Siemens Healthineers’s new High-V MRI a paradigm shift in pulmonary MRI

Siemens Healthineers has unveiled their new Magnetom Free.Max MRI which is set to open new opportunities in magnetic resonance imaging. The Magnetom Free.Max, the company’ smallest, most lightweight and compact whole-body scanner, was revealed at Shape 21, a virtual event held on 17 November.

This new low-field MRI, combined with imaging AI, is ideally suited to pulmonary imaging – and in patients with implants – as it produces far fewer imaging artifacts compared to conventional MRI.

The Magnetom Free.Max is still being clinically evaluated and is expected to start shipping to countries with regulatory approval in August 2021.

Referred to as ‘High-V MRI’ by the company, the scanner has been designed with an enlarged bore size of 80 cm and a table load of 320 kg, making it comfortable for large patients.

But what sets it apart from conventional MRI is the scanner’s low-field strength of just 0.55 Tesla. This is combined with a number of digital technologies, such as deep-learning Artificial Intelligence (AI), to produce images equivalent to 1.5 Tesla in certain scanning procedures.

The Magnetom Free.Max uses a unique combination of AI and algorithms to reconstruct images to create high quality imaging with low-field MR. The lower field strength enables better imaging of the lung – producing fewer artifacts, said Arthur Kaindl, head of Magnetic Resonance Imaging at Siemens Healthineers.

Deep Resolve

One of the key digital technologies incorporated in the scanner is Siemens’s new Deep Resolve AI, which has been in development for the past two years.

Daniel Fischer, Head of Clinical and Scientific Marketing, MRI, Siemens Healthineers, explained that Deep Resolve “addresses the challenge of getting sharper images without sacrificing resolution or scan time. To do this, it uses a deep convolutional neural network to take low resolution input data and create a higher resolution image. An important job of this network is to recognize fine structures and enhance the level of differentiation between them. For example, the border between grey and white matter in the brain. The algorithm was trained using thousands of low-resolution and high-resolution data set pairs. Through the training data, the algorithm can take low-resolution input data and generate images with up to factor 2 higher image resol ution. Additionally, the originally acquired data are incorporated into the image reconstruction process. This guarantees that the resulting image is congruent with the originally acquired data.”

Asked how the AI reconstruction has been validated, Fischer explained that there is a two-fold validation process. “Internally, the algorithm is tested on trainings data and then validations data. This process validates the performance and robustness of the algorithm. Once it is through this process, we deploy the application as part of our clinical use test process at multiple sites. During this period, we observe the performance based on the feedback from our clinical partners.”

Pulmonary imaging

The scanner is being promoted for use in pulmonary imaging because the low-field MR produces fewer artifacts. Fischer explained the technical reasons for this and the clinical effect.

To understand the technical background he said we have to look at MR physics. “This has to do with what is known in MRI as susceptibility. Susceptibility is a measure of how much a substance is magnetized when exposed to a magnetic field. All tissues show a varying range of susceptibility and this can have an adverse effect on the overall image quality. This is especially true in areas where there is a large change in susceptibility – resulting in what are called susceptibility artifacts. Images with susceptibility artifacts show geometric distortions and/or areas of signal “pile-up”, i.e., artificially high or low levels of signal intensity. The magnitude of these artifacts scale with field strength, that is, they are much more pronounced at higher field strengths. Two very common areas for high susceptibility in MRI are anywhere there is an air-tissue interface or in the presence of metal. At lower field strengths, MR physics works in our favour: susceptibility is inherently lower. When combined with modern imaging techniques, this can create new opportunities.”

Regarding the clinical effect, he explained: “With pulmonary MRI, we deal primarily with the lung. Because the lung is typically full of air, imaging any tissue or structure within the lung (e.g., parenchyma) presents a huge challenge at conventional MRI field strengths. At lower field strengths, the susceptibility and thus resulting artifacts from the air-tissue interface in the lung are comparably much lower. When combined with modern MR imaging techniques (e.g. BLADE – a technique Siemens developed to reduce sensitivity to motion in MRI), pulmonary imaging using MRI, which uses no ionizing radiation, becomes a very attractive proposition. This holds true especially for populations with chronic diseases that require repeated follow-up examinations over many years, or even paediatric patients.

Patients with implants

The Magnetom Free.Max is also beneficial for imaging patients with implants. Fischer explained: “We know that susceptibility increases around metal implants, causing geometric distortions and/or signal pile-up, resulting in images full of artifacts that are worst-case non-diagnostic. The higher the field strength, the more pronounced the image artifacts. As with pulmonary MR at lower field strengths, MR physics works in our favour here as well when it comes to implants. Additionally, SAR heating at lower field is lower, allowing for greater flexibility in the acquisition strategy. (SAR or ‘specific absorption rate’ is a measure of the amount of power deposited by a radiofrequency field in a certain mass of tissue.) Lower field MR offers an opportunity to better manage these effects, especially when combined with modern imaging techniques

“Due to changing demographics we are seeing an increasing need for scanning patients with implants (e.g., for knee and hip joints). Scanning patients with implants at conventional field strengths is challenging because of the resulting susceptibility artifacts. Scanning at lower field strengths with modern techniques for image artifact reduction in patients with implants (i.e., WARP or SEMAC) offers an opportunity to bring the value of MRI to this rapidly growing patient group.”

User guidance

With Magnetom Free.Max, Siemens Healthineers is introducing myExam Companion to the field of MRI. myExam Companion is an AI-based user guidance system which is already successfully used in modalities such as CT and X-ray imaging. It enables routine examinations to be automated, eliminating repetitive tasks and allows even novice technologists to operate the MR with ease. Despite the high degree of automation, experienced users can fully configure the scanner at any time to meet more complex scanning requirements.

Installation

With a footprint of just 23 sq. m, the Magnetom Free.Max can be installed in locations where it was previously impossible for MRI installations, opening up a whole swathe of options in this regard, such as near or in an ICU, in communitytype urgent care settings or as an add-on system in radiology, said Kaindl.

At just over three metric tonnes in weight and just below two metres in transportation height, the machine is the most lightweight compact wholebody scanner Siemens Healthineers has built.

The company developed a new magnet for this purpose with so-called DryCool technology, which requires less than one litre of liquid helium for cooling and no quench pipe. Such machines used to require several hundred litres of helium and a costly quench pipe.

Speaking at Shape 21, Prof. Elmar Merkle, University Hospital Basel, commented: “I see great benefit in, for example, bringing MRI directly to hte intensive care unit, as patient transport of critically ill patients to the central radiology department is risky and cumbersome, particularly during this time of Covid-19.

“In addition, I believe MRI can significantly improve patient care directly at the frontline of diagnostics, in outpatient centres or even the emergency room, and could be implemented in bespoke locations where today only CT or X-ray systems are available,” he added.

Service support

The Magnetom Free.Max is also fully connected for remote monitoring and continuous service support. This shortens service intervals and helps to quickly transmit system diagnostics, noted Siemens Healthineers. Remote access by a service technician is often sufficient to detect and correct a defect, thus considerably improving system uptime, the company added.