Application Of 1.5T Advanced MR In Coronary MR Angiography And The Detection Of Coronary Microembolization

PartⅠApplication of parallel imaging technique in free-breathing three dimensionalcoronary MR angiography with a navigator-gated sequenceObjective: The purpose of this study is to evaluate the value of parallel-imaging methods applied to free-breathing three dimensional coronary MR angiography with a navigator-gated sequence and to assess the feasibility and preliminary clinical application of free-breathing whole-heart coronary MR angiography using parallel imaging.Materials and methods: Signal-to-noise ratio(SNR), contrast-to-noise ratio(CNR), aliasing artifacts and fat suppression on GRAPPA and mSENSE images were analyzed in vitro phantom MRI using sequence for free-breathing 3D coronary angiography. We applied GRAPPA parallel imaging to coronary MR angiography of 23 healthy subjects who were performed by using T2-prepared truefisp three dimensional navigator-gated fat-saturation coronary MR angiography sequences through targeted-volume way. We measured the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), acquisition time and assessed aliasing artifacts on images with and without GRAPPA respectively and these items were compared using paired t test and/or paired rank sum test, with P values less than 0．05 considered significant. We performed free-breathing whole-heart coronary MR angiography using parallel imaging on 49 individuals including 43 volunteers, 4 cases with coronary stents, one with three vessel disease and one with Kawasaki disease. The visualization of the major coronary arteries was evaluated. We compared the features of ID-PACE and 2D-PACE. In addition, we evaluated the advantage of MR scanner as a single modality capable of defining cardiac anatomy and function, myocardial perfusion, myocardial viability, and coronary anatomy in cases with coronary stents and three-vessel disease.Results: In vitro phantom MRI, GRAPPA yields a higher SNR and CNR than mSENSE with substantial decrease in aliasing artifacts at the same acceleration factor. Fat suppression was failed on the edge images of 3D slab obtained after either GRAPPA or mSENSE reconstruction. The mean acquisition time, SNR, CNR were 4．62±2．61 min, 29．84±3．01 and 21．26±16．10 for sequences with GRAPPA versus 7．51±3．12 min(P<0．05) , 36．27±2．82 (P<0．05) and 25．17±20．51 (P<0．05) for sequences without GRAPPA, respectively. A reduction of 41±13% in scanning time was obtained using GRAPPA for targeted-volume right coronary MR angiography. 4 of 19 individuals using 1D-PACE and 1 of 30 individuals using 2D-PACE failed to complete free-breathing whole-heart coronary MR angiography. Compared with 1D-PACE, 2D-PACE ensured that magnetization was not saturated and so dark lines in the images were avoided. In 38 volunteers who completed the free-breathing whole-heart coronary MR angiography using GRAPPA parallel imaging, adequate visualization was achieved in 92．1%-97．4% of the proximal and middle segments and 76．3%-78．9% of the distal segments. Regional dilated coronary artery was detected in Kawasaki disease. Coronary MR angiography together with cine MR imaging, perfusion imaging and myocardial viability imaging provided valuable information for clinical diagnosis.Conclusion: GRAPPA is superior to mSENSE for free-breathing 3D coronary MR angiography in terms of SNR, CNR and aliasing artifacts. In free-breathing navigator three-dimensional coronary MR angiography, GRAPPA may be used to reduce scanning time and yield good visualizations of major coronary arteries without obviously decreasing image quality at an acceleration factor of two. We suggested that whole-heart 3D coronary MR angiography is a promising method for clinical application and 2D-PACE is a better navigation technique than ID-PACE. 锘库槄Part鈪?The value of applying nitroglycerin in free-breathing three dimensional coronary MR angiography with real-time navigation technique a prospective own-control studyObjective: The aim of this study is to evaluate the impact of exogenous nitroglycerin on image quality of free breathing 3D coronary MR angiography.鈽匨aterials and methods: Free-breathing 3D whole-heart coronary MR angiography was performed in 12 healthy volunteers at a 1．5T System (Magnetom Avanto, Siemens AG, Erlangen, Germany) before and after sublingual nitroglycerin (NTG) at a dose of 0．5mg, using GRAPPA parallel imaging at an acceleration factor of two. For each coronary segment, image quality was visually rated using a five point grading scale. Measurements of visualized vessel diameter were performed on equivalent segments of the coronary arteries in the sequences with and without nitroglycerin. Continuous data were analyzed by paired t test and/or paired rank sum test, with P values less than 0．05 considered significant.鈽匯esults: All individuals completed the coronary MR angiography without complications. Heart rate increased significantly (rest 72卤13 vs. NTG 85卤11 beats per minute; P<0．05) . No significant difference was found between scans with and without nitroglycerin as to acquisition time (rest 8．53卤2．25 vs. NTG 9．35卤3．21 minute; P>0．05) . The mean diameter of the coronary arteries was significantly higher after NTG with an increase of (25卤18) %. There was significant difference in the coronary MR angiography with and without nitroglycerin in the visualized vessel diameter of LM (3．0卤0．6 vs. 3．5卤0．7 mm; P<0．05) , proximal(2．5卤0．4 vs. 3．0 + 0．6 mm; P<0．05) and middle (2．2卤0．4 vs. 2．8卤0．6 mm; P<0．05) and distal (1．7卤0．3 vs. 2．2卤0．4 mm; P<0．05) LAD, proximal (2．2卤0．4 vs. 2．8卤0．5 mm; P<0．05) and distal(1．7卤0．4 vs. 2．3+0．4 mm; P<0．05) LCX, and proximal (2．6卤0．7 vs. 3．1卤0．7 mm; P<0．05) and middle(2．5卤0．7 vs. 2．9卤0．6 mm; P<0．05) and distal (1．8卤0．5 vs. 2．1卤0．4 mm; P<0．05) RCA. Significant difference was also found in the coronary MR angiography with and without nitroglycerin in the average qualitative assessment score of image quality (P<0．05) .鈽匔onclusion: Sublingual administration of nitroglycerin is capable of improving visualization of the coronary arteries in free-breathing 3D whole-heart coronary MR angiography. Nitroglycerin administration results in dilation of epicardial coronary vessels by an average of (25卤18) %. The increase and alteration of heart rate during the scanning may be a disadvantage factor for free-breathing whole-heart coronary MR angiography. PartⅢMultimodality MR imaging in the detection of coronary microembolization: an animal experiment correlating with MR features and pathological findingsObjective: The purpose of this study is to asses the value of multimodality MR imaging in the detection of coronary microembolization.Materials and methods: Coronary microembolization was induced in eight swines by injection of 50,000, 120,000 and 150,000 microspheres (42μm in diameter) into the left anterior descending coronary artery in one, six and one swine respectively. MR imaging was performed by using a 1．5-T System (Magnetom Avanto, Siemens AG, Erlangen,Germany) before and repeated six hours and one week after coronary microembolization, including cine MR imaging, first-pass perfusion imaging and delayed contrast enhancement. We analyzed the features of first-pass perfusion imaging and delayed contrast enhancement and evaluated the left ventricular end-systolic volume(LVESV), left ventricular end-diastolic volume(LVEDV) and left ventricular ejection fraction(LVEF) for each MR scanning. After all the MRI exams were completed, the animals were then sacrificed for pathologic analyses (NBT and HE).Results: No abnormality was found on coronary angiography (DSA) before and after coronary microembolization. Hypoenhanced region was only observed on first-pass perfusion imaging of the swine with an injection of 150,000 microspheres during acute stage (six hours after coronary microembolization) and it became less obvious one week later (subacute-chronic stage). Delayed enhanced areas were found on short-axis sections in all the swines during acute stage. However, the delayed enhanced areas disappeared or diminished on repeated MR imaging at subacute-chronic stage and only existed on one short-axis section in the swine injected with 150,000 microspheres, which were consistent with NBT pathologic findings. Systolic function of anterior wall and anterior septal was impaired in all eight swines variably during acute stage and improved slightly one week later. LVEF and LVEDV of six swines injected with 120,000 microspheres were (45．1±6．3) %/(36．6±4．5) ml, (36．2±7．0) %/(37．2±4．5) ml and (43．1±5．3) %/(46．6±4．1) ml at the initial, acute and subacute-chronic stage respectively and significant difference was found in LVEF between initial and acute stage (P<0．05) and LVEDV between initial and subacute-chronic stage (P<0．05) . LVEF and LVEDV of the swine injected with 150,000 microspheres were 45．1%/35．9ml, 39．2%/39．8ml and 41．9%/44．9ml at the initial, acute and subacute-chronic stage respectively, and the swine injected with 50,000 microspheres were 50．0%/31．8ml, 42．9%/32．4ml and 48．0%/37．1ml. Coronary microembolizations were demonstrated pathologically.Conclusion: Coronary angiography (DSA) is unable to show the coronary abnormality caused by coronary microembolization. Multimodality MR imaging is useful for the detection of coronary microembolization. Systolic function of myocardial wall is impaired. LVEF decreases during acute stage and recovers gradually accompanying the dilation of ventricular cavity, which indicates the procedure of ventricular remodeling. Hypoenhanced region was only detected on first-pass perfusion imaging of the swine with an injection of 150,000 microspheres. Delayed enhanced areas were observed in all the swine during acute stage and disappeared or diminished one week after coronary microembolization, which were consistent with pathologic analyses (NBT).