Open magnetic resonance imaging

open high-field MRI system

Open magnetic resonance tomography ( open MRT ) refers to magnetic resonance tomography (MRT) with devices in a special design in which the main magnet is not built in the form of a long closed tube ("tunnel"), but with better access to the patient. Important areas of application for open MRI are the examination of patients with claustrophobia and the implementation of surgical interventions under MRI control.

Designs

When designing open MRT systems, particular technical, physical and structural difficulties have to be overcome. Different types of systems have been developed depending on the manufacturer: The earlier open system concepts mostly worked on the basis of permanent magnets or conventional (non-superconducting) electromagnets with a relatively low magnetic field strength (up to approx. 0.6  Tesla ).

So-called open high-field MRT systems with superconducting electromagnets and field strengths of up to approx. 1 Tesla (as of 2010) have been available recently . The advantages of these systems are not only the improved space and the good accessibility to the patient, but also the image quality that comes close to that of standard tunnel systems.

Today, open MRI systems are usually built in the form of a C-shaped magnet with a vertical field profile (see figure). Alternative forms, for example with two ring-shaped magnets lying one behind the other and a horizontal magnetic field course ( double donut system) have so far not been able to establish themselves.

Upright MRI is also a new, open system. It works with vertical magnetic poles, in contrast to the cylindrically wound magnetic coils of the tube MRI and the magnets attached parallel to the floor in conventional (sandwich) systems.

This enables the doctor to determine the causes of certain complaints under real stress conditions. Some shifts or changes in the spine only become visible when it is exposed to its natural weight load while sitting or standing, or when the patient assumes a specific painful position. Movement studies with multiple recordings and different body positions are also possible.

The upright MRT method has proven itself, for example, in the diagnosis of herniated discs , spondylolisthesis (vertebral sliding) and load-dependent back problems. Among other things, it is suitable for examining complaints and injuries to the skull , spine , knee joint , hip joint , nerves , pelvis and osteoarthritis .

One area of ​​application of the upright MRT is the examination of patients who suffer from claustrophobia or when the closed environment of the tube MRT leads to oppression. It is not uncommon for a tube MRI scan to be discontinued for these reasons.

The magnetic field of the upright MRT is generated by a water-cooled electromagnet with a field strength of 0.6 Tesla . A steel core weighing 130 tons gives this magnetic field a high degree of homogeneity. It also runs across the patient - unlike in tube MRI, in which the magnetic field is aligned parallel to the body axis. This design of the upright MRT is essentially responsible for the fact that the examination can be carried out in different body positions.

Intervention in the open magnetic resonance tomograph

Operation on the open magnetic resonance tomograph at the University Hospital Magdeburg

Successful interventions under MRI control require two conditions. On the one hand, the doctor must be able to access the patient accordingly; on the other hand, the quality and speed of the imaging are relevant for interventions and functional examinations. Where the prerequisites for functional examinations in open high-field MRT have already been created, there are still further challenges to be overcome for successful operations in MRT.

Since many conventional instruments cannot be used in magnetic resonance tomographs due to their magnetic properties, there is a need to use specially manufactured MRT-compatible surgical instruments. At the Charité one of which is from January 2007 as part of TSB and the European Union ( ERDF funded) research project on the development of complex surgical instruments and their application worked in the open MRI. In particular, minimally invasive interventions are addressed that were previously carried out under X-ray CT control.

With the option of free choice of image planes, the open design and the execution of examinations with fast image sequences, it is possible to assess the surgical result directly after operations under MRI control and, if necessary, to make corrections immediately.

Interventions such as biopsies , periradicular therapies or the catheter system for brachytherapy on the open magnetic resonance tomograph have been carried out routinely at the Magdeburg University Hospital since October 2007 .

literature

• T. Kahn: Interventional MR Tomography . In: Maximilian F. Reiser , Wolfhard Semmler (Ed.): Magnetic resonance tomography . Springer, 2002, ISBN 3-540-66668-0 , pp. 939–966 ( limited preview in Google Book Search).

Individual evidence

1. ↑ Katharina Huneck: Claustrophobia in the MRI or the fear of the tube - the right way to deal with the patient. Diploma thesis at the Academy for Teachers in Health Care e. V., carried out in the radiological practice of Dr. med. Andreas Förg. Munich
2. ^ H. Frey: Positional and functional imaging in upright MRI. In: Mt-Medizintechnik. Volume 136, No. 5, 2016, p. 24.

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