Background

Magnetic Resonance Imaging (MRI) has become an indispensable medical imaging modality with about 30 million patient exams in the EU every year and an excellent history of safe use. Nevertheless, it is continuously evolving and several recent technological developments such as ultrahigh magnetic fields, parallel transmission, or MRI guided radiotherapy promise to significantly enhance the quality and the range of applicability of MRI. The main reason why these technological developments haven’t yet made it to product level and clinical application are their unresolved safety issues for patients and staff. For example an estimated 8 – 10 % of the European population, namely those carrying metallic medical implants, are effectively excluded from MRI scanning because these devices interfere with the MRI related radio-frequency (RF) fields inside the human body which might result in impermissible local “hot spots”. The issue is that the associated patient risks cannot currently be quantified in this situation and in the case of such uncertainty a ‘safety first’ attitude naturally prevails and prohibits the clinical use of MRI for such cases. The overall goal of this JRP is to provide metrics for the assessment of the associated risks with MRI and to define scan parameters or limiting values for the safe use of MRI.

Project organisation

Tissue heating by absorbed RF power (described by the Specific Absorption Rate, SAR) is an established health risk for patients. In the most advanced MRI scanners operating at “ultrahigh (magnetic) fields” ( ≥7 T) the RF wavelengths in water-like tissue come down to ~12 cm, smaller than body dimensions. This brings the danger of temperature hot spots and emphasizes the need for local SAR control. At present, however, the local SAR distribution inside a human body can only be derived from numerical simulations. But these cannot sufficiently be trusted as no established means exist to validate them. Advanced modelling concepts for electromagnetic fields (EMF) inside phantoms and human computer models will be developed and applied in WP 2 and will be validated by comparison to calibrated EMF measurements in WP 1.

Physiological effects and potential hazards (especially) for clinical and maintenance staff moving through the strong magnetic stray fields of up to several tesla around MRI scanners will be investigated in WP 3, combining dosimetric measurements and simulations to assess physiological effects.

Emerging technologies in MRI, such as ultrahigh fields or parallel transmission (pTx) technology, promise better image quality, shorter scan times, and better diagnostic value. With respect to SAR control, the transition from a conventional single-channel MRI scanner to a prototype 8-channel pTx system implies going from a 1-dimensional to a 15-dimensional parameter space. Established concepts to handle this challenge are currently missing and will be developed in WP 4.

The absence of ionizing radiation and the unmatched soft-tissue contrast make MRI the ideal candidate for the recent development of image guided radiotherapy of thoracic and abdominal tumours that exhibit large variation in position, size, and shape during the course of the radiotherapy treatment. This provoked the development of another emerging technology in MRI: despite the enormous technical difficulties to combine a linear accelerator (linac) for radiotherapy with an MRI scanner, a prototype system of an MRI linac has been developed. The additional challenge of how to provide reliable and traceable photon dosimetry within the (electromagnetically) harsh environment of an MRI scanner will be solved in WP 5.

An estimated 8 – 10% of the European population are carrying medical implants. At present, this excludes them from receiving an MRI scan as no metrics exists to assess the specific safety risks related to these implants. For the subgroup of passive implants the proposed JRP will investigate implant associated risks in WP 6 and propose such a metric, which is urgently requested by patients, physicians, manufacturers, and regulatory bodies.

 

The major goals and objectives of the project are given in more detail in the Publishable JRP Summary.