If you buy a second-hand machine, get one with the highest specification you can and make sure it has the functions you need. A machine that is a few years old should easily give you 2 to 4 years of use. They generally need very little maintenance, although batteries may need to be replaced after a few years.
The general rule is higher frequency = higher image definition, but lower depth of scanning. For MSK, a linear probe with bandwidth 4-12MHz or 5-16MHz covers most applications. A hockey stick probe (8-18MHz or higher) is useful if you often scan feet and hands and prefer a small probe footprint and higher frequency. Curved probes (3-6MHz) are good for deeper structures, but the picture quality is less, which may not provide enough diagnostic detail.
What functions are useful?
Pre-sets for various areas in MSK (shoulder, knee, ankle), split screen, extended field of view, easy video (pro and retro recording, adjustable lengths) and still-picture saving. Tissue Harmonic imaging, Good Color and Power Doppler. Elastography and 3D imaging do not yet have many applications within MSK.
Like driving a car. You do not by a Ferrari before you have a driving license and if you only need it to do the shopping.
Make sure you get the best out of the machine by having good scanning skills. A good machine is only as good as the clinician using it.
Before buying any ultrasound machine, ask the supplier to drop it off for a few days 'test drive' in your clinic. Compare a few machines; they all vary and, like with cars, you have to feel comfortable with it before you commit to it.