Navigator-Based Slice Tracking for Multiband Accelerated Liver DWI.

PURPOSE: Clinical liver diffusion-weighted imaging (DWI) suffers from long measurement time and respiratory motion. In this study, we employ a navigator-based slice tracking technique (NAV) to prospectively compensate for respiratory motion in multiband (MB) accelerated liver DWI.

METHODS

A single gradient-echo slice readout at the location of the diaphragm along the inferior-superior direction was acquired as a navigator. Navigator acquisition and fat suppression were inserted before each transverse imaging slice of the readouts of a 2D spin-echo EPI based DWI sequence, with 20 repeats including 32 training navigators (4 preparing scans) at the beginning of the measurement obtained in about 3 min. For comparison, MB accelerated DWI without NAV during free breathing was also acquired. To evaluate the effect of NAV on image quality, coefficients of variation (CoV), signal to noise ratio (SNR), and sharpness were calculated. Six healthy volunteers and three patients with lesions were examined at 1.5 T.

RESULTS

The motion caused by respiratory activity was effectively computed using the navigator signal. For measurement with NAV, averaged CoV was significantly lower when compared to without NAV (0.256 ± 0.086 vs. 0.262 ± 0.091, p < 0.001). SNR and liver sharpness were also increased. The shapes of both kidney and spleen were continuous and smooth in the coronal view with NAV. Detailed structure in different organs could be found with NAV compared to without NAV in the cyst and tumor patients.

CONCLUSION

This study demonstrates the feasibility of a NAV technique to reduce respiratory motion in MB accelerated liver DWI.