Coronary MR angiography with steady-state free precession: individually adapted breath-hold technique versus free-breathing technique

Denoising parameter dependence of coronary artery depictability in compressed sensing magnetic resonance angiography

Using numerical indices and visual evaluation, we evaluated the dependence of coronary-artery depictability on the denoising parameter in compressed sensing magnetic resonance angiography (CS-MRA). This study was conducted to clarify the acceleration factor (AF) and denoising factor (DF) dependence of CS-MRA image quality. Vascular phantoms and clinical images were acquired using three-dimensional CS-MRA on a clinical 1.5 T system. For the phantom measurements, we compared the full width at half maximum (FWHM), sharpness, and contrast ratio of the vascular profile curves for various AFs and DFs. In the clinical cases, the FWHM, sharpness, contrast ratio, signal-to-noise ratio, noise level values, and visual evaluation results were compared for various DFs. Phantom image analyses demonstrated that the respective measurements of the FWHM, sharpness, and contrast ratios did not significantly change with an increase in AF. The FWHM and sharpness measurements slightly changed with the DF level. However, the contrast ratio tended to increase with an increase in the DF level. In the clinical cases, the FWHM and sharpness showed no significant differences, even when the DF level was changed. However, the contrast ratio tended to decrease as the DF level increased. When the DF levels of the clinical cases increased, the background signals of the myocardium, fat, and noise levels decreased. We investigated the dependence of the coronary-artery depictability on AF and DF using CS-MRA. Analysis of the coronary-artery profile curves indicated that a better image quality was achieved with a stronger DF on coronary CS-MRA.

Quantitative evaluation of coronary artery visibility on CT angiography in Kawasaki disease: young vs. old children

Coronary artery visibility on coronary CT angiography has rarely been investigated in young children with Kawasaki disease. This retrospective study was performed to quantitatively evaluate and compare coronary artery visibility with sufficient quality to measure it on coronary CT angiography among younger and older children with Kawasaki disease. Seventy-eight consecutive children with Kawasaki disease who underwent coronary CT angiography were divided into two groups: group 1 (age ≤ 6 years; n = 37) and group 2 (age > 6 years and < 18 years; n = 41). The visibility of the right coronary artery, left anterior descending artery, and left circumflex artery was quantitatively evaluated by dividing the length of the assessable coronary artery by the length of the corresponding groove, and compared between the two groups. The coronary artery visibility in group 1 was significantly lower than that in group 2 for the right coronary artery (77.8 ± 26.3% vs. 94.2 ± 13.6%, p < 0.002) and left anterior descending artery (54.8 ± 19.5% vs. 69.6 ± 21.3%, p < 0.003, but the difference was not significant for the left circumflex artery (43.7 ± 23.1% vs. 43.9 ± 26.7%, p > 0.9). In both groups, the visibility of the right coronary artery was the highest, followed by those of the left anterior descending artery and left circumflex artery. Compared with older children with Kawasaki disease, younger children with Kawasaki disease demonstrate significantly lower visibility of the right coronary artery and left anterior descending artery on coronary CT angiography. In contrast, the visibility of the left circumflex artery showed no significant difference between younger and older children with Kawasaki disease.

Contribution of cardiovascular magnetic resonance in the evaluation of coronary arteries

Cardiovascular magnetic resonance (CMR) allows the nonradiating assessment of coronary arteries; to achieve better image quality cardiorespiratory artefacts should be corrected. Coronary MRA (CMRA) at the moment is indicated only for the detection of abnormal coronary origin, coronary artery ectasia and/or aneurysms (class I indication) and coronary bypass grafts (class II indication). CMRA utilisation for coronary artery disease is not yet part of clinical routine. However, the lack of radiation is of special value for the coronary artery evaluation in children and women. CMRA can assess the proximal part of coronary arteries in almost all cases. The best results have been observed in the evaluation of the left anterior descending and the right coronary artery, while the left circumflex, which is located far away from the coil elements, is frequently imaged with reduced quality, compared to the other two. Different studies detected an increase in wall thickness of the coronaries in patients with type I diabetes and abnormal renal function. Additionally, the non-contrast enhanced T1-weighed images detected the presence of thrombus in acute myocardial infarction. New techniques using delayed gadolinium enhanced imaging promise the direct visualization of inflamed plaques in the coronary arteries. The major advantage of CMR is the potential of an integrated protocol offering assessment of coronary artery anatomy, cardiac function, inflammation and stress perfusion-fibrosis in the same study, providing an individualized clinical profile of patients with heart disease.

Separate pulmonary artery and vein magnetic resonance angiography by use of an arterial spin labeling method

A separate pulmonary vein (PV) is difficult to depict with the commonly used bright-blood magnetic resonance angiography method. Until now, no study has described the depiction of peripheral PVs without the artery. Our purpose in this study was to develop an arterial spin labeling (ASL)-based magnetic resonance angiography sequence to depict the pulmonary artery (PA) and vein separately. We developed such a sequence by using two inversion recovery pulses. The first pulse was non-selective, and the second pulse was selective and was applied to the aorta and heart. All studies were conducted on a 1.5-T clinical magnetic resonance system with six different inversion times for seven healthy volunteers. For evaluation, we categorized the inversion times by using visual scoring. Then, we used the magnitude image to evaluate the PA, and we used the real image to evaluate the PV. For the PA, an inversion time of 300 ms had the lowest score (1.43), and the score changed with increasing times; an inversion time of 1,100 ms had the highest score (3.85). For the PV, an inversion time of 300 ms had the highest score (2.68), and the score decreased with increasing times. The results indicated that the PA and vein could be depicted separately by the use of an ASL-based magnetic resonance angiography method. The optimal inversion times for the PV and artery were 300 and 1,100 ms, respectively.

Automatic calibration of trigger delay time for cardiac MRI

This study aimed to automatically identify the cardiac rest period using a rapid free-breathing (FB) calibration scanning procedure, and to determine the optimal trigger delay for cardiac imaging. A standard deviation (SD) method was used to rapidly identify cardiac quiescent phases employing multiphase cine cardiac images. The accuracy of this method was investigated using 46 datasets acquired from 22 healthy volunteers. The possibility of using a low-resolution FB method to rapidly acquire cine images was also evaluated. The reproducibility and accuracy of the trigger delay obtained using the rapid calibration scanning process were assessed before its application to a real-time feedback system. The real-time trigger delay calibration system was then used to perform T1 -weighted, short-axis imaging at the end of the cardiac systolic period. Linear regression analysis of the trigger times obtained using the SD method and a reference method indicated that the SD algorithm accurately identified the cardiac rest period (linear regression: slope = 0.94-1, R(2)  = 0.68-0.84). Group analysis showed that the number of pixels in the left ventricular blood pool in images acquired at the end-systolic time calculated in real time was significantly lower than in those acquired 50 ms in advance or later (p < 0.01, paired t-test). The low-resolution FB imaging method was reproducible for the calibration scanning of an image in a vertical long-axis slice position (average SD of trigger times, 16-39 ms). Combined with rapid FB calibration scanning, the real-time feedback system accurately adjusted the trigger delay for T1 -weighted short-axis imaging. The real-time feedback method is rapid and reliable for trigger time calibration, and could facilitate cardiac imaging during routine examination.

Advances in cardiac magnetic resonance imaging and computed tomography

Imaging evaluation of the heart encompasses structural evaluation of the chambers, valves and coronary arteries, and functional evaluation, including assessment of perfusion, wall motion and myocardial viability. Magnetic resonance imaging is well established for the structural and functional evaluation of the heart, and benefits from direct multiplanar image acquisition and a lack of ionizing radiation. Magnetic resonance imaging assessment of myocardial viability after myocardial infarction appears to be helpful in predicting benefit from revascularization procedures. Magnetic resonance imaging continues to hold promise as the least invasive method of coronary artery evaluation, and continuing developments are improving image quality and decreasing examination time. The development of cardiac-gating techniques for multidetector computed tomography has the potential to provide widespread availability of cardiac computed tomography. Short examination times and straightforward scanning procedures promise a convenient method for the examination of cardiac structure and function. However, this convenience must be balanced against radiation dose and contrast-media requirements when determining the appropriate use of cardiac computed tomography. Computed tomography coronary-calcium scoring can aid in the prediction of significant coronary events in all but the lowest-risk patients. The high negative-predictive value of computed tomography coronary angiography may allow some patients to avoid cardiac catheterization, but its role in the assessment of patients with moderate coronary atherosclerosis remains unclear. New software tools can assist in the complex and tedious analysis of the large volumes of data produced by these examinations.

Imaging characteristics of cardiac dominant diffuse large B-cell lymphoma demonstrated with MDCT and PET/CT

PURPOSE

To investigate the specific imaging findings of multidetector row CT (MDCT) and PET/CT with(18)F-FDG in cardiac dominant diffuse large B-cell lymphoma (DLBCL) in comparison with other cardiac tumours.

METHODS

Five patients with DLBCL and 12 patients with other cardiac tumours including pericardial tumours were retrospectively reviewed. Among the patients with other cardiac tumours, seven had metastatic tumours, three had benign tumours, and two had other malignant cardiac tumours. The location of the cardiac mass, the encasement of the coronary artery surrounded by the mass, and pericardial effusion were evaluated using MDCT. The disease activity of the cardiac tumour was also evaluated by PET/CT.

RESULTS

Four of the five DLBCL patients had primarily right-sided cardiac lesions, which was seen significantly more frequently in DLBCL than in other cardiac tumours (p = 0.028). All cardiac DLBCL lesions were located around the atrioventricular groove and encased the coronary arteries. ECG-gated cardiac MDCT showed that there was no apparent stenosis of the coronary arteries. Large amounts of pericardial effusion were seen in all DLBCL patients. PET/CT revealed significantly higher FDG uptake in DLBCL than in other cardiac malignant tumours, with no overlap (p = 0.0007).

CONCLUSION

The combination of a right-sided cardiac mass with a large pericardial effusion and no apparent stenosis of the encased coronary artery revealed by MDCT and a high maximum standard uptake value were the specific findings in cardiac dominant DLBCL.

Magnetic resonance coronary angiography: where are we today?

Although cardiovascular magnetic resonance allows the non-invasive and radiation free visualization of both the coronary arteries and veins, coronary vessel wall imaging is still undergoing technical development to improve diagnostic quality. Assessment of the coronary vessels is a valuable addition to the analysis of cardiac function, cardiac anatomy, viability and perfusion which magnetic resonance imaging reliably allows. However, cardiac and respiratory motion and the small size of the coronary vessels present a challenge and require several technical solutions for image optimization. Furthermore, the acquisition protocols need to be adapted to the specific clinical question. This review provides an update on the current clinical applications of cardiovascular magnetic resonance coronary angiography, recent technical advances and describes the acquisition protocols in use.

Comparison of three-dimensional volume-targeted thin-slab FIESTA magnetic resonance angiography and 64-multidetector computed tomographic angiography for the identification of proximal coronary stenosis

BACKGROUND

Based on recent clinical data, an imaging strategy of identifying proximal coronary disease allows further management decisions in patients with stable angina pectoris. We aimed to compare diagnostic accuracy of non-contrast fast steady-state (FIESTA) magnetic resonance angiography (MRA) with 64-multidetector computed tomographic angiography (CTA), using conventional coronary angiography (CA) as the reference standard.

METHODS

Thirty patients with suspected coronary artery disease consented to participate in an institutional review board-approved protocol. Coronary MRA was performed at 1.5 T using a respiratory navigator and electrocardiogram-gated three-dimensional FIESTA pulse sequence. CTA images were acquired using a 64-multidetector computed tomographic scanner, using beta blockade to reduce the heart rate to less than 70 bpm. Coronary luminal stenosis >50% was identified. Plaques were classified as non-calcified, mixed, or calcified on CTA, and as high-, intermediate-, or low-signal on FIESTA MRA.

RESULTS

Compared to CA, the sensitivity, specificity, and overall accuracy for detection of >50% proximal coronary stenoses were 83.0%, 86.9%, and 86.1% for MRA and 85.1%, 87.2%, and 86.8% for CTA, respectively. For the 24 calcified stenoses, MRA corrected 16 segments that overestimated on CTA and MRA had an accuracy of 75% in evaluating calcified plaques.

CONCLUSIONS

High-resolution three-dimensional FIESTA MRA and CTA have a similar accuracy in detecting proximal coronary stenosis. The clinical impact of identification of proximal disease in patients with stable CAD needs to be examined in future studies.

Coronary imaging with cardiovascular magnetic resonance: current state of the art

Cardiovascular magnetic resonance allows noninvasive and radiation-free visualization of both the coronary arteries and veins, with the advantage of an integrated assessment of cardiac function, viability, perfusion, and anatomy. This combined approach provides valuable integrated information for patients with coronary artery disease and patients undergoing cardiac resynchronization therapy. Moreover, magnetic resonance offers the possibility of coronary vessel wall imaging, therefore assessing the anatomy and pathology of the normal and diseased coronary vessels noninvasively. Coronary magnetic resonance angiography is challenging because of cardiac and respiratory motion and the small size and tortuous path of the coronary vessels. Several technical solutions have been developed to optimize the acquisition protocol to the specific clinical question. The aims of this review are to provide an update on current technical improvements in coronary magnetic resonance angiography, including how to optimize the acquisition protocols, and to give an overview of its current clinical application.

Diagnostic accuracy of contrast-enhanced MR angiography and unenhanced proton MR imaging compared with CT pulmonary angiography in chronic thromboembolic pulmonary hypertension

OBJECTIVE

To evaluate the diagnostic accuracy of contrast-enhanced MR angiography (CE-MRA) and the added benefit of unenhanced proton MR angiography compared with CT pulmonary angiography (CTPA) in patients with chronic thromboembolic disease (CTE).

METHODS

A 2 year retrospective study of 53 patients with chronic thromboembolic pulmonary hypertension who underwent CTPA and MRI for suspected pulmonary hypertension and a control group of 36 patients with no CT evidence of pulmonary embolism. The MRI was evaluated for CTE and the combined diagnostic accuracy of ce-MRA and unenhanced proton MRA was determined. CE-MRA generated lung perfusion maps were also assessed.

RESULTS

The overall sensitivity and specificity of CE-MRA in diagnosing proximal and distal CTE were 98% and 94%, respectively. The sensitivity improved from 50% to 88% for central vessel disease when CE-MRA images were analysed with unenhanced proton MRA. The CE-MRA identified more stenoses (29/18), post-stenosis dilatation (23/7) and occlusions (37/29) compared with CTPA. The CE-MRA perfusion images showed a sensitivity of 92% for diagnosing CTE.

CONCLUSION

CE-MRA has high sensitivity and specificity for diagnosing CTE. The sensitivity of CE-MRA for visualisation of adherent central and lobar thrombus significantly improves with the addition of unenhanced proton MRA which delineates the vessel wall.

Coronary MR imaging: lumen and wall

Coronary MR imaging is a promising noninvasive technique for the combined assessment of coronary artery anatomy and function. Anomalous coronary arteries and aneurysms can reliably be assessed in clinical practice using coronary MR imaging and the presence of significant left main or proximal multivessel coronary artery disease detected. Technical challenges that need to be addressed are further improvements in motion suppression and abbreviated scanning times aimed at improving spatial resolution and patient comfort. The development of new and specific contrast agents, high-field MR imaging with improved spatial resolution, and continued progress in MR imaging methods development will undoubtedly lead to further progress toward the noninvasive and comprehensive assessment of coronary atherosclerotic disease.

Feasibility of navigator setting on the left diaphragm for whole-heart coronary MRA: a study in healthy volunteers

PURPOSE

We prospectively compared the quality of images obtained by navigator setting on the left and right diaphragm on whole-heart coronary magnetic resonance angiography (WHCMRA).

METHODS

In 10 healthy volunteers, we performed free-breathing, 3-dimensional segmented true fast imaging with steady-state precession (trueFISP) WHCMRA by setting the navigator on the left and right diaphragm in random order. For the left diaphragm, we set the navigator outside the scope of the heart to avoid the influence on coronary arteries. We compared image acquisition time and visible length of coronary arteries using paired t-test and subjective image quality on a 4-point scale (1, poor; 4, excellent) using Wilcoxon signed-rank test.

RESULTS

Mean overall subjective image quality was significantly better in the left diaphragm than the right (3.3+/-0.7 versus 2.9+/-0.9, P=0.02). Mean overall visible length of the coronary arteries was significantly better in the left diaphragm than the right (115.4+/-31.1 vs. 112.6+/-29.9 mm, P=0.02). Mean acquisition time between the left and right diaphragm was not significantly different (15.6+/-5.0 versus 16.0+/-5.7 min, P=0.79).

CONCLUSION

In this small group of healthy volunteers, navigator setting for WHCMRA was superior on the left diaphragm than the right; however, feasibility of the technique requires additional consideration in a larger group of actual patients.

Coronary MR imaging: navigator echo biofeedback increases navigator efficiency--initial experience

RATIONALE AND OBJECTIVES

The aim of this study was to investigate whether a respiratory biofeedback system could increase navigator efficiency and maintain image quality compared to conventional respiratory-gated magnetic resonance coronary angiography (MRCA).

MATERIALS AND METHODS

Eighteen healthy volunteers underwent MRCA using three different respiratory-gating protocols. A conventional expiratory free-breathing (FB) sequence was compared to two approaches using navigator echo biofeedback (NEB), a midinspiratory approach (NEBin) and an expiratory approach (NEBex). Navigator data reflecting the position of the diaphragm relative to a 3-mm gating window were made available to the subject using a video projector in combination with a Plexiglas screen and mirror goggles. Image quality was graded by two radiologists in consensus using a visual score ranging from 1 (not visible) to 4 (excellent vessel depiction).

RESULTS

The NEB approaches improved navigator efficiency (71.1% with NEBex and 68.0% with NEBin vs 42.2% with FB), thus reducing total imaging time. This difference was statistically significant (P(NEBin)=.007; P(NEBex)=.001). Image quality in the NEBex group was comparable to that in the FB group (median score, 2.44 vs 2.52), but it proved to be significantly lower (median score, 1.94 vs 2.52) for the right coronary artery and the left anterior descending coronary artery in the NEBin group.

CONCLUSION

NEB maintains image quality and significantly increases navigator efficiency, thereby decreasing total imaging time by about 40% compared to a conventional FB acquisition strategy.

[Comparison of 3 Tesla whole heart coronary MRA (WHCA) with 1.5 Tesla]

Whole heart coronary MRA (WHCA) is a noninvasive method used to image all coronary arteries with cardiac and real-time respiratory gating. We compared the coronary depiction ability of 3T WHCA with that of 1.5T using healthy volunteers. In addition, we compared the study performance rate, which might differ at 3T and 1.5T due to the difference in specific absorption rate (SAR) limits. The coronary artery was classified into nine segments, based on the classification of the American Heart Association (AHA). Each observer was asked to evaluate WHCA with the three-point scale rating for each segment, and to measure the visible length of each coronary artery utilizing reconstructed CPR and VR images. Depiction at 3T was superior to that at 1.5T. The completion rate of study was 100% at 1.5T, but just 63% at 3T owing to SAR limits. Thus it was suggested that 3T WHCA might be feasible with the advantage of high depiction ability, if adequate SAR reduction techniques were developed.

Compression belt for navigator-triggered trueFISP whole-heart coronary magnetic resonance angiography: study in healthy volunteers

PURPOSE

To evaluate in healthy volunteers the usefulness of an abdominal compression belt in reducing acquisition time by stabilizing respiratory motion during whole-heart coronary magnetic resonance angiography (WHCMRA) using conventional navigator triggering.

METHODS

In 10 healthy volunteers, we performed free-breathing 3-dimensional segmented true fast imaging with steady-state precession (trueFISP) WHCMRA using conventional navigator triggering without motion-adapted gating. We acquired images with the abdominal compression belt rolled tightly around the upper abdomen and without the belt. We compared image acquisition time, navigator efficiency, and visible length of coronary arteries using paired t-test and subjective image quality on a 4-point scale (1, poor; 4, excellent) using Wilcoxon signed-rank test.

RESULTS

There were no statistically significant differences for mean acquisition time (11.5+/-5.0 vs. 9.3+/-2.4 min, P=0.150); navigator efficiency (38.7+/-13.6 vs. 42.8+/-11.0%, P=0.336); mean overall visible length of the coronary arteries (99.7+/-22.7 vs. 105.0+/-16.5 mm, P=0.530); or mean overall subjective image quality (2.5 vs. 2.7, P=0.297) between results obtained with and without the abdominal compression belt.

CONCLUSION

In this small group of healthy volunteers, the use of an abdominal compression belt did not reduce image acquisition time or improve image quality in trueFISP WHCMRA using conventional navigator triggering; however, the technique's feasibility requires additional consideration using other navigator-triggering methods for patients with irregular respiratory cycles.

Nonenhanced MR angiography

While nonenhanced magnetic resonance (MR) angiographic methods have been available since the earliest days of MR imaging, prolonged acquisition times and image artifacts have generally limited their use in favor of gadolinium-enhanced MR angiographic techniques. However, the combination of recent technical advances and new concerns about the safety of gadolinium-based contrast agents has spurred a resurgence of interest in methods that do not require exogenous contrast material. After a review of basic considerations in vascular imaging, the established methods for nonenhanced MR angiographic techniques, such as time of flight and phase contrast, are considered and their advantages and disadvantages are discussed. This article then focuses on new techniques that are becoming commercially available, such as electrocardiographically gated partial-Fourier fast spin-echo methods and balanced steady-state free precession imaging both with and without arterial spin labeling. Challenges facing these methods and possible solutions are considered. Since different imaging techniques rely on different mechanisms of image contrast, recommendations are offered for which strategies may work best for specific angiographic applications. Developments on the horizon include techniques that provide time-resolved imaging for assessment of flow dynamics by using nonenhanced approaches.

Cardiovascular MRI: its current and future use in clinical practice

Cardiovascular magnetic resonance (CMR) imaging is a comprehensive clinical tool for assessing a large variety of cardiovascular diseases. Using the clinical service of the Duke Cardiovascular Magnetic Resonance Center as an example, we describe how to perform image contractile function, myocardial perfusion at stress and rest, myocardial viability, cardiovascular morphology, vascular anatomy and blood flow tests. The emergence of successful dedicated CMR services presents an opportunity to optimize patient throughput by streamlining the user interface of CMR scanners, standardizing the viewing format and reporting software, and customizing training programs to focus on the standardized CMR approaches. Accordingly, we discuss potential pathways to create these standards. Finally, we discuss several promising new CMR techniques we expect will complement existing clinical procedures.

[Magnetic resonance imaging for the assessment of myocardial perfusion: value of various semiquantitative perfusion parameters]

PURPOSE

The aim of this study was to determine the diagnostic accuracy of various semiquantitative perfusion parameters of the magnetic resonance perfusion examination of the myocardium compared to conventional coronary angiography.

PATIENTS, MATERIAL AND METHODS

Twenty patients with suspicion of coronary artery disease who underwent coronary angiography were examined by MR imaging within 14 days before or after coronary angiography. A perfusion examination during adenosine application (140 microg/kg/min) and at rest was performed using a saturation recovery turboFLASH sequence. The semi-quantitative parameters maximum signal intensity (SIM), time-to-peak (TTP), area under the curve (AUC) and upslope (US) were determined using dedicated software (Dynamic Signal Analysis, ARGUS, Siemens Medical Solutions) for the evaluation of the signal-intensity-time curves. In addition, the ratio of these parameters (MPRI: myocardial perfusion reserve index) were determined by dividing the values of the stress examination by the values of the rest examination.

RESULTS

Accuracy was 78.4% (SIM), 64.9% (TTP), 64.2% (AUC) and 70.4% (US) for the evaluation of the stress examination. Accuracy for the MPRI of the semi-quantitative parameters was 72.2% (SIM), 50.9% (TTP), 72.2% (AUC) und 89.1% (US).

CONCLUSION

A combined semi-quantitative evaluation of the MPRI values using the ratio of the upslope values of the stress and rest examination was shown to be the most accurate method. MPRI (US(Stress)/US(Rest)) is superior to an evaluation of the stress examination alone.

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.

Magnetic resonance imaging for ischemic heart disease

Cardiac MRI has long been recognized as an accurate and reliable means of evaluating cardiac anatomy and ventricular function. Considerable progress has been made in the field of cardiac MRI, and cardiac MRI can provide accurate evaluation of myocardial ischemia and infarction (MI). Late gadolinium (Gd)-enhanced MRI can clearly delineate subendocardial infarction, and the assessment of transmural extent of infarction on late enhanced MRI has been shown to be useful in predicting functional recovery of dysfunctional myocardium in patients after MI. Stress first-pass contrast-enhanced (CE) myocardial perfusion MRI can be used to detect subendocardial ischemia, and recent studies have demonstrated the high diagnostic accuracy of stress myocardial perfusion MRI for detecting significant coronary artery disease (CAD). Free-breathing, whole-heart coronary MR angiography (MRA) was recently introduced as a method that can provide visualization of all three major coronary arteries within a single three-dimensional (3D) acquisition. With further improvements in MRI techniques and the establishment of a standardized study protocol, cardiac MRI will play a pivotal role in managing patients with ischemic heart disease.

Improved bulk myocardial motion suppression for navigator-gated coronary magnetic resonance imaging

PURPOSE

To evaluate the impact of a new, cross-correlation based method for compensation of respiratory induced motion of the heart using an individually adapted three-dimensional (3D) translation or affine transformation approach.

MATERIALS AND METHODS

A total of 32 patients underwent a routine cardiac MR examination. In each patient, a calibration scan was performed during free-breathing to register breathing-related motion within a 3D ellipsoid registration kernel covering the entire heart. Three navigators were employed for all three spatial dimensions (feet-head, anterior-posterior, and left-right) and the optimal translatory correction factors for each spatial dimension were determined. In addition, the cross-correlations for different motion models (no compensation, fixed 1D-translation, adapted 3D-translation, and affine transformation) were calculated.

RESULTS

The mean correction factor for the feet-head direction was 0.45 +/- 0.13. Though the mean correction factors for the anterior-posterior and left-right direction were nearly zero (-0.01 +/- 0.08 and 0.02 +/- 0.09, respectively), the correction factors exceeded the amount of 0.1 in 12 (19%) and in 19 patients (30%), respectively. All motion compensation models showed significantly higher cross-correlations when compared to "no compensation" (P < 0.05). In particular, the affine transformation algorithm achieved the highest cross-correlation values (88.3 +/- 5.1%) with a significant increase compared to fixed 1D translation (84.7 +/- 6.5%, P < 0.05).

CONCLUSION

A considerable number of patients demonstrated relevant breathing-related movement of the heart in the anterior-posterior or left-right direction in addition to the predominant breathing-related movement in the feet-head direction. Thus, it is recommended to compensate for all three spatial dimensions. The affine transformation algorithm combined with three navigators significantly improved breathing-related cardiac motion compensation when compared to the conventionally applied 1D translation with a fixed correction factor.

Evaluation of three-dimensional navigator-gated whole heart MR coronary angiography: The importance of systolic imaging in subjects with high heart rates

PURPOSE

To evaluate the influence of heart rate (HR) on magnetic resonance coronary angiography (MRCA) image quality in diastolic and systolic phases.

MATERIALS AND METHODS

Twenty-seven healthy volunteers (9 men; 33+/-9 years, HR 53-110 bpm), were evaluated with the electrocardiography and three-dimensional navigator-gating MRCA in a 1.5-T MR scanner (Avanto, Siemens) in diastolic and systolic phases (steady-state free precession; TR/TE/flip angle=3.2 ms/1.6 ms/90 degrees). The timing of scanning was individually adapted to the cardiac rest periods obtained in the prescanning, by visually identifying when the movement of right coronary artery was minimized during diastole and systole. Images of two phases were side-by-side compared on a four-point scale (from 1=poor to 4=excellent visibility; score of 3 or 4 as diagnostic).

RESULTS

Of 13 subjects with HR < or =65 bpm (low HR group, mean 59.8+/-4.9 bpm, range 53-65), the image quality scores were significantly better than that with higher heart rates (73.9+/-9.0 bpm, range 68-110) in diastolic MRCA. The image quality was significantly improved during systole in high HR group. Overall, 91.3% of low HR group had MRCA image of diagnostic quality acquired at diastole, while 88.3% of high HR group had diagnostic images at systole by segmental analysis (p=NS).

CONCLUSIONS

MRCA at systole offered superior quality in patients with high heart rates.

Clinical implication of adenosine-stress cardiac magnetic resonance imaging as potential gatekeeper prior to invasive examination in patients with AHA/ACC class II indication for coronary angiography

BACKGROUND

Real world cardiology is faced with a low diagnostic yield of coronary angiography (CXA) in patients presenting with ACC/AHA class II CXA indication. Our aim was to analyze the clinical implication of a Cardiac MR (CMR) protocol including adenosine stress perfusion in this patient population. We examined whether CMR could enhance appropriate CXA indication and thus reduce the rate of pure diagnostic CXA. In addition, we compared the relative impact of CMR exam components (perfusion, function and viability assessment) in achieving this target.

METHODS

176 patients were referred for CXA with class II indication. 171 underwent complete additional CMR exam in a 1.5-T whole body CMR-scanner for myocardial function, ischemia and viability prior to CXA. The routine protocol for assessment of CAD consisted of functional imaging (long and short axes), adenosine stress- and rest-perfusion in short axis orientation and "late enhancement" imaging in long and short axes. Images were analyzed by two independent and blinded investigators. Interobserver differences were resolved by a third reader.

RESULTS

There was a high association between CMR results and subsequent invasive findings (chi square for CMR perfusion deficit and stenosis >70% in CXA: 113.7, p<0.0001). 109 (63.7%) of our patients had relevant perfusion deficits as seen by CMR and matching coronary artery stenosis >70%. Four (2.3%) patients had false negative CMR findings. In 58 patients (33.9%) no relevant coronary artery stenosis could be observed, correctly predicted by CMR in 48 cases; in 10 (5.8%) patients CMR provided false positive results. Sensitivity of CMR to detect relevant CAD (>70% luminal narrowing) was 0.96, specificity 0.83, positive predictive value 0.92 and negative predictive value 0.92. Of the CMR components, perfusion deficit was the strongest independent predictor (odds ratio 132.3, p < 0.0001).

CONCLUSION

In a great number of patients being referred to cath lab with ACC/AHA class II indication for CXA, CMR provides a high accuracy for decision making regarding appropriateness of the invasive exam. CMR prior to CXA could substantially reduce pure diagnostic coronary angiographies in patients with intermediate probability for CAD, in our patient-cohort from approximately 34% to 6%. Further studies are warranted to identify rare false negative CMR results.

Imaging of atherosclerosis using magnetic resonance: state of the art and future directions

Atherosclerosis is the leading cause of morbidity and mortality in industrialized societies, and its incidence is projected to increase in the future. Because the atherosclerotic process begins in the vessel wall, the focus of cardiovascular imaging is shifting from the arterial lumen to imaging of the vessel wall, with the goal of detecting preclinical atherosclerosis. MRI, because of its high resolution, three-dimensional capabilities, noninvasive nature, and capacity for soft tissue characterization, is emerging as an important modality to assess the atherosclerotic plaque burden in the arterial wall and can monitor atherosclerosis in different arterial beds, including the carotid arteries, aorta, and more recently, the coronary arteries. Furthermore, it has also been successfully utilized to monitor plaque regression following therapeutic interventions. Finally, the emergence of high-resolution MRI and development of sophisticated contrast agents offers tremendous promise for in vivo molecular imaging of the atherosclerotic plaque.

Breath-hold 3D steady-state free precession coronary MRA compared with conventional X-ray coronary angiography

PURPOSE

To evaluate the use of breath-hold three-dimensional (3D) steady-state free precession (SSFP) coronary magnetic resonance angiography (MRA) in patients with coronary artery disease (CAD) in comparison with conventional coronary x-ray angiography (XRA).

MATERIALS AND METHODS

Twenty-eight patients with suspected CAD were examined with the use of a breath-hold 3D-SSFP-MRA sequence and conventional XRA. To assess the accuracy of MRA, two clinicians who were blinded to patient information independently reviewed the MRA and XRA data, which were presented in a randomized order. To identify discrepancies between MRA and XRA, and assess features of coronary lesions on MRA, two additional clinicians examined MRA and XRA data that were presented side by side, divided into proximal, mid, and distal segments, and compared them segment by segment.

RESULTS

The sensitivity and specificity for diagnosing significant coronary stenoses (> 50% diameter narrowing) were 64% and 94%, respectively. At sites of coronary lesions identified on XRA, bright signals and enlarged vessel profiles, in addition to the characteristic narrow lumen, were frequently observed on MRA.

CONCLUSION

Breath-hold SSFP coronary MRA has good specificity but inconclusive sensitivity in diagnosing significant coronary stenoses, and provides important image features for depicting coronary lesions.

Coronary MR imaging: breath-hold capability and patterns, coronary artery rest periods, and beta-blocker use

PURPOSE

To prospectively evaluate breath-hold capability and patterns, coronary artery rest periods, and beta-blocker use in coronary magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Ethics committee approval and informed consent were obtained. In 210 consecutive patients (mean age, 61.8 years +/- 10.3 [standard deviation]; 146 men, 64 women), breath-hold patterns and maximal capability were assessed at expiration with dynamic navigator MR imaging (temporal resolution, 1 second). Left coronary artery (LCA) and right coronary artery (RCA) rest periods were determined at transverse cine imaging (steady-state free precession, retrospective gating, 40 phases per cycle). Before and after beta-blockade, rest periods were assessed in 25 additional patients (mean age, 61.4 years +/- 7.1; 20 men, five women). Differences were tested within groups with paired Student t test and between groups with unpaired Student t test (continuous variables) and chi(2) test (categoric variables). Pearson correlation was used to test the relationship between rest period and heart rate.

RESULTS

Four distinct breath-hold patterns, characterized by diaphragmatic motion, were identified: pattern 1, steady plateau (55% of patients); 2, initial drift followed by plateau (12%); 3, continuous drift (19%); and 4, irregular, unsteady behavior (14%). Mean breath-hold capability with patterns 1 and 2 was 29 seconds +/- 13 (range, 10-64 seconds). The rest period of LCA was longer than that of RCA (163 msec +/- 75 vs 123 msec +/- 60; P < .01) and began earlier in the cardiac cycle (521 msec +/- 149 vs 540 msec +/- 160; P < .01); In a minority of patients, LCA rest period began later (21%) or was shorter (14%). With no pharmacologic intervention, correlation between rest period duration and heart rate was weak (LCA, r = -0.52; RCA, r = -0.38; P < .01). However, beta-blockade significantly lowered heart rate (61.3 beats/min +/- 7.2 vs 82.6 beats/min +/- 12.5, P < .001) and increased rest duration (LCA, 201.8 msec +/- 83.6 vs 111.8 msec +/- 44.55; RCA, 134.8 msec +/- 57.3 vs 83.1 msec +/- 35.8; P < .001).

CONCLUSION

In 33% of patients (patterns 3 and 4), breath-hold pattern was unsuitable for high-spatial-resolution breath-hold MR imaging. LCA and RCA rest periods showed large variability in starting point and duration, with no correlation to heart rate.

Meta-analysis of comparative diagnostic performance of magnetic resonance imaging and multislice computed tomography for noninvasive coronary angiography

BACKGROUND

Magnetic resonance imaging (MRI) and multislice computed tomography (MSCT) have emerged as potential noninvasive coronary imaging techniques. The objective of the present study was to clarify the current accuracy of both modalities in the detection of significant coronary artery lesions (compared to conventional angiography as the gold standard) by means of a comprehensive meta-analysis of the presently available literature.

METHODS

A total of 51 studies on the detection of significant coronary artery stenoses (> or = 50% diameter stenosis) and comparing results with conventional angiography were identified by means of a MEDLINE search. Weighted sensitivities, specificities, and predictive values, all with 95% CIs, as well as summary odds ratios, were calculated for both techniques. In addition, the relationship between diagnostic specificity and disease prevalence was determined using metaregression analysis.

RESULTS

A comparison of sensitivities and specificities revealed significantly higher values for MSCT (weighted average 85% [95% CI 86%-88%] and 95% [95% CI 95%]) as compared with MRI (weighted average 72%, 95% CI 69%-75% and 87%, 95% CI 86%-88%). A significantly higher odds ratio (16.9-fold) for the presence of significant stenosis was observed for MSCT as compared with MRI (6.4-fold) (P < .0001). Linear regression analysis revealed a better specificity for MSCT versus MRI in lower disease prevalence populations (P = .056).

CONCLUSION

Meta-analysis of the available studies with MRI and MSCT for noninvasive coronary angiography indicates that MSCT has currently a significantly higher accuracy to detect or exclude significant coronary artery disease.

Kardio-MRT

With cardiovascular magnetic resonance imaging (CMR), the necessity of invasive coronary angiography may be increasingly avoided. CMR provides information about the anatomy of the coronaries themselves (e.g. anomalies, aneurysm), functional information on myocardial blood flow (dobutamine-stress-MR, perfusion measurement) and detailed information on cell-mediated alterations (e.g. fibrosis, necrosis). However, visualization of distal coronary vessels and the small side branches is not yet adequate, so that complete replacement of invasive coronary angiography by CMR is not possible.

Comprehensive assessment of patients after coronary artery bypass grafting by 16-detector-row computed tomography

BACKGROUND

Multidetector-row computed tomography (MDCT) is a versatile modality to evaluate stenoses in native coronary arteries and bypass grafts. Acquired MDCT data can additionally be used to assess left ventricular ejection fraction (LVEF). The purpose was to use MDCT for the assessment of bypass graft and coronary artery disease combined with evaluation of LVEF.

METHODS

Twenty-five patients underwent 16-detector-row CT examination and coronary angiography. Bypass grafts and nongrafted coronary artery segments at MDCT were evaluated on eligibility, patency, and > or = 50% stenosis. The MDCT data set was used to calculate LVEF and was divided into patients with no/subendocardial/transmural myocardial infarctions (MIs).

RESULTS

Ninety vessels were evaluated: 14 arterial grafts/53 vein grafts/23 nongrafted vessels. Of 225 segments, 17 were ineligible for evaluation because of metal clips. With MDCT, patency in segments of arterial grafts/vein grafts/nongrafted vessels could be evaluated with high accuracy in 100%/100%/97% of segments. In arterial grafts, stenoses > or = 50% did not occur at angiography, which was for all eligible segments correctly diagnosed at MDCT. Stenosis > or = 50% could be correctly detected by MDCT with a sensitivity/specificity of 100%/94% for vein grafts and 100%/89% for nongrafted vessels. Negative predictive value was 100% for vein grafts and nongrafted vessels. In patients with transmural MI, MDCT revealed a significant lower LVEF as compared with patients without or with subendocardial MI (P < .05).

CONCLUSION

Comprehensive assessment of bypass grafts, nongrafted vessels, and LVEF is feasible with MDCT. Owing to the high negative predictive value this noninvasive approach may be used as gatekeeper before coronary angiography.

Coronary magnetic resonance imaging: visualization of the vessel lumen and the vessel wall and molecular imaging of arteriothrombosis

Coronary magnetic resonance (MR) imaging has dramatically emerged over the last decade. Technical improvements have enabled reliable visualization of the proximal and midportion of the coronary artery tree for exclusion of significant coronary artery disease. However, current technical developments focus also on direct visualization of the diseased coronary vessel wall and imaging of coronary plaque because plaques without stenoses are typically more vulnerable with higher risk of plaque rupture. Plaque rupture with subsequent thrombosis and vessel occlusion is the main cause of myocardial infarction. Very recently, the first success of molecular imaging in the coronary arteries has been demonstrated using a fibrin-specific contrast agent for selective visualization of coronary thrombosis. This demonstrates in general the high potential of molecular MR imaging in the field of coronary artery disease. In this review, we will address recent technical advances in coronary MR imaging, including visualization of the lumen and the vessel wall and molecular imaging of coronary arteriothrombosis. First results of these new approaches will be discussed.

Rapid and complete coronary arterial tree visualization with magnetic resonance imaging: feasibility and diagnostic performance

AIMS

Current imaging of the coronary arteries with magnetic resonance coronary angiography (MRCA) is restricted to limited coverage of the coronary arterial tree and requires complex planning. We present and evaluate a rapid, single-scan MRCA approach with complete coverage of the coronary arterial tree.

METHODS AND RESULTS

Fifty-five consecutive patients with suspected coronary artery disease underwent free-breathing, navigator-gated MRCA using a single three-dimensional volume with transversal slice orientation and nearly isotropic spatial resolution (1.2 x 1.2 x 1.4 mm(3)) with coverage of the whole heart [steady-state free precession (SSFP); TR/TE/flip angle: 5.3 ms/2.6 ms/90 degrees ; Philips Intera CV 1.5T]. The acquisition duration per heart beat was individually adapted to the cardiac rest period. Correction of respiratory motion was done using a patient-specific affine prospective navigator technique (two navigator beams: cranio-caudal position on the dome of the right hemidiaphragm and anterior-posterior position on the right chest wall; gating window 10 mm). The diagnostic performance of MRCA in detecting significant coronary stenoses was evaluated against X-ray angiography as the standard of reference (32 patients) using a 16-segment model. Effective scan duration was 18+/-6 min (navigator efficiency: 68+/-14%). In all examinations, the main epicardial vessels [left anterior descending artery (LAD), left circumflex artery (LCX), and right coronary artery (RCA)], including their distal segments and major side branches (number of visible side branches: LAD, 2.0+/-0.9; LCX, 1.5+/-0.6; RCA, 2.3+/-0.9), were reliably visualized. Eighty-three per cent of all coronary segments were evaluable; sensitivity, specificity, and diagnostic accuracy were 78, 91, and 89%, respectively.

CONCLUSION

The combination of an imaging sequence with an intrinsically high contrast (SSFP) and a sophisticated navigator technique (affine transformation) resulted in high quality, high resolution imaging of the whole coronary arterial tree within a short examination duration. Robustness and diagnostic accuracy may allow for a routine application in the near future.