Synopsis

Keywords: Data Acquisition, Liver, Free breathing, Radial sampling

The gadoxetic acid-enhanced hepatobiliary phase imaging is an effective sequence for detecting hepatic lesions; however, degraded image quality is often observed due to poor breath holding. Free-breathing sequence using radial stack-of-stars acquisition (3D VANE) has been introduced and can provide diagnosable image quality. Recently, Compressed SENSE (CS), that is one of the acceleration techniques, has been applicable in 3D VANE. In this study, we evaluated the feasibility of 3D VANE with CS in hepatobiliary phase imaging. Our results showed that 3D VANE with CS at section thickness of 2 mm had almost comparable image quality as conventional breath-holding cartesian sampling.

Purpose

The gadoxetic acid-enhanced hepatobiliary phase imaging is an effective imaging tool for detecting hepatic lesions¹. However, degraded image quality is often observed due to poor breath holding, and thin slice data acquisition is difficult because of breath-holding acquisition sequence. The purpose of study was to evaluate the feasibility of newly adapted free-breathing sequence using radial stack-of-stars acquisition with spectral fat suppression (3D VANE)² with Compressed SENSE (CS)³ in gadoxetic acid-enhanced hepatobiliary phase imaging.

Materials and Methods:

This prospective study was approved by our Institutional Review Board, and written informed consent was obtained from all participants. Fourteen participants (10 men and 4 women, median age, 68 years; interquartile age range, 54–71 years) with suspected liver diseases underwent gadoxetic acid-enhanced MRI between June 2022 and September 2022 were included. Participants’ demographics are summarized in Table 1. All examinations were performed using a 3T MRI scanner (Ingenia 3.0T CX; Philips Healthcare) equipped with a 32-channel digital coil. The hepatobiliary phase imaging was scanned by conventional breath-holding sequence (BH group), 3D VANE with CS at section thickness of 4 mm (FB_4mm group), and that of 2 mm (FB_2mm group). Scanning parameters were detailed in Table 2. As navigator technique, the position of the diaphragm is automatically tracked, and the acquired data was corrected according to the monitored diaphragm positions in free-breathing sequence (track technique). The hepatobiliary phase image scanning was started after 15 minutes of contrast agent injection, and the order of the three sequences was randomly determined. For qualitative analysis, a radiologist, who was unaware of the scan sequence, randomly reviewed the images and assigned confidence scores for sharpness of the liver edge, visibility of intrahepatic vessels, motion artifacts, and overall image noise using a 5-point scale. For quantitative analysis, a radiologist measured mean signal intensity (SI) using region-of-interests (ROIs) placing on the liver parenchyma (SI_liver) and paraspinal muscle (SI_muscle). Standard deviation of SIliver (SD_liver) was also measured. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated as SI_liver/SD_liver and (SI_liver – SI_muscle)/SDliver, respectively. The Freedman test for comparison among the three groups and Mann-Whitney U test with Bonferroni adjustment for post analysis were conducted. A P value of less than .05 for Freedman test and .017 for Mann-Whitney U test with Bonferroni adjustment were considered to be significant.

Results

All qualitative and quantitative parameters were different among the three groups (P < .0001–.0021) (Tables 3 and 4). All qualitative parameters were higher in BH group than in FB_4mm group (P < .0001–.016), but no difference was found between BH and FB_2mm groups (P = .049–.38) and FB_4mm and FB_2mm groups (P = .027–.41). Median SI_liver (P < .0001), SD_liver (P < .0001), and SI_muscle (P < .0001) were higher in FB_4mm and FB_2mm groups than in BH group, but no difference was found between FB_4mm and FB_2mm groups (P =.035–.52). Median SNR was higher in FB_4mm group than in BH (P = .0003) and FB_2mm groups (P = .0051), but no difference was found between BH and FB_2mm groups (P = .14). The median CNR had no difference between each group (P = .017–.68).

Discussion

Pseudo-golden-angle radial stack-of-stars acquisition comprised radial k-space sampling spaced at a constant azimuthal increment of approximately 111.25°. This angle related to the golden ratio with the added fine adjustment and causes radial lines to be very evenly spaced over time. Pseudo-golden-angle radial stack-of-stars acquisition could reduce motion artifacts compared with cartesian acquisition, but it led to prolonged acquisition time⁴. In this study, we applied 3D VANE with CS and track technique to the hepatobiliary phase scanning and as a result, it allowed shorter and within a fixed acquisition time (51 sec in FB_4mm group and 81 sec in FB_2mm group). In this study, qualitative scores were better in BH group than in FB_4mm group, but FB_2mm group showed almost comparable image quality to BH group. Additionally, we did not observe statistical difference in terms of the SNR and CNR between HB and FB_2mm groups. Therefore, we believed that 3D VANE with CS at slice thickness of 2 mm could be applicable in clinical use and provides the usefulness for poor breath holding case.

Conclusion

Free-breathing scanning using 3D VANE with CS and track technique was feasible in gadoxetic acid-enhanced hepatobiliary phase imaging. 3D VANE with CS at section thickness of 2 mm demonstrated almost comparable image quality compared with conventional breath-holding scans.

Acknowledgements

The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

References

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