Optimising the scan delay for arterial phase imaging of the liver using the bolus tracking technique

Triple-phase MDCT of liver: Scan protocol modification to obtain optimal vascular and lesional contrast

Context:

With advances in 16-slice multidetector computed tomography (MDCT), the entire liver can be scanned in 4–6 s and a single breath-hold dual-phase scan can be performed in 12–16 s. Consequently, optimizing the scan window has become critical.

Aim:

The purpose of our study was to optimize scan delays using bolus-tracking techniques for triple-phase CT of the liver.

Settings and Design:

Fifty patients with liver lesions were randomly divided into two groups with 25 patients each. The patients were subjected to triple-phase MDCT of liver with two different scan protocols.

Materials and Methods:

They were administered 1.5 mL/kg of 300 mg/mL of iohexol at a rate of 3.0 mL/s with a pressure injector. Using bolus-tracking program, scans were commenced at 4, 19, and 44 s and 8, 23, and 48 s for the first, second, and third phases, respectively. The mean CT values [Hounsfield unit (HU)] were measured in the aorta, hepatic artery, portal vein, hepatic vein, liver parenchyma, and lesion using circular region of interest cursor ranging in size from 5 to 20 mm in diameter on all phases.

Statistical Analysis Used:

Statistical analysis was carried out using paired Student's t-test.

Results:

In hepatic arterial phase, hepatic artery has shown better enhancement in Group B (8 s) (P = 0.0498) compared with Group A (4 s). In portal venous phase, there were no significant differences in contrast enhancement index (CEI) values at any of the six measured regions between the groups. In the hepatic venous phase, liver parenchyma has shown nearly significant (P = 0.0664) higher CEI values in Group B (48 s) when compared with Group A (44 s).

Conclusion:

A scan delay of 8 s, after trigger threshold (100 HU) is reached in the lower thoracic aorta, is optimal for the early arterial phase imaging, this phase being most helpful for assessment of hepatic arterial tree (CT angiography). The liver parenchyma showed maximum enhancement at 48 s scan delay.

Comparison of the Timing of Hepatic Arterial Phase and Image Quality Using Test-Bolus and Bolus-Tracking Techniques in Gadolinium-Ethoxybenzyl-Diethylenetriamine Pentaacetic Acid-Enhanced Hepatic Dynamic Magnetic Resonance Imaging

Objectives

The aim of this study was to compare the image quality, the degree of artifacts and the percentage of timing of the optimal hepatic arterial phase (HAP) between test-bolus and bolus-tracking methods on gadolinium–ethoxybenzyl–diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)–enhanced magnetic resonance imaging (MRI).

Methods

In this prospective study, 60 patients who underwent 3-dimensional dynamic Gd-EOB-DTPA–enhanced hepatic 3-T MRI were enrolled in this study. We randomly assigned the 30 patients to the bolus-tracking method, and another 30 patients to the test-bolus method. Signal-to-noise ratios of the liver and spleen in HAP were compared in the 2 groups. Two radiologists independently assessed the ratio of optimal timing of HAP and the degree of ringing and motion artifacts of the 2 protocols.

Results

The signal-to-noise ratios of the liver (24.0 [SD, 6.4] vs 20.4 [SD, 4.0]) and spleen (30.0 [SD, 13.3] vs 23.6 [SD, 9.9]) were significantly higher in the test-bolus protocol than in the bolus-tracking protocol. The ratio of optimal timing was also significantly higher with the test-bolus protocol than with the bolus-tracking protocol (76.7% vs 40.0%). The degree of ringing and motion artifacts of test-bolus protocol was significantly lower than that of the bolus-tracking protocol (P < 0.01).

Conclusions

The test-bolus protocol in dynamic 3-T MRI can yield better qualitative image quality and more optimal timing of HAP images, while reducing the degree of artifacts compared with the bolus-tracking protocol.

Is 3-Tesla Gd-EOB-DTPA-enhanced MRI with diffusion-weighted imaging superior to 64-slice contrast-enhanced CT for the diagnosis of hepatocellular carcinoma?

Objectives

To compare 64-slice contrast-enhanced computed tomography (CT) with 3-Tesla magnetic resonance imaging (MRI) using Gd-EOB-DTPA for the diagnosis of hepatocellular carcinoma (HCC) and evaluate the utility of diffusion-weighted imaging (DWI) in this setting.

Methods

3-phase-liver-CT was performed in fifty patients (42 male, 8 female) with suspected or proven HCC. The patients were subjected to a 3-Tesla-MRI-examination with Gd-EOB-DTPA and diffusion weighted imaging (DWI) at b-values of 0, 50 and 400 s/mm². The apparent diffusion coefficient (ADC)-value was determined for each lesion detected in DWI. The histopathological report after resection or biopsy of a lesion served as the gold standard, and a surrogate of follow-up or complementary imaging techniques in combination with clinical and paraclinical parameters was used in unresected lesions. Diagnostic accuracy, sensitivity, specificity, and positive and negative predictive values were evaluated for each technique.

Results

MRI detected slightly more lesions that were considered suspicious for HCC per patient compared to CT (2.7 versus 2.3, respectively). ADC-measurements in HCC showed notably heterogeneous values with a median of 1.2±0.5×10⁻³ mm²/s (range from 0.07±0.1 to 3.0±0.1×10⁻³ mm²/s). MRI showed similar diagnostic accuracy, sensitivity, and positive and negative predictive values compared to CT (AUC 0.837, sensitivity 92%, PPV 80% and NPV 90% for MRI vs. AUC 0.798, sensitivity 85%, PPV 79% and NPV 82% for CT; not significant). Specificity was 75% for both techniques.

Conclusions

Our study did not show a statistically significant difference in detection in detection of HCC between MRI and CT. Gd-EOB-DTPA-enhanced MRI tended to detect more lesions per patient compared to contrast-enhanced CT; therefore, we would recommend this modality as the first-choice imaging method for the detection of HCC and therapeutic decisions. However, contrast-enhanced CT was not inferior in our study, so that it can be a useful image modality for follow-up examinations.