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MR in RT: MR Pulse Sequences and Image Acquisition (Including Radiation Therapy Applications)

N Yanasak

K Sheng
no image available
H Gach

N Yanasak1*, K Sheng2*, H Gach3*, (1) Georgia Regents University, Augusta, GA, (2) UCLA School of Medicine, Los Angeles, CA, (3) Washington University in St. Louis, St. Louis, MO


1:45 PM : Overview of MRI pulse sequences and image acquisition - N Yanasak, Presenting Author
2:25 PM : Dynamic MRI for radiation therapy - K Sheng, Presenting Author
3:05 PM : Optimizing and troubleshooting MRI for radiation therapy - H Gach, Presenting Author

MO-DE-702-0 (Monday, July 31, 2017) 1:45 PM - 3:45 PM Room: 702

The continuing evolution of MRI technology has produced a wealth of different methods for generating tissue contrast over the 40-year timeline of the modality. Indeed, a physicist from the early 1980's traveling into the future would hardly recognize the plethora of pulse sequences at his or her disposal. That being said, some of the sequences that serve as clinical “workhorses” were in use at the time or in early stages of development. This session provides a taxonomy of the different pulse sequences available to the modern hospital, with a focus on sequences that provide utility to radiation therapy.

Dynamic MRI is an attractive modality for imaging internal anatomy motion that is of paramount importance in radiation therapy. Compared to CT or X-ray imaging, dynamic MRI is more flexible in imaging plane orientation, more sensitive to soft tissue contrast and completely free of ionizing radiation dose. Multiple fast dynamic MR sequences have been developed and each has its own strengths and weaknesses. They also provide distinctly different imaging characteristics that are suitable for different radiation therapy purposes. A common limitation of dynamic MRI is the unavoidable compromise between image quality, speed, dimensionality, and resolution. Active research including 4D-MRI is ongoing to mitigate the compromise and optimize the performance of dynamic MRI. This session will introduce several common dynamic MRI sequences in the context of radiation therapy. A description of recent research directions to improve and utilize dynamic MRI for radiation therapy will also be provided.

In radiation therapy, MRI-based treatment planning and MRI-guided radiotherapy (MRIgRT) are becoming common practices. MRI permits the acquisition of functional information (e.g., flow, perfusion, diffusion, motion characterization) in addition to a variety of tissue contrast types. However, MRI has some disadvantages and limitations including geometric distortion, a variety of image artifacts, long acquisition times, and low signal-to-noise ratios.

This session will provide examples of these limitations with some strategies for overcoming them. In addition, we will present some quick diagnostic methods for troubleshooting common MRI performance issues that may not be detected using standard QA procedures.

Learning Objectives:
1. Identify appropriate MRI pulse sequences for common clinical tasks.
2. Implement MRI techniques and protocol changes to optimize for desired contrast, noise, temporal resolution, and SAR objectives.
3. Describe MRI techniques and pulse sequences used in MRI for radiation therapy planning and treatment assessment.


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