A Simple 4D MRI Technique for Radiation Therapy Planning
S Yee*, D Ionascu, D Yan, William Beaumont Hospital, Royal Oak, MISU-E-J-176 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: 4D CT is routinely performed for radiation therapy planning when patient motion is a significant factor. As more benefits of using MRI become clearer in treatment planning, the feasibility of 4D MRI, however, has been questionable. The challenge of 4D MRI is the balance between satisfactory image quality and the speed to capture patient breathing cycle. So far, neither the image quality nor the speed has been satisfactory. Here, a simple MRI technique to do 4D MRI is introduced.
Methods: 3T MRI (Philips Ingenia) was used for scanning. For monitoring breathing cycles, a regular respiratory belt was used. The breathing cycle was then divided into multiple phases. For each breathing phase, a predefined respiratory trigger time was set and the multi-slice (30 slices) MRI scan was performed for each breathing phase. A single-shot fast spin echo with partial k-space filling was used with varied trigger time from 0 up to the length of breathing cycle.
Results: As seen in Fig 1 (1 of 30 slices), the image quality for each breathing phase is quite good. The line profiles from the line ROI in Fig 1, which was placed over the liver dome, are shown in Fig 2 for a few different breathing phases. The position of the line was fixed across the breathing phases to see the displacement caused by breathing. This demonstrates the liver dome displacement (along the x axis) during breathing cycles.
Conclusion: The 4D MRI for treatment planning can be done with satisfactory imaging quality and speed with a regular respiratory triggering technique, which can be directly implemented on most MRI devices without the need of extra device. However, since only a brief time-window during each breathing cycle is used for acquisition, total acquisition time may be longer (~30 min), and the improvement is undergoing.
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