Preoperative simultaneous dynamic FDOPA-PET/MRI for differentiating the two histopathological forms of congenital hyperinsulinism: Initial experience

1581 Introduction: Congenital hyperinsulinism (CHI) is the most common cause of persistent hypoglycemia in neonates and infants, and is associated with a significant risk of permanent brain damage. The treatment and therapeutic outcome is heavily depend on distinguishing between the two distinct histopathological subtypes of CHI, diffuse and focal. Preoperative differentiating the two types can be challenging, focal CHI does not distort the surrounding pancreatic structure, thus CT and MRI, are not helpful in identifying focal lesions. In the last several years, FDOPA-PET has been found to be more accurate in differentiating diffuse from focal CHI compared to others imaging techniques, but limited in providing exact anatomical localization within the pancreas. Objectives: This study evaluated the feasibility and accuracy of simultaneous FDOPA-PET/MRI for distinguishing focal from diffuse disease in patients with CHI that underwent pancreatic surgery. Methods: FDOPA-PET/MRI was performed in pediatric patients with CHI who do not respond to pharmacological therapy and were being considered for surgery. All patients underwent PET/MRI imaging on a 3.0 Tesla Siemens Biograph mMR PET/MRI scanner. A dose of 3.0-4.5 MBq/kg (0.08-0.12 mCi/kg) of FDOPA was injected intravenously over approximately 1 minute, and scanning was initiated within 15 minutes of injection. The PET and MRI scans were acquired simultaneously with an average duration of 60 minutes. The acquisition was performed on multiple-station mode for abdomen imaging and consisted of standard of care MR sequences with simultaneous PET acquisition for 2-5 min per bed position. The MR sequences include Dixon, T2 HASTE, STIR, and T1-weighted Siemens Star VIBE. The 2-point Dixon sequence was acquired for attenuation correction. The PET images were evaluated qualitatively and quantitatively, and co-registered with the MR images. The study was considered positive for focal adenomatosis when the uptake of the radiotracer in a part of the pancreas, head, body or tail, was visually higher than the uptake in the remaining pancreatic tissue. A uniform uptake throughout the pancreas was considered diffuse. Quantitative Identification of focal CHI lesions used the standardized uptake value (SUV) ratio to identify focal lesions. The approach by Christiansen et al. (2017) was used, with the maximum SUV (SUVmax) ratio cut-off of 1.44 in the pancreas. Time-activity curve were generated and the highest SUVmax ratio used to diagnose focal CHI. Results: Two patients have been enrolled in this study. The first case was a male newborn that presented with hypoglycemia with transient respiratory distress. The initial workup confirmed a diagnosis of hyperinsulinism. FDOPA-PET/MRI scan was performed which showed diffuse pancreatic uptake, suggesting the diffuse form of CHI (Figure 1). The second case was a 6-month-old baby girl with recurrent hypoglycemic seizures. The differential diagnosis included hyperinsulinism, insulinoma, turner syndrome and exogenous insulin administration. The patient underwent FDOPA-PET/MRI scan, with imaging findings concerning for focal CHI (Figure 2). Conclusions: Our results suggest that FDOPA-PET/MRI is feasible and accurately differentiates focal from diffuse CHI. The superior soft-tissue contrast of PET/MRI permits precise preoperative localization of the lesion and anatomical landmarks such as the bile duct, spleen, blood vessels, and duodenum. In addition, PET/MRI offers substantial dose reduction compared to PET/CT.