Introduction

3D-TOF magnetic resonance angiography (MRA)1 enables non-invasive visualization of the anatomical structure of blood vessels. It has been widely used for the measurement of vascular morphology and detection of carotid artery stenosis 2. However, the traditional 3D-TOF MRA often needs a relatively long scan time, during which the patient's swallowing, respiratory movement, neck movement, etc. might result in motion artifacts and thus hamper the follow-up diagnosis3. For patients with carotid artery stenosis, it is difficult to maintain a long time immobile state due to cerebral hemodynamic insufficiency. The CS technique 4 was proven a powerful tool for MR imaging acceleration 5-6. The purpose of this study was to explore the impact of acceleration factors of CS on the image quality of 3D-TOF-MRA for cervical vessels and to find an optimal acceleration factor to reduce the scan time without degeneration of image quality.

Materials and methods

22 healthy volunteers (15 males, 54.41±18.18 years) were recruited and underwent the 3D-TOF MRA scan of neck vessels on a 3.0 T MR scanner (Ingenia CX, Philips Healthcare, Best, the Netherlands). Four groups with different acceleration schemes were set up in our study, group A with a routine clinical setup of SENSE acceleration factor 3, and groups B, C, and D with CS factors of 4, 6, and 8. The scan time for the 4 groups were 258s, 206s, 138s, and 106 s, respectively. Other scan parameters were shown in Table 1. Regions of interest were placed manually at both sides of the carotid artery and nearby sternocleidomastoid muscle by experienced radiologists for measurement of signal intensity, standard deviation, and diameter of carotid artery vessels (Figure 1). Signal to Noise Ratio (SNR) and Contrast to Noise Ratio (CNR) were calculated from the labeled ROIs for all volunteers. The two observers used a four-point scoring method to evaluate the quality of the four groups of images: 3, excellent (high quality, high intensity of arterial vessels, clear contour, no artifacts, and clear display of primary and secondary branch vessels); 2, good (strong signal of arterial vessels, clear contour, and clear first-grade branch vessels); 1, fair (strong signal of the artery, moderately clear contour, and unclear branch of the artery, with a few artifacts which did not hamper the diagnosis); 0, poor (shallow arterial angiography, unclear contour which can not meet the diagnostic requirements). The SNR and CNR on the left and right sides of the carotid artery and nearby sternocleidomastoid muscle were compared with a Wilcoxon-rank sum test. The Kappa statistics were calculated for determining the interobserver agreement. The assessment of intermethod agreement was based on the evaluation of the senior physicians. Kruskal-Wallis test was employed to assess the difference of SNR, CNR, the largest, smallest diameters of the common carotid arteries and image scores between the 4 groups. Mann-Whitney U test was used to make a pairwise comparison. This study has been approved by the local IRB.

Results

SNR and CNR from two sides of the carotid artery are in good agreement (Table. 2). Scores measured by two observers are in good agreement (p=0.880). There were no statistically significant differences in SNR, CNR, the largest and smallest diameters of the common carotid arteries between the four groups. However, if CS acceleration factor of 8 was used, the subjective scores decreased obviously (p < 0.05, Table. 3). And no significant differences of image quality were detected between conventional SENSE acceleration with a factor of 3 and CS acceleration with factors of 4 and 6.

Discussion and Conclusions

Scan time for the cervical vascular 3D-TOF MRA could be reduced significantly by CS technique. However, if a large CS acceleration factor (≥ 8) is used, the image quality degrades evidently. CS acceleration factor of 6 is recommended for clinical 3D-TOF carotid MRA to achieve an optimal balance between imaging time and image quality.

Acknowledgements

No acknowledgement found.