3D Turbo Spin Echo Imaging Research Articles

Improvement in the contrast-to-noise ratio and quantitative measurement of T1 and T2* values for carotid atherosclerotic plaque using multi-echo phase-sensitive inversion recovery.

Quantitative magnetic resonance imaging is required to accurately evaluate carotid plaque vulnerability. We prospectively evaluated the potential for fast quantitative black-blood carotid vessel wall imaging using a three-dimensional (3D) multi-echo phase-sensitive inversion recovery (mPSIR) sequence. Forty-nine patients with carotid atherosclerotic plaques were examined. Two-dimensional (2D) turbo spin-echo (TSE), 3D volumetric isotropic turbo spin-echo, and 3D mPSIR imaging were performed. The contrast-to-noise ratios (CNRs) between the carotid plaque and adjacent muscle were compared for the three imaging methods. The T1 and T2* values of the carotid plaques were measured using 3D mPSIR images. These values were compared with those of symptomatic and asymptomatic plaques. For carotid plaques with a signal intensity ratio ≥ 1.55, between the carotid plaque and adjacent muscle in 2D TSE images, the CNR of the mPSIR images was significantly higher than that of the other sequences. T1 values for symptomatic and asymptomatic plaques were 544.0 ± 258.0 and 569.1 ± 301.7, respectively. T2* values for symptomatic and asymptomatic plaques were 34.0 ± 33.0 and 21.8 ± 20.3ms, respectively. There were no significant differences in the T1 and T2* values between the symptomatic and asymptomatic plaques. 3D mPSIR improves the CNR of T1-weighted images for carotid plaques and the adjacent muscle while simultaneously providing the T1 and T2* values of the carotid plaque. This improved CNR may be useful for assessing the vulnerability of carotid plaques.

Simultaneous super-resolution and contrast synthesis of routine clinical magnetic resonance images of the knee for improving automatic segmentation of joint cartilage: data from the Osteoarthritis Initiative.

High resolution three-dimensional (3D) magnetic resonance (MR) images are well suited for automated cartilage segmentation in the human knee joint. However, volumetric scans such as 3D Double-Echo Steady-State (DESS) images are not routinely acquired in clinical practice which limits opportunities for reliable cartilage segmentation using (fully) automated algorithms. In this work, a method for generating synthetic 3D MR (syn3D-DESS) images with better contrast and higher spatial resolution from routine, low resolution, two-dimensional (2D) Turbo-Spin Echo (TSE) clinical knee scans is proposed. A UNet convolutional neural network is employed for synthesizing enhanced artificial MR images suitable for automated knee cartilage segmentation. Training of the model was performed on a large, publically available dataset from the OAI, consisting of 578 MR examinations of knee joints from 102 healthy individuals and patients with knee osteoarthritis. The generated synthetic images have higher spatial resolution and better tissue contrast than the original 2D TSE, which allow high quality automated 3D segmentations of the cartilage. The proposed approach was evaluated on a separate set of MR images from 88 subjects with manual cartilage segmentations. It provided a significant improvement in automated segmentation of knee cartilages when using the syn3D-DESS images compared to the original 2D TSE images. The proposed method can successfully synthesize 3D DESS images from 2D TSE images to provide images suitable for automated cartilage segmentation.

Magnetic resonance neurography of the lumbosacral plexus at 3 Tesla – CSF-suppressed imaging with submillimeter resolution by a three-dimensional turbo spin echo sequence

PurposeTo investigate magnetic resonance neurography (MRN) of the lumbosacral plexus (LSP) with cerebrospinal fluid (CSF) suppression by using submillimeter resolution for three-dimensional (3D) turbo spin echo (TSE) imaging. Materials and methodsUsing extended phase graph (EPG) analysis, the signal response of CSF was simulated considering dephasing from coherent motion for frequency-encoding voxel sizes ranging from 0.3 to 1.3 mm and for CSF velocities ranging from 0 to 4 cm/s. In-vivo MRN included 3D TSE data with frequency encoding parallel to the feet/head axis from 15 healthy adults (mean age: 28.5 ± 3.8 years, 5 females; acquisition voxel size: 2 × 2 × 2 mm3) and 16 pediatric patients (mean age: 6.7 ± 4.1 years, 7 females; acquisition voxel size: 0.7 × 0.7 × 1.4 mm3) acquired at 3 Tesla. Five of the adults were scanned repetitively with changing acquisition voxel sizes (1 × 2 × 2 mm3, 0.7 × 2× 2 mm3, and 0.5 × 2 × 2 mm3). Measurements of the bilateral ganglion of the L5 nerve root, averaged between sides, as well as the CSF in the thecal sac were obtained for all included subjects and compared between adults and pediatric patients and between voxel sizes, using a CSF-to-nerve signal ratio (CSFNR). ResultsAccording to simulations, the CSF signal is reduced along the echo train for moving spins. Specifically, it can be reduced by over 90% compared to the maximum simulated signal for flow velocities above 2 cm/s, and could be most effectively suppressed by considering a frequency-encoding voxel size of 0.8 mm or less. For in-vivo measurements, mean CSFNR was 1.52 ± 0.22 for adults and 0.10 ± 0.03 for pediatric patients (p < .0001). Differences in CSFNR were significant between measurements using a voxel size of 2 × 2 × 2 mm3 and measurements in data with reduced voxel sizes (p ≤ .0012), with submillimeter resolution (particularly 0.5 × 2 × 2 mm3) providing highest CSF suppression. ConclusionsApplying frequency-encoding voxel sizes in submillimeter range for 3D TSE imaging with frequency encoding parallel to the feet/head axis may considerably improve MRN of LSP pathology in adults in the future because of favorable CSF suppression.

Self-calibrating wave-encoded 3D turbo spin echo imaging using subspace model based autofocusing.

To develop a self-calibrating approach for the estimation of wave point spread function (PSF) and coil sensitivities from the subsampled wave-encoded k-space, and evaluate its performance for wave-encoded 3D turbo spin echo (TSE) imaging. A low rank subspace parametric model was demonstrated in simulation to improve the representation for practical wave encoding k-space trajectories with aperiodicity, and an autofocus metric for the entire imaging volume was used to calibrate the wave PSF in a 2-stage manner from coarse to refined estimation. The coil sensitivities can be extracted from the shifted central region of wave PSF corrected subsampled k-space, and further used with wave PSF for wave-encoded parallel imaging (PI) reconstruction. The wave encoding gradients were integrated into the 3D TSE sequence considering eddy current reduction aspects and maintaining of the Carr-Purcell-Meiboom-Gill condition. Phantom and in vivo brain experiments were performed to evaluate the accuracy of wave PSF self-calibration and to compare the PI reconstruction performance between wave and Cartesian encoding scheme. The self-calibrated wave PSF, estimated from different k-space undersampling patterns can robustly correct the wave encoding induced image artifacts given sufficient central autocalibration data. The self-calibrating wave-encoded PI reconstruction has demonstrated its improved performance in reduced aliasing artifacts and noise amplification in comparison to the Cartesian-encoded PI reconstruction results for 3D TSE imaging. The proposed self-calibrating wave-encoded method allows robust calibration of wave PSF and coil sensitivities from the subsampled k-space, and improves the overall image quality for accelerated 3D TSE imaging.

Accelerated 3D T2 w-imaging of the prostate with 1-millimeter isotropic resolution in less than 3 minutes.

PurposeTo achieve 3D T2w imaging of the prostate with 1‐mm isotropic resolution in less than 3 min.MethodsWe devised and implemented a 3D T2‐prepared multishot balanced steady state free precession (T2prep‐bSSFP) acquisition sequence with a variable density undersampled trajectory combined with a total variation regularized iterative SENSE (TV‐SENSE) reconstruction. Prospectively undersampled images of the prostate (acceleration factor R = 3) were acquired in 11 healthy subjects in an institutional review board‐approved study. Image quality metrics (subjective signal‐to‐noise ratio, contrast, sharpness, and overall prostate image quality) were evaluated by 2 radiologists. Scores of the proposed accelerated sequence were compared using the Wilcoxon signed‐rank and Kruskal‐Wallis non‐parametric tests to prostate images acquired using a fully sampled 3D T2prep‐bSSFP acquisition, and with clinical standard 2D and 3D turbo spin echo (TSE) T2w acquisitions. A P‐value < 0.05 was considered significant.ResultsThe 3× accelerated 3D T2prep‐bSSFP images required a scan time (min:s) of 2:45, while the fully sampled 3D T2prep‐bSSFP and clinical standard 3D TSE images were acquired in 8:23 and 7:29, respectively. Image quality scores (contrast, sharpness, and overall prostate image quality) of the accelerated 3D T2prep‐bSSFP, fully sampled T2prep‐bSSFP, and clinical standard 3D TSE acquisitions along all 3 spatial dimensions were not significantly different (P > 0.05).Conclusion3D T2w images of the prostate with 1‐mm isotropic resolution can be acquired in less than 3 min, with image quality that is comparable to a clinical standard 3D TSE sequence but only takes a third of the acquisition time.

Three-dimensional turbo spin-echo sequence versus conventional two-dimensional turbo spin-echo sequences in the evaluation of lumbar intervertebral discs

Objective: The aim of this study was to evaluate the efficacy of a three-dimensional (3D) turbo spin-echo (TSE) sequence for determining lumbar disc protrusions, and to compare the findings with those of conventional two-dimensional (2D) TSE sequences and reveal the interobserver and intermethod agreements of both sequences. Methods: A total of 127 discs from 84 patients were evaluated by three radiologists. Conventional 2D TSE images and 3D TSE images were independently interpreted with regard to disc pathology and herniation zones and were scored for the degree of spinal stenosis and lumbar neural foraminal stenosis by the three reviewers. To evaluate the lumbar discs, areas of protrusion or extrusion were classified. Interobserver and intermethod reliabilities were calculated using Krippendorff’s alpha (Kα) test. Results: Lumbar disc pathology identification was similar between the 2D TSE and 3D TSE sequences. Interobserver agreements were better for 3D TSE than 2D TSE in the evaluation of disc hernias (Kα ratio; 0.965 vs. 0.944), herniation zones (Kα ratio; 0.894 vs. 0.847), and foraminal narrowing (Kα ratio; 0.965 vs. 0.924). Both 2D and 3D TSE had 100% sensitivity for disc pathologies and spinal stenosis, 81% sensitivity for herniation zones, and 92.5% sensitivity for foraminal stenosis in only operated patients. Conclusions: The 3D TSE sequence was comparable to conventional magnetic resonance imaging (MRI) sequences in the evaluation of lumbar disc herniation. This approach can be used in radiology departments either alone or combined with routine MRI for lumbar disc hernias as a diagnostic sequence and an approach to overcome problems.

Contrast-Enhanced High-Resolution MRI for Evaluating Time Course Changes in Middle Cerebral Artery Plaques.

It is clinically important to evaluate time course changes in symptomatic middle cerebral artery (MCA) stenotic plaques because of likely recurrence. The objective of this study is to determine whether contrast-enhanced high-resolution magnetic resonance imaging (MRI) is a feasible method for this purpose. Contrast-enhanced, high-resolution, 3D turbo spin-echo images with low refocusing flip angle control (3D LOWRAT) applied to 7 patients with symptomatic MCA stenosis were evaluated at the initial (1 month after stroke onset) and follow-up (7 months after stroke onset) stages, and statistical variables, including plaque-to-thalamus signal intensity ratio, degree of stenosis, and stroke recurrence obtained at the 2 stages, were compared. Stenotic change at the initial stage was compared to that at the follow-up stage using MR angiography. In 4 of the 7 patients, the signal intensity ratio measured at the follow-up stage was lower than that measured at the initial stage and in 1 patient, the stenosis subsequently improved. We used a Chi-Square Test. In the other 3 patients, the signal intensity ratios did not differ between the 2 stages, and ischemic stroke occurred in 2 of these 3 patients. Gadolinium contrast enhancement was found to be useful for effective evaluation of time course changes in the stability of symptomatic MCA stenotic plaques.

In vivo MRI of the human finger at 7 T.

PurposeTo demonstrate a dedicated setup for ultrahigh resolution MR imaging of the human finger in vivo.MethodsA radiofrequency coil was designed for optimized signal homogeneity and sensitivity in the finger at ultrahigh magnetic field strength (7 T), providing high measurement sensitivity. Imaging sequences (2D turbo‐spin echo (TSE) and 3D magnetization‐prepared rapid acquisition gradient echo (MPRAGE)) were adapted for high spatial resolution and good contrast of different tissues in the finger, while keeping acquisition time below 10 minutes. Data was postprocessed to display finger structures in three dimensions.Results3D MPRAGE data with isotropic resolution of 200 µm, along with 2D TSE images with in‐plane resolutions of 58 × 78 µm2 and 100 × 97 µm2, allowed clear identification of various anatomical features such as bone and bone marrow, tendons and annular ligaments, cartilage, arteries and veins, nerves, and Pacinian corpuscles.ConclusionUsing this dedicated finger coil at 7 T, together with adapted acquisition sequences, it is possible to depict the internal structures of the human finger in vivo within patient‐compatible measurement time. It may serve as a tool for diagnosis and treatment monitoring in pathologies ranging from inflammatory or erosive joint diseases to injuries of tendons and ligaments to nervous or vascular disorders in the finger. Magn Reson Med 79:588–592, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Orthogonally combined motion- and diffusion-sensitized driven equilibrium (OC-MDSDE) preparation for vessel signal suppression in 3D turbo spin echo imaging of peripheral nerves in the extremities.

To design a preparation module for vessel signal suppression in MR neurography of the extremities, which causes minimal attenuation of nerve signal and is highly insensitive to eddy currents and motion. The orthogonally combined motion- and diffusion-sensitized driven equilibrium (OC-MDSDE) preparation was proposed, based on the improved motion- and diffusion-sensitized driven equilibrium methods (iMSDE and FC-DSDE, respectively), with specific gradient design and orientation. OC-MDSDE was desensitized against eddy currents using appropriately designed gradient prepulses. The motion sensitivity and vessel signal suppression capability of OC-MDSDE and its components were assessed in vivo in the knee using 3D turbo spin echo (TSE). Nerve-to-vessel signal ratios were measured for iMSDE and OC-MDSDE in 7 subjects. iMSDE was shown to be highly sensitive to motion with increasing flow sensitization. FC-DSDE showed robustness against motion, but resulted in strong nerve signal loss with diffusion gradients oriented parallel to the nerve. OC-MDSDE showed superior vessel suppression compared to iMSDE and FC-DSDE and maintained high nerve signal. Mean nerve-to-vessel signal ratios in 7 subjects were 0.40 ± 0.17 for iMSDE and 0.63 ± 0.37 for OC-MDSDE. OC-MDSDE combined with 3D TSE in the extremities allows high-near-isotropic-resolution imaging of peripheral nerves with reduced vessel contamination and high nerve signal. Magn Reson Med 79:407-415, 2018. © 2017 Wiley Periodicals, Inc.

Efficacy of Maximum Intensity Projection of Contrast-Enhanced 3D Turbo-Spin Echo Imaging with Improved Motion-Sensitized Driven-Equilibrium Preparation in the Detection of Brain Metastases

ObjectiveTo evaluate the diagnostic benefits of 5-mm maximum intensity projection of improved motion-sensitized driven-equilibrium prepared contrast-enhanced 3D T1-weighted turbo-spin echo imaging (MIP iMSDE-TSE) in the detection of brain metastases. The imaging technique was compared with 1-mm images of iMSDE-TSE (non-MIP iMSDE-TSE), 1-mm contrast-enhanced 3D T1-weighted gradient-echo imaging (non-MIP 3D-GRE), and 5-mm MIP 3D-GRE.Materials and MethodsFrom October 2014 to July 2015, 30 patients with 460 enhancing brain metastases (size > 3 mm, n = 150; size ≤ 3 mm, n = 310) were scanned with non-MIP iMSDE-TSE and non-MIP 3D-GRE. We then performed 5-mm MIP reconstruction of these images. Two independent neuroradiologists reviewed these four sequences. Their diagnostic performance was compared using the following parameters: sensitivity, reading time, and figure of merit (FOM) derived by jackknife alternative free-response receiver operating characteristic analysis. Interobserver agreement was also tested.ResultsThe mean FOM (all lesions, 0.984; lesions ≤ 3 mm, 0.980) and sensitivity ([reader 1: all lesions, 97.3%; lesions ≤ 3 mm, 96.2%], [reader 2: all lesions, 97.0%; lesions ≤ 3 mm, 95.8%]) of MIP iMSDE-TSE was comparable to the mean FOM (0.985, 0.977) and sensitivity ([reader 1: 96.7, 99.0%], [reader 2: 97, 95.3%]) of non-MIP iMSDE-TSE, but they were superior to those of non-MIP and MIP 3D-GREs (all, p < 0.001). The reading time of MIP iMSDE-TSE (reader 1: 47.7 ± 35.9 seconds; reader 2: 44.7 ± 23.6 seconds) was significantly shorter than that of non-MIP iMSDE-TSE (reader 1: 78.8 ± 43.7 seconds, p = 0.01; reader 2: 82.9 ± 39.9 seconds, p < 0.001). Interobserver agreement was excellent (κ > 0.75) for all lesions in both sequences.ConclusionMIP iMSDE-TSE showed high detectability of brain metastases. Its detectability was comparable to that of non-MIP iMSDE-TSE, but it was superior to the detectability of non-MIP/MIP 3D-GREs. With a shorter reading time, the false-positive results of MIP iMSDE-TSE were greater. We suggest that MIP iMSDE-TSE can provide high diagnostic performance and low false-positive rates when combined with 1-mm sequences.

Three-Dimensional CAIPIRINHA SPACE TSE for 5-Minute High-Resolution MRI of the Knee.

The aim of this study was to prospectively test the hypothesis that a 2-dimensional (2D) CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration) sampling pattern facilitates 5-minute high spatial resolution 3-dimensional (3D) sampling perfection with application optimized contrast using different flip angle evolutions (SPACE) magnetic resonance imaging (MRI) of the knee with image quality similar or better than current 2D turbo spin echo (TSE) and 3D SPACE standards. The study was approved by our institutional review board. Twenty asymptomatic subjects (12 men, 8 women; mean age, 42 years; age range, 24-65 years) underwent 3 T MRI of the knee. A 4-fold accelerated 3D SPACE TSE prototype with 2D CAIPIRINHA sampling pattern and 5-minute acquisition time was compared with commercially available 2-fold and 4-fold accelerated 3D SPACE and 2D TSE pulse sequences with acquisition times of 11 minutes and 15 seconds, 6 minutes and 30 seconds, as well as 9 minutes and 48 seconds, respectively. Outcome variables included image quality, anatomic visibility, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Statistical analysis included Friedman, repeated measures analysis of variances, and Cohen's weighted κ tests. Bonferroni-corrected P values of 0.005 and less were considered statistically significant. Overall, image quality, visibility of anatomic structures, SNR, and CNR of 3D CAIPIRINHA SPACE were statistically similar to 2-fold accelerated 3D SPACE and significantly better than 4-fold accelerated 3D SPACE, which exhibited degrading parallel imaging artifacts. Compared with 2.5-mm 2D TSE images, 0.5-mm 3D CAIPIRINHA SPACE images showed statistically similar good edge sharpness and very good contrast resolution, and significantly less partial volume as well as absent chemical shift and pulsatile flow artifacts. Visibility of menisci, anterior cruciate ligament, posterior cruciate ligament, medial collateral ligament, and lateral collateral ligament was good to very good on 0.5-mm 3D CAIPIRINHA SPACE images as compared with good on 2.5-mm 2D TSE image (P < 0.005). The SNR of fat, fluid, and cartilage as well as CNR between cartilage, fluid, fat, posterior cruciate ligament, and menisci were minimally higher on 2.5-mm 2D TSE image (P < 0.005). Image quality, visibility of anatomic structures, SNR, and CNR of 2.5-mm 3D CAIPIRINHA SPACE and 2.5-mm 2D TSE images were good to very good without significant differences. Three-dimensional SPACE with 2D CAIPIRINHA sampling pattern enables high-quality 3D TSE MRI of the knee at an acquisition time of 5 minutes and image quality, visibility of anatomic structures, SNR, and CNR similar to conventional 3D SPACE and 2D TSE, both of which require approximately 10-minute acquisition times.

Sliding-slab three-dimensional TSE imaging with a spiral-In/Out readout.

T2 -weighted imaging is of great diagnostic value in neuroimaging. Three-dimensional (3D) Cartesian turbo spin echo (TSE) scans provide high signal-to-noise ratio (SNR) and contiguous slice coverage. The purpose of this preliminary work is to implement a novel 3D spiral TSE technique with image quality comparable to 2D/3D Cartesian TSE. The proposed technique uses multislab 3D TSE imaging. To mitigate the slice boundary artifacts, a sliding-slab method is extended to spiral imaging. A spiral-in/out readout is adopted to minimize the artifacts that may be present with the conventional spiral-out readout. Phase errors induced by B0 eddy currents are measured and compensated to allow for the combination of the spiral-in and spiral-out images. A nonuniform slice encoding scheme is used to reduce the truncation artifacts while preserving the SNR performance. Preliminary results show that each of the individual measures contributes to the overall performance, and the image quality of the results obtained with the proposed technique is, in general, comparable to that of 2D or 3D Cartesian TSE. 3D sliding-slab TSE with a spiral-in/out readout provides good-quality T2 -weighted images, and, therefore, may become a promising alternative to Cartesian TSE.

Improving the robustness of 3D turbo spin echo imaging to involuntary motion.

3D TSE imaging is very prone to motion artifacts, especially from uncooperative patients, because of the long scan duration. The need to repeat this time-consuming 3D acquisition in the event of large motion artifacts substantially reduces patient comfort and increases the workload of the scanner. A new sampling strategy enables homogenized collection of k-space data for 3D TSE imaging. It is combined with Frobenius norm-based motion-detection to enable freely stopped acquisition in 3D TSE imaging whenever excessive subject motion is detected. The feasibility and reliability of the proposed method were demonstrated and evaluated in in-vivo experiments. It is shown that the additional overhead related to repeat scanning of the 3D TSE sequence as a result of patient motion can be substantially reduced by using the homogenized k-space sampling strategy with automatic scan completion as determined by Frobenius norm-based motion-detection.

Validation of a semiautomated spinal cord segmentation method

To validate semiautomated spinal cord segmentation in healthy subjects and patients with neurodegenerative diseases and trauma. Forty-nine healthy subjects, as well as 29 patients with amyotrophic lateral sclerosis, 19 with spinal muscular atrophy, and 14 with spinal cord injuries were studied. Cord area was measured from T2 -weighted 3D turbo spin echo images (cord levels from C2 to T9) using the semiautomated segmentation method of Losseff et al (Brain [1996] 119(Pt 3):701-708), compared with manual segmentation. Reproducibility was evaluated using the inter- and intraobserver coefficient of variation (CoV). Accuracy was assessed using the Dice similarity coefficient (DSC). Robustness to initialization was assessed by simulating modifications to the contours drawn manually prior to segmentation. Mean interobserver CoV was 4.00% for manual segmentation (1.90% for Losseff's method) in the cervical region and 5.62% (respectively 2.19%) in the thoracic region. Mean intraobserver CoV was 2.34% for manual segmentation (1.08% for Losseff's method) in the cervical region and 2.35% (respectively 1.34%) in the thoracic region. DSC was high (0.96) in both cervical and thoracic regions. DSC remained higher than 0.8 even when modifying initial contours by 50%. The semiautomated segmentation method showed high reproducibility and accuracy in measuring spinal cord area.

Three-dimensional turbo spin-echo magnetic resonance imaging (MRI) and semiquantitative assessment of knee osteoarthritis: comparison with two-dimensional routine MRI

The aim of this study was to evaluate three-dimensional (3D) turbo spin-echo (TSE) magnetic resonance imaging (MRI) for semiquantitative assessment of knee OA. Twenty subjects fulfilling the American College of Rheumatology clinical criteria of knee OA underwent both two-dimensional (2D) and 3D MRIs on the same day. The 2D MRI protocol included triplanar fat-suppressed (FS) intermediate-weighted (Iw) TSE. For the 3D TSE technique, a sagittal FS Iw sequence was acquired and triplanar reformations were constructed. 2D and 3D MRIs were read separately by two radiologists using the Whole-Organ Magnetic Resonance Imaging Score (WORMS) system. Agreement was determined using weighted kappa statistics and percentage of overall agreement. The diagnostic performance of WORMS readings using 3D TSE MRI to detect the presence or absence of features was assessed using readings from 2D TSE images as a reference. Agreement for the scored features ranged between 0.62 (osteophytes (OS)) and 0.94 (meniscal extrusion). The sensitivity of WORMS readings using the 3D TSE technique ranged between 80% (periarticular cysts) and 100% (several features), the specificity ranged between 62.3% (OS) and 100% (several features), and accuracy ranged between 77.2% (OS) and 99.3% (subchondral cysts). Semiquantitative assessment of knee OA can be reliably performed using 3D TSE MRI, showing substantial to almost perfect agreement and high accuracy when compared to routine 2D TSE MRI. 3D TSE MRI also takes less time, which is important for large OA studies.

Detection of Small Metastatic Brain Tumors

Early and accurate diagnosis of small metastatic brain tumors may affect outcomes and treatment strategies. For this reason, 3-dimensional (3D) thin-section imaging is preferred. However, with conventional contrast-enhanced (CE) 3D imaging, such as magnetization-prepared rapid gradient echo (MP-RAGE), many visually enhanced vessels may mimic small metastatic tumors, hindering tumor detection. CE black-blood single-slab 3D turbo-spin echo imaging (BB-ssTSE) was recently developed, which uses variable refocusing flip angles and flow-sensitizing gradient schemes, to enhance metastatic brain tumors while selectively suppressing blood vessels. The purpose of this work was to investigate the efficiency of the proposed CE BB-ssTSE in detecting small metastatic brain tumors as compared with conventional MP-RAGE. Numerical comparisons of MP-RAGE and BB-ssTSE were performed by simulation studies to investigate the signal/contrast behaviors of flowing blood and stationary CE tumors. For in vivo studies, we enrolled 35 patients (18 women; mean age, 58.1 years) with breast or lung cancer who underwent brain magnetic resonance imaging. After administering a double dose of contrast medium, whole-brain 2-dimensional T1-weighted imaging followed by high-resolution isotropic 3D BB-ssTSE and MP-RAGE was performed at 3.0 T. Two reviewers independently evaluated the presence of metastatic brain tumors using: (1) MP-RAGE; (2) BB-ssTSE; and (3) MP-RAGE + BB-ssTSE sequentially in 3 review sessions, 2 weeks apart. The lesions were classified by size into 2 groups: large (≥5 mm) and small (<5 mm). Both reviewers marked all tumors detected at each session. Another reviewer combined the results of the 2 reviewers and compared the detection rates of metastatic brain tumors between BB-ssTSE and MP-RAGE by using follow-up imaging. Intraclass correlation coefficients between the 2 reviewers were measured. Numerical simulations showed that the proposed BB-ssTSE effectively attenuated the signal intensity of flowing blood over the entire echo train, resulting in CE tumor-to-white matter contrast comparable with conventional MP-RAGE. The combined evaluation of MP-RAGE + BB-ssTSE showed 242 tumors in 28 patients. Of these, 153 lesions were <5 mm. MP-RAGE found 111 small metastatic brain tumors, BB-ssTSE found 150, and MP-RAGE + BB-ssTSE found 153. Significantly, more small tumors were detected by BB-ssTSE than MP-RAGE (P = 0.001, Wilcoxon signed-rank test). All large tumors were detected similarly by both MP-RAGE and BB-ssTSE. By combined results for MP-RAGE + BB-ssTSE, sensitivities for detection of small metastatic tumors were 72.5% for MP-RAGE and 98.0% for BB-ssTSE (P < 0.0001, McNemar test). Intraclass correlation coefficients between the 2 reviewers were 0.826 for MP-RAGE and 0.954 for BB-ssTSE. Compared with conventional MP-RAGE, the proposed CE BB-ssTSE imaging, which enhances tumors while selectively suppressing blood vessels, leads to significantly better detection of small metastatic brain tumors <5 mm.

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 B(1) amplitudes. In this work we develop a B(1) 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 B(1) sensitivity in single-slab 3D turbo/fast SE imaging with very long echo trains.

Preoperative 3 T MR imaging of rectal cancer: Local staging accuracy using a two-dimensional and three-dimensional T2-weighted turbo spin echo sequence

Purpose The purpose of our study was to evaluate the image quality and diagnostic performance of two-dimensional (D) turbo spin echo (TSE) and 3D T2-weighted TSE MR imaging in local staging of rectal cancer at 3 T. Materials and methods 3 T phased-array MR imaging was performed in 36 consecutive patients with biopsy-proven rectal cancer. High-resolution 2D TSE images in three planes and 3D TSE images of the rectum were obtained. Two independent observers performed an image quality assessment using eight image quality characteristics. All 2D and 3D datasets were evaluated separately. MR images were prospectively evaluated by two experienced radiologists in consensus with regard to local disease. Total mesorectal excision was used as the standard of reference. The sensitivity, specificity, positive and negative predictive value, and overall accuracy were calculated. Areas under the receiver operating characteristic (ROC) curve (AUC) were determined. Results Twenty-two patients who underwent a total mesorectal excision were enrolled in this study. Significantly more motion artifacts were present with 3D TSE imaging ( P = 0.04). The overall sensitivity, specificity, and accuracy of muscularis propria invasion in rectal cancer using 2D T2-weighted images were 100%, 66%, and 95%, respectively. There was a statistical significant greater AUC using 2D T2-weighted images compared to 3D T2-weighted MR images ( P = 0.04). The ROC curves describing the results of the interpretation of 2D and 3D T2-weighted datasets regarding perirectal tissue invasion showed no statistical significant difference ( P = 0.41). Conclusions In this study, high local staging accuracies with 3 T 2D T2-weighted MR imaging were demonstrated. 3D T2-weighted MR imaging cannot replace 2D MR imaging for local staging of rectal cancer. However, 3D MR imaging can be used for visualization of the complex pelvic anatomy for treatment planning purposes.

Bright and black blood imaging of the carotid bifurcation at 3.0 T

Purpose The aim of this study was to evaluate our preliminary experience at 3.0 T with imaging of the carotid bifurcation in healthy and atherosclerotic subjects. Application at 3.0 T is motivated by the signal-to-noise gain for improving spatial resolution and reducing signal averaging requirements. Materials and methods We utilized a dual phased array coil and applied 2D, 3D time of flight (TOF) and turbo spin echo (TSE) sequences with comparison of two lumen signal suppression methods for black blood (BB) TSE imaging including double inversion preparation (DIR) and spatial presaturation pulses. The signal-to-noise ratios (SNR) of healthy carotid vessel walls were compared in 2D and 3D BB TSE acquisitions. The bright and black blood multi-contrast exam was demonstrated for a complex carotid plaque. Results Contrast-to-noise (CNR) greater than 150 was achieved between the lumen and suppressed background for 3D TOF. For BB, both methods provided sufficient lumen signal suppression but slight residual flow artifacts remained at the bifurcation level. As expected 3D TSE images had higher SNR compared to 2D, but increased motion sensitivity is a significant issue for 3D at high field. For multi-contrast imaging of atherosclerotic plaque, fibrous, calcified and lipid components were resolved. The CNR ratio of fibrous (bright on PDW, T2W) and calcified (dark in T1W, T2W, PDW) plaque components was maximal in the T2W images. The 3D TOF angiogram indicating a 40% stenosis was complemented by 3D multi-planar reformat of BB images that displayed plaque extent. Detection of intimal thickening, the earliest change associated with atherosclerotic progression was observed in BB PDW images at 3.0 T. Conclusions High SNR and CNR images have been demonstrated for the healthy and diseased carotid. Improvements in RF coils along with pulse sequence optimization, and evaluation of endogenous and exogenous contrast mechanisms will further enhance carotid imaging at 3.0 T.