Technical challenges and opportunities of whole-body magnetic resonance imaging at 3T.

An increasing number of magnetic resonance whole-body units operating at field strengths of 3T and beyond are currently installed in research institutions as well as clinical facilities. This review wants to describe the changes in physical properties at higher field strength and the resulting implications for clinical and experimental examinations of the whole body. An overview is provided on the resulting advantages and disadvantages for anatomical, functional and biochemical MR examinations in different regions of the body (except the brain). It is demonstrated that susceptibility and chemical shift effects increase linearly with field strengths and provide clearly higher sensitivity of most spectroscopic or blood oxygen level dependent (BOLD) techniques. On the other hand, homogeneity of the radiofrequency (RF) field is reduced in the body trunk at higher field strength due to the shorter wavelength. Examinations of the head or extremities provide sufficient homogeneity of the RF field for common examination techniques in most cases, whereas abdominal and pelvic examinations are still sometimes hampered by undesired dielectric effects. Nearly quadratic increase of RF energy deposition with increasing field strengths results in clear limitations for some common sequence types which work without any problems at 1.5 T. New strategies with multi-channel RF excitation have the potential to overcome limitations due to RF inhomogeneities, but a few years of further technological development seem necessary. Many problems have to be solved in the near future regarding the variety of MR techniques and applications in all parts of the human body.