Parallel Imaging: Acceleration with SENSE and SMASH
We have already seen many ways to image faster and better. Why do we need to develop another class of imaging techniques and another set of MRI acronyms? MR people do seem to be quite fond of those! Parallel imaging, it turns out, is a truly revolutionary development, a quantum leap, that overcomes many of the practical limitations of high-speed imaging techniques like EPI. Looking back at the improvements in gradient performance that we benefit from today, it is easy to imagine even faster imaging by using faster and more powerful gradient magnetic fields and spacing echoes closer together. Other than the practical limitation of achieving such high performance, there are other real issues surrounding such gradient-intensive techniques. Very-high-gradient duty cycles can and do lead to painful peripheral nerve stimulation, and close spacing of RF pulses increases power deposition creating safety concerns (see Chapter 11). Image quality can also suffer, especially in EPI, where magnetic susceptibility artifacts may manifest as severe signal loss and distortion. All of these issues become more problematic at higher field strength. Parallel imaging methods accelerate imaging without any of these nasty effects. Although they have only become available recently, we are likely to see widespread development and dissemination of these methods in the near future.
KeywordsParallel Imaging High Field Strength Coil Element Parallel Imaging Technique Coil Sensitivity
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