A pilot investigation of new superparamagnetic iron oxide (ferumoxytol) as a contrast agent for cardiovascular MRI

Purpose: To evaluate the imaging potential of ferumoxytol, a new superparamagnetic iron oxide colloidal blood pool contrast agent.Materials and Methods: Magnetic resonance (MR) imaging at 1.5 Tesla was performed before and after intravenous injection of ferumoxytol using escalating doses of 0.4, 0.8, 1.2 and 1.6 mg Fe/kg for a total of 4 mg Fe/kg in five subjects imaged with 3D MR Angiography (MRA) of the trifurcation after each dose. In five subjects cardiac cine MRI was performed pre and post 4.0 mg Fe/kg. Image quality was assessed by measuring signal to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in the vascular structures. Pre- and post-dose urine and blood tests as well as EKG/vital sign monitoring were performed to evaluate safety and blood samples were collected for T1 relaxivity measurements.Results: Cumulative doses of 0, 0.4, 1.2, 2.4 and 4 mg Fe/kg yielded mean SNR in the arteries of 10, 16, 39, 57 and 69 respectively indicating that the higher doses produced higher SNR on 3D vascular images. Similarly aorta SNR on 2D time-of-flight increased from 11.8 without Fe to 15.4 post Fe (p = 0.004) indicating improved image quality on MRA sequences optimized for use without contrast. At 4 mg Fe/kg there was a substantial T1 shortening measured in the blood from 1990 ± 573 ms to 80 ± 42 ms (p < 0.0001), corresponding to the increased SNR. Images of large vascular structures including cardiac chambers, aorta, and pulmonary arteries were excellent post ferumoxytol but images of smaller arteries of the trifurcation were difficult to evaluate due to enhancement of the overlapping veins. No serious adverse events occurred.Conclusion: The new superparamagnetic iron oxide colloid ferumoxytol is a promising blood pool agent especially for cardiac, aorta and pulmonary imaging.     

Cardiac cine MRI: comparison of 1.5 T, non-enhanced 3.0 T and blood pool enhanced 3.0 T imaging

INTRODUCTION: Cardiac cine imaging using balanced steady state free precession sequences (bSSFP) suffers from artefacts at 3.0 T. We compared bSSFP cardiac cine imaging at 1.5 T with gradient echo imaging at 3.0 T with and without a blood pool contrast agent. MATERIALS AND METHODS: Eleven patients referred for cardiac cine imaging underwent imaging at 1.5 T and 3.0 T. At 3.0 T images were acquired before and after administration of 0.03 mmol/kg gadofosveset. Blood pool signal-to-noise ratio (SNR), temporal variations in SNR, ejection fraction and myocardial mass were compared. Subjective image quality was scored on a four-point scale. RESULTS: Blood pool SNR increased with more than 75% at 3.0 T compared to 1.5 T (p<0.001); after contrast administration at 3.0 T SNR increased with 139% (p<0.001). However, variations in blood pool SNR at 3.0 T were nearly three times as high versus those at 1.5 T in the absence of contrast medium (p<0.001); after contrast administration this was reduced to approximately a factor 1.4 (p=0.21). Saturation artefacts led to significant overestimation of ejection fraction in the absence of contrast administration (1.5 T: 44.7+/-3.1 vs. 3.0 T: 50.7+/-4.2 [p=0.04] vs. 3.0 T post contrast: 43.4+/-2.9 [p=0.55]). Subjective image quality was highest for 1.5 T (2.8+/-0.3), and lowest for non-enhanced 3.0 T (1.7+/-0.6; p=0.006). CONCLUSIONS: GRE cardiac cine imaging at 3.0 T after injection of the blood pool agent gadofosveset leads to improved objective and subjective cardiac cine image quality at 3.0 T and to the same conclusions regarding cardiac ejection fraction compared to bSSFP imaging at 1.5 T.     

Cinematic three-dimensional surface display of cardiac blood pool tomography

A method of three-dimensional cinematic display (3D cine) of cardiac blood pool tomography is described. ECG-gated transaxial blood pool imaging was obtained from a set of projection images that were collected from 32 images with 10 ECG-gated images per projection during a 180 degrees arc of a rotating gamma camera. A surface contour of the blood pool was determined by a set of isocount lines (40-55% of the maximum pixel counts) of the transaxial images. 3D cine was made by a depth-shading method, in which brightness of a given point on the contour was set proportional to the distance between the viewing plane and the point and to the incident angle formed by the viewing line and the surface of the point. In 15 patients, 3D cine showed hypokinesia, akinesia, dyskinesia, ventricular aneurysm, and opposite motions of the atria and ventricles. Diagnoses of left ventricular motion by 3D cine agreed well with those by echocardiography and contrast left ventriculography.     

Reduction in flow artifacts by using interleaved data acquisition in segmented balanced steady-state free precession cardiac MRI.

Balanced steady-state free precession (SSFP) magnetic resonance (MR) imaging is feasible for cine cardiac images because of the high contrast between myocardium and blood pool and robustness to rapid blood flow. Nonetheless, the flow artifacts are often observed because of off-resonance effects and to in-flow effects of the blood flow. Although reshimming the gradients or readjusting the center frequency reduces the artifacts, the technique can be susceptible for respiratory and cardiac motion and operator-dependent. The purpose of this study is to use another MR imaging technique for the reduction in the flow artifacts in the heart: odd-even interleaved data acquisition in segmented balanced SSFP imaging. The flow artifacts in the ventricle, ghost outside the heart, and visualization of the myocardial border were visually compared between sequential and odd-even interleaved k-space data acquisitions in cine balanced SSFP cardiac MR imaging. The odd-even interleaved k-space data acquisition significantly reduced dark flow artifacts in the left ventricle, improved the visualization of the myocardial border, and was easily installed. This imaging technique should be applied to cine segmented balanced SSFP cardiac MR imaging.     

Automatic left ventricular volume measurements on contrast-enhanced ultrafast cine magnetic resonance imaging

To assess the accuracy of automatic extraction of the left ventricular inner contour on contrast-enhanced ultrafast cine magnetic resonance (MR) images, we compared the values obtained by this method with those obtained using intravenous digital subtraction left ventriculography. High-quality single breath-hold contrast-enhanced ultrafast cine MR images were obtained in all cardiac phases on horizontal and vertical long axis sections of the left ventricle. For ultrafast cine MR imaging, a phase-rewind gradient-echo (rewind-SMASH) sequence was used. Automatic extraction of the left ventricular inner contour on contrast-enhanced ultrafast cine MR images was performed in all cardiac phases. High-quality left ventricular images of the horizontal long axis section were obtained in 127 of 160 patients (79%). The automatic extraction of the left ventricular contour was easily performed on high-quality images with very short processing time (4 s/frame). The values for left ventricular volumes obtained with the automatic extraction method on contrast-enhanced ultrafast cine MR imaging were correlated well with those obtained with the manual extraction method and IV-DSA in high quality cardiac images. The biplane modified Simpson's method using automatic extraction is an accurate and highly reproducible method for evaluating left ventricular volumes.     

Cardiac masses: signal intensity features on spin-echo, gradient-echo, gadolinium-enhanced spin-echo, and TurboFLASH images.

Fifteen patients with cardiac or paracardiac masses underwent magnetic resonance (MR) imaging with spin-echo (n = 15), cine gradient-echo (n = 15), gadopentetate dimeglumine-enhanced spin-echo (n = 15), and TurboFLASH (fast low-angle shot) (n = 7) sequences. All masses had either histologic confirmation (n = 11) or confirmation with other imaging modalities (n = 4). Myxomas (n = 6) were characterized by an intermediate signal intensity (SI) on spin-echo (n = 6) and low SI on cine gradient-echo (n = 6) images and moderately high-SI contrast enhancement (n = 5). Percent contrast enhancement for myxomas was 57% +/- 11%. Thrombus (n = 4) had intermediate (n = 3) or high (n = 1) SI on spin-echo images and low (n = 2) or intermediate (n = 2) SI on gradient-echo images and did not show substantial contrast enhancement. Postcontrast first-pass TurboFLASH images were useful by clearly demonstrating the nonenhancing mass lesion in a high-SI blood pool. Other cardiac and paracardiac tumors (n = 5) showed variable pre- and postcontrast spin-echo SI; however, no other tumor showed low SI on cine gradient-echo images.     

Evaluation of global cardiac functional parameters using single-breath-hold three-dimensional cine steady-state free precession MR imaging with two types of speed-up techniques: comparison with two-dimensional cine imaging.

The purpose of this study was to demonstrate the feasibility of single-breath-hold three-dimensional (3D) cine cardiac magnetic resonance (MR) imaging using steady-state free precession (SSFP) and two types of speed-up techniques for evaluation of global cardiac function. Twenty-one patients with acquired cardiac diseases were enrolled and underwent two-dimensional (2D) and 3D cine cardiac SSFP MR imaging using a 1.5T unit. Sensitivity encoding (n=12) and k-t broad-use linear acquisition speed-up (BLAST; n=9) were employed for the 3D cine imaging. High correlations for cardiac functional parameters were observed between 2D and 3D cine images (P<0.0001, r>0.94). However, end-diastolic volume and ejection fraction of the left ventricle were significantly lower in the 3D cine imaging with k-t BLAST than in the 2D cine imaging (P<0.0025). On the other hand, k-t BLAST allowed for a shorter breath-holding time owing to the higher acceleration factor. In conclusion, the single-breath-hold 3D cine imaging combined with speed-up techniques provided global cardiac functional parameters comparable to 2D cine imaging.     

Multimodality MR imaging assessment of myocardial viability: combination of first-pass and late contrast enhancement to wall motion dynamics and comparison with FDG PET-initial experience

PURPOSE: To combine three magnetic resonance (MR) imaging modalities-dobutamine stress cine, first pass, and late contrast material-enhanced T1-weighted imaging-and to compare the results with 2-[fluorine 18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in the assessment of unviable myocardium in coronary artery disease. MATERIALS AND METHODS: Ten patients with multivessel coronary artery disease underwent MR imaging before and 6 months after bypass surgery. Left ventricular cine MR imaging was performed at rest and during dobutamine infusion. Inversion-recovery gradient-echo images were obtained to study myocardial contrast enhancement at first pass and 5 minutes later. FDG PET was performed with orally administered acipimox before surgery. RESULTS: With dobutamine cine MR imaging, unviable myocardium was detected with a sensitivity of 79% and a specificity of 93%; postoperative wall thickening was the standard. First-pass analysis increased these values to 97% and 96%; analysis of late enhancement with T1-weighted imaging, to 62% and 98%. FDG PET had a sensitivity of 81% and a specificity of 86%. CONCLUSION: The combination of first-pass enhancement analysis and wall motion assessment with stress significantly increases the specificity of MR imaging in the detection of unviable sectors.     

Keyhole method for high-speed human cardiac cine MR imaging.

Although electrocardiographic (ECG)-gated magnetic resonance (MR) imaging is widely used for cardiac imaging, it has several disadvantages, such as long imaging time, respiratory artifacts, and motion artifacts induced by arrhythmia. An MR image can be acquired within about 0.3 seconds by using a fast gradient-echo imaging method. When this method is continuously applied, only two to three images can be obtained during a single cardiac cycle. The goal of this study is to obtain cine MR images in a single cardiac cycle using fast gradient-echo imaging combined with the "keyhole" method. The optimal conditions for the keyhole method for cardiac cine imaging were obtained by computer simulation based on a simplified cardiac model. When the read-out direction was set parallel to the cardiac short axis, left ventricular motion was almost correctly reproduced by the keyhole method with acquisition time reduced to one-fourth. J. Magn. Reson. Imaging 1999;10:778-783.     

Comparison of cine MR imaging with Doppler echocardiography for the evaluation of aortic regurgitation

Regurgitant blood flow is associated with localized signal loss of the blood pool within the recipient chamber on cine MR images, which may be useful for assessing regurgitant valvular disease. To evaluate the potential of this technique for determining the severity of aortic regurgitation, multilevel cine MR imaging was performed in 10 normal volunteers and in 25 patients with aortic regurgitation documented and graded for severity by Doppler echocardiography. Cine MR images were analyzed to obtain cardiac chamber volumes and to measure the extent of the signal loss associated with regurgitation. All regurgitant lesions were visualized on cine MR images as areas of diastolic signal loss extending from the aortic valve into the left ventricle. The extent of signal loss and the regurgitant volume determined from analysis of MR images correlated with the echocardiographic severity of the lesion. The total area of diastolic left ventricular signal loss was 0 cm2 in 10 normal volunteers, 24 +/- 13 (+/- SD) cm2 in eight patients with mild aortic regurgitation, 49 +/- 11 cm2 in nine patients with moderate aortic regurgitation, and 62 +/- 20 cm2 in eight patients with severe aortic regurgitation (p less than .05 for moderate and severe vs mild). Left ventricular volumes calculated from MR images correlated well with echocardiographic volumes (r = .92, SEE = 30 ml, p less than .0001). Regurgitant fraction calculated from analysis of cine MR images was 4 +/- 7% in normal volunteers and 31 +/- 8% in mild, 45 +/- 11% in moderate, and 56 +/- 9% in severe aortic regurgitation (p less than .05 for moderate and severe vs mild and normal). Thus, cine MR imaging can provide useful qualitative and quantitative data regarding cardiac dimensions and regurgitant valvular flow in patients with aortic regurgitation.     

MR imaging with remote control: feasibility study in cardiovascular disease

The institutional review board approved this HIPAA-compliant study and waived informed consent. The purpose was to retrospectively evaluate remote control magnetic resonance (MR) imaging in complex cardiovascular procedures, whereby operational expertise was made available locally from a remote location. Thirty patients underwent cardiac (12 patients) and/or vascular (30 patients) 1.5-T MR imaging with a remote operator by using a personal computer. All patient studies were compared with 30 control studies obtained with conventional local imaging. Cardiac cine, myocardial delayed enhancement, and MR angiograms were assessed for overall image quality and motion artifact. MR angiograms were evaluated for vascular definition. Image quality was excellent in 90% (38 of 42) of remote images versus 60% (25 of 42) of control group images (P < .01). Scores for motion artifact were not significantly different (P = .11). Interactive MR imaging was successfully implemented with remote control in complex cardiovascular cases; diagnostic quality of images was superior to that of images obtained locally.     

Infarcted myocardium in pigs: MR imaging enhanced with slow-interstitial-diffusion gadolinium compound P760.

PURPOSE: To assess the value of P760, a gadolinium chelate with slow interstitial diffusion and high relaxivity, for magnetic resonance (MR) imaging of acute myocardial infarction in pigs. MATERIALS AND METHODS: First-pass gradient-echo MR imaging and spin-echo MR imaging were performed with P760 and then with gadoterate meglumine in eight pigs with occlusive acute myocardial infarction. P760 signal intensity enhancement and clearance were compared with those of gadoterate meglumine. RESULTS: The first-pass enhancement ratio of P760 in normal myocardium was higher than that in infarcted myocardium (1.37 +/- 0.06 [SEM] vs 1.05 +/- 0.03, P = .03). The myocardial first pass showed a blood pool-like curve for P760. The blood pool enhancement ratio 40 seconds after injection was higher for P760 than for gadoterate meglumine (left ventricular cavity, 1.75 +/- 0.06 vs 1.45 +/- 0.06, P = .009). Spin-echo MR imaging showed improved contrast between normal and infarcted myocardium after P760 administration: The ratio before contrast material administration was 0.21 +/- 0.03, that at 15 minutes was 0.48 +/- 0.05 (P = .002), and that at 25 minutes was 0.47 +/- 0.07 (P = .003). CONCLUSION: P760 is an MR imaging contrast agent characterized by low diffusion, a blood pool effect soon after low-dose administration, and fast elimination. This agent is useful for improved myocardial perfusion MR imaging of acute myocardial infarction.     

Cerebral hemodynamics and cerebral blood volume: MR assessment using gadolinium contrast agents and T1-weighted Turbo-FLASH imaging.

PURPOSE: To assess the degree and regional pattern of first-pass brain enhancement using dynamic MR imaging. MATERIALS AND METHODS: Ultrafast MR imaging (1.06-second acquisition time per image) was performed in 19 healthy subjects following a bolus IV injection of a gadolinium contrast agent; 36 patients with suspected pathology were studied using the same protocol. RESULTS: Calculated percent blood volumes were 4.9% for right cortical gray matter, 4.8% for left cortical gray matter, and 2.6% for white matter. Subtraction images were obtained that depicted the first pass "blood pool" pattern of enhancement (gray and white matter) which was significant. CONCLUSION: Preliminary evidence suggests utility for cerebral "blood pool" imaging, especially if reduced image acquisition times can be achieved.     

Contrast-dose relation in first-pass myocardial MR perfusion imaging

PURPOSE: To determine the regime of linear contrast enhancement in human first-pass perfusion cardiovascular magnetic resonance (CMR) imaging to improve accuracy in myocardial perfusion quantification. MATERIALS AND METHODS: A total of 10 healthy subjects were studied on a clinical 1.5T MR scanner. Seven doses of Gd-DTPA ranging from 0.00125 to 0.1 mmol/kg of body weight (b.w.) were administered as equal volumes by rapid bolus injection (6 mL/second). Resting periods of 15 minutes were introduced after delivery of Gd doses >0.01 mmol/kg b.w. For each subject, two series of rest perfusion scans were performed using two different multislice saturation-recovery perfusion sequences. Maximum contrast enhancement and maximum upslope were obtained in the blood pool of the left ventricular (LV) cavity and in the myocardium. The range of linear contrast-dose relation was determined by linear regression analysis. RESULTS: MR signal intensity increased linearly for contrast agent concentrations up to 0.01 mmol/kg b.w. in the LV blood pool and up to 0.05 mmol/kg b.w. in the myocardium. For Gd concentrations exceeding these thresholds the signal intensity response was not linear with respect to the contrast agent dose. CONCLUSION: Quantitative evaluation of cardiac MR perfusion data needs to account for signal saturation in both the LV blood pool and the myocardium.     

Acute myocardial infarction: tissue characterization with T1rho-weighted MR imaging--initial experience

Acute myocardial injury was evaluated in 21 patients by using a contrast material-enhanced T1rho-weighted cine turbo field-echo magnetic resonance (MR) imaging sequence and a delayed-enhancement sequence. In 12 of 21 patients, conventional T1-weighted contrast-enhanced cine turbo field-echo MR images were also collected for direct comparison with T1rho-weighted images. Delayed-enhancement technique distinctly characterized irreversible injury (percentage enhancement, 588% +/- 344). With T1rho weighting, percentage enhancement of irreversibly injured myocardium was 68% +/- 41, compared with 23% +/- 24 without T1rho weighting (P <.006). The addition of T1rho weighting to contrast-enhanced cine turbo field-echo MR sequences may offer a new contrast enhancement mechanism for characterization of acutely infarcted myocardium.     

Dual contrast TrueFISP imaging for left ventricular segmentation.

Based on varying tissue contrasts at different RF flip angles, a new TrueFISP imaging strategy for cardiac function measurement is presented. A single breath-hold dual RF flip angle cine multi-slice TrueFISP imaging sequence was implemented which provides a significant increase in signal contrast between blood and myocardium. The increase in image contrast combined with different characteristics in RF response facilitates the delineation of cardiovascular borders. Based on this imaging strategy it is demonstrated how a simple 2D histogram clustering algorithm can be used for the fully automatic segmentation of the left ventricular (LV) blood pool. The method is validated with data acquired from 10 asymptomatic subjects, and the results are shown to be comparable to that of manual delineation by experienced observers.     

Fast 3D cardiac cine MR imaging.

We describe a technique for three-dimensional cine MR imaging. By using short repetition times (TR) and interleaved slice encoding, volumetric cine data can be acquired throughout the cardiac cycle with a temporal resolution of approximately 80 msec. A T1-shortening agent is used to produce contrast between blood and myocardium. A comparison between the acquisition times of this and several other two-dimensional techniques is presented.     

Self-gated cardiac cine MRI.

The need for ECG gating presents many difficulties in cardiac magnetic resonance imaging (CMRI). Real-time imaging techniques eliminate the need for ECG gating in cine CMRI, but they cannot offer the spatial and temporal resolution provided by segmented acquisition techniques. Previous MR signal-based techniques have demonstrated an ability to provide cardiac gating information; however, these techniques result in decreased imaging efficiency. The purpose of this work was to develop a new "self-gated" (SG) acquisition technique that eliminates these efficiency deficits by extracting the motion synchronization signal directly from the same MR signals used for image reconstruction. Three separate strategies are proposed for deriving the SG signal from data acquired using radial k-space sampling: echo peak magnitude, kymogram, and 2D correlation. The SG techniques were performed on seven normal volunteers. A comparison of the results showed that they provided cine image series with no significant differences in image quality compared to that obtained with conventional ECG gating techniques. SG techniques represent an important practical advance in clinical MRI because they enable the acquisition of high temporal and spatial resolution cardiac cine images without the need for ECG gating and with no loss in imaging efficiency.     

Feasibility of Three-Dimensional Balanced Steady-State Free Precession Cine Magnetic Resonance Imaging Combined with an Image Denoising Technique to Evaluate Cardiac Function in Children with Repaired Tetralogy of Fallot

ObjectiveTo investigate the feasibility of cine three-dimensional (3D) balanced steady-state free precession (b-SSFP) imaging combined with a non-local means (NLM) algorithm for image denoising in evaluating cardiac function in children with repaired tetralogy of Fallot (rTOF).Materials and MethodsThirty-five patients with rTOF (mean age, 12 years; range, 7–18 years) were enrolled to undergo cardiac cine image acquisition, including two-dimensional (2D) b-SSFP, 3D b-SSFP, and 3D b-SSFP combined with NLM. End-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), and ejection fraction (EF) of the two ventricles were measured and indexed by body surface index. Acquisition time and image quality were recorded and compared among the three imaging sequences.Results3D b-SSFP with denoising vs. 2D b-SSFP had high correlation coefficients for EDV, ESV, SV, and EF of the left (0.959–0.991; p < 0.001) as well as right (0.755–0.965; p < 0.001) ventricular metrics. The image acquisition time ± standard deviation (SD) was 25.1 ± 2.4 seconds for 3D b-SSFP compared with 277.6 ± 0.7 seconds for 2D b-SSFP, indicating a significantly shorter time with the 3D than the 2D sequence (p < 0.001). Image quality score was better with 3D b-SSFP combined with denoising than with 3D b-SSFP (mean ± SD, 3.8 ± 0.6 vs. 3.5 ± 0.6; p = 0.005). Signal-to-noise ratios for blood and myocardium as well as contrast between blood and myocardium were higher for 3D b-SSFP combined with denoising than for 3D b-SSFP (p < 0.05 for all but septal myocardium).ConclusionThe 3D b-SSFP sequence can significantly reduce acquisition time compared to the 2D b-SSFP sequence for cine imaging in the evaluation of ventricular function in children with rTOF, and its quality can be further improved by combining it with an NLM denoising method.     

Whole-heart cine MRI using real-time respiratory self-gating.

Two-dimensional (2D) breath-hold cine MRI is used to assess cardiac anatomy and function. However, this technique requires cooperation from the patient, and in some cases the scan planning is complicated. Isotropic nonangulated three-dimensional (3D) cardiac MR can overcome some of these problems because it requires minimal planning and can be reformatted in any plane. However, current methods, even those that use undersampling techniques, involve breath-holding for periods that are too long for many patients. Free-breathing respiratory gating sequences represent a possible solution for realizing 3D cine imaging. A real-time respiratory self-gating technique for whole-heart cine MRI is presented. The technique enables assessment of cardiac anatomy and function with minimum planning or patient cooperation. Nonangulated isotropic 3D data were acquired from five healthy volunteers and then reformatted into 2D clinical views. The respiratory self-gating technique is shown to improve image quality in free-breathing scanning. In addition, ventricular volumetric data obtained using the 3D approach were comparable to those acquired with the conventional multislice 2D approach.