Optimized scan delay for late hepatic arterial or pancreatic parenchymal phase in dynamic contrast-enhanced computed tomography with bolus-tracking method

Objectives: To determine the optimal scan delay corresponding to individual hemodynamic status for pancreatic parenchymal phase in dynamic contrast-enhanced CT of the abdomen. Methods: One hundred and fourteen patients were included in this retrospective study (69 males and 45 females; mean age, 67.9 +/- 12.1 years; range, 39-87 years). These patients underwent abdominal dynamic contrast-enhanced CT between November 2019 and May 2020. We calculated and recorded the time from contrast material injection to the bolus-tracking trigger of 100 Hounsfield unit (HU) at the abdominal aorta (s) (Time(TRIG)) and scan delay from the bolus-tracking trigger to the initiation of pancreatic parenchymal phase scanning (s) (Time(SD)). The scan delay ratio (SDR) was defined by dividing the Time(SD) by TimeTRIG. Non-linear regression analysis was conducted to assess the association between CT number of the pancreas and SDR and to reveal the optimal SDR, which was >= 120 HU in pancreatic parenchyma. Results: The non-linear regression analysis showed a significant association between CT number of the pancreas and the SDR (p < 0.001). The mean Time(TRIG) and Time(SD) were 16.1 s and 16.8 s, respectively. The SDR to peak enhancement of the pancreas (123.5 HU) was 1.00. An SDR between 0.89 and 1.18 shows an appropriate enhancement of the pancreas (>= 120 HU). Conclusion: The CT number of the pancreas peaked at an SDR of 1.00, which means Time(SD) should be approximately the same as Time(TRIG) to obtain appropriate pancreatic parenchymal phase images in dynamic contrast-enhanced CT with bolus-tracking method. Advances in knowledge: The hemodynamic state is different in each patient; therefore, scan delay from the bolus-tracking trigger should also vary based on the time from contrast material injection to the bolus-tracking trigger. This is necessary to obtain appropriate late hepatic arterial or pancreatic parenchymal phase images in dynamic contrast-enhanced CT of the abdomen.