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.     

Fast three‐dimensional proton spectroscopic imaging of the human brain at 3 T by combining spectroscopic missing pulse steady‐state free precession and echo planar spectroscopic imaging

The combination of the principles of two fast spectroscopic imaging (SI) methods, spectroscopic missing pulse steady‐state free precession and echo planar SI (EPSI) is described as an approach toward fast 3D SI. This method, termed missing pulse steady‐state free precession echo planar SI, exhibits a considerably reduced minimum total measurement time T_min, allowing a higher temporal resolution, a larger spatial matrix size, and the use of k‐space weighted averaging and phase cycling, while maintaining all advantages of the original spectroscopic missing pulse steady‐state free precession sequence. The minor signal‐to‐noise ratio loss caused by using oscillating read gradients can be compensated by applying k‐space weighted averaging. The missing pulse steady‐state free precession echo planar SI sequence was implemented on a 3 T head scanner, tested on phantoms and applied to healthy volunteers. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

In vivo single scan detection of both iron-labeled cells and breast cancer metastases in the mouse brain using balanced steady-state free precession imaging at 1.5 T

Purpose:

To simultaneously detect iron‐labeled cancer cells and brain tumors in vivo in one scan, the balanced steady‐state free precession (b‐SSFP) imaging sequence was optimized at 1.5 T on mice developing brain metastases subsequent to the injection of micron‐sized iron oxide particle‐labeled human breast cancer cells.

Materials and Methods:

b‐SSFP sequence parameters (repetition time, flip angle, and receiver bandwidth) were varied and the signal‐to‐noise ratio, contrast between the brain and tumors, and the number of detected iron‐labeled cells were evaluated.

Results:

Optimal b‐SSFP images were acquired with a 26 msec repetition time, 35° flip angle, and bandwidth of ±21 kHz. b‐SSFP images were compared with T₂‐weighted 2D fast spin echo (FSE) and 3D spoiled gradient recalled echo (SPGR) images. The mean tumor‐brain contrast‐to‐noise ratio and the ability to detect iron‐labeled cells were the highest in the b‐SSFP images.

Conclusion:

A single b‐SSFP scan can be used to visualize both iron‐labeled cells and brain metastases. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Imaging iron‐loaded mouse glioma tumors with bSSFP at 3 T

The poor prognosis for patients with high‐grade glioma is partly due to the invasion of tumor cells into surrounding brain tissue. The goal of the present work was to develop a mouse model of glioma that included the potential to track cell invasion using MRI by labeling GL261 cells with iron oxide contrast agents prior to intracranial injection. Two types of agents were compared with several labeling schemes to balance between labeling with sufficient iron to curb the dilution effect of cell division while avoiding overwhelming signal loss that could prevent adequate visualization of tumor boundaries. The balanced steady‐state free precession (bSSFP) pulse sequence was evaluated for its suitability for imaging glioma tumors and compared to T₂‐weighted two‐dimensional fast spin echo (FSE) and T₁‐weighted spoiled gradient recalled echo (SPGR) at 3 T in terms of signal‐to‐noise ratio and contrast‐to‐noise ratio efficiencies. Ultimately, a three‐dimensional bSSFP protocol consisting of a set of two images with complementary contrasts was developed, allowing excellent tumor visualization with minimal iron contrast when using pulse repetition time = 6 ms and α = 40°, and extremely high sensitivity to iron when using pulse repetition time = 22 ms and α = 20°. Quantitative histologic analysis validated that the strong signal loss seen in balanced steady state free precession pulse sequence images of iron‐loaded tumors correlated well with the presence of iron. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

3D flow‐independent peripheral vessel wall imaging using T2‐prepared phase‐sensitive inversion‐recovery steady‐state free precession

Purpose:

To develop a 3D flow‐independent peripheral vessel wall imaging method using T₂‐prepared phase‐sensitive inversion‐recovery (T₂PSIR) steady‐state free precession (SSFP).

Materials and Methods:

A 3D T₂‐prepared and nonselective inversion‐recovery SSFP sequence was designed to achieve flow‐independent blood suppression for vessel wall imaging based on T₁ and T₂ properties of the vessel wall and blood. To maximize image contrast and reduce its dependence on the inversion time (TI), phase‐sensitive reconstruction was used to restore the true signal difference between vessel wall and blood. The feasibility of this technique for peripheral artery wall imaging was tested in 13 healthy subjects. Image signal‐to‐noise ratio (SNR), wall/lumen contrast‐to‐noise ratio (CNR), and scan efficiency were compared between this technique and conventional 2D double inversion recovery – turbo spin echo (DIR‐TSE) in eight subjects.

Results:

3D T₂PSIR SSFP provided more efficient data acquisition (32 slices and 64 mm in 4 minutes, 7.5 seconds per slice) than 2D DIR‐TSE (2–3 minutes per slice). SNR of the vessel wall and CNR between vessel wall and lumen were significantly increased as compared to those of DIR‐TSE (P < 0.001). Vessel wall and lumen areas of the two techniques are strongly correlated (intraclass correlation coefficients: 0.975 and 0.937, respectively; P < 0.001 for both). The lumen area of T₂PSIR SSFP is slightly larger than that of DIR‐TSE (P = 0.008). The difference in vessel wall area between the two techniques is not statistically significant.

Conclusion:

T₂PSIR SSFP is a promising technique for peripheral vessel wall imaging. It provides excellent blood signal suppression and vessel wall/lumen contrast. It can cover a 3D volume efficiently and is flow‐ and TI‐independent. J. Magn. Reson. Imaging 2010;32:399–408. © 2010 Wiley‐Liss, Inc.     

Dynamic visualization of arachnoid adhesions in a patient with idiopathic syringomyelia using high‐resolution cine magnetic resonance imaging at 3T

A 39‐year‐old female patient with thoracic syringomyelia underwent routine magnetic resonance imaging (MRI) and 3 T MRI to investigate the value of retrospectively cardiac‐gated cine steady‐state free precession (SSFP) MRI in the preoperative and postoperative diagnosis of arachnoid membranes in the spinal subarachnoid space. Therefore, 3T MRI included sagittal and transverse retrospectively cardiac‐gated cine balanced fast‐field echo (balanced‐FFE) sequences both preoperatively and after microsurgical lysis of arachnoid adhesions and expansive duraplasty. Arachnoid membranes were detected and this result was correlated with intraoperative findings and the results of routine cardiac‐gated phase‐contrast cerebrospinal fluid (CSF) flow MRI. Retrospectively cardiac‐gated cine SSFP MRI enabled imaging of arachnoid membranes with high spatial resolution and sufficient contrast to delineate them from hyperintense CSF preoperatively and postoperatively. The images were largely unaffected by artifacts. Surgery confirmed the presence of arachnoid adhesions in the upper thoracic spine. Not all arachnoid membranes that were seen on cine balanced‐FFE sequences caused significant spinal CSF flow blockages in cardiac‐gated phase‐contrast CSF flow studies. In conclusion, retrospectively cardiac‐gated cine SSFP MRI may become a valuable tool for the preoperative detection of arachnoid adhesions and the postoperative evaluation of microsurgical adhesiolysis in patients with idiopathic syringomyelia. J. Magn. Reson. Imaging 2010. © 2010 Wiley‐Liss, Inc.     

Quantitative mapping of T2 using partial spoiling

Fast quantitative MRI has become an important tool for biochemical characterization of tissue beyond conventional T₁, T₂, and T₂*‐weighted imaging. As a result, steady‐state free precession (SSFP) techniques have attracted increased interest, and several methods have been developed for rapid quantification of relaxation times using steady‐state free precession. In this work, a new and fast approach for T₂ mapping is introduced based on partial RF spoiling of nonbalanced steady‐state free precession. The new T₂ mapping technique is evaluated and optimized from simulations, and in vivo results are presented for human brain at 1.5 T and for human articular cartilage at 3.0 T. The range of T₂ for gray and white matter was from 60 msec (for the corpus callosum) to 100 msec (for cortical gray matter). For cartilage, spatial variation in T₂ was observed between deep (34 msec) and superficial (48 msec) layers, as well as between tibial (33 msec), femoral, (54 msec) and patellar (43 msec) cartilage. Excellent correspondence between T₂ values derived from partially spoiled SSFP scans and the ones found with a reference multicontrast spin‐echo technique is observed, corroborating the accuracy of the new method for proper T₂ mapping. Finally, the feasibility of a fast high‐resolution quantitative partially spoiled SSFP T₂ scan is demonstrated at 7.0 T for human patellar cartilage. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

T2‐weighted 3D fMRI using S2‐SSFP at 7 tesla

In this study, the sensitivity of the S₂‐steady‐state free precession (SSFP) signal for functional MRI at 7 T was investigated. In order to achieve the necessary temporal resolution, a three‐dimensional acquisition scheme with acceleration along two spatial axes was employed. Activation maps based on S₂‐steady‐state free precession data showed similar spatial localization of activation and sensitivity as spin‐echo echo‐planar imaging (SE‐EPI), but data can be acquired with substantially lower power deposition. The functional sensitivity estimated by the average z‐values was not significantly different for SE‐EPI compared to the S₂‐signal but was slightly lower for the S₂‐signal (6.74 ± 0.32 for the TR = 15 ms protocol and 7.51 ± 0.78 for the TR = 27 ms protocol) compared to SE‐EPI (7.49 ± 1.44 and 8.05 ± 1.67) using the same activated voxels, respectively. The relative signal changes in these voxels upon activation were slightly lower for SE‐EPI (2.37% ± 0.18%) compared to the TR = 15 ms S₂‐SSFP protocol (2.75% ± 0.53%) and significantly lower than the TR = 27 ms protocol (5.38% ± 1.28%), in line with simulations results. The large relative signal change for the long TR SSFP protocol can be explained by contributions from multiple coherence pathways and the low intrinsic intensity of the S₂ signal. In conclusion, whole‐brain T₂‐weighted functional MRI with negligible image distortion at 7 T is feasible using the S₂‐SSFP sequence and partially parallel imaging. Magn Reson Med 63:1015–1020, 2010. © 2010 Wiley‐Liss, Inc.     

Improved 3‐Tesla cardiac cine imaging using wideband

Cine balanced steady‐state free precession (SSFP) is the most widely used sequence for assessing cardiac ventricular function at 1.5 T because it provides high signal‐to‐noise ratio efficiency and strong contrast between myocardium and blood. At 3 T, the use of SSFP is limited by susceptibility‐induced off‐resonance, resulting in either banding artifacts or the need to use a short‐sequence pulse repetition time that limits the readout duration and hence the achievable spatial resolution. In this work, we apply wideband SSFP, a variant of SSFP that uses two alternating pulse repetition times to establish a steady state with wider band spacing in its frequency response and overcome the key limitations of SSFP. Prospectively gated cine two‐dimensional imaging with wideband SSFP is evaluated in healthy volunteers and compared to conventional balanced SSFP, using quantitative metrics and qualitative interpretation by experienced clinicians. We demonstrate that by trading off temporal resolution and signal‐to‐noise ratio efficiency, wideband SSFP mitigates banding artifacts and enables imaging with approximately 30% higher spatial resolution compared to conventional SSFP with the same effective band spacing. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

CEST‐FISP: A novel technique for rapid chemical exchange saturation transfer MRI at 7 T

Chemical exchange saturation transfer (CEST) and magnetization transfer techniques provide unique and potentially quantitative contrast mechanisms in multiple MRI applications. However, the in vivo implementation of these techniques has been limited by the relatively slow MRI acquisition techniques, especially on high‐field MRI scanners. A new, rapid CEST‐fast imaging with steady‐state free precession technique was developed to provide sensitive CEST contrast in ～20 sec. In this study at 7 T with in vitro bovine glycogen samples and initial in vivo results in a rat liver, the CEST‐fast imaging with steady‐state free precession technique was shown to provide equivalent CEST sensitivity in comparison to a conventional CEST‐spin echo acquisition with a 50‐fold reduction in acquisition time. The sensitivity of the CEST‐fast imaging with steady‐state free precession technique was also shown to be dependent on k‐space encoding with centric k‐space encoding providing a 30–40% increase in CEST sensitivity relative to linear encoding for 256 or more k‐space lines. Overall, the CEST‐fast imaging with steady‐state free precession acquisition technique provides a rapid and sensitive imaging platform with the potential to provide quantitative CEST and magnetization transfer imaging data. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

3D velocity quantification in the heart: Improvements by 3D PC‐SSFP

Purpose:

To test whether a 3D imaging sequence with phase contrast (PC) velocity encoding based on steady‐state free precession (SSFP) improves 3D velocity quantification in the heart compared to the currently available gradient echo (GE) approach.

Materials and Methods:

The 3D PC‐SSFP sequence with 1D velocity encoding was compared at the mitral valve in 12 healthy subjects with 3D PC‐GE at 1.5T. Velocity measurements, velocity‐to‐noise‐ratio efficiency (VNR_eff), intra‐ and interobserver variability of area and velocity measurements, contrast‐to‐noise‐ratio (CNR), and artifact sensitivity were evaluated in both long‐ and short‐axis orientation.

Results:

Descending aorta mean and peak velocities correlated well (r² = 0.79 and 0.93) between 3D PC‐SSFP and 3D PC‐GE. At the mitral valve, mean velocity correlation was moderate (r² = 0.70 short axis, 0.56 long axis) and peak velocity showed good correlation (r² = 0.94 short axis, 0.81 long axis). In some cases VNR_eff was higher, in others lesser, depending on slab orientation and cardiac phase. Intra‐ and interobserver variability was generally better for 3D PC‐SSFP. CNR improved significantly, especially at end systole. Artifact levels did not increase.

Conclusion:

3D SSFP velocity quantification was successfully tested in the heart. Blood‐myocardium contrast improved significantly, resulting in more reproducible velocity measurements for 3D PC‐SSFP at 1.5T. J. Magn. Reson. Imaging 2009;30:947–955. © 2009 Wiley‐Liss, Inc.     

Fundamentals of balanced steady state free precession MRI

Balanced steady state free precession (balanced SSFP) has become increasingly popular for research and clinical applications, offering a very high signal‐to‐noise ratio and a T₂/T₁‐weighted image contrast. This review article gives an overview on the basic principles of this fast imaging technique as well as possibilities for contrast modification. The first part focuses on the fundamental principles of balanced SSFP signal formation in the transient phase and in the steady state. In the second part, balanced SSFP imaging, contrast, and basic mechanisms for contrast modification are revisited and contemporary clinical applications are discussed. J. Magn. Reson. Imaging 2013;38:2–11. © 2013 Wiley Periodicals, Inc.     

In vivo high‐resolution magnetic resonance skin imaging at 1.5 T and 3 T

As a noninvasive modality, MR is attractive for in vivo skin imaging. Its unique soft tissue contrast makes it an ideal imaging modality to study the skin water content and to resolve the different skin layers. In this work, the challenges of in vivo high‐resolution skin imaging are addressed. Three 3D Cartesian sequences are customized to achieve high‐resolution imaging and their respective performance is evaluated. The balanced steady‐state free precession (bSSFP) and gradient echo (GRE) sequences are fast but can be sensitive to off‐resonance artifacts. The fast large‐angle spin echo (FLASE) sequence provides a sharp depiction of the hypodermis structures but results in more specific absorption rate (SAR). The effect of increasing the field strength is assessed. As compared to 1.5 T, signal‐to‐noise ratio at 3 T slightly increases in the hypodermis and almost doubles in the dermis. The need for fat/water separation is acknowledged and a solution using an interleaved three‐point Dixon method and an iterative reconstruction is shown to be effective. The effects of motion are analyzed and two techniques to prevent motion and correct for it are evaluated. Images with 117 × 117 × 500 μm³ resolution are obtained in imaging times under 6 min. Magn Reson Med, 2010. © 2010 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

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.     

Cartilage morphology at 3.0T: Assessment of three‐dimensional magnetic resonance imaging techniques

Purpose:

To compare six new three‐dimensional (3D) magnetic resonance (MR) methods for evaluating knee cartilage at 3.0T.

Materials and Methods:

We compared: fast‐spin‐echo cube (FSE‐Cube), vastly undersampled isotropic projection reconstruction balanced steady‐state free precession (VIPR‐bSSFP), iterative decomposition of water and fat with echo asymmetry and least‐squares estimation combined with spoiled gradient echo (IDEAL‐SPGR) and gradient echo (IDEAL‐GRASS), multiecho in steady‐state acquisition (MENSA), and coherent oscillatory state acquisition for manipulation of image contrast (COSMIC). Five‐minute sequences were performed twice on 10 healthy volunteers and once on five osteoarthritis (OA) patients. Signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR) were measured from the volunteers. Images of the five volunteers and the five OA patients were ranked on tissue contrast, articular surface clarity, reformat quality, and lesion conspicuity. FSE‐Cube and VIPR‐bSSFP were compared to IDEAL‐SPGR for cartilage volume measurements.

Results:

FSE‐Cube had top rankings for lesion conspicuity, overall SNR, and CNR (P < 0.02). VIPR‐bSSFP had top rankings in tissue contrast and articular surface clarity. VIPR and FSE‐Cube tied for best in reformatting ability. FSE‐Cube and VIPR‐bSSFP compared favorably to IDEAL‐SPGR in accuracy and precision of cartilage volume measurements.

Conclusion:

FSE‐Cube and VIPR‐bSSFP produce high image quality with accurate volume measurement of knee cartilage. J. Magn. Reson. Imaging 2010;32:173–183. © 2010 Wiley‐Liss, Inc.     

Pilot study of improved lesion characterization in breast MRI using a 3D radial balanced SSFP technique with isotropic resolution and efficient fat‐water separation

Purpose

To assess a 3D radial balanced steady‐state free precession (SSFP) technique that provides submillimeter isotropic resolution and inherently registered fat and water image volumes in comparison to conventional T2‐weighted RARE imaging for lesion characterization in breast magnetic resonance imaging (MRI).

Materials and Methods

3D projection SSFP (3DPR‐SSFP) combines a dual half‐echo radial k‐space trajectory with a linear combination fat/water separation technique (linear combination SSFP). A pilot study was performed in 20 patients to assess fat suppression and depiction of lesion morphology using 3DPR‐SSFP. For all patients fat suppression was measured for the 3DPR‐SSFP image volumes and depiction of lesion morphology was compared against corresponding T2‐weighted fast spin echo (FSE) datasets for 15 lesions in 11 patients.

Results

The isotropic 0.63 mm resolution of the 3DPR‐SSFP sequence demonstrated improved depiction of lesion morphology in comparison to FSE. The 3DPR‐SSFP fat and water datasets were available in a 5‐minute scan time while average fat suppression with 3DPR‐SSFP was 71% across all 20 patients.

Conclusion

3DPR‐SSFP has the potential to improve the lesion characterization information available in breast MRI, particularly in comparison to conventional FSE. A larger study is warranted to quantify the effect of 3DPR‐SSFP on specificity. J. Magn. Reson. Imaging 2009;30:135–144. © 2009 Wiley‐Liss, Inc.     

Assessment of fast dynamic imaging and the use of Gd‐EOB‐DTPA for MR‐guided liver interventions

Purpose:

1) To analyze and compare fast dynamic imaging sequences to biopsy suspect liver lesions. 2) To evaluate the additional use of hepatocyte‐specific contrast agent compared to the nonenhanced fast dynamic scans and diagnostic liver imaging.

Materials and Methods:

Image acquisition was performed using a 1T open‐configured scanner suitable for interventional purposes. Transversal postcontrast T1‐weighted (T1w) fat‐saturated 3D high‐resolution examination (THRIVE) images were acquired >20 minutes postintravenous application of gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd‐EOB‐DTPA). A single slice, crossing the level of the lesion, was acquired using intermediate‐weighted steady‐state free‐precession (bTFE), T1w‐gradient echo and spin echo (T1FFE/TSE), T2w‐spin echo (sshTSE) sequences. T1w imaging was acquired prior and after contrast media application. Diagnostic and fast dynamic images were compared based on a 10‐point rating scale. In addition, the liver‐to‐lesion‐contrast ratio was measured.

Results:

A total of 39 malignant lesions with a mean diameter of 13 mm (5–30 mm) in 39 patients were included. Concerning a test of noninferiority, there was no significant difference between rating score values of fast dynamic imaging employing contrast‐enhanced T1FFE‐sequences compared to diagnostic THRIVE (P = 0.001). Calculated liver‐to‐lesion contrast also showed no difference for either imaging sequence (P = 1.0). All other sequences tested showed significant inferiority (P ≤ 0.001).

Conclusion:

T1w Gd‐EOB‐DTPA contrast‐enhanced fast dynamic GRE imaging significantly improves the contrast behavior of malignant liver lesions comparable to diagnostic imaging and is best suited for liver intervention, especially at 1T open magnetic resonance imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Modulated repetition time look‐locker (MORTLL): A method for rapid high resolution three‐dimensional T1 mapping

Purpose

To demonstrate a modification of the Look‐Locker (LL) technique that enables rapid high resolution T1 mapping over the physiologic range of intracranial T1 values, ranging from white matter to cerebrospinal fluid (CSF). This is achieved by use of a three‐dimensional (3D) balanced steady‐state free precession (b‐SSFP) acquisition (for high signal‐to‐noise and resolution) along with variable repetition time to allow effective full recovery of longitudinal magnetization.

Materials and Methods

Two modifications to the Look‐Locker technique were made to realize high resolution imaging in a clinically reasonable scan time. The 3D b‐SSFP acquisition after an initial inversion pulse was followed by a variable repetition time. This technique makes it possible to image a volume of thin contiguous slices with high resolution and accuracy using a simple fitting procedure and is particularly useful for imaging long T1 species such as CSF. The total scan time is directly proportional to the number of slices to be acquired. The scan time was reduced by almost half when the repetition time was modified using a predesigned smooth function. Phantoms and volunteers were imaged at different resolutions on a 3 Tesla scanner. Results were compared with other accepted techniques.

Results

T1 values in the brain corresponded well with full repetition time imaging as well as inversion recovery spin echo imaging. T1 values for white matter, gray matter, and CSF were measured to be 755 ± 10 ms, 1202 ± 9 ms, and 4482 ± 71 ms, respectively. Scan times were reduced by approximately half over full repetition time measurements.

Conclusion

High resolution T1 maps can be obtained rapidly and with a relatively simple postprocessing method. The technique is particularly well suited for long T1 species. For example, changes in the composition of proteins in CSF are linked to various pathologies. The T1 values showed excellent agreement with values obtained from inversion recovery spin‐echo imaging. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.     

Fast diffusion‐weighted steady state free precession imaging of in vivo knee cartilage

Quantification of molecular diffusion with steady state free precession (SSFP) is complicated by the fact that diffusion effects accumulate over several repetition times (TR) leading to complex signal dependencies on transverse and longitudinal magnetization paths. This issue is commonly addressed by setting TR > T₂, yielding strong attenuation of all higher modes, except of the shortest ones. As a result, signal attenuation from diffusion becomes T₂ independent but signal‐to‐noise ratio (SNR) and sequence efficiency are remarkably poor. In this work, we present a new approach for fast in vivo steady state free precession diffusion‐weighted imaging of cartilage with TR << T₂ offering a considerable increase in signal‐to‐noise ratio and sequence efficiency. At a first glance, prominent coupling between magnetization paths seems to complicate quantification issues in this limit, however, it is observed that diffusion effects become rather T₂(ΔD ～ 1/10 ΔT₂) but not T₁ independent (ΔD ～ 1/2 ΔT₁) for low flip angles α ～ 10 ? 15°. As a result, fast high‐resolution (0.35 × 0.35 ? 0.50 × 0.50 mm² in‐plane resolution) quantitative diffusion‐weighted imaging of human articular cartilage is demonstrated at 3.0 T in a clinical setup using estimated T₁ and T₂ or a combination of measured T₁ and estimated T₂ values. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

Cine cardiac imaging using black‐blood steady‐state free precession (BB‐SSFP) at 3T

Purpose

To propose a new black‐blood (BB) pulse sequence that provides BB cine cardiac images with high blood‐myocardium contrast. The proposed technique is based on the conventional steady‐state free precession (SSFP) sequence.

Materials and Methods

Numerical simulations of the Bloch equation were conducted to compare the resulting signal‐to‐noise ratio (SNR) to that of conventional BB imaging, including the effects of changing the imaging flip angle and heart rates. Simulation results were verified using a gel phantom experiment and five normal volunteers were scanned using the proposed technique.

Results

The new sequence showed higher SNR and contrast‐to‐noise ratio (CNR) (≈100%) compared to the conventional BB imaging. Also, the borders of the left ventricle (LV) and right ventricle (RV) appear more distinguishable than the conventional SSFP. We were also able to cover about 80% of the cardiac cycle with short breath‐hold time (≈10 cardiac cycles) and with reasonable SNR and CNR.

Conclusion

Based on an SSFP conventional sequence, the new sequence provides BB cines that cover most of the cardiac cycle and with higher SNR and CNR than the conventional BB sequences. J. Magn. Reson. Imaging 2009;30:94–103. © 2009 Wiley‐Liss, Inc.