Echo Train Length Research Articles

Whole-brain vessel wall MRI: A parameter tune-up solution to improve the scan efficiency of three-dimensional variable flip-angle turbo spin-echo.

To propose and evaluate a parameter tune-up solution to expedite a three-dimensional (3D) variable-flip-angle turbo spin-echo (TSE) sequence for whole-brain intracranial vessel wall (IVW) imaging. Elliptical k-space sampling and prolonged echo train length (ETL), were used to expedite a 3D variable-flip-angle TSE-based sequence. To compensate for the potential loss in vessel wall signal, optimal combination of prescribed T2 and ETL was experimentally investigated on 22 healthy volunteers at 3 Tesla. The optimized protocol (7-8 min) was then compared with a previous protocol (reference protocol, 11-12 min) in terms of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), vessel wall sharpness, and wall delineation quality on a 4-point scale (0:poor; 3:excellent) in 10 healthy volunteers. A pilot study of five patients was performed and lesion delineation score was used to demonstrate the diagnostic quality. A protocol with ETL = 52 and prescribed T2 = 170 ms was deemed an optimized one, which, compared with the reference protocol, provided significantly improved wall SNR (12.0 ± 1.3 versus 10.0 ± 1.1; P = 0.002), wall-lumen CNR (9.7 ± 1.2 versus 8.0 ± 0.9; P = 0.002), wall-CSF CNR (2.8 ± 1.0 versus 1.7 ± 1.0; P = 0.026), similar vessel wall sharpness at both inner (1.59 ± 0.18 versus 1.58 ± 0.14, P = 0.87) and outer (1.71 ± 0.25 versus 1.83 ± 0.30; P = 0.18) boundaries, and comparable vessel wall delineation score for individual segments (1.95-3; P > 0.06). In all patients, atherosclerotic plaques (10) or wall dissection (5) were identified with a delineation score of 3 or 2. A parameter tune-up solution can accelerate 3D variable-flip-angle TSE acquisitions, particularly allowed for expedited whole-brain IVW imaging with preserved wall delineation quality. 2. Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:751-757.

Fundamental Study of Three-dimensional Fast Spin-echo Imaging with Spoiled Equilibrium Pulse.

Three-dimensional fast spin-echo (3D FSE) imaging with variable refocusing flip angle has been recently applied to pre- or post-enhanced T1-weighted imaging. To reduce the acquisition time, this sequence requires higher echo train length (ETL), which potentially causes decreased T1 contrast. Spoiled equilibrium (SpE) pulse consists of a resonant +90° radiofrequency (RF) pulse and is applied at the end of the echo train. This +90° RF pulse brings residual transverse magnetization to the negative longitudinal axis, which makes it possible to increase T1 contrast. The purpose of our present study was to examine factors that influence the effect of spoiled equilibrium pulse and the relationship between T1 contrast improvement and imaging parameters and to understand the characteristics of spoiled equilibrium pulse. Phantom studies were conducted using an magnetic resonance imaging (MRI) phantom made of polyvinyl alcohol gel. To evaluate the effect of spoiled equilibrium pulse with changes in repetition time (TR), ETL, and refocusing flip angle, we measured the signal-to-noise ratio and contrast-to-noise ratio (CNR). The effect of spoiled equilibrium pulse was evaluated by calculating the enhancement rate of CNR. The factors that influence the effect of spoiled equilibrium pulse are TR, ETL, and relaxation time of tissues. Spoiled equilibrium pulse is effective with increasing TR and decreasing ETL. The shorter the T1 value, the better the spoiled equilibrium pulse functions. However, for tissues in which the T1 value is long (>600 ms), at a TR of 600 ms, improvement in T1 contrast by applying spoiled equilibrium pulse cannot be expected.

Optimizing MRI Logistics: Focused Process Improvements Can Increase Throughput in an Academic Radiology Department.

The purpose of this study was to describe and evaluate the effect of focused process improvements on protocol selection and scheduling in the MRI division of a busy academic medical center, as measured by examination and room times, magnet fill rate, and potential revenue increases and cost savings to the department. Focused process improvements, led by a multidisciplinary team at a large academic medical center, were directed at streamlining MRI protocols and optimizing matching protocol ordering to scheduling while maintaining or improving image quality. Data were collected before (June 2013) and after (March 2015) implementation of focused process improvements and divided by subspecialty on type of examination, allotted examination time, actual examination time, and MRI parameters. Direct and indirect costs were compiled and analyzed in consultation with the business department. Data were compared with evaluated effects on selected outcome and efficiency measures, as well as revenue and cost considerations. Statistical analysis was performed using a t test. During the month of June 2013, 2145 MRI examinations were performed at our center; 2702 were performed in March 2015. Neuroradiology examinations were the most common (59% in June 2013, 56% in March 2015), followed by body examinations (25% and 27%). All protocols and parameters were analyzed and streamlined for each examination, with slice thickness, TR, and echo train length among the most adjusted parameters. Mean time per examination decreased from 43.4 minutes to 36.7 minutes, and mean room time per patient decreased from 46.3 to 43.6 minutes (p = 0.009). Potential revenue from increased throughput may yield up to $3 million yearly (at $800 net revenue per scan) or produce cost savings if the facility can reduce staffed scanner hours or the number of scanners in its fleet. Actual revenue and expense impacts depend on the facility's fixed and variable cost structure, payer contracts, MRI fleet composition, and unmet MRI demand. Focused process improvements in selecting MRI protocols and scheduling examinations significantly increased throughput in the MRI division, thereby increasing capacity and revenue. Shorter scan and department times may also improve patient experience.

Comparison of FSE T2 W PROPELLER and 3D–FIESTA of 3 T MR for the internal auditory canal

ObjectiveThe study compared the use of periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) technique fast spin echo (FSE) T2 W and the sequence of three-dimensional fast imaging employing steady-state acquisition (3D–FIESTA) technique in the MRI of the internal auditory canal for overall image quality improvement. Materials and methodsOne hundred thirty-two patients undergoing FSE T2 W PROPELLER and 3D–FIESTA examinations of the internal auditory canal were included. All examinations were performed at 3.0 T with comparison of a sagittal oblique FSE T2 W sequence with the PROPELLER technique to 3D–FIESTA in the same reconstructed orientation with PROPELLER. Image quality was evaluated by two radiologists using a 4-point scale. The Wilcoxon signed rank test was used to compare the data of the two techniques. ResultsThe image quality of FSE T2 W PROPELLER was significantly improved compared to the reconstructed images of 3D–FIESTA. Observer 1: median FSE T2 W with PROPELLER, 4 [mean, 3.455] versus median reconstructed 3D–FIESTA, 3 [mean, 3.15], (P<.001); Observer 2: median FSE T2 W with PROPELLER, 4 [mean, 3.47] versus median reconstructed 3D–FIESTA, 3 [mean, 3.25], (P<.001). Interobserver agreement was good (k value, 0.73) for the rating of the overall image quality. ConclusionThe FSE T2 W PROPELLER technique for MRI of internal auditory canal reduced uncertainty caused by motion artifact and improved the quality of the image compared to the reconstructed 3D–FIESTA. It was affected by different parameters including the blade width, echo train length (ETL). This is explained by data oversampling at the center region of k-space, which requires additional imaging time over conventional MRI techniques. Increasing blade was expected to improve motion correction effects but also the signal-to-noise ratio. ETL increases the image sharpness and the overall image quality.

MRI of the knees in asymptomatic adolescent soccer players: A case-control study.

To determine the range of asymptomatic abnormal findings in adolescent soccer players at 3.0T MRI of the knee. In all, 87 knees of asymptomatic 14-17-year-old male adolescents were evaluated at 3T, using a standardized examination protocol comprising four sequences: two fat-suppressed T2 -weighted fast spin-echo sequences (T2 FSE), in the sagittal (repetition time / echo time [TR/TE], 5.300/71, echo train length [ETL] 17) and coronal planes (TR/TE, 4234/70, ETL 17), one fat-suppressed proton density (PD) sequence in the axial plane (TR/TE, 2.467/40, ETL 9), and one T1 -weighted spin-echo (T1 SE) sequence in the sagittal plane (TR/TE, 684/12.5). Soccer players (46 knees) were paired with controls (41 knees) by age and weight. Bone marrow, articular cartilage, meniscus, tendons, ligaments, fat pad abnormalities, and joint fluid were assessed. One or more abnormalities were detected in 31 knees (67.4%) in the soccer player group, compared to 20 knees (48.8%) in the control group. The prevalence of bone marrow edema was higher in the soccer group (19 knees, 41.3%) than in the control group (3 knees, 7.3%), P = 0.001. Other abnormalities found in this sample (joint effusion, cartilage lesions, tendinopathy, ganglion cysts, and infrapatellar fat pat edema) were not significantly different between the two study groups. Asymptomatic adolescents had a high prevalence of abnormal findings on knee imaging, especially bone marrow edema. This prevalence was higher among soccer players. 4 J. Magn. Reson. Imaging 2017;45:59-65.

TU‐H‐CAMPUS‐IeP2‐01: Quantitative Evaluation of PROPELLER DWI Using QIBA Diffusion Phantom

Purpose:The purpose of this study is to determine the quantitative variability of apparent diffusion coefficient (ADC) values when varying imaging parameters in a diffusion‐weighted (DW) fast spin echo (FSE) sequence with Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction (PROPELLER) k‐space trajectory.Methods:Using a 3T MRI scanner, a NIST traceable, quantitative magnetic resonance imaging (MRI) diffusion phantom (High Precision Devices, Inc, Boulder, Colorado) consisting of 13 vials filled with various concentrations of polymer polyvinylpyrrolidone (PVP) in aqueous solution was imaged with a standard Quantitative Imaging Biomarkers Alliance (QIBA) DWI spin echo, echo planar imaging (SE EPI) acquisition. The same phantom was then imaged with a DWI PROPELLER sequence at varying echo train lengths (ETL) of 8, 20, and 32, as well as b‐values of 400, 900, and 2000. QIBA DWI phantom analysis software was used to generate ADC maps and create region of interests (ROIs) for quantitative measurements of each vial. Mean and standard deviations of the ROIs were compared.Results:The SE EPI sequence generated ADC values that showed very good agreement with the known ADC values of the phantom (r2 = 0.9995, slope = 1.0061). The ADC values measured from the PROPELLER sequences were inflated, but were highly correlated with an r2 range from 0.8754 to 0.9880. The PROPELLER sequence with an ETL=20 and b‐value of 0 and 2000 showed the closest agreement (r2 = 0.9034, slope = 0.9880).Conclusion:The DW PROPELLER sequence is promising for quantitative evaluation of ADC values. A drawback of the PROPELLER sequence is the longer acquisition time. The 180° refocusing pulses may also cause the observed increase in ADC values compared to the standard SE EPI DW sequence. However, the FSE sequence offers an advantage with in‐plane motion and geometric distortion which will be investigated in future studies.

SU‐F‐J‐163: In Vivo Quantification of Sequence Parameter Effect On Geometric Distortion Caused by Implanted Titanium Brachytherapy Applicator

Purpose:The use of MR to plan and evaluate brachytherapy treatment for cervical cancer is increasing given the availability of MR conditional or safe applicators and MRI's proven superiority to CT for characterizing soft tissue lesions. The titanium applicators, however, cause geometric distortions or imaging artifacts, which reduce the utility of MRI for dosimetry. We sought to quantify the observed volume of the same applicator on a previously optimized T2 sequence in comparison to the conventional T2 sequence and CT obtained for brachytherapy planning.Methods:Prior work with testing in phantoms showed that increases in readout bandwidth yielded reductions in artifact area and distortion measurements even with voxel increases. Following IRB approval, nine patients with titanium tandem &amp; ovoid applicator (Varian Medical Systems) in place were scanned with a standard periprocedural protocol which included sagittal T2 fast spin echo (FSE) acquisition (res 0.98×0.78×4.0 mm3; BW 200Hz). An additional T2‐weighted FSE sequence (res 0.98×0.98×3–4 mm3; BW500Hz) with increased readout bandwidth, readout voxel size, and echo train length was added to the protocol. Volume measurements of the applicator (from tip to cervical stop) were hand‐segmented in Velocity AI 3.1 (Velocity Medical Solutions) for the two T2 FSE sequences and a planning CT obtained shortly after MRI. Differences were analyzed using a paired t‐test.Results:Average apparent volumes of the applicator on standard T2 sequence, decreased bandwidth T2 sequence and CT were 5.922±1.283 cm3, 4.544±1.524 cm3, and 2.304±0.509 cm3 respectively.Conclusion:Apparent volumes of a brachytherapy applicator can be compared in vivo. The modified sequence results in decreased apparent size of the cervical applicator. Both MR sequence volumes were larger than the planning CT, which was expected. Future work will focus on the diagnostic quality of the new sequence and quantifying any geometric shifts after CT to MRI registration based on anatomical landmarks.

Abstract TP219: Eight-minute Whole-brain Intracranial Vessel Wall MRI at 3 Tesla: Toward a Practical Imaging Protocol for Diagnosis of Stroke Etiology

Introduction: T1-weighted variable-flip-angle 3D turbo spin-echo (TSE), has emerged as a vessel wall MRI technique promising for elucidating underlying intracranial vessel wall pathologies associated with stroke. Whole-brain 0.5-mm isotropic-resolution 3D TSE has recently been proposed at 3 Tesla. However, its scan time of 12 min renders it impractical for a clinical setting. This work aimed to design an expedited protocol and conduct a pilot study to demonstrate its potential for diagnosis of wall abnormalities. Methods: To expedite the acquisition, one may exploit an elliptical data sampling strategy and prolonged echo train length (ETL). However, this would reduce image SNR and compromise vessel wall delineation. On the other hand, SNR is intimately related to refocusing flip angles that are calculated for a prescribed tissue with specific T1 and T2 values (denoted as simulation T1 and T2). In this work, the effects of simulation T2 and ETL on the SNR/CNR performance were first explored on 9 healthy subjects. An optimized imaging protocol was then determined from a narrowed range of choices on 7 healthy subjects and finally applied to a pilot study of 10 patients with known wall disease. Results: Wall SNR, wall-CSF CNR, and white-gray matter CNR generally increased with simulation T2 and decreased with ETL. Optimization was focused on a narrowed range of protocol choices (ETL = 52; T2 = 140, 170, 200 ms) which enable a scan time of 8 min. ETL=52/T2=170ms was shown (Figure a.) to provide significantly higher (t-test) SNR/CNR performance than the original 12-min protocol (ETL=36/T2=100ms). With the 8-min protocol pre/post contrast, wall abnormalities (Figure b.) were correctly detected in all patients. Conclusion: An 8-min whole-brain intracranial vessel wall imaging protocol is developed which has demonstrated the potential of accurately identifying various wall abnormalities. A large-scale trial on using the technique for diagnosis of stroke etiology is underway.

T2 shuffling: Sharp, multicontrast, volumetric fast spin-echo imaging.

A new acquisition and reconstruction method called T2 Shuffling is presented for volumetric fast spin-echo (three-dimensional [3D] FSE) imaging. T2 Shuffling reduces blurring and recovers many images at multiple T2 contrasts from a single acquisition at clinically feasible scan times (6-7 min). The parallel imaging forward model is modified to account for temporal signal relaxation during the echo train. Scan efficiency is improved by acquiring data during the transient signal decay and by increasing echo train lengths without loss in signal-to-noise ratio (SNR). By (1) randomly shuffling the phase encode view ordering, (2) constraining the temporal signal evolution to a low-dimensional subspace, and (3) promoting spatio-temporal correlations through locally low rank regularization, a time series of virtual echo time images is recovered from a single scan. A convex formulation is presented that is robust to partial voluming and radiofrequency field inhomogeneity. Retrospective undersampling and in vivo scans confirm the increase in sharpness afforded by T2 Shuffling. Multiple image contrasts are recovered and used to highlight pathology in pediatric patients. A proof-of-principle method is integrated into a clinical musculoskeletal imaging workflow. The proposed T2 Shuffling method improves the diagnostic utility of 3D FSE by reducing blurring and producing multiple image contrasts from a single scan. Magn Reson Med 77:180-195, 2017. © 2016 Wiley Periodicals, Inc.

Mono-Exponential Fitting in T2-Relaxometry: Relevance of Offset and First Echo.

IntroductionT2 relaxometry has become an important tool in quantitative MRI. Little focus has been put on the effect of the refocusing flip angle upon the offset parameter, which was introduced to account for a signal floor due to noise or to long T2 components. The aim of this study was to show that B1 imperfections contribute significantly to the offset. We further introduce a simple method to reduce the systematic error in T2 by discarding the first echo and using the offset fitting approach.Materials and MethodsSignal curves of T2 relaxometry were simulated based on extended phase graph theory and evaluated for 4 different methods (inclusion and exclusion of the first echo, while fitting with and without the offset). We further performed T2 relaxometry in a phantom at 9.4T magnetic resonance imaging scanner and used the same methods for post-processing as in the extended phase graph simulated data. Single spin echo sequences were used to determine the correct T2 time.ResultsThe simulation data showed that the systematic error in T2 and the offset depends on the refocusing pulse, the echo spacing and the echo train length. The systematic error could be reduced by discarding the first echo. Further reduction of the systematic T2 error was reached by using the offset as fitting parameter. The phantom experiments confirmed these findings.ConclusionThe fitted offset parameter in T2 relaxometry is influenced by imperfect refocusing pulses. Using the offset as a fitting parameter and discarding the first echo is a fast and easy method to minimize the error in T2, particularly for low to intermediate echo train length.

MR Imaging with Metal-suppression Sequences for Evaluation of Total Joint Arthroplasty.

Metallic artifact at orthopedic magnetic resonance (MR) imaging continues to be an important problem, particularly in the realm of total joint arthroplasty. Complications often follow total joint arthroplasty and can be expected for a small percentage of all implanted devices. Postoperative complications involve not only osseous structures but also adjacent soft tissues-a highly problematic area at MR imaging because of artifacts from metallic prostheses. Without special considerations, susceptibility artifacts from ferromagnetic implants can unacceptably degrade image quality. Common artifacts include in-plane distortions (signal loss and signal pileup), poor or absent fat suppression, geometric distortion, and through-section distortion. Basic methods to reduce metallic artifacts include use of spin-echo or fast spin-echo sequences with long echo train lengths, short inversion time inversion-recovery (STIR) sequences for fat suppression, a high bandwidth, thin section selection, and an increased matrix. With care and attention to the alloy type (eg, titanium, cobalt-chromium, stainless steel), orientation of the implant, and magnetic field strength, as well as use of proprietary and nonproprietary metal-suppression techniques, previously nondiagnostic studies can yield key diagnostic information. Specifically, sequences such as the metal artifact reduction sequence (MARS), WARP (Siemens Healthcare, Munich, Germany), slice encoding for metal artifact correction (SEMAC), and multiacquisition with variable-resonance image combination (MAVRIC) can be optimized to reveal pathologic conditions previously hidden by periprosthetic artifacts. Complications of total joint arthroplasty that can be evaluated by using MR imaging with metal-suppression sequences include pseudotumoral conditions such as metallosis and particle disease, infection, aseptic prosthesis loosening, tendon injury, and muscle injury.

Evaluation of a three‐dimensional MR acoustic radiation force imaging pulse sequence using a novel unbalanced bipolar motion encoding gradient

MR guided focused ultrasound procedures require accurate focal spot localization in three dimensions. This study presents a three-dimensional (3D) pulse sequence for acoustic radiation force imaging (ARFI) that efficiently localizes the focal spot by means of ultrasound induced tissue displacement over a large field-of-view. A novel unbalanced bipolar motion encoding gradient was implemented to maximize time available for motion encoding, reduce echo times, and allow for longer echo train lengths. Two advanced features, kz reduction factor (KZRF) and kz -level interleaving, were implemented to reduce tissue heating. Studies in gelatin phantoms compared the location of peak displacement and temperature measured by 3D MR thermometry. MR-ARFI induced tissue heating was evaluated through a parametric study of sequence parameters and MR thermometry measurements during repeated application of ARFI sonication patterns. Sequence performance was characterized in the presence of respiration and tissue inhomogeneity. The location of peak displacement and temperature rise agreed within 0.2 ± 0.1 mm and 0.5 ± 0.3 mm in the transverse and longitudinal direction, respectively. The 3D displacement maps were acquired safely, and the KZRF and kz -level interleaving features reduced tissue heating by 51%. High quality displacement maps were obtained despite respiration and tissue inhomogeneities. This sequence provides a safe, accurate, and simple approach to localizing the focal spot in three dimensions with a single scan. Magn Reson Med 76:803-813, 2016. © 2015 Wiley Periodicals, Inc.

Multislice localized parallel excitation for EPI applications in humans

ABSTRACTIn this work, the opportunities and challenges for the use of parallel transmission in combination with 2D RF pulses designed on EPI‐based excitation trajectories for diffusion‐weighted imaging (DWI) with reduced FOV are presented and analyzed in detail. The use of localized excitation allows for shortening of the EPI read‐out, which is especially important for EPI applications outside of the brain. DWI is chosen as a practically important and relevant example demonstrating the key aspects of 2D spatial selection. The properties of accelerated pulses are explored experimentally in phantoms for two different schemes, in which the thickness of the excited limited slices is encoded either along the frequency or phase encoding directions of the excitation trajectory. The feasibility of application of parallel transmission for MR imaging in humans is analyzed based on several pilot experiments. Although the parallel transmission acceleration is demonstrated to work in some examples in the spinal cord and abdomen, the results also uncover a number of challenges. Nonetheless, the reduction of FOV in the phase encoding direction of the read‐out train along with the associated substantial shortening of the minimum echo train length and reduction of geometric distortions motivates further search for an advantageous use of the parallel transmit technology in EPI applications. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 153–173, 2015

Small Field-of-view single-shot EPI-DWI of the prostate: Evaluation of spatially-tailored two-dimensional radiofrequency excitation pulses

PurposeSpatially-tailored (RF) excitation pulses in echo-planar imaging (EPI), combined with a decreased FOV in the phase-encoding direction, enable a reduction of k-space acquisition lines, which shortens the echo train length (ETL) and reduces susceptibility artifacts. The purpose of this study was to evaluate the image quality of a zoomed EPI (z-EPI) sequence in diffusion-weighted imaging (DWI) of the prostate in comparison to a conventional single-shot EPI using single-channel (c-EPI1) and multi-channel (c-EPI2) RF excitation, with and without use of an endorectal coil. Materials and Methods33 consecutive patients (mean age: 61 +/- 9 years; mean PSA: 8.67±6.23 ng/ml) with examinations between 10/2012 and 02/2014 were analyzed in this retrospective study. In 26 of 33 patients the initial multiparametric (mp)-MRI was performed on a whole-body 3T scanner (Magnetom Trio, Siemens, Erlangen, Germany) using an endorectal coil (c (conventional)-EPI1). Zoomed-EPI (Z-EPI) examinations of these patients and a complete mp-MRI protocol including c-EPI2 of 7 additional patients were carried out on another 3T wb MR scanner with two-channel dynamic parallel transmit capability (Magnetom Skyra with TimTX TrueShape, Siemens). For z-EPI, the one-dimensional spatially selective RF excitation pulse was replaced by a two-dimensional RF pulse. Degree of image blur and susceptibility artifacts (0=not present to 3= non-diagnostic), maximum image distortion (mm), apparent diffusion coefficient (ADC) values, as well as overall scan preference were evaluated. SNR maps were generated to compare c-EPI2 and z-EPI. ResultsOverall image quality of z-EPI was preferred by both readers in all examinations with a single exception. Susceptibility artifacts were rated significantly lower on z-EPI compared to both other methods (z-EPI vs c-EPI1: p<0.01; z-EPI vs c-EPI2: p<0.01) as well as image blur (z-EPI vs c-EPI1: p<0.01; z-EPI vs c-EPI2: p<0.01). Image distortion was not statistically significantly reduced with z-EPI (z-EPI vs c-EPI1: p=0.12; z-EPI vs c-EPI2: p=0.42). Interobserver agreement for ratings of susceptibility artifacts, image blur and overall scan preference was good. SNR was higher for z-EPI than for c-EPI1 (n=1). ConclusionZ-EPI leads to significant improvements in image quality and artifacts as well as image blur reduction improving prostate DWI and enabling accurate fusion with conventional sequences. The improved fusion could lead to advantages in the field of MRI-guided biopsy suspicous lesions and performance of locally ablative procedures for prostate cancer.

High resolution three dimensional intracranial arterial wall imaging at 3 T using T1 weighted SPACE

ObjectiveTo study the effect of imaging parameters on the contrast of T1 weighted SPACE (Sampling Perfection with Application optimized Contrast using different angle Evolutions, a 3D TSE variant) at 3T for high resolution imaging of intracranial plaques before contrast and with post-gadolinium induced enhancement, and evaluate its relevance to patients with intracranial atherosclerosis. Materials and MethodsOptimized parameters giving good T1 contrast between intracranial vessel wall and cerebrospinal fluid within a specific scan time and reasonable coverage were found by simulation and validated in a healthy volunteer study. Based on the results, a clinical protocol covering the three major intracranial arteries (middle cerebral arteries, basilar arteries, and petrous internal carotid arteries) was developed. It was applied in ten patients diagnosed with intracranial arterial lesions. The accuracy of the technique in depicting vessel lumen was assessed by comparison to contrast enhanced MR angiography. The contrast enhancement ratios of the vessel wall/plaque identified were analyzed. ResultsSimulation and volunteer study showed that using T1 weighted SPACE, good T1 contrast between vessel wall and cerebrospinal fluid occurred at TR of around 1000ms using an echo train length of 21 within 10minutes at an isotropic spatial resolution of 0.5mm. In the 10 patients, 24 plaques were identified in the various segments of the intracranial arterial system of which eight appeared normal on MR angiography. Post-contrast enhancement ratio of these plaques varied from 0% up to 156%. ConclusionsT1 weighted SPACE provides good T1 contrast between intracranial arterial wall and cerebrospinal fluid with high resolution and good coverage within a clinically acceptable scan time. It can depict plaques pre- and post-contrast along the vessels surrounded by cerebrospinal fluid in the intracranial arterial system, and would be a useful tool in the clinical assessment of intracranial arterial diseases.

SU-E-I-62: Reduction of Susceptibility Artifacts by Increasing the Bandwidth (BW) and Echo Train Length (ETL)

Purpose: The aim of this present study is to increase bandwidth (BW) and echo train length (ETL) in Proton Density Turbo Spin Echo (PD TSE) sequences with and without fat saturation (FS) as well as in Turbo Inversion Recovery Magnitude sequences (TIRM) in order to assess whether these sequences are capable of reducing susceptibility artifacts. Methods: We compared 1) TIRM coronal (COR) with the same sequence with increased both BW and ETL 2) Conventional PD TSE sagittal (SAG) with FS with an increased BW 3) Conventional PD TSE SAG without FS with an increased BW 4) Conventional PD TSE SAG without FS with increased both BW and ETL. A quantitative analysis was performed to measure the extent of the susceptibility artifacts. Furthermore, a qualitative analysis was performed by two radiologists in order to evaluate the susceptibility artifacts, image distortion and fat suppression. The depiction of cartilage, menisci, muscles, tendons and bone marrow were also qualitatively analyzed. Results: The quantitative analysis found that the modified TIRM sequence is significantly superior to the conventional one regarding the extent of the susceptibility artifacts. In the qualitative analysis, the modified TIRM sequence was superior to the corresponding conventional one in eight characteristics out of ten that were analyzed. The modified PD TSE with FS was superior to the corresponding conventional one regarding the susceptibility artifacts, image distortion and depiction of bone marrow and cartilage while achieving effective fat saturation. The modified PD TSE sequence without FS with a high (H) BW was found to be superior corresponding to the conventional one in the case of cartilage. Conclusion: Consequently, TIRM sequence with an increased BW and ETL is proposed for producing images of high quality and modified PD TSE with H BW for smaller metals, especially when FS is used.

Flow void artifact mimicking aneurysm in the anterior communicating artery region on T1- and T2-weighted images.

We observed an unusual magnetic resonance imaging (MRI) artifact on T1- and T2-weighted sequences resembling an aneurysm in the region of anterior communicating artery (ACoA) in a child patient. A 6-year-old patient with neurofibromatosis underwent brain MRI for a follow-up investigation. Imaging was performed at 1.5 T scanner (Philips Gyroscan Intera, Best, Netherlands). The protocol consisted of axial and coronal T2-weighted turbo spin echo images [repetition time (TR) =4,616 ms, echo time (TE) =100 ms, slice thickness =5 mm, spacing between slices =1 mm, field of view (FOV) =260 mm × 182 mm, acquisition matrix: 228×150, echo train length =15], and 3D T1-weighted turbo field echo [TR =8.27 ms, TE =3.83 ms, flip angle =8°, FOV =256 mm × 192 mm, acquisition matrix: 116×93, Sensitivity Encoding (SENSE) acceleration factor (out-of-plane) =3]. Signal void near ACoA resembling an aneurysm was observed on axial and coronal T2-weighted and T1-weighted images ( Figure 1A-C ). The signal void was initially interpreted as an aneurysm based on its appearance on three sequences. Time-of-flight (TOF) angiography was requested and performed on a different scanner (1.5 T, Magnetom Aera, Siemens, Erlangen, Germany) together with conventional MRI. The second MRI showed no evidence of aneurysm ( Figure 1D-F ) indicating the findings in the first acquisition to be an artifact. What is interesting about this artifact is its appearance on three sequences (T2 axial, T2 coronal, and 3D T1) contrary to the acknowledged radiological rule that artifacts usually appear in one sequence. In practice, if a radiologist suspects an unseemly signal to be an artifact on an axial image, he/she checks with coronal/sagittal images and other sequences to confirm his interpretation. Since the signal void appeared on both turbo spin echo (T2-weighted) and turbo field echo (T1-weighted) sequences, it was independent of magnetic resonance (MR) sequence. We came to the conclusion that it is a flowvoid artifact in the region of ACoA where flow dynamics is complex (1). ACoA bridges two anterior cerebral arteries, separates the junction between A1 and A2 segments, and gives rise to a number of small branches. Due to its complex anatomy, flow direction changes at ACoA. This may cause disorderly and turbulent flow and formation of eddy currents. Turbulent flow causes dephasing of proton signal, resulting in signal loss artifacts on conventional MRI, mimicking aneurysms. False aneurysms in the ACoA due to flow effects were reported to occur on TOF MR angiograms (2,3). When evaluating such lesions on conventional MRI, the possibility of being a flow artifact should be kept in mind and the techniques such as TOF angiography should be exploited prior to invasive techniques such as catheter angiography (2).

MR T1ρ and T2 of meniscus six months and one year after acute anterior cruciate ligament injury

s / Osteoarthritis and Cartilage 23 (2015) A82eA416 A223 354 MR T1r AND T2 OF MENISCUS SIX MONTHS AND ONE YEAR AFTER ACUTE ANTERIOR CRUCIATE LIGAMENT INJURY A. Wang, F. Su, V. Pedoia, M. Kretzschmar, L. Nardo, T.M. Link, C.B. Ma, X. Li. Univ. of California, San Francisco, San Francisco, CA, USA Purpose: Acute anterior cruciate ligament (ACL) injury, a high-risk factor for post-traumatic osteoarthritis, is often concomitant with meniscal lesions and tears. In our previous cross-sectional study, we found that acute ACL injuries were associated with significantly elevated meniscal T1r and T2 values compared to healthy knees, even in menisci without morphological signs of damage. The goal of this longitudinal study was to evaluate intermediate-term changes in meniscal T1r and T2 quantification in ACL-injured patients six months and one year after ACL reconstruction and to compare these changes to baseline results. Methods: Using a 3T MR scanner, a closed cohort of 39 patients (age 1⁄4 29.4 ± 7.5 years; 16 females) with acute ACL injuries was scanned at an average of 8.4 ± 6.4 weeks post-injury and prior to ACL reconstruction. After ACL reconstruction, follow-up scans of ACL-injured knees were completed at six months and one year after baseline scan. Subjects were categorized by no lateral meniscectomy (n 1⁄4 32) and partial lateral meniscectomy (n 1⁄4 7). Effects of medial meniscectomy were not evaluated due to small sample size (n 1⁄4 2). Imaging protocol included sagittal T2-weighted 3D fast spin-echo (CUBE) images [repetition time (TR)/echo time (TE) 1⁄4 1500/25 ms, field of view (FOV)1⁄4 16 cm, matrix1⁄4 384 x 384, slice thickness1⁄4 1mm, echo train length 1⁄4 50, bandwidth 1⁄4 50 kHz, number of excitations 1⁄4 0.5] and sagittal 3D T1r and T2 quantification sequences [TR/TE 1⁄4 9 ms/min full, FOV1⁄4 14 cm, matrix1⁄4 256 x 128, slice thickness1⁄4 4mm, Views Per Segment 1⁄4 64, time of recovery 1⁄4 1.2 s, spin-lock frequency 1⁄4 500 Hz, ARC phase AF1⁄4 2. TSL1⁄4 0/10/40/80 ms for T1r, and preparation TE1⁄4 0/ 13.7/27.3/54.7 ms for T2]. Menisci were segmented using CUBE images into four sub-compartments: anterior horn of the lateral/medial meniscus (AHLAT/AHMED) and the posterior horn of the lateral/medial meniscus (PHLAT/PHMED). These regions of interest (ROI) were overlaid onto T1r and T2 maps, andmean T1r and T2 values were calculated for each ROI. Paired t-tests were performed when comparing the same cohort at different time points, and unpaired t-tests were performed when comparing patients who had a partial meniscectomy and patients who did not have a meniscectomy. An alpha of less than 0.05 was considered significant. Results: In ACL-injured knees without meniscectomy, T1r values increased significantly from baseline to six months in the AHLAT, AHMED, and PHMED (all p r > -0.46; p r > -0.30; p<0.005). Intraclass correlation coefficients ranged between 0.95-1.00 for the DCE-MRI variables and 0.80-1.00 for the static MRI variables. Conclusions: The results confirm an association between pain and synovitis assessed on both DCEand CE-MRI in obese patients with knee OA. The whole-knee synovitis score on CE-MRI and most of the DCE-MRI variables were also significantly associated with the remaining KOOS items. DCE-MRI analyses were robust and highly reproducible and have the potential to be used to further investigate the role of inflammation and perfusion in knee OA, in a similar way it has been used in inflammatory joint diseases.

Evaluation of MR issues for the latest standard brands of orthopedic metal implants: Plates and screws

PurposeThe study was performed to evaluate magnetic resonance (MR) issues for the latest standard brands of plates and screws used in orthopedic surgery at a 1.5-T MR system, including the safety and metallic artifacts. MethodsThe plates and screws (made of titanium alloy and stainless steel materials, according to the latest standard brands) were assessed for displacement in degrees, MRI-related heating and artifacts at a 1.5-T MR system. The displacement in degrees of the plates and screws was evaluated on an angel-measurement instrument at the entrance of the MR scanner. The MRI-related heating was assessed on a swine leg fixed with a plate by using a “worst-case” pulse sequence. A rectangular water phantom was designed to evaluate metallic artifacts of a screw on different sequences (T1/T2-weighted FSE, STIR, T2-FSE fat saturation, GRE, DWI) and then artifacts were evaluated on T2-weighted FSE sequence by modifying the scanning parameters including field of view (FOV), echo train length (ETL) and bandwidth to identify the influence of parameters on metallic artifacts. 15 volunteers with internal vertebral fixation (titanium alloy materials) were scanned with MR using axial and sagittal T2-FSE, sagittal T2-FSE fat suppression and STIR with conventional and optimized parameters, respectively. Then all images were graded by two experienced radiologists having the experience of more than 7 years under double-blind studies that is neither of them knew which was conventional parameter group and optimized parameter group. ResultsThe average deflection angle of titanium alloy and stainless steel implants were 4.3° and 7.7°, respectively, (less than 45°) which indicated that the magnetically induced force was less than the weight of the object. The deflection angle of the titanium alloy implants was less than the stainless steel one (t=9.69, P<0.001). The average temperature changes of titanium alloy before and after the scan was 0.48°C and stainless steel implants was 0.74°C, respectively, with the background temperature changes of 0.24°C. The water phantom test indicated that the DWI sequence produced largest artifacts, while FSE pulse sequence produced smallest artifacts. And T2-weighted FSE fat saturation sequence produced larger artifacts than STIR sequence. The influence of the scanning parameters on metallic artifacts was verified that metallic artifacts increased with longer echo train length and bigger FOV, while decreased with larger bandwidth. The interreader agreement was good or excellent for each set of images graded with Cohen's Kappa statistic. Image grading of axial and sagittal T2-FSE with optimized parameters were significantly superior to that with conventional parameters (grade, 3.3±0.5 vs 2.7±0.6, P=0.003; 3.2±0.4 vs 1.9±0.7, P=0.001) and image of STIR sequence received a better grade than T2-FSE FS sequence (grade, 3.4±0.5 vs 1.7±0.6, P<0.001). ConclusionsThe latest standard plates and screws used in orthopedic surgery do not pose an additional hazard or risk to patients undergoing MR imaging at 1.5-T or less. Though artifacts caused by them cannot be ignored because of their relatively large size, it is possible to be minimized by choosing appropriate pulse sequences and optimizing scanning parameters, such as FSE and STIR sequence with large bandwidth, small FOV and appropriate echo train length.

Optimizing isotropic three-dimensional fast spin-echo methods for imaging the knee.

To optimize acquisition parameters for three dimensional fast spin-echo (3D FSE) imaging of the knee. The knees of eight healthy volunteers were imaged in a 3 Tesla MRI scanner using an eight-channel knee coil. A total of 146 intermediate weighted isotropic resolution 3D FSE (3D-FSE-Cube)images with varied acquisition parameter settings were acquired with an additional reference scan performed for subjective image quality assessment. Images were graded for overall quality, parallel imaging artifact severity and blurring. Cartilage, muscle, and fluid signal-to-noise ratios and fluid-cartilage contrast-to-noise ratios were quantified by acquiring scans without radio frequency excitation and custom-reconstructing the k-space data.Mixed effects regression modeling was used to determine statistically significant effects of different parameters on image quality. Changes in receiver bandwidth, repetition time and echo train length significantly affected all measurements of image quality (P < 0.05). Reducing band width improved all metrics of image quality with the exception of blurring. Reader agreement was slight to fair for subjective metrics, but overall trends in quality ratings were apparent. We used a systematic approach to optimize 3D-FSE-Cube parameters for knee imaging. Image quality was overall improved using a receiver bandwidth of 631.25 kHz, and blurring increased with lower band width and longer echo trains.