Ultrafast fetal MR images of sacrococcygeal teratoma: a case report.

A case of sacrococcygeal teratoma diagnosed at 31 weeks' gestation by fetal MR imaging is presented. For fetal MR imaging, an ultrafast imaging sequence, Half-Fourier acquisition single shot turbo spin echo (HASTE) was employed. The HASTE sequence enabled us to obtain high resolution images in a short time and was particularly useful in enabling better contrast between the cystic and solid components of the tumor.     

Fundamental study of the fat-suppressed three-dimensional coherent oscillatory state acquisition for the manipulation of image contrast (3D-COSMIC) sequence in the knee joint cartilage

Fat-suppressed three-dimensional coherent oscillatory state acquisition for the manipulation of image contrast (3D-COSMIC) is a sequence that is based on fast imaging employing steady state acquisition (FIESTA) of balanced steady-state free precession (balanced SSFP). Since the data acquisition of steady-state transition is filled up with the center of k-space, improvement in the contrast of the cartilage, which is a low T?/T? value domain, is expected. This time we report on the usability in applying the above sequence to cartilage imaging of the knee joint and comparing and examining this sequence with the sequence in the past from the viewpoints of the contrast and scan time. As a result, compared with fat-suppressed three-dimensional spoiled gradient echo (3D-SPGR), the contrast of marrow and synovial fluid was equivalent to that of the cartilage, and imaging time was shorter than half of that with the cartilage. Compared with a fat-suppressed two-dimensional proton density weighted image (2D-PDWI), the contrast of the cartilage and synovial fluid was significantly improved, and spatial resolution was also excellent. As a short imaging time and a high resolution image pick-up are possible for fat-suppressed 3D-COSMIC, and it can describe minute damage of the cartilage since it depicts synovial fluid as high-level signals, I think this technique is useful.     

Double average parallel steady-state free precession imaging: optimized eddy current and transient oscillation compensation.

Balanced steady-state free precession (SSFP) imaging is sensitive to off-resonance effects, which can lead to considerable artifacts during a transient phase following magnetization preparation or steady-state interruption. In addition, nonlinear k-space encoding is required if contrast-relevant k-space regions need to be acquired at specific delays following magnetization preparation or for transient artifact reduction in cardiac-gated k-space segmented CINE imaging. Such trajectories are problematic for balanced SSFP imaging due to nonconstant eddy current effects and resulting disruption of the steady state.In this work, a novel acquisition strategy for balanced SSFP imaging is presented that utilizes scan time reduction by parallel imaging for optimized "double average" eddy current compensation and artifact reduction during the transient phase following steady-state storage and magnetization preparation. Double average parallel SSFP imaging was applied to k-space segmented CINE SSFP tagging as well as nongated centrically encoded SSFP imaging. Phantom and human studies exhibit substantial reduction in steady-state storage and eddy current artifacts while maintaining spatial resolution, signal-to-noise ratio, and similar total scan time of a standard SSFP acquisition. The proposed technique can easily be extended to other acquisition schemes that would benefit from nonlinear reordering schemes and/or rely on interruption of the balanced SSFP steady state.     

On the transient phase of balanced SSFP sequences.

The signal intensity of balanced steady-state free precession (SSFP) imaging is a function of the proton density, T(1), T(2), flip angle (alpha), and repetition time (TR). The steady-state signal intensity that is established after about 5*T(1)/TR can be described analytically. The transient phase or the approach of the echo amplitudes to the steady state is an exponential decay from the initial amplitude after the first excitation pulse to the steady-state signal. An analytical expression of the decay rate of this transient phase is presented that is based on a simple analysis derived from the Bloch equations. The decay rate is a weighted average of the T(1) and T(2) relaxation times, where the weighting is determined by the flip angle of the excitation pulses. Thus, balanced SSFP imaging during the transient phase can provide various contrasts depending on the flip angle and the number of excitation pulses applied before the acquisition of the central k-space line. In addition, transient imaging of hyperpolarized nuclei, such as (3)He, (129)Xe, or (13)C, can be optimized according to their T(1) and T(2) relaxation times.     

Localization by nonlinear phase preparation and k-space trajectory design

A technique is described to localize MR signals from a target volume using nonlinear pulsed magnetic fields and spatial encoding trajectories designed using local k-space theory. The concept of local k-space is outlined theoretically, and this principle is applied to simulated phantom and cardiac MRI data in the presence of surface and quadrupolar gradient coil phase modulation. Phantom and in vivo human brain images are obtained using a custom, high-performance quadrupolar gradient coil integrated with a whole-body 3-T MRI system to demonstrate target localization using three-dimensional T 2*-weighted spoiled gradient echo, two-dimensional segmented, multiple gradient encoded spin echo, and three-dimensional balanced steady-state free precession acquisitions. This method may provide a practical alternative to selective radiofrequency excitation at ultra-high-field, particularly for steady-state applications where repetition time (TR) must be minimized and when the amount of energy deposited in human tissues is prohibitive. There are several limitations to the approach including the spatial variation in resolution, high frequency aliasing artifacts, and spatial variation in echo times and contrast.     

MR angiography using steady-state free precession.

Contrast-enhanced MR angiography (CE-MRA) using steady-state free precession (SSFP) pulse sequences is described. Using SSFP, vascular structures can be visualized with high signal-to-noise ratio (SNR) at a substantial (delay) time after the initial arterial pass of contrast media. The peak blood SSFP signal was diminished by <20% 30 min after the initial administration of 0.2 mmol/kg of Gd-chelate. The proposed method allows a second opportunity to study arterial or venous structures with high image SNR and high spatial resolution. A mask subtraction scheme using spin echo SSFP-S(-) acquisition is also described to reduce stationary background signal from the delayed SSFP angiography images.     

ACUT2E TSE-SSFP: a hybrid method for T2-weighted imaging of edema in the heart.

ACUT(2)E TSE-SSFP is a hybrid between steady state free precession (SSFP) and turbo spin echo (TSE) for bright-blood T2-weighted imaging with signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) similar to dark-blood TSE. TSE-SSFP uses a segmented SSFP readout during diastole with 180 degrees pulses following a 90 degrees preparation. The 180 degrees refocusing pulses make TSE-SSFP similar to TSE but TSE-SSFP uses gradient moment nulling, whereas TSE uses gradient crushing. TSE-SSFP produced T2-weighted images with minimal T1 weighting. TSE-SSFP and TSE had similar SNR (155.9 +/- 6.0 vs 160.9 +/- 7.0; P = NS) for acute myocardial infarction (MI) and twice the SNR of T2-prepared SSFP (73.1 +/- 3.4, P < 0.001). TSE-SSFP and TSE had approximately double the CNR of T2-prepared SSFP for differentiating acute MI from normal myocardium. Imperfect blood suppression, present in all animals on some TSE images, was a problem eliminated by TSE-SSFP and T2-prepared SSFP.     

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.     

FADE--a new fast imaging sequence

A series of rapid, equally spaced rf pulses of constant amplitude produces two distinct components of transverse magnetization. FADE (fast acquisition double echo) is a new Fourier steady-state free precession (SSFP) imaging sequence which images both components separately in each interpulse interval. The first component gives more signal than the second but lacks contrast while the second is strongly T2 weighted.     

Fast breath-hold T2-weighted MRI of the kidney by means of half-Fourier single-shot turbo spin echo: comparison with high resolution turbo spin echo sequence

PURPOSE: The value of the fast half-Fourier single-shot turbo spin echo (HASTE) sequence in T2-weighted MRI of the kidney was evaluated as a substitute for the conventional turbo spin echo (TSE) sequence. METHOD: Forty-five patients with suspected abnormalities of the kidney underwent MRI with a 1.5 T system. Breath-hold HASTE and respiratory-triggered TSE sequences were performed. Qualitative and quantitative analyses were performed for comparison of these sequences. RESULTS: The signal-to-noise ratio (SNR) with HASTE was higher than that with TSE. The lesion-to-kidney contrast-to-noise ratio for solid masses with HASTE was almost equal to that with TSE. For cystic masses, the CNR with HASTE was significantly higher than that with TSE (p < 0.05). Respiratory and chemical shift artifacts were significantly smaller on HASTE than on TSE (p < 0.01). However, the blurring artifact was higher on HASTE than on TSE (p = 0.01). CONCLUSION: The HASTE sequence generates high contrast images and is free of motion and chemical shift artifacts, with much better time efficacy. The sequence provides comparable diagnostic information to TSE sequences.     

Fast magnetic resonance imaging in steady-state precession (true FISP) in the prenatal diagnosis of a congenital brain teratoma

Teratomas are the most common congenital intracranial tumor. Although fetal magnetic resonance (MR) imaging is becoming more popular for prenatal diagnosis, only 2 cases of congenital intracranial teratoma have been reported, and these cases relied on half-Fourier single-shot turbo spin echo (HASTE) imaging. We report the first known case of congenital intracranial teratoma diagnosed by means of a fast imaging in steady-state precession (true FISP) MR sequence. True FISP can be obtained in almost 20 seconds and provides superior contrast resolution compared with HASTE.     

Resolution enhancement in lung 1H imaging using parallel imaging methods.

Resolution in (1)H lung imaging is limited mainly by the acquisition time. Today, half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences, with short echo time (TE) and short interecho spacing (T(inter)) have found increased use in lung imaging. In this study, a HASTE sequence was used in combination with a partially parallel acquisition (PPA) strategy to increase the spatial resolution in single-shot (1)H lung imaging. To investigate the benefits of using a combination of single-shot sequences and PPA, five healthy volunteers were examined. Compared to conventional imaging methods, substantially increased resolution is obtained using the PPA approach. Representative in vivo (1)H lung images acquired with a HASTE sequence in combination with the generalized autocalibrating partially parallel acquisition (GRAPPA) method, up to an acceleration factor of three, are presented.     

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

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

Ultrafast MR imaging of the pelvis.

MR gradient systems with higher slew rates and gradient amplitude enable certain forms of imaging that are not practical with older gradient systems. These newer pulse sequences include single shot half-Fourier T2-weighted images and echo planar imaging. More important in MR imaging of the pelvis, these gradient systems benefit more conventional imaging methods such as gadolinium-enhanced 3D MR angiography, dynamic gradient echo contrast-enhanced images, and T2-weighted fast spin echo images, by shortening echo times. For most MR imaging of the pelvis, spatial resolution is paramount, and therefore sequences such as half-Fourier acquisition Turbo spin echo (HASTE) and 3D gadolinium-enhanced dynamic imaging play a less important role than in the upper abdomen. The potential of these techniques for diffusion or perfusion studies in the pelvis has not been explored.     

Hepatic T2-weighted MRI: A prospective comparison of sequences,including breath-hold,half-Fourier turbo spin echo (HASTE)

The purpose of this study was to quantitatively compare the hepatic contrast characteristics of conventional spin-echo (CSE) and fast spin-echo (FSE) sequences with breath-hold T2-weighted images acquired with half-Fourier turbo spin echo (HASTE). Forty-five patients were examined with a phased-array surface coil. Nineteen patients had focal hepatic lesions, including eight malignant tumors, 10 cavernous hemangiomas, and one hepatic adenoma. Twenty-six patients had no focal hepatic lesions. T2-weighted images with comparable TE were acquired with CSE, FSE, and HASTE pulse sequences. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) for liver, spleen, and lesions were measured. FSE demonstrated significantly better quantitative performance than CSE for liver-spleen CNR (P = .0084). No statistically significant difference was demonstrated between FSE and CSE for liver or spleen SNR. FSE demonstrated clear scan time and resolution advantages over CSE. HASTE performed significantly poorer than CSE and FSE for liver-spleen CNR (P < .0001), liver SNR (P = .0002 for CSE and P < .0001 for FSE), and spleen SNR (P < .0001). Optimized FSE images with a short echo train length performed comparably to CSE images of equivalent TE. Liver-lesion CNR was suppressed on HASTE images, suggesting that long echo train length FSE sequences could diminish solid lesion detection compared to CSE and short echo train length FSE.     

MRI of the female pelvis at 3T compared to 1.5T: evaluation on high-resolution T2-weighted and HASTE images

Purpose

To evaluate the feasibility of MRI of the female pelvis using high‐resolution T2‐weighted imaging (T2WI) and the half‐Fourier acquisition single‐shot turbo spin‐echo (HASTE) technique at 3 Tesla (T) compared to 1.5T, while focusing on the uterine body and cervical anatomy.

Materials and Methods

A total of 19 healthy women underwent pelvic MR scans on 3T and 1.5T scanners. Axial and sagittal T2W (voxel size of 0.6 × 0.8 × 2 mm) and sagittal HASTE images were obtained. The images were evaluated qualitatively for overall image quality, contrast in the uterine zonal appearance and cervical structure, image inhomogeneity, and artifacts. A quantitative evaluation was performed regarding zonal contrast and image inhomogeneity.

Results

On T2WI, the image contrast in the uterine cervix and vagina were significantly higher at 3T than at 1.5T, although there was no significant difference in the overall image quality or contrast in the uterine zonal appearance. Image inhomogeneity was more prominent at 3T, and motion artifact was more severe at 1.5T.

Conclusion

Our results suggest that MRI of the female pelvis at 3T may potentially provide excellent images of the uterine cervix on high‐resolution T2WI. New techniques to reduce inhomogeneity are thus called for. J. Magn. Reson. Imaging 2007;25:527–534. © 2007 Wiley‐Liss, Inc.     

K-space sampling strategies

The k-space algorithm offers a comprehensive way for classification and understanding of the imaging properties of all commonly used MR sequences. This presentation describes the basic concepts of k-space and its most relevant properties for MR imaging. The ramifications of k-space sampling is discussed for the most commonly used groups of MR sequences including gradient-echo techniques, echo-planar imaging, spin echo, and rapid acquisition relation enhanced imaging (e. g., turbo spin echo, fast spin echo). In addition, the basic problems and properties of sequences based on non-rectilinear k-space sampling, such as spiral imaging, are discussed. Their artifact behavior is significantly different from rectilinear scans, which project all imperfections along the phase-encoding directions, whereas the artifact produced by spirals are more complex and not always easily recognizable as such. An understanding of the k-space sampling offers important insight into the basic properties of a given sequence regarding signal-to-noise ratio, image distortion, resolution and contrast. It is demonstrated that the ultimate limitation in imaging speed is given by the loss of signal-to-noise ratio inherent to faster data sampling.     

MR ventilation-perfusion imaging of human lung using oxygen-enhanced and arterial spin labeling techniques.

Magnetic resonance ventilation-perfusion (V/Q) imaging has been demonstrated using oxygen and arterial spin labeling techniques. Inhaled oxygen is used as a paramagnetic contrast agent in ventilation imaging using a multiple inversion recovery (MIR) approach. Pulmonary perfusion imaging is conducted using a flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER) technique. A half Fourier single-short turbo spin echo (HASTE) sequence is used for data acquisition in both techniques. V/Q imaging was performed in ten of the twenty volunteers, while either ventilation or perfusion was imaged in the other ten. This V/Q imaging scheme is completely noninvasive, does not involve ionized radiation, and shows promising potential for clinical use in the diagnosis of lung diseases such as pulmonary embolism.     

Magnetic resonance imaging at 3.0 tesla detects more lesions in acute optic neuritis than at 1.5 tesla

OBJECTIVE: We sought to assess whether magnetic resonance imaging (MRI) at 3.0 T detects more brain lesions in acute optic neuritis (ON) than MRI at 1.5 T. MATERIALS AND METHODS: Twenty-eight patients with acute ON were scanned at both field-strengths using fast-fluid-attenuated inversion recovery (FLAIR), proton density and T2-weighted turbo spin echo, and T1-weighted spin echo after contrast. In addition, magnetization-prepared rapid acquisition gradient echo (MPRAGE) was obtained after contrast at 3.0 T. Lesion number and volumes were assessed by an observer blind to patient identity and field strength. RESULTS: Scans at 3.0 T showed a significantly increase in number of lesions detected on FLAIR images (P = 0.002) relative to scanning at 1.5 T. MPRAGE proved to be suitable for detecting enhancing lesions in ON. CONCLUSION: The MRI protocol at 3.0 T was more sensitive to hyperintense brain lesions in ON than the standard MRI protocol at 1.5 T.