MR evaluation of ventricular function: true fast imaging with steady-state precession versus fast low-angle shot cine MR imaging: feasibility study

Cardiac functional analysis with multi-detector row CT and segmental reconstruction algorithm: comparison with echocardiography, SPECT, and MR imaging

PURPOSE

To evaluate accuracy of cardiac functional analysis with multi-detector row computed tomography (CT) and segmental reconstruction algorithm over a range of heart rates.

MATERIALS AND METHODS

Institutional review board approval was obtained. Informed consent was not required. Multi-detector row CT (500-msec rotation time, 8 x 1-mm detector collimation) and magnetic resonance (MR) imaging were performed in 50 patients (28 men, 22 women; age range, 46-84 years; mean age, 67 years). Two-dimensional echocardiography was performed in 41 patients, and electrocardiographically (ECG)-gated single photon emission computed tomography (SPECT) was performed in 27. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and left ventricular (LV) mass were estimated with multi-detector row CT and compared with values estimated with MR imaging, which served as the reference standard. Additionally, EF values estimated with multi-detector row CT, echocardiography, and SPECT were compared with those estimated with MR imaging. Systemic error and degree of agreement of global functional parameters measured with MR imaging and other modalities were assessed. In a second analysis, linear regression analysis was added.

RESULTS

EF estimated with multi-detector row CT agreed and correlated well with EF estimated with MR imaging (bias +/- standard deviation, -1.2% +/- 4.6; r = 0.96). Agreement and correlation were similar for EDV (-0.35 mL +/- 15.2; r = 0.97), ESV (1.1 mL +/- 8.6; r = 0.99), and LV mass (2.5 mL +/- 15.0; r = 0.96). Standard deviation of EF difference between multi-detector row CT and MR imaging was significantly less than that between echocardiography and MR imaging (P < .001) or that between SPECT and MR imaging (P < .001).

CONCLUSION

Various LV functional parameters were measured with multi-detector row CT with a segmental approach, and measurements correlated and agreed with those obtained with MR imaging. Moreover, functional analysis with multi-detector row CT was more accurate than that with two-dimensional echocardiography or ECG-gated SPECT.

Assessment of Left Ventricular Parameters Using 16-MDCT and New Software for Endocardial and Epicardial Border Delineation

OBJECTIVE

The purpose of our study was to quantify left ventricular function and mass derived from retrospectively ECG-gated 16-MDCT coronary angiography data sets using a new analysis software based on automatic contour detection in comparison to corresponding standard of reference measurements acquired with MRI.

SUBJECTS AND METHODS

Multiplanar reformations in the short-axis orientation were calculated from axial contrast-enhanced CT images in 18 patients (men, 15; women, three; age range, 38-70 years; mean, 57.4 +/- 10.2 [SD] years) who were referred for CT coronary angiography. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), and left ventricular mass (LVM) were analyzed with a recently developed imaging software using an automated contour detection algorithm of left ventricular endo- and epicardial contours and by manual tracing. The data were compared with similar measurements on MRI as the standard of reference.

RESULTS

EDV, ESV, EF, and LVM derived from an automated contour detection algorithm were not statistically significantly different from manual tracing (CT(auto) vs CT(manual): EDV = 137.1 +/- 45.7 mL vs 134.2 +/- 39.9 mL, ESV = 58.8 +/- 34.2 mL vs 58.1 +/-30.1 mL, EF = 59.2% +/- 13.7% vs 58.1% +/- 12.0%, LVM = 130.9 +/- 29.1 g vs 133.7 +/- 33.2 g; p > 0.05). However, EDV (118.7 +/- 43.6 mL), ESV (50.1 +/- 33.5 mL), and LVM (142.8 +/-38.4 g) as calculated on MR data sets were statistically significantly different from those calculated on CT (p < 0.05), whereas MRI-based EF (59.9% +/- 14.4%) did not differ statistically significantly from those based on both CT algorithms (p > 0.05).

CONCLUSION

Automatic and manual analysis of data acquired during CT coronary angiography using a 16-MDCT scanner allows a reliable assessment of left ventricular ejection fraction and a rough estimation of left ventricular volumes and mass.

Full-Body Cardiovascular and Tumor MRI for Early Detection of Disease: Feasibility and Initial Experience in 298 Subjects

OBJECTIVE

High diagnostic accuracy, emerging whole-body concepts, and lack of side effects combine to render MRI a natural candidate for screening purposes. The aim of this study was to evaluate the technical feasibility of a comprehensive multiorgan-targeting MRI examination and determine the frequency of findings in subjects without a history of serious disease.

SUBJECTS AND METHODS

The study group was composed of 331 subjects. The MRI protocol (mean examination time, 63 min) encompassed the target organs: the brain, arterial system, heart, and colon. Diagnoses were deemed relevant if the physician had to inform the subject about the findings. Subjects with a history of serious illnesses were excluded from subsequent analysis (n=33). All analyses were performed for the resulting subgroup of 298 subjects (247 men, 51 women; mean age, 49.7 years).

RESULTS

All 298 examinations were diagnostic excluding eight MR colonography components in which remaining stool hampered reliable diagnosis. Follow-up or radiologic confirmation could be obtained in 75% of all cases with relevant findings (128/169); only one false-positive result was encountered. Of the study group, 21% exhibited signs of atherosclerotic disease. Two cerebral infarctions and one myocardial infarction, previously unknown, were encountered; 12% had peripheral vascular disease. Twelve colonic polyps and nine pulmonary lesions were correctly detected. Of all MRI examinations, 29% revealed relevant additional findings in nontargeted organs. Only one minor allergoid reaction was encountered.

CONCLUSION

The presented data point toward an increased use of MRI for screening in the future, but to date screening MRI should not be performed outside a research setting because the cost-benefit relation is unclear.

Assessment of left ventricular function by breath-hold cine MR imaging: Comparison of different steady-state free precession sequences

PURPOSE

To compare steady-state free precession (SSFP) sequence protocols with different acquisition times (TA) and temporal resolutions (tRes) due to the implementation of a view sharing technique called shared phases for the assessment of left ventricular (LV) function by breath-hold cine magnetic resonance (MR) imaging.

MATERIALS AND METHODS

End-diastolic and end-systolic volumes (EDV, ESV) were measured in contiguous short-axis slices with a thickness of 8 mm acquired in 10 healthy male volunteers. The following true fast imaging with steady-state precession (TrueFISP) sequence protocols were compared: protocol A) internal standard of reference, segmented: tRes 34.5 msec, TA 18 beats per slice; protocol B) segmented, shared phases: tRes 34.1 msec, TA 10 beats per slice; and protocol C) real-time, shared phases, parallel acquisition technique: tRes 47.3 msec, TA 24 beats for 12 slices covering the entire left ventricle.

RESULTS

Phase sharing leads to a significant decrease in EDV, stroke volume (SV), and ejection fraction (EF) (median difference -7.0 mL [*], -9.6 mL, and -3.4%, respectively, for protocol B; -15.3 mL, -13.3 mL, and -2.4% for protocol C; P = 0.002, *P = 0.021). The observed median difference of real-time EDV and SV estimates is of clinical relevance. Real-time cine MR imaging shows a greater variability of EDV and SV. No relevant differences in ESV were observed.

CONCLUSION

The true cine frame duration of both shared phases sequence protocols exceeds the period of isovolumetric contraction (IVCT) of the left ventricle resulting in a systematic and significant underestimation of EDV and consequently SV and EF. SSFP sequence protocol parameters, particularly tRes and use of view sharing techniques, should therefore be known at follow-up examinations in order to be able to assess LV remodeling in patients with heart failure.

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.

Towards a Single-Sequence Neurologic Magnetic Resonance Imaging Examination: Multiple-Contrast Images From an IR TrueFISP Experiment

OBJECTIVE

The objective of this study was to reconstruct images bearing multiple contrasts from a single sequence magnetic resonance imaging (MRI) experiment.

MATERIALS AND METHODS

Using a segmented IR-TrueFISP imaging sequence, the signal recovery after inversion and alpha/2 preparation was sampled in 6 volunteers. These images were used to generate T1, T2, and spin-density maps, allowing construction of images with multiple contrasts, including T1-, T2-, spin-density-weighted, and also FLAIR contrast. Traditionally acquired images bearing the corresponding contrast were obtained for comparison. Regression analysis was performed to compare the synthetic and traditionally acquired images for the whole brain and a region of interest in the occipital region.

RESULTS

The synthetic images closely reproduced the contrast from the "standard" examination. Using regression analysis, the obtained image signal intensities for the calculated images compare favorably (P <0.0001-<<0.000001) with images acquired using multiple sequences.

CONCLUSIONS

Perfectly registered images with any desired contrast based on T1, T2, and spin density, along with underlying quantitative maps, can be obtained using a single IR-TrueFISP sequence.

Imaging of myocardial perfusion with magnetic resonance

Coronary artery disease (CAD) is currently the leading cause of death in developed nations. Reflecting the complexity of cardiac function and morphology, noninvasive diagnosis of CAD represents a major challenge for medical imaging. Although coronary artery stenoses can be depicted with magnetic resonance (MR) and computed tomography (CT) techniques, its functional or hemodynamic impact frequently remains elusive. Therefore, there is growing interest in other, target organ-specific parameters such as myocardial function at stress and first-pass myocardial perfusion imaging to assess myocardial blood flow. This review explores the pathophysiologic background, recent technical developments, and current clinical status of first-pass MR imaging (MRI) of myocardial perfusion.

Évaluation de la fonction cardiaque en imagerie par résonance magnétique et scanner hélicoïdal multicoupe

Magnetic resonance imaging and multislice spiral computed tomography are ideal techniques for assessing cardiac function. The main objectives of this article are to describe the different aspects, global and regional systolic left ventricular function, diastolic left ventricular function and right ventricular function, and to introduce the agreed parameters for this evaluation.

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.

MRI in coronary artery disease

Diagnosis of coronary artery disease (CAD) is a major challenge for medical imaging, because CAD is the leading cause of death in developed nations. Several non-invasive tests are used in clinical routine for the detection of CAD. However, due to limited sensitivity and specificity, the reliable diagnosis as well as the exclusion of CAD can only be established by catheter angiography. In patients with known CAD, therapeutic decisions require accurate information on myocardial function, ischemia and viability. Recently, magnetic resonance (MR) imaging has emerged as a non-invasive cardiac imaging technique that provides information on cardiac morphology, cardiac function, myocardial viability, and coronary morphology. This review discusses technical aspects and the clinical impact of different MR techniques.

Is Postcontrast trueFISP Imaging Advantageous?

RATIONALE AND OBJECTIVES

Contrast of trueFISP images depends mainly on the T2/T1 ratio. Consequently, there is a potential gain in signal intensity after administration of paramagnetic contrast medium despite the strong T2 weighting. The purpose of this study was to analyze signal intensities of abdominal organs after applying contrast medium and to determine whether this yields an improved contrast for pathologies compared with precontrast trueFISP.

MATERIALS AND METHODS

Fifty patients underwent an abdominal examination, including the trueFISP sequence before and after the administration of contrast medium. All images were obtained with a 1.5 T system. The mean signal-to-noise ratio before and after contrast medium was assessed for abdominal organs, vessels, muscle, and fat. The contrast-to-noise ratio (CNR) of pathologic lesions was calculated.

RESULTS

The trueFISP sequence yielded a higher signal-to-noise ratio after application of contrast medium for all organs except for fat and the aorta. CNR of solid lesions (angiomyolipoma, liver adenoma, liver hemangioma, hepatocellular carcinoma) increased whereas contrast of cysts decreased.

CONCLUSIONS

TrueFISP imaging after application of contrast medium led to better CNR for many solid lesions while cysts showed a diminished contrast. We advise trueFISP imaging sequences before and after contrast medium application.

Multislice first-pass myocardial perfusion imaging: Comparison of saturation recovery (SR)-TrueFISP-two-dimensional (2D) and SR-TurboFLASH-2D pulse sequences

PURPOSE

To compare signal-to-noise ratio (SNR), contrast-to-noise (CNR) ratio, and diagnostic accuracy of a newly developed saturation recovery (SR)-TrueFISP-two-dimensional (2D) sequence with an SR-TurboFLASH-2D sequence.

MATERIALS AND METHODS

In seven healthy subjects and nine patients with coronary artery disease (CAD), contrast-enhanced perfusion imaging (with Gd-DTPA) was performed with SR-TrueFISP and SR-TurboFLASH sequences. Hypoperfused areas were assessed qualitatively (scale = 0-4). Furthermore, SNR and CNR were calculated and semiquantitative perfusion parameters were determined from signal intensity (SI) time curves. Standard of reference for patient studies was single-photon emission computer tomography (SPECT) and angiography.

RESULTS

The perception of perfusion deficits was superior in TrueFISP images (2.6 +/- 1.0) than in TurboFLASH (1.4 +/- 0.6) (P < 0.001). Phantom measurements yielded increased SNR (143 +/- 34%) and CNR (158 +/- 64%) values for TrueFISP. In patient/volunteer studies SNR was 61% to 100% higher and signal enhancement was 110% to 115% higher with TrueFISP than with TurboFLASH. Qualitative and semiquantitative assessment of perfusion defects yielded higher sensitivities for detection of perfusion defects with TrueFISP (68% to 78%) than with TurboFLASH (44% to 59%).

CONCLUSION

SR-TrueFISP-2D perfusion imaging provides superior SNR and CNR than TurboFLASH imaging. Moreover, the dynamic range of SIs was found to be higher with TrueFISP, resulting in an increased sensitivity for detection of perfusion defects.

HASTE MRI Versus Chest Radiography in the Detection of Pulmonary Nodules: Comparison with MDCT

OBJECTIVE

The purpose of our study was to compare the diagnostic accuracy of an ultrafast ECG-triggered black blood-prepared HASTE sequence with chest radiography for the detection of pulmonary nodules. SUBJECTS AND METHODS. Sixty-four patients with various primary malignancies who had undergone radiography and MDCT of the chest also underwent ECG-triggered black blood-prepared HASTE MRI of the lung. MR images and radiographs were interpreted separately. The number, location, and size of detected lesions were recorded, and each hemithorax was classified as affected or not affected on the basis of a grade reflecting the conspicuity of nodular involvement. Sensitivity, specificity, and positive and negative predictive values for the detection of pulmonary nodules with diameters of 5 mm or larger were determined, using MDCT findings as the standard of reference. Lesions with diameters smaller than 5 mm were not evaluated. Additional lesion-by-lesion comparisons between MDCT and MRI findings were performed.

RESULTS

MDCT confirmed pulmonary lesions in 32 patients, whereas HASTE MRI revealed lesions in 30 patients and chest radiography, in 19 patients. MDCT revealed 226 nodules in 32 patients, whereas MRI HASTE revealed 227 lesions in 30 patients. Conspicuity scale-based sensitivity and specificity for chest radiography were 55.8% and 92.4%, respectively, whereas HASTE MRI had a sensitivity of 93.0% and a specificity of 96.2%. Positive and negative predictive values for chest radiography were 80% and 79.3%, respectively, and for HASTE MRI, 93.0% and 96.2%, respectively. The sensitivity of HASTE MRI increased with lesion size, ranging from 94.9% for nodules between 5 and 10 mm in diameter to 100% for lesions exceeding 3 cm in diameter.

CONCLUSION

ECG-triggered black blood-prepared HASTE MRI is reliable for detecting pulmonary nodules exceeding 5 mm and has proven significantly more accurate than conventional chest radiography. The technique appears useful as an adjunct to MRI of the heart, great vessels, or chest, potentially increasing the diagnostic yield of MRI examinations.

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.

Reduced data acquisition methods in cardiac imaging

In cardiac imaging, acquisition speed is of primary importance. While improved performance has mainly been achieved through improvements in gradient hardware in the past, further developments along this direction are limited due to physiological constraints such as the risk of peripheral nerve stimulation. With the introduction of parallel imaging, alternative means for increasing acquisition speed have become available. Using information from multiple receiver coils, images can be reconstructed from a sparsely sampled set of data. In practice, parallel imaging allows for 2- to 3-fold acceleration of the imaging process in typical cardiac applications. Further increases in acquisition speed are, however, difficult to achieve for current clinical field strengths and typical field of views. To address the limited gain in acquisition speed achievable with parallel imaging, a new set of methods has been proposed to take into account the similarity of image information at different time points during a dynamic series. Using these methods, 5- to 8-fold acceleration can be achieved in cardiac imaging. It is the purpose of this paper to review cardiac applications of reduced data acquisition methods with focus on parallel imaging and the recently developed k-t BLAST and k-t SENSE techniques.

Assessment of Myocardial Function with Interactive Non–Breath-hold Real-time MR Imaging: Comparison with Echocardiography and Breath-hold Cine MR Imaging

PURPOSE

To compare a spiral gradient-echo sequence with a radial steady-state free precession sequence and to compare these two interactive real-time cardiac magnetic resonance (MR) imaging examinations with harmonic two-dimensional echocardiography (ECHO) for the evaluation of regional myocardial function.

MATERIALS AND METHODS

Electrocardiographically triggered breath-hold steady-state free precession (BH-SSFP) MR imaging was the reference standard. Thirty-five nonselected patients scheduled for routine ECHO were included. Data from corresponding two-, three-, and four-chamber long-axis views and a midventricular short-axis view were acquired with each modality. Image quality and depiction of segmental wall motion were scored semiquantitatively by using the 16-segment model of the American Society of Echocardiography. Repeated-measures analysis of variance was performed to assess differences in image quality and wall motion depiction scores among the four imaging methods. Agreement was assessed by using Cohen kappa statistics.

RESULTS

Compared with the image quality achieved with BH-SSFP MR imaging, the image quality achieved with radial MR imaging was similar (nonsignificant difference), but that achieved with spiral MR imaging and ECHO was significantly inferior (P <.0001). There were no significant differences in the image quality of the long- and short-axis views between the radial and BH-SSFP sequences, while the image quality of the long-axis spiral (P <.05) and the short- and long-axis ECHO (P <.0001) views was lower than that of the BH-SSFP views. Compared with the mean wall motion score for BH-SSFP MR imaging, the mean wall motion score for radial MR imaging was not significantly different, but those for ECHO (P <.05) and spiral MR imaging (P =.0003) were significantly lower. Cohen kappa coefficients for agreement with the BH-SSFP sequence regarding wall motion scoring were 0.47 for ECHO, 0.67 for the spiral sequence, and 0.89 for the radial sequence.

CONCLUSION

The radial sequence enables similar accurate assessment of regional wall motion compared with the BH-SSFP sequence and yields image quality that is superior to that yielded by the spiral sequence and ECHO.

Improved functional cardiac MR imaging using the intravascular contrast agent CLARISCAN

PURPOSE

Using segmented k-space turbo gradient echo MR techniques (TGE) contrast between blood and myocardium is often reduced in long axis views due to reduced in plane spin-refreshment, particularly in patients with low ejection fraction. The application of an intravascular contrast agent (CA) may improve endocardial border delineation.

MATERIALS AND METHODS

In 15 patients cardiac cine loops in two long axis and two short axis views were acquired during breath hold using a TGE sequence without and with increasing doses of CA (0.75, 2.0, 5.0 mg Fe/kg). Two independent observers evaluated left ventricular function (LVEF, modified Simpson's rule) and assigned a visual score (range: 0 = 'not visualized' to 6 = 'excellent visualization') for endocardial border delineation. Signal- and contrast-to-noise ratios (SNR; CNR) were determined.

RESULTS

Endocardial border delineation score for TGE was 1.7 +/- 0.6 and 3.9 +/- 0.6**, 4.4 +/- 0.5**, 4.6 +/- 0.4** for 0.75, 2.0, 5.0 mg Fe/kg of CA, respectively (**p < 0.01 vs. TGE). SNR of blood increased significantly with any dose of CA with a mild drop of myocardial SNR resulting in a significant increase of CNR blood/myocardium. The maximum effect with 2.0 mg Fe/kg was a >2-fold CNR increase. Inter- and intraobserver variability assessed according to the method of Bland-Altmann was reduced at 2.0 mg Fe/kg for determination of LVEF and reached statistical significance for LVEF <50%.

CONCLUSION

Intravascular CA increased CNR between blood and myocardium by a factor >2 and significantly improved the determination of cardiac volumes. The benefit in accuracy was most for patients with left ventricular ejection fraction <50%.

Left Ventricular Mass: Manual and Automatic Segmentation of True FISP and FLASH Cine MR Images in Dogs and Pigs

PURPOSE

To evaluate the accuracy of manually and automatically segmented true fast imaging with steady-state precession (FISP) and fast low-angle shot (FLASH) cine magnetic resonance (MR) imaging in the determination of left ventricular (LV) mass.

MATERIALS AND METHODS

Nine dogs and five pigs underwent cine MR imaging of the entire LV from base to apex. Manual and automatic segmentation times were recorded, and LV masses determined with each were compared with each other and with the true LV mass at autopsy. Estimated mass and true mass at autopsy were compared by calculating the correlation coefficient and the mean difference between the two for each MR sequence and segmentation method.

RESULTS

True LV mass at autopsy correlated well with masses determined with manual and automatic contours on true FISP MR images. Mean differences between true LV mass and masses determined from manual contours on true FISP and FLASH images were -0.8 g +/- 2.6 and 3.7 g +/- 6.8, respectively. When manually drawn end-diastolic contours were automatically propagated to end systole, mean differences were 2.0 g +/- 3.6 (P =.05) and 9.1 g +/- 6.5 (P <.05) for true FISP and FLASH images, respectively. For automatic contours, mean differences were 10.6 g +/- 8.5 (P <.05) and 27.7 g +/- 13.4 (P <.05) for true FISP and FLASH images, respectively. Mean automatic segmentation time was six times less than mean manual segmentation time.

CONCLUSION

LV mass was determined most accurately by using manual contours on true FISP images. In these animal models, fully automatic segmentation of true FISP images was performed in one-sixth of the time of manual segmentation and yielded LV masses with a mean error of approximately 5% of true LV mass.

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.

Accurate Quantification of Right Ventricular Mass at MR Imaging by Using Cine True Fast Imaging with Steady-State Precession: Study in Dogs

PURPOSE

To assess the accuracy of cine magnetic resonance (MR) imaging with a segmented true fast imaging with steady-state precession (FISP) technique for right ventricular (RV) mass quantification.

MATERIALS AND METHODS

Fourteen dogs were imaged with a 1.5-T clinical MR imaging unit by using an electrocardiographically gated true FISP sequence. Contiguous segmented k-space cine images were acquired from the base of the RV to the apex during suspended respiration (repetition time msec/echo time msec, 3.2/1.6; section thickness, 5 mm; in-plane resolution, 1.0 x 1.3 mm2). After imaging, each dog was sacrificed, and the RV free wall was isolated and weighed. Each MR imaging data set was analyzed twice by each of two independent observers who were blinded to the results of RV mass measurement at autopsy, and the mass measurements at MR imaging were compared with the autopsy results by using linear regression and Bland-Altman analysis.

RESULTS

RV mass measurements calculated by using the true FISP cine MR images were nearly identical to those at autopsy (R = 0.82, standard error of the estimate = 1.7 g, P >.05), with a mean difference between the autopsy and MR imaging measurements of 0.3 g +/- 1.7 (1.9% +/- 8.2) (P >.05). Inter- and intraobserver variations were small, with a mean interobserver variability of -0.1 g +/- 2.3 and a mean intraobserver variability of 0.2 g +/- 1.6 at every-section analysis.

CONCLUSION

In this animal model, true FISP cine MR imaging enabled accurate quantification of RV mass.

Parallel acquisition techniques in cardiac cine magnetic resonance imaging using TrueFISP sequences: Comparison of image quality and artifacts

PURPOSE

To compare image quality, artifacts, and signal-to-noise ratio (SNR) in cardiac cine TrueFISP magnetic resonance imaging (MRI) with and without parallel acquisition techniques (PAT).

MATERIALS AND METHODS

MRI was performed in 16 subjects with a TrueFISP sequence (1.5 T; Magnetom Sonata, Siemens): TR, 3.0 msec; TE, 1.5 msec; flip angle (FA), 60 degrees. Three axes were scanned without PAT (no PAT) and using the generalized autocalibrating partially parallel acquisition (GRAPPA) and modified sensitivity encoding (mSENSE) reconstruction algorithms with an autocalibration mode to reduce scan time. A conventional spine array and a body flex array were used. Artifacts, image noise, and overall image quality were classified on a 4-point scale by an observer blinded to the implemented technique; for quantitative comparison, SNR was measured.

RESULTS

With a PAT factor of two, acquisition time could be reduced by 39%. No PAT did not show artifacts, and GRAPPA revealed fewer artifacts than mSENSE. PAT provided inferior-quality scores concerning image noise and overall image quality. In quantitative measurements, GRAPPA and mSENSE (20.1 +/- 6.2 and 15.6 +/- 6.2, respectively) yielded lower SNR than no PAT (30.6 +/- 20.1; P < 0.05) and P < 0.001).

CONCLUSION

Time savings in PAT are accompanied by artifacts and an increase in image noise. The GRAPPA algorithm was superior to mSENSE concerning image quality, noise, and SNR.

Accelerating cardiac cine 3D imaging usingk-t BLAST

By exploiting spatiotemporal correlations in cardiac acquisitions using k-t BLAST, gated cine 3D acquisitions of the heart were accelerated by a net factor of 4.3, making single breathhold acquisitions possible. Sparse sampling of k-t space along a sheared grid pattern was implemented into a cine 3D SSFP sequence. The acquisition of low-resolution training data, which was required to resolve aliasing in the k-t BLAST method, was either interleaved into the sampling process or obtained in a separate prescan to allow for shorter breathhold durations in patients with heart disease. Volumetric datasets covering the heart with 20 slices at a spatial resolution of 2 x 2 x 5 mm3 were recorded with 20 cardiac phases in a total breathhold duration of 25-27 sec, or 18 sec if partial Fourier sampling was additionally employed. The feasibility of the method was demonstrated on healthy volunteers and on patients. The comparison of endocardial area derived from single slices of the 3D dataset with values extracted from separate single-slice acquisitions showed no significant differences. By shortening the acquisition substantially, k-t BLAST may greatly facilitate volumetric imaging of the heart for evaluation of regional wall motion and the assessment of ventricular volume and ejection fraction.

MR imaging assessment of cardiac function

Magnetic resonance (MR) imaging is an accurate and reproducible technique for assessment of ventricular function. Although echocardiography is the mainstay for evaluation of cardiac function, dobutamine stress MR imaging has been shown to be as safe as echocardiography for patients with coronary artery disease and more accurate in patients with suboptimal echocardiographic image quality. This article reviews MR imaging techniques, methods of pharmacologic stress, and clinical applications for assessment of cardiac function, primarily left ventricular function.

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.

Regional myocardial function: advances in MR imaging and analysis

Cardiovascular magnetic resonance (MR) imaging can provide three-dimensional analysis of global and regional cardiac function with great accuracy and reproducibility. Quantitative assessment of regional function with cardiac MR imaging previously was limited by long acquisition times and time-consuming analysis. The use of steady-state free precession cine MR imaging substantially improves assessment of myocardial wall motion. Advances in gradient technology and reconstruction techniques have increased MR image acquisition speed and made real-time cine MR imaging possible. Myocardial deformation may be measured with cine MR tagging, and interpretation of the resultant tagged MR images by means of harmonic phase analysis enables prompt and precise strain measurements. Velocity-encoded and stimulated-echo techniques such as phase-contrast MR imaging and displacement encoding with stimulated echoes, or DENSE, provide high-resolution strain maps. Clinical validation of these strain imaging techniques will depend on future assessments of their effect on the management of cardiac disease.

Principles and applications of balanced SSFP techniques

During the past 5 years balanced steady-state free precession (SSFP) has become increasingly important for diagnostic and functional imaging. Balanced SSFP is characterized by two unique features: it offers a very high signal-to noise ratio and a T2/T1-weighted image contrast. This article focuses on the physical principles, on the signal formation, and on the resulting properties of balanced SSFP. Mechanisms for contrast modification, recent clinical application, and potential extensions of this technique are discussed.

Role of echocardiography versus MRI for the diagnosis of congenital heart disease

During the last few decades, significant strides have been made in the field of noninvasive imaging for the patient with congenital heart disease. Echocardiography and MRI continue to provide improved means of anatomic and functional assessment in children and adults with congenital heart lesions. This review reports some of the recent advances in tissue Doppler, strain rate, and integrated backscatter, and highlights exciting current and future potential developments in their application. We also discuss advances in MR in evaluation of cardiac anatomy and function in congenital heart disease.

Evaluation of left ventricular dysfunction using multiphasic reconstructions of coronary multi-slice computed tomography data in patients with chronic ischemic heart disease: validation against cine magnetic resonance imaging

PURPOSE

Multi-slice computed tomography (MSCT) is an emerging technique for the angiographic assessment of coronary artery disease (CAD). The purpose of this work was to determine if multiphasic reconstructions of the same data used for the assessment of CAD could also be used for global functional evaluation of the left ventricle (LV).

MATERIALS AND METHODS

Fifteen patients with chronic ischemic heart disease (CIHD) were imaged for CAD using a contrast-enhanced retrospective electrocardiographic-gated spiral technique on a MSCT scanner. The same data were reconstructed at both end-diastole and end-systole in order to measure left ventricular end-diastolic volume (LVEDV), end-systolic volume (LVESV), and ejection fraction (LVEF). The results were compared to values obtained using a cine true-fast imaging with steady-state precession technique on a magnetic resonance imaging (MRI) scanner. Interobserver variability in the measurement from MSCT images was also evaluated.

RESULTS

For LVEF, there was substantial agreement between MSCT and MRI (intraclass correlation coefficient of 0.825); the intermodality reproducibility for LVEF (5%) was within an acceptable clinical range. However, mean values of LVEDV and LVESV with MSCT compared to cine MRI (LVEDV: 262.0 +/- 85.6 ml and 297.2 +/- 98.8 ml, LVESV: 196.2 +/- 75.6 ml and 218.6 +/- 90.99 ml, respectively) were significantly less for both volumes (p < 0.015). Intermodality variabilities for these measurements were high (15 and 13% for LVEDV and LVESV, respectively). Readers' mean measurements of LVESV from MSCT images were significantly different (p = 0.003) resulting in differences in calculation of LVEF (p < 0.024). Still, interobserver variabilities for all values were acceptable (6, 8, and 5% for LVEDV, LVESV, and LVEF, respectively).

CONCLUSION

Although values for LVEDV and LVESV were less with MSCT than with MRI, LVEF values were in agreement. This suggests that combined imaging of CAD and the evaluation of global LV dysfunction due to CIHD is feasible with the same MSCT acquisition.

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.

Three-dimensional true FISP for high-resolution imaging of the whole brain

While high-resolution T1-weighted sequences, such as three-dimensional magnetization-prepared rapid gradient-echo imaging, are widely available, there is a lack of an equivalent fast high-resolution sequence providing T2 contrast. Using fast high-performance gradient systems we show the feasibility of three-dimensional true fast imaging with steady-state precession (FISP) to fill this gap. We applied a three-dimensional true-FISP protocol with voxel sizes down to 0.5 x 0.5 x 0.5 mm and acquisition times of approximately 8 min on a 1.5-T Sonata (Siemens, Erlangen, Germany) magnetic resonance scanner. The sequence was included into routine brain imaging protocols for patients with cerebrospinal-fluid-related intracranial pathology. Images from 20 patients and 20 healthy volunteers were evaluated by two neuroradiologists with respect to diagnostic image quality and artifacts. All true-FISP scans showed excellent imaging quality free of artifacts in patients and volunteers. They were valuable for the assessment of anatomical and pathologic aspects of the included patients. High-resolution true-FISP imaging is a valuable adjunct for the exploration and neuronavigation of intracranial pathologies especially if cerebrospinal fluid is involved.

Comparison of 99mTc tetrofosmin gated SPECT measurements of left ventricular volumes and ejection fraction with MRI over a wide range of values

The calculation of ejection fraction using gated single photon emission computed tomography (SPECT) has been widely validated against a range of other techniques. There have been fewer studies validating left ventricular volumes. We compared quantitative gated SPECT (QGS) with magnetic resonance imaging (MRI) measurements of left ventricular ejection fraction and end diastolic volume in 50 patients with a large range of ventricular dimensions. MRI data were obtained using a turbo gradient echo pulse sequence (TGE) in 17 patients and a steady state free precession pulse sequence (SSFP) in 33 patients. There was good correlation between ejection fraction and end diastolic volume measurements from SPECT and MRI (r=0.82, r=0.90, respectively) but the mean SPECT values were significantly lower (ejection fraction, 6.6+/-6.4% points; end diastolic volume, 18.4+/-25.4 ml) than those obtained from MRI. Bland-Altman analysis showed some large differences in individual patients but no trends in the data either in ejection fraction over a range from 15% to 70% or in end diastolic volume, range 75-400 ml. SSFP gave a larger difference for end diastolic volume measurement compared to SPECT than did TGE, although this difference did not reach significance. Both SSFP and TGE gave similar values for the difference between MRI and SPECT for the measurement of ejection fraction. We suggest that the difference in EF may be a result of 8 frames being used for gating in QGS but 12-18 for MR. Differences in volumes may be related to the different spatial resolution and the exclusion or inclusion of trabeculation and papillary muscles between SPECT and MRI. Differences between SSFP and TGE may be caused by differing delineation of the endocardial border, dependent on the particular acquisition sequence. In conclusion, QGS values correlated well with MRI, but a correction factor may be needed if direct comparison is made.

Quantitative assessment of left ventricular function with interactive real-time spiral and radial MR imaging

An interactive real-time spiral gradient-echo and an interactive real-time radial steady-state free precession sequence were investigated for the quantitative assessment of left ventricular function. Data were acquired in 18 patients without electrocardiographic triggering and breath holding. With the interactive real-time spiral gradient-echo sequence, significant underestimation of endocardial and epicardial volumes was demonstrated; with the interactive real-time radial steady-state free precession sequence, excellent agreement was shown with standard cardiac-triggered segmented k-space breath-hold steady-state free precession MR imaging. Interactive real-time radial steady-state free precession imaging allows accurate quantitative assessment of left ventricular volumes.

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.

Coronary artery bypass graft patency: assessment with true ast imaging with steady-state precession versus gadolinium-enhanced MR angiography

PURPOSE

To compare the accuracy of multisection true fast imaging with steady-state precession (FISP) with gadolinium-enhanced magnetic resonance (MR) angiography for the detection of coronary artery bypass graft patency.

MATERIALS AND METHODS

Twenty-five patients with coronary artery bypass grafts who had recently undergone conventional coronary angiography underwent MR angiography with a 1.5-T system. True FISP angiographic images were acquired in transverse and coronal planes. Coronal cardiac-gated MR angiography was performed with 0.2 mL per kilogram of body weight of gadopentetate dimeglumine injected at a rate of 2 mL/sec. With conventional angiography as the reference standard, the sensitivity, specificity, and accuracy of each technique for the detection of graft patency were determined. Image quality and duration of analysis were determined by two experienced radiologists.

RESULTS

In 25 patients, 46 of 56 venous grafts were patent and 22 of 23 arterial grafts were patent. In all grafts at true FISP angiography, sensitivity for patency was 84% (57 of 68 grafts), specificity was 45% (five of 11 grafts), and accuracy was 78% (62 of 79 grafts). At MR angiography, sensitivity was 85% (58 of 68 grafts), specificity was 73% (eight of 11 grafts), and accuracy was 84% (66 of 79 grafts) (difference not significant). Image quality scores were similar with both techniques, but duration of analysis was significantly longer with MR angiography than with true FISP angiography (29 minutes 24 seconds vs 14 minutes 6 seconds, P <.001).

CONCLUSION

Accuracy for detection of coronary artery bypass graft patency was similar with gadolinium-enhanced MR angiography and true FISP angiography, with a trend toward more false-positive findings for occlusion and reduced visualization of arterial grafts with true FISP angiography.

Preoperative evaluation of the entire hepatic vasculature in living liver donors with use of contrast-enhanced MR angiography and true fast imaging with steady-state precession

PURPOSE

To preoperatively assess the entire hepatic vasculature in living related liver donors with use of a combination of contrast material-enhanced magnetic resonance (MR) angiography and true fast imaging with steady-state precession (FISP).

MATERIALS AND METHODS

Twenty-five living potential liver donors were examined preoperatively on a 1.5T Siemens Sonata system. Twenty-four underwent surgery and two had catheter angiography performed to delineate complex anatomy. Contiguous 5-mm-thick, sub-second true FISP images of the liver were initially obtained during breath-holding in axial and coronal planes (repetition time [TR]/echo time [TE], 3.2/1.6; flip angle, 70 degrees ). MR angiography was performed with use of a three-dimensional (3D) gradient-echo fast low-angle shot (FLASH) pulse sequence (TR/TE, 3.0/1.2; flip angle, 25 degrees ), with 40 mL of Gadolinium DTPA injected at a rate of 2 mL/sec. One precontrast and two postcontrast coronal 3D volumes were acquired, each in a 20-second breath-hold, and two subtracted 3D sets were calculated. Arterial anatomy was assessed with use of maximum-intensity projection, volume rendering, and multiplanar reformatting algorithms. Hepatic and portal venous anatomy was evaluated with use of the true FISP images and the venous phase of the MR angiogram. Visualization of hepatic arterial branches was noted. Visualization of portal vein branches was scored on a scale of 0-5. The presence of anatomic variants was noted. Vascular anatomy was confirmed at the time of surgery and at catheter angiography.

RESULTS

Segmental branch vessels were visualized on MR angiography in the majority of cases. The segment four branch was identified in 96% patients. Variant arterial anatomy was seen in 50% of patients. MR angiography detected 10 of 11 arterial variants found at surgery and angiography. Visualization of portal vein branches was generally higher with true FISP compared to MR angiography. Twenty-four percent of patients had variant portal venous anatomy. Caudal hepatic veins were identified in 60% of patients, of which eight were significant (>5 mm). Hepatic and portal venous anatomy was accurately predicted by true FISP and MR angiography in all patients who went on to undergo surgery.

CONCLUSION

Preoperative imaging with use of a combination of contrast-enhanced MR angiography and true FISP provides a comprehensive assessment of the entire hepatic vasculature in living liver donors.

Validation of an evaluation routine for left ventricular volumes, ejection fraction and wall motion from gated cardiac FDG PET: a comparison with cardiac magnetic resonance imaging

The aim of this study was to validate the estimation of left ventricular end-diastolic and end-systolic volumes (EDV, ESV) and ejection fraction (LVEF) as well as wall motion analysis from gated fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) in patients with severe coronary artery disease (CAD) using software originally designed for gated single-photon emission tomography (SPET). Thirty patients with severe CAD referred for myocardial viability diagnostics were investigated using a standard FDG PET protocol enhanced with gated acquisition (8 gates per cardiac cycle). EDV, ESV and LVEF were calculated using standard software designed for gated SPET (QGS). Wall motion was analysed using a visual four-point wall motion score on a 17-segment model. As a reference, all patients were also examined within a median of 3 days with cardiovascular cine magnetic resonance imaging (cMRI) (20 gates per cardiac cycle). Furthermore, all gated FDG PET data sets were reoriented in a second run with deliberately misaligned axes to test the quantification procedure for robustness. Correlation between the results of gated FDG PET and cMRI was very high for EDV and ESV ( R=0.96 and R=0.97) and for LVEF ( R=0.95). With gated FDG PET, there was a non-significant tendency to underestimate EDV (174+/-61 ml vs 179+/-59 ml, P=0.21) and to overestimate ESV (124+/-58 ml vs 122+/-60 ml, P=0.65), resulting in underestimated LVEF values (31.5%+/-9.4% vs 34.2%+/-12.4%, P<0.003). The results of reorientations 1 and 2 showed very high correlations (for all R>/=0.99). Segmental wall motion analysis revealed good agreement between gated FDG PET data and cMRI (kappa =0.62+/-0.03). In conclusion, despite small systematic differences which contributed mainly to the lower temporal resolution of gated FDG PET, agreement between gated FDG PET and cMRI was good across a wide range of volumes and LVEF values as well as for wall motion analysis. Therefore, gated FDG PET provides clinically relevant information on function and volumes, using the commercially available software package QGS.

An analytical solution for the SSFP signal in MRI

Among previous analyses of the steady-state free-precession (SSFP) signal in rapid MRI, one treatment resulted in equations that require the evaluation of infinite binomial series. Here, an analytical solution is derived by a transformation into the power series expansion of the derivative of the inverse sine function, which is essentially a root. The treatment is extended to include higher-order signals. The results demonstrate the identity of the vastly different equations for the SSFP signals reported so far. Applications consist of the derivation of closed expressions for the signal in echo-shifted MRI and a corresponding analysis of TrueFISP sequences.

TrueFISP--technical considerations and cardiovascular applications

Magnetic resonance imaging (MRI) using steady-state free precession (SSFP) sequences was described in the early years of MR imaging. However, due to hardware imperfections, these techniques were not robust enough at the time to play any significant role in clinical MRI. More recently, significant hardware improvements became widely available, and the SSFP sequences such as TrueFISP (true fast imaging with steady-state precession) became very popular for a variety of clinical applications due to the distinct improvements in signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). The purpose of this article is to give an overview on the basics of TrueFISP imaging and to demonstrate its potential for current clinical applications with a focus on cardiovascular MRI.

Detecting acute coronary syndrome in the emergency department with cardiac magnetic resonance imaging

BACKGROUND

Managing chest pain in the emergency department remains a challenge with current diagnostic strategies. We hypothesized that cardiac MRI could accurately identify patients with possible or probable acute coronary syndrome.

METHODS AND RESULTS

The diagnostic performance of MRI was evaluated in a prospective study of 161 consecutive patients. Enrollment required 30 minutes of chest pain compatible with myocardial ischemia but an ECG not diagnostic of acute myocardial infarction. MRI was performed at rest within 12 hours of presentation and included perfusion, left ventricular function, and gadolinium-enhanced myocardial infarction detection. MRI was interpreted qualitatively but also analyzed quantitatively. The sensitivity and specificity, respectively, for detecting acute coronary syndrome were 84% and 85% by MRI, 80% and 61% by an abnormal ECG, 16% and 95% for strict ECG criteria for ischemia (ST depression or T-wave inversion), 40% and 97% for peak troponin-I, and 48% and 85% for a TIMI risk score > or =3. The MRI was more sensitive than strict ECG criteria for ischemia (P<0.001), peak troponin-I (P<0.001), and the TIMI risk score (P=0.004), and MRI was more specific than an abnormal ECG (P<0.001). Multivariate logistic regression analysis showed MRI was the strongest predictor of acute coronary syndrome and added diagnostic value over clinical parameters (P<0.001).

CONCLUSIONS

Resting cardiac MRI exhibited diagnostic operating characteristics suitable for triage of patients with chest pain in the emergency department. Performed urgently to evaluate chest pain, MRI accurately detected a high fraction of patients with acute coronary syndrome, including patients with enzyme-negative unstable angina.

MR imaging of myocardial perfusion and viability

CMR is a rapidly developing new modality with applications in clinical cardiology for detection and assessment of myocardial ischemia and viability. CMR perfusion results for the detection of ischemia in comparison with stress echocardiography and scintigraphic techniques are reasonable, but all the studies reported to date have been conduced in selected patients. Larger studies in patient populations reflecting a broader spectrum of disease are necessary before perfusion CMR can be envisaged as a clinically reliable and robust diagnostic tool. Other CMR techniques provide a variety of novel methods of obtaining information on postischemic viability. Signs of viability that can be observed by CMR are the absence of late gadolinium-based contrast enhancement in a myocardial region involved in a recent infarct, any sign of wall thickening at rest (which is detectable with high accuracy by CMR), wall thickening after stimulation by low-dose dobutamine, and preserved wall thickness. Conversely, myocardial necrosis is characterized by signal enhancement of the infarct area after injection of Gd-DTPA, reduced wall thickness in chronic infarcts, and absence of a contractile reserve during dobutamine stimulation. Dobutamine CMR and late enhancement contrast-enhanced CMR predict contractile improvement after revascularization.

Assessment of cardiac function with MR imaging

A variety of black or white blood imaging techniques are available for assessing global and regional LV and RV function during cardiovascular MR imaging examinations. In addition to providing information about LV function at rest, these techniques provide diagnostic and prognostic information regarding myocardial ischemia and viability during MR imaging stress tests.

MR imaging of the thoracic aorta

There are numerous pulse sequences available for evaluating the diverse pathology that affects the thoracic aorta. Preliminary imaging using TrueFISP and precontrast and postcontrast T1 GRE-FS is usually required to assess morphology of the aorta and adjacent structures. CE-MRA is the mainstay in the investigative approach. The addition of temporally resolved subsecond CE-MRA is particularly useful for assessing high-flow vascular lesions such as shunts, while at the same time not adding much to the overall contrast load. PC-MRA may help further characterize stenotic lesions and can be useful for monitoring progression of disease.

Myocardial tagging with SSFP

This work presents the first implementation of myocardial tagging with refocused steady-state free precession (SSFP) and magnetization preparation. The combination of myocardial tagging (a noninvasive method for quantitative measurement of regional and global cardiac function) with the high tissue signal-to-noise ratio (SNR) obtained with SSFP is shown to yield improvements in terms of the myocardium-tag contrast-to-noise ratio (CNR) and tag persistence when compared to the current standard fast gradient-echo (FGRE) tagging protocol. Myocardium-tag CNR and tag persistence were studied using numerical simulations as well as phantom and human experiments. Both quantities were found to decrease with increasing imaging flip angle (alpha) due to an increased tag decay rate and a decrease in myocardial steady-state signal. However, higher alpha yielded better blood-myocardium contrast, indicating that optimal alpha is dependent on the application: higher alpha for better blood-myocardium boundary visualization, and lower alpha for better tag persistence. SSFP tagging provided the same myocardium-tag CNR as FGRE tagging when acquired at four times the bandwidth and better tag- and blood-myocardium CNRs than FGRE tagging when acquired at equal or twice the receiver bandwidth (RBW). The increased acquisition efficiency of SSFP allowed decreases in breath-hold duration, or increases in temporal resolution, as compared to FGRE.

Evaluation of left ventricular dysfunction using multiphasic reconstructions of coronary multi-slice computed tomography data in patients with chronic ischemic heart disease: validation against cine magnetic resonance imaging

PURPOSE

Multi-slice computed tomography (MSCT) is an emerging technique for the angiographic assessment of coronary artery disease (CAD). The purpose of this work was to determine if multiphasic reconstructions of the same data used for the assessment of CAD could also be used for global functional evaluation of the left ventricle (LV).

MATERIALS AND METHODS

Fifteen patients with chronic ischemic heart disease (CIHD) were imaged for CAD using a contrast-enhanced retrospective electrocardiographic-gated spiral technique on a MSCT scanner. The same data were reconstructed at both end-diastole and end-systole in order to measure left ventricular end-diastolic volume (LVEDV), end-systolic volume (LVESV), and ejection fraction (LVEF). The results were compared to values obtained using a cine true-fast imaging with steady-state precession technique on a magnetic resonance imaging (MRI) scanner. Interobserver variability in the measurement from MSCT images was also evaluated.

RESULTS

For LVEF, there was substantial agreement between MSCT and MRI (intraclass correlation coefficient of 0.825); the intermodality reproducibility for LVEF (5%) was within an acceptable clinical range. However, mean values of LVEDV and LVESV with MSCT compared to cine MRI (LVEDV: 262.0 +/- 85.6 ml and 297.2 +/- 98.8 ml, LVESV: 196.2 +/- 75.6 ml and 218.6 +/- 90.99 ml, respectively) were significantly less for both volumes (p < 0.015). Intermodality variabilities for these measurements were high (15 and 13% for LVEDV and LVESV, respectively). Readers' mean measurements of LVESV from MSCT images were significantly different (p = 0.003) resulting in differences in calculation of LVEF (p < 0.024). Still, interobserver variabilities for all values were acceptable (6, 8, and 5% for LVEDV, LVESV, and LVEF, respectively).

CONCLUSION

Although values for LVEDV and LVESV were less with MSCT than with MRI, LVEF values were in agreement. This suggests that combined imaging of CAD and the evaluation of global LV dysfunction due to CIHD is feasible with the same MSCT acquisition.

Magnetic resonance imaging assessment of cardiac function

Measurements of left ventricular function at rest and during stress are useful for identifying myocardial ischemia, injury, and the risk of subsequent myocardial infarction. Without ionizing radiation or intravascular contrast administration, magnetic resonance imaging techniques can be used to acquire precise measurements of left ventricular function. This relatively new development may enhance a physician's ability to provide care to patients with cardiovascular disease.

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.