Functional cardiac MR imaging with steady-state free precession (SSFP) significantly improves endocardial border delineation without contrast agents

Evaluation of left ventricular function with cardiac magnetic resonance imaging using Fourier fitting

The aims of this study were to investigate the applicability of Fourier fitting in the magnetic resonance (MR) evaluation of left ventricular (LV) function and to determine the optimal number of harmonics for fitting. Cine cardiac MR imaging was performed in 10 subjects, and an LV time-volume curve was generated. Fourier fitting was applied to the original curve using 1-10 harmonics, and the qualities of the time-volume curve and first-derivative curve were evaluated. LV functional parameters were calculated from curves generated with and without fitting. The quality of the original time-volume curve was good, and Fourier fitting had no substantial effect on functional parameters obtained directly from the time-volume curve such as ejection fraction. The first-derivative curve generated without fitting showed substantial artificial fluctuation. The application of Fourier fitting depressed the fluctuation and tended to decrease estimates of peak ejection rate and peak filling rate. Five or six harmonics appeared to be appropriate for obtaining a high-quality first-derivative curve. In conclusion, Fourier fitting was indicated to aid in reducing the artificial fluctuation of the first-derivative curve generated from cine cardiac MR imaging and to contribute to the evaluation of functional parameters derived from the first-derivative curve.

Cardiac stress MR imaging with dobutamine

Stress testing for detection of ischemia-induced wall-motion abnormalities has become a mainstay for noninvasive diagnosis and risk stratification of patients with suspected coronary artery disease (CAD). Recent technical developments in magnetic resonance imaging (MRI), including the adoption of balanced steady-state free precession (b-SSFP) sequences-preferentially in combination with parallel imaging techniques-have led to a significant reduction of imaging time and improved patient safety. The stress protocol includes application of high-dose dobutamine (up to 40 microg/kg/min) combined with fractionated atropine (up to a maximal dose of 1.0 mg). High-dose dobutamine stress MRI revealed good sensitivity (83-96%) and specificity (80-100%) for detection of significant CAD. Myocardial tagging methods have been shown to further increase sensitivity for CAD detection. Severe complications (sustained tachycardia, ventricular fibrillation, myocardial infarction, cardiogenic shock) are rare but may be expected in 0.1-0.3% of patients. Dobutamine stress MRI has emerged as a reliable and safe clinical alternative for noninvasive assessment of CAD. New pulse sequences, such as real-time imaging, might obviate the need for breath holding and electrocardiogram (ECG) triggering in patients with severe dyspnoea and cardiac arrhythmias, which may further improve the clinical impact and acceptance of stress MRI in the future.

Cardiac CINE MR imaging with a 32-channel cardiac coil and parallel imaging: impact of acceleration factors on image quality and volumetric accuracy

PURPOSE

To assess the impact of parallel imaging algorithms on image quality and volumetric accuracy of CINE magnetic resonance imaging (MRI) with high temporal and spatial resolution using a new 32-channel dedicated cardiac phased array coil.

MATERIALS AND METHODS

Fourteen individuals underwent steady-state free precession (SSFP) CINE MRI using a 32-element phased-array coil and parallel imaging acceleration using spatiotemporal sensitivity encoding (TSENSE). Acquisition acceleration ranged from R = 2 to 7. In conjunction with data extracted from phantom measurements, contrast-to-noise ratio (CNR) performance was evaluated for each acceleration factor and subjective image quality was evaluated by two independent readers. In addition, volumetric assessment was performed for each acceleration factor based on a single breath-hold multi-slice data acquisition. Results were compared to nonTSENSE measurements.

RESULTS

CNR for non-accelerated CINE (R = 1) was 45.7 +/- 12.8 and showed a constant decrease with increase in acceleration of 51% at R = 4 and 86% at R = 7. CNR losses accompanied reductions in subjective image quality. Volumetric evaluation was accurate for R <or= 4, with significant underestimation of ejection fraction (EF) at higher accelerations.

CONCLUSION

This study shows that one-dimensional acceleration factors up to R = 4 allow accurate SSFP CINE MRI even though CNR is significantly reduced. This allows for a marked reduction in scan time and allows for multi-slice CINE imaging with high spatial and temporal resolution.

Dual breath-hold magnetic resonance cine evaluation of global and regional cardiac function

The purpose of our study was to evaluate the accuracy of a multislice cine magnetic resonance imaging (MRI) technique with parallel imaging in regard to global and regional left ventricular function. Forty-two individuals underwent cine MRI on a 1.5-tesla scanner. Cine MRI used a steady-state free precession technique and was performed as a single-slice technique (nonTSENSE cine) and an accelerated multislice technique (TSENSE cine) with five slices per breath-hold. End diastolic volume (EDV), end systolic volume (ESV), and ejection fraction (EF) were evaluated for all data sets and in regard to regional wall motion and regional wall motion analysis, and quantitative regional wall thickness and systolic thickening were also assessed. EDV, ESV, and EF based on TSENSE cine showed excellent correlation to the nonTSENSE cine approach (all r(2)=0.99, P<0.001). While EDV evaluations showed a small underestimation for TSENSE cine, ESV and EF showed accurate results compared with nonTSENSE cine. Both readers showed good agreement (kappa=0.72) in regional wall motion assessment comparing both techniques. Data acquisition for the multislice approach was significantly shorter ( approximately 75%) that in single-slice cine. We conclude that accurate evaluation of regional wall motion and left ventricular EF is possible using accelerated multislice cine MR with high spatial and temporal resolution.

Determination of interobserver variability for identifying inducible left ventricular wall motion abnormalities during dobutamine stress magnetic resonance imaging

AIMS

To determine the interobserver variability for identifying inducible left ventricular (LV) wall motion abnormalities during high-dose dobutamine/atropine stress cardiovascular magnetic resonance (DSMR).

METHODS AND RESULTS

Four readers from various institutions were supplied with the image data from 150 consecutive DSMR examinations and asked to grade wall motion and image quality throughout graded doses of dobutamine infusion administered to achieve 85% of the maximum age-predicted heart rate. Inducible ischaemia was identified if more than one segment demonstrated a new or worsening LV wall motion abnormality, and significant stenosis was defined as > or =50% luminal diameter reduction by quantitative contrast coronary angiography. Seventy-seven patients (51%) had luminal narrowings > or =50%. Diagnostic performance (sensitivity, specificity, diagnostic accuracy) of all readers was 78.2, 87.0 and 82.5%. Disagreement between two readers occurred in every seventh examination. Agreement on the presence or absence of inducible wall motion abnormalities was moderate (mean kappa value 0.59, range 0.52-0.76). Diagnostic performance and disagreement were independent of the presence of luminal narrowings > or =50% or the number of diseased coronary vessels. Image quality was regarded excellent in 89.3% of standard views.

CONCLUSION

In the setting of multiple observers from different institutions performing a diagnostic reading of DSMR examinations carried out at a single centre, the interobserver variability was low for identifying inducible LV wall motion abnormalities indicative of coronary arterial luminal narrowings > or =50%.

MR imaging of cardiac tumors

Magnetic resonance (MR) imaging is an important tool in the evaluation of cardiac neoplasms. T1-weighted, T2-weighted, and gadolinium-enhanced sequences are used for anatomic definition and tissue characterization, whereas cine gradient-echo imaging is used to assess functional effects. Recent improvements in pulse sequences for cardiac MR imaging have led to superior image quality, with reduced motion artifact and improved signal-to-noise ratio and tissue contrast. Although there is some overlap in the MR imaging appearances of cardiac tumors, particularly of primary malignancies, differences in characteristic locations and features should allow confident differentiation between benign and malignant tumors. Indicators of malignancy at MR imaging are invasive behavior, involvement of the right side of the heart or the pericardium, tissue inhomogeneity, diameter greater than 5 cm, and enhancement after administration of gadolinium contrast material (as a result of higher tissue vascularity). Concomitant pericardial or pleural effusions are rare in benign processes but occur in about 50% of cases of malignant tumors. MR imaging offers improved resolution, a larger field of view, and superior soft-tissue contrast compared with those of echocardiography, suggesting that knowledge of the MR imaging features of cardiac neoplasms is important for accurate diagnosis and management.

Cardiac Steady-State Free Precession CINE Magnetic Resonance Imaging at 3.0 Tesla

OBJECTIVES

We sought to evaluate the impact of 3.0 T on accelerated CINE steady-state free precession (SSFP) regarding signal parameters and its volumetric accuracy.

MATERIAL AND METHODS

Ten individuals underwent cardiac CINE imaging at 1.5 T and 3.0 T using standard single-slice CINE and multislice TSENSE-accelerated CINE (5 slices/breath-hold) with 4-fold acceleration. Data were evaluated for left ventricular volumetric parameters (EDV, ESV, and EF) as well as for SNR and CNR. Phantom based data allowed for g-factor evaluation for estimation of noise levels for accelerated data sets. Volumetric results and signal parameters were compared with results of single-slice CINE SSFP at 1.5 T as standard of reference (SOR).

RESULTS

Single-slice CINE at 3.0 T showed a approximately 90% increase in CNR compared with the SOR (P < 0.001). At 3.0 T, TSENSE CINE showed a less pronounced estimated loss in CNR (-58 +/- 6%) compared with single-slice CINE than at 1.5 T (-71 +/- 2%). 3.0 T TSENSE CINE showed a 21 +/- 18% lower CNR than the nonaccelerated 1.5 T CINE (P < 0.05). EF results for all data sets did not show any significant error while for EDV some errors have been encountered.

CONCLUSION

3.0 T permits compensation for the high CNR loss, which accompanies the 4-fold TSENSE acceleration at 1.5 T and shows volumetric accuracy. The use of parallel imaging may help to alleviate SAR limitations at higher field strength.

Flow compensation in balanced SSFP sequences

In balanced steady-state free precession (b-SSFP) sequences, uncompensated first-order moments of encoding gradients induce a nonconstant phase evolution for moving spins within the excitation train, resulting in signal loss and image artifacts. To restore these flow-related phase perturbations, "pairing" of consecutive phase-encoding (PE) steps is compared with a fully flow-compensated sequence using compensating gradient waveforms along all three encoding directions. In volunteer studies, the quality of images acquired with the "pairing" technique was comparable to that of images obtained with the fully flow-compensated technique, regardless of the selected view-ordering scheme used for data acquisition. Nevertheless, the results of phantom experiments indicate that the pairing technique becomes ineffective at flow velocities exceeding roughly 0.5-1 m/s. Consequently, the additional scan time required to null the first gradient moments in a flow-compensated b-SSFP sequence makes the "pairing" technique preferable for applications in which slow to moderate flow velocities can be expected.

Kardio-MRT

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

Physiological determinants of the variation in left ventricular mass from early adolescence to late adulthood in healthy subjects

BACKGROUND

The physiological determinants of left ventricular mass (LVM) measured by cardiac magnetic resonance (CMR) imaging are not well defined as prior investigators have studied either adults or adolescents in isolation or have not strictly excluded hypertension or accounted for the effects of exercise habits, haemodynamic, demographic, or body shape characteristics.

METHODS

A total of 102 healthy volunteers (12-81 years, 53 males) underwent CMR. All parameters [unstandardized and adjusted for body surface area (BSA)] were analysed according to gender and by adolescence versus adulthood (adolescents <20 years, adults > or = 20 years). The influence of haemodynamic factors, exercise, and demographic factors on LVM were determined with multivariate linear regression.

RESULTS

LVM rose during adolescence and declined in adulthood. LVM and LVMBSA were higher in males both in adults (LVM: 188 +/- 22 g versus 139 +/- 21 g, P < 0.001; LVMBSA: 94 +/- 11 g m(-2) versus 80 +/- 11 g m(-2), P < 0.001) and in adolescents when adjusted for BSA (LVM: 128 +/- 29 g versus 107 +/- 20 g, P = 0.063; LVMBSA: 82 +/- 8 g m(-2) versus 71 +/- 10 g m(-2), P = 0.025). In adults, systolic blood pressure (SBP) and self-reported physical activity increased while meridional and circumferential wall stress were constant with age. Multivariate regression analysis revealed age, gender, and BSA as the major determinants of LVM (global R2 = 0.69).

CONCLUSIONS

Normal LVM shows variation over a broad age range in both genders with a rise in adolescence and subsequent decline with increasing age in adulthood despite an increase in SBP and physical activity. BSA, age, and gender were found to be major contributors to the variation in LVM in healthy adults, while haemodynamic factors, exercise, and wall stress were not.

Single-breathhold, four-dimensional, quantitative assessment of LV and RV function using triggered, real-time, steady-state free precession MRI in heart failure patients

PURPOSE

To validate a novel, real-time, steady-state free precession (SSFP), single-breathhold technique for the assessment of left ventricular (LV) and right ventricular (RV) function in heart failure patients.

MATERIALS AND METHODS

A total of 20 heart failure patients (mean age 59 +/- 17 years) underwent scanning with our new, real-time, spiral SSFP sequence in which each cardiac phase was acquired in 118 msec at a resolution of 1.8 x 1.8 mm. Each cardiac slice (1-cm thick) was automatically advanced based on a cardiac trigger, allowing complete coverage of the heart in a single breathhold. The patients also underwent LV and RV assessment with the gold standard: multiple breathhold, cardiac-gated, segmented k-space strategy. LV and RV end-systolic volume (ESV) and end-diastolic volume (EDV) and LV mass were compared between the two imaging techniques.

RESULTS

The new real-time strategy was highly concordant with the gold standard technique in the assessment of LVEDV (r = 0.98), LVESV (r = 0.98), RVESV (r = 0.86), RVEDV (r = 0.91), LVMASS (r = 0.95), RVEF (r = 0.70), and LVEF (r = 0.94). The mean bias (95% confidence interval [CI]) for each parameter is LVEDV: 10.6 cc (cm(3)) (3.8-17.4 cc), LVESV: -0.8 cc (-5.3 to 3.7 cc), RVEDV: 3.7 cc (-5.6 to 13.2 cc), RVESV: -3.1 cc (-11.1 to 4.9 cc), LVMASS: 26 g (12.4-39.8 g), RVEF: -2.9% (1.3 to -7.2 %), LVEF: 1.9% (5 to -1.1%). In addition, data acquisition was only nine +/- two seconds with the real-time strategy vs. 312 +/- 41 seconds for the standard technique.

CONCLUSION

In patients with heart failure, real-time, spiral SSFP allows rapid and accurate assessment of RV and LV function in a single-breath hold. Using the same strategy, increased temporal resolution will allow real-time assessment of cardiac wall motion during stress studies.

The reproducibility of left ventricular volume and mass measurements: a comparison between dual-inversion-recovery black-blood sequence and SSFP

The aim of this study was to compare a dual-inversion-recovery black-blood (BB) magnetic resonance imaging (MRI) sequence with steady-state free precession (SSFP) for the assessment of left ventricular parameters. The improved endocardial border definition seen with SSFP was not observed at the epicardial border. Improvements in segmentation at the left ventricular epicardial border have been observed with this black-blood sequence. Left ventricular (LV) mass and LV end-diastolic volume (EDV) measurements as well as inter-observer and intra-observer variability were compared between images acquired with a dual inversion BB and SSFP sequence. The mean+/-1 standard deviation (SD) for LV EDV was 178.3+/-52.7 ml measured with SSFP and 158.8+/-62.2 ml with BB. This difference was not statistically significant (p=0.22). For SSFP, the mean value of LV mass was 124.0+/-27.0 g and 147.5+/-37.4 g for BB, a statistically significant difference (p<0.0001). The dual-inversion-recovery BB imaging showed improved reproducibility for LV mass measurements compared with SSFP and improved spatial resolution. For studies requiring LV mass measurements, the dual-inversion-recovery BB sequence offers improved spatial resolution and improved reproducibility to SSFP.

Left ventricular function studied with MDCT

Accurate determination of left ventricular (LV) myocardial function is fundamental for clinical diagnosis, risk stratification, and estimation of prognosis in patients with ischemic and nonischemic cardiomyopathy. Primarily, multi-detector-row spiral CT (MDCT) of the heart aimed at detecting coronary artery obstruction and cardiac morphology. Multiple studies have demonstrated that retrospectively, ECG-gated MDCT determination of LV volumes and consequently global LV function parameters is feasible in good agreement with established imaging modalities such as cineventriculography, echocardiography, and cine magnetic resonance imaging (CMR). Post-processing tools allow fast and semi-automatic determination of LV function parameters from MDCT data in analogy to known CMR evaluation approaches. Although MDCT is not considered to be first-line modality for LV function assessment, this technique provides accessory dynamic information in patients undergoing MDCT coronary angiography, contributing to combined assessment of cardiac morphology and function without need of additional radiation exposure. MDCT regional LV wall motion analysis at rest is feasible, but further improvement in temporal resolution seems mandatory to match results obtained from competing modalities. This paper will discuss the diagnostic potential of MDCT for assessment of LV function with regards to accuracy and clinical applications, as well as limitations, particularly in comparison with CMR as modality of reference.

Comparison of pre-hospital combination-fibrinolysis plus conventional care with pre-hospital combination-fibrinolysis plus facilitated percutaneous coronary intervention in acute myocardial infarction

AIMS

Early and complete reperfusion is the main treatment goal in ST-elevation myocardial infarction (STEMI). The timely optimal reperfusion strategy might be a pre-hospital initiated pharmacological reperfusion with subsequent facilitated percutaneous coronary intervention (PCI). This approach has been compared with pre-hospital combination-fibrinolysis only to determine whether either one of these methods offer advantages with respect to final infarct size.

METHODS AND RESULTS

Patients with STEMI were randomized to either pre-hospital combination-fibrinolysis (half-dose reteplase+abciximab) with standard care (n=82) or pre-hospital combination-fibrinolysis with facilitated PCI (n=82). Primary endpoint was the infarct size assessed by delayed enhancement magnetic resonance. Secondary endpoints were ST-segment resolution at 90 min and a composite of death, re-myocardial infarction, major bleeding, and stroke at 6 months. The infarct size was lower after facilitated PCI with 5.2% [interquartile range (IQR) 1.3-11.2] as opposed to 10.4% (IQR 3.4-16.3) after pre-hospital combination-fibrinolysis (P=0.001). Complete ST-segment resolution was 80.0% after facilitated PCI vs. 51.9% after pre-hospital combination-fibrinolysis (P<0.001). After facilitated PCI, there was a trend towards a lower event rate in the combined clinical endpoint (15 vs. 25%, P=0.10, relative risk 0.57, 95% CI 0.28-1.13).

CONCLUSION

In patients with STEMI, additional facilitated PCI after pre-hospital combination-fibrinolysis results in an improved tissue perfusion with subsequent smaller infarct size as opposed to pre-hospital combination-fibrinolysis alone. This translates into a trend towards a better clinical outcome.

Effect of Endocardial Trabeculae on Left Ventricular Measurements and Measurement Reproducibility at Cardiovascular MR Imaging

PURPOSE

To prospectively assess the effect of including or excluding endocardial trabeculae in left ventricular (LV) measurements and the reproducibility of these measurements at cine cardiovascular magnetic resonance (MR) imaging with true fast imaging with steady-state precession (FISP).

MATERIALS AND METHODS

The study was approved by the local ethics committee, and each subject gave informed consent before participating. Twenty healthy subjects and 20 consecutive patients underwent 1.5-T cardiovascular MR imaging. Seven to 12 short-axis views encompassing the entire LV were acquired by using true FISP. Endocardial and epicardial contours were traced manually. The data sets in each patient were analyzed twice: with inclusion of endocardial trabeculae in the LV cavity volume and with exclusion of endocardial trabeculae from the cavity volume. On the basis of these two contour sets, the end-diastolic (ED) and end-systolic (ES) LV volumes, ejection fraction (EF), and LV mass were calculated. Additionally, interobserver and interexamination reproducibility was assessed by using Bland-Altman analysis.

RESULTS

Compared with exclusion of trabeculae, inclusion of trabeculae in the LV cavity volume resulted in significantly larger ED and ES LV volumes (mean differences, 21 mL +/- 11 [standard deviation] and 19 mL +/- 33, respectively; P < .001) and lower EFs (mean difference, -2% +/- 2; P < .001). The calculated LV mass was significantly smaller with inclusion than with exclusion of trabeculae (mean difference, -21 g +/- 12; P < .001). All interobserver and interexamination limits of agreement based on inclusion of trabeculae, except those for EF measurements, were superior to those based on exclusion of trabeculae. At measurement reproducibility comparisons, differences in interobserver ED LV volume and LV mass and interexamination LV mass were statistically significant, favoring the inclusion of trabeculae in the LV cavity volume.

CONCLUSION

Trabeculae significantly affect quantifications of LV volume and mass. The superior reproducibility of LV measurements with the inclusion of endocardial trabeculae in the cavity volume favors this tracing algorithm for clinical use.

Optimizing spatiotemporal sampling fork-t BLAST andk-t SENSE: Application to high-resolution real-time cardiac steady-state free precession

In k-t BLAST and k-t SENSE, data acquisition is accelerated by sparsely sampling k-space over time. This undersampling in k-t space causes the object signals to be convolved with a point spread function in x-f space (x = spatial position, f = temporal frequency). The resulting aliasing is resolved by exploiting spatiotemporal correlations within the data. In general, reconstruction accuracy can be improved by controlling the k-t sampling pattern to minimize signal overlap in x-f space. In this work, we describe an approach to obtain generally favorable patterns for typical image series without specific knowledge of the image series itself. These optimized sampling patterns were applied to free-breathing, untriggered (i.e., real-time) cardiac imaging with steady-state free precession (SSFP). Eddy-current artifacts, which are otherwise increased drastically in SSFP by the undersampling, were minimized using alternating k-space sweeps. With the synergistic combination of the k-t approach with optimized sampling and SSFP with alternating k-space sweeps, it was possible to achieve a high signal-to-noise ratio, high contrast, and high spatiotemporal resolutions, while achieving substantial immunity against eddy currents. Cardiac images are shown, demonstrating excellent image quality and an in-plane resolution of approximately 2.0 mm at >25 frames/s, using one or more receiver coils.

Assessment of left ventricular function with steady-state-free-precession magnetic resonance imaging. Reference values and a comparison to left ventriculography

Ejection fraction (EF) and end-diastolic and end-systolic volume index (EDVI/ ESVI) derived from ventriculography are important prognostic parameters. Cine magnetic resonance imaging (MRI) using a steady-state, free-precession sequence (SSFP) offers excellent delineation of the endocardial borders and highly reproducible and accurate results for cardiac volumes. We evaluated MRI volumetry against routine x-ray ventriculography. In 200 patients EF, EDVI and ESVI were measured with MRI volumetry and x-ray ventriculography. The same MRI protocol was applied to 102 healthy persons in order to establish reference values. In healthy subjects mean EF was 68.8% +/- 5.4% (range 59-84%), mean EDVI 69 +/- 10 (43-90) and mean ESVI 22 +/- 5.8 (10-35 ml). In the patients, overall correlation (Spearman's R) of MRI with ventriculography was 0.86 for EF, 0.77 for EDVI and 0.88 for ESVI. For postextrasystolic beats (38% of the measurements), R was 0.73/0.65/0.73 for EF/EDVI/ESVI. MRI correlated best with biplane ventriculography during sinus rhythm (0.96/0.85/0.93); the worst correlation (0.78/0.81/0.83) resulted from patients with wall motion abnormalities in comparison to monoplane x-ray ventriculography.

CONCLUSION

Contemporary MRI volumetry compares well to invasive data obtained under optimal conditions. In view of the known limitations of single plane ventriculography, MRI seems to allow exact volumetry independent from regional wall motion abnormalities.

High-Dose Dobutamine-Atropine Stress Cardiovascular MR Imaging after Coronary Revascularization in Patients with Wall Motion Abnormalities at Rest

PURPOSE

To determine the value of high-dose dobutamine-atropine stress cardiovascular magnetic resonance (MR) imaging for diagnosis of ischemia in patients with coronary artery disease (CAD) who had undergone revascularization and have wall motion abnormalities at rest, with quantitative invasive coronary angiography serving as reference standard.

MATERIALS AND METHODS

One hundred sixty consecutive patients (mean age, 59 years +/- 8 [standard deviation]) who had undergone revascularization for CAD and have wall motion abnormalities at rest underwent stress cardiovascular MR imaging prior to clinically indicated invasive coronary angiography. Turbo gradient-echo MR images were acquired at rest and during a standardized high-dose dobutamine-atropine protocol with three short-axis and two long-axis views. Regional wall motion was assessed by a blinded observer by using a 16-segment model and a four-point scoring system. New or worsening wall motion abnormality in at least one segment was considered positive for myocardial ischemia.

RESULTS

Significant CAD (stenoses of at least 50% diameter at angiography) was found in 119 patients (74%). Target heart rate was not reached in nine patients (6%). Overall sensitivity and specificity for detection of significant CAD were 89% and 84%, respectively. Diagnostic accuracy was 88%, and positive and negative predictive values were 94% and 73%, respectively. Overall sensitivity for detection of significant CAD in patients with single-, double-, and triple-vessel disease was 87%, 88%, and 100%, respectively.

CONCLUSION

High-dose stress cardiovascular MR imaging can be used for follow-up of patients after coronary revascularization procedures. Diagnostic accuracy is similar to stress cardiovascular MR imaging data for patients suspected of having CAD and compares favorably with that of other established noninvasive techniques.

Evaluation of aortic stenosis by cardiovascular magnetic resonance imaging: comparison with established routine clinical techniques

OBJECTIVE

To evaluate whether direct planimetry of aortic valve area (AVA) by cardiac magnetic resonance (CMR) imaging is a reliable tool for determining the severity of aortic stenosis compared with transthoracic echocardiography (TTE), transoesophageal echocardiography (TOE), and cardiac catheterisation.

METHODS

44 symptomatic patients with severe aortic stenosis were studied. By cardiac catheterisation AVA was calculated by the Gorlin equation. AVA was measured with CMR from steady state free precession (true fast imaging with steady state precession) by planimetry. AVA was also determined from TOE images by planimetry and from TTE images by the continuity equation.

RESULTS

Bland-Altman analysis evaluating intraobserver and interobserver variability showed a very small bias for both (-0.016 and 0.019, respectively; n = 20). Bias and limits of agreement between CMR and TTE were 0.05 (-0.35, 0.44) cm2 (n = 37), between CMR and TOE 0.02 (-0.39, 0.42) cm2 (n = 32), and between CMR and cardiac catheterisation 0.09 (-0.30, 0.47) cm2 (n = 36). The sensitivity and specificity of CMR to detect AVA < or = 0.80 cm2 measured by cardiac catheterisation was 78% and 89%, of TOE 70% and 70%, and of TTE 74% and 67%, respectively.

CONCLUSION

CMR planimetry is highly reliable and reproducible. Further, CMR planimetry had the best sensitivity and specificity of all non-invasive methods for detecting severe aortic stenosis in comparison with cardiac catheterisation. Therefore, CMR planimetry of AVA with steady state free precession is a new powerful diagnostic tool, particularly for patients with uncertain or discrepant findings by other modalities.

Visualization and tracking of an inflatable balloon catheter using SSFP in a flow phantom and in the heart and great vessels of patients

Passive catheter tracking involves direct interaction between the device and its surroundings, creating a local signal loss or enhancement of the image. Using only standard balloon catheters filled with CO(2) and imaged with a steady-state free precession sequence, it was possible to visualize and passively track catheters in a flow phantom and in the heart and great vessels of 20 patients without any additional image processing. The phantom work demonstrated that it was advantageous to sacrifice spatial resolution in order to increase temporal resolution. Frame rates greater than 10/sec were necessary for ease of catheter manipulation. Although only the tip of the catheter was visualized, this technique proved to be effective in patients undergoing cardiac catheterization.

Comparison of dobutamine stress magnetic resonance, adenosine stress magnetic resonance, and adenosine stress magnetic resonance perfusion

BACKGROUND

Dobutamine stress MR (DSMR) is highly accurate for the detection of inducible wall motion abnormalities (IWMAs). Adenosine has a more favorable safety profile and is well established for the assessment of myocardial perfusion. We evaluated the diagnostic value of IWMAs during dobutamine and adenosine stress MR and adenosine MR perfusion compared with invasive coronary angiography.

METHODS AND RESULTS

Seventy-nine consecutive patients (suspected or known coronary disease, no history of prior myocardial infarction) scheduled for cardiac catheterization underwent cardiac MR (1.5 T). After 4 minutes of adenosine infusion (140 microg x kg(-1) x min(-1) for 6 minutes), wall motion was assessed (steady-state free precession), and subsequently perfusion scans (3-slice turbo field echo-echo planar imaging; 0.05 mmol/kg Gd-BOPTA) were performed. After a 15-minute break, rest perfusion was imaged, followed by standard DSMR/atropine stress MR. Wall motion was classified as pathological if > or =1 segment showed IWMAs. The transmural extent of inducible perfusion deficits (<25%, 25% to 50%, 51% to 75%, and >75%) was used to grade segmental perfusion. Quantitative coronary angiography was performed with significant stenosis defined as >50% diameter stenosis. Fifty-three patients (67%) had coronary artery stenoses >50%; sensitivity and specificity for detection by dobutamine and adenosine stress and adenosine perfusion were 89% and 80%, 40% and 96%, and 91% and 62%, respectively. Adenosine IWMAs were seen only in segments with >75% transmural perfusion deficit.

CONCLUSIONS

DSMR is superior to adenosine stress for the induction of IWMAs in patients with significant coronary artery disease. Visual assessment of adenosine stress perfusion is sensitive with a low specificity, whereas adenosine stress MR wall motion is highly specific because it identifies only patients with high-grade perfusion deficits. Thus, DSMR is the method of choice for current state-of-the-art treatment regimens to detect ischemia in patients with suspected or known coronary artery disease but no history of prior myocardial infarction.

Cardiac SSFP imaging at 3 Tesla

Balanced steady-state free precession (SSFP) techniques provide excellent contrast between myocardium and blood at a high signal-to-noise ratio (SNR). Hence, SSFP imaging has become the method of choice for assessing cardiac function at 1.5T. The expected improvement in SNR at higher field strength prompted us to implement SSFP at 3.0T. In this work, an optimized sequence protocol for cardiac SSFP imaging at 3.0T is derived, taking into account several partly adverse effects at higher field, such as increased field inhomogeneities, longer T(1), and power deposition limitations. SSFP contrast is established by optimizing the maximum amplitude of the radiofrequency (RF) field strength for shortest TR, as well as by localized linear or second-order shimming and local optimization of the resonance frequency. Given the increased SNR, sensitivity encoding (SENSE) can be employed to shorten breath-hold times. Short-axis, long-axis, and four-chamber cine views obtained in healthy adult subjects are presented, and three different types of artifacts are discussed along with potential methods for reducing them.

Detection of apical hypertrophic cardiomyopathy by cardiovascular magnetic resonance in patients with non-diagnostic echocardiography

OBJECTIVE

To investigate the role of cardiovascular magnetic resonance (CMR) in a series of patients with ECG repolarisation changes and normal echocardiography.

PATIENTS AND DESIGN

10 patients with anterolateral T wave inversion for which there was no obvious pathological cause who had normal routine echocardiography without contrast for the exclusion of hypertrophic cardiomyopathy (HCM) also had CMR that was diagnostic of apical HCM.

RESULTS

Apical HCM detected by CMR could be morphologically severe with wall thickness up to 28 mm, or mild. The extent of repolarisation abnormalities did not correlate to the morphological severity.

CONCLUSIONS

In patients with unexplained repolarisation abnormalities, a normal routine echocardiogram without contrast does not exclude apical HCM. Further imaging with CMR or contrast echocardiography may be required. The reliance on routine echocardiography to exclude apical HCM may have led to underreporting of this condition.

MR imaging in ischemic heart disease

This article reviews the current MR imaging literature with respect to ischemic heart disease and focuses on the clinical practicalities of cardiac MR imaging today.

Flow effects in balanced steady state free precession imaging

An analysis of the effect of flow on 2D fully balanced steady state free precession (SSFP) imaging is presented. Transient and steady-state SSFP signal intensities in the presence of steady and pulsatile flow were simulated using a matrix formalism based on the Bloch equations. Various through-plane flow waveforms and rates were modeled numerically considering factors such as the excitation slice profile and both in- and out-flow effects. Phantom measurements in an experimental setup that allowed the assessment of SSFP signal properties as a function of frequency offset and flow rate demonstrated that the computer simulations provided a suitable description of the effects of flow in SSFP imaging. A volunteer scan was performed to provide in vivo validations. For accurate modeling of SSFP signal intensities it is crucial to include effects such as imperfect slice profiles and, more importantly, "out-of-slice" contributions to the signal. Both simulations and experiments show that there can be considerably large-frequency offset dependent-signal contributions from flowing spins that have already left the imaging slice but still add to the SSFP signal. Although spins leaving the slice do not experience additional RF-excitation, gradient activity is not confined to the region of excitations and the balanced nature of the SSFP imaging gradients allows "out-of-slice" transverse magnetization to contribute to the total SSFP signal, effectively by broadening the slice thickness for flowing spins. This results in a frequency dependence of in-flow related signal enhancement and flow artifacts.

Dark Flow Artifacts with Steady-State Free Precession Cine MR Technique: Causes and Implications for Cardiac MR Imaging

Steady-state free precession cine images from cardiac magnetic resonance imaging studies of 24 patients were reviewed retrospectively to identify dark flow artifacts. The cause and features of the artifacts were studied in flow phantom experiments. Dark flow artifacts were recognized in eight of the 24 cases and were characterized by low or inhomogeneous signal intensity in blood pools with little change in adjacent tissues. The artifacts could be mimicked in flow phantom experiments by deliberately deshimming the gradients and appeared periodically during imaging with off-centered frequencies. These artifacts appeared to be caused by spins moving within an inhomogeneous magnetic field.

Myocardial delayed enhancement imaging using inversion recovery single-shot steady-state free precession: Initial experience

PURPOSE

To evaluate the feasibility of using an inversion recovery single-shot steady-state free precession (SS_SSFP) sequence for myocardial delayed enhancement (MDE) imaging, and to compare SS_SSFP with the conventional inversion recovery segmented fast gradient echo (IR_FGRE) technique.

MATERIALS AND METHODS

Ten subjects (four volunteers and six patients with suspected or known coronary disease) were included in this study. All subjects were scanned with both IR_FGRE and SS_SSFP sequences 15-25 minutes after gadopentetate dimeglumine injection. Overall image quality, signal-to-noise ratios (SNRs), and contrast-to-noise ratios (CNRs) between the two techniques were compared.

RESULTS

Compared to IR_FGRE, SS_SSFP exhibited adequate image quality (average scores = 3.8 for IR_FGRE and 3.9 for SS_SSFP) with much shorter acquisition time (14.4 seconds for IR_FGRE and 1.3 seconds for SS_SSFP). SS_SSFP images showed higher SNRs (P < 0.05) and less motion artifact from breathing. Enhanced myocardium was detected by both techniques in three patients, but the image sharpness is compromised in SS_SSFP images.

CONCLUSION

SS_SSFP provides adequate image quality compared to IR_FGRE, while requiring a much shorter acquisition time. It is feasible to use SS_SSFP as an alternative method for MDE imaging, especially in patients who have difficulty with holding their breath.

Cine MR imaging of heart valve dysfunction with segmented true fast imaging with steady state free precession

PURPOSE

To evaluate the value of cine true fast imaging with steady-state free precession (SSFP) for semiquantitative assessment of valvular dysfunction in the heart and to compare the results to that obtained with a standard breath-hold segmented gradient-recalled echo-planar imaging sequence (GE-EPI).

MATERIALS AND METHODS

Twenty-three patients with known valvular dysfunction (main component: 16 with aortic valve stenosis, nine with aortic valve insufficiency, three with mitral stenosis, two with mitral regurgitation, two with tricuspidal regurgitation, and one with pulmonary stenosis) and 23 control subjects with normal valvular function underwent MR imaging on a 1.5-T system (ACS-NT, Philips, Best, The Netherlands). Cine SSFP and GE-EPI images were acquired in identical long-axis views. Images were evaluated for the presence and extent of the signal void arising from the valves and for image quality consensus by two experienced radiologists. Results were compared to those obtained by cardiac catheterization (in 16 patients) or color Doppler (in the remaining seven patients).

RESULTS

On SSPF images, the complex flow pattern in valvular regurgitant or stenotic lesions caused signal void within the bright blood pool of the atria or ventricles, similar to GE-EPI, in all patients. Valvular dysfunction was delineated using SSFP with the same high sensitivity (100%) as using the GE-EPI sequence. Results correlated to those obtained by cardiac catheterization or color Doppler ultrasonography (P < 0.001, r = 0.97). However, the jet phenomenon was slightly more pronounced in five patients on GE-EPI. There was no significant signal void in the 23 control subjects with both sequences. In all 46 subjects, the image quality of SSFP images was rated higher (P < 0.05; 2.6 +/- 0.1; using a scale ranging from 0-3) compared to GE-EPI (1.7 +/- 0.1).

CONCLUSION

The results of this study suggest that valvular dysfunction can be semiquantitatively assessed using SSFP cine MR imaging.

Assessment of myocardial ischemia and viability using cardiac magnetic resonance

Cardiac magnetic resonance (CMR) is a burgeoning area of noninvasive cardiac imaging. Today, its clinical utility spans from the qualitative and quantitative assessment of cardiac function and morphology to the challenging task of determining the severity and reversibility of coronary heart disease. Advances in magnet and coil design, pulse sequence, and contrast media have contributed greatly, helping CMR become the multipurpose tool of today's cardiac imaging. This article reviews and explores some of the most exciting clinical applications of CMR in the assessment of coronary artery disease.

Comparison of right ventricular volume measurements between axial and short axis orientation using steady-state free precession magnetic resonance imaging

PURPOSE

To compare right ventricular (RV) volume measurements and their reproducibility between axial and short axis orientation acquisition techniques.

MATERIALS AND METHODS

Measurements of RV volumes from data sets acquired in axial and short axis orientations were compared in 20 normal subjects. The observer variabilities were assessed and the left ventricle (LV) and RV stroke volumes (SV) were compared.

RESULTS

There was a significant and systematic difference in the EDV and ESV volumes between the axial and short axis methods. The latter method resulted in larger volumes (mean bias EDV 7.5 +/- 13.2, 4.7% difference; ESV 7.2 +/- 8.6, 10.7% difference). The axial method had lower intra- and interobserver variability than the short axis method. The standard deviation of the difference (SDD) and the limits of agreement were consistently lower for the axial method. The mean differences between LV and RV stroke volumes expressed as mean +/- 1 SD (r(2) =correlation coefficient) were: axial 7.6 +/- 9.1 (r(2) = 0.93); and short axis 7.4 +/- 10.8 (r(2) = 0.90).

CONCLUSION

There is a significant systematic difference between volumes measured using the two different orientations. The axial orientation resulted in better inter- and intraobserver reproducibility.

Fast interactive real-time magnetic resonance imaging of cardiac masses using spiral gradient echo and radial steady-state free precession sequences

RATIONALE AND OBJECTIVES

Cardiac and respiratory controlled MR-imaging is the gold standard for imaging of cardiac masses. However, this technique may be limited in patients with dyspnoe or arrhythmia. The aim of this study was the evaluation of an interactive MR-approach for the detection and localization of cardiac masses.

METHODS

Interactive real-time spiral gradient-echo (spiralGE) and radial steady-state-free-precession (radialSSFP) MR-imaging was performed during free-breathing and without cardiac triggering in 15 patients with 14 intracardiac or paracardiac masses. Standard cardiac triggered segmented k-space breath-hold steady-state-free-precession cine MR-imaging was used as the reference MR-imaging technique. Two groups of investigators blinded to clinical data were ask to rank image quality and to identify cardiac masses on real-time MR-images.

RESULTS

Image quality was superior using radialSSFP when compared with spiralGE. Using radialSSFP all masses were correctly detected while 6 of 14 masses were missed on spiralGE. Mean real-time MR-imaging time was less than 3 minutes for both techniques.

CONCLUSION

Interactive real-time radialSSFP MR-imaging allows for accurate and fast detection of cardiac masses without the need of cardiac or respiratory triggering.

Normal human left and right ventricular dimensions for MRI as assessed by turbo gradient echo and steady-state free precession imaging sequences

PURPOSE

To establish normal ranges of left ventricular (LV) and right ventricular (RV) dimensions as determined by the current pulse sequences in cardiac magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Sixty normal subjects (30 male and 30 female; age range, 20-65) were examined; both turbo gradient echo (TGE) and steady-state free precession (SSFP) pulse sequences were used to obtain contiguous short-axis cine data sets from the ventricular apex to the base of the heart. The LV and RV volumes and LV mass were calculated by modified Simpson's rule.

RESULTS

Normal ranges were established and indexed to both body surface area (BSA) and height. There were statistically significant differences in the measurements between the genders and between TGE and SSFP pulse sequences. For TGE the LV end-diastolic volume (EDV)/BSA (mL/m(2)) in males was 74.4 +/- 14.6 and in females was 70.9 +/- 11.7, while in SSFP in males it was 82.3 +/- 14.7 and in females it was 77.7 +/- 10.8. For the TGE the LV mass/BSA (g/m(2)) in males was 77.8 +/- 9.1 and in females it was 61.5 +/- 7.5, while in SSFP in males it was 64.7 +/- 9.3 and in females it was 52.0 +/- 7.4. For TGE the RV EDV/BSA (mL/m(2)) in males was 78.4 +/- 14.0 and in females it was 67.5 +/- 12.7, while in SSFP in males it was 86.2 +/- 14.1 and in females it was 75.2 +/- 13.8.

CONCLUSION

We have provided normal ranges that are gender specific as well as data that can be used for age-specific normal ranges for both SSFP and TGE pulse sequences.

Future prospects in cardiac magnetic resonance imaging

To appreciate the impact that key developments will have on the future of cardiovascular magnetic resonance (CMR) imaging, it is instructive to consider its present status. CMR has passed the threshold of being used primarily by innovators, and is now in the early adopter stage. To reach this threshold has taken many years, but its adoption by early majority users is expected to accelerate the growth of CMR. A number of factors govern its natural growth potential, including physician education and credentialing, scanner availability, technology, and reimbursement policies. The intrinsic dimensional accuracy of CMR, coupled with its high level of reproducibility, make it ideal for inclusion in trials, potentially with dramatic reductions in trial duration and the number of subjects required. Clinically, there are a number of applications for which CMR is widely regarded as being the diagnostic test of choice. Software and hardware developments that speed up the basic CMR procedure are being incorporated into scanners, extending the functionality of routine applications such as flow imaging and tag visualization. Exciting areas that are close to routine application include coronary artery imaging, and evaluation of myocardial perfusion and viability status.

MR angiography of the chest

Using the described strategies all relevant disease processes of the thoracic vessels can be fully depicted using contrast-enhanced three-dimensional MRA. The aorta and the major neck and arm vessels are well visualized. Vascular pathologies, such as aneurysms, dissections, and occlusions, are readily recognized. With the implementation of high-performance gradients, three-dimensional MRA of the pulmonary vasculature has become possible even in dyspneic patients. Congenital lesions, such as coarctations, are particularly well suited for analysis with these techniques.

Optimization of signal behavior in the transition to driven equilibrium in steady-state free precession sequences

A new technique to avoid the initial signal fluctuations in steady-state free precession (SSFP)-sequences, such as trueFISP, FIESTA, and refocused FFE, is presented. The "transition into driven equilibrium" (TIDE) sequence uses modified flip angles over the initialization phase of a SSFP experiment, which not only avoids image artifacts but also improves the signal-to-noise ratio (SNR) and contrast behavior compared to conventional approaches. TIDE is demonstrated to be robust against variations of T(1) and T(2), and leads to a monotonous signal evolution for off-resonance spins. The basic principles can also be applied repetitively to optimize continuous 3D acquisitions.

MR assessment of left ventricular function: quantitative comparison of fast imaging employing steady-state acquisition (FIESTA) with fast gradient echo cine technique

PURPOSE

To evaluate the agreement of fast imaging employing steady-state acquisition (FIESTA) cine technique with segmented k-space fast gradient echo (GRE) cine technique when using them for assessment of cardiac function.

MATERIALS AND METHODS

Eleven MR cine studies were performed on six healthy volunteers and five patients, using FIESTA and fast GRE techniques. The quantitative measurements of ventricular function obtained from the two techniques were compared. The data analysis was performed by two observers independently.

RESULTS

Compared to fast GRE cine technique, FIESTA cine technique consistently resulted in higher end-diastolic volume (10.2%) and end-systolic volume (21.6%), but lower myocardial mass of left ventricle (19.2%) and ejection fraction (9.9%). The stroke volume obtained from the two techniques was very close. The primary explanation for this variability is that the two techniques have different mechanisms on establishing signal contrast.

CONCLUSION

Compared to fast GRE technique, FIESTA provides significantly different results when using it for assessment of left ventricular function. It is important to consider this difference in the assessment of cardiac function.

Improved visualization of coronary arteries using a new three-dimensional submillimeter MR coronary angiography sequence with balanced gradients

OBJECTIVE

The goal of our study was to evaluate a new three-dimensional real-time navigator MR coronary angiography sequence to noninvasively visualize the coronary arteries.

SUBJECTS AND METHODS

Fifteen healthy volunteers underwent MR coronary angiography with a new balanced turbo field-echo sequence in comparison with the standard turbo field-echo sequence. Signal-to-noise, blood-to-myocardium, blood-to-fat, and blood-to-pericardial fluid contrast ratios of the left and right coronary artery systems were measured. Image quality was graded, the length and diameter of the coronary arteries were measured, and the number of visible side branches was assessed.

RESULTS

The balanced turbo field-echo images yielded a higher blood-to-myocardium and blood-to-pericardial fluid contrast ratio, a similar blood-to-fat contrast ratio, and a lower signal-to-noise ratio than the turbo field-echo images. On a 5-point grading scale (1, nondiagnostic or unreadable; 2, poor; 3, moderate; 4, good; 5, excellent), image quality was rated significantly better for the balanced turbo field-echo sequence than for the turbo field-echo sequence (left coronary artery, 4.0 +/- 0.6 vs 3.6 +/- 0.5 [p = 0.015]; right coronary artery, 4.4 +/- 0.4 vs 3.6 +/- 0.4 [p < 0.0001], respectively), resulting in a significantly longer segment of the three major coronary arteries visualized (left anterior descending coronary artery, 92 +/- 21 mm vs 79 +/- 24 mm; left circumflex coronary artery, 70 +/- 7 mm vs 60 +/- 18 mm; right coronary artery, 112 +/- 28 mm vs 95 +/- 27 mm) and a significantly higher number of side branches visualized (left anterior descending coronary artery, 2.9 +/- 1.3 vs 1.5 +/- 1.3; left circumflex coronary artery, 2.1 +/- 1.7 vs 1.0 +/- 1.2; right coronary artery, 3.7 +/- 1.7 vs 2.6 +/- 1.5). Mean imaging time per coronary artery was significantly shorter for the balanced turbo field-echo sequence (5.7 +/- 1.0 min) than for the turbo field-echo sequence (8.4 +/- 1.4 min) (p < 0.0001).

CONCLUSION

Compared with standard turbo field-echo MR coronary angiography, optimized balanced turbo field-echo MR coronary angiography improves the visualization of the coronary arteries and their side branches within a significantly shorter imaging time.

Comparison of right ventricular volume measurement between segmented k-space gradient-echo and steady-state free precession magnetic resonance imaging

PURPOSE

To compare right ventricular volume measurements and their reproducibility between steady-state free precession (SSFP) and conventional turbo gradient-echo (TGE) imaging.

MATERIALS AND METHODS

Right ventricular volumes and observer variabilities were compared between SSFP and TGE in 31 subjects (21 normal volunteers and 10 subjects with heart failure). For further internal validation of the right ventricular volumes, the left ventricle (LV) and right ventricle (RV) stroke volumes were compared for the normal volunteers.

RESULTS

The volumes as measured by SSFP were significantly larger than for TGE (mean bias end-diastolic volume [EDV] 11.1 +/- 14.2, end-systolic volume [ESV] 9.8 +/- 9.75). SSFP had lower interobserver variability (SSFP EDV -10.1 +/- 11.6 vs. TGE EDV -6.2 +/- 18.5) and intra-observer variability (SSFP EDV -2.0 +/- 6.3 vs. TGE EDV -6.1 +/- 14.8). The mean absolute differences between LV and RV stroke volumes for 21 normal volunteers were: TGE 5.8 +/- 12.9 (r(2) = 0.72), SSFP 4.6 +/- 6.9 (r(2) = 0.92).

CONCLUSION

SSFP and TGE yield different measurement values of RV volumes with SSFP, providing a more reproducible measurement.