Navigator-gated free-breathing three-dimensional balanced fast field echo (TrueFISP) coronary magnetic resonance angiography

Cardiovascular Imaging: The Past and the Future, Perspectives in Computed Tomography and Magnetic Resonance Imaging

Today's noninvasive imaging of the cardiovascular system has revolutionized the approach to various diseases and has substantially affected prognostic information. Cardiovascular magnetic resonance (MR) and computed tomographic (CT) imaging are at center stage of these approaches, although 5 decades ago, these technologies were unheard of. Both modalities had their inception in the 1970s with a primary focus on noncardiovascular applications. The technical development of the various decades, however, substantially pushed the envelope for cardiovascular MR and CT applications. Within the past 10-15 years, MR and CT technologies have pushed each other in cardiac applications; and without the "rival" modality, neither one would likely not have reached its potential today. This view on the history of MR and CT in the field of cardiovascular applications provides insight into the story of success of applications that once have been ideas only but are at prime time today.

Non-contrast coronary artery wall and plaque imaging using inversion-recovery prepared steady-state free precession

Background

The objective of this study was to investigate whether three-dimensional (3D) single inversion-recovery prepared steady-state free precession (IR-SSFP) could characterize the coronary artery wall.

Methods

IR-SSFP was scanned on a 1.5-T MR scanner with a five element cardiac coil. One hundred and twenty-one subjects with known or suspected coronary artery disease who had undergone X-ray coronary angiography (XCA) underwent coronary artery wall imaging using IR-SSFP sequences. In each coronary segment, the detection of the coronary wall was categorized, and contrast (signal of plaque minus signal of blood in the aorta divided by the signal of plaque plus signal of blood in the aorta) was calculated.

Results

422 of 517 segments (82 %) were successfully visualized, and the detection scores tended to be higher at the proximal coronary artery when compared with other segments of the coronary artery. High contrast (contrast ≥ 0.75) areas were observed in 62 of 218 segments with ≥50 % coronary artery stenosis by XCA but also in 25 of 299 segments without ≥50 % coronary stenosis.

Conclusions

IR-SSFP provided good visualization of the coronary wall. This approach represents a promising noninvasive strategy for the assessment of the coronary artery wall.

Imaging pulmonary arterial thromboembolism: challenges and opportunities

Magnetic resonance (MR) angiography of the pulmonary arteries is a rapidly evolving technique with proven clinical usefulness. Multiple-step protocols, such as MR perfusion followed by high-spatial resolution MR angiography, seem to be a good approach for the assessment of different vascular diseases affecting the pulmonary arteries. In combination with other imaging sequences, MR imaging is one of the most comprehensive potential noninvasive imaging techniques available.

Robust volume-targeted balanced steady-state free-precession coronary magnetic resonance angiography in a breathhold at 3.0 Tesla: a reproducibility study

BACKGROUND

Transient balanced steady-state free-precession (bSSFP) has shown substantial promise for noninvasive assessment of coronary arteries but its utilization at 3.0 T and above has been hampered by susceptibility to field inhomogeneities that degrade image quality. The purpose of this work was to refine, implement, and test a robust, practical single-breathhold bSSFP coronary MRA sequence at 3.0 T and to test the reproducibility of the technique.

METHODS

A 3D, volume-targeted, high-resolution bSSFP sequence was implemented. Localized image-based shimming was performed to minimize inhomogeneities of both the static magnetic field and the radio frequency excitation field. Fifteen healthy volunteers and three patients with coronary artery disease underwent examination with the bSSFP sequence (scan time = 20.5 ± 2.0 seconds), and acquisitions were repeated in nine subjects. The images were quantitatively analyzed using a semi-automated software tool, and the repeatability and reproducibility of measurements were determined using regression analysis and intra-class correlation coefficient (ICC), in a blinded manner.

RESULTS

The 3D bSSFP sequence provided uniform, high-quality depiction of coronary arteries (n = 20). The average visible vessel length of 100.5 ± 6.3 mm and sharpness of 55 ± 2% compared favorably with earlier reported navigator-gated bSSFP and gradient echo sequences at 3.0 T. Length measurements demonstrated a highly statistically significant degree of inter-observer (r = 0.994, ICC = 0.993), intra-observer (r = 0.894, ICC = 0.896), and inter-scan concordance (r = 0.980, ICC = 0.974). Furthermore, ICC values demonstrated excellent intra-observer, inter-observer, and inter-scan agreement for vessel diameter measurements (ICC = 0.987, 0.976, and 0.961, respectively), and vessel sharpness values (ICC = 0.989, 0.938, and 0.904, respectively).

CONCLUSIONS

The 3D bSSFP acquisition, using a state-of-the-art MR scanner equipped with recently available technologies such as multi-transmit, 32-channel cardiac coil, and localized B0 and B1+ shimming, allows accelerated and reproducible multi-segment assessment of the major coronary arteries at 3.0 T in a single breathhold. This rapid sequence may be especially useful for functional imaging of the coronaries where the acquisition time is limited by the stress duration and in cases where low navigator-gating efficiency prohibits acquisition of a free breathing scan in a reasonable time period.

Acquired coronary disease in children: the role of multimodality imaging

Coronary sequelae of Kawasaki disease, post-surgical coronary lesions and cardiac allograft vasculopathy are the main causes of acquired coronary pathology in childhood. Surveillance and timely recognition of coronary problems in children who are at risk of ischemic events are imperative and noninvasive imaging is increasingly utilized for these purposes. Herein, we summarize the causes of acquired coronary disease in children and discuss the role of various imaging techniques that are available to establish the diagnosis and guide management.

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.

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.

Magnetic resonance angiography: current status and future directions

With recent improvement in hardware and software techniques, magnetic resonance angiography (MRA) has undergone significant changes in technique and approach. The advent of 3.0 T magnets has allowed reduction in exogenous contrast dose without compromising overall image quality. The use of novel intravascular contrast agents substantially increases the image windows and decreases contrast dose. Additionally, the lower risk and cost in non-contrast enhanced (NCE) MRA has sparked renewed interest in these methods. This article discusses the current state of both contrast-enhanced (CE) and NCE-MRA. New CE-MRA methods take advantage of dose reduction at 3.0 T, novel contrast agents, and parallel imaging methods. The risks of gadolinium-based contrast media, and the NCE-MRA methods of time-of-flight, steady-state free precession, and phase contrast are discussed.

Estimation of perfusion and arterial transit time in myocardium using free-breathing myocardial arterial spin labeling with navigator-echo

Arterial spin labeling (ASL) provides noninvasive measurement of tissue blood flow, but sensitivity to motion has limited its application to imaging of myocardial blood flow. Although different cardiac phases can be synchronized using electrocardiography triggering, breath holding is generally required to minimize effects of respiratory motion during ASL scanning, which may be challenging in clinical populations. Here a free-breathing myocardial ASL technique with the potential for reliable clinical application is presented, by combining ASL with a navigator-gated, electrocardiography-triggered TrueFISP readout sequence. Dynamic myocardial perfusion signals were measured at multiple delay times that allowed simultaneous fitting of myocardial blood flow and arterial transit time. With the assist of a nonrigid motion correction program, the estimated mean myocardial blood flow was 1.00 ± 0.55 mL/g/min with a mean transit time of ∼ 400 msec. The intraclass correlation coefficient of repeated scans was 0.89 with a mean within subject coefficient of variation of 22%. Perfusion response during mild to moderate stress was further measured. The capability for noninvasive, free-breathing assessment of myocardial blood flow using ASL may offer an alternative approach to first-pass perfusion MRI for clinical evaluation of patients with coronary artery disease.

MRI of coronary wall remodeling in a swine model of coronary injury using an elastin-binding contrast agent

BACKGROUND

The extracellular matrix (ECM) plays an important role in the pathogenesis of atherosclerosis and in-stent restenosis. Elastin is an essential component of the ECM. ECM degradation can lead to plaque destabilization, whereas enhanced synthesis typically leads to vessel wall remodeling resulting in arterial stenosis or in-stent restenosis after stent implantation. The objective of this study was to demonstrate the feasibility of MRI of vascular remodeling using a novel elastin-binding contrast agent (BMS-753951).

METHODS AND RESULTS

Coronary injury was induced in 6 pigs by endothelial denudation and stent placement. At day 28, delayed-enhancement MRI coronary vessel wall imaging was performed before and after injection of gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA). Two days later, DE-MRI was repeated after administration of BMS-753951. Contrast-to-noise-ratio and areas of enhancement were determined. Delayed-enhancement MRI with BMS-753951 caused strong enhancement of the aortic, pulmonary artery, and injured coronary artery walls, whereas Gd-DTPA did not. Delayed-enhancement MRI of the stented coronary artery with BMS-753951 yielded a 3-fold higher contrast-to-noise-ratio when compared with the balloon-injured and control coronary artery (21±6 versus 7±3 versus 6±4; P<0.001). The area of enhancement correlated well with the area of remodeling obtained from histological data (R(2)=0.86, P<0.05).

CONCLUSIONS

We demonstrate the noninvasive detection and quantification of vascular remodeling in an animal model of coronary vessel wall injury using an elastin-specific MR contrast agent. This novel approach may be useful for the assessment of coronary vessel wall remodeling in patients with suspected coronary artery disease. Further studies in atherosclerotic animal models and degenerative ECM disease are now warranted.

Contrast-enhanced whole-heart coronary MRA using Gadofosveset 3.0 T versus 1.5 T

RATIONALE AND OBJECTIVES

To compare contrast-enhanced coronary magnetic resonance angiography (MRA) at 3.0 T with the same technique performed at 1.5 T using the contrast agent gadofosveset.

MATERIALS AND METHODS

In this prospective randomized study, 19 healthy male volunteers (mean age 28 years, mean weight 79.8 kg), after signing informed consents, underwent contrast-enhanced inversion recovery three-dimensional fast low angle shot (FLASH) MRA at 1.5 and at 3.0 T. Prospective electrocardiogram-triggering was combined with adaptive respiratory gating. For contrast-enhanced images, the intravascular contrast agent gadofosveset was used. Acquisition time, signal-to-noise ratio (SNR) of coronary blood, contrast-to-noise ratio (CNR) between coronaries and adjacent myocardium or epicardial fat and image quality were analyzed for statistical differences by using a two-tailed paired-sample t-test. The ratio calculations were based on measurements performed on the raw data and the image quality was blinded and independently evaluated by two experienced radiologists using a five-point scale.

RESULTS

The mean values for the acquisition time were 14.58 +/- 0.1 minutes at 1.5 T and 16.40 +/- 0.2 minutes at 3.0 T. Overall SNR of all evaluated coronary segments proved higher at 3.0 T compared to 1.5 T (74.0 +/- 42.1 at 3.0 T vs. 50.2 +/- 20.2 at 1.5 T, P = .04). Overall CNR between coronaries and myocardium was significantly increased at 3.0 T in comparison to 1.5 T (40.1 +/- 21.9 at 3.0 T vs. 24.4 +/- 17.2 at 1.5 T, P = .01). Between the two methods, no significant difference in overall CNR between coronaries and epicardial fat was observed (P = .08, NS). The 3.0 T MRA demonstrated superior overall image quality with respect to 1.5 T (2.28 +/- 0.71 at 3.0 T vs. 1.92 +/- 0.38 at 1.5T, P = .004).

CONCLUSION

The use of higher field strength, 3.0 T instead of 1.5 T, resulted in similar CNR between coronaries and epicardial fat, higher SNR values and CNR between blood and myocardium, as well as an improved overall image quality, when gadofosveset in combination with electrocardiogram and respiratory triggering for coronary MRA was used.

Utility of balanced steady-state free precession MR venography in the diagnosis of lower extremity deep venous thrombosis

OBJECTIVE

The purpose of this study was to determine the sensitivity and specificity of balanced steady-state free precession MR venography in the diagnosis of lower extremity deep venous thrombosis.

SUBJECTS AND METHODS

After undergoing lower extremity ultrasound because of suspicion of deep venous thrombosis, 64 patients were prospectively recruited to undergo balanced steady-state free precession MR venography with ultrasound as the reference standard. Ultrasound images were independently interpreted by two blinded ultrasound radiologists, and MR venograms were independently interpreted by two blinded MRI radiologists. The sensitivity, specificity, positive predictive value, and negative predictive value of MR venography were calculated for the diagnoses of all deep venous thrombosis, acute thrombi, and thrombosis of the popliteal, femoral, and common femoral veins individually. Proximal extent, thrombus age, ancillary findings, and interobserver agreement calculated with the Cohen kappa test were evaluated for ultrasound and MRI. The McNemar test was used to evaluate for statistical differences in diagnostic accuracy.

RESULTS

MR venography had a sensitivity of 94.7%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 97.7% for the diagnosis of all thrombi. For acute thrombi, the MR venography and ultrasound results were completely concordant. MR venography depicted greater proximal extent in five of 18 cases in which thrombosis was found. The MR venographic findings agreed completely with the ultrasound findings in determination of thrombus age. For both ultrasound and MR venography, interobserver agreement was 100% on a per-patient basis. No statistical difference was identified in the diagnostic performance of the two techniques.

CONCLUSION

Balanced steady-state free precession MR venography is highly accurate in the diagnosis of lower extremity deep venous thrombosis.

Hybrid ultrasound MRI for improved cardiac imaging and real-time respiration control

A hybridized dual-imaging system combining real-time ultrasound imaging and MRI was utilized for cardiac imaging at 1.5 T and 3 T. The ultrasound scanner with a programmable software interface was connected via computer to the MRI scanner. Electronic noise was eliminated with electromagnetic shielding and grounding to the screen room. At 3 T, real-time prospective motion compensation in dynamic cine cardiac imaging was implemented using B-mode ultrasound imaging. The ultrasound technique avoided drawbacks such as signal saturation or steady-state interruption of the MR navigator gating. At 1.5 T, a low-latency real-time feedback to balanced steady state free precision MR imaging was performed in three normal volunteers. Results showed active tracking of the heart during respiratory motion and improvement in time-averaged cardiovascular images. Future studies can fully exploit the potential of the high-frequency position information provided by the ultrasound system for more advanced applications in real-time organ tracking.

Direct comparison of sensitivity encoding (SENSE) accelerated and conventional 3D contrast enhanced magnetic resonance angiography (CE-MRA) of renal arteries: effect of increasing spatial resolution

PURPOSE

To assess the effect of attaining higher spatial resolution in contrast-enhanced magnetic resonance angiography (MRA) of renal arteries using parallel imaging, sensitivity encoding (SENSE), by comparing the SENSE contrast-enhanced (CE) MRA against a conventional CE-MRA protocol with identical scan times, injection protocol, and other acquisition parameters.

MATERIALS AND METHODS

Numerical simulations and a direct comparison of SENSE-accelerated versus conventional acquisitions were performed. A total of 41 patients (18 male) were imaged using both protocols for a direct comparison. Both protocols used fluoroscopic triggering, centric encoding, breath-holding, equivalent injection protocol, and lasted approximately 30 seconds.

RESULTS

Simulated point-spread functions were narrower for the SENSE protocol compared to the conventional protocol. In the patient study, although the SENSE protocol produced images with lower signal-to-noise ratio (SNR), image quality was better for all segments of the renal arteries. In addition, ringing of kidney parenchyma and renal artery blurring were significantly reduced in the SENSE protocol. Finally, reader confidence improved with the SENSE protocol.

CONCLUSION

Despite a reduction in SNR, the higher-resolution SENSE CE-MRA provided improved image quality, reduced artifacts, and increased reader confidence compared to the conventional protocol.

Renovascular imaging in the NSF Era

The detection of the association between nephrogenic systemic fibrosis (NSF), a rare but potentially life-threatening disease only encountered in patients with severely impaired renal function, and the previous administration of some Gd-chelates has cast a shadow on the administration of Gd-chelates in patients with chronic renal failure. So far, contrast-enhanced MR-angiography (MRA) was considered the best diagnostic modality in patients with suspected renal disease. This review explores the most appropriate use of renal MRA with a focus on newly developed nonenhanced MRA techniques. Nonenhanced MRA techniques mainly based on SSFP with ECG-gating allow for acceptable spatial resolution to visualize at least the proximal parts of the renal arteries. In addition functional renal imaging techniques and their current clinical role are critically appreciated. J. Magn. Reson. Imaging 2009;30:1323-1334. (c) 2009 Wiley-Liss, Inc.

Contrast-enhanced whole-heart MR coronary angiography at 3.0 T using the intravascular contrast agent gadofosveset

OBJECTIVES

The purpose of this study was to compare contrast-enhanced (CE) whole-heart coronary magnetic resonance angiography (MRA) at 3.0 T using gadofosveset to noncontrast-enhanced steady-state free precession (SSFP) coronary MRA at 1.5 T.

MATERIALS AND METHODS

A prospective randomized study was conducted among 20 healthy male volunteers. The same group of subjects underwent CE whole heart MRA at 3.0 T employing a 3D FLASH sequence with IR prepulse after gadofosveset injection as well as noncontrast-enhanced coronary MRA at 1.5 T using a 3D SSFP sequence with T2-preparation. Both techniques were performed using prospective ECG-triggering and adaptive respiratory gating. Acquisition time, signal-to-noise ratio of coronary blood, contrast-to-noise ratio (CNR) between coronaries and adjacent myocardium or epicardial fat, and image quality were evaluated in each case.

RESULTS

A significant increase of the overall CNR between coronary blood and adjacent myocardium was measured on images acquired at 3 T in comparison to 1.5 T. The mean values were 38.9 +/- 19.6 and 26.3 +/- 15.4, respectively (P[r] < 0.005). There was no significant difference in CNR between coronary blood and epicardial fat. The mean image quality for the proximal and mid coronary segments was not statistically different between 1.5 T and 3.0 T (P > 0.05), however, the distal coronary segments were rated significantly higher for the CE MRA at 3.0 T (P = 0.02). The average acquisition time (15.29 +/- 5.73 minutes at 1.5 T vs. 17.29 +/- 5.18 minutes at 3 T) and overall image quality (2.15 +/- 0.49 at 1.5 T vs. 2.35 +/- 0.39 at 3 T) were similar for both methods.

CONCLUSIONS

CE whole-heart coronary MRA at 3.0 T demonstrated higher overall CNR between coronary blood and myocardium and an improved image quality of the distal coronary segments compared with noncontrast-enhanced SSFP coronary MRA at 1.5 T.

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.

Non-contrast-enhanced MR imaging of renal artery stenosis at 1.5 tesla

Balanced steady-state free precession (Bal-SSFP) techniques produce excellent anatomic images of renal arteries without the use of contrast agents and are relatively flow-insensitive. Electrocardiography (ECG)-triggered and non-ECG-triggered sequences have been shown to be quite sensitive for detection of regional arterial stenosis (RAS), and the already high specificity is likely to increase with further refinement of the techniques. Bal-SSFP sequences can be used as a screening tool or as an alternative to contrast-enhanced (CE) magnetic resonance angiography (MRA) when contrast agents are contraindicated. In addition to morphologic imaging of RAS, non-CE techniques can be used in functional assessment of hemodynamic significance. The complimentary tools can be used alone or in combination with CE-MRA for MR imaging of renal vascular hypertension.

Serial contrast-enhanced cardiac magnetic resonance imaging demonstrates regression of hyperenhancement within the coronary artery wall in patients after acute myocardial infarction

OBJECTIVES

Our aim was to determine whether serial contrast-enhanced cardiac magnetic resonance (CE-CMR) is useful for the characterization of tissue signal changes within the coronary vessel wall in patients after acute myocardial infarction (AMI).

BACKGROUND

Inflammation plays a key role in the development of AMI. CE-CMR of the vessel wall has been found useful for the characterization of inflammatory tissue signal changes in patients with carotid artery stenosis, giant cell arteritis, or Takayasu's arteritis; however, it has never been serially performed in the coronary artery wall in patients with acute and chronic myocardial infarction using a gadolinium-based contrast medium and compared with systemic markers of inflammation.

METHODS

CE-CMR using a T1-weighted 3-dimensional gradient echo inversion recovery sequence of the coronary artery wall and 0.2 mmol/kg of gadolinium-diethylenetriaminepentaacetic acid was performed in 10 patients with AMI 6 days and 3 months after coronary intervention and in 9 subjects without coronary artery disease on invasive coronary angiography. Contrast-to-noise ratio (CNR) within the coronary artery wall was quantified in comparison with blood signal.

RESULTS

Patients with AMI demonstrated a significantly increased coronary vessel wall enhancement 6 days after infarction compared with normal subjects (CNR 7.8 +/- 4.4 vs. 5.3 +/- 3.2, p < 0.001). Three months after infarction, CNR decreased to 6.5 +/- 4.7 (p < 0.03). This decrease paralleled declines in C-reactive protein. Angiographically normal segments showed no contrast changes, but CNR significantly decreased in stenotic segments, from 10.9 +/- 3.8 to 6.8 +/- 5.0 (p < 0.002), resulting in a reduction of enhanced segments from 70% to 25% (p < 0.01).

CONCLUSIONS

Serial CE-CMR identified changes in spatial extent and intensity of coronary contrast enhancement in patients after AMI. This technique may be useful for the characterization of transient coronary tissue signal changes, which may represent edema or inflammation during the post-infarction phase. In addition, CE-CMR may offer the potential for visualization of inflammatory activity in atherosclerosis associated with acute coronary syndromes.

Noncontrast 3D steady-state free-precession magnetic resonance angiography of the whole chest using nonselective radiofrequency excitation over a large field of view: comparison with single-phase 3D contrast-enhanced magnetic resonance angiography

OBJECTIVES

To evaluate the feasibility of three-dimensional (3D) steady-state free-precession (SSFP) magnetic resonance angiography (MRA) using nonselective radiofrequency excitation in the assessment of cardiac morphology, thoracic aorta, main pulmonary, and proximal coronary arteries.

MATERIAL AND METHODS

Thirty consecutive patients (19 males; 11 females; age range, 20-74) with various cardiac and thoracic vascular diseases underwent free-breathing respiratory navigator-gated electrocardiogram-triggered noncontrast SSFP MRA and conventional high-resolution 3D contrast-enhanced MRA (CE-MRA) of the thorax at 1.5 T. Two readers evaluated both datasets for findings, vascular delineation and sharpness (from 0, not visualized to 3, excellent definition), artifacts, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) in 14 vascular segments including aorta, supra-aortic, pulmonary, and coronary arteries, and in cardiac chambers. Statistical analysis was performed using Wilcoxon test for vessel delineation, and [kappa] coefficient for interobserver variability.

RESULTS

3D SSFP and CE-MRA were successfully performed in all patients. Scan time for SSFP MRA ranged from 5 to 10 minutes (mean +/- standard deviation, 7 +/- 2 minutes). On SSFP MRA, readers 1 and 2 graded 233 (97.1%) and 234 (97.5%) coronary arterial segments and cardiac chambers, and 275 (91.7%) and 278 (92.7%) noncoronary arterial segments with diagnostic definition (grades 2 and 3) (k = 0.86). On conventional CE-MRA, readers 1 and 2 graded 10 (4.2%) and 12 (5%) coronary arterial segments and cardiac chambers, and 272 (90.7%) and 270 (90%) noncoronary arterial segments with diagnostic definition (grades 2 and 3) (k = 0.89). Segmental visibility was higher for aortic root, pulmonary trunk, proximal coronary arteries, and heart chambers (P < 0.001), and lower for supra-aortic arteries (P < 0.001) on SSFP MRA for each reader. SNR and CNR values were higher for aortic root and aorta on SSFP MRA (P < 0.001 for both). No significant difference existed between SNR and CNR values for the other vascular segments and cardiac chambers on SSFP and CE-MRA (P > 0.05 for all). The 2 readers demonstrated vascular stenosis and dilatation/aneurysm in 7 and 35 segments on both datasets, respectively.

CONCLUSION

Noncontrast 3D SSFP MRA with nonselective radiofrequency excitation provides high image quality and sufficient SNR and CNR for confident assessment of cardiac and thoracic vascular diseases including congenital heart diseases. Our results suggest that noncontrast SSFP MRA outperforms CE-MRA in visualization of cardiac chambers, proximal coronary arteries, pulmonary trunk, and aortic root.

Coronary magnetic resonance angiography

Coronary magnetic resonance angiography (MRA) is a powerful noninvasive technique with high soft-tissue contrast for the visualization of the coronary anatomy without X-ray exposure. Due to the small dimensions and tortuous nature of the coronary arteries, a high spatial resolution and sufficient volumetric coverage have to be obtained. However, this necessitates scanning times that are typically much longer than one cardiac cycle. By collecting image data during multiple RR intervals, one can successfully acquire coronary MR angiograms. However, constant cardiac contraction and relaxation, as well as respiratory motion, adversely affect image quality. Therefore, sophisticated motion-compensation strategies are needed. Furthermore, a high contrast between the coronary arteries and the surrounding tissue is mandatory. In the present article, challenges and solutions of coronary imaging are discussed, and results obtained in both healthy and diseased states are reviewed. This includes preliminary data obtained with state-of-the-art techniques such as steady-state free precession (SSFP), whole-heart imaging, intravascular contrast agents, coronary vessel wall imaging, and high-field imaging. Simultaneously, the utility of electron beam computed tomography (EBCT) and multidetector computed tomography (MDCT) for the visualization of the coronary arteries is discussed.

Delayed-enhancement cardiovascular magnetic resonance coronary artery wall imaging: comparison with multislice computed tomography and quantitative coronary angiography

OBJECTIVES

We examined whether delayed-enhancement cardiovascular magnetic resonance (DE-CMR) coronary artery wall imaging correlated with atherosclerosis detected by using multislice computed tomography (MSCT) and quantitative coronary angiography (QCA).

BACKGROUND

The use of DE-CMR coronary vessel wall imaging may provide a noninvasive method to assess diseased coronary vessel walls.

METHODS

We performed DE-CMR coronary artery wall imaging in 14 patients with cardiovascular risk factors and 6 healthy subjects without risk factors.

RESULTS

A greater prevalence of strong DE was noted with greater MSCT evidence of disease, with DE in 2 (7%) of 30 coronary segments with no plaque by MSCT, in 1 (10%) of 10 segments with noncalcified plaque on MSCT, and in 16 (36%) of 44 segments with calcifications by MSCT (p = 0.009, adjusted p = 0.035). Delayed enhancement was observed in 8 (53%) of 15 segments with >20% coronary artery stenosis by QCA but also in 12 (15%) of 80 segments without angiographically apparent coronary disease (p = 0.004, adjusted p = 0.01).

CONCLUSIONS

The use of DE-CMR allowed us to identify areas of DE that correlate with severity of atherosclerosis by MSCT and QCA. This novel approach may be useful for the assessment of coronary vessel wall in patients with suspected coronary artery disease.

Feasibility and diagnostic accuracy of whole heart coronary MR angiography using free-breathing 3D balanced turbo-field-echo with SENSE and the half-fourier acquisition technique

OBJECTIVE

We wanted to assess the feasibility and diagnostic accuracy of whole heart coronary magnetic resonance angiography (MRA) with using 3D balanced turbo-field-echo (b-TFE) with SENSE and the half-Fourier acquisition technique for identifying stenoses of the coronary artery.

MATERIALS AND METHODS

Twenty-one patients who underwent both whole heart coronary MRA examinations and conventional catheter coronary angiography examinations were enrolled in the study. The whole heart coronary MRA images were acquired using a navigator gated 3D b-TFE sequence with SENSE and the half-Fourier acquisition technique to reduce the acquisition time. The imaging slab covered the whole heart (80 contiguous slices with a reconstructed slice thickness of 1.5 mm) along the transverse axis. The quality of the images was evaluated by using a 5-point scale (0 - uninterpretable, 1 - poor, 2 - fair, 3 - good, 4 - excellent). Ten coronary segments of the heart were evaluated in each case; the left main coronary artery (LM), and the proximal, middle and distal segments of the left anterior descending (LAD), the left circumflex (LCX) and the right coronary artery (RCA). The diagnostic accuracy of whole heart coronary MRA for detecting significant coronary artery stenosis was determined on the segment-by-segment basis, and it was compared with the results obtained by conventional catheter angiography, which is the gold standard.

RESULTS

The mean image quality was 3.7 in the LM, 3.2 in the LAD, 2.5 in the LCX, and 3.3 in the RCA, respectively (the overall image quality was 3.0 +/- 0.1). 168 (84%) of the 201 segments had an acceptable image quality (> or =grade 2). The sensitivity, specificity, accuracy, negative predictive value and positive predictive value of the whole heart coronary MRA images for detecting significant stenosis were 81.3%, 92.1%, 91.1%, 97.9%, and 52.0%, respectively. The mean coronary MRA acquisition time was 9 min 22 sec (+/-125 sec).

CONCLUSION

Whole heart coronary MRA is a feasible technique, and it has good potential to evaluate the major portions of the coronary arteries with an acceptable image quality within a reasonable scan time.

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.

Combination of free-breathing and breathhold steady-state free precession magnetic resonance angiography for detection of coronary artery stenoses

PURPOSE

To analyze the incremental diagnostic value of a combination of two approaches (free-breathing and breathhold) vs. the sole free-breathing approach to coronary magnetic resonance angiography (CMRA) for detection of significant stenoses.

MATERIALS AND METHODS

Thirty patients were consecutively included in this prospective trial. CMRA was performed on a 1.5-T MR scanner (Magnetom Sonata, Siemens) using a balanced steady-state free precession (SSFP) sequence during free-breathing (2.4 x 0.9 x 0.7 mm3). Breathholding acquisitions (3.0 x 1.5 x 0.7 mm3) were only performed in cases in which the quality of free-breathing CMRA precluded assessment. Patients with contraindications to CMRA, claustrophobia, or nonassessable images were not excluded from the assessment of diagnostic accuracy (intention-to-diagnose design).

RESULTS

In 60% of all free-breathing coronary acquisitions the image quality was adequate for diagnostic assessment. For the remaining 40% of the cases, breathhold acquisitions were obtained. The sensitivity, specificity, nonassessable rate, and accuracy in identifying main coronary branches with significant stenoses using the combination of both breathing approaches and the free-breathing approach alone were 65% vs. 32%, 73% vs. 53%, 24% vs. 52%, and 71% vs. 46%, respectively (P < 0.001).

CONCLUSION

In this consecutive cohort of patients, the combination of free-breathing and breathhold CMRA significantly improved diagnostic accuracy. Nevertheless, even this combination did not reach accuracies sufficient for routine clinical application.

MRI of coronary vessel walls using radial k-space sampling and steady-state free precession imaging

OBJECTIVE

The objective of our study was to investigate the impact of radial k-space sampling and steady-state free precession (SSFP) imaging on image quality in MRI of coronary vessel walls.

SUBJECTS AND METHODS

Eleven subjects were examined on a 1.5-T MR system using three high-resolution navigator-gated and cardiac-triggered 3D black blood sequences (cartesian gradient-echo [GRE], radial GRE, and radial SSFP) with identical spatial resolution (0.9 x 0.9 x 2.4 mm3). The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), vessel wall sharpness, and motion artifacts were analyzed.

RESULTS

The mean SNR and CNR of the coronary vessel wall were improved using radial imaging and were best using radial k-space sampling combined with SSFP imaging. Vessel border definition was similar for all three sequences. Radial k-space sampling was found to be less sensitive to motion. Consistently good image quality was seen with the radial GRE sequence.

CONCLUSION

Radial k-space sampling in MRI of coronary vessel walls resulted in fewer motion artifacts and improved SNR and CNR. The use of SSFP imaging, however, did not result in improved coronary vessel wall visualization.

Analysis of cardiac function--comparison between 1.5 Tesla and 3.0 Tesla cardiac cine magnetic resonance imaging: preliminary experience

PURPOSE

We sought to assess the feasibility of magnetic resonance imaging to evaluate cardiac function at 3.0 T compared with 1.5 T.

MATERIAL AND METHODS

In a prospective intraindividual comparative study, 12 volunteers (range, 18-54 years), and 2 patients (range, 43-53 years) underwent cardiac cine magnetic resonance at both 3.0 T and 1.5 T. Data were acquired both with a steady-state free precession sequence (SSFP) and a spoiled gradient echo (SGE) sequence. If necessary, a frequency scout was used to correct for off-resonance artifacts. For both SSFP and SGE imaging, 6-mm thick retrospectively EKG-gated short axis views were acquired with equal matrix size (192 x 163) and comparable repetition time (TR). Cardiac function parameters were determined manually by a single investigator. Cardiac function parameters, signal to noise ratio (SNR), contrast to noise ratio (CNR), and the presence of artifacts were compared between the 2 magnetic field strengths. For statistical analysis, a Pearson's correlation coefficient was calculated, and a paired Student t test was used to test statistical significance.

RESULTS

Very good correlations between cardiac function parameters at 1.5 T and 3.0 T (r > 0.84, P < 0.0011) were obtained. Compared with SGE, SSFP more frequently was prone to artifacts. With SSFP/SGE at 3.0 T, a SNR gain of 9.4/16% was achieved compared with 1.5 T.

CONCLUSION

Functional cardiac cine magnetic resonance imaging can be regarded as equally accurate at 3.0 T compared with 1.5 T. Compared with SSFP imaging, the SGE sequence benefits more from higher field strengths and is less affected by artifacts.

Parallel imaging in cardiovascular MRI: methods and applications

Cardiovascular MR imaging (CVMR) has become a valuable modality for the non-invasive detection and characterization of cardiovascular diseases. CVMR requires high imaging speed and efficiency, which is fundamentally limited in conventional cardiovascular MRI studies. With the introduction of parallel imaging, alternative means for increasing acquisition speed beyond these limits have become available. In parallel imaging some image data are acquired simultaneously, using RF detector coil sensitivities to encode simultaneous spatial information that complements the information gleaned from sequential application of magnetic field gradients. The resulting improvements in imaging speed can be used in various ways, including shortening long examinations, improving spatial resolution and/or anatomic coverage, improving temporal resolution, enhancing image quality, overcoming physiological constraints, detecting and correcting for physiologic motion, and streamlining work flow. Examples of each of these strategies will be provided in this review. First, basic principles and key concepts of parallel MR are described. Second, practical considerations such as coil array design, coil sensitivity calibrations, customized pulse sequences and tailored imaging parameters are outlined. Next, cardiovascular applications of parallel MR are reviewed, ranging from cardiac anatomical and functional assessment to myocardial perfusion and viability to MR angiography of the coronary arteries and the large vessels. Finally, current trends and future directions in parallel CVMR are considered.

Analysis of residual coronary artery motion for breath hold and navigator approaches using real-time coronary MRI

Coronary artery MRI methods utilize breath holds, or diaphragmatic navigators, to compensate for respiratory motion. To increase image quality and navigator (NAV) gating efficiency, slice tracking is used, with more sophisticated affine motion models recently introduced. This study assesses the extent of remaining coronary artery motion in free breathing NAV and single and multi breath hold coronary artery MRI. Additionally, the effect of the NAV gating window size was examined. To visualize and measure the respiratory induced motion, an image containing a coronary artery cross section was acquired at each heartbeat. The amount of residual coronary artery displacement was used as a direct measure for the performance of the respiratory motion correction method. Free breathing studies with motion compensation (slice tracking with 5 mm gating window) had a similar amount of residual motion (0.76+/-0.17 mm) as a single breath hold (0.52+/-0.20 mm) and were superior to multiple breath holds (1.22+/-0.60 mm). Affine NAV methods allowed for larger gating windows ( approximately 10 mm windows) with similar residual motion (0.74+/-0.17 mm). In this healthy adult cohort (N=10), free-breathing NAV methods offered respiratory motion suppression similar to a single breath hold.

Comparison of 3D segmented gradient-echo and steady-state free precession coronary MRI sequences in patients with coronary artery disease

OBJECTIVE

Our objective was to compare two state-of-the-art coronary MRI (CMRI) sequences with regard to image quality and diagnostic accuracy for the detection of coronary artery disease (CAD).

SUBJECTS AND METHODS

Twenty patients with known CAD were examined with a navigator-gated and corrected free-breathing 3D segmented gradient-echo (turbo field-echo) CMRI sequence and a steady-state free precession sequence (balanced turbo field-echo). CMRI was performed in a transverse plane for the left coronary artery and a double-oblique plane for the right coronary artery system. Subjective image quality (1- to 4-point scale, with 1 indicating excellent quality) and objective image quality parameters were independently determined for both sequences. Sensitivity, specificity, and accuracy for the detection of significant (> or = 50% diameter) coronary artery stenoses were determined as defined in invasive catheter X-ray coronary angiography.

RESULTS

Subjective image quality was superior for the balanced turbo field-echo approach (1.8 +/- 0.9 vs 2.3 +/- 1.0 for turbo field-echo; p < 0.001). Vessel sharpness, signal-to-noise ratio, and contrast-to-noise ratio were all superior for the balanced turbo field-echo approach (p < 0.01 for signal-to-noise ratio and contrast-to-noise ratio). Of the 103 segments, 18% of turbo field-echo segments and 9% of balanced turbo field-echo segments had to be excluded from disease evaluation because of insufficient image quality. Sensitivity, specificity, and accuracy for the detection of significant coronary artery stenoses in the evaluated segments were 92%, 67%, 85%, respectively, for turbo field-echo and 82%, 82%, 81%, respectively, for balanced turbo field-echo.

CONCLUSION

Balanced turbo field-echo offers improved image quality with significantly fewer nondiagnostic segments when compared with turbo field-echo. For the detection of CAD, both sequences showed comparable accuracy for the visualized segments.

Navigator-gated three-dimensional MR angiography of the pulmonary arteries using steady-state free precession

PURPOSE

To assess the quality of a navigator-gated, free breathing, steady-state free precession (SSFP) technique in comparison to a single breathhold for pulmonary artery imaging in normal volunteers.

MATERIALS AND METHODS

Sagittal sections of the left pulmonary arteries of 10 volunteers were obtained with a three-dimensional SSFP sequence using both a single breathhold of 30 seconds and a navigator-gated version of the same sequence. The images were compared and rated by a blinded cardiovascular radiologist for image quality, sharpness, and artifact.

RESULTS

On a scale ranging from -2 to 2, in which positive numbers denote that the navigator method was favorable compared to the single breathhold method, image quality was rated 0.7+/-1.4, sharpness 0.6+/-1.5, and artifact 0.1+/-1.4. Thus, there was no statistical difference between the two methods.

CONCLUSION

The navigator-gated SSFP sequence is able to acquire images equal in quality to the breathhold sequence. This may be of clinical importance for pulmonary imaging in patients who are unable to sustain a long breathhold.

Magnetic resonance angiography of coronary arteries with a 3-dimensional magnetization-prepared true fast imaging with steady-state precession sequence compared with conventional coronary angiography

BACKGROUND

The aim of the study was to compare the detection of clinically significant coronary artery stenosis using a magnetic resonance 3-dimensional (3D) breath-hold true fast imaging with steady-state precession (trueFISP) sequence with conventional coronary angiography.

METHODS

Twenty-nine patients who were scheduled to undergo or had recently undergone diagnostic conventional coronary angiogram participated in this study. The left main, left anterior descending, left circumflex, and right coronary arteries were studied using the 3D breath-hold trueFISP technique. Each artery was imaged with 1 acquisition in 16 to 32 heartbeats. The image quality, vessel length, and presence or absence of stenosis were evaluated. A score of 1 to 3 (1 = noninterpretable, 2 = good, 3 = excellent) was used to assess image quality. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of magnetic resonance angiography in detecting significant coronary artery stenosis (> 50% luminal narrowing) on conventional coronary angiogram were calculated.

RESULTS

Of 116 vessels, 108 were assessed in 29 patients. Twenty vessels that had image quality score of 1 were excluded from further evaluation. The mean lengths of vessels visualized were the following: left anterior descending 3.6 cm, left circumflex 3.4 cm, and right coronary 6.6 cm. The entire length of the left main coronary artery was visualized. For the visualized arterial segments, the sensitivity, specificity, accuracy, positive predictive value, and negative predictive value for detecting significant coronary artery stenosis were 92.8%, 95.3%, 95.0%, 68.4%, and 99.2%, respectively.

CONCLUSIONS

The 3D breath-hold trueFISP technique, which uses the endogenous contrast of blood, is potentially useful in ruling out significant coronary artery stenosis but not yet sensitive enough as a screening tool.

Spin-labeling Coronary MR Angiography with Steady-State Free Precession and Radial k-Space Sampling: Initial Results in Healthy Volunteers

The purpose of this study was to prospectively compare free-breathing navigator-gated cardiac-triggered three-dimensional steady-state free precession (SSFP) spin-labeling coronary magnetic resonance (MR) angiography performed by using Cartesian k-space sampling with that performed by using radial k-space sampling. A new dedicated placement of the two-dimensional selective labeling pulse and an individually adjusted labeling delay time approved by the institutional review board were used. In 14 volunteers (eight men, six women; mean age, 28.8 years) who gave informed consent, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), vessel sharpness, vessel length, and subjective image quality were investigated. Differences between groups were analyzed with nonparametric tests (Wilcoxon, Pearson chi2). Radial imaging, as compared with Cartesian imaging, resulted in a significant reduction in the severity of motion artifacts, as well as an increase in SNR (26.9 vs 12.0, P < .05) in the coronary arteries and CNR (23.1 vs 8.8, P < .05) between the coronary arteries and the myocardium. A tendency toward improved vessel sharpness and vessel length was also found with radial imaging. Radial SSFP imaging is a promising technique for spin-labeling coronary MR 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.

Free-breathing renal magnetic resonance angiography with steady-state free-precession and slab-selective spin inversion combined with radialk-space sampling and water-selective excitation

The impact of radial k-space sampling and water-selective excitation on a novel navigator-gated cardiac-triggered slab-selective inversion prepared 3D steady-state free-precession (SSFP) renal MR angiography (MRA) sequence was investigated. Renal MRA was performed on a 1.5-T MR system using three inversion prepared SSFP approaches: Cartesian (TR/TE: 5.7/2.8 ms, FA: 85 degrees), radial (TR/TE: 5.5/2.7 ms, FA: 85 degrees) SSFP, and radial SSFP combined with water-selective excitation (TR/TE: 9.9/4.9 ms, FA: 85 degrees). Radial data acquisition lead to significantly reduced motion artifacts (P < 0.05). SNR and CNR were best using Cartesian SSFP (P < 0.05). Vessel sharpness and vessel length were comparable in all sequences. The addition of a water-selective excitation could not improve image quality. In conclusion, radial k-space sampling reduces motion artifacts significantly in slab-selective inversion prepared renal MRA, while SNR and CNR are decreased. The addition of water-selective excitation could not improve the lower CNR in radial scanning.

Artifact-free coronary magnetic resonance angiography and coronary vessel wall imaging in the presence of a new, metallic, coronary magnetic resonance imaging stent

BACKGROUND

Coronary in-stent restenosis cannot be directly assessed by magnetic resonance angiography (MRA) because of the local signal void of currently used stainless steel stents. The aim of this study was to investigate the potential of a new, dedicated, coronary MR imaging (MRI) stent for artifact-free, coronary MRA and in-stent lumen and vessel wall visualization.

METHODS AND RESULTS

Fifteen prototype stents were deployed in coronary arteries of 15 healthy swine and investigated with a double-oblique, navigator-gated, free-breathing, T2-prepared, 3D cartesian gradient-echo sequence; a T2-prepared, 3D spiral gradient-echo sequence; and a T2-prepared, 3D steady-state, free-precession coronary MRA sequence. Furthermore, black-blood vessel wall imaging by a dual-inversion-recovery, turbo spin-echo sequence was performed. Artifacts of the stented vessel segment and signal intensities of the coronary vessel lumen inside and outside the stent were assessed. With all investigated sequences, the vessel lumen and wall could be visualized without artifacts, including the stented vessel segment. No signal intensity alterations inside the stent when compared with the vessel lumen outside the stent were found.

CONCLUSIONS

The new, coronary MRI stent allows for completely artifact-free coronary MRA and vessel wall imaging.

Magnetic resonance coronary angiography with 3D TrueFISP: breath-hold versus respiratory gated imaging

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.

Initial experience with balanced turbo field echo in depicting carotid artery stenosis: Comparison with multiple overlapping thin slab acquisition and 3D contrast-enhanced magnetic resonance angiography

PURPOSE

To compare balanced turbo field echo (bTFE) with multiple overlapping thin slice acquisition (MOTSA) and contrast-enhanced MR angiography (CE-MRA) in depicting carotid artery stenosis.

MATERIALS AND METHODS

In this study 86 patients with cerebrovascular disease, who had been referred for a carotid examination, were imaged. All of the patients underwent MOTSA and one of four bTFE sequences followed by CE-MRA. Formatted maximum intensity projections (MIPs) and source images were read in a blinded fashion by a radiologist. Inter- and intrasequence statistical analyses were performed.

RESULTS

We first compared image quality (IQ) and fat, background, and venous suppression using four distinct bTFE protocols in 118 carotid arteries, and found that bTFE4 performed the best. We then compared IQ, grades of stenosis, and background and venous suppression among bTFE4, MOTSA, and CE-MRA. bTFE produced significantly better IQ and venous suppression (P < 0.001), and higher SNR and CNR (P < 0.05) when compared to MOTSA.

CONCLUSION

The bTFE sequence is robust and provides high-quality images in patients with mild to moderate carotid artery stenosis. Even though there is a tendency to overestimate stenosis with bTFE compared to CE-MRA, the shorter scan time of bTFE coupled with enhanced SNR and CNR measurements validates it as a clinically useful adjunct to MOTSA, if not a replacement.

Short breath-hold, volumetric coronary MR angiography employing steady-state free precession in conjunction with parallel imaging

An ECG-gated, 3D steady-state free precession (SSFP) technique in conjunction with sensitivity encoding (SENSE)-based parallel imaging was implemented for short breath-hold, volumetric coronary MR angiograpy (CMRA). Two parallel imaging acquisition strategies (employing 1 R-R and 2 R-R intervals, respectively) were developed to achieve 1) very short breath-hold times (12 s for a heart rate of 60 bpm), and 2) small acquisition windows to minimize sensitivity to physiologic motion. Both strategies were examined in CMRA applications over a range of heart rates. A four-point scale blinded reading (with 4 indicating the most desirable features) revealed substantial image quality improvements for the accelerated data as compared to the nonaccelerated approach. The 1 R-R interval scheme yielded an image score of 3.39 +/- 0.60, and was found to be particularly suitable for low heart rates (P = 0.0008). The 2 R-R interval strategy yielded an image score of 3.35 +/- 0.64, and was more appropriate for higher heart rates (P = 0.03). The results demonstrate that 3D SSFP combined with parallel imaging is a versatile method for short breath-hold CMRA while maintaining high spatial resolution. This strategy permits imaging of the major coronary artery distributions in two to three breath-holds using targeted slabs, and offers the potential for single breath-hold, large-volume CMRA.