Introduction

Lumbar magnetic resonance imaging has a wide range of clinical applications due to its good soft-tissue contrast, high spatial resolution, and no ionizing radiation¹. During the scan examination, patients must remain still for a long time to prevent motion artifacts. However, it is difficult for the patients with severe lumbar disease². Compressed sensing (CS) can significantly shorten the scan time, and ensure image quality via sparse sampling at the same time^3,4. The purpose of this study was to explore the influence of CS on the lumbar image quality and to find an optimal acceleration factor.

Materials and methods

A total of twenty healthy volunteers (mean age: 37.2 ± 11.3, range: 21-57 years; 7 women) with informed consent were scanned using a 3.0 T MR scanner (Ingenia CX, Philips Healthcare, Best, the Netherlands). The performed MR protocols included sagittal T1WI, T2WI TSE and transverse T2WI TSE sequences without SENSE and CS-SENSE, with SENSE factor (SENSE=2), with CS-SENSE factors (CS=2, 3, 4, 5), respectively. Other scan parameters were shown in Table 1 as below. Regions of interest (ROIs) for signal intensity and standard deviation measurements were manually placed on the first to fifth lumbar spines, the psoas major and the middle spinal cord. Signal to noise ratio (SNR) and contrast to noise ratio (CNR) were calculated for all volunteers accordingly. Two radiologists scored the images independently based on the anatomical structures, diagnostic certainty and artifacts. Five-point scale criteria was used (the scoring system was listed in Table 2) to evaluate the image quality, and the score more than 3 was considered to meet clinical requirements. The Kappa test was adopted to evaluate the consistency of the scores from the two radiologists. If the consistency was in good agreement, the corresponding images would be adopted for the analysis in further by senior physicians. In the following analysis, the Kruskal-Wallis test was used to assess the difference of SNR, CNR and score between groups, and the LSD test was employed to make a pairwise comparison.

Results

The scores by the two observers were in good agreement (=0.757-0.997). In Table 3, it was shown that there were statistically significant differences in SNR, CNR and score of sagittal T1WI, T2WI TSE and transverse T2WI TSE sequences. When CS=5, the SNR, CNR and scores of sagittal T1WI are significantly different from those of conventional sequences (p<0.05); when CS=4, the SNR, CNR and subjective scores of sagittal and axial T2WI were significantly different from conventional sequences (p<0.05).

Discussion and Conclusions

Scan time for the lumbar spine decreased gradually with increase of the CS acceleration factor. CS factor of 4 was recommended for clinical sagittal T1WI, and CS factor of 3 was best for clinical sagittal and transverse T2WI to achieve an optimal balance between scan time and image quality.

Acknowledgements

No acknowledgement found.