Influence of dilution on arterial-phase artifacts and signal intensity on gadoxetic acid-enhanced liver MRI

Abstract

Objectives: To investigate the effect of saline-diluted gadoxetic acid, done for arterial-phase (AP) artifact reduction, on signal intensity (SI), and hence focal lesion conspicuity on MR imaging.

Methods: We retrospectively examined 112 patients who each had at least two serial gadoxetic acid-enhanced liver MRIs performed at 1 ml/s, first with non-diluted (ND), then with 1:1 saline-diluted (D) contrast. Two blinded readers independently analyzed the artifacts and graded dynamic images using a 5-point scale. The absolute SI of liver parenchyma, focal liver lesions (if present), aorta, and portal vein at the level of the celiac trunk and the SI of the paraspinal muscle were measured in all phases. The signal-to-norm (SI_Norm) of the vascular structures, hepatic parenchyma and focal lesions, and the contrast-to-norm (C_Norm) of focal liver lesions were calculated.

Results: AP artifacts were significantly reduced with dilution. Mean absolute contrast-enhanced liver SI was significantly higher on the D exams compared to the ND exams. Likewise, SI_Norm of liver parenchyma was significantly higher in all contrast-enhanced phases except transitional phase on the D exams. SI_Norm values in the AP for the aorta and in the PVP for portal vein were significantly higher on the diluted exams. The C_Norm was not significantly different between ND and D exams for lesions in any imaging phase. The interclass correlation coefficient was excellent (0.89).

Conclusion: Gadoxetic acid dilution injected at 1ml/s produces images with significantly fewer AP artifacts but no significant loss in SI_Norm or C_Norm compared to standard non-diluted images.

Key points: • Diluted gadoxetic acid at slow injection (1 ml/s) yielded images with higher SI_Norm of the liver parenchyma and preserved C_Norm for focal liver lesions. • Gadoxetic acid-enhanced MRI injected at 1 ml/s is associated with arterial-phase (AP) artifacts in 31% of exams, which may degrade image quality and limits focal liver lesion detection. • Saline dilution of gadoxetic acid 1:1 combined with a slow injection rate of 1 ml/s significantly reduced AP artifacts from 31 to 9% and non-diagnostic AP artifacts from 16 to 1%.

Keywords: Artifacts; Gadolinium ethoxybenzyl DTPA; Liver; Magnetic resonance imaging; Signal intensity.

Fig. 1

Flowchart of the exclusion criteria yielding eligible patients. MRI = magnetic resonance imaging

Fig. 2

Three columns of axial liver MR images showing non-diluted and diluted injections in the same patient. The last column shows the regions of interest (ROI) as measured in the five specified locations: aorta (green), portal vein (blue), liver parenchyma (red), focal liver lesion (yellow), and paraspinal muscle (white) in all phases

Fig. 3

SI_Norm. Boxplot graphic of liver parenchyma signal intensity normalized to muscle SI (SI_Norm) in all phases. The blue boxes represent exams performed with non-diluted contrast media, the green boxes diluted contrast media. The SI_Norm was found to be significantly higher with the diluted injection protocol in the arterial, portal venous, and hepatobiliary phases

Fig. 4

a C_Norm FNH. Boxplot graphic of the absolute difference between SI_Norm of FNHs and SI_Norm of the liver, called contrast-to-norm (C_Norm) in all phases. The blue boxes represent exams performed with non-diluted contrast media, the green boxes diluted contrast media. There were no significant differences between the non-diluted and the diluted injection protocol in all phases. b C_Norm metastases. Boxplot graphics of the absolute difference between SI_Norm of metastases and SI_Norm of the liver, called contrast-to-norm (C_Norm) in all phases. The blue boxes represent exams performed with non-diluted contrast media, the green boxes diluted contrast media. There were no significant differences between the non-diluted and the diluted injection protocol in all phases