Evaluation of Segmental Pancreatic Function Using 11C-Methionine Positron Emission Tomography for Safe Operation of Living Donor Pancreas Transplantation

**-Postprandial pancreatic [11C]methionine uptake after pancreaticoduodenectomy mirrors basal beta cell function and insulin release

Purpose

[S-methyl-¹¹C]-L-methionine ([¹¹C]MET) uptake in the pancreas might be a central indicator of beta cell function. Since gastric emptying was recently shown to influence glycemic control in subjects after pancreaticoduodenectomy (PD, the surgical treatment of neoplasms of the pancreas head), we looked for imaginable relationships between gastric emptying, pre- and postprandial insulin concentrations, and [¹¹C]MET uptake.

Methods

Nineteen tumor-free survivors after PD (age mean ± SD: 61 ± 8.7 yrs.; 10 male, 9 female) and 10 healthy controls (age: 27 ± 8.7 yrs.; 7 male, 3 female) were given a mixed test meal. One gram of paracetamol was ingested with the meal to evaluate the speed of gastric emptying. Insulin, glucose, and paracetamol plasma concentrations were measured before and over 180 minutes after ingestion. Beta cell function was calculated from fasting glucose and insulin plasma concentrations. Simultaneously, 800 MBq of [¹¹C]MET were administered and the activity (maximum tissue standardized uptake values [SUVmax]) over the pancreas was measured at 15, 30, and 60 minutes after injection. Total integrated SUVmax (area under the curve [AUC]) and incremental SUVmax were calculated.

Results

The uptake of [¹¹C]MET in the pancreas was significantly higher (p < 0.0001) in controls compared to the PD group. Gastric emptying was significantly slower in controls compared to pancreatectomy subjects (p < 0.0001). Paracetamol AUC₃₀ correlated with the SUVmax increment between 15 and 30 minutes (R² = 0.27, p = 0.0263), suggesting a relationship between gastric emptying and the uptake of [¹¹C]MET. Total integrated SUVmax correlated with insulin AUC₆₀ (R² = 0.66,p < 0.0001) in patients after PD. Multivariate regression analysis revealed insulin AUC₆₀ and beta cell function, calculated from the fasting insulin to glucose ratio, as independent predictors of ¹¹C-methionine uptake, i.e. total integrated SUVmax, in patients after PD (R² = 0.78, p < 0.0001).

Conclusion

Postprandial [¹¹C]MET uptake may represent basal and postprandial beta cell function. The findings suggest a possible usefulness of this imaging procedure for further studying beta cell function.

Evaluation of insulin independence using 11C-methionine positron emission tomography after living-donor and brain-dead donor pancreas transplantation

We recently reported that (11)C-methionine positron-emission tomography (PET) is clinically useful for the evaluation of the pancreatic function of the living donor. The objective of this study was to evaluate the postoperative insulin independence in 10 living donor (LD) and 10 brain-dead donor (BD) pancreas transplantations for 20 patients with type I diabetes mellitus by using (11)C-methionine PET. After 6 months, PET/computed tomography was performed 30 minutes after (11)C-methionine (370-740 MBq) injection. The uptake in the pancreas was expressed as the standardized uptake value (SUV). Patient survival rates were 100% at 5 years for LD transplantations and at 2 years for BD transplantations. Insulin independence was 60% for LD transplantations at 5 years and 75% for BD transplantations at 2 years. There were no major surgical complications such as vascular thrombosis, intra-abdominal abscess, and graft pancreatitis. The SUVs for LD and BD pancreas transplantations with insulin independence were 7.2 ± 1.8 and 10.4 ± 2.3, respectively. The SUVs for LD pancreas transplantations with insulin dependence and BD pancreas transplantations with graft failure were 3.6 ± 1.1 and 2.9 ± 1.0, respectively. At 5 years after transplantation, for the LD transplants, the insulin-independent rate was 100% for the graft recipients with an SUV higher than 5, and the median insulin independence duration of the graft recipients with an SUV less than 5 was 7 months (P < .01). The (11)C-methionine PET may be a potent modality to predict long-term insulin independence and the avoidance of pancreas graft failure.

Optimization of [11C]methionine PET study: appropriate scan timing and effect of plasma amino acid concentrations on the SUV

Background

[¹¹C]methionine (MET) has been used to monitor amino acid metabolism in tumors, the pancreas, liver, and myocardium. The aim of the present study was to standardize [¹¹C]MET positron emission tomography (PET) by optimizing the timing of initiation of the scan and applying correction to the plasma concentrations of neutral amino acids (NAAs), where necessary.

Methods

Sequential whole-body MET PET/computed tomography (CT) was performed in 11 normal adults after they had fasted for at least 4 h. After whole-body CT for attenuation correction and intravenous bolus injection of MET, the subjects were scanned from the parietal to the groin. The scanning was repeated six to seven times. Decay of radioactivity during the PET scan was corrected to the time of initiation of the first scan. The standardized uptake values (SUVs) were evaluated in various organs by setting regions of interest on the tomographic images. Plasma concentrations of NAAs were examined in relation to the SUV values.

Results

The SUVs in the pancreas reached their plateau from 6.5 to 11 min after the MET injection, and in the brain, lung, and myocardium, they reached their plateau from 19.6 to 24.1 min. The MET uptake in the spleen and kidney peaked early after the injection and steadily decreased thereafter. The SUVs in the liver and stomach wall rapidly increased during the first 0 to 4.5 min and gradually elevated thereafter during the scan period. Urinary radioactivity in the bladder reached its plateau from 26.1 to 30.6 min after the MET injection. There were no correlations between the plasma concentrations of NAAs and the maximal SUV in any organs.

Conclusions

The present study revealed the times taken to reach the plateau of MET uptake in various important organs, and little effects of the plasma neutral amino acid concentrations on the SUVs in PET studies conducted after the patients had fasted for at least 4 h. In the MET PET study, 4 h fasting period before MET administration and the scan initiation 20 min after MET administration provide the SUV values independent of scan initiation time and the plasma neutral amino acid concentrations.

Histological loss of pancreatic exocrine cells correlates with pancreatic exocrine function after pancreatic surgery

OBJECTIVE

The aim of this study was to investigate the relationship between histological findings of the pancreatic stump and postoperative pancreatic exocrine function.

METHODS

One hundred ten patients including 80 patients undergoing pancreatoduodenectomy (PD) and 30 patients undergoing distal pancreatectomy (DP) were enrolled into this study. Postoperative exocrine pancreatic function was evaluated by 13C-labeled mixed triglyceride breath test. The areas of acinar cells, fibrotic tissues, and fatty replacement were histologically calculated in surgical specimens of the pancreatic stump.

RESULTS

Histologically, acinar cell area of patients undergoing PD was significantly less than that of patients undergoing DP (P = 0.025). The values of the mean percentage dose 13C cumulative 7 hours of patients undergoing PD were significantly lower than those of patients undergoing DP (P < 0.001). The rate of pancreatic exocrine insufficiency in patients undergoing PD is significantly higher than that in patients with DP (P = 0.002). There was a significant correlation between acinar cell area of the pancreatic stump and the percentage dose 13C cumulative 7 hours (R = 0.35, P < 0.001).

CONCLUSIONS

Pancreatoduodenectomy induced pancreatic exocrine insufficiency more frequently than DP. Histological loss of acinar cells in the pancreatic stump was strongly correlated with postoperative pancreatic exocrine function.