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British Journal of Radiology (2005) 78, 116-121
© 2005 British Institute of Radiology
doi: 10.1259/bjr/66677575
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Magnetic resonance coronary angiography with 3D TrueFISP: breath-hold versus respiratory gated imaging

N M C So, MBBS, FRCR, FHKCR1, W W M Lam, MBBS, FRCR, FHKCR1, D Li, MD3, A K Y Chan, MBChB2, J E Sanderson, MD, FRCP, FACC2 and C Metreweli, FRCR, FRCP1

1 Department of Diagnostic Radiology and Organ Imaging, 2 Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Hong Kong, China and 3 Department of Radiology, Northwestern University, Chicago, Illinois, USA

Correspondence: Dr W W M Lam, Department of Diagnostic Radiology and Organ Imaging, Prince of Wales Hospital, Ngan Shing Street, Shatin. N.T., Hong Kong


   Abstract
Top
 Abstract
Introduction
 Methods and materials
 Results
 Discussion
 References
 
To compare the diagnostic accuracy of coronary magnetic resonance angiography with three-dimensional (3D) trueFISP breath-hold and respiratory gated techniques for the detection of significant coronary artery stenosis. 15 patients who recently underwent elective coronary angiogram were studied and a total of 60 arteries and 48 arteries were assessed by breath-hold and respiratory gated 3D trueFISP techniques, respectively. The image quality, length of artery visualized and the presence or absence of significant coronary artery stenosis were recorded. 83.3% and 81.7% of the arteries obtained with the respiratory gated and the breath-hold techniques, respectively, had an image quality suitable for further analysis. There was no significant difference in the length of artery visualized. Sensitivity and specificity of 80%, 100% and 75% and 100%, respectively, were obtained with the breath-hold and respiratory gated techniques in detecting significant stenosis in the coronary arteries. Both techniques have moderate sensitivity and high specificity in detection of significant stenosis in the visualized segments of the major coronary arteries. However, they cannot replace conventional coronary angiogram for diagnosing coronary artery disease at present. Further studies are required to evaluate whether breath-hold approach is more efficient, therefore should be performed first and respiratory gated approach reserved for those who cannot breath-hold.


   Introduction
Top
 Abstract
 Introduction
Methods and materials
 Results
 Discussion
 References
 
MR coronary angiography can be used to identify anomalous origin of the coronary arteries. It is potentially useful in screening, diagnosis and monitoring of the progress of coronary artery disease. Different methods and pulse sequences have been used to suppress the pericardial fat, enhance the coronary artery to myocardium signal-to-noise ratio (SNR) and contrast-to-noise ratio, as well as compensate for respiratory and cardiac motions [1]. Recently true-FISP (true fast imaging with steady state precession) technique has emerged as a new MR angiographic technique [2, 3]. We compared the use of breath-hold and respiratory gated true-FISP techniques in assessing coronary artery stenosis.


   Methods and materials
Top
 Abstract
 Introduction
 Methods and materials
Results
 Discussion
 References
 
Patients
15 patients with suspected coronary artery disease, who had a diagnostic coronary angiogram recently were included in the study. Patients were excluded if they had contraindications to MRI, claustrophobic, had non-sinus rhythm or had interventional procedures to the coronary arteries. There were 9 men and 6 women with mean age of 63.8 years (range 42–82 years). Informed written consent was obtained from all patients.

MRI
All subjects were imaged in the supine position, with a four-channel body array coil placed over the thorax, in a 1.5 T whole body MRI system (Sonata; Siemens Medical Solutions, Erlangen, Germany). Consecutive axial HASTE images (repetition time/echo time (TR/TE) 600/24; flip angle 160°; field of view (FOV) 340 mm; rectangular FOV varied according to patient's body habitus; matrix 256 x 108; acquisition time, 7 s; number of excitations 1; slice thickness 4 mm) were obtained from the aortic arch to the diaphragm. These images allowed the identification of the course of the major right and left coronary arteries. With the use of the three-point planscan tool on the scanner, a plane through the major axis of the proximal and middle segments of the right coronary artery was prescribed.

The position of the artery was confirmed by a double oblique scout using a three-dimensional (3D) breath-hold fat-suppressed, segmented true-FISP sequence (TR/TE 3.1/1.3; flip angle 60°; bandwidth per pixel 610 Hz; FOV 350 mm, rectangular FOV varied according to patient's body habitus; matrix 130 x 256; number of lines per cardiac cycle 35; slices reconstructed per volume after sinc interpolation 16; slice thickness after sinc interpolation 2 mm; voxel size 2.7 mm x 1.4 mm x 2 mm; acquisition time per breath-hold scan, ~16 s).

Double oblique 3D volumes were then acquired with a 3D fat-suppressed segmented True-FISP sequence. The breath-hold sequence was performed first, followed by the navigator triggering respiratory gated sequence, with the navigator column positioned in right hemidiaphragm. The parameters used were as follows: (a) breath-hold sequence (TR/TE 3.8/1.6; flip angle 60°; bandwidth per pixel 610 Hz; FOV 350 mm, rectangular FOV varied according to patient's body habitus; matrix 161 x 512; number of lines per cardiac cycle 35–43; slices reconstructed per volume after sinc interpolation 12; slice thickness after sinc interpolation 1.8 mm; voxel size: 2.1 mm x 0.7 mm x 1.6 mm; acquisition time: 14–27 s; (b) respiratory gated sequence (TR/TE 3.8/1.62; flip angle 60°; bandwidth per pixel 610 Hz; FOV 350 mm, rectangular FOV varied according to patient's body habitus; matrix 163 x 512; number of lines per cardiac cycle 31–35; slices reconstructed per volume after sinc interpolation 12; slice thickness after sinc interpolation 1.3 mm; voxel size: 2.1 mm x 0.7 mm x 1.3 mm; acceptance window: ±3 mm; acquisition time: 53 s–11 min 33 s, imaging efficiency 23–75%.

Interpretation of MR coronary angiograms
Two assessors blinded to the clinical data and coronary arteriogram results reviewed the images and a result was reached by consensus.

The left main coronary artery (LM), right coronary artery (RCA), left anterior descending artery (LAD), and left circumflex artery (LCx) were assessed. The image quality of the scan were graded qualitatively on a three point scale: 1, non-interpretable (artery obscured by pericardial fat and myocardium); 2, good (artery can be distinguished from the pericardial fat and myocardium); 3, excellent (sharp margin of artery, good suppression of pericardial fat and myocardium). The reasons for the non-interpretable images were recorded. The length of each assessable artery was measured with the standard linear measurement tool on the scanner. Presence of signal void segment or marked narrowing of luminal diameter on the assessable arteries (proximal and mid for RCA and LAD, proximal and distal for LM and LCx) was regarded as positive for significant stenosis. The branch arteries were not evaluated.

Conventional coronary angiography
Conventional coronary angiograms were performed with multiple projections. The intervals between the conventional coronary angiograms and the MR examination were between 1 day and 14 days (mean 4 days). All patients had the MR examination after the conventional coronary angiogram. The cardiologist, who was blinded to the MRI results, interpreted the conventional coronary angiograms visually. The presence of significant disease was defined as >50% diameter narrowing of the lumen.

Statistics
The selective coronary angiogram of the patient served as the gold standard for determining the diagnostic value of the non-invasive coronary angiogram. Analysis was carried out on arteries that had an image quality score of >1. The assessable arteries were divided into groups according to their location. The length of each group of arteries was expressed as mean±standard deviation (SD) cm. The mean lengths of each group of arteries obtained by each technique were compared by the Mann-Whitney's test. The image quality for the arteries obtained with each technique was compared by the Wilcoxon Signed Ranks test. Significance test were 2-tailed and a p-value of <0.05 was considered statistically significant.

The diagnostic accuracy of MR coronary angiography for detecting significant stenosis in a per artery basis was limited to the most distal segment of the coronary artery visualized on the MRA. The sensitivity, specificity, accuracy, positive predictive value, negative predictive value for the detection of significant stenosis were calculated. Statistical values for breath-hold and respiratory gated techniques in detecting stenosis were compared by McNemar's test.


   Results
Top
 Abstract
 Introduction
 Methods and materials
 Results
Discussion
 References
 
All patients underwent the MRA without any complication. A total of 60 arteries were imaged with breath-hold technique, 48 arteries were imaged with respiratory gated technique as some of the patients refused further investigation after one or two arteries had been imaged by respiratory gated technique. Eleven (18.3%) arteries imaged with the breath-hold technique and eight (16.7%) arteries imaged with the respiratory technique had an image quality score of 1 were excluded from further analysis. 25 arteries obtained with the breath-hold technique had an image quality score of 2 and 24 arteries had an image quality score of 3. 29 arteries obtained with the respiratory gated technique had an image quality score of 2 and 11 had an image quality score of 3 (Table 1Go). A significantly higher number of arteries obtained with the breath-hold technique had an image quality of =>ge;2 (p=0.049). For the 10 arteries that had an image quality score of 1 using the breath-hold technique, 5 were due to motion artefacts, three were due to suboptimal image plane (one vessel was outside the image volume, another due to tortuousity, the third obscured by the right ventricle), two were affected by technical problems with poor SNR and artefacts. For the 8 arteries that had an image quality score of 1 on the respiratory gated technique, 7 had motion artefacts and one was obscured by the right ventricle.


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  		Table 1. Image quality score of coronary artery by breath-hold and respiratory gated technique MR angiography, score 1 refers non interpretable, score 2 refers to good image quality, score 3 refers to excellent image quality

 
The average length of artery visualized using the breath-hold technique were: left main 1.1±0.3 cm (range 0.6–1.7 cm); left anterior descending 6.9±1.9 cm (range 2.8–10.6 cm); left circumflex 4.0±1.7 cm (range 1.9–6.9 cm); right coronary 8.8±1.6 cm (range 4.5–10.1 cm).

The average length of artery visualized using the respiratory gated technique were: left main 1.2±0.4 cm (range 0.7–1.8 cm); left anterior descending 6.7±2.1 cm (range 3.7–11.5 cm); left circumflex 4.5±2.1 cm (range 2.3–7.7 cm); right coronary 7.8±2.5 cm (range 3.8–10.7 cm). There is no statistically significant difference between the length of the left main, left anterior descending, left circumflex and right coronary arteries visualized with the two techniques (p>0.05).

On the conventional coronary angiogram, 10 arteries showed significant stenosis: left circumflex arteries (four, 70–100%), left anterior descending arteries (three, 70–90%), and right coronary arteries (three, 70–80%).

Of the 49 arteries that were analysed using the breath-hold technique, there were 5 arteries with >50% stenosis on the conventional coronary angiogram. MRA correctly identified 4 of them. Of the 40 arteries that were analysed using the respiratory gated technique, there were 4 arteries with >50% stenosis on the conventional coronary angiogram. MRA correctly identified three of them (Table 2Go).


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  		Table 2. Comparison of MR angiography (MRA) and conventional coronary angiogram for the detection of significant coronary artery stenosis (a total of 49 arteries and 40 arteries were assessed breath-hold and respiratory gated technique, respectively)

 
Compared with the conventional coronary angiogram, the sensitivity, specificity, accuracy, positive and negative predictive values for the detection of significant coronary artery stenosis for the segments of arteries that could be visualized were 80%, 100%, 98%, 100% and 98% for the breath-hold technique, 75%, 100%, 97%, 100% and 97% for the respiratory gated technique, respectively. There was no statistically significant difference in the detection of stenosis by both techniques compared with the conventional angiogram (p=1) (Figures 1 and 2GoGo). There was only one false negative case in both techniques. It was from the proximal left anterior descending artery of the same patient, who had a 90% stenosis on the conventional angiogram.



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  		Figure 1. Coronary magnetic resonance angiogram showing mild stenosis at the proximal left anterior descending artery. (a) Breath-hold magnetic resonance angiogram image showing mild stenosis at the origin of the left anterior descending artery (white arrow). (b) Navigator gated magnetic resonance angiogram image showing mild stenosis at the origin of the left anterior descending artery (white arrow). (c) Conventional coronary angiogram image showing mild stenosis at the origin of the left anterior descending artery (white arrow).

 


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  		Figure 2. True positive case with > 50% luminal narrowing in the left circumflex artery. (a) Breath-hold magnetic resonance angiogram image showing significant stenosis at the proximal left circumflex artery (white arrow). (b) Navigator gated magnetic resonance angiogram image showing significant stenosis at the proximal left circumflex artery (white arrow). (c) Conventional coronary angiogram image showing >50% luminal narrowing at the proximal left circumflex artery (white arrow).

 
When all 60 arteries were considered the breath-hold technique had a sensitivity of 40% specificity of 100%, positive predictive value of 100% and negative predictive value of 89% in detection of significant coronary artery stenosis. The respiratory gated technique had a sensitivity of 30%, specificity of 100%, positive predictive value of 100% and negative predictive value of 88%.


   Discussion
Top
 Abstract
 Introduction
 Methods and materials
 Results
 Discussion
References
 
Both breath-hold and navigator-echo techniques have been used to reduce respiratory motion for coronary artery imaging using 3D TrueFISP. Each technique has its own advantages and limitations. A larger volume of data or higher resolution can be acquired with the respiratory gated technique. However, it requires a longer imaging time and is sensitive to irregular breathing patterns. Breath-hold imaging, on the other hand, could more completely eliminate respiratory motion with cooperative patients and can be repeated more easily because of the short imaging time. Nevertheless, the spatial coverage and resolution are limited by the short breath-hold time. A direct comparison of the two techniques for detecting significant coronary stenoses on patients has not been performed before.

The proximal and mid segments of the arteries could be consistently visualized with both approaches. This makes the trueFISP technique valuable in assessing the anatomy of the coronary arteries and useful in cases with suspected anomalous origin of the coronary arteries and/or surgical planning. Inadequate image quality was seen more often in the RCA than the other arteries and one reason for this could be that the right coronary artery moves faster in diastole [4]. Acquiring cine images of the mid segment of the artery at a plane perpendicular to the segment may help to define the period in diastole when the artery is relatively stationary.

Our study shows that there were fewer vessels with adequate image quality for analysis using the respiratory gated technique compared with the breath-hold technique. This is consistent with the 40–75% success rate found in other studies [5, 6] with respiratory gating. Most of the arteries with poor image quality using the respiratory gated approach were due to motion artefact. The breath-hold images were acquired before the free breathing images, and some patients might be tired after the first part of the exam, resulting in irregular breathing patterns. The latter may improve with additional coaching and practice prior to the examination. For those who failed both approaches, 2D imaging with contrast and adaptive vessel tracking [7] or recently developed real-time imaging techniques are potential alternatives [8]. However, real-time imaging has lower resolution with pixel size >2.5 mm [9–11]. As there are now several approaches available to image the coronary arteries, a patient tailored approach depending on the patient's unique physical ability and respiratory attributes may be a viable option [12]. As blood in the artery and the vein both show relatively high signal intensity in trueFISP images, it was not possible to differentiate between the two in one case. The application of contrast agent, either intravascular or extracellular, combined with first pass technique may help to resolve the problem [13, 14].

The limitations of the study include a small number of patients, low prevalence of stenosis (10%), inability to visualize the distal arterial segments and that no major branches were evaluated. Despite the small number of patients recruited in this study, this is the first study that both MR and angiography techniques were performed in the same group of the patients. The results would therefore highlight the potential limitation of different technique in individual patients. The sensitivity and specificity in the present study was comparable with that reported in the literature: 38–90% sensitivity, 37–92% specificity [15–21]. Neither technique could consistently visualize the distal segment of the coronary arteries. As stenosis in the distal segment will also require intervention, this has limited the clinical use of coronary MRA. Combining coronary MRA with MR perfusion imaging has been advocated for a more comprehensive assessment of coronary artery disease [22].

A focal 90% stenosis in the proximal LAD was missed in the MRA images. Image blur caused by residual motion and overlapping ventricular myocardium may have contributed to the problem. Further improvements in resolution and more complete elimination of motion effects may reduce false negative diagnosis with MRA.

In conclusion, both breath-hold and free breathing techniques could achieve moderate sensitivity and high specificity in detecting significant stenosis in the proximal and mid segments of the coronary arteries. Neither technique could consistently visualize the full length of all arteries and replace the conventional coronary angiogram for diagnosing coronary artery disease at present. In our small series, more images with adequate image quality could be obtained with the breath-hold than the free breathing technique. Further studies, preferably multicentre studies are required for further evaluation of the most effective and efficient approach.

Received for publication January 5, 2004. Revision received August 26, 2004. Accepted for publication October 4, 2004.


   References
Top
 Abstract
 Introduction
 Methods and materials
 Results
 Discussion
 References
 

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