4D‐CT has been widely used in radiotherapy for imaging moving tumors, especially in the thoracic regions. In other body sites such as the abdominal, 4D‐CT is limited due to its low soft‐tissue contrast. Additional concern for 4D‐CT includes increased radiation dose to the patient. On the other hand, MRI has no known radiation hazard and has excellent soft‐tissue contrast. It is desirable to develop 4D‐MRI techniques to address the problems associated with 4D‐CT. There are different methods of 4D‐MRI imaging. One is to use sophisticated MR pulse sequence and/or use advanced software and hardware. Another method is to retrospectively sort slice MR images acquired continuously throughout the volume based on respiratory phases. The first method typically results in a temporal resolution of ∼0.7 frame/s and a spatial resolution of 3–4 mm. The second method requires simultaneously acquired respiratory signals, either by using external surrogate or internal/image‐based surrogate. The temporal resolution is ∼ 3 frames/s, the in‐plane spatial resolution is ∼1.5–2 mm, and the slice thickness is ∼ 3–5 mm. Both methods are doable using commercially available MR sequences. 4D‐MRI can be used to improve the determination of patient specific tumor motion margin for radiation therapy, especially for the tumors in the abdominal regions where 4D‐CT has limitations. We presented this topic as a joint imaging/therapy scientific symposium in 2011 AAPM annual meeting. This proposal aims to provide a follow up education on this topic and present technical details on how to establish the 4D‐MRI program in the clinic. Learning Objectives: 1. Discuss the need of 4D‐MRI technique for improving patient care in radiation therapy 2. Understand technical aspects of different 4D‐MRI imaging techniques 3. Discuss the procedures to establish 4D‐MRI program in a radiation oncology clinic.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging