Region-specific motion destmation in rodent using PET and MRI image

The acute organ motion estimation in multimodal imaging improves quality of diagnosis and therapy of tumor. It is particularly important in the organ related involuntary movement such as lung and liver. The aim of this study was to compare the region specific motion in rodent using radioactive molecular sieve PET image and MRI image. The molecular sieve was contained 0.37 MBq F-18 and coated with hydrogel. For comparison of internal and external motion, molecular sieve was placed inside lung and liver and attached on the surface of each organ region in SD-rat. PET study was performed using a small animal PET scanner (Inveon) after IV injection of FDG 37 MBq/0.2 mL. List-mode data was synchronized with respiratory gating trigger signal from external monitoring system (Biovet). MRI study was performed using 3-T clinical MRI system (Magnetom Tim Trio) with human wrist coil. Coronal MRI images were acquired using T2-weighted turbo spin echo (TSE) sequence with respiratory triggering. The parameter is as follow settings: TR = 1000 ms, TE = 36 ms, FA = 20. We analyzed moving pattern and variation of movement in lung and liver region following respiratory cycle in both of PET and MRI images. Moving patterns in PET image were different in accordance with where molecular sieve was placed. The variation of lung and liver internal motion was 0.93 and 0.52 in PET image, respectively. Estimated organ motion in MRI image revealed moving pattern based on respiratory cycle. The maximum variation of lung and liver region was 1.75 and 1.36 in MRI image, respectively. We recognized organ motion was different depending on the region and the monitoring signal was overestimated compared to real motion in both of region in PET. This study demonstrated that region-specific motion estimation would realize through aid of MRI images without external device.