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Low-Field Open MRI vs. Closed MRI Solution

By Steve Rentz

Underpowered, underutilized, but frequently misunderstood, open MRI systems are under-appreciated here in the USA and virtually ignored in other “developed” countries. Many radiologists don’t want to read from open MRIs, governments and insurers don’t want to pay for them, and the appetite for higher and higher magnet power has, in many cases, relegated the open MRI to a “back-up” role in larger imaging facilities. Whether or not that relegation is deserved, it’s a fact that the demand for low-field open MRI (.2T – .35T) has never been greater in developing countries. So what exactly is the market for open MRI vs closed MRI?
No Power? No Helium? No Problem!

Steve Rentz

Though there are exceptions, most low-field opens (LFOs) use permanent magnets, which means that they are always “at field.” While this might necessitate a few more transportation precautions (make sure you work with a shipping company that has some experience), it’s a major selling point for countries where power isn’t so clean and the liquid helium used in higher-field closed MRIs isn’t readily available or is extremely expensive. Once installed, these systems tend to have very low maintenance costs relative to closed MRI and, if properly cared for, can run for years.
If You’re Not in Deep Tissue, it May Not Be an Issue
Don’t forget that, in many instances (even in the U.S.), open MRI is more than adequate for imaging needs. In addition to being invaluable as a solution for larger or claustrophobic patients, many orthopedic studies in particular can be adequately performed with an open MRI. In addition, newer versions from Hitachi like the Airis Elite and Aperto have fat saturation capabilities. Still, it is outside the USA that most of the current demand for low-field open MRIs exists.
Care and Handling of a Permanent Magnet
In this age of wider bores and higher Tesla strengths, low-field open MRIs are almost solely a product dealt in the secondary market. If you have one to sell, or if you’re in the market to buy, make sure you’re dealing with a company that is used to working with these units. Even though you’re not dealing with cryogens and potential quenching, exit pathways, containers, crating, and craning can ALL be expensive and complicated.  “Always at field” means just that – and it also means they are typically very heavy.  If you are outsourcing, be sure to share any issues that might arise with the exit pathway. This is always an issue with MRI systems, but it is especially an issue with open MRIs due to the weight involved.
HighTube MHU Capacity
Creating an accurate treatment plan requires a lot of images, which produces a lot of heat in a scanner’s X-ray tube over a short amount of time. A system with a high tube heat capacity (expressed in millions of heat units or MHU) is needed to accommodate this. CT scanners designed for simulation use generally have tubes rated at 5 MHU or above.
Buying and Selling an Open MRI
Just because these systems are older and often being replaced in favor of newer short/wide bore MRIs doesn’t mean that, with proper placement, they can’t be valuable assets. It also doesn’t mean they aren’t the right option if you’re buying and want to keep your equipment, maintenance and energy costs low. Is open MRI “niche equipment”? Perhaps, but in the right niche, it may be the right equipment.
Steve Rentz is the Product Manager-MRI for Block Imaging International. He has been managing the MRI business at Block Imaging since 2003.