Showing papers on "Steady-state free precession imaging published in 2009"

T2 quantification for improved detection of myocardial edema

Abstract: Background: T2-Weighted (T2W) magnetic resonance imaging (MRI) pulse sequences have been used to detect edema in patients with acute myocardial infarction and differentiate acute from chronic infarction. T2W sequences have suffered from several problems including (i) signal intensity variability caused by phased array coils, (ii) high signal from slow moving ventricular chamber blood that can mimic and mask elevated T2 in sub-endocardial myocardium, (iii) motion artifacts, and (iv) the subjective nature of T2W image interpretation. In this work we demonstrate the advantages of a quantitative T2 mapping technique to accurately and reliably detect regions of edematous myocardial tissue without the limitations of qualitative T2W imaging. Methods: Methods of T2 mapping were evaluated on phantoms; the best of these protocols was then optimized for in vivo imaging. The optimized protocol was used to study the spatial, viewdependent, and inter-subject variability and motion sensitivity in healthy subjects. Using the insights gained from this, the utility of T2 mapping was demonstrated in a porcine model of acute myocardial infarction (AMI) and in three patients with AMI. Results: T2-prepared SSFP demonstrated greater accuracy in estimating the T2 of phantoms than multi-echo turbo spin echo. The T2 of human myocardium was found to be 52.18 ± 3.4 ms (range: 48.96 ms to 55.67 ms), with variability between subjects unrelated to heart rate. Unlike T2W images, T2 maps did not show any signal variation due to the variable sensitivity of phased array coils and were insensitive to cardiac motion. In the three pigs and three patients with AMI, the T2 of the infarcted region was significantly higher than that of remote myocardium. Conclusion: Quantitative T2 mapping addresses the well-known problems associated with T2W imaging of the heart and offers the potential for increased accuracy in the detection of myocardial edema.

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

Abstract: Quantification of ventricular volume by Steady State Free Precession (SSFP) cardiovascular magnetic resonance is accurate and reproducible. Normal values exist for adults, but are lacking for children. We sought to establish normal values for left and right ventricular volumes, mass and function in healthy children by using SSFP. Fifty children (27 females, 23 males) without cardiovascular disease were evaluated. Median age was 11 years (range 7 months – 18 years), weight 35 kg (range 7–77 kg), height 146 cm (range 66–181 cm). Thirty-six examinations were performed with breath holding, 14 in freely breathing sedated children. Ventricular volumes and mass were measured in the end systolic and end diastolic phase on SSFP cine images acquired in a short axis plane as a stack of 12 contiguous slices covering full length of both ventricles. Regression analysis showed an exponential relationship between body surface area (BSA) and ventricular volumes and mass (normal value = a*BSA b ). Normative curves for males and females are presented in relation to BSA for the enddiastolic volume, endsystolic volume and mass of both ventricles. Intra- and interobserver variability of the measurements was within the limits of 2% and 7% respectively, except for right ventricular mass (10%). The exponential equation for calculation of normal values for each ventricular parameter and graphical display of normative curves for data acquired in healthy children by SSFP cardiovascular magnetic resonance are provided.

Appearance of Normal Cranial Nerves on Steady-State Free Precession MR Images

Abstract: As radiologic imaging technology improves and more intricate details of the anatomy can be evaluated, images provide more precise diagnostic information and allow better localization of abnormalities. For example, standard T2-weighted magnetic resonance (MR) imaging sequences adequately depicted only the larger cranial nerves, whereas current steady-state free precession (SSFP) sequences are capable of depicting the cisternal segments of all 12 cranial nerves. SSFP sequences provide submillimetric spatial resolution and high contrast resolution between cerebrospinal fluid and solid structures, allowing the reconstruction of elegant multiplanar images that highlight the course of each nerve. These sequences have become a mainstay in the evaluation of the cerebellopontine angles and inner ear. Usually referred to by their trade names or acronyms (eg, constructive interference steady state, or CISS, and fast imaging employing steady-state acquisition, or FIESTA), SSFP sequences allow precise differentiation between branches of the facial and vestibulocochlear nerves, accurate detection of small masses in the cerebellopontine angles and internal auditory canals, and detailed evaluation of endolymph and perilymph within the inner ear. To take full advantage of these imaging sequences, radiologists must be familiar with the appearances of similar anatomic details of all 12 cranial nerves on SSFP MR images.

Vastly Undersampled Isotropic Projection Steady-State Free Precession Imaging of the Knee: Diagnostic Performance Compared with Conventional MR

Abstract: Purpose: To compare a vastly undersampled isotropic projection steady-state free precession (VIPR-SSFP) sequence and routine magnetic resonance (MR) imaging for evaluating the cartilage, ligaments, menisci, and osseous structures of the knee in symptomatic patients. Materials and Methods: All subjects signed written informed consent prior to participation in this prospective, HIPAA-compliant, institutional review board–approved study. VIPR-SSFP was added to the routine 1.5-T MR imaging performed on 95 symptomatic patients (52 men, 43 women; average age, 41.6 years) who subsequently underwent arthroscopic knee surgery. All MR examinations were independently reviewed twice by two musculoskeletal radiologists to detect cartilage lesions, anterior and posterior cruciate ligament tears, meniscal tears, and bone marrow edema lesions, first by using routine MR and second by using VIPR-SSFP. By using arthroscopy as the reference standard, the sensitivity and specificity of both MR protocols were calculated. The z...

Transverse relaxation time (T2) mapping in the brain with off-resonance correction using phase-cycled steady-state free precession imaging.

Abstract: Purpose To investigate a new approach for more completely accounting for off-resonance affects in the DESPOT2 (driven equilibrium single pulse observation of T2) mapping technique Materials and Methods The DESPOT2 method derives T2 information from fully balanced steady-state free precession (bSSFP) images acquired over multiple flip angles Off-resonance affects, which present as bands of altered signal intensity throughout the bSSFP images, results in erroneous T2 values in the corresponding calculated maps Radiofrequency (RF) phase-cycling, in which the phase of the RF pulse is incremented along the pulse train, offers a potential method for eliminating these artifacts In this work we present a general method, referred to as DESPOT2, with full modeling (DESPOT2-FM), for deriving T2, as well as off-resonance frequency, from dual flip angle bSSFP data acquired with two RF phase increments Results The method is demonstrated in vivo through the acquisition of whole-brain, 1 mm3 isotropic T2 maps at 3T and shown to provide near artifact-free maps, even in areas with steep susceptibility-induced gradients Conclusion DESPOT2-FM offers an efficient method for acquiring high spatial resolution, whole-brain T2 maps at 3T with high precision and free of artifact J Magn Reson Imaging 2009;30:411–417 © 2009 Wiley-Liss, Inc

Lung morphology assessment using MRI: a robust ultra-short TR/TE 2D steady state free precession sequence used in cystic fibrosis patients.

Abstract: To evaluate feasibility and diagnostic quality of ultra-short TR/TE two-dimensional (2D) steady state free precession (SSFP) MRI for cystic fibrosis (CF) patients. We performed lung MRI at 1.5 Tesla in 20 CF-patients (6–17 years, 12 males). Axial, coronal, and sagittal sections were acquired in inspiration and expiration with maximum breath-hold time 10 s. MR and CT images were scored using a modified Brody scoring system to assess bronchiectasis, mucous plugging, atelectasis/consolidations, and air trapping. All images were scored by two experienced observers. A complete MR investigation took maximally 15 min. Maximal breath-holds were only 10 s and well tolerated. MRI identified major bronchiectasis, mucous plugging and atelectasis. End-expiratory scans showed patches of parenchyma with reduced signal intensity that may corresponded to areas of trapped air on expiratory CT scans. This MRI protocol based on ultra-short TR/TE 2D SSFP is quick and well tolerated and provides highly relevant imaging features as seen on CT in CF patients. Most importantly, the SNR of the expiratory scans enables to visualize air trapping. The preliminary results of this study suggest MRI as a noteworthy additional imaging tool for routine monitoring of CF patients. Magn Reson Med 61:299–306, 2009. © 2009 Wiley-Liss, Inc.

Interleaved T(1) and T(2) relaxation time mapping for cardiac applications.

Abstract: PURPOSE To diagnose acute myocardial infarction (MI) with MRI, T(1)-weighted and T(2)-weighted images are required to detect necrosis and edema. The calculation of both T(1) and T(2) maps can be relevant for quantitative diagnosis. In this work, we present a simultaneous quantification of T(1)-T(2) relaxation times of a short-axis view of the heart in a single scan. MATERIALS AND METHODS An electrocardiograph (ECG)-triggered, navigator-gated, interleaved T(1) and T(2) mapping sequence was implemented for the quantification of the T(1) and T(2) values of phantoms, healthy volunteers, and three patients with acute MI. The proposed acquisition scheme consisted of an interleaved two-dimensional (2D) steady-state free precession (SSFP) sequence with three different modules: an inversion-recovery (IR) sequence with multiple time delays, followed by a delay of one cardiac cycle for magnetization recovery and a T(2)-preparation pulse with multiple echo-times for T(2) quantification. RESULTS Measurements of in vivo relaxation times were in good agreement with literature values. The interleaved sequence was able to measure T(1) and T(2) relaxation times of the myocardium. CONCLUSION The interleaved sequence acquires data for the calculation of T(1) and T(2) maps in only one scan without the need for registration. This technique has the potential to differentiate between acute and chronic MI by estimating the concentration of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) in the necrotic tissue and to assess the extent of edema from T(2) maps.

Feasibility of cardiac gating free of interference with electro-magnetic fields at 1.5 Tesla, 3.0 Tesla and 7.0 Tesla using an MR-stethoscope.

Abstract: OBJECTIVES: To circumvent the challenges of conventional electrocardiographic (ECG)-gating by examining the efficacy of an MR stethoscope, which offers (i) no risk of high voltage induction or patient burns, (ii) immunity to electromagnetic interference, (iii) suitability for all magnetic field strengths, and (iv) patient comfort together with ease of use for the pursuit of reliable and safe (ultra)high field cardiac gated magnetic resonance imaging (MRI). MATERIALS AND METHODS: The acoustic gating device consists of 3 main components: an acoustic sensor, a signal processing unit, and a coupler unit to the MRI system. Signal conditioning and conversion are conducted outside the 0.5 mT line using dedicated electronic circuits. The final waveform is delivered to the internal physiological signal controller circuitry of a clinical MR scanner. Cardiovascular MRI was performed of normal volunteers (n = 17) on 1.5 T, 3.0 T and 7.0 T whole body MR systems. Black blood imaging, 2D CINE imaging, 3D phase contrast MR angiography, and myocardial T2* mapping were carried out. RESULTS: The MR-stethoscope provided cardiograms at 1.5 T, 3.0 T and 7.0 T free of interference from electromagnetic fields and magneto-hydrodynamic effects. In comparison, ECG waveforms were susceptible to T-wave elevation and other distortions, which were more pronounced at higher fields. Acoustically gated black blood imaging at 1.5 T and 3.0 T provided image quality comparable with or even superior to that obtained from the ECG-gated approach. In the case of correct R-wave recognition, ECG-gated 2D CINE SSFP imaging was found to be immune to cardiac motion effects -even at 3.0 T. However, ECG-gated 2D SSFP CINE imaging was prone to cardiac motion artifacts if R-wave mis-registration occurred because of T-wave elevation. Acoustically gated 3D PCMRA at 1.5 T, 3.0 T and 7.0 T resulted in images free of blood pulsation artifacts because the acoustic gating approach provided cardiac signal traces free of interference with electromagnetic fields or magneto-hydrodynamic effects even at 7.0 Tesla. Severe ECG-trace distortions and T-wave elevations occurred at 3.0 T and 7.0 T. Acoustically cardiac gated T2* mapping at 3.0 T yielded a T2* value of 22.3 +/- 4.8 ms for the inferoseptal myocardium. CONCLUSIONS: The proposed MR-stethoscope presents a promising alternative to currently available techniques for cardiac gating of (ultra)high field MRI. Its intrinsic insensitivity to interference from electromagnetic fields renders it suitable for clinical imaging because of its excellent trigger reliability, even at 7.0 Tesla.

Real-Time Reconstruction of Sensitivity Encoded Radial Magnetic Resonance Imaging Using a Graphics Processing Unit

Abstract: A barrier to the adoption of non-Cartesian parallel magnetic resonance imaging for real-time applications has been the times required for the image reconstructions. These times have exceeded the underlying acquisition time thus preventing real-time display of the acquired images. We present a reconstruction algorithm for commodity graphics hardware (GPUs) to enable real time reconstruction of sensitivity encoded radial imaging (radial SENSE). We demonstrate that a radial profile order based on the golden ratio facilitates reconstruction from an arbitrary number of profiles. This allows the temporal resolution to be adjusted on the fly. A user adaptable regularization term is also included and, particularly for highly undersampled data, used to interactively improve the reconstruction quality. Each reconstruction is fully self-contained from the profile stream, i.e., the required coil sensitivity profiles, sampling density compensation weights, regularization terms, and noise estimates are computed in real-time from the acquisition data itself. The reconstruction implementation is verified using a steady state free precession (SSFP) pulse sequence and quantitatively evaluated. Three applications are demonstrated; real-time imaging with real-time SENSE 1) or k-t SENSE 2) reconstructions, and 3) offline reconstruction with interactive adjustment of reconstruction settings.

Improving Non-Contrast-Enhanced Steady-State Free Precession Angiography with Compressed Sensing

Abstract: Flow-independent angiography offers the ability to produce vessel images without contrast agents. Angiograms are acquired with magnetization-prepared three-dimensional balanced steady-state free precession sequences, where the phase encodes are interleaved and the preparation is repeated prior to each interleaf. The frequent repetition of the preparation significantly decreases the scan efficiency. The number of excitations can instead be reduced with compressed sensing by exploiting the compressibility of the angiograms. Hence, the phase encodes can be undersampled to save scan time without significantly degrading image quality. These savings can be allotted for preparing the magnetization more often, or alternatively, improving resolution. The enhanced resolution and contrast achieved with the proposed method are demonstrated with lower leg angiograms. Depiction of the vasculature is significantly improved with the increased resolution in the phase-encode plane and higher blood-to-background contrast.

Renal Transplant: Nonenhanced Renal MR Angiography with Magnetization-prepared Steady-State Free Precession

Abstract: The institutional review board approved this HIPAA-compliant study and waived informed consent. The purpose was to investigate nonenhanced magnetic resonance (MR) angiography with steady-state free precession (SSFP) with inversion recovery for assessing renal arteries in patients with renal transplants. Thirteen recipients of renal transplants underwent SSFP MR angiography before contrast material-enhanced MR angiography. Three stenoses (two mild, one severe) were identified at SSFP MR angiography in agreement with findings at contrast-enhanced MR angiography. There was no significant difference in image quality between the two methods. Results suggest SSFP MR angiography permits image quality of renal transplant arteries and detection of arterial stenosis comparable with those at contrast-enhanced MR angiography.

Morphological analysis in patients with sciatica: a magnetic resonance imaging study using three-dimensional high-resolution diffusion-weighted magnetic resonance neurography techniques.

Abstract: Study Design.A prospective observational study of patients with sciatica.Objective.We investigated the effectiveness of 3-dimensional high-spatial resolution diffusion-weighted MR neurography based on steady state free precession (3-dimensional diffusion-weighted steady-state free precession [DW-SSF

Non-contrast-enhanced flow-independent peripheral MR angiography with balanced SSFP.

Abstract: Flow-independent angiography is a non-contrast-enhanced technique that can generate vessel contrast even with reduced blood flow in the lower extremities. A method is presented for producing these angiograms with magnetization-prepared balanced steady-state free precession (bSSFP). Because bSSFP yields bright fat signal, robust fat suppression is essential for detailed depiction of the vasculature. Therefore, several strategies have been investigated to improve the reliability of fat suppression within short scan times. Phase-sensitive (PS) SSFP can efficiently suppress fat; however, partial volume effects due to fat and water occupying the same voxel can lead to the loss of blood signal. In contrast, alternating repetition time (ATR) SSFP minimizes this loss; however, the level of suppression is compromised by field inhomogeneity. Finally, a new double-acquisition ATR-SSFP technique reduces this sensitivity to off-resonance. In vivo results indicate that the two ATR-based techniques provide more reliable contrast when partial volume effects are significant.

Contrast-Enhanced Whole-Heart MR Coronary Angiography at 3.0 T Using the Intravascular Contrast Agent Gadofosveset

Abstract: OBJECTIVES The purpose of this study was to compare contrast-enhanced (CE) whole-heart coronary magnetic resonance angiography (MRA) at 3.0 T using gadofosveset to noncontrast-enhanced steady-state free precession (SSFP) coronary MRA at 1.5 T. MATERIALS AND METHODS A prospective randomized study was conducted among 20 healthy male volunteers. The same group of subjects underwent CE whole heart MRA at 3.0 T employing a 3D FLASH sequence with IR prepulse after gadofosveset injection as well as noncontrast-enhanced coronary MRA at 1.5 T using a 3D SSFP sequence with T2-preparation. Both techniques were performed using prospective ECG-triggering and adaptive respiratory gating. Acquisition time, signal-to-noise ratio of coronary blood, contrast-to-noise ratio (CNR) between coronaries and adjacent myocardium or epicardial fat, and image quality were evaluated in each case. RESULTS A significant increase of the overall CNR between coronary blood and adjacent myocardium was measured on images acquired at 3 T in comparison to 1.5 T. The mean values were 38.9 +/- 19.6 and 26.3 +/- 15.4, respectively (P[r] 0.05), however, the distal coronary segments were rated significantly higher for the CE MRA at 3.0 T (P = 0.02). The average acquisition time (15.29 +/- 5.73 minutes at 1.5 T vs. 17.29 +/- 5.18 minutes at 3 T) and overall image quality (2.15 +/- 0.49 at 1.5 T vs. 2.35 +/- 0.39 at 3 T) were similar for both methods. CONCLUSIONS CE whole-heart coronary MRA at 3.0 T demonstrated higher overall CNR between coronary blood and myocardium and an improved image quality of the distal coronary segments compared with noncontrast-enhanced SSFP coronary MRA at 1.5 T.

Improved arterial visibility using short-tau inversion-recovery (STIR) fat suppression in non-contrast-enhanced time–spatial labeling inversion pulse (Time-SLIP) renal MR angiography (MRA)

Abstract: Purpose To evaluate whether short-tau inversion-recovery (STIR) fat suppression is worthwhile in non-contrast-enhanced respiration-triggered free-breathing time–spatial labeling inversion pulse (Time-SLIP) renal magnetic resonance angiography (MRA) compared with chemical shift selective (CHESS) fat suppression Materials and Methods Simulation-based analyses of inversion time (TI) for spatial-selective inversion-recovery (ssIR) pulse and breathing rate were performed, and confirmed on a phantom and in human subjects using a three-dimensional (3D) coherent steady-state free precession (SSFP) sequence on a 15T Toshiba scanner Results The STIR fat suppression successfully suppressed signals from the intestines and parenchymous organs and provided better contrast between the arteries and the background, although an extension of TI was required for the ssIR pulse when a patient's respiration was extremely slow Conclusion STIR fat suppression provides better renal artery contrast than CHESS fat suppression in non-contrast free-breathing Time-SLIP MRA; it is also an effective screening tool for renal artery stenosis because of the lack of interference from intestinal signals However, close attention is needed if the patient has slow respiration As the TI for the ssIR pulse decreases, the STIR method requires faster-paced respiration J Magn Reson Imaging 2009;29:1471–1477 © 2009 Wiley-Liss, Inc

Non‐contrast‐enhanced MR portography with time‐spatial labeling inversion pulses: Comparison of imaging with three‐dimensional half‐fourier fast spin‐echo and true steady‐state free‐precession sequences

Abstract: Purpose To compare and evaluate images acquired with two different MR angiography (MRA) sequences, three-dimensional (3D) half-Fourier fast spin-echo (FSE) and 3D true steady-state free-precession (SSFP) combined with two time-spatial labeling inversion pulses (T-SLIPs), for selective and non-contrast-enhanced (non-CE) visualization of the portal vein. Materials and Methods Twenty healthy volunteers were examined using half-Fourier FSE and true SSFP sequences on a 1.5T MRI system with two T-SLIPs, one placed on the liver and thorax, and the other on the lower abdomen. For quantitative analysis, vessel-to-liver contrast (Cv-l) ratios of the main portal vein (MPV), right portal vein (RPV), and left portal vein (LPV) were measured. The quality of visualization was also evaluated. Results In both pulse sequences, selective visualization of the portal vein was successfully conducted in all 20 volunteers. Quantitative evaluation showed significantly better Cv-l at the RPVs and LPVs in half-Fourier FSE (P < 0.0001). At the MPV, Cv-l was better in true SSFP, but was not statistically different. Visualization scores were significantly better only at branches of segments four and eight for half-Fourier FSE (P = 0.001 and 0.03, respectively). Conclusion Both 3D half-Fourier FSE and true SSFP scans with T-SLIPs enabled selective non-CE visualization of the portal vein. Half-Fourier FSE was considered appropriate for intrahepatic portal vein visualization, and true SSFP may be preferable when visualization of the MPV is required. J. Magn. Reson. Imaging 2009;29:1140–1146. © 2009 Wiley-Liss, Inc.

SSFP signal with finite RF pulses.

Abstract: The theoretical description of steady state free precession (SSFP) sequences is generally well accepted and unquestioned, although it is based on instantaneously acting radiofrequency (RF) pulses. In practice, however, all excitation processes are finite, thereby questioning the overall validity of the common SSFP signal description for use with finite RF pulses. In this paper, finite RF pulse effects on balanced SSFP signal formation are analyzed as a function of the RF time, the pulse repetition time, the flip angle (alpha) and relaxation times (T(1,2)). The observed signal modulations from finite RF pulses (compared to infinitesimal ones) can range from only a few percent (for RF time/pulse repetition time 1 (for alpha approximately 90 degrees, T(2)/T(1) << 1). As a result, a revision of SSFP signal theory is indicated not only for reasons of completeness but also seems advisable, e.g., for all quantitative SSFP methods. A simple modification for the common balanced SSFP equation is derived that provides an accurate framework for SSFP signal description over a wide variety of practical and physiologic parameters.

High resolution MR imaging of the fetal heart with cardiac triggering: a feasibility study in the sheep fetus

Abstract: The aim of this study was to perform fetal cardiac magnetic resonance imaging (MRI) with triggering of the fetal heart beat in utero in a sheep model. All experimental protocols were reviewed and the usage of ewes and fetuses was approved by the local animal protection authorities. Images of the hearts of six pregnant ewes were obtained by using a 1.5-T MR system (Philips Medical Systems, Best, Netherlands). The fetuses were chronically instrumented with a carotid catheter to measure the fetal heart frequency for the cardiac triggering. Pulse wave triggered, breath-hold cine-MRI with steady-state free precession (SSFP) was achieved in short axis, two-, four- and three-chamber views. The left ventricular volume and thus the function were measured from the short axis. The fetal heart frequencies ranged between 130 and 160 bpm. The mitral, tricuspid, aortic, and pulmonary valves could be clearly observed. The foramen ovale could be visualized. Myocardial contraction was shown in cine sequences. The average blood volume at the end systole was 3.4 ± 0.2 ml (± SD). The average volume at end diastole was 5.2 ± 0.2 ml; thus the stroke volumes of the left ventricle in the systole were between 1.7 and 1.9 ml with ejection fractions of 38.6% and 39%, respectively. The pulse wave triggered cardiac MRI of the fetal heart allowed evaluation of anatomical structures and functional information. This feasibility study demonstrates the applicability of MRI for future evaluation of fetuses with complex congenital heart defects, once a noninvasive method has been developed to perform fetal cardiac triggering.

Three-dimensional imaging of pulmonary veins by a novel steady-state free-precession magnetic resonance angiography technique without the use of intravenous contrast agent: initial experience.

Abstract: Purpose:To evaluate the feasibility of 3-dimensional (3D) steady-state free-precession (SSFP) magnetic resonance angiography (MRA) using nonselective radiofrequency excitation for imaging of pulmonary veins (PVs) without intravenous gadolinium chelate and to correlate the results with conventional c

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

Abstract: Purpose: To determine whether unenhanced magnetic resonance (MR) angiography performed with a three-dimensional (3D) segmented steady-state free precession (SSFP) sequence would be an alternative to contrast material–enhanced MR angiography for evaluating pulmonary veins (PVs) prior to and following radiofrequency (RF) ablation for atrial fibrillation. Materials and Methods: MR angiographic examinations of PVs, performed in 20 patients (nine men, 11 women; mean age, 56.4 years ± 12.7 [standard deviation]), were retrospectively reviewed according to an institutional review board–approved protocol. The number of PVs and their orthogonal measurements obtained from the 3D SSFP images were compared with those obtained from contrast-enhanced MR angiography. Signal-to-noise and contrast-to-noise ratios were also compared. Qualitative assessment of both techniques was performed by independent reviewers who scored the image quality (on a scale of 1 to 5) on the basis of PV conspicuity. The presence of cardiac and ...

Improved shim method based on the minimization of the maximum off-resonance frequency for balanced steady-state free precession (bSSFP).

Abstract: In this article, a shim method that minimizes the maximum off-resonance frequency (min-max shim) in balanced steady-state free precession (bSSFP) is tested for brain imaging at 3 T with contrast and linear shim terms. The method demonstrates improvement of spatial coverage and banding artifact reduction over standard least-squares shimming. In addition, a new method (modified min-max shim) is introduced. This method reduces boundary band regions where the artifact is inevitable due to the excessive off-resonance frequency distribution. In comparison to standard least-squares shimming, the min-max based shim method either eliminate or reduce the size of banding artifacts. The method can be used to increase the SNR in bSSFP imaging or to increase the functional contrast in bSSFP fMRI by allowing a longer usable repetition time (TR).

Non-contrast-enhanced MR angiography for selective visualization of the hepatic vein and inferior vena cava with true steady-state free-precession sequence and time-spatial labeling inversion pulses: preliminary results.

Abstract: Purpose To selectively visualize the hepatic vein and inferior vena cava (IVC) using three-dimensional (3D) true steady-state free-precession (SSFP) MR angiography with time-spatial labeling inversion pulse (T-SLIP), and to optimize the acquisition protocol. Materials and Methods Respiratory-gated 3D true SSFP scans were conducted in 23 subjects in combination with two different T-SLIPs (one placed in the thorax to suppress the arterial signal and the other in the abdomen to suppress the portal venous signal). One of the most important factors was the inversion time (TI) of abdominal T-SLIP, and the image quality was evaluated at four different TIs of 800, 1200, 1600, and 2000 msec in terms of relative signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and mean visualization scores. Results No significant difference was observed in SNR and CNR between each TI. However, IVC visualization scores were better at TIs of 1600 and 2000 msec, and overall image quality was better at TIs of 1200 and 1600 msec. Therefore, the TI of 1600 msec was considered to provide the optimal balance between IVC visualization and signal suppression of the portal vein in our protocol. Conclusion True SSFP scan with T-SLIPs enabled selective visualization of the hepatic vein and IVC without an exogenous contrast agent. J. Magn. Reson. Imaging 2009;29:474–479. © 2009 Wiley-Liss, Inc.

Low dose gadobenate dimeglumine for imaging of chronic myocardial infarction in comparison with standard dose gadopentetate dimeglumine.

Abstract: OBJECTIVES Gadobenate dimeglumine has a 2-fold higher T1 relaxivity compared with gadopentetate dimeglumine and can be used for imaging delayed enhancement in the assessment of myocardial infarction. The purpose of this study was to compare 0.1 mmoL/kg gadobenate dimeglumine (Gd-BOPTA, MultiHance, Bracco Imaging SpA, Milan, Italy) with 0.2 mmoL/kg gadopentetate dimeglumine (Gd-DTPA, Magnevist, Bayer-Schering Pharma AG, Berlin, Germany) in cardiac magnetic resonance imaging. MATERIALS AND METHODS The study was performed in accordance with the institutional review board. Two groups of 20 patients underwent magnetic resonance examinations for evaluation of chronic myocardial infarction. Although group 1 received gadobenate dimeglumine at a dose of 0.1 mmoL/kg, group 2 received gadopentetate dimeglumine at a dose of 0.2 mmoL/kg. Single shot inversion recovery (IR) steady-state free precession (SSFP), and IR gradient echo sequence (GRE) sequences were used for imaging delayed enhancement. The sizes of myocardial infarctions were measured for both contrast agents in both imaging techniques by 2 readers. Bland-Altman analyses were performed for each sequence and gadolinium chelate. Furthermore, the transmural extent of myocardial infarction was assessed by 2 readers according to the 17-segment model for both contrast media and both sequences and kappa values were calculated. Signal-to-noise ratios for infarcted myocardium, normal myocardium, and the left ventricular cavity were measured, and the contrast-to-noise ratios of infarcted compared with normal myocardium (CNRinf-myo) and infarcted myocardium in relation to the left ventricular cavities (CNRinf-LVC) were calculated. RESULTS The Bland-Altman plots in the assessment of infarction size did not reveal a systematic bias between the 2 readers. The mean difference between reader 1 and 2 was less than 0.9 cm3 of mean infarction volume. Assessment of interobserver agreement regarding the transmural extent of myocardial infarction resulted in kappa values of kappa = 0.845 (IR SSFP) and kappa = 0.874 (IR GRE) in gadobenate-enhanced images and kappa = 0.841 (IR SSFP) and kappa = 0.833 (IR GRE) after administration of gadopentetate. CNRinf-normal was significantly higher on the images of group 1 (gadobenate) compared with group 2 (gadopentetate) in both sequences (single shot IR SSFP: 18.1 +/- 10.1 vs. 12.1 +/- 6.7; P = 0.032 and IR GRE: 27.2 +/- 5.8 vs. 19.7 +/- 5.9; P = 0.005). The mean value of CNRinf-LVC for the group examined with Gd-BOPTA was lower, though not significantly, compared with the group examined with Gd-DTPA in IR GRE technique, whereas CNRinf-LVC for IR SSFP resulted in equal values (single shot IR SSFP: 1.2 +/- 5.2 vs. 1.1 +/- 6.8; P = n.s. and IR GRE 2.4 +/- 5.8 vs. 5.8 +/- 7.9; P = n.s.). CONCLUSIONS Low dose Gd-BOPTA resulted in significantly higher CNRinf-myo compared with standard dose Gd-DTPA in imaging of myocardial infarction with IR SSFP and IR GRE sequences. Demarcation of infarcted myocardium from the left ventricular cavity assessed by CNR showed no significant difference after application of either contrast media in both imaging techniques.

Volume-targeted and whole-heart coronary magnetic resonance angiography using an intravascular contrast agent

Abstract: Purpose To compare volume-targeted and whole-heart coronary magnetic resonance angiography (MRA) after the administration of an intravascular contrast agent. Materials and Methods Six healthy adult subjects underwent a navigator-gated and -corrected (NAV) free breathing volume-targeted cardiac-triggered inversion recovery (IR) 3D steady-state free precession (SSFP) coronary MRA sequence (t-CMRA) (spatial resolution = 1 × 1 × 3 mm3) and high spatial resolution IR 3D SSFP whole-heart coronary MRA (WH-CMRA) (spatial resolution = 1 × 1 × 2 mm3) after the administration of an intravascular contrast agent B-22956. Subjective and objective image quality parameters including maximal visible vessel length, vessel sharpness, and visibility of coronary side branches were evaluated for both t-CMRA and WH-CMRA. Results No significant differences (P = NS) in image quality were observed between contrast-enhanced t-CMRA and WH-CMRA. However, using an intravascular contrast agent, significantly longer vessel segments were measured on WH-CMRA vs. t-CMRA (right coronary artery [RCA] 13.5 ± 0.7 cm vs. 12.5 ± 0.2 cm; P < 0.05; and left circumflex coronary artery [LCX] 11.9 ± 2.2 cm vs. 6.9 ± 2.4 cm; P < 0.05). Significantly more side branches (13.3 ± 1.2 vs. 8.7 ± 1.2; P < 0.05) were visible for the left anterior descending coronary artery (LAD) on WH-CMRA vs. t-CMRA. Scanning time and navigator efficiency were similar for both techniques (t-CMRA: 6.05 min; 49% vs. WH-CMRA: 5.51 min; 54%, both P = NS). Conclusion Both WH-CMRA and t-CMRA using SSFP are useful techniques for coronary MRA after the injection of an intravascular blood-pool agent. However, the vessel conspicuity for high spatial resolution WH-CMRA is not inferior to t-CMRA, while visible vessel length and the number of visible smaller-diameter vessels and side-branches are improved. J. Magn. Reson. Imaging 2009;30:1191–1196. © 2009 Wiley-Liss, Inc.

Multiple Repetition Time Balanced Steady-State Free Precession Imaging

Abstract: Although balanced steady-state free precession (bSSFP) imaging yields high signal-to-noise ratio (SNR) efficiency, the bright lipid signal is often undesirable. The bSSFP spectrum can be shaped to suppress the fat signal with scan-efficient alternating repetition time (ATR) bSSFP. However, the level of suppression is limited, and the pass-band is narrow due to its non-uniform shape. A multiple repetition time (TR) bSSFP scheme is proposed that creates a broad stop-band with a scan efficiency comparable to ATR-SSFP. Furthermore, the pass-band signal uniformity is improved, resulting in fewer shading/banding artifacts. When data acquisition occurs in more than a single TR within the multiple-TR period, the echoes can be combined to significantly improve the level of suppression. The signal characteristics of the proposed technique were compared with bSSFP and ATR-SSFP. The multiple-TR method generates identical contrast to bSSFP, while achieving up to an order of magnitude higher stop-band suppression than ATR-SSFP. In vivo studies at 1.5 T and 3 T demonstrate the superior fat suppression performance of multiple-TR bSSFP.

Referenceless phase velocity mapping using balanced SSFP

Abstract: Phase contrast MRI (PC-MRI) is an established technique for measuring blood flow velocities in vivo. Although spoiled gradient recalled echo (GRE) PC-MRI is the most widely used pulse sequence today, balanced steady state free precession (SSFP) PC-MRI has been shown to produce accurate velocity estimates with superior SNR efficiency. We propose a referenceless approach to flow imaging that exploits the intrinsic refocusing property of balanced SSFP, and achieves up to a 50% reduction in total scan time. With the echo time set to exactly one half of the sequence repetition time (TE = TR/2), we show that non-flow-related image phase tends to vary smoothly across the field-of-view, and can be estimated from static tissue regions to produce a phase reference for nearby voxels containing flowing blood. This approach produces accurate in vivo one-dimensional velocity estimates in half the scan time compared with conventional balanced SSFP phase-contrast methods. We also demonstrate the feasibility of referenceless time-resolved 3D flow imaging (called “7D” flow) in the carotid bifurcation from just three acquisitions. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc.

Rapid water and lipid imaging with T2 mapping using a radial IDEAL‐GRASE technique

Abstract: Reliable and fast separation of tissue water and lipid components is desired in many clinical applications to improve the diagnosis of disease. Conventional chemical-shift saturation techniques for suppressing the water or lipid component are problematic due to the presence of static field inhomogeneities (1-4). Chemical shift imaging based on phase sensitive methods has been widely investigated to overcome the problems in lipid-water imaging caused by field inhomogeneities. There have been many approaches, including the two-point method acquiring “in-phase” and “opposed-phase” images originally proposed by Dixon (5) and a refinement with possible phase correction due to field inhomogeneities (6,7). The two-point Dixon method was followed by the three-point Dixon approach with symmetric sampling (e.g., the acquisition of images with phase shifts between lipid and water of −π,0,π; 0,π,2π; or the more general scheme −α,0,α). The three points were used to resolve lipid and water and a field map (8-11). These methods relied on a phase unwrapping algorithm to estimate the field map which in many cases complicated the separation of lipid and water. As an alternative, Xiang et al introduced the use of asymmetric sampling with direct phase encoding to directly separate lipid and water without the need for an initial estimation of the field map (12,13). Another advantage of asymmetric sampling is that the redundancy of symmetrically sampled data is removed yielding a more efficient utilization of the data (13). Recently an iterative algorithm for the decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL) was developed (14,15). IDEAL is also based on the asymmetric acquisition and requires at least three images to resolve the lipid and water images and the field map. In IDEAL the field map is calculated in an iterative fashion and does not require a specific algorithm to unwrap the phase. IDEAL has been implemented with FSE, gradient-echo (GRE), and steady-state free precession (SSFP) sequences (14-16) and is reported to yield robust lipid-water imaging for various clinical applications. In these applications the collection of the three phase-shifted echoes is done in separate TR periods. In FSE applications this results in long scan times, which is not adequate for imaging anatomic locations where fast imaging is required. In order to reduce scan time for lipid-water imaging in FSE acquisitions we developed the IDEAL Gradient and Spin Echo method (IDEAL-GRASE) (17) where multiple gradient echoes are collected within each spin-echo period so that the data with different phase-shifts for lipid-water imaging are obtained within the same TR period. The IDEAL-GRASE method was developed for conventional Cartesian data acquisition. The Cartesian IDEAL-GRASE technique was shown to produce comparable separation of lipid and water to IDEAL-FSE in 1/3 of the imaging time. Another method based on the collection of multiple echoes within a spin-echo (SE) period was also recently developed for fast lipid-water imaging by Ma et al (18). The acquisition of data using a radial k-space trajectory offers robustness to motion and flow (19-22). We have shown that radial MRI is a good alternative to Cartesian MRI for T2-weighted imaging where the image quality of the conventional Cartesian-based methods is deteriorated by motion and flow artifacts (22). Moreover, due to the oversampling in the center of k-space a single radial FSE or GRASE k-space data set can be processed to generate high resolution T2 maps (23-26). The T2 information obtained from radial FSE data successfully discriminated benign from malignant liver lesions (22,26). In this work, we describe a radial GRASE technique combined with the IDEAL algorithm (radial IDEAL-GRASE) to achieve time-efficient lipid-water decomposition as well as T2 mapping. The radial IDEAL-GRASE technique is demonstrated in phantoms and in vivo for applications including pelvic, cardiac, and abdominal imaging.

Multicontrast late gadolinium enhancement imaging enables viability and wall motion assessment in a single acquisition with reduced scan times

Abstract: Purpose To determine the accuracy of multicontrast late enhancement imaging (MCLE) in the assessment of myocardial viability and wall motion compared to the conventional wall motion and viability cardiac magnetic resonance imaging (MRI) pulse sequences. Materials and Methods Forty-one patients with suspected myocardial infarction were studied. Patients underwent assessment of cardiac function with cine steady-state free-precession (SSFP), followed by late gadolinium enhancement (LGE) imaging using inversion recovery gradient echo scanning (IR-GRE) sequence and MCLE. MCLE was compared to cine SSFP in the assessment of wall motion, ejection fraction (EF), left ventricular (LV) mass, LV end-diastolic volume (EDV), and to IR-GRE for measuring infarct size. Results MCLE, IR-GRE, and SSFP imaging demonstrated excellent agreement in the assessment of EF, LV infarct size, and LV mass (r > 0.95, P < 0.001 for all measures), as well as in the assessment of wall motion (κ statistic 0.75). Conclusion MCLE provided coregistered images for the assessment of viability and wall motion without loss of accuracy in the assessment of quantitative cardiac parameters. MCLE provides accurate quantitative cardiac assessment with reduced scan times compared to the conventional sequences and thus may be used as an alternative to conventional cine SSFP and IR-GRE imaging. J. Magn. Reson. Imaging 2009;30:771–777. © 2009 Wiley-Liss, Inc.

Simulation of coupled-spin systems in the steady-state free-precession acquisition mode for fast magnetic resonance (MR) spectroscopic imaging

Abstract: The steady-state free-precession (SSFP) acquisition mode may be found useful for fast in vivo proton magnetic resonance spectroscopic imaging in high-field MR systems because of the achievable signal-to-noise ratio and the avoidance of RF pulses with large flip angles. Detection of signals from metabolites with coupled-spin systems under SSFP has not yet been accomplished, but should be possible in high field, albeit with substantial signal truncation. It must be expected that the spin system evolution and the spectra will be affected by the steady-state conditions, which prevent the spin systems from returning to the Boltzmann equilibrium. Computer simulation is needed for the experiment design and spectrum quantification. This work outlines a suitable simulation method (QuaM-EPG), which combines and extends two pre-existing approaches: the density matrix calculation, used in high-resolution NMR, and the extended phase graph method, used to describe cyclic excitation in fast MRI of water protons. The method is illustrated by its application to model molecules and myo-inositol, which is one of the clinically relevant target molecules. It is shown that antiphase and multiple-quantum coherences may represent a considerable portion of the steady-state magnetization in a quantum-mechanical sense and that the spectral patterns are affected thereby.