Role of N-13 ammonia PET/CT in diagnosing pancreatic necrosis in patients with acute pancreatitis as compared to contrast enhanced CT – Results of a pilot study

Abstract

BackgroundContrast enhanced computerized tomography (CECT) is used to determine severity of acute pancreatitis based upon the presence and extent of necrosis. However limitations do exist precluding its applicability in renal failure. Positron emission tomography (PET) imaging for cardiac perfusion shows good uptake of N-13 ammonia (13NH3) metabolites in pancreas owing to high perfusion. AimTo evaluate the role of 13NH3 PET/CT in acute pancreatitis and compare it with CECT in diagnosing and quantifying pancreatic necrosis. Material and methodsPatients presenting within 1 week of acute pancreatitis were studied. Static PET images were acquired after intravenous injection of 370–740 MBq of 13NH3. 13NH3 PET/CT was followed by CECT in the absence of renal impairment. Maximum standard-uptake-value (SUVmax) of pancreas (P) and liver (L) were taken and their ratio (P/L) was estimated to determine perfusion. Areas within pancreas with no tracer uptake were considered necrotic. These patients were managed as per institutional protocol. Patients undergoing 13NH3 PET/CT for coronary artery disease were used as controls. Results29 patients (72% males) were studied of whom 6 had elevated serum creatinine. 13NH3 PET/CT was done in all patients along with 9 controls while CECT was carried out after PET/CT in 23 patients. Median levels of SUVmax (P/L) in the controls, uninvolved pancreas and necrotic areas were 1.0 (0.86–1.03), 0.66 (0.50–0.92) and 0.12 (0.07–0.21) respectively (p < 0.001). Necrosis estimation was similar in 22/23 patients without renal failure while in one patient only 13NH3 PET/CT picked up necrosis (<30%). 5/6 patients with renal failure had necrosis on 13NH3 PET/CT which was confirmed on surgery or subsequent CECT after improvement of renal failure. ConclusionThis pilot study is the first in literature to diagnose necrosis in patients with acute pancreatitis using 13NH3 PET/CT. With minimal additional radiation burden, it is possible to estimate the absolute tissue perfusion as well. With no adverse renal side effects, this can be an alternative to CECT in patients with renal failure giving similar information. It has good agreement with CECT with a good interobserver acceptability.