Spiral flow-generating tube for saline chaser improves aortic enhancement in Gd-EOB-DTPA-enhanced hepatic MRI

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

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%.

Efficacy of the spiral flow generating extended tube during paediatric CCTA

INTRODUCTION

To compare the computed tomography (CT) number for paediatric cardiac computed tomography angiography (CCTA) and visualisation score of the three-dimensional (3D) images using the conventional T-shaped extended tube (T-tube) and spiral flow-generating extended tube (spiral-tube) connected between the contrast injector and cannula.

METHODS

In total, 108 patients suspected to have congenital heart disease (CHD) were considered for inclusion. We utilised the T-tube for intravenous contrast and spiral-tube in 54 patients each. Observers individually inspected randomized volume rendering images of the internal thoracic artery, each acquired from the with or without spiral-tube groups, using a four-point scale. We compared the mean CT number of the ascending aorta (AAO) and pulmonary artery (PA), contrast noise ratio (CNR), CT number for the AAO and PA enhancement ratio, and the visualisation scores between the groups.

RESULTS

There were no significant differences in patient characteristics between the with or without spiral-tube groups (p > 0.05). The mean CT number ±standard deviation for the AAO and PA, and the CNR without or with spiral-tube groups were 441.2 ± 89.2 and 489.8 ± 86.1 HU for the AAO, 436.3 ± 100.6 and 475.3 ± 85.2 HU for the PA, and 9.5 ± 2.2 and 10.8 ± 2.4 for the CNR, respectively (p < 0.05). In the spiral-tube group, the CT number, CNR, and visualisations score of the 3D images were significantly higher for the AAO and PA than those in the T-tube group (p < 0.05).

CONCLUSION

The spiral-tube proved to be beneficial in improving the CT number for the AAO and PA, CNR, and visualisation score compared with the conventional T-tube during paediatric CCTA.

IMPLICATIONS FOR PRACTICE

The spiral-tube may allow the visualisation of smaller blood vessels than those visualised by the conventional T-tube for paediatric patients in CCTA.

Effect of Gadoxetic Acid Injection Duration on Tumor Enhancement in Arterial Phase Liver MRI

RATIONALE AND OBJECTIVES

Rapid injection of gadoxetic acid has been shown not to increase tumor enhancement in arterial phase liver MRI for unknown reasons. This study aimed to investigate the effect of injection durations on peak contrast concentration in tumors and to correlate it with signal enhancement in gadoxetic acid-enhanced arterial phase MRI.

MATERIALS AND METHODS

Gadoxetic acid-enhanced arterial phase MRI was obtained using a bolus-tracking technique with injection durations of 1, 3, and 6s in six rabbits with VX2 liver tumors. The peak concentration of gadoxetic acid in the aorta and tumor was estimated by iopromide-enhanced time-resolved CT using the same injection volume and durations with those for MRI. Signal enhancement on MRI and peak enhancement on CT were compared and correlated.

RESULTS

There was no significant difference in MR signal enhancement of tumors among the 3 injection durations (p = 0.87). In CT, shorter injection durations significantly increased peak contrast concentration in the aorta (p < 0.01) but produced equivalent peak contrast concentration in tumors (p = 0.24). The longer injections resulted in the stronger correlation between peak contrast concentration in CT and MR signal enhancement in tumors (r = 0.31, 0.43, and 0.86 with 1s-, 3s-, and 6s-injection, respectively) with a statistical significance only found with 6s-injection (p = 0.03).

CONCLUSION

Estimation of contrast concentration by CT demonstrated that shorter injections did not increase peak contrast concentration in tumors despite increased peak concentration in the aorta. Furthermore, tumor signal enhancement in gadoxetic acid-enhanced arterial phase MRI was less correlated with the peak contrast concentration with shorter injections.