Establishment of Clinical Post Yttrium-90 Radioembolization Liver PET/MR Imaging Workflow

2014 Objectives: Establishment of Clinical Post Yttrium-90 Radioembolization Liver PET/MR Imaging WorkflowMatthew King, CNMT, RT(N) – Yuxiang Zhou, Ph.D – Michael Roarke, MD – Ming Yang, MD Background: The current standard of care for imaging post Yttrium(Y)-90 transarterial radioembolization patients is with Y-90 Bremsstrahlung SPECT/CT to confirm Y-90 particle deposition. This modality, however, suffers from low spatial resolution, long image acquisition times with patients still under sedation, and the inability to quantify dosimetry. It has been found that Y-90 emits a small amount of positrons that can be imaged directly with PET. Compared with SPECT/CT and PET/CT, PET/MRI has improved spatial resolution, excellent soft tissue delineation, and more accurate quantification of dosimetry to target tumor. In this study, we aim to establish a practical post Y-90 treatment hybrid liver PET/MR imaging workflow to confirm Y-90 particle deposition. Methods: Five patients (three male, two female; age range 54-68 years) with confirmed liver malignancies were enrolled in this institutional review board approved study. All patients were scheduled for Y-90 TheraSphere radioembolizaton therapy and passed MR safety screening. Each patient underwent pre-procedure Tc-99m MAA mapping and immediate post-radioembolization Y-90 Bremsstrahlung SPECT/CT imaging as a standard of care. In addition, 3-5 hour delayed PET/MR imaging was performed using a GE SIGNA 3T Hybrid PET/MR system after full recovery from sedation (Figure 1). A single bed position, 20-minute PET scan was performed using 3D time-of-flight acquisition, and was accompanied by a Dixon LAVA MRAC scan for attenuation correction. The images were re-constructed with 3 iterations and 21 subsets in a 172x172 matrix with a post-processing Gaussian filter of 5mm FWHM. During the PET acquisition, multi-planar, multi-sequence, non-contrast enhanced liver MRI scans were simultaneously performed utilizing a low attenuation phase-array coil. Both the SPECT/CT and PET/MR imaging data were sent to the MIM Vista workstation (MIM Software, Inc.) for image evaluation and comparison. Results: All five patients completed the 20-minute simultaneous hybrid liver PET/MR scans without complications. Both SPECT/CT and PET/MR scans demonstrated Y-90 particle deposition at the target tumor; however, compared to the standard-of-care SPECT/CT images, the hybrid liver PET/MR images demonstrated superior spatial resolution, excellent delineation of active lesion(s), and improved co-registration (Figures 2 & 3). Interventional radiology recovery room nursing staff reported favorability of the delayed imaging as it is difficult to monitor recovering patients during a timely SPECT/CT acquisition, and nuclear medicine technologist staff reported favorability of the delayed procedure in order to avoid unnecessary delays in caring for a monitored post-procedure patient. Conclusions: Hybrid liver PET/MRI post Y-90 radioembolization offers an improved practical workflow for nuclear medicine technologist staff, IR nursing staff, and the patient over traditional SPECT/CT. In addition, PET/MRI provides improved image quality and may provide post-therapy Y-90 dosimetry information for serial evaluations of repeated therapy.