Conventional Spin-echo Imaging Research Articles

Precision in Practice: A Cross-sectional Study Involving MRI T2 Dixon and Conventional Sequence in Detecting Focal Multiple Myeloma Lesions

Introduction: Multiple Myeloma (MM) represents a malignant proliferation of plasma cells derived from a single clone. Imaging of the skeleton beyond symptomatic areas is useful for myeloma staging and subsequent follow-up for treatment response and disease relapse. Despite research comparing the Dixon sequence to conventional sequences in a variety of musculoskeletal disorders, there is a lack of studies regarding the Dixon sequence’s application in MM. Aim: To compare the contrast of MM focal lesions in all four T2- weighted Dixon and Conventional T1-weighted spin-echo and Short Tau Inversion Recovery (STIR) images. Materials and Methods: This cross-sectional study was conducted in the Department of Radiology at Kovai Medical Centre and Hospitals (KMCH), Coimbatore, Tamil Nadu, India. All newly diagnosed and known cases of MM, either biopsyproven or strongly suspected based on other diagnostic testing conforming to International Myeloma Working Group (IMWG) criteria from December 2020 to July 2022, were included in the study. A total of 43 patients with 142 focal MM lesions were included. Contrast between focal MM lesions and surrounding bone marrow was calculated on T1-weighted spin-echo, STIR, and T2-weighted Dixon (all four) images. Statistical analysis was done using repeated measures of Analysis of Variance (ANOVA) with Bonferroni correction to control the type I error on multiple comparisons to find the significant difference between multivariate analyses. A probability value of 0.05 was considered a significant level for all statistical tools. Results: The study population consisted of 21 men and 22 women with a mean age of 65.3±8.6 years {Mean±Standard Deviation (SD)}. Contrast values in all four T2 Dixon images, STIR, and T1-weighted images were as follows: T2 Dixon Fat-only (FO) images (0.86.±0.09) (SD); range: (0.46-0.99), T2-weighted Dixon Water-only (WO) images (0.54±0.14) (SD); range: (0.14-0.82), T2 Dixon In-phase (IP) images (0.20±0.13) (SD); range: (0.02-0.41), T2-weighted Dixon Out-phase (OP) images (0.53±0.19) (SD); range: (0.12-0.87), STIR images (0.47±0.12) (SD); range: (0.12-0.73), and T1 images (0.23±0.12) (SD); range: (0.01-0.55). The mean contrast was highest on T2 Dixon fat-only images (p<0.0005) compared to T1 images, with the lowest contrast seen in IP images and intermediate values in OP images. Conclusion: In conclusion, fat-only images of the T2 multipoint Dixon sequence provide significant contrast compared to conventional T1-weighted imaging. Dixon water-only images provide fat suppression that is not inferior to STIR images. While Dixon techniques in the diagnosis of MM did not significantly differ from the conventional sequence, Dixon stands out from conventional sequences when considering the study duration and contrast between the lesion and normal bone marrow.

High-Resolution Single-Shot Fast Spin-Echo MR Imaging with Deep Learning Reconstruction Algorithm Can Improve Repeatability and Reproducibility of Follicle Counting.

To investigate the diagnostic performance of high-resolution single-shot fast spin-echo (SSFSE) imaging with deep learning (DL) reconstruction algorithm on follicle counting and compare it with original SSFSE images and conventional fast spin-echo (FSE) images. This study included 20 participants (40 ovaries) with clinically confirmed polycystic ovary syndrome (PCOS) who underwent high-resolution ovary MRI, including three-plane T2-weighted FSE sequences and slice-matched T2-weighted SSFSE sequences. A DL reconstruction algorithm was applied to the SSFSE sequences to generate SSFSE-DL images, and the original SSFSE images were also saved. Subjective evaluations such as the blurring artifacts, subjective noise, and clarity of the follicles on the SSFSE-DL, SSFSE, and conventional FSE images were independently conducted by two observers. Intra-class correlation coefficients and Bland-Altman plots were used to present the repeatability and reproducibility of the follicle number per ovary (FNPO) based on the three types of images. SSFSE-DL images showed less blurring artifact, subjective noise, and better clarity of the follicles than SSFSE and FSE (p < 0.05). For the repeatability of the FNPO, SSFSE-DL showed the highest intra-observer (ICC = 0.930; 95% CI: 0.878-0.962) and inter-observer (ICC = 0.914; 95% CI: 0.843-0.953) agreements. The inter-observer 95% limits of agreement (LOA) for SSFSE-DL, SSFSE, and FSE ranged from -3.7 to 4.5, -4.4 to 7.0, and -7.1 to 7.6, respectively. The intra-observer 95% LOA for SSFSE-DL, SSFSE, and FSE ranged from -3.5 to 4.0, -5.1 to 6.1, and -5.7 to 4.2, respectively. The absolute values of intra-observer and inter-observer differences for SSFSE-DL were significantly lower than those for SSFSE and FSE (p < 0.05). Compared with the original SSFSE images and the conventional FSE images, high-resolution SSFSE images with DL reconstruction algorithm can better display follicles, thus improving FNPO assessment.

Simultaneous T1 -weighted and T2 -weighted 3D MRI using RF phase-modulated gradient echo imaging.

T1 -weighted and T2 -weighted (T1w and T2w) imaging are essential sequences in routine clinical practice to detect and characterize a wide variety of pathologies. Many approaches have been proposed to obtain T1w and T2w contrast, although many challenges still remain, including long acquisition time and limitations that favor 2D imaging. In this study, we propose a novel method for simultaneous T1w and T2w imaging using RF phase-modulated 3D gradient-echo imaging. Configuration theory is used to derive closed-form equations for the steady state of RF phase-modulated gradient-echo signal. These equations suggest the use of small RF phase increments to provide orthogonal signal contrast with T2w and T1w in the real and imaginary components, respectively. Background phase can be removed using a two-pass acquisition with opposite RF phase increments. Simulation and phantom experiments were performed to validate our proposed method. Volunteer images of the brain and knee were acquired to demonstrate the clinical feasibility. The proposed method was compared with T1w and T2w fast spin-echo imaging. The relative signal intensity of images acquired using the proposed method agreed closely with simulations and fast spin-echo imaging in phantoms. Images from volunteer imaging showed very similar contrast compared to conventional fast spin-echo imaging. Radiofrequency phase-modulated gradient-echo with small RF phase increments is an alternative method that provides simultaneous T1w and T2w contrast in short scan times with 3D volumetric coverage.

Diffusion in Sephadex Gel Structures: Time Dependency Revealed by Multi-Sequence Acquisition over a Broad Diffusion Time Range.

It has been increasingly reported that in biological tissues diffusion-weighted MRI signal attenuation deviates from mono-exponential decay, especially at high b-values. A number of diffusion models have been proposed to characterize this non-Gaussian diffusion behavior. One of these models is the continuous-time random-walk (CTRW) model, which introduces two new parameters: a fractional order time derivative α and a fractional order spatial derivative β. These new parameters have been linked to intravoxel diffusion heterogeneities in time and space, respectively, and are believed to depend on diffusion times. Studies on this time dependency are limited, largely because the diffusion time cannot vary over a board range in a conventional spin-echo echo-planar imaging sequence due to the accompanying T2 decays. In this study, we investigated the time-dependency of the CTRW model in Sephadex gel phantoms across a broad diffusion time range by employing oscillating-gradient spin-echo, pulsed-gradient spin-echo, and pulsed-gradient stimulated echo sequences. We also performed Monte Carlo simulations to help understand our experimental results. It was observed that the diffusion process fell into the Gaussian regime at extremely short diffusion times whereas it exhibited a strong time dependency in the CTRW parameters at longer diffusion times.

Single-plate method for practical modulation transfer function measurement in magnetic resonance imaging.

A new "single-plate method" is presented for measuring the modulation transfer function (MTF) in magnetic resonance imaging (MRI). This method sets a slice plane perpendicular to a single-plate phantom to eliminate contamination effects from the direction perpendicular to the measurement direction in the image plane, which occur with a conventional ramp method. As no practical method for measuring the MTF has been established for MRI, we examined whether the MTF can be measured practically using the single-plate method for various fast imaging sequences. Furthermore, the MTFs of T1-weighted (T1W) fast spin echo (FSE) and conventional spin echo (CSE) images obtained using the single-plate method and ramp method were compared. The measured MTFs of T1W CSE images revealed rectangular shapes with a sharp decrease near the Nyquist cutoff frequency in both phase-encoding (PE) and frequency-encoding (readout, RO) directions. The measured MTFs of T1W FSE images obtained with centric-order acquisition showed symmetric step-function shapes reflecting k-space segmentation determined by the echo train length (ETL). The measured MTFs of T2-weighted (T2W) FSE images showed asymmetric step-function shapes reflecting differences in T2 decay of signals from samples. The MTFs obtained using the single-plate method significantly reduced the collapse caused by the contamination effect, which is observed in all the MTF measurements of the ramp method. The proposed "single-plate method" simplified the complicated MTF measurement procedure and eliminated the contamination effect. This method is expected to be useful for evaluating the resolution properties of MR fast imaging techniques with a complicated k-space trajectory.

Is Magnetic Resonance Imaging Superior to Conventional Radiography in Neonates with Anorectal Malformation?

Introduction This study was conducted to evaluate the role of magnetic resonance imaging (MRI) in neonates with anorectal malformation (ARM). Materials and Methods Newborns, referred to Pediatric Surgical Ward through General Surgery Outpatient Department and Emergency Department of Sir Sunderlal Hospital as a case of ARM, were included in the study. Unstable patients requiring urgent primary colostomy were excluded from the study. Forty neonates with ARM and 20 neonates having no ARM were included in the study (2 years, i.e., conducted between September 2018 and July 2020). The included patients were evaluated clinically and were subjected to an invertogram (after 24 hours of delivery), which is conventional radiography. Further, MRI was performed using 1.5 T superconductive system; 5 to 6 mm contiguous sections were obtained using a head or a body coil according to the size of the infant patient to obtain images with sharp anatomical detail: Sagittal, coronal, and axial conventional spin-echo T1-weighted images of the pelvic region were obtained in all patients, with perpendicular coronal plane and the axial plane parallel to pelvic floor. Results The majority of patients (60%) were referred on day 3 of birth and rest were referred after 3 days of birth. Conventional radiography, that is, invertogram was done in all study population. Sixty per cent of the total included patients had supralevator location of rectal pouch. Conventional radiography was detected to be low type of ARM—all had infralevator position of rectal pouch in MRI, but 60% of the intermediate had supralevator level and all high abnormalities had supralevator level. These distribution anomalies were statistically significant. The levator ani length index and external anal sphincter length index were also compared and found to be thickest in intermediate type, thick in low types, and thin in high type of abnormalities, which is an added advantage of MRI over radiography. Conclusion Preoperative assessment of ARM with MRI gives useful information regarding type of malformation as well as sphincter muscle and associated malformations. Large sample size was needed for future landmark in the field of ARM.

Assessing image artifacts from radiotherapy electromagnetic transponders with metal-artifact reduction imaging

Image artifacts due to 14 gauge radiotherapy electromagnetic (EM) transponders were assessed on conventional spin echo images, and corrected using metal artifact reduction techniques: high bandwidth, view angle tilting (VAT), and slice encoding for metal artifact correction (SEMAC). Large areas of signal loss and/or pile-up were produced in an area extending up to 15.3 mm in radius for 14G transponders in standard imaging. Using high bandwidth imaging with VAT, in-plane artifact sizes were reduced by up to 35%. SEMAC did not significantly reduce in-plane or through plane artifact size for axially oriented images, but was effective in reducing through-plane artifacts for sagittal images. Using the experimental data, magnetic field maps were simulated so that the magnetic susceptibility of the transponder could be estimated and slice profiles could be visualized. Due to the large susceptibilities involved, current correction techniques are unable to fully correct artifacts due to EM transponders and significant areas of signal loss and distortion remain. Care should be taken when planning MRI following EM transponder implantation.

Comparison of 2D BLADE Turbo Gradient- and Spin-Echo and 2D Spin-Echo Echo-Planar Diffusion-Weighted Brain MRI at 3 T: Preliminary Experience in Children

We describe our preliminary experience using a 2D turbo gradient- and spin-echo (TGSE) diffusion-weighted (DW) pulse sequence with non-Cartesian BLADE trajectory at 3 T in pediatric patients. We compared the TGSE BLADE to conventional DW spin-echo echo-planar imaging (SE-EPI) in pediatric brain imaging, assessing the presence of artifacts from signal pile-ups, geometric distortion, motion, susceptibility from air-tissue interface, shunts and orthodontia, and diagnostic image quality. Data were acquired in 53 patients (10.4 ± 7.9 years). All DW imaging data were acquired precontrast, with SE-EPI first. A four-point scale for rating was used-1 (best) and 4 (worst). A neuroradiologist scored the two sequences and further noted whether the TGSE BLADE approach or SE-EPI was preferred in each case. Apparent diffusion coefficients were compared quantitatively between the two sequences in a subset of 16 patients, in 41 separate regions of interests including caudate nucleus, putamen, globus pallidus, thalamus, and pathological areas. In 43.4% of the cases, TGSE BLADE was preferred; in 49.1% of the cases, both sequences were preferred equally. Average scores for SE-EPI were 2.2 ± 0.8 versus TGSE's 1.2 ± 0.4 in assessing diagnostic quality (p < 0.05). Motion artifacts were minimal on both sequences in 92.5% of the cases. In the TGSE BLADE scores, no case received a "4" for significant artifacts with marginally acceptable image quality. Apparent diffusion coefficients values between the two sequences were statistically similar, with a linear regression slope of 0.92 (r2 = 0.97). TGSE BLADE DW imaging exhibited less geometric distortion in the brain and reduced signal pile-ups in areas of high susceptibility than conventional SE-EPI.

Accelerated T2 mapping combining parallel MRI and model-based reconstruction: GRAPPATINI.

Quantitative T2 measurements are sensitive to intra- and extracellular water accumulation and myelin loss. Therefore, quantitative T2 promises to be a good biomarker of disease. However, T2 measurements require long acquisition times. To accelerate T2 quantification and subsequent generation of synthetic T2 -weighted (T2 -w) image contrast for clinical research and routine. To that end, a recently developed model-based approach for rapid T2 and M0 quantification (MARTINI) based on undersampling k-space, was extended by parallel imaging (GRAPPA) to enable high-resolution T2 mapping with access to T2 -w images in less than 2 minutes acquisition time for the entire brain. Prospective cross-sectional study. Fourteen healthy subjects and a multipurpose phantom. Carr-Purcell-Meiboom-Gill sequence at a 3T scanner. The accuracy and reproducibility of the accelerated T2 quantification was assessed. Validations comprised MRI studies on a phantom as well as the brain, knee, prostate, and liver from healthy volunteers. Synthetic T2 -w images were generated from computed T2 and M0 maps and compared to conventional fast spin-echo (SE) images. Root mean square distance (RMSD) to the reference method and region of interest analysis. The combination of MARTINI and GRAPPA (GRAPPATINI) lead to a 10-fold accelerated T2 mapping protocol with 1:44 minutes acquisition time and full brain coverage. The RMSD of GRAPPATINI increases less (4.3%) than a 10-fold MARTINI reconstruction (37.6%) in comparison to the reference. Reproducibility tests showed low standard deviation (SD) of T2 values in regions of interest between scan and rescan (<0.4 msec) and across subjects (<4 msec). GRAPPATINI provides highly reproducible and fast whole-brain T2 maps and arbitrary synthetic T2 -w images in clinically compatible acquisition times of less than 2 minutes. These abilities are expected to support more widespread clinical applications of quantitative T2 mapping. 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2018;48:359-368.

T1-weighted MR imaging of glioma at 3T: a comparative study of 3D MPRAGE vs. conventional 2D spin-echo imaging

PurposeThis study aims to investigate difference between magnetization-prepared rapid gradient-echo imaging (MPRAGE) and spin-echo (SE) imaging for evaluating glioma on pre-contrast-enhanced (CE) and post-CE T1-weighted images at 3 T. Materials and methodsWe retrospectively assessed pre-CE and post-CE T1-weighted images for tumor contrast in 64 consecutive glioma patients. ResultsIn the nonenhancing tumors, the contrast was significantly clearer in MPRAGE than SE. In the enhancing tumors, post-CE contrast ratio was significantly higher in SE than MPRAGE, but when subtraction images are evaluated, the difference got smaller. ConclusionMPRAGE can be a good substitute of SE for T1-weighted imaging of glioma.

MONITORING EARLY RADIATION-INDUCED LIVER INJURY USING FERUCARBOTRAN-ENHANCED MRI AT 3 T: AN ANIMAL MODEL

The aim of this study was to find the time window for monitoring early radiation-induced liver injury (RILI) of rats using ferucarbotran-enhanced magnetic resonance imaging (MRI) at 3 T. Six rats were irradiated with 20 Gy 6 MV X-ray on right side liver and the other six non-irradiated rats were used as the control. Three or four days after irradiation, the rats were examined using MRI. The conventional spin echo (CSE) pulse sequence with various scanning parameters (CSE1: TR/TE = 200/8 ms, CSE2: TR/TE = 1000/8 ms and CSE3: TR/TE = 1000/22 ms) was performed before, 20 min, 1 h, 7 days, 14 days and 21 days after injecting 80 μmol/kg ferucarbotran, a kind of commercialized superparamagnetic iron oxide (SPIO). The ferucarbotran particles were macrophaged by Kupffer cells and this caused decreased signal intensity on MR images because of the T2and susceptibility effect. The irradiated liver had less reduction of MR signal intensity than the non-irradiated liver because radiation impaired the function of Kupffer cells. All CSE images of the irradiated group showed higher right-to-left ratio of the MR signal intensity in the liver than the control group after ferucarbotran injection. Furthermore, CSE2 demonstrated higher efficacy than CSE1 and CSE3. The optimal time window to observe an obvious contrast between the right side and left side liver in the irradiated group was from 20 min to 7 days after a single bolus injection of ferucarbotran. This protocol may be helpful to investigate the effects of radioprotectors and radiosensitizers on the reticuloendothelial system.

Pediatric MRI of the Brain: A Primer

1. Kamakshya P. Patra, MD* 2. Jeffrey D. Lancaster, MD* 3. Jeffery Hogg, MD† 4. Jeffrey S. Carpenter, MD† 1. *Department of Pediatrics, Section of Hospital Pediatrics, West Virginia University Children’s Hospital, Morgantown, WV. 2. †Department of Neuroradiology, West Virginia University Health Sciences Center, Morgantown, WV. * Abbreviations: ADHD: : attention-deficit/hyperactivity disorder CSF: : cerebrospinal fluid CT: : computed tomography DWI: : diffusion-weighted magnetic resonance imaging FLAIR: : fluid-attenuated inversion recovery fMRI: : functional magnetic resonance imaging MRI: : magnetic resonance imaging MRV: : magnetic resonance venography NAA: : N -acetylaspartate SDH: : subdural hematoma Because of recent advances in magnetic resonance imaging (MRI) techniques, pediatricians should be aware of the different modalities and their unique advantages and appropriateness in different clinical situations. After completing this article, readers should be able to: 1. Understand the pros and cons of MRI and computed tomography of the brain. 2. Know the basic principles of MRI and its different image modalities. 3. Be aware of the appropriateness of different modalities in specific clinical situations. Magnetic resonance imaging (MRI) is based on the absorption and emission of radiofrequency energy by hydrogen protons whose spin is influenced by changing magnetic fields (0.3 to 1.5 T). Unlike computed tomography (CT), there is no radiation exposure. T1-weighted images cause fat (eg, myelin in white matter) to appear bright and water (eg, cerebrospinal fluid [CSF] or edema) to appear dark on this sequence. The gray-white interfaces of the brain are well depicted on these sequences, especially if with the images are thinly sliced. T2-weighted images cause water (eg, CSF and edema) to appear bright and fat to appear dark. The MRI-based intravenous contrast agents (eg, gadolinium) are frequently used in T1-weighted images (Fig 1A and B) to make serum appear bright. The blood-brain barrier typically serves to limit the passage of many molecules out of the blood vessels. If disease processes break down this barrier (such as infection, tumors, or inflammation), intravenous contrast agents can cross into the brain, causing areas of contrast entry to appear very bright. Figure 1. T1-weighted image at the level of midbrain. A. The cerebrospinal fluid (CSF) appears dark. B. The CSF appears bright. Note the gray and white matter differentiation …

New phase‐based B1 mapping method using two‐dimensional spin‐echo imaging with hyperbolic secant pulses

To propose a new phase-based B1-mapping method that exploits phase information created by hyperbolic secant (HS) pulses in conventional 2D spin-echo imaging. In this B1-mapping method, HS pulses are used to accomplish π/2 excitation and π refocusing in standard multislice spin-echo imaging. When setting the ratio of pulse lengths of the π/2 and π HS pulses to 2:1, the spin-echo phase is independent of offset frequency and varies as a function of B1 strength. To eliminate undesired phase accumulations induced by unknown factors other than the B1 strength, two spin-echo images are acquired using HS pulses applied with opposite frequency-sweep directions, and the resulting phase images are subtracted from each other. To demonstrate the performance of the proposed method, phantom and in vivo experiments were performed using a surface coil and a volume coil. The B1 maps obtained by using the proposed method were in accordance with the B1 maps obtained using previous methods in both phantom and in vivo experiments. The proposed method is easy to implement without any sequence modification, is insensitive to B0 inhomogeneity and chemical shift, and is robust in a reasonably wide range of B1 field strength.

EVALUATION OF THE WARP‐TURBO SPIN ECHO SEQUENCE FOR 3 TESLA MAGNETIC RESONANCE IMAGING OF STIFLE JOINTS IN DOGS WITH STAINLESS STEEL TIBIAL PLATEAU LEVELING OSTEOTOMY IMPLANTS

Susceptibility artifacts caused by ferromagnetic implants compromise magnetic resonance imaging (MRI) of the canine stifle after tibial plateau leveling osteotomy (TPLO) procedures. The WARP-turbo spin echo sequence is being developed to mitigate artifacts and utilizes slice encoding for metal artifact reduction. The aim of the current study was to evaluate the WARP-turbo spin echo sequence for imaging post TPLO canine stifle joints. Proton density weighted images of 19 canine cadaver limbs were made post TPLO using a 3 Tesla MRI scanner. Susceptibility artifact sizes were recorded and compared for WARP vs. conventional turbo spin echo sequences. Three evaluators graded depiction quality for the tibial tuberosity, medial and lateral menisci, tibial osteotomy, and caudal cruciate ligament as sufficient or insufficient to make a diagnosis. Artifacts were subjectively smaller and local structures were better depicted in WARP-turbo spin echo images. Signal void area was also reduced by 75% (sagittal) and 49% (dorsal) in WARP vs. conventional turbo spin echo images. Evaluators were significantly more likely to grade local anatomy depiction as adequate for making a diagnosis in WARP-turbo spin echo images in the sagittal but not dorsal plane. The proportion of image sets with anatomic structure depiction graded adequate to make a diagnosis ranged from 28 to 68% in sagittal WARP-turbo spin echo images compared to 0-19% in turbo spin echo images. Findings indicated that the WARP-turbo spin echo sequence reduces the severity of susceptibility artifacts in canine stifle joints post TPLO. However, variable depiction of local anatomy warrants further refinement of the technique.

Apparent Diffusion Coefficient Mapping Using a Multi-Shot Spiral MRI Sequence of the Rat Brain

Purpose: Commonly used diffusion weighted (DW) imaging such as DW spin echo (SE) type echo planar imaging (DW-SE-EPI) is known to be a snapshot-like acquisition and to have a relatively high signal-to-noise ratio. Spiral MRI sequence (SPIRAL) has characteristics similar to these of EPI, but it has rarely been used for diffusion-weighted imaging (DWI). In vivo DW-SPIRAL of the rat brain has almost never been reported. Our purpose in this study was to examine the potential of SE-type two-dimensional (2D) multi-shot spiral acquisition MRI for apparent diffusion coefficient (ADC) mapping of the rat brain in vivo. Materials and Methods: We made an SE-type DW-2D-spiral MRI sequence (DW-SPIRAL) which was prepared on a 2.0-T animal-experiment MR scanner. Comparing the phantom experimental result of DW-SPIRAL with the phantom experimental result of DW SE-type echo-planar imaging (DW-SE-EPI) and conventional DW spin echo imaging (DW-SE), we estimated the characteristics of DW-SPIRAL and assessed the clinical application of DW-SPIRAL in an animal experiment on the rat brain. Results: There was not much difference between the calculated water/glycerol phantom diffusion coefficient of DW-SPIRAL and the calculated diffusion coefficient of DW-SE. This result shows that the DW-SPIRAL sequence is appropriate for use in diffusion weighted imaging. There were fewer phantom image distortions and ghosting artifacts with DW-SPIRAL than with DW-SE-EPI, and this tendency was similar in the animal experiment on the rat brain. Conclusion: The DW-SPIRAL sequence had been successfully tested in phantom experiments and rat brain experiments. It has been demonstrated that the DW-SPIRAL sequence is capable of producing in vivo rat brain DWI.

Osteochondral Repair: Evaluation with Sweep Imaging with Fourier Transform in an Equine Model

To evaluate the status of articular cartilage and bone in an equine model of spontaneous repair by using the sweep imaging with Fourier transform (SWIFT) magnetic resonance (MR) imaging technique. Experiments were approved by the Utrecht University Animal Ethics Committee. Six-millimeter-diameter chondral (n = 5) and osteochondral (n = 5, 3-4 mm deep into subchondral bone) defects were created in the intercarpal joints of seven 2-year-old horses and examined with SWIFT at 9.4 T after spontaneous healing for 12 months. Conventional T2 maps and gradient-echo images were obtained for comparison, and histologic assessment of cartilage and micro-computed tomography (CT) of bone were performed for reference. Signal-to-noise ratio (SNR) analysis was performed, and a radiologist evaluated the MR images. Structural bone parameters were derived from SWIFT and micro-CT datasets. Significance of differences was investigated with the Wilcoxon signed rank test and Pearson correlation analysis. SWIFT was able to depict the different outcomes of spontaneous healing of focal chondral versus osteochondral defects. SWIFT produced constant signal intensity throughout cartilage, whereas T2 mapping showed elevated T2 values (P = .06) in repair tissue (mean T2 in superficial region of interest in an osteochondral lesion = 50.0 msec ± 10.2) in comparison to adjacent intact cartilage (mean T2 = 32.7 msec ± 4.2). The relative SNR in the subchondral plate with SWIFT (0.91) was more than four times higher than that with conventional fast spin-echo (0.12) and gradient-echo (0.19) MR imaging. The correlation between bone volume-to-tissue volume fractions determined with SWIFT and micro-CT was significant (r = 0.83, P < .01). SWIFT enabled assessment of spontaneous osteochondral repair in an equine model.

Knee Derangements: Comparison of Isotropic 3D Fast Spin-Echo, Isotropic 3D Balanced Fast Field-Echo, and Conventional 2D Fast Spin-Echo MR Imaging

To compare diagnostic performance, subjective image quality, and artifacts of isotropic three-dimensional (3D) intermediate-weighted (IW) fast spin-echo (SE), isotropic 3D balanced fast field-echo (FFE), and conventional two-dimensional (2D) fast SE 3.0-T MR sequences in evaluation of cartilage, ligaments, menisci, and osseous knee structures in symptomatic patients. Institutional review board approval and waiver of informed consent were obtained for this HIPAA-compliant study. One hundred MR studies, each with three data sets (3D IW fast SE, 3D balanced FFE, 2D fast SE), were reviewed retrospectively. Two radiologists independently evaluated images for cartilaginous defects, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial meniscus (MM), lateral meniscus (LM) tears, subchondral bone marrow signal abnormalities, subjective image quality, and image artifacts. Arthroscopic results were the reference standard. Statistical analysis was performed to calculate interobserver agreement and compare diagnostic performance of sequences. Sensitivity and specificity were greater than 85% for all lesions. For cartilaginous defects, sensitivity of 3D IW fast SE was significantly greater than that of 3D balanced FFE (95.5% vs 89.7%). Sensitivity of 3D IW fast SE and 2D fast SE for MM, LM, and ACL tears tended to be greater than that of 3D balanced FFE. IW fast SE had a higher detection rate for subchondral bone marrow signal abnormality than did 3D balanced FFE (34% vs 21%); it also had the best image quality and fewest artifacts, followed by 2D fast SE and 3D balanced FFE. Interobserver agreement was excellent for evaluation of all intraarticular structures (κ = 0.85-1) and good to excellent for detection of subchondral bone marrow signal abnormality (κ = 0.76-0.91). The performance of IW fast SE is superior to that of balanced FFE in evaluation of cartilaginous defects, with no significant difference in performance between 2D fast SE, 3D IW fast SE, and 3D balanced FFE in evaluation of meniscal and ligament tears. Subchondral bone marrow signal abnormality is more easily seen on 3D IW fast SE images, with better subjective image quality and fewer artifacts, than on images obtained with other techniques.

Motion Correction of Multi-b-value Diffusion-weighted Imaging in the Liver

Motion artifacts are a significant source of error in the acquisition and quantification of parameters from multi-b-value diffusion-weighted imaging (DWI). The objective of this article is to present a reliable method to reduce motion-related artifacts during free-breathing at higher b-values when signal levels are low. Twelve patients referred for magnetic resonance imaging of the liver underwent a clinical magnetic resonance imaging examination of the abdominal region that included DWI. Conventional single-shot spin-echo echo planar imaging acquisitions of the liver during free breathing were repeated in a "time-resolved" manner during a single acquisition to obtain data for multi-b-value analysis, alternating between low and high b-values. Image registration using a normalized mutual information similarity measure was used to correct for spatial misalignment of diffusion-weighted volumes caused by motion. Registration error was estimated indirectly by comparing the normalized root-mean-square error (NRMSE) values of data fitted to the biexponential intra-voxel incoherent motion model before and after motion correction. Regions of interest (ROIs) were selected in the liver close to the surface of the liver and close to internal structures such as large bile ducts and blood vessels. For the 12 patient datasets, the mean NRMSE value for the motion-corrected ROIs (0.38 ± 0.16) was significantly lower than the mean NRMSE values for the non-motion-corrected ROIs (0.41 ± 0.13) (P < .05). In cases where there was substantial respiratory motion during the acquisition, visual inspection verified that the algorithm markedly improved alignment of the liver contours between frames. The proposed method addresses motion-related artifacts to increase robustness in multi-b-value acquisitions.

Artifact reduction from metallic dental materials in T1‐weighted spin‐echo imaging at 3.0 tesla

To investigate and propose a method of artifact reduction arising from metallic dental materials by applying a slice-encoding for metal artifact correction (SEMAC) technique on T1-weighted spin-echo (SE) imaging at 3 Tesla. The view angle tilting (VAT) technique was adapted to conventional T1-weighted spin-echo (SE) sequence to correct the in-plane distortion, and the SEMAC technique was used for correcting the remaining through-plane distortions. Fourier transform based B0 field simulations were performed to estimate the amount of field perturbation and a scout imaging method was developed which guide in selecting the number of slice-encodings needed in SEMAC sequences. Phantoms of six different dental materials with various shapes and sizes that are used in practice (amalgam; titanium implant; gold and Ni-Cr crowns; Ni-Ti and stainless steel orthodontic wires) were imaged. In vivo images of two subjects were also acquired. The amounts of artifact reduction were quantified in phantom studies. Compared with conventional SE imaging in phantom studies, in-plane artifacts were reduced by up to 43% in the VAT SE images and 80% in the SEMAC images. Through-plane artifacts were reduced by up to 65% in SEMAC images. In vivo SEMAC images also showed reduced artifacts. The SEMAC technique can mitigate artifact caused by metallic dental materials for T1w-SE imaging.

Computed Tomography and Magnetic Resonance Imaging Features of Posterior Mediastinal Ganglioneuroma

To evaluate computed tomography (CT) and magnetic resonance (MR) imaging findings of posterior mediastinal ganglioneuromas. Of 14 pathologically confirmed ganglioneuromas seen in 13 patients, 13 were evaluated by CT images with and without contrast, 11 were evaluated with conventional spin-echo MR images, and 5 were evaluated with contrast-enhanced MR examination. The morphologic features, attenuation, signal intensity, and dynamic enhancement pattern of the neoplasms were evaluated. All lesions were identified as a well-demarcated oval and/or lobular mass. CT attenuation was predominantly low. Calcification on CT scan was seen in 38% of the cases. Whorled appearance (42%) and tailed-shaped edge (14%) were seen on both CT and MR images. Fat components (29%) observed histologically were also detected in tumors on CT and MR images. MR signal intensity in the lesions was mainly low on T1-weighted images and high on T2-weighted images. Contrast enhancement of the tumors was poor in 46% on dynamic CT study. In all 5 contrast-enhanced MR examinations, all lesions were enhanced. The characteristic findings of posterior mediastinal ganglioneuromas are a craniocaudally oblong-shaped mass, calcification, whorled appearance, tail-like extension, and fat component. Poor enhancement on dynamic CT studies is commonly observed.