Rationale and Objectives
To compare contrast-enhanced coronary magnetic resonance angiography (MRA) at 3.0 T with the same technique performed at 1.5 T using the contrast agent gadofosveset.
Materials and Methods
In this prospective randomized study, 19 healthy male volunteers (mean age 28 years, mean weight 79.8 kg), after signing informed consents, underwent contrast-enhanced inversion recovery three-dimensional fast low angle shot (FLASH) MRA at 1.5 and at 3.0 T. Prospective electrocardiogram-triggering was combined with adaptive respiratory gating. For contrast-enhanced images, the intravascular contrast agent gadofosveset was used. Acquisition time, signal-to-noise ratio (SNR) of coronary blood, contrast-to-noise ratio (CNR) between coronaries and adjacent myocardium or epicardial fat and image quality were analyzed for statistical differences by using a two-tailed paired-sample t -test. The ratio calculations were based on measurements performed on the raw data and the image quality was blinded and independently evaluated by two experienced radiologists using a five-point scale.
Results
The mean values for the acquisition time were 14.58 ± 0.1 minutes at 1.5 T and 16.40 ± 0.2 minutes at 3.0 T. Overall SNR of all evaluated coronary segments proved higher at 3.0 T compared to 1.5 T (74.0 ± 42.1 at 3.0 T vs. 50.2 ± 20.2 at 1.5 T, P = .04). Overall CNR between coronaries and myocardium was significantly increased at 3.0 T in comparison to 1.5 T (40.1 ± 21.9 at 3.0 T vs. 24.4 ± 17.2 at 1.5 T, P = .01). Between the two methods, no significant difference in overall CNR between coronaries and epicardial fat was observed ( P = .08, NS). The 3.0 T MRA demonstrated superior overall image quality with respect to 1.5 T (2.28 ± 0.71 at 3.0 T vs. 1.92 ± 0.38 at 1.5T, P = .004).
Conclusion
The use of higher field strength, 3.0 T instead of 1.5 T, resulted in similar CNR between coronaries and epicardial fat, higher SNR values and CNR between blood and myocardium, as well as an improved overall image quality, when gadofosveset in combination with electrocardiogram and respiratory triggering for coronary MRA was used.
Coronary artery disease (CAD) remains one of the leading causes of morbidity and mortality in developed countries. Recent surveys suggest that three-dimensional whole-heart coronary magnetic resonance angiography (MRA) at 1.5 T is a promising technique for non-invasive assessment of the coronary arteries . When a contrast-enhanced whole-heart approach is used, electrocardiogram (ECG) and respiratory triggering require a contrast agent that enables increased blood signal intensity for a longer period than the first pass of an extravascular contrast agent. In theory, field strength of 3.0 T offers an almost twofold higher signal intensity and signal-to-noise ratio (SNR), than a 1.5 T system, if the same pulse sequence technique is used . In contrast to a steady-state free-precession (SSFP) readout technique, a spoiled gradient-echo sequence, such as fast low-angle shot (FLASH), proved relatively insensitive to the increased field inhomogeneities of 3.0 T .
Various contrast agents have been used at 3.0T in previous investigations for coronary MRA, such as gadopentetate dimeglumine or gadobenate dimeglumine . The intravascular contrast media provide long time windows for coronary MRA acquisition because of prolonged plasma half-life and slow extravasation in the interstitial space .
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Materials and methods
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Study Population
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Table 1
Characteristics of the Volunteers Group
No Volunteer Age (Years) Weight (kg) Body Mass Index 1 31 70 22.3 2 37 82 22.7 3 30 68 21.2 4 36 73 22.5 5 33 75 23.7 6 25 52 17.2 7 24 74 21.6 8 28 83 25.6 9 24 72 19.5 10 35 90 26.0 11 21 74 23.4 12 26 73 21.8 13 34 86 22.4 14 22 115 31.9 15 28 93 27.8 16 25 108 32.6 17 30 91 29.7 18 22 80 22.6 19 23 62 20.0
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MRI
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Contrast-enhanced Coronary MRA at 1.5 and 3.0 T
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Contrast Agent
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Quantitative Analysis
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SNR =SI/SDnoise; SNR =
SI
/
S
D
noise;
CNRcor/myo=(SIcor-SImyo)/SDnoise CN
R
cor
/
myo
=
(
S
I
cor
-S
I
myo
)
/
S
D
noise
CNRcor/fat=(SIcor-SIfat)/SDnoise CN
R
cor
/
fat
=
(
S
I
cor
-S
I
fat
)
/
S
D
noise
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Qualitative Analysis
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Statistical Analysis
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Results
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SNR and CNR Measurements
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Table 2
Measurements Result of Both Methods Concerning the Mean SNR Values
Mean SNR_P_ Value Evaluated
Regions 1.5 T 3.0 T 1.5 T vs. 3.0 T LMS 54.2 ± 20.6 78.5 ± 40.6 .04 Prox. LAD 50.1 ± 18.4 81.2 ± 49.1 .02 Prox. LCX 48.2 ± 17.4 71.4 ± 45.6 .06 Prox. RCA 48.3 ± 24.6 65.0 ± 32.9 .10 Overall segments 50.2 ± 20.2 74.0 ± 42.1 .04 Fat 15.2 ± 7.4 21.1 ± 11.0 .06 Myocardium 25.8 ± 10.4 34.2 ± 34.2 .32
LMS, left main stem coronary artery; LAD, left anterior descending coronary artery; RCA, right coronary artery; LCX, left circumflex artery; prox, proximal coronary segment.
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Table 3a
Measurements Results of Both Methods Concerning the Values of CNR cor/fat
CNR cor/fat P Value Coronary
Segments 1.5 T 3.0 T 1.5 T vs. 3.0 T LMS 39.0 ± 14.5 57.4 ± 38.0 .07 Prox. LAD 34.9 ± 13.3 60.0 ± 46.5 .04 Prox. LCX 32.9 ± 12.0 50.2 ± 43.2 .12 Prox. RCA 33.1 ± 18.4 43.8 ± 31.3 .23 Overall 35.0 ± 14.7 52.9 ± 39.9 .08
Table 3b
Measurements Results of Both Methods Concerning the Values of CNR cor/myo
CNR cor/myo P Value Coronary
Segments 1.5 T 3.0 T 1.5 T vs. 3.0 T LMS 28.4 ± 17.7 44.3 ± 21.1 .02 Prox. LAD 24.2 ± 14.0 47.0 ± 23.6 .002 Prox. LCX 22.3 ± 13.7 37.1 ± 21.9 .02 Prox. RCA 22.5 ± 22.7 31.8 ± 19.0 .16 Overall 24.4 ± 17.2 40.1 ± 21.9 .01
LMS, left main stem coronary artery; LAD, left anterior descending coronary artery; RCA, right coronary artery; LCX, left circumflex artery; CNR cor/myo , CNR between coronary blood and myocardium; prox, proximal coronary segment.
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Image Quality
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Table 4a
Image Quality Results of Both Readers for Both Methods using Paired t-test
Mean Image Quality_P_ Value Coronary
Segments 1.5 T 3.0 T 1.5 T vs. 3.0 T LMS 2.2 ± 0.7 2.5 ± 0.5 .14 Proximal 2.2 ± 0.5 2.6 ± 0.4 .01 Middle 1.8 ± 0.3 2.3 ± 0.4 .002 Distal 1.5 ± 0.3 1.8 ± 0.4 .02 Overall 1.9 ± 0.7 2.2 ± 0.7 .004
Table 4b
Image Quality Results of Both Methods for Each Reader Individually using Wilcoxon Test
Wilcoxon Test
1.5 T vs 3.0 T Coronary
Segments Reader 1 Reader 2 LMS 0.19 0.26 Proximal 0.003 0.04 Middle 0.003 0.009 Distal 0.03 0.04 Overall 0.004 0.01
LMS, left main stem coronary artery; proximal, middle, distal, and overall, proximal, middle, distal, and all coronary segments of left anterior descending coronary artery, left circumflex artery, and right coronary artery.
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Discussion
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Limitations
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Conclusion
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