IN BRIEF, WHAT ARE NMR AND MRI? 
HOW MANY MR MACHINES ARE THERE? 
ARE THERE OTHER THAN MEDICAL APPLICATIONS OF MR?
IS MR IMAGING A SAFE PROCEDURE OR ARE THERE SIDE EFFECTS? 
HOW DID MAGNETIC RESONANCE IMAGING DEVELOP?
I DO NOT UNDERSTAND ALL THE ACRONYMS USED FOR 
CAN YOU PROVIDE AN OVERVIEW OF MR CONTRAST AGENTS?
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 | In the early 1980s, there were 12 machines, and everybody knew each other. Then it went like this (Figure 1). The biggest markets are still the United States of America with some 46% of worldwide sales followed by Europe which buys approximately one quarter of all units, and Japan with 15%. Worldwide, there are approximately 25,000 MR machines. However, meanwhile it is very difficult to get an overview or even estimations on the number of MR machines worldwide. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 1: Sales of MR machines by field strength per year between 1983 and 2001 (EMRF estimates). Low
field: < or = 0.5T x-axis:
year |  | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| In the United States, there are approximately 11,000 MRI system. Between 60% and 75% operate at 1.5; less than 10% at 1.0 Tesla, slightly less than 15% below 1.0 Tesla, less than 5% at 3.0 Tesla (rounding error). One quarter of all systems in the United States are open, the rest conventional closed systems. Markets differ in their demands. Open systems are mostly sold in the United States, the market share of open system is limited in Europe and Japan. Three-Tesla whole-body systems are fashionable, but of marginal importance in sales and clinical examinations. Table 1 gives an overview of MRI in Europe. Table 2 shows a comparison of the density of MR equipment worldwide. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Table 1: Overall number of MR machines in selected countries; * = authorized 484 (EMRF estimates). |
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Table 2: Comparison of quantity of MRI equipment between U.S.A., Europe, India, China and Japan; 2006; (Europe = European Union and Switzerland; China = Mainland China, without Hong Kong, Macao, Taiwan). (EMRF estimates). |
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AT WHAT FIELD STRENGTH DO THEY OPERATE? MR systems are available in the well-known tunnel shape or as open systems. The latter reduce patient claustrophobia and are better suited for interventional purposes because there is access to the patient from all sides. Open systems are available between 0.3 T with permanent magnets to 1.5 T with superconducting magnets. Most clinical systems operate at field strengths of 1.0 and 1.5 T. The recent trend towards ultrahigh field scanners is aimed at research and commercially competitive sites. At present, there is no proof that such 3-Tesla imagers are of better clinical value than medium or high-field machines although there are numerous claims of better "patient outcome"; in addition, there are still safety considerations for machines operating above 2.0 Tesla, although the US-American FDA allows clinical examinations in adults on systems up to 8 Tesla. The choice of an MR system might be quite agonizing. Field strength is one, but not the only and most important, parameter; higher field strength does not necessarily guarantee a better quality system or better diagnostic outcome for the patient. Needs must be carefully assessed in the choice of an MR imager. The quality of the component parts, both in terms of hardware and software, makes a considerable impact. Service, maintenance, and knowledge of how to run the system are of pivotal importance for image quality and assessment. The lowest quoted price of a new 1.5-Tesla state-of-the-art clinical MR imager is below € 600,000 (US$ 1,000,000). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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