Impact of Lesion Size on Navigator-Triggered vs Free-Breathing Liver DWI MRI

Overview

This study evaluated the effect of lesion size on the detection and contrast-to-noise ratio (CNR) of focal liver lesions (FLL) using navigator-triggered (TRIG) versus free-breathing (FB) diffusion-weighted MRI. Results suggest that TRIG acquisition improves detection of smaller lesions and reduces missed lesions compared to FB, while acquisition times were kept comparable.

Background

Diffusion-weighted imaging (DWI) of the liver is frequently used to assess tumor burden, which is critical for prognosis in malignant liver diseases. However, liver DWI is susceptible to motion artifacts from breathing and cardiac motion, particularly affecting the left liver lobe. Free-breathing acquisitions allow more data collection but can cause blurring and lesion misregistration, whereas navigator-triggered acquisitions adapt to respiratory motion to reduce artifacts but may prolong scan time. Prior studies have shown conflicting results regarding which technique is superior, possibly due to differences in lesion size ranges studied.

Data Highlights

The study included 43 patients with known or suspected liver lesions undergoing both FB and TRIG DWI acquisitions on a 1.5-T MRI scanner. Lesions were segmented and characterized at b = 800 s/mm². Acquisition times for FB and TRIG sequences were matched by adjusting TRIG parameters. Lesions visible only in one technique were counted as additional lesions. Lesion sizes ranged broadly, allowing analysis of detection rates and CNR by lesion dimension.

Key Findings

• Navigator-triggered (TRIG) DWI detected a higher number of small focal liver lesions compared to free-breathing (FB) DWI.
• TRIG acquisition reduced the fraction of missed lesions, particularly for lesions smaller than 1 cm.
• Contrast-to-noise ratio (CNR) was generally improved with TRIG, enhancing lesion conspicuity.
• Acquisition times for TRIG and FB sequences were kept roughly equal to allow fair comparison.
• Motion artifacts and lesion misregistration were less frequent with TRIG, especially in the left liver lobe near the heart.

Clinical Implications

For clinical liver DWI, navigator-triggered acquisitions should be considered when detecting small focal liver lesions is critical, as they reduce missed lesions and improve image quality despite slightly longer or variable scan times. Free-breathing acquisitions may be more time-efficient but risk lesion blurring and misregistration, potentially impacting diagnostic accuracy in smaller lesions. Patient cooperation and clinical context should guide the choice of acquisition technique.

Conclusion

Navigator-triggered DWI offers superior detection and characterization of smaller liver lesions compared to free-breathing DWI, supporting its use in clinical scenarios where lesion conspicuity is paramount. Balancing acquisition time and image quality remains essential for optimal liver MRI protocols.

References

1. Choi et al 2016 -- Comparison of FB and TRIG DWI for Liver Lesions
2. Takayama et al 2018 -- Lesion CNR in FB vs TRIG Liver DWI
3. Szklaruk et al 2017 -- Image Quality in TRIG Liver DWI
4. Nasu et al 2019 -- Lesion Contrast and Misregistration in FB vs Breath-Triggered DWI
5. Recent Study 2021 -- Small Lesion Detection with TRIG Acquisition