The high sensitivity of MRI to pathologies in soft tissues was recognized already at the introduction of the modality. Therefore, it seemed to be applicable in emergency and trauma departments e.g., in the diagnosis of internal hemorrhages. In the early eighties, a 20 mT scanner was introduced to solve some acute diagnostic problems. The marketing of a completely different concept in the environment of fast-developing high-field and high-resolution imaging was challenging. This presentation gives an overview of the course of the project./1/ The early market for MRI was mainly radiological departments. The quality of images in terms of resolution and contrast-to-noise was a vital competition parameter. Even more critical were the staying power of the manufacturer and the upgrade path of the imaging system. There was not real markets for MRI systems for emergency departments. The unit, installation, and running costs of low field MRI were considerably lower than mid- and high-field MRI. There was a market for these systems in rural hospitals, private clinics, and especially in countries like Sovjet Union and some South American countries. The operation at a very low field provided some inherent advantages such as high T1 contrast and safety. The high contrast between lesions with increased free water content and normal tissue was beneficial in the diagnosis of pathologies such as internal hemorrhages /2/, abscesses, tumors, and pneumonia./3/ The use of field-cycling was tested for improvement of the signal to noise ratio. In this technique, the polarization in generated with a higher filed pulse, and the imaging operations are performed at a homogenous lower field./4/ The system was technically challenging, and the pulsed magnetic field generated some unwanted effects in the environment. However, the imaging results were quite promising. The low RF frequency provided the capability to use RF intensive sequences and still have a low SAR. This gave the possibility to exploit techniques such as T1r- and Overhauser -imaging./5, 6, 7/ T1rho dispersion imaging demonstrated to have some exciting features e.g., in the studies of muscular dystrophies./8/ T1r-weighted and magnetization transfer imaging provided a high contrast of liver lesions. T1r- and magnetization transfer- weighted images could be generated effectively using three-dimensional scanning. Dispersion imaging expected to provide a tool for improved tissue characterization. These possibilities are not yet fully exploited. The Overhauser imaging technique seemed quite promising. There is a potential to improve the signal significantly, and the necessary contrast agent gave promises for improved sensitivity and specificity. The field cycling technique was utilized. The required irradiation at high frequency was performed at lower field strength than the imaging operations./9/ The requirement of a proper contrast agent with a narrow ESR peak and high coupling between electrons and protons was too hard problem to be solved with compounds that could be used for medical imaging. Technically the scanners were based on the resistive magnet technology. The power consumption of the magnets was high, which assumed the use of a cooling water system. The signal and image processing electronics were quite expensive. The units were installed in shielded rooms with some active field compensation systems. Therefore the competition arguments claiming compactness and low costs were not so strong as expected. After two new generations of very low field units, an open MRI scanner operating at 0.22 T was introduced. This product was really successful. The diagnostic results obtained at 20 mT and later at 0.1 T were quite promising. The new magnet and signal processing technologies make it possible to design dedicated imaging systems to provide high-value information in specific medical or non-medical situations. The introduction of novel nanomaterial contrast agents may open the diagnostic capabilities of Overhauser imaging./10/

Acknowledgements

No acknowledgement found.

References

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