METHOD FOR RF SHIMMING TO IMPROVE THE B1 TRANSMISSION UNIFORMITY OF SPIN-ECHO BASED MR IMAGING AND SPECTROSCOPY
Publication Date: 2017-May-15
The IP.com Prior Art Database
A method for RF shimming using a parallel transmit system for fast spin-echo sequences in ultra-high field MR systems utilize a health check of the optimization to greatly improve the image uniformity.
The present disclosure relates generally to magnetic resonance (MR) imaging systems, and more particularly to improving imaging quality in ultra-high field MR systems.
The development and applications of MRI systems at ultra-high field (7T and above) provide several new opportunities. For example, the increased signal strength at higher fields may be used to obtain higher resolution images, high quality MR spectra, which can in turn be used to improve detection of lesions, for more accurate assessment of structural anatomy of body parts, e.g. the brain, and achieve improved sensitivity in functional MRI. However, several technical challenges must be overcome to achieve these results. For example, the non-uniform RF (transmit B1) fields within large objects at ultra-field can cause big shading in MR images/spectroscopy, and is a major disadvantage.
Use of parallel transmit coil arrays with basic or tailored RF shimming technique has emerged as a promising solution to provide better transmit B1 homogeneity at ultra-high field. However, in practical implementations, RF shimming techniques only work well for gradient echo based sequence, and a small tip angle. For spin echo based sequences, the refocus pulse needs to maintain a large tip angle condition (> 100Â°) with the RF shimming set. A failure to meet this condition results in a significant drop in the signal, especially for fast spin-echo sequences.
Therefore, there exists a need to optimize the RF shimming set for spin-echo based sequences.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 depicts a workflow diagram of a method for RF shimming to improve the B1 transmission uniformity of spin-echo based MR imaging and spectroscopy.
The present disclosure employs a new RF shimming method for spin-echo based sequences. The key to implement a workable RF shimming method for spin-echo based sequences is to keep the RF amplitude of each transmit channel the same, and to minimize the following function with a cons...