Synopsis

Keywords: Liver, Liver

A modified version of LI-RADS was devised for abbreviated MRI (AMRI) with second shot arterial phase (SSAP) by referring to CEUS LI-RADS. The modified LI-RADS scores using AMRI with SSAP showed a high concordance rate with the conventional LI-RADS score using full-protocol MRI. The recall rate significantly decreased when the HCC surveillance and diagnosis strategy was changed from strategy 1 (AMRI without SSAP; surveillance then recall test) to strategy 2 (AMRI with SSAP; simultaneous surveillance and diagnosis).

INTRODUCTION

Although dynamic contrast-enhanced CT and MRI are widely used imaging modalities for the HCC diagnosis, the applicability of CT and MRI as surveillance tools for patients with cirrhosis is controversial from a health economic perspective¹. There have been several studies that use various abbreviated MRI (AMRI) strategies in the HCC surveillance in patients with cirrhosis^1-9.
In our institution, a modified injection protocol was developed to overcome arterial phase (AP) degradation, which consisted of routine dynamic imaging after a first injection of 6 ml and second shot AP (SSAP) imaging after a second injection of 4 ml. This modified injection protocol demonstrated that motion artifacts were reduced while maintaining vascularity in the SSAP images of patients with HCC and hepatic metastasis^10-11.
If SSAP is combined with AMRI strategy, it may be more cost-effective as diagnosis can be made simultaneously with surveillance, which eliminates the need for additional recall tests. The aim of this study was to evaluate the feasibility of simulated AMRI with SSAP for HCC surveillance and diagnosis.

METHODS

Patients
This retrospective study was approved by our Institutional Review Board, and the requirement for informed consent was waived. A total 129 consecutive patients (92 men and 37 women; mean age, 58.8 ± 11.4 years; age range, 37–82 years) underwent gadoxetic acid-enhanced MRI using a modified injection protocol for HCC evaluation from July 2017 to February 2018. The modified injection protocol consists of routine dynamic imaging (6-ml) and SSAP imaging (4-ml).

Image analysis
Two radiologists independently reviewed full-protocol MRI and two AMRI sets: AMRI without SSAP (surveillance set) and AMRI with SSAP (diagnosis set). To reduce recall bias, image interpretation was performed during three separate sessions with a 4-week interval and the images were randomly given to both reviewers.
1) First session: Full-protocol MRI
In the full-protocol MRI, both reviewers assigned observations according to conventional Liver Imaging Reporting and Data System (LI-RADS).
2) Second session: Surveillance set (AMRI without SSAP)
The surveillance set consists of T2-weighted image (T2WI), diffusion-weighted imaging (DWI), and HBP image (Figure 1). In the surveillance set, patients and lesions were assigned to four categories (negative, subthreshold, positive, and inadequate).
3) Third session: Diagnosis set (AMRI with SSAP)
The diagnosis set consists of T2WI, DWI, HBP image, and SSAP image (Figure 1). In the diagnosis set, both reviewers additionally evaluated arterial phase hyperenhancement (APHE) using SSAP and its subtraction images. Because AMRI did not include portal venous and delayed (or transitional) phase images, washout and enhancing capsule could not be evaluated. Therefore, we devised a modified version of CT/MRI LI-RADS for the diagnostic algorithm using AMRI with SSAP by referring to CEUS LI-RADS (Figure 2). In the modified version of LI-RADS, observations were assigned from abbLR-3 to abbLR-5 according to observation size, APHE, and HBP hypointensity (Figure 2). Since the portal venous phase (PVP) was not included in AMRI with SSAP, HBP hypointensity was adopted as a major feature instead of washout appearance.

Recall strategy
In the strategy 1 (AMRI without SSAP), patients classified as negative are returned to surveillance, those classified as subthreshold are subject to short-term follow-up, and those classified as positive and inadequate are subject to recall tests (Figure 3a).
In the strategy 2 (AMRI with SSAP), patients classified as abbLR-3 are subject to short-term follow-up, those classified as abbLR-4 are subject to recall tests, those classified as abbLR-5 are confirmed with HCC, and those classified as abbLR-M are referred for multidisciplinary decision (Figure 3b).

RESULTS

Sixty-seven patients with HCC and 62 patients without HCC were included. In the surveillance set, sensitivity and specificity for the detection of patients with HCC were 95.5% and 96.8%, and 94.0% and 96.8% in reviewer 1 and 2, respectively. In the diagnosis set, the scores of most HCCs (76/78, 97.4%) were consistent between LI-RADS of full-protocol and modified LI-RADS of AMRI with SSAP protocol. When the HCC surveillance and diagnosis strategy was changed from strategy 1 (AMRI without SSAP) to strategy 2 (AMRI with SSAP), the recall rate significantly decreased from 52.7% to 3.9% (p <0.001) (Figure 4a and 4b).

DISCUSSION

In this study, we devised a modified version of LI-RADS using AMRI with SSAP. A previous study by Brunsing et al. introduced a structured reporting system for AMRI that classifies each examination into four categories (negative, subthreshold, positive, and inadequate) similar to US LI-RADS⁹. In our study, we devised a modified version of LI-RADS for AMRI with SSAP in which observations are categorized from abbLR-1 (definitely benign) to abbLR-5 (definitely HCC) using size, APHE, and HBP hypointensity, which is similar to CEUS LI-RADS.

CONCLUSION

The modified LI-RADS score using the AMRI with SSAP demonstrated a high concordance rate with the LI-RADS score of the full-protocol MRI. The recall rate decreased when the HCC surveillance and diagnosis strategy was changed from a strategy of recall test after surveillance using AMRI without SSAP to a strategy of simultaneous surveillance and diagnosis with AMRI with SSAP. These results will enable AMRI with SSAP to diagnose HCC simultaneously with surveillance, which is expected to improve energy efficiency as well as cost-effectiveness.

Acknowledgements

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