Breathheld autocalibrated phase‐contrast imaging

Purpose:

To compare generalized autocalibrating partially parallel acquisitions (GRAPPA), modified sensitivity encoding (mSENSE), and SENSE in phase‐contrast magnetic resonance imaging (PC‐MRI) applications.

Materials and Methods:

Aliasing of the torso can occur in PC‐MRI applications. If the data are further undersampled for parallel imaging, SENSE can be problematic in correctly unaliasing signals due to coil sensitivity maps that do not match that of the aliased volume. Here, a method for estimating coil sensitivities in flow applications is described. Normal volunteers (n = 5) were scanned on a 1.5 T MRI scanner and underwent PC‐MRI scans using GRAPPA, mSENSE, SENSE, and conventional PC‐MRI acquisitions. Peak velocity and flow through the aorta and pulmonary artery were evaluated.

Results:

Bland–Altman statistics for flow in the aorta and pulmonary artery acquired with mSENSE and GRAPPA methods (R = 2 and R = 3 cases) have comparable mean differences to flow acquired with conventional PC‐MRI. GRAPPA and mSENSE PC‐MRI have more robust measurements than SENSE when there is aliasing artifact caused by insufficient coil sensitivity maps. For peak velocity, there are no considerable differences among the mSENSE, GRAPPA, and SENSE reconstructions and are comparable to conventional PC‐MRI.

Conclusion:

Flow measurements of images reconstructed with autocalibration techniques have comparable agreement with conventional PC‐MRI and provide robust measurements in the presence of wraparound. J. Magn. Reson. Imaging 2010;31:1004–1014. ©2010 Wiley‐Liss, Inc.     

Effects of MRI scan acceleration on brain volume measurement consistency

Purpose:

To evaluate the effects of recent advances in magnetic resonance imaging (MRI) radiofrequency (RF) coil and parallel imaging technology on brain volume measurement consistency.

Materials and Methods:

In all, 103 whole‐brain MRI volumes were acquired at a clinical 3T MRI, equipped with a 12‐ and 32‐channel head coil, using the T1‐weighted protocol as employed in the Alzheimer's Disease Neuroimaging Initiative study with parallel imaging accelerations ranging from 1 to 5. An experienced reader performed qualitative ratings of the images. For quantitative analysis, differences in composite width (CW, a measure of image similarity) and boundary shift integral (BSI, a measure of whole‐brain atrophy) were calculated.

Results:

Intra‐ and intersession comparisons of CW and BSI measures from scans with equal acceleration demonstrated excellent scan–rescan accuracy, even at the highest acceleration applied. Pairs‐of‐scans acquired with different accelerations exhibited poor scan–rescan consistency only when differences in the acceleration factor were maximized. A change in the coil hardware between compared scans was found to bias the BSI measure.

Conclusion:

The most important findings are that the accelerated acquisitions appear to be compatible with the assessment of high‐quality quantitative information and that for highest scan–rescan accuracy in serial scans the acquisition protocol should be kept as consistent as possible over time. J. Magn. Reson. Imaging 2012;36:1234–1240. ©2012 Wiley Periodicals, Inc.     

Four-dimensional flow-sensitive MRI of the thoracic aorta: 12- versus 32-channel coil arrays

Purpose:

To evaluate the performance of four‐dimensional (4D) flow‐sensitive MRI in the thoracic aorta using 12‐ and 32‐channel coils and parallel imaging.

Materials and Methods:

4D flow‐sensitive MRI was performed in the thoracic aorta of 11 healthy volunteers at 3 Tesla (T) using different coils and parallel imaging (GRAPPA) accelerations (R): (i) 12‐channel coil, R = 2; (ii) 12‐channel coil, R = 3; (iii) 32‐channel coil, R = 3. The quantitative analysis included SNR, residual velocity divergence and length and curvature of traces (streamlines and pathlines) as used for 3D flow visualization. In addition, semi‐quantitative image grading was performed to assess quality of phase‐contrast angiography and 3D flow visualization.

Results:

Parallel imaging with an acceleration factor R = 3 allowed to save 19.5 ± 5% measurement time compared with R = 2 (14.2 ± 2.4 min). Acquisition using 12 channels with R = 2 and 32 channels with R = 3 produced data with significantly (P < 0.05) higher quality compared with 12 channels and R = 3. There was no significant difference between 12 channels with R = 2 and 32 channels with R = 3 but for the depiction of supra‐aortic branches where the 32‐channel coil proved superior.

Conclusion:

Using 32‐channel coils is beneficial for 4D flow‐sensitive MRI of the thoracic aorta and can allow for a reduction of total scan time while maintaining overall image quality. J. Magn. Reson. Imaging 2012;35:190‐195. © 2011 Wiley Periodicals, 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.     

High‐resolution spiral imaging on a whole‐body 7T scanner with minimized image blurring

High‐resolution (～0.22 mm) images are preferably acquired on whole‐body 7T scanners to visualize minianatomic structures in human brain. They usually need long acquisition time (～12 min) in three‐dimensional scans, even with both parallel imaging and partial Fourier samplings. The combined use of both fast imaging techniques, however, leads to occasionally visible undersampling artifacts. Spiral imaging has an advantage in acquisition efficiency over rectangular sampling, but its implementations are limited due to image blurring caused by a strong off‐resonance effect at 7T. This study proposes a solution for minimizing image blurring while keeping spiral efficient. Image blurring at 7T was, first, quantitatively investigated using computer simulations and point‐spread functions. A combined use of multishot spirals and ultrashort echo time acquisitions was then employed to minimize off‐resonance‐induced image blurring. Experiments on phantoms and healthy subjects were performed on a whole‐body 7T scanner to show the performance of the proposed method. The three‐dimensional brain images of human subjects were obtained at echo time = 1.18 ms, resolution = 0.22mm (field of view = 220mm, matrix size = 1024), and in‐plane spiral shots = 128, using a home‐developed ultrashort echo time sequence (acquisition‐weighted stack of spirals). The total acquisition time for 60 partitions at pulse repetition time = 100 ms was 12.8 min without use of parallel imaging and partial Fourier sampling. The blurring in these spiral images was minimized to a level comparable to that in gradient‐echo images with rectangular acquisitions, while the spiral acquisition efficiency was maintained at eight. These images showed that spiral imaging at 7T was feasible. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Custom‐fitted 16‐channel bilateral breast coil for bidirectional parallel imaging

A 16‐channel receive‐only, closely fitted array coil is described and tested in vivo for bilateral breast imaging at 3 T. The primary purpose of this coil is to provide high signal‐to‐noise ratio and parallel imaging acceleration in two directions for breast MRI. Circular coil elements (7.5‐cm diameter) were placed on a closed “cup‐shaped” platform, and nearest neighbor coils were decoupled through geometric overlap. Comparisons were made between the 16‐channel custom coil and a commercially available 8‐channel coil. SENSitivity Encoding (SENSE) parallel imaging noise amplification (g‐factor) was evaluated in phantom scans. In healthy volunteers, we compared signal‐to‐noise ratio, parallel imaging in one and two directions, Autocalibrating Reconstruction for Cartesian sampling (ARC) g‐factor, and high spatial resolution imaging. When compared with a commercially available 8‐channel coil, the 16‐channel custom coil shows 3.6× higher mean signal‐to‐noise ratio in the breast and higher quality accelerated images. In patients, the 16‐channel custom coil has facilitated high‐quality, high‐resolution images with bidirectional acceleration of R = 6.3. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

32‐channel phased‐array receive with asymmetric birdcage transmit coil for hyperpolarized xenon‐129 lung imaging

Hyperpolarized xenon‐129 has the potential to become a noninvasive contrast agent for lung MRI. In addition to its utility for imaging of ventilated airspaces, the property of xenon to dissolve in lung tissue and blood upon inhalation provides the opportunity to study gas exchange. Implementations of imaging protocols for obtaining regional parameters that exploit the dissolved phase are limited by the available signal‐to‐noise ratio, excitation homogeneity, and length of acquisition times. To address these challenges, a 32‐channel receive‐array coil complemented by an asymmetric birdcage transmit coil tuned to the hyperpolarized xenon‐129 resonance at 3 T was developed. First results of spin‐density imaging in healthy subjects and subjects with obstructive lung disease demonstrated the improvements in image quality by high‐resolution ventilation images with high signal‐to‐noise ratio. Parallel imaging performance of the phased‐array coil was demonstrated by acceleration factors up to three in 2D acquisitions and up to six in 3D acquisitions. Transmit‐field maps showed a regional variation of only 8% across the whole lung. The newly developed phased‐array receive coil with the birdcage transmit coil will lead to an improvement in existing imaging protocols, but moreover enable the development of new, functional lung imaging protocols based on the improvements in excitation homogeneity, signal‐to‐noise ratio, and acquisition speed. Magn Reson Med 70:576–583, 2013. © 2012 Wiley Periodicals, Inc.     

Blipped‐controlled aliasing in parallel imaging for simultaneous multislice echo planar imaging with reduced g‐factor penalty

Simultaneous multislice Echo Planar Imaging (EPI) acquisition using parallel imaging can decrease the acquisition time for diffusion imaging and allow full‐brain, high‐resolution functional MRI (fMRI) acquisitions at a reduced repetition time (TR). However, the unaliasing of simultaneously acquired, closely spaced slices can be difficult, leading to a high g‐factor penalty. We introduce a method to create interslice image shifts in the phase encoding direction to increase the distance between aliasing pixels. The shift between the slices is induced using sign‐ and amplitude‐modulated slice‐select gradient blips simultaneous with the EPI phase encoding blips. This achieves the desired shifts but avoids an undesired “tilted voxel” blurring artifact associated with previous methods. We validate the method in 3× slice‐accelerated spin‐echo and gradient‐echo EPI at 3 T and 7 T using 32‐channel radio frequency (RF) coil brain arrays. The Monte‐Carlo simulated average g‐factor penalty of the 3‐fold slice‐accelerated acquisition with interslice shifts is <1% at 3 T (compared with 32% without slice shift). Combining 3× slice acceleration with 2× inplane acceleration, the g‐factor penalty becomes 19% at 3 T and 10% at 7 T (compared with 41% and 23% without slice shift). We demonstrate the potential of the method for accelerating diffusion imaging by comparing the fiber orientation uncertainty, where the 3‐fold faster acquisition showed no noticeable degradation. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

Self-calibrated multiple-echo acquisition with radial trajectories using the conjugate gradient method (SMART-CG)

Purpose:

To remove phase inconsistencies between multiple echoes, an algorithm using a radial acquisition to provide inherent phase and magnitude information for self correction was developed. The information also allows simultaneous support for parallel imaging for multiple coil acquisitions.

Materials and Methods:

Without a separate field map acquisition, a phase estimate from each echo in multiple echo train was generated. When using a multiple channel coil, magnitude and phase estimates from each echo provide in vivo coil sensitivities. An algorithm based on the conjugate gradient method uses these estimates to simultaneously remove phase inconsistencies between echoes, and in the case of multiple coil acquisition, simultaneously provides parallel imaging benefits. The algorithm is demonstrated on single channel, multiple channel, and undersampled data.

Results:

Substantial image quality improvements were demonstrated. Signal dropouts were completely removed and undersampling artifacts were well suppressed.

Conclusion:

The suggested algorithm is able to remove phase cancellation and undersampling artifacts simultaneously and to improve image quality of multiecho radial imaging, the important technique for fast three‐dimensional MRI data acquisition. J. Magn. Reson. Imaging 2011;33:980–987. © 2011 Wiley‐Liss, Inc.     

Rapid in vivo musculoskeletal MR with parallel imaging at 7T

The purpose of this work was to implement autocalibrating GRAPPA-based parallel imaging (PI) for in vivo high-resolution (HR) MRI of cartilage and trabecular bone micro-architecture at 7T and to evaluate its performance based on comparison of MR-derived morphology metrics between accelerated and conventional images and comparison of geometry factor measures between 3T and 7T. Using an eight channel coil array for trabecular MRI at the ankle, a higher maximum feasible acceleration (R) = 6 and lower geometry factor values than that at 3T were observed. The advantages of two-dimensional acceleration were also demonstrated. In knee cartilage and bone acquisitions, feasibility of PI with a dual-channel quadrature coil was investigated. Robust quantification of bone and cartilage metrics could be derived from accelerated ankle and knee acquisitions. PI can enhance the clinical feasibility of in vivo bone and cartilage HR-MRI for osteoporosis and osteoarthritis at 7T.     

Fast dixon‐based multisequence and multiplanar MRI for whole‐body detection of cancer metastases

Purpose

To develop and demonstrate the feasibility of multisequence and multiplanar MRI for whole‐body cancer detection.

Materials and Methods

Two fast Dixon‐based sequences and a diffusion‐weighted sequence were used on a commercially available 1.5 T scanner for whole‐body cancer detection. The study enrolled 19 breast cancer patients with known metastases and in multistations acquired whole‐body axial diffusion‐weighted, coronal T2‐weighted, axial/sagittal pre‐ and postcontrast T1‐weighted, as well as triphasic abdomen images. Three radiologists subjectively scored Dixon images of each series for overall image quality and fat suppression uniformity on a 4‐point scale (1 = poor, 2 = fair, 3 = good, and 4 = excellent).

Results

Eighteen of the 19 patients completed the whole‐body MRI successfully. The mean acquisition time and overall patient table time were 46 ± 3 and 69 ± 5 minutes, respectively. The average radiologists' scores for overall image quality and fat suppression uniformity were both 3.4 ± 0.5. The image quality was consistent between patients and all completed whole‐body examinations were diagnostically adequate.

Conclusion

Whole‐body MRI offering essentially all the most optimal tumor‐imaging sequences in a typical 1‐hour time slot can potentially become an appealing “one‐stop‐shop” for whole‐body cancer imaging. J. Magn. Reson. Imaging 2009;29:1154–1162. © 2009 Wiley‐Liss, Inc.     

Imaging of the wrist at 1.5 Tesla using isotropic three-dimensional fast spin echo cube

Purpose:

To compare three‐dimensional fast spin echo Cube (3D‐FSE‐Cube) with conventional 2D‐FSE in MR imaging of the wrist.

Materials and Methods:

The wrists of 10 volunteers were imaged in a 1.5 Tesla MRI scanner using an eight‐channel wrist coil. The 3D‐FSE‐Cube images were acquired in the coronal plane with 0.5‐mm isotropic resolution. The 2D‐FSE images were acquired in both coronal and axial planes for comparison. An ROI was placed in fluid, cartilage, and muscle for SNR analysis. Comparable coronal and axial images were selected for each sequence, and paired images were randomized and graded for blurring, artifact, anatomic details, and overall image quality by three blinded musculoskeletal radiologists.

Results:

SNR of fluid, cartilage and muscle at prescribed locations were higher using 3D‐FSE‐Cube, without reaching statistical significance. Fluid–cartilage CNR was also higher with 3D‐FSE‐Cube, but not statistically significant. Blurring, artifact, anatomic details, and overall image quality were significantly better on coronal 3D‐FSE‐Cube images (P < 0.001), but significantly better on axial 2D‐FSE images compared with axial 3D‐FSE‐Cube reformats (P < 0.01).

Conclusion:

Isotropic data from 3D‐FSE‐Cube allows reformations in arbitrary scan planes, which may make multiple 2D acquisitions unnecessary, and improve depiction of complex wrist anatomy. However, axial reformations suffer from blurring, likely due to T2 decay during the long echo train, limiting overall image quality in this plane. J. Magn. Reson. Imaging 2011;33:908–915. © 2011 Wiley‐Liss, Inc.     

MRI of prostate cancer at 1.5 and 3.0 T: comparison of image quality in tumor detection and staging

OBJECTIVE: This prospective study was performed to compare the image quality, tumor delineation, and depiction of staging criteria on MRI of prostate cancer at 1.5 and 3.0 T. SUBJECTS AND METHODS: Twenty-four patients with prostate cancer underwent MRI at 1.5 T using the combined endorectal-body phased-array coil and at 3.0 T using the torso phased-array coil, among them 22 before undergoing radical prostatectomy. The prostate was imaged with T2-weighted sequences in axial and coronal orientations at both field strengths and, in addition, with an axial T1-weighted sequence at 1.5 T. Preoperative analysis of all MR images taken together was compared with the histologic findings to determine the accuracy of MRI for the local staging of prostate cancer. In a retroanalysis, the image quality, tumor delineation, and conspicuity of staging criteria were determined separately for both field strengths and compared. Statistical analysis was performed using Wilcoxon's and the McNemar tests. RESULTS: In the preoperative analysis, MRI (at both 1.5 and 3.0 T) had an accuracy of 73% for the local staging of prostate cancer. The retroanalysis yielded significantly better results for 1.5-T MRI with the endorectal-body phased-array coil in terms of image quality (p < 0.001) and tumor delineation (p = 0.012) than for 3.0-T MRI with the torso phased-array coil. Analysis of the individual staging criteria for extracapsular disease did not reveal a superiority of either of the two field strengths in the depiction of any of the criteria. CONCLUSION: Intraindividual comparison shows that image quality and delineation of prostate cancer at 1.5 T with the use of an endorectal coil in a pelvic phased-array is superior to the higher field strength of 3.0 T with a torso phased-array coil alone. As long as no endorectal coil is available for 3-T imaging, imaging at 1.5 T using the combined endorectal-body phased-array coil will continue to be the gold standard for prostate imaging.     

MRI of the wrist at 7 tesla using an eight‐channel array coil combined with parallel imaging: Preliminary results

Purpose:

To determine the feasibility of performing MRI of the wrist at 7 Tesla (T) with parallel imaging and to evaluate how acceleration factors (AF) affect signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), and image quality.

Materials and Methods:

This study had institutional review board approval. A four‐transmit eight‐receive channel array coil was constructed in‐house. Nine healthy subjects were scanned on a 7T whole‐body MR scanner. Coronal and axial images of cartilage and trabecular bone micro‐architecture (3D‐Fast Low Angle Shot (FLASH) with and without fat suppression, repetition time/echo time = 20 ms/4.5 ms, flip angle = 10°, 0.169–0.195 × 0.169–0.195 mm, 0.5–1 mm slice thickness) were obtained with AF 1, 2, 3, 4. T1‐weighted fast spin‐echo (FSE), proton density‐weighted FSE, and multiple‐echo data image combination (MEDIC) sequences were also performed. SNR and CNR were measured. Three musculoskeletal radiologists rated image quality. Linear correlation analysis and paired t‐tests were performed.

Results:

At higher AF, SNR and CNR decreased linearly for cartilage, muscle, and trabecular bone (r < ?0.98). At AF 4, reductions in SNR/CNR were:52%/60% (cartilage), 72%/63% (muscle), 45%/50% (trabecular bone). Radiologists scored images with AF 1 and 2 as near‐excellent, AF 3 as good‐to‐excellent (P = 0.075), and AF 4 as average‐to‐good (P = 0.11).

Conclusion:

It is feasible to perform high resolution 7T MRI of the wrist with parallel imaging. SNR and CNR decrease with higher AF, but image quality remains above‐average. J. Magn. Reson. Imaging 2010;31:740–746. © 2010 Wiley‐Liss, Inc.

     

Three‐element phased‐array coil for imaging of rat spinal cord at 7T

To overcome some of the limitations of an implantable coil, including its invasive nature and limited spatial coverage, a three‐element phased‐array coil is described for high‐resolution magnetic resonance imaging (MRI) of rat spinal cord. This coil allows imaging both thoracic and cervical segments of rat spinal cord. In the current design, coupling between the nearest neighbors was minimized by overlapping the coil elements. A simple capacitive network was used for decoupling the next neighbor elements. The dimensions of individual coils in the array were determined based on the signal‐to‐noise ratio (SNR) measurements performed on a phantom with three different surface coils. SNR measurements on a phantom demonstrated higher SNR for the phased array coil relative to two different volume coils. In vivo images acquired on rat spinal cord with our coil demonstrated excellent gray and white matter contrast. To evaluate the performance of the phased array coil under parallel imaging, g‐factor maps were obtained for acceleration factors of 2 and 3. These simulations indicate that parallel imaging with an acceleration factor of 2 would be possible without significant image reconstruction–related noise amplifications. Magn Reson Med 60:1498–1505, 2008. © 2008 Wiley‐Liss, Inc.     

Model-based nonlinear inverse reconstruction for T2 mapping using highly undersampled spin-echo MRI

Purpose:

To develop a model‐based reconstruction technique for T2 mapping based on multi‐echo spin‐echo MRI sequences with highly undersampled Cartesian data encoding.

Materials and Methods:

The proposed technique relies on a nonlinear inverse reconstruction algorithm which directly estimates a T2 and spin‐density map from a train of undersampled spin echoes. The method is applicable to acquisitions with single receiver coils but benefits from multi‐element coil arrays. The algorithm is validated for trains of 16 spin echoes with a spacing of 10 to 12 ms using numerical simulations as well as human brain MRI at 3 Tesla (T).

Results:

When compared with a standard T2 fitting procedure using fully sampled T2‐weighted images, and depending on the available signal‐to‐noise ratio and number of coil elements, model‐based nonlinear inverse reconstructions for both simulated and in vivo MRI data yield accurate T2 estimates for undersampling factors of 5 to 10.

Conclusion:

This work describes a promising strategy for T2‐weighted MRI that simultaneously offers accurate T2 relaxation times and properly T2‐weighted images at arbitrary echo times. For a standard spin‐echo MRI sequence with Cartesian encoding, the method allows for a much higher degree of undersampling than obtainable by conventional parallel imaging. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Optimizing signal‐to‐noise ratio of high‐resolution parallel single‐shot diffusion‐weighted echo‐planar imaging at ultrahigh field strengths

The potential signal‐to‐noise ratio (SNR) gain at ultrahigh field strengths offers the promise of higher image resolution in single‐shot diffusion‐weighted echo‐planar imaging the challenge being reduced T₂ and T₂* relaxation times and increased B₀ inhomogeneity which lead to geometric distortions and image blurring. These can be addressed using parallel imaging (PI) methods for which a greater range of feasible reduction factors has been predicted at ultrahigh field strengths—the tradeoff being an associated SNR loss. Using comprehensive simulations, the SNR of high‐resolution diffusion‐weighted echo‐planar imaging in combination with spin‐echo and stimulated‐echo acquisition is explored at 7 T and compared to 3 T. To this end, PI performance is simulated for coil arrays with a variable number of circular coil elements. Beyond that, simulations of the point spread function are performed to investigate the actual image resolution. When higher PI reduction factors are applied at 7 T to address increased image distortions, high‐resolution imaging benefits SNR‐wise only at relatively low PI reduction factors. On the contrary, it features generally higher image resolutions than at 3 T due to smaller point spread functions. The SNR simulations are confirmed by phantom experiments. Finally, high‐resolution in vivo images of a healthy volunteer are presented which demonstrate the feasibility of higher PI reduction factors at 7 T in practice. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

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.     

Simultaneous bilateral magnetic resonance imaging of the femoral arteries in peripheral arterial disease patients

Purpose:

To image the femoral arteries in peripheral arterial disease (PAD) patients using a bilateral receive coil.

Materials and Methods:

An eight‐channel surface coil array for bilateral MRI of the femoral arteries at 3T was constructed and evaluated.

Results:

The bilateral array enabled imaging of a 25‐cm segment of the superficial femoral arteries (SFA) from the profunda to the popliteal. The array provided improved the signal‐to‐noise ratio (SNR) at the periphery and similar SNR in the middle of a phantom compared to three other commercially available coils (4‐channel torso, quadrature head, whole body). Multicontrast bilateral images of the in vivo SFA with 1 mm in‐plane resolution made it possible to directly compare lesions in the index SFA to the corresponding anatomical site in the contralateral vessel without repositioning the patient or coil. A set of bilateral time‐of‐flight, T1‐weighted, T2‐weighted, and proton density‐weighted images was acquired in a clinically acceptable exam time of ≈45 minutes.

Conclusion:

The developed bilateral coil is well suited for monitoring dimensional changes in atherosclerotic lesions of the SFA. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Rapid PROPELLER‐MRI: A combination of iterative reconstruction and under‐sampling

Purpose:

To develop a technique that is able to reduce acquisition time and remove uneven blurring in reconstructed image for PROPELLER MRI. By using under‐sampling and iterative reconstruction, this proposed technique will be less sensitive to subject motion.

Materials and Methods:

Numerical simulations, as well as experiments on a phantom and healthy human subjects were performed to demonstrate advantages of a combination of under‐sampled acquisition and iterative reconstruction. Method of motion correction was modified to increase accuracy of motion correction for the under‐sampled PROPELLER acquisition.

Results:

It was demonstrated that the proposed approach achieved substantial acceleration of PROPELLER acquisition while maintaining its motion correction advantage.

Conclusion:

An effective method for reducing imaging time in PROPELLER was introduced in this study, which minimizes typical under‐sampling artifacts without uneven spatial resolution and maintains the ability of motion correction. J. Magn. Reson. Imaging 2012;36:1241–1247. © 2012 Wiley Periodicals, Inc.