Free-breathing, three-dimensional coronary artery magnetic resonance angiography: comparison of sequences

Utility of free-breathing, whole-heart, three-dimensional magnetic resonance imaging in the assessment of coronary anatomy for congenital heart disease

The incidence of coronary anomalies is increased in congenital heart disease (CHD). Whole-heart magnetic resonance imaging (MRI) has been proposed as a robust approach to coronary artery imaging without ionizing radiation. The proximal coronary arteries were imaged in 112 CHD patients (63 males) age 17 ± 13 years (range 11 days-68 years) using a navigator-gated, whole-heart, three-dimensional (3D) technique at 1.5 T. Two observers assessed image quality overall and for left anterior descending coronary artery (LAD), left circumflex coronary artery (LCX), and right coronary artery (RCA) using a 5-point scale ranging from 0 (not visible) to 4 (clear margins). Weighted kappa was used to assess interobserver agreement. Coronary artery origins were visible in 99% of the patients. The left main origin was not visualized in one patient, although the LAD, LCX, and RCA were visualized. Eight patients (7%) had anomalies. The overall image quality was 3.3 ± 0.8 for reader 1 and 3.1 ± 1.0 for reader 2. Age had a significant effect on image quality, with younger patients having lower scores. Agreement between readers was moderate (overall kappa, 0.60). Free-breathing, navigator-gated, whole-heart 3D MRI is a useful, robust, and reliable noninvasive technique for assessing coronary artery origins and their proximal course with diagnostic quality in CHD patients.

Contrast-enhanced whole-heart coronary magnetic resonance angiography at 3 T with radial EPI

Whole-heart coronary magnetic resonance angiography is a promising method for detecting coronary artery disease. However, the imaging time is relatively long (typically 10-15 min). The goal of this study was to implement a radial echo planar imaging sequence for contrast-enhanced whole-heart coronary magnetic resonance angiography, with the aim of combining the scan efficiency of echo planar imaging with the motion insensitivity of radial k-space sampling. A self-calibrating phase correction technique was used to correct for off-resonance effects, trajectory measurement was used to correct for k-space trajectory errors, and variable density sampling was used in the partition direction to reduce streaking artifacts. Seven healthy volunteers and two patients were scanned with the proposed radial echo planar imaging sequence, and the images were compared with a traditional gradient echo and X-ray angiography techniques, respectively. Whole-heart images with the radial EPI technique were acquired with a resolution of 1.0 × 1.0 × 2.0 mm(3) in a scan time of 5 min. In healthy volunteers, the average image quality scores and visualized vessel lengths of the RCA and LAD were similar for the radial EPI and gradient echo techniques (P value > 0.05 for all). Anecdotal patient studies showed excellent agreement of the radial EPI technique with X-ray angiography.

Beat-to-beat respiratory motion correction with near 100% efficiency: a quantitative assessment using high-resolution coronary artery imaging

This study quantitatively assesses the effectiveness of retrospective beat-to-beat respiratory motion correction (B2B-RMC) at near 100% efficiency using high-resolution coronary artery imaging. Three-dimensional (3D) spiral images were obtained in a coronary respiratory motion phantom with B2B-RMC and navigator gating. In vivo, targeted 3D coronary imaging was performed in 10 healthy subjects using B2B-RMC spiral and navigator gated balanced steady-state free-precession (nav-bSSFP) techniques. Vessel diameter and sharpness in proximal and mid arteries were used as a measure of respiratory motion compensation effectiveness and compared between techniques. Phantom acquisitions with B2B-RMC were sharper than those acquired with navigator gating (B2B-RMC vs. navigator gating: 1.01±0.02 mm(-1) vs. 0.86±0.08 mm(-1), P<.05). In vivo B2B-RMC respiratory efficiency was significantly and substantially higher (99.7%±0.5%) than nav-bSSFP (44.0%±8.9%, P<.0001). Proximal and mid vessel sharpnesses were similar (B2B-RMC vs. nav-bSSFP, proximal: 1.00±0.14 mm(-1) vs. 1.08±0.11 mm(-1), mid: 1.01±0.11 mm(-1) vs. 1.05±0.12 mm(-1); both P=not significant [ns]). Mid vessel diameters were not significantly different (2.85±0.39 mm vs. 2.80±0.35 mm, P=ns), but proximal B2B-RMC diameters were slightly higher (2.85±0.38 mm vs. 2.70±0.34 mm, P<.05), possibly due to contrast differences. The respiratory efficiency of B2B-RMC is less variable and significantly higher than navigator gating. Phantom and in vivo vessel sharpness and diameter values suggest that respiratory motion compensation is equally effective.

MRI and CT in the diagnosis of coronary artery disease: indications and applications

In recent years, technical advances and improvements in cardiac computed tomography (CT) and cardiac magnetic resonance imaging (MRI) have provoked increasing interest in the potential clinical role of these techniques in the non-invasive work-up of patients with suspected coronary artery disease (CAD) and correct patient selection for these emerging imaging techniques. In the primary detection or exclusion of significant CAD, e.g. in the patient with unspecific thoracic complaints, and also in patients with known CAD or advanced stages of CAD, both CT and MRI yield specific advantages. In this review, the major aspects of non-invasive MR and CT imaging in the diagnosis of CAD will be discussed. The first part describes the clinical value of contrast-enhanced non-invasive CT coronary angiography (CTCA), including the diagnostic accuracy of CTCA for the exclusion or detection of significant CAD with coronary artery stenoses that may require angioplastic intervention, as well as potentially valuable information on the coronary artery vessel wall. In the second section, the potential of CT for the imaging of myocardial viability and perfusion will be highlighted. In the third and final part, the range of applications of cardiac MRI in CAD patients will be outlined.

Evaluation of coronary atherosclerotic plaques

In many patients, unheralded myocardial infarction associated with a mortality of approximately 20% is the first manifestation of coronary artery disease. Approximately 40% of the population is considered to have a moderate midterm risk of 10% to 20%. Any of the stratification schemes suffers from a lack of accuracy to correctly determine the risk, and uncertainty exists regarding how to treat individuals who have been identified to be at intermediate risk. Other tools providing information about the necessity to reassure or to treat these patients are warranted. Currently, the assessment of the atherosclerotic plaque burden by CT may be able provide valid information for this cohort. This article discusses the potential value and limitations of cardiac CT for evaluating coronary atherosclerotic plaque.

In vivo quantification of femoral-popliteal compression during isometric thigh contraction: Assessment using MR angiography

PURPOSE

To quantify femoral-popliteal vessel deformation during thigh contraction.

MATERIALS AND METHODS

Eleven subjects underwent a magnetic resonance (MR) examination of the femoral-popliteal vasculature on a 1.5 T system. A custom 3D balanced steady-state free precession (SSFP) sequence was implemented to image a 15-20-cm segment of the vasculature during relaxation and voluntary isometric thigh contraction. The arterial and venous lumina were outlined using a semiautomated method. For the artery, this outline was fit to an ellipse whose aspect ratio was used to describe arterial deformation, while venous deformation was characterized by its cross-sectional area.

RESULTS

Focal compression of the femoral-popliteal artery during contraction was observed 94-143 mm superior to the condyle that corresponds to the distal adductor canal (AC) immediately superior to the adductor hiatus. This was illustrated by a significant reduction (P < or = 0.05) in aspect ratio from 0.88 +/- 0.06 during relaxation to 0.77 +/- 0.09 during contraction. A negligible change in arterial aspect ratio was observed inferior to the AC and in the proximal AC. Similarly, venous area was dramatically reduced in the distal AC region during contraction.

CONCLUSION

Rapid 3D SSFP MR angiography of the femoral-popliteal vasculature during thigh contraction demonstrated focal compression of the artery in the distal AC region. This may help explain the high stent failure rate and the high likelihood of atherosclerotic disease in the AC. J. Magn. Reson.

Inflow quantification in three-dimensional cardiovascular MR imaging

PURPOSE

To investigate blood inflow enhancement (or lack thereof) in three-dimensional (3D) cardiovascular MR for both single phase whole-heart and cine biventricular functions.

MATERIALS AND METHODS

A 3D imaging sequence is proposed in which radiofrequency excitation gradient is changed without modifying image acquisition or phase/slice encoding. This imaging sequence enables direct inflow measurement while retaining static voxel signal-to-noise ratio. Inflow measurements were performed for both spoiled gradient-echo (GRE) imaging and balanced steady-state free precession (SSFP) in 18 healthy subjects.

RESULTS

For single phase imaging, increasing slab thickness from 3 to 10 cm lead to 73% and 59% reductions in contrast-to-noise ratio (CNR) with GRE and SSFP, respectively. For cine acquisitions, systolic CNR was reduced by 85% and 50% for the GRE and SSFP acquisitions, respectively, while diastolic CNR was reduced by 64% and 42%.

CONCLUSION

There is significant loss of CNR between blood and myocardium when using larger 3D slabs due to saturation of inflowing spins. The loss of contrast is less pronounced for SSFP than for GRE, though both acquisition techniques suffer.

The vulnerable, or high-risk, atherosclerotic plaque: noninvasive MR imaging for characterization and assessment

"Vulnerable" plaques are atherosclerotic plaques that have a high likelihood to cause thrombotic complications, such as myocardial infarction or stroke. Plaques that tend to progress rapidly are also considered to be vulnerable. Besides luminal stenosis, plaque composition and morphology are key determinants of the likelihood that a plaque will cause cardiovascular events. Noninvasive magnetic resonance (MR) imaging has great potential to enable characterization of atherosclerotic plaque composition and morphology and thus to help assess plaque vulnerability. A classification for clinical, as well as pathologic, evaluation of vulnerable plaques was recently put forward in which five major and five minor criteria to define vulnerable plaques were proposed. The purpose of this review is to summarize the status of MR imaging with regard to depiction of the criteria that define vulnerable plaques by using existing MR techniques. The use of MR imaging in animal models and in human disease in various vascular beds, particularly the carotid arteries, is presented.

Reduction of flow- and eddy-currents-induced image artifacts in coronary magnetic resonance angiography using a linear centric-encoding SSFP sequence

Coronary magnetic resonance angiography (MRA) acquired using steady-state free precession (SSFP) sequences tends to suffer from image artifacts caused by local magnetic field inhomogeneities. Flow- and gradient-switching-induced eddy currents are important sources of such phase errors, especially under off-resonant conditions. In this study, we propose to reduce these image artifacts by using a linear centric-encoding (LCE) scheme in the phase-encoding (PE) direction. Abrupt change in gradients, including magnitude and polarity between consecutive radiofrequency cycles, is minimized using the LCE scheme. Results from numeric simulations and phantom studies demonstrated that signal oscillation can be markedly reduced using LCE as compared to conventional alternating centric-encoding (ACE) scheme. The image quality of coronary arteries was improved at both 1.5 and 3.0 T using LCE compared to those acquired using ACE PE scheme (1.5 T: ACE/LCE=2.2+/-0.8/3.0+/-0.6, P=.02; 3.0 T: ACE/LCE=2.1+/-1.1/3.0+/-0.8, P=.01). In conclusion, flow- and eddy-currents-induced imaging artifacts in coronary MRA using SSFP sequence can be markedly reduced with LCE acquisition of PE lines.

Whole heart coronary magnetic resonance angiography for the detection of coronary artery stenosis and atherosclerotic coronary artery plaque in a patient with unstable angina

Whole heart coronary magnetic resonance angiography (MRA) has been established as a totally noninvasive diagnostic modality for the assessment of coronary artery disease. We report a case with unstable angina, in whom coronary artery stenosis with an atherosclerotic plaque was detected by whole heart coronary MRA. Intravascular ultrasound in the stenotic lesion revealed a soft plaque containing focal calcification, corresponding to a low-signal mass containing a no-signal mass on MRA. Whole heart coronary MRA can become a useful diagnostic tool for the diagnosis of acute coronary syndrome.

Coronary Magnetic Resonance Imaging

This article highlights the technical challenges and general imaging strategies for coronary MRI. This is followed by a review of the clinical results for the assessment of anomalous CAD, coronary artery aneurysms, native vessel integrity, and coronary artery bypass graft disease using the more commonly applied MRI methods. It concludes with a brief discussion of the advantages/disadvantages and clinical results comparing coronary MRI with multidetector CT (MDCT) coronary angiography.

MRI of the coronary vessel wall at 3 T: comparison of radial and cartesian k-space sampling

OBJECTIVE

The purpose of our study was to compare the quality of 3D gradient-echo images obtained using radial versus cartesian k-space sampling at 3 T.

CONCLUSION

This study shows that the quality of coronary vessel wall imaging of the right coronary artery with radial k-space sampling in 3D turbo field-echo sequences is superior to cartesian k-space sampling at 3 T. Radial k-space sampling at 3 T makes it possible to combine low motion artifact susceptibility with high signal-to-noise ratio.

Whole-heart coronary vein imaging: A comparison between non-contrast-agent- and contrast-agent-enhanced visualization of the coronary venous system

The feasibility of three-dimensional (3D) whole-heart imaging of the coronary venous (CV) system was investigated. The hypothesis that coronary magnetic resonance venography (CMRV) can be improved by using an intravascular contrast agent (CA) was tested. A simplified model of the contrast in T(2)-prepared steady-state free precession (SSFP) imaging was applied to calculate optimal T(2)-preparation durations for the various deoxygenation levels expected in venous blood. Non-contrast-agent (nCA)- and CA-enhanced images were compared for the delineation of the coronary sinus (CS) and its main tributaries. A quantitative analysis of the resulting contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) in both approaches was performed. Precontrast visualization of the CV system was limited by the poor CNR between large portions of the venous blood and the surrounding tissue. Postcontrast, a significant increase in CNR between the venous blood and the myocardium (Myo) resulted in a clear delineation of the target vessels. The CNR improvement was 347% (P < 0.05) for the CS, 260% (P < 0.01) for the mid cardiac vein (MCV), and 430% (P < 0.05) for the great cardiac vein (GCV). The improvement in SNR was on average 155%, but was not statistically significant for the CS and the MCV. The signal of the Myo could be significantly reduced to about 25% (P < 0.001).

Coronary vessel-wall and lumen imaging using radial k-space acquisition with MRI at 3 Tesla

This study investigates the feasibility of imaging the coronary lumen and vessel-wall, using MRI with a radial k-space trajectory at 3 T. Such radial trajectories offer the advantage of greater vessel sharpness than traditional Cartesian trajectories. This field strength offers an increased signal-to-noise ratio (SNR) compared with 1.5 T, which compensates for the slight SNR reduction due to the radial sequence. Images of the coronary lumen were acquired for seven healthy volunteers. In ten volunteers the vessel wall was scanned, with blood suppression using oblique-slab adiabatic re-inversion. Scans were performed during free breathing, using prospective respiratory navigator-gating. Coronary lumen scans had SNR of 16.0+/-1.9 and contrast-to-noise ratio (CNR) of 10.3+/-2.1, showing acceptable image quality. Vessel wall images showed good image quality, with mean SNR of 16.6+/-2.0/5.8+/-2.8/10.1+/-2.2 for vessel wall/lumen/epicardial fat. The wall-blood CNR was 10.7+/-2.7, and wall-fat CNR was 6.5+/-2.5. It is concluded that radial gradient-echo imaging at 3 T is a promising method for coronary vessel-wall imaging, and is also feasible for imaging the coronary lumen.

Coronary artery abnormalities after Kawasaki disease in an adult: depiction at whole heart coronary magnetic resonance angiography

Whole heart coronary magnetic resonance angiography (MRA) was performed in a 57-year-old man with a provisional diagnosis coronary artery aneurysm due to Kawasaki disease. MRA revealed aneurysms in the left anterior descending artery and the left circumflex artery. It also revealed stenosis in the left anterior descending artery and occlusion in the right coronary artery with a collateral vessel connecting between the proximal and distal sites of the occlusion.

3D MR coronary angiography: optimization of the technique and preliminary results

OBJECTIVE

Current clinical full MR angiography with multiple breathhold multiple thin slab acquisition (MTS) is difficult and arduous. This study describes the optimisation of the whole heart free - breathing balanced turbo field echo (B-TFE) protocol. A high-resolution image of the whole heart is produced in less or comparable time to MTS acquisition and allows for reconstruction afterwards to visualise the individual coronary arteries. The scan is easily performed because the volume has to be targeted only once.

DESIGN AND SETTING

Eighteen healthy adults without a history of cardiovascular disease underwent free-breathing 3D MR angiography with the B-TFE protocol. The whole-heart data set was reformatted in identical orientations in all subjects to visualise the major coronary arteries.

MAIN OUTCOME MEASURES

Vessel length, signal and contrast to noise ratio were determined and compared for each vessel.

RESULTS

Mean visible vessel lengths were 116 mm for the right, 102 mm for the left main and left descending and 76 mm for the left circumflex coronary artery. The average signal to noise ratio was 7.5 and contrast to noise ratio was 4.9. Because of the need for synchronised cardiac and respiratory triggering the coronaries could not be judged in 25% of the subjects.

CONCLUSIONS

The optimised B-TFE protocol had equal judgeability and vessels could be judged over longer contiguous distances compared to earlier implementations of the B-TFE protocol. We conclude whole heart free breathing navigator-gated and slice-tracked 3D coronary MR angiography with use of the adjusted B-TFE protocol is possible, but still suboptimal for clinical use.

Quantitative parameters of image quality in 64-slice computed tomography angiography of the coronary arteries

We explored quantitative parameters of image quality in consecutive patients undergoing 64-slice multi-detector computed tomography (MDCT) coronary angiography for clinical reasons. Forty-two patients (36 men, mean age 61 +/- 11 years, mean heart rate 63 +/- 10 bpm) underwent contrast-enhanced MDCT coronary angiography with a 64-slice scanner (Siemens Sensation 64, 64 mm x 0.6 mm collimation, 330 ms tube rotation, 850 mAs, 120 kV). Two independent observers measured the overall visualized vessel length and the length of the coronary arteries visualized without motion artifacts in curved multiplanar reformatted images. Contrast-to-noise ratio was measured in the proximal and distal segments of the coronary arteries. The mean length of visualized coronary arteries was: left main 12 +/- 6 mm, left anterior descending 149 +/- 25 mm, left circumflex 89 +/- 30 mm, and right coronary artery 161 +/- 38 mm. On average, 97 +/- 5% of the total visualized vessel length was depicted without motion artifacts (left main 100 +/- 0%, left anterior descending 97 +/- 6%, left circumflex 98 +/- 5%, and right coronary artery 95 +/- 6%). In 27 patients with a heart rate < or = 65 bpm, 98 +/- 4% of the overall visualized vessel length was imaged without motion artifacts, whereas 96+/-6% of the overall visualized vessel length was imaged without motion artifacts in 15 patients with a heart rate > 65 bpm (p < 0.001). The mean contrast-to-noise ratio in all measured coronary arteries was 14.6 +/- 4.7 (proximal coronary segments: range 15.1 +/- 4.4 to 16.1 +/- 5.0, distal coronary segments: range 11.4 +/- 4.2 to 15.9 +/- 4.9). In conclusion, 64-slice MDCT permits reliable visualization of the coronary arteries with minimal motion artifacts and high CNR in consecutive patients referred for non-invasive MDCT coronary angiography. Low heart rate is an important prerequisite for excellent image quality.

Fr�hdiagnostik der funktionell relevanten koronaren Herzerkrankung

In cases of stable or to a large extent symptom-free coronary heart disease (CHD) and atypical symptomatology, the indication for diagnostic cardiac catheterization is first confirmed by noninvasive diagnostics of ischemia. This can be carried out either with ergometric stress tests or imaging procedures in combination with ergometric or pharmacological stress. Myocardial scintigraphy and stress echocardiography are established techniques and to an increasing extent stress magnetic resonance imaging (MRI). In addition to sensitivity in providing evidence for ischemia, technical improvements in computed tomography (CT) and MRI have opened up new possibilities for visualizing coronary vessels and vascular wall morphology. While CT coronary angiography with its high spatial resolution is on the threshold of clinical application for selected patients, MRI has the potential for furnishing information on wall movement analysis, perfusion, coronary flow measurement, and plaque characterization to become the future cardiovascular "all-round examination".