Sixty-Four-Multidetector-Row Computed Tomography Angiography With Bolus Tracking to Time Arterial-Phase Imaging in Healthy Liver: Is There a Correlation Between Quantitative and Qualitative Scores?

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 Time_TRIG. 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.

Multi-detector CT: Liver protocol and recent developments

Multi-detector computed tomography is today the workhorse in the evaluation of the vast majority of patients with known or suspected liver disease. Reasons for that include widespread availability, robustness and repeatability of the technique, time-efficient image acquisitions of large body volumes, high temporal and spatial resolution as well as multiple post-processing capabilities. However, as the technique employs ionizing radiation and intravenous iodine-based contrast media, the associated potential risks have to be taken into account. In this review article, liver protocols in clinical practice are discussed with emphasis on optimisation strategies. Furthermore, recent developments such as perfusion CT and dual-energy CT and their applications are presented.

Automatic bolus tracking versus fixed time-delay technique in biphasic multidetector computed tomography of the abdomen

Background

Bolus tracking can individualize time delay for the start of scans in spiral computed tomography (CT).

Objectives

We compared automatic bolus tracking method with fixed time-delay technique in biphasic contrast enhancement during multidetector CT of abdomen.

Patients and Methods

Adult patients referred for spiral CT of the abdomen were randomized into two groups; in group 1, the arterial and portal phases of spiral scans were started 25 s and 55 s after the start of contrast material administration; in group 2, using the automatic bolus tracking software, repetitive monitoring scans were performed within the lumen of the descending aorta as the region of interest with the threshold of starting the diagnostic scans as 60 HU. The contrast enhancement of the aorta, liver, and spleen were compared between the groups.

Results

Forty-eight patients (23 males, 25 females, mean age=56.4±13.5 years) were included. The contrast enhancement of the aorta, liver, and spleen at the arterial phase was similar between the two groups (P>0.05). Regarding the portal phase, the aorta and spleen were more enhanced in the bolus-tracking group (P<0.001). The bolus tracking provided more homogeneous contrast enhancement among different patients than the fixed time-delay technique in the liver at portal phase, but not at the arterial phase.

Conclusions

The automatic bolus-tracking method, results in higher contrast enhancement of the aorta and spleen at the portal phase, but has no effect on liver enhancement. However, bolus tracking is associated with reduced variability for liver enhancement among different patients.

The optimal contrast media policy in CT of the liver. Part II: Clinical protocols

The advent of multidetector computed tomography (MDCT) revolutionized abdominal imaging. In particular, the definitive assessment of CT injection protocols, for the evaluation of the liver parenchyma, is still a critical issue for radiologists. Over the last years, this feature encouraged several authors to address their efforts to find the most accurate delay between the contrast medium injection and the effective scan-start, for the identification and characterization of liver lesions. Technological developments of the present century such as number of slices, submillimetric collimation, and the use of multiple dynamic post-contrast phases per single examination, may all contribute to increase the radiation exposure of single patients. The aim of this review is to propose liver imaging protocols, taking into consideration different clinical needs such as patients with chronic liver disease, healthy patients with focal liver lesion, and oncological patients to minimize radiation exposure. Finally, two recent innovations in MDCT which illustrate the potential application of multi-energy computed tomography (MECT) and perfusion computed tomography (CTp) when evaluating liver parenchyma will be discussed in a short closing paragraph.