Cine MR Angiography of the Heart with Segmented True Fast Imaging with Steady-State Precession

A method to assess spatially variant noise in dynamic MR image series

Accurate measurement of spatially variant noise in MR images acquired using parallel imaging techniques is challenging. Image-based noise measurement methods such as the subtraction method proposed by the National Electrical Manufacturers Association or the multiple acquisition method often cannot be applied in vivo due to motion and/or dynamic contrast changes. Based on the Karhunen-Loeve transform and random matrix theory, we propose a novel method to accurately assess the noise variance in image series bearing temporal redundancy. The method fits the probability density function of eigenvalues from the temporal covariance matrix of the image series to the Marcenko-Pastur distribution. The accuracy of our method was validated using numerical simulation and an MR noise measurement experiment. The ability of this method to derive the g-factor map of a static phantom was validated against the multiple acquisition method. The method was applied to in vivo cardiac and brain image series and the results agreed with subtraction and multiple acquisition methods, respectively. This new image-based noise measurement method provides a practical means of retrospectively evaluating the noise level and/or g-factor map from multiframe image series.

Analysis of the factors influencing the cardiac phenotype in Friedreich's ataxia

Friedreich's ataxia (FRDA) has been associated with both cardiac hypertrophy and to a lesser degree dilated cardiomyopathy. We have conducted a cross sectional magnetic resonance imaging (MRI) study of 25 patients with clinically and genetically confirmed FRDA and 24 healthy controls to analyse how disease parameters influence cardiac features in FRDA. MR cine imaging in the long and short axis planes was performed alongside clinical assessments. LV mass was most pronounced in FRDA patients with a larger genetic mutation (GAA1 repeats >600), earlier age of onset (<16years) and a shorter disease duration (<15 years). LV mass decreased with longer disease duration (>15 years), and independent of GAA1 repeat size and age of onset, suggesting cardiac thinning occurred with prolonged disease. Heart function was lower in patients with larger GAA1 repeat number and longer disease duration. Consequently, cardiac hypertrophy was more marked in FRDA patients with a larger GAA1 repeat number and younger age of onset, while prolonged disease duration was associated with lower LV mass and decreased heart function. It is important not only to understand the biochemical basis for these cardiac changes but also allow for these changes when assessing the effect of treatment of FRDA patients.

Cardiac magnetic resonance assessment of left and right ventricular morphologic and functional adaptations in professional soccer players

BACKGROUND

Professional, long-term physical training is associated with cardiac morphologic and functional changes that depend on the type of exercise performed. So far, the specific effect of soccer training on cardiac morphology has not been investigated with cardiac magnetic resonance imaging (CMRI). We sought to use CMRI to study left ventricular (LV) and right ventricular (RV) morphologic and functional adaptations in professional soccer players.

METHODS

Twenty-nine male professional soccer players (mean age 24.6 +/- 3.9 years, range 18-31 years) in different playing positions and 29 nonathlete male controls (27.0 +/- 3.7 years, 21-34 years) underwent CMRI. Electrocardiographic-gated steady-state free-precession cine CMRI was used to measure myocardial mass (MM), end-diastolic volume (EDV) and end-systolic volume, stroke volume (SV), ejection fraction, and cardiac index at rest. We calculated the ventricular remodeling index (RI) to describe the pattern of cardiac hypertrophy.

RESULTS

Ventricular volume and mass indices were significantly (P < .001) higher in athletes. LVEDV and RVEDV on MRI was above normal in 27/29 athletes. There was a strong positive correlation between EDV and myocardial mass (P < .01). The LVRI and RVRI were similar (0.73 +/- 0.1 g/mL; 0.22 +/- 0.01 g/mL) to that of controls (0.71 +/- 0.1 g/mL; 0.22 +/- 0.01 g/mL). No significant differences were observed for LV ejection fraction and cardiac index. Neither the comparison of athletes in different playing positions nor the comparison of younger and older players revealed statistically significant differences.

CONCLUSION

Cardiac magnetic resonance imaging measurements enable studying the mechanisms of LV and RV adaptation in professional soccer players and reflect the ventricular response to combined endurance and strength based training.

High spatial and temporal resolution cardiac cine MRI from retrospective reconstruction of data acquired in real time using motion correction and resorting

Cine MRI is used for assessing cardiac function and flow and is typically based on a breath-held, segmented data acquisition. Breath holding is particularly difficult for patients with congestive heart failure or in pediatric cases. Real-time imaging may be used without breath holding or ECG triggering. However, despite the use of rapid imaging sequences and accelerated parallel imaging, real-time imaging typically has compromised spatial and temporal resolution compared with gated, segmented breath-held studies. A new method is proposed that produces a cardiac cine across the full cycle, with both high spatial and temporal resolution from a retrospective reconstruction of data acquired over multiple heartbeats during free breathing. The proposed method was compared with conventional cine images in 10 subjects. The resultant image quality for the proposed method (4.2 +/- 0.4) without breath holding or gating was comparable to the conventional cine (4.4 +/- 0.5) on a five-point scale (P = n.s.). Motion-corrected averaging of real-time acquired cardiac images provides a means of attaining high-quality cine images with many of the benefits of real-time imaging, such as free-breathing acquisition and tolerance to arrhythmias.

Accelerated two- and three-dimensional cine MR imaging of the heart by using a 32-channel coil

PURPOSE

To compare accelerated real-time two-dimensional (2D) and segmented three-dimensional (3D) cine steady-state free precession magnetic resonance (MR) imaging techniques by using a 32-channel coil with a conventional 2D cine imaging approach for imaging the heart and to evaluate any difference caused by free breathing and breath holding for real-time imaging.

MATERIALS AND METHODS

In this institutional review board-approved HIPAA-compliant study, 10 healthy volunteers and 22 consecutive patients who were suspected of having or were known to have heart disease underwent cardiac MR imaging by using a 32-channel coil. A conventional multisection 2D real-time cine sequence was used as the reference standard, and three additional accelerated cine sequences were implemented. Volumetric parameters, including ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume(SV), and myocardial mass, were derived. Wall motion and image quality were assessed by two radiologists. In addition, image time was registered. An additional set of images was acquired by using real-time sequences with free breathing, and quantitative measurements were compared with measurements on images obtained with breath holding. For quantitative analysis, repeated-measures analysis of variance, paired t test, and Bland-Altman analysis were used; for qualitative analysis, nonparametric Wilcoxon signed-rank test was used.

RESULTS

All volumetric measurements were significantly correlated with those of the standard sequence (r > 0.80, P < .01). No significant difference among protocols was observed in terms of mean levels for EF or ESV (P > .05). However, a significant difference was indicated for EDV and SV (P < .01).The accelerated protocols had significantly shorter image times (P < .001). Wall motion scores were concordant with the standard sequence in 43-44 (93%-96%) segments for the accelerated protocols, with a strong interreader agreement (intraclass correlation coefficient, > or =0.93). No significant difference was identified between real-time protocols with free breathing and those with breath holding for measurement of volumetric parameters.

CONCLUSION

Accelerated real-time 2D and segmented 3D cine techniques are comparable to the standard clinical protocol in assessment of left ventricular global and regional parameters in substantially shorter image times.

Advances in Cardiovascular MRI for Diagnostics: Applications in Coronary Artery Disease and Cardiomyopathies

BACKGROUND: Cardiac magnetic resonance (CMR) imaging has emerged as an important cardiac imaging technique for the evaluation of multiple cardiac pathologies. OBJECTIVE/METHOD: The goal of this review is to describe recent advances in techniques which have extended the potential applications of CMR. The focus will be on the clinical applications of CMR for the evaluation of coronary artery disease and heart failure/cardiomyopathies which are major causes of morbidity and mortality worldwide. CONCLUSION: CMR provides unique tissue characterization which is not available from other imaging modalities and has demonstrated important diagnostic and prognostic information in many forms of heart disease.

Single-shot steady-state free precession can detect myocardial edema in patients: a feasibility study

PURPOSE

To demonstrate the ability of single-shot, T(2)/T(1) weighted steady-state free precession (SSFP) to detect myocardial edema in patients with an acute myocardial infarction.

MATERIALS AND METHODS

This study was performed in a series of patients (n = 10) referred for the assessment of acute myocardial infarcts (AMI). Localizers were used to obtain true short axis views of the left ventricle (LV). These views were used to plan and obtain T(2)-weighted STIR (short TI inversion recovery) images of the LV. These slices were then acquired using single-shot dark blood-prepared SSFP with a large (31) number of dummy pulses. Lastly, Contrast agent was injected, and late enhancement (LE) images were acquired. Images were analyzed using a multi-segment model of the heart. SSFP images were compared with STIR images, with STIR images used as the standard of truth for the presence of edema. LE images were used to identify segments which were positive for microvascular obstruction.

RESULTS

All techniques were successful in all patients. A total of 312 segments were analyzed. Excluding segments positive for microvascular obstruction, SSFP had a sensitivity/specificity of 80%/89%. Including segments positive for microvascular obstruction, sensitivity/specificity was 71%/88%. On a patient-based analysis, no AMI was missed using SSFP (sensitivity = 100%).

CONCLUSION

Using single-shot SSFP to detect myocardial edema in patients with AMI is feasible with a moderate sensitivity and high specificity.

Unsupervised fully automated inline analysis of global left ventricular function in CINE MR imaging

OBJECTIVES

To implement and evaluate the accuracy of unsupervised fully automated inline analysis of global ventricular function and myocardial mass (MM). To compare automated with manual segmentation in patients with cardiac disorders.

MATERIALS AND METHODS

In 50 patients, cine imaging of the left ventricle was performed with an accelerated retrogated steady state free precession sequence (GRAPPA; R = 2) on a 1.5 Tesla whole body scanner (MAGNETOM Avanto, Siemens Healthcare, Germany). A spatial resolution of 1.4 x 1.9 mm was achieved with a slice thickness of 8 mm and a temporal resolution of 42 milliseconds. Ventricular coverage was based on 9 to 12 short axis slices extending from the annulus of the mitral valve to the apex with 2 mm gaps. Fully automated segmentation and contouring was performed instantaneously after image acquisition. In addition to automated processing, cine data sets were also manually segmented using a semi-automated postprocessing software. Results of both methods were compared with regard to end-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and MM. A subgroup analysis was performed in patients with normal (> or =55%) and reduced EF (<55%) based on the results of the manual analysis.

RESULTS

Thirty-two percent of patients had a reduced left ventricular EF of <55%. Volumetric results of the automated inline analysis for EDV (r = 0.96), ESV (r = 0.95), EF (r = 0.89), and MM (r = 0.96) showed high correlation with the results of manual segmentation (all P < 0.001). Head-to-head comparison did not show significant differences between automated and manual evaluation for EDV (153.6 +/- 52.7 mL vs. 149.1 +/- 48.3 mL; P = 0.05), ESV (61.6 +/- 31.0 mL vs. 64.1 +/- 31.7 mL; P = 0.08), and EF (58.0 +/- 11.6% vs. 58.6 +/- 11.6%; P = 0.5). However, differences were significant for MM (150.0 +/- 61.3 g vs. 142.4 +/- 59.0 g; P < 0.01). The standard error was 15.6 (EDV), 9.7 (ESV), 5.0 (EF), and 17.1 (mass). The mean time for manual analysis was 15 minutes.

CONCLUSIONS

Unsupervised fully automated segmentation and contouring during image reconstruction enables an accurate evaluation of global systolic cardiac function.

Rationale and design for the Defibrillators to Reduce Risk by Magnetic Resonance Imaging Evaluation (DETERMINE) trial

BACKGROUND

Cardiac magnetic resonance imaging (CMR) can accurately determine infarct size. Prior studies using indirect methods and CMR to assess infarct size have shown that patients with larger myocardial infarctions have worse prognoses. Implantable cardioverter defibrillators (ICD) have been shown to improve survival among patients with severe left ventricular (LV) dysfunction. However, the majority of cardiac arrests occur in patients with higher ejection fractions.

METHODS

The Defibrillators To Reduce Risk By Magnetic Resonance Imaging Evaluation study (DETERMINE) is a prospective, multicenter, randomized, clinical trial in patients with coronary artery disease (CAD) and mild-to-moderate LV dysfunction. The purpose of this trial is to test the hypothesis that patients with an infarct size > or = 10% of LV mass, randomized to ICD plus appropriate medical therapy will have improved survival compared with patients randomized to medical therapy alone. Cine and myocardial delayed contrast CMR will be performed in patients with CAD. The primary endpoint will be death from any cause. At least 10,000 patients with CAD will undergo CMR. The target enrollment is 1,550 patients with an estimated 36-month enrollment period. The patients will be followed up for 24 months after the last patient randomization. During the follow-up period, 330 deaths are estimated to occur. This study is powered to detect a 28% reduction in mortality by ICD therapy.

CONCLUSION

The DETERMINE trial will assess the efficacy of ICD therapy to improve survival among patients with CAD, mild-to-moderate LV dysfunction, and infarct size > or = 10% of LV mass as measured by CMR.

Calculations of cardiovascular shunts and regurgitation using magnetic resonance ventricular volume and aortic and pulmonary flow measurements

BACKGROUND

Cardiovascular magnetic resonance measurements of the volumes of the right and left ventricle and of the flows in the ascending aorta and main pulmonary artery contribute to the assessment of patients with valvular regurgitation or intracardiac or extracardiac shunts. Ventricular volumes are measured by planimetry and summation of end-diastolic and end-systolic areas measured in a stack of ventricular short-axis cines. The volumes of blood flowing through planes transecting the great arteries are measured using phase contrast velocity mapping. The two approaches are essentially different and can be used either for mutual validation, or separately or in combination to quantify regurgitation and/or shunting. In the presence of shunts, the relations between the stroke volumes and arterial flows of each side of the heart vary depending on the level of shunting (for example, atrial, ventricular or ductal).

CONCLUSION

This article aims to explain and illustrate the technical and theoretical basis for calculations using volumetric and flow measurements, providing formulae and diagrams to facilitate the interpretation of results.

Pilot study of improved lesion characterization in breast MRI using a 3D radial balanced SSFP technique with isotropic resolution and efficient fat-water separation

PURPOSE

To assess a 3D radial balanced steady-state free precession (SSFP) technique that provides submillimeter isotropic resolution and inherently registered fat and water image volumes in comparison to conventional T2-weighted RARE imaging for lesion characterization in breast magnetic resonance imaging (MRI).

MATERIALS AND METHODS

3D projection SSFP (3DPR-SSFP) combines a dual half-echo radial k-space trajectory with a linear combination fat/water separation technique (linear combination SSFP). A pilot study was performed in 20 patients to assess fat suppression and depiction of lesion morphology using 3DPR-SSFP. For all patients fat suppression was measured for the 3DPR-SSFP image volumes and depiction of lesion morphology was compared against corresponding T2-weighted fast spin echo (FSE) datasets for 15 lesions in 11 patients.

RESULTS

The isotropic 0.63 mm resolution of the 3DPR-SSFP sequence demonstrated improved depiction of lesion morphology in comparison to FSE. The 3DPR-SSFP fat and water datasets were available in a 5-minute scan time while average fat suppression with 3DPR-SSFP was 71% across all 20 patients.

CONCLUSION

3DPR-SSFP has the potential to improve the lesion characterization information available in breast MRI, particularly in comparison to conventional FSE. A larger study is warranted to quantify the effect of 3DPR-SSFP on specificity.

Normal right- and left ventricular volumes and myocardial mass in children measured by steady state free precession cardiovascular magnetic resonance

BACKGROUND

Quantification of ventricular volume by steady state free precession (SSFP) cardiovascular magnetic resonance is accurate and reproducible. Normal values exist for adults, but are lacking for children.We sought to establish normal values for left and right ventricular volumes, mass and function in healthy children by using SSFP.

METHODS AND RESULTS

Fifty children (27 females, 23 males) without cardiovascular disease were evaluated. Median age was 11 years (range 7 months - 18 years), weight 35 kg (range 7-77 kg), height 146 cm (range 66-181 cm). Thirty-six examinations were performed with breath holding, 14 in freely breathing sedated children.Ventricular volumes and mass were measured in the end systolic and end diastolic phase on SSFP cine images acquired in a short axis plane as a stack of 12 contiguous slices covering full length of both ventricles. Regression analysis showed an exponential relationship between body surface area (BSA) and ventricular volumes and mass (normal value = a*BSAb). Normative curves for males and females are presented in relation to BSA for the end-diastolic volume, end-systolic volume and mass of both ventricles. Intra- and interobserver variability of the measurements was within the limits of 2% and 7% respectively, except for right ventricular mass (10%).

CONCLUSION

The exponential equation for calculation of normal values for each ventricular parameter and graphical display of normative curves for data acquired in healthy children by SSFP cardiovascular magnetic resonance are provided.

Application of the Karhunen-Loeve transform temporal image filter to reduce noise in real-time cardiac cine MRI

Real-time dynamic magnetic resonance imaging (MRI) typically sacrifices the signal-to-noise ratio (SNR) to achieve higher spatial and temporal resolution. Spatial and/or temporal filtering (e.g., low-pass filtering or averaging) of dynamic images improves the SNR at the expense of edge sharpness. We describe the application of a temporal filter for dynamic MR image series based on the Karhunen-Loeve transform (KLT) to remove random noise without blurring stationary or moving edges and requiring no training data. In this paper, we present several properties of this filter and their effects on filter performance, and propose an automatic way to find the filter cutoff based on the autocorrelation of the eigenimages. Numerical simulation and in vivo real-time cardiac cine MR image series spanning multiple cardiac cycles acquired using multi-channel sensitivity-encoded MRI, i.e., parallel imaging, are used to validate and demonstrate these properties. We found that in this application, the noise standard deviation was reduced to 42% of the original with no apparent image blurring by using the proposed filter cutoff. Greater noise reduction can be achieved by increasing the length of the image series. This advantage of KLT filtering provides flexibility in the form of another scan parameter to trade for SNR.

Theory and validation of magnetic resonance fluid motion estimation using intensity flow data

Background

Motion tracking based on spatial-temporal radio-frequency signals from the pixel representation of magnetic resonance (MR) imaging of a non-stationary fluid is able to provide two dimensional vector field maps. This supports the underlying fundamentals of magnetic resonance fluid motion estimation and generates a new methodology for flow measurement that is based on registration of nuclear signals from moving hydrogen nuclei in fluid. However, there is a need to validate the computational aspect of the approach by using velocity flow field data that we will assume as the true reference information or ground truth.

Methodology/Principal Findings

In this study, we create flow vectors based on an ideal analytical vortex, and generate artificial signal-motion image data to verify our computational approach. The analytical and computed flow fields are compared to provide an error estimate of our methodology. The comparison shows that the fluid motion estimation approach using simulated MR data is accurate and robust enough for flow field mapping. To verify our methodology, we have tested the computational configuration on magnetic resonance images of cardiac blood and proved that the theory of magnetic resonance fluid motion estimation can be applicable practically.

Conclusions/Significance

The results of this work will allow us to progress further in the investigation of fluid motion prediction based on imaging modalities that do not require velocity encoding. This article describes a novel theory of motion estimation based on magnetic resonating blood, which may be directly applied to cardiac flow imaging.

Pulmonary vein imaging with unenhanced three-dimensional balanced steady-state free precession MR angiography: initial clinical evaluation

PURPOSE

To determine whether unenhanced magnetic resonance (MR) angiography performed with a three-dimensional (3D) segmented steady-state free precession (SSFP) sequence would be an alternative to contrast material-enhanced MR angiography for evaluating pulmonary veins (PVs) prior to and following radiofrequency (RF) ablation for atrial fibrillation.

MATERIALS AND METHODS

MR angiographic examinations of PVs, performed in 20 patients (nine men, 11 women; mean age, 56.4 years +/- 12.7 [standard deviation]), were retrospectively reviewed according to an institutional review board-approved protocol. The number of PVs and their orthogonal measurements obtained from the 3D SSFP images were compared with those obtained from contrast-enhanced MR angiography. Signal-to-noise and contrast-to-noise ratios were also compared. Qualitative assessment of both techniques was performed by independent reviewers who scored the image quality (on a scale of 1 to 5) on the basis of PV conspicuity. The presence of cardiac and extracardiac pathologic indicators was also determined. Bland-Altman and Wilcoxon signed rank statistical analyses were performed.

RESULTS

The mean difference in PV diameter measurements between contrast-enhanced MR angiography and 3D SSFP was -0.02 cm +/- 0.25. Signal-to-noise and contrast-to-noise ratios were higher for 3D SSFP images than for contrast-enhanced MR angiograms. Qualitatively, there was no significant difference in PV conspicuity between the techniques. Noncardiac pathologic indicators were detected in 10 of 20 patients on 3D SSFP images but not on contrast-enhanced MR angiograms.

CONCLUSION

Unenhanced PV MR angiography performed by using a free-breathing 3D SSFP technique is as accurate as contrast-enhanced MR angiography for measuring PV diameter. This technique can be used for patients in whom contrast-enhanced computed tomographic or MR angiography is contraindicated and may be sufficient in all patients.

Cardiac cine MRI: Quantification of the relationship between fast gradient echo and steady-state free precession for determination of myocardial mass and volumes

PURPOSE

To determine the correlation function between the steady-state free precession (SSFP) and fast gradient echo (FGRE) cine MRI pulse sequences for measuring the myocardial mass and volumes.

MATERIALS AND METHODS

Cardiac cine MRI examinations were acquired in 50 individuals (female: 35, male: 15, mean age 64.1 +/- 9.1 years, range 48-83) using SSFP and FGRE cardiac pulse sequences.

RESULTS

The mean (standard deviation [SD]) left ventricular end diastolic volume measured by SSFP was significantly larger (4.5%) than by FGRE (P < 0.001); this was also the case for end systolic volume (15.0%, P < 0.001). The relationship between SSFP and FGRE measures were linear and highly correlated (P < 0.001) for both left ventricular end diastolic and end systolic volumes (r(2) = 0.90 vs. 0.91, respectively). We determined linear regression models to estimate the SSFP values based on the FGRE measures. Slope (intercept) for ejection fraction, stroke volume, and cardiac output were 0.99 (-2.79), 0.77 (17.5), and 0.76 (1.29), respectively.

CONCLUSION

Linear relationships exist for key LV function parameters when comparing SSFP and FGRE cine MRI. These results indicate that existing databases and normal values for FGRE LV function may be converted to corresponding LV function values for SSFP MRI.

Assessment of left ventricular volumes and function by cine-MR imaging depending on the investigator's experience

AIMS

To analyze the reproducibility of LV volumes calculated by cardiac magnetic resonance imaging (CMRI) and to compare them to those obtained by conventional ventriculography.

METHODS

A total of 30 patients with stable ischemic heart disease were prospectively included. Each underwent CMRI twice and ventriculography. Left ventricular end diastolic volume (EDV), end systolic volume (ESV) and LV ejection fraction (EF) were calculated by two radiologists at different level of experience. Intraobserver, interobserver and interstudy variabilities were assessed.

RESULTS

The cut off values were: intraobserver variability (EDV, ESV, EF): 9.4 ml, 5.3 ml, 3.3% for well-trained radiologist; 13.1 ml, 7.5 ml, 4.1% for less-trained radiologist. interobserver variability: EDV: 11.7 and 10.4 ml; ESV: 7.0 and 6.6 ml; EF: 3.9 and 4.2%. interstudy variability (EDV, ESV, EF): 11.6 and 12.6 ml, 7.1 and 7.4 ml, 3.9 and 3.5%, for experienced and less-trained observers. Statistical differences were found between CMRI and ventriculography: CMRI underestimation of EDV and EF, overestimation of ESV.

CONCLUSIONS

CMRI volumetric quantification of LV volumes and function is highly reproducible at different levels of experience, but not interchangeable with those obtained by ventriculography.

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.

Evaluation of right ventricular function with multidetector computed tomography: comparison with magnetic resonance imaging and analysis of inter- and intraobserver variability

This study was performed to prospectively compare multidetector computed tomography (MDCT) with 16 simultaneous sections and magnetic resonance imaging (MRI) for the assessment of global right ventricular function in 50 patients. MDCT using a semiautomatic analysis tool showed good correlation with MRI for end-diastolic volume (EDV, r=0.83, p<0.001), end-systolic volume (ESV, r=0.86, p<0.001) and stroke volume (SV, r=0.74, p<0.001), but only a moderate correlation for the ejection fraction (EF, r=0.67, p<0.001). Bland Altman analysis revealed a slight, but insignificant overestimation of EDV (4.0 ml, p=0.08) and ESV (2.4 ml, p=0.07), and underestimation of EF (0.1%, p=0.92) with MDCT compared with MRI. All limits of agreement between both modalities (EF: +/-15.7%, EDV: +/-31.0 ml, ESV: +/-18.0 ml) were in a moderate but acceptable range. Interobserver variability of MDCT was not significantly different from that of MRI. For MDCT software, the post-processing time was significantly longer (19.6+/-5.8 min) than for MRI (11.8+/-2.6 min, p<0.001). Accurate assessment of right ventricular volumes by 16-detector CT is feasible but still rather time-consuming.

Current status of 3-T cardiovascular magnetic resonance imaging

Continued advances in radiofrequency hardware and tailored software have, in recent times, greatly increased the power and performance of magnetic resonance imaging for noninvasive evaluation of cardiovascular diseases. Magnetic resonance imaging can uniquely be manipulated to trade temporal resolution and spatial resolution against each other, depending on whether detailed structural or functional information is required. However, to date, a number of cardiovascular magnetic resonance applications have been somewhat limited due to signal-to-noise ratio constraints, reflecting the narrow imaging window imposed by physiological cardiac motion. By increasing the operating field strength from 1.5 to 3 T, it is possible (in principle) to double the signal-to-noise ratio, which in turn may be "traded" for improvements in spatial resolution, coverage, or imaging speed. In this context, the development of parallel imaging has set the stage for impressive performance improvements in contrast-enhanced magnetic resonance angiography at 3 T. Indeed, one could argue that without parallel acquisition, the bang for the buck in going from 1.5 to 3 T would be limited. In this paper, we discuss the current status of 3-T magnetic resonance imaging for cardiovascular imaging, considering the relative gains and limitations relative to 1.5 T.

Quantitative MR measurements of regional and global left ventricular function and strain after intramyocardial transfer of VM202 into infarcted swine myocardium

Previous studies have shown the beneficial effects of the hepatocyte growth factor (HGF) gene on myocardial perfusion and infarction size but not on the regional strain in relationship to global left ventricular function. A noninvasive magnetic resonance (MR) study was performed to determine the effect of a new HGF gene, VM202, expressing two isoforms of HGF, on regional and global left ventricular function. Pigs (8/group) were divided into three groups: 1) controls without infarction; 2) reperfused, infarcted controls; and 3) infarcted, treated (1 h after reperfusion) with VM202 injected at eight sites. Cine, tagging, and delayed enhancement MR images were acquired at 3 and 50 +/- 3 days after infarction. At 50 days, ejection fraction in infarcted, treated animals increased (38 +/- 1% to 47 +/- 2%, P < 0.01) to the level of controls without infarction (52 +/- 1%, P = 0.16) but decreased in infarcted controls (41 +/- 1% to 37 +/- 1%, P < 0.05). Two-dimensional strain improved in remote, peri-infarcted, and infarcted myocardium. Furthermore, the infarction size was smaller in infarcted, treated animals (7.0 +/- 0.5%) compared with infarcted controls (13.2 +/- 1.6%, P < 0.05). Histopathology showed a lack of hypertrophy in myocytes in peri-infarcted and remote myocardium and the formation of islands/peninsulas of myocytes in infarcted, treated animals but not in infarcted controls. In conclusion, the plasmid HGF gene caused a near complete recovery of ejection fraction and improved the radial and circumferential strain of remote, peri-infarcted, and infarcted regions within 50 days. These beneficial effects may be explained by the combined effects of a speedy and significant infarct resorption and island/peninsulas of hypertrophied myocytes within the infarcted territory but not by compensatory hypertrophy. The combined use of cine and tagging MR imaging provides valuable information on the efficacy of gene therapy.

Contrast changes in portal vein and bile duct between centric and linear k-space ordering on three-dimensional segmented true fast imaging with steady-state precession magnetic resonance imaging

PURPOSE

To compare the degree of visualization of the bile duct and portal vein in terms of the difference in k-space ordering on a three-dimensional (3D) segmented true fast imaging with steady-state precession (trueFISP) sequence.

MATERIALS AND METHODS

A breath-hold coronal 3D segmented trueFISP sequence was prospectively performed on 14 healthy volunteers. Images obtained with centric and linear k-space ordering in the k(x)-k(y) plane were compared by two independent radiologists qualitatively with depiction scores on a five-point scale (1=not seen to 5=excellent depiction) using the Wilcoxon signed-rank test. Images were also compared quantitatively using relative contrast values for the bile duct and portal vein against the hepatic parenchyma using a paired t-test.

RESULTS

With centric ordering, both the mean depiction scores and relative contrast values for the portal vein were significantly lower than those with linear ordering (1.5 vs. 3.5, P<.01; and 0.08+/-0.19 vs. 0.51+/-0.10, P<.01, respectively). However, in the bile duct, there were no significant differences, only slight differences were found among the results obtained with centric and linear ordering (3.9 vs. 3.8, P=.72; and 0.59+/-0.06 vs. 0.68+/-0.06, P<.01, respectively).

CONCLUSION

For visualizing the bile duct, centric k-space ordering on 3D segmented trueFISP sequence is recommended, while linear ordering is recommended for portal vein visualization.

Cardiac MRI of ischemic heart disease at 3 T: potential and challenges

Cardiac MRI has become a routinely used imaging modality in the diagnosis of cardiovascular disease and is considered the clinically accepted gold standard modality for the assessment of cardiac function and myocardial viability. In recent years, commercially available clinical scanners with a higher magnetic field strength (3.0 T) and dedicated multi-element coils have become available. The superior signal-to-noise ratio (SNR) of these systems has lead to their rapid acceptance in cranial and musculoskeletal MRI while the adoption of 3.0 T for cardiovascular imaging has been somewhat slower. This review article describes the benefits and pitfalls of magnetic resonance imaging of ischemic heart disease at higher field strengths. The fundamental changes in parameters such as SNR, transversal and longitudinal relaxation times, susceptibility artifacts, RF (B1) inhomogeneity, and specific absorption rate are discussed. We also review approaches to avoid compromised image quality such as banding artifacts and inconsistent or suboptimal flip angles. Imaging sequences for the assessment of cardiac function with CINE balanced SSFP imaging and MR tagging, myocardial perfusion, and delayed enhancement and their adjustments for higher field imaging are explained in detail along with several clinical examples. We also explore the use of parallel imaging at 3.0 T to improve cardiac imaging by trading the SNR gain for higher field strengths for acquisition speed with increased coverage or improved spatial and temporal resolution. This approach is particularly useful for dynamic applications that are usually limited to the duration of a single breath-hold.

[Quantification of ventricular mass and function using real-time free-breathing SSFP sequences]

OBJECTIVES

To compare real-time free-breathing steady-state free precession (SSFP) sequences with conventional breath-hold segmented SSFP sequences on the quantification of ventricular mass and function.

MATERIAL AND METHODS

Cardiac function and mass were assessed in 15 consecutive patients with cardiopathies who underwent MRI for diverse indications. Sequences were planned in the short axis to include the area from the base to the apex of the ventricle. Two sequences were used: 1) a conventional breath-hold segmented SSFP sequence with 7-mm-thick slices and 3-mm gap between slices and 2) a real-time free-breathing SSFP sequence with 10-mm-thick slices. The systolic and diastolic volumes (VTD, VTS) and ejection fraction (EF) of both ventricles were evaluated and the mass of the left ventricle (LVM) was measured. The correlation between the different sequences was studied for each variable.

RESULTS

An excellent correlation was observed between the two sequences on the quantification of cardiac parameters in both ventricles (0.9; p < 0.01). The mean differences for EF, VTD, VTS, and stroke volume (VTD-VTS) were 2.5% (2.1), 5.6 ml (14.2), -0.8 ml (6.4), 6.4 ml (9.4), respectively, for the left ventricle and 1.7% (3.1), 1.8 ml (18.7), -1.9 ml (9.8), 3.7 ml (10.8), respectively, for the right ventricle. The mean difference between the LVM was 4.8 g (6.3).

CONCLUSIONS

The real-time free-breathing SSFP sequence is useful for the quantification of ventricular mass and function. The correlation with conventional SSFP is excellent. Both sequences allow the cardiac parameters to be precisely quantified and the results are reproducible.

Cardiac MR imaging: new advances and role of 3T

Over the last decade, cardiac magnetic resonance imaging has increasingly evolved into a useful diagnostic tool among the radiology and cardiology communities. Ongoing improvements in MR imaging hardware, processing speed, and pulse sequence development have laid the foundation for rapid progress in cardiac MR imaging. This article summarizes developing techniques and technique-related aspects, and the advantages and possible pitfalls of 3T in particular.