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SENSE or k-MAG to Accelerate Free Breathing Navigator-Guided Coronary MR Angiography

Raja Muthupillai1,2, Jouke Smink2, Steve Hong1, Roshan Ravindran1, Vei Vei Lee3 and Scott D. Flamm1,4

1 Department of Radiology, St. Luke's Episcopal Hospital and Texas Heart Institute and Baylor College of Medicine, 6720 Bertner Ave., MC 2-256, Houston, TX 77030.
2 Philips Medical Systems, Cleveland, OH.
3 Department of Biostatistics, Texas Heart Institute, Houston, TX 77030.
4 Department of Cardiology, St. Luke's Episcopal Hospital and Texas Heart Institute, Houston, TX 77030.


Figure 1
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  		Fig. 1 —Graph shows k-space modulation used to smoothly vary acceptance window from 4 mm at central 25% of k-space to 8 mm (26-100% of k-space). Modulation function is given by w = {alpha} +(ß - {alpha})exp(-{eta}/|k|))3, in which {alpha} is starting window width; ß is ending gate width; ß is central window width; and w is resulting acceptance window width as function of k-space value, k.

 

Figure 2
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  		Fig. 2 —Reformatted left main and left anterior descending coronary MR angiography obtained in four volunteers using conventional navigator-guided coronary artery imaging technique (NAV), NAV + k-space weighted motion-adapted gating (k-MAG), NAV + sensitivity encoding (SENSE), and NAV+SENSE+k-MAG (from left to right). Notice slight increase in noise in two right-most images due to incorporation of SENSE. Curved black protrusions into right ventricular outflow tract seen on images in row 3 and row 4 are due to "flattening" effect of displaying curvilinear reformation of left main and left anterior descending coronary artery as single image.

 

Figure 3
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  		Fig. 3A —Pairwise statistical comparison of four techniques for two quantitative metrics, R-R interval (A) and scan efficiency (B). Filled circular dots (bullet) indicate statistical significance between techniques (p < 0.05). k-space weighted motion-adapted gating (k-MAG) and sensitivity encoding (SENSE) reduce scan time both independently and in combination.

 

Figure 4
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  		Fig. 3B —Pairwise statistical comparison of four techniques for two quantitative metrics, R-R interval (A) and scan efficiency (B). Filled circular dots (bullet) indicate statistical significance between techniques (p < 0.05). scan efficiency of traditional conventional navigator-guided (NAV) coronary artery imaging technique sequence with addition of k-MAG is better than that of NAV sequence as well as that of NAV + SENSE sequence without k-MAG.

 

Figure 5
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  		Fig. 4A —Subjective image quality of all four techniques: navigator-guided (NAV) coronary MR angiography, k-space weighted motion-adapted gating (k-MAG), and sensitivity encoding (SENSE, factor = 2). Image quality of all four techniques is greater than 2.5, indicating that the overall image quality was between good and very good (see text for description of scale). Mean image scores of techniques without SENSE were rated slightly above 3.0, and mean scores of techniques using SENSE were rated slightly above 2.5.

 

Figure 6
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  		Fig. 4B —Subjective image quality of all four techniques: navigator-guided (NAV) coronary MR angiography, k-space weighted motion-adapted gating (k-MAG), and sensitivity encoding (SENSE, factor = 2). Pairwise statistical comparison of four techniques for image quality assessment. Only comparisons of conventional NAV coronary artery imaging technique and NAV + SENSE, NAV + k-MAG, and NAV + SENSE were statistically significant.

 

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