Optimizing scan timing of hepatic arterial phase by physiologic pharmacokinetic analysis in bolus-tracking technique by multi-detector row computed tomography

Abstract

Our aim in this study was to determine an optimal delay time of hepatic arterial phase (HAP) imaging of hypervascular hepatocellular carcinomas (HCCs) in dynamic contrast-enhanced MDCT (DCE-CT) by use of the bolus-tracking method. The time-enhancement curves (TECs) of the aorta and the contrast of the hepatic arterial and portal system (APC) in the pharmacokinetic analysis were calculated. The clinical study included 41 patients with known or suspected HCC who underwent DCE-CT. The TECs of the aorta and the tumor-liver contrast (TLC) in the clinical study were calculated. On pharmacokinetic analysis, the peak aortic enhancement and the peak APC simulated under conditions of an injection duration of 30 s and an iodine load of 500 mg I/kg body weight were observed 18.5 and 22.5 s, respectively, after the trigger threshold (increased CT value 100 Hounsfield units), respectively. In the clinical study, the peak aortic enhancement and the peak TLC were observed 17.2 and 24.8 s after the trigger threshold, respectively. The optimal delay times until peak aortic enhancement and peak HAP were 15-17 and 19-21 s after the trigger threshold, respectively, under the following conditions: injection dose, 500 mg I/kg body weight; injection duration, 30 s; acquisition time, 5 s; and the trigger threshold. In addition, the peak TLC was achieved 4-7 s after the time to peak aortic enhancement.

Challenges to Protocol Optimization Due to Unexpected Variation of CT Contrast Dose Amount and Flow

“…The total amount of contrast to a patient can affect the degree of organ enhancement [2,3,7,13], while changes in the flow rate can affect the magnitude and timing of peak vascular enhancement [2,3]. The results of this study revealed 12.2 % of administrations from a large data base deviated from the prescribed amounts by more than 10 % and that 97 % of these deviations involved delivering too much contrast rather than too little based on the protocol.…”

“…Contrast flow rate has been seen to have a large effect on study quality as it changes the timing of contrast enhancement [2,3]. Limiting this variable as much as possible would allow for more consistent phases of enhancement, especially during multiphase exams [7].…”

“…In computed tomography (CT), there are many factors contributing to the overall quality of the exam: patient anatomy and physiology, acquisition settings, and contrast administration [1][2][3][4][5][6][7]. Patient-related factors such as cardiac output, intravascular volume, patient weight, patient height, renal function, and concurrent comorbidities are known to affect contrast enhancement timing, with the most important factors being patient weight, cardiac output, and intravascular volume affecting arterial enhancement [3,8,9].…”

“…Patient-related factors such as cardiac output, intravascular volume, patient weight, patient height, renal function, and concurrent comorbidities are known to affect contrast enhancement timing, with the most important factors being patient weight, cardiac output, and intravascular volume affecting arterial enhancement [3,8,9]. Acquisition parameters including mA, kVp, noise index, bolus tracking technique, and reconstruction algorithms have a significant effect on study quality and have been studied extensively [2,3,7,8,10]. Radiation reduction techniques, including lowdose protocols and new reconstruction algorithms, have garnered the most recent attention due to the inherent and sometimes unknown exposure risks [10,11].…”

“…Most evaluation to date regarding contrast administration has been centered on contrast timing using manual delays, a test bolus, or bolus tracking technology [8,9,12,13]. Although static contrast volume and flow rates based on patient weight have traditionally been used, recently there has been more interest in looking at individualized patient protocols to take into account patient physiology which achieves more consistent organ enhancement, decrease overall iodine dose, and reduce costs [5,7,9].…”