Technical Factors of mri liver (Magnetic Field Strength)

The magnetic field strength of choice currently employed for body MRI is 1.5 T. At the current state of development, this field strength provides an optimal combination of SNR and speed, allowing optimization of rapid acquisition techniques while staying within government institution-determined energy deposition-rate limits. These systems
also provide a good balance between T1 values, that are dependent on field strength, and achievable contrast effects. In addition, field distortion and paramagnetic effects that increase with increasing field strength possibly resulting in undesirable image artifacts remain within tolerable limits at 1.5 T. There are theoretical considerations
favouring development of higher field systems for body MRI and efforts are well underway to transfer techniques used at 1.5 T to 3 T. However, it has become apparent that the approaches used previously to migrate from lower to higher (1.5 T) field systems have not proven successful in migrating from 1.5 T to 3 T.

The relative strengths of higher field imaging at 3 T, in general, are more easily realized when using longer acquisition techniques such as fast spin echo (FSE) T1- and T2- weighted images, or multi-excitation gradient echo with oversampling. This explains the relative ease with which implementation of 3 T imaging has occurred for brain, spine, and musculoskeletal applications where longer acquisition imaging is used predominantly (in the order of minutes) and the relative difficulty in implementing 3 T imaging for the abdomen, where faster acquisition sequences are needed (in the order of seconds). Specific challenges for body imaging at 3 T are detailed below.

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