Phase‐sensitive,dual‐acquisition,single‐slab, 3D,turbo‐spin‐echo pulse sequence for simultaneous T2‐weighted and fluid‐attenuated whole‐brain imaging

Conventional T₂‐weighted turbo/fast spin echo imaging is clinically accepted as the most sensitive method to detect brain lesions but generates a high signal intensity of cerebrospinal fluid (CSF), yielding diagnostic ambiguity for lesions close to CSF. Fluid‐attenuated inversion recovery can be an alternative, selectively eliminating CSF signals. However, a long time of inversion, which is required for CSF suppression, increases imaging time substantially and thereby limits spatial resolution. The purpose of this work is to develop a phase‐sensitive, dual‐acquisition, single‐slab, three‐dimensional, turbo/fast spin echo imaging, simultaneously achieving both conventional T₂‐weighted and fluid‐attenuated inversion recovery–like high‐resolution whole‐brain images in a single pulse sequence, without an apparent increase of imaging time. Dual acquisition in each time of repetition is performed, wherein an in phase between CSF and brain tissues is achieved in the first acquisition, while an opposed phase, which is established by a sequence of a long refocusing pulse train with variable flip angles, a composite flip‐down restore pulse train, and a short time of delay, is attained in the second acquisition. A CSF‐suppressed image is then reconstructed by weighted averaging the in‐ and opposed‐phase images. Numerical simulations and in vivo experiments are performed, demonstrating that this single pulse sequence may replace both conventional T₂‐weighted imaging and fluid‐attenuated inversion recovery. Magn Reson Med 63:1422–1430, 2010. © 2010 Wiley‐Liss, Inc.     

Optimized three‐dimensional fast‐spin‐echo MRI

Spin‐echo‐based acquisitions are the workhorse of clinical MRI because they provide a variety of useful image contrasts and are resistant to image artifacts from radio‐frequency or static field inhomogeneity. Three‐dimensional (3D) acquisitions provide datasets that can be retrospectively reformatted for viewing in freely selectable orientations, and are thus advantageous for evaluating the complex anatomy associated with many clinical applications of MRI. Historically, however, 3D spin‐echo‐based acquisitions have not played a significant role in clinical MRI due to unacceptably long acquisition times or image artifacts associated with details of the acquisition method. Recently, optimized forms of 3D fast/turbo spin‐echo imaging have become available from several MR‐equipment manufacturers (for example, CUBE [GE], SPACE [Siemens], and VISTA [Philips]). Through specific design strategies and optimization, including short non–spatially selective radio‐frequency pulses to significantly shorten the echo spacing and variable flip angles for the refocusing radio‐frequency pulses to suppress blurring or considerably lengthen the useable duration of the spin‐echo train, these techniques permit single‐slab 3D imaging of sizeable volumes in clinically acceptable acquisition times. These optimized fast/turbo spin‐echo pulse sequences provide a robust and flexible approach for 3D spin‐echo‐based imaging with a broad range of clinical applications. J. Magn. Reson. Imaging 2014;39:745–767. © 2014 Wiley Periodicals, Inc .     

3D steady‐state diffusion‐weighted imaging with trajectory using radially batched internal navigator echoes (TURBINE)

While most diffusion‐weighted imaging (DWI) is acquired using single‐shot diffusion‐weighted spin‐echo echo‐planar imaging, steady‐state DWI is an alternative method with the potential to achieve higher‐resolution images with less distortion. Steady‐state DWI is, however, best suited to a segmented three‐dimensional acquisition and thus requires three‐dimensional navigation to fully correct for motion artifacts. In this paper, a method for three‐dimensional motion‐corrected steady‐state DWI is presented. The method uses a unique acquisition and reconstruction scheme named trajectory using radially batched internal navigator echoes (TURBINE). Steady‐state DWI with TURBINE uses slab‐selection and a short echo‐planar imaging (EPI) readout each pulse repetition time. Successive EPI readouts are rotated about the phase‐encode axis. For image reconstruction, batches of cardiac‐synchronized readouts are used to form three‐dimensional navigators from a fully sampled central k‐space cylinder. In vivo steady‐state DWI with TURBINE is demonstrated in human brain. Motion artifacts are corrected using refocusing reconstruction and TURBINE images prove less distorted compared to two‐dimensional single‐shot diffusion‐weighted‐spin‐EPI. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.     

Contrast‐enhanced,three‐dimensional,whole‐brain,black‐blood imaging: Application to small brain metastases

Contrast‐enhanced three‐dimensional T₁‐weighted imaging based on magnetization‐prepared rapid‐gradient recalled echo is widely used for detecting small brain metastases. However, since contrast materials remain in both blood and the tumor parenchyma and thus increase the signal intensity of both regions, it is often challenging to distinguish brain tumors from blood. In this work, we develop a T₁‐weighted, black‐blood version of single‐slab three‐dimensional turbo/fast spin echo whole‐brain imaging, in which the signal intensity of the brain tumor is selectively enhanced while that of blood is suppressed. For blood suppression, variable refocusing flip angles with flow‐sensitizing gradients are employed. To avoid a signal loss resulting from the flow‐sensitizing scheme, the first refocusing flip angle is forced to 180°. Composite restore pulses at the end of refocusing pulse train are applied to achieve partial inversion recovery for the T₁‐weighted contrast. Simulations and in vivo volunteer and patient experiments are performed, demonstrating that this approach is highly efficient in detecting small brain metastases. Magn Reson Med 63:553–561, 2010. © 2010 Wiley‐Liss, Inc.     

Fast‐spin‐echo imaging of inner fields‐of‐view with 2D‐selective RF excitations

Purpose:

To demonstrate the feasibility of two‐dimensional selective radio frequency (2DRF) excitations for fast‐spin‐echo imaging of inner fields‐of‐view (FOVs) in order to shorten acquisitions times, decrease RF energy deposition, and reduce image blurring.

Materials and Methods:

Fast‐spin‐echo images (in‐plane resolution 1.0 × 1.0 mm² or 0.5 × 1.0 mm²) of inner FOVs (40 mm, 16 mm oversampling) were obtained in phantoms and healthy volunteers on a 3 T whole‐body MR system using blipped‐planar 2DRF excitations.

Results:

Positioning the unwanted side excitations in the blind spot between the image section and the slice stack to measure yields minimum 2DRF pulse durations (about 6 msec) that are compatible with typical echo spacings of fast‐spin‐echo acquisitions. For the inner FOVs, the number of echoes and refocusing RF pulses is considerably reduced which compared to a full FOV (182 mm) reduces the RF energy deposition by about a factor of three and shortens the acquisition time, e.g., from 39 seconds to 12 seconds for a turbo factor of 15 or from 900 msec to 280 msec for a single‐shot acquisition, respectively. Furthermore, image blurring occurring for high turbo factors as in single‐shot acquisitions is considerably reduced yielding effectively higher in‐plane resolutions.

Conclusion:

Inner‐FOV acquisitions using 2DRF excitations may help to shorten acquisitions times, ameliorate image blurring, and reduce specific absorption rate (SAR) limitations of fast‐spin‐echo (FSE) imaging, in particular at higher static magnetic fields. J. Magn. Reson. Imaging 2010;31:1530–1537. © 2010 Wiley‐Liss, Inc.     

3D fast spin echo with out‐of‐slab cancellation: A technique for high‐resolution structural imaging of trabecular bone at 7 tesla

Spin‐echo‐based pulse sequences are desirable for the application of high‐resolution imaging of trabecular bone but tend to involve high‐power deposition. Increased availability of ultrahigh field scanners has opened new possibilities for imaging with increased signal‐to‐noise ratio (SNR) efficiency, but many pulse sequences that are standard at 1.5 and 3 T exceed specific absorption rate limits at 7 T. A modified, reduced specific absorption rate, three‐dimensional, fast spin‐echo pulse sequence optimized specifically for in vivo trabecular bone imaging at 7 T is introduced. The sequence involves a slab‐selective excitation pulse, low‐power nonselective refocusing pulses, and phase cycling to cancel undesired out‐of‐slab signal. In vivo images of the distal tibia were acquired using the technique at 1.5, 3, and 7 T field strengths, and SNR was found to increase at least linearly using receive coils of identical geometry. Signal dependence on the choice of refocusing flip angles in the echo train was analyzed experimentally and theoretically by combining the signal from hundreds of coherence pathways, and it is shown that a significant specific absorption rate reduction can be achieved with negligible SNR loss. Magn Reson Med 63:719–727, 2010. © 2010 Wiley‐Liss, Inc.     

Spectrally selective 3D TSE imaging of phosphocreatine in the human calf muscle at 3 T

Quantitative information about concentrations of several metabolites in human skeletal muscle can be obtained through localized ³¹P magnetic resonance spectroscopy methods. However, these methods have shortcomings: long acquisition times, limited volume coverage, and coarse resolution. Significantly higher spatial and temporal resolution of imaging of single metabolites can be achieved through spectrally selective three‐dimensional imaging methods. This study reports the implementation of a three‐dimensional spectrally selective turbo spin‐echo sequence, on a 3T clinical system, to map the concentration of phosphocreatine in the human calf muscle with significantly increased spatial resolution and in a clinically feasible scan time. Absolute phosphocreatine quantification was performed with the use of external phantoms after relaxation and flip angle correction of the turbo spin‐echo voxel signal. The mean ± standard deviation of the phosphocreatine concentration measured in five healthy volunteers was 29.4 ± 2.5 mM with signal‐to‐noise ratio of 14:1 and voxel size of 0.52 mL. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Comparison of wideband steady‐state free precession and T2‐weighted fast spin echo in spine disorder assessment at 1.5 and 3 T

Wideband steady‐state free precession (WB‐SSFP) is a modification of balanced steady‐state free precession utilizing alternating repetition times to reduce susceptibility‐induced balanced steady‐state free precession limitations, allowing its use for high‐resolution myelographic‐contrast spinal imaging. Intertissue contrast and spatial resolution of complete‐spine‐coverage 3D WB‐SSFP were compared with those of 2D T₂‐weighted fast spin echo, currently the standard for spine T₂‐imaging. Six normal subjects were imaged at 1.5 and 3 T. The signal‐to‐noise ratio efficiency (SNR per unit‐time and unit‐volume) of several tissues was measured, along with four intertissue contrast‐to‐noise ratios; nerve‐ganglia:fat, intradural‐nerves:cerebrospinal fluid, nerve‐ganglia:muscle, and muscle:fat. Patients with degenerative and traumatic spine disorders were imaged at both MRI fields to demonstrate WB‐SSFP clinical advantages and disadvantages. At 3 T, WB‐SSFP provided spinal contrast‐to‐noise ratios 3.7–5.2 times that of fast spin echo. At 1.5 T, WB‐SSFP contrast‐to‐noise ratio was 3–3.5 times that of fast spin echo, excluding a 1.7 ratio for intradural‐nerves:cerebrospinal fluid. WB‐SSFP signal‐to‐noise ratio efficiency was also higher. Three‐dimensional WB‐SSFP disadvantages relative to 2D fast spin echo are reduced edema hyperintensity, reduced muscle signal, and higher motion sensitivity. WB‐SSFP's high resolution and contrast‐to‐noise ratio improved visualization of intradural nerve bundles, foraminal nerve roots, and extradural nerve bundles, improving detection of nerve compression in radiculopathy and spinal‐stenosis. WB‐SSFP's high resolution permitted reformatting into orthogonal planes, providing distinct advantages in gauging fine spine pathology. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Implementation of vascular‐space‐occupancy MRI at 7T

Vascular‐space‐occupancy (VASO) MRI exploits the difference between blood and tissue T₁ to null blood signal and measure cerebral blood volume changes using the residual tissue signal. VASO imaging is more difficult at higher field because of sensitivity loss due to the convergence of tissue and blood T₁ values and increased contamination from blood‐oxygenation‐level‐dependent (BOLD) effects. In addition, compared to 3T, 7T MRI suffers from increased geometrical distortions, e.g., when using echo‐planar‐imaging, and from increased power deposition, the latter especially problematic for the spin‐echo‐train sequences commonly used for VASO MRI. Third, non‐steady‐state blood spin effects become substantial at 7T when only a head coil is available for radiofrequency transmit. In this study, the magnetization‐transfer‐enhanced‐VASO approach was applied to maximize tissue‐blood signal difference, which boosted signal‐to‐noise ratio by 149% ± 13% (n = 7) compared to VASO. Second, a 3D fast gradient‐echo sequence with low flip‐angle (7°) and short echo‐time (1.8 ms) was used to minimize the BOLD effect and to reduce image distortion and power deposition. Finally, a magnetization‐reset technique was combined with a motion‐sensitized‐driven‐equilibrium approach to suppress three types of non‐steady‐state spins. Our initial functional MRI results in normal human brains at 7T with this optimized VASO sequence showed better signal‐to‐noise ratio than at 3T. Magn Reson Med 69:1003–1013, 2013. © 2012 Wiley Periodicals, Inc.     

Spin‐locked balanced steady‐state free‐precession (slSSFP)

A spin‐locked balanced steady‐state free‐precession (slSSFP) pulse sequence is described that combines a balanced gradient‐echo acquisition with an off‐resonance spin‐lock pulse for fast MRI. The transient and steady‐state magnetization trajectory was solved numerically using the Bloch equations and was shown to be similar to balanced steady‐state free‐precession (bSSFP) for a range of T₂/T₁ and flip angles, although the slSSFP steady‐state could be maintained with considerably lower radio frequency (RF) power. In both simulations and brain scans performed at 7T, slSSFP was shown to exhibit similar contrast and signal‐to‐noise ratio (SNR) efficiency to bSSFP, but with significantly lower power. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Reduction of B1 sensitivity in selective single‐slab 3d turbo spin echo imaging with very long echo trains

Single‐slab 3D turbo/fast spin echo (SE) imaging with very long echo trains was recently introduced with slab selection using a highly selective excitation pulse and short, nonselective refocusing pulses with variable flip angles for high imaging efficiency. This technique, however, is vulnerable to image degradation in the presence of spatially varying B₁ amplitudes. In this work we develop a B₁ inhomogeneity‐reduced version of single‐slab 3D turbo/fast SE imaging based on the hypothesis that it is critical to achieve spatially uniform excitation. Slab selection was performed using composite adiabatic selective excitation wherein magnetization is tipped into the transverse plane by a nonselective adiabatic‐half‐passage pulse and then slab is selected by a pair of selective adiabatic‐full‐passage pulses. Simulations and experiments were performed to evaluate the proposed technique and demonstrated that this approach is a simple and efficient way to reduce B₁ sensitivity in single‐slab 3D turbo/fast SE imaging with very long echo trains. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Simultaneous estimation of T(2) and apparent diffusion coefficient in human articular cartilage in vivo with a modified three-dimensional double echo steady state (DESS) sequence at 3 T

T₂ mapping and diffusion‐weighted imaging complement morphological imaging for assessing cartilage disease and injury. The double echo steady state sequence has been used for morphological imaging and generates two echoes with markedly different T₂ and diffusion weighting. Modifying the spoiler gradient area and flip angle of the double echo steady state sequence allows greater control of the diffusion weighting of both echoes. Data from two acquisitions with different spoiler gradient areas and flip angles are used to simultaneously estimate the T₂ and apparent diffusion coefficient of each voxel. This method is verified in phantoms and validated in vivo in the knee; estimates from different regions of interest in the phantoms and cartilage are compared to those obtained using standard spin‐echo methods. The Pearson correlations were 0.984 for T₂ (～2% relative difference between spin‐echo and double echo steady state estimates) and 0.997 for apparent diffusion coefficient (?1% relative difference between spin‐echo and double echo steady state estimates) for the phantom study and 0.989 for T₂ and 0.987 for apparent diffusion coefficient in regions of interest in the human knee in vivo. High accuracy for simultaneous three‐dimensional T₂ and apparent diffusion coefficient measurements are demonstrated, while also providing morphologic three‐dimensional images without blurring or distortion in reasonable scan times. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Half‐fourier‐acquisition single‐shot turbo spin‐echo (HASTE) MRI of the lung at 3 Tesla using parallel imaging with 32‐receiver channel technology

Purpose

To assess the feasibility of half‐Fourier‐acquisition single‐shot turbo spin‐echo (HASTE) of the lung at 3 Tesla (T) using parallel imaging with a prototype of a 32‐channel torso array coil, and to determine the optimum acceleration factor for the delineation of intrapulmonary anatomy.

Materials and Methods

Nine volunteers were examined on a 32‐channel 3T MRI system using a prototype 32‐channel‐torso‐array‐coil. HASTE‐MRI of the lung was acquired at both, end‐inspiratory and end‐expiratory breathhold with parallel imaging (Generalized autocalibrating partially parallel acquisitions = GRAPPA) using acceleration factors ranging between R = 1 (TE = 42 ms) and R = 6 (TE = 16 ms). The image quality of intrapulmonary anatomy and subjectively perceived noise level was analyzed by two radiologists in consensus. In addition quantitative measurements of the signal‐to‐noise ratio (SNR) of HASTE with different acceleration factors were assessed in phantom measurements.

Results

Using an acceleration factor of R = 4 image blurring was substantially reduced compared with lower acceleration factors resulting in sharp delineation of intrapulmonary structures in expiratory scans. For inspiratory scans an acceleration factor of 2 provided the best image quality. Expiratory scans had a higher subjectively perceived SNR than inspiratory scans.

Conclusion

Using optimized multi‐element coil geometry HASTE‐MRI of the lung is feasible at 3T with acceleration factors up to 4. Compared with nonaccelerated acquisitions, shorter echo times and reduced image blurring are achieved. Expiratory scanning may be favorable to compensate for susceptibility associated signal loss at 3T. J. Magn. Reson. Imaging 2009;30:541–546. © 2009 Wiley‐Liss, Inc.     

Compatible dual‐echo arteriovenography (CODEA) using an echo‐specific K‐space reordering scheme

An improved dual‐echo sequence magentic resonance (MR) imaging technique was developed to simultaneously acquire a time‐of‐flight MR angiogram (MRA) and a blood oxygenation level‐dependent MR venogram (MRV) in a single MR acquisition at 3 T. MRA and MRV require conflicting scan conditions (e.g., excitation RF profile, flip angle, and spatial presaturation pulse) for their optimal image quality. This conflict was not well counterbalanced or reconciled in previous methods reported for simultaneous acquisition of MRA and MRV. In our dual‐echo sequence method, an echo‐specific K‐space reordering scheme was used to uncouple the scan parameter requirements for MRA and MRV. The MRA and MRV vascular contrast was enhanced by maximally separating the K‐space center regions acquired for the MRA and MRV, and by adjusting and applying scan parameters compatible between the MRA and MRV. As a preliminary result, we were able to acquire a simultaneous dual‐echo MRA and MRV with image quality comparable to that of the conventional single‐echo MRA and MRV that were acquired separately at two different sessions. Furthermore, integrated with tilted optimized nonsaturating excitation and multiple overlapping thin‐slab acquisition techniques, our dual‐echo MRA and MRV provided seamless vascular continuity over a large coverage volume of the brain anatomy. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Three‐dimensional biexponential weighted 23Na imaging of the human brain with higher SNR and shorter acquisition time

A new method is presented for acquiring 3D biexponential weighted sodium images of the in vivo human brain with up to three times higher signal‐to‐noise ratio compared with conventional six‐step phase‐cycling triple‐quantum‐filtered imaging. To excite and detect multiple‐quantum coherences, a three‐pulse preparation is used. During the pulse train, two images are obtained. The first image is acquired with ultrashort echo time (0.3 ms) during preparation between the first two pulses to yield a spin‐density‐weighted image. After the last pulse, a single‐quantum‐filtered image is acquired with an echo time of 11 ms that maximizes the resulting signal. The biexponential weighted image is calculated by subtracting the single‐quantum‐filtered image from the spin‐density‐weighted image. The resulting image mainly shows signal from sodium ions with biexponential quadrupolar relaxation behavior. In isotropic environments, the resulting image mainly contains triple‐quantum‐filtered signal. The four‐step phase cycling yields similar signal‐to‐noise ratio in shorter acquisition time compared with six‐step phase‐cycling biexponential weighted imaging. Magn Reson Med 70:754–765, 2013. © 2012 Wiley Periodicals, Inc.     

Investigation and modeling of magnetization transfer effects in two‐dimensional multislice turbo spin echo sequences with low constant or variable flip angles at 3 T

Magnetization transfer effects represent a major source of contrast in multislice turbo spin echo sequences (TSE)/fast spin echo sequences. Generally, low refocusing flip angles have become common in such MRI sequences, especially to mitigate specific absorption rate problems. Since the strength of magnetization transfer effects is related to the radiofrequency power and therefore specific absorption rate applied, magnetization transfer induced signal attenuations are investigated for a variety of TSE sequences with low constant and variable flip angles. Noticeable differences between the sequences have been observed. In particular, fewer signal attenuations are observed for TSE with low flip angles such as hyperecho‐TSE and smooth transitions between pseudo steady states–TSE, leading to contrast that is less dependent on the number of slices. It is shown that the strength of the magnetization transfer‐induced signal attenuations can be understood and described by a physical framework, which is based on the mean square flip angle of a given TSE sequence. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Small‐tip fast recovery imaging using non‐slice‐selective tailored tip‐up pulses and radiofrequency‐spoiling

Small‐tip fast recovery (STFR) imaging is a new steady‐state imaging sequence that is a potential alternative to balanced steady‐state free precession. Under ideal imaging conditions, STFR may provide comparable signal‐to‐noise ratio and image contrast as balanced steady‐state free precession, but without signal variations due to resonance offset. STFR relies on a tailored “tip‐up,” or “fast recovery,” radiofrequency pulse to align the spins with the longitudinal axis after each data readout segment. The design of the tip‐up pulse is based on the acquisition of a separate off‐resonance (B0) map. Unfortunately, the design of fast (a few ms) slice‐ or slab‐selective radiofrequency pulses that accurately tailor the excitation pattern to the local B0 inhomogeneity over the entire imaging volume remains a challenging and unsolved problem. We introduce a novel implementation of STFR imaging based on “non‐slice‐selective” tip‐up pulses, which simplifies the radiofrequency pulse design problem significantly. Out‐of‐slice magnetization pathways are suppressed using radiofrequency‐spoiling. Brain images obtained with this technique show excellent gray/white matter contrast, and point to the possibility of rapid steady‐state T₂/T₁‐weighted imaging with intrinsic suppression of cerebrospinal fluid, through‐plane vessel signal, and off‐resonance artifacts. In the future, we expect STFR imaging to benefit significantly from parallel excitation hardware and high‐order gradient shim systems. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Time‐efficient fast spin echo imaging at 4.7 T with low refocusing angles

An implementation of fast spin echo at 4.7 T designed for versatile and time‐efficient T₂‐weighted imaging of the human brain is presented. Reduced refocusing angles (α < 180°) were employed to overcome specific absorption rate (SAR) constraints and their effects on image quality assessed. Image intensity and tissue contrast variations from heterogeneous RF transmit fields and incidental magnetization transfer effects were investigated at reduced refocusing angles. We found that intraslice signal variations are minimized with refocusing angles near 180°, but apparent gray/white matter contrast is independent of refocusing angle. Incidental magnetization transfer effects from multislice acquisitions were shown to attenuate white matter intensity by 25% and gray matter intensity by 15% at 180°; less than 5% attenuation was seen in all tissues at flip angles below 60°. We present multislice images acquired without excess delay time for SAR mitigation using a variety of protocols. Subsecond half Fourier acquisition single‐shot turbo spin echo (HASTE) images were obtained with a novel variable refocusing angle echo train (20° < α < 58°) and high‐resolution scans with a voxel volume of 0.18 mm³ were acquired in 6.5 min with refocusing angles of 100°. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

A phase‐sensitive method of flip angle mapping

A radiofrequency (RF) excitation scheme is presented in which flip angle is encoded in the phase of the resulting excitation. This excitation is implemented with nonselective hard pulses, and is used to give flip angle maps over three‐dimensional volumes. This phase‐sensitive B1 mapping excitation can be combined with various acquisition methods such as gradient recalled echo (GRE) and echo‐planar (EP) readouts. Imaging time depends primarily on the readout method, and is roughly equivalent to the imaging time of conventional double‐angle techniques for three‐dimensional acquisition. The phase‐sensitive method allows imaging over a much wider range of flip angles than double‐angle methods. Phantom and in vivo results are presented comparing the phase‐sensitive method with the conventional double‐angle method, demonstrating the ability of the phase‐sensitive method to measure a wider range of flip angles than double‐angle methods. Magn Reson Med 60:889–894, 2008. © 2008 Wiley‐Liss, Inc.     

Intuitive design guidelines for fast spin echo imaging with variable flip angle echo trains.

We present a simple and intuitive means for determining the flip angles (FAs) required for smooth transitions between static pseudo steady states (SPSSs) in fast spin echo (FSE) imaging with variable FA (VFA) echo trains. We demonstrate the effectiveness of single and multiple transition pulses to successfully vary refocusing FAs while retaining high signal levels. The graphical interpretation presented here is consistent with previous analytical techniques and permits accurate signal-intensity predictions along the echo train.