Variable Refocusing Flip Angle Research Articles

Assessment of Lower Limb Artery Stent Placement with 3D Variable Refocusing Flip Angle Turbo Spin Echo : A Report on Two Cases

Assessment of Lower Limb Artery Stent Placement with 3D Variable Refocusing Flip Angle Turbo Spin Echo : A Report on Two Cases

3D phase-sensitive inversion recovery sequence for intracranial vertebrobasilar artery dissection

BackgroundT1-weighted 3D turbo spin echo (T1W-3D-TSE) sequences with variable refocusing flip angle are commonly used to diagnose intracranial vertebrobasilar artery dissection (iVAD). However, magnetic susceptibility artifacts of the cavernous sinus may cause loss of the basilar and vertebral arteries. This study investigated the effectiveness of a 3D phase-sensitive inversion recovery (3D-PSIR) sequence in reducing magnetic susceptibility artifacts in the cavernous sinus, and its imaging findings for iVAD. MethodsTwelve volunteers and eleven patients with iVAD were included. Magnetic resonance imaging (MRI) was performed using a 3.0-T MRI system. 3D-PSIR and T1W-3D-TSE sequences were used. Vessel wall defects and contrast-to-noise ratio (CNR) were evaluated. The MRI findings were visually evaluated. ResultsIn the 3D-PSIR images, one volunteer (8 %) had vessel wall defects, and five (42 %) had vessel wall defects (p = 0.046) in the T1W-3D-TSE images. CNR was higher in 3D-PSIR images for vessel wall-to-lumen, whereas it was higher in T1W-3D-TSE images for vessel wall-to-CSF (p < 0.001). Visual evaluation revealed similar MRI findings between the two sequences. ConclusionsThe 3D-PSIR sequence may be able to improve the vessel wall defects and achieve MRI findings comparable to those of the T1W-3D-TSE sequence in iVAD. The 3D-PSIR sequence can be a useful tool for the imaging-based diagnosis of iVAD.

Three-dimensional vessel wall imaging with 1.5-T MRI to visualize invisible occluded cerebral artery.

Endovascular thrombectomy (EVT) is performed for acute ischemic stroke (AIS) caused by large vessel occlusion; therefore, preoperative visualization of the occluded invisible vessel course reduces complications and ensures success. Three-dimensional (3D) proton density-weighted (PDW) vessel wall imaging (VWI) using variable refocusing flip angle pulse-turbo spin-echo sequences (VRFA-TSE) with 3.0-T magnetic resonance imaging (MRI) can provide this information. To assess the effectiveness of 3D PDW-VWI using 1.5-T MRI without VRFA function. Five consecutive patients with AIS caused by large vessel occlusion underwent EVT in our institute. VWI with 1.5-T MRI using 3D PDW-fast spin echo (FSE) technique was added to conventional brain imaging. PDW-FSE was successfully performed in all cases. 3D PDW-FSE was useful to visualize both the anterior and posterior circulations by clearly revealing invisible vessels but could not demonstrate the length and size of the clot in all five cases. 3D PDW-FSE with 1.5-T MRI without VRFA could clearly depict the course of the invisible occluded artery and might support favorable outcomes after EVT in patients with AIS.

The Influence of Echo Train Duration on Heavily T2-weighted-dimensional MR Cholangiopancreatography Using Turbo Spin-echo Technique: A Phantom Study

Magnetic resonance cholangiopancreatography (MRCP) is a valuable non-invasive technique that depicts bile or pancreatic juice as hyperintense in heavily T2-weighted images. Data acquisition in the three-dimensional multi-slice MRCP method is acquired with respiratory triggered. Echo train duration (ETD) is the data acquisition time every breath is in inverse proportion to total acquisition time, and has influence of image contrast and spatial resolution in turbo spin echo (TSE) imaging. Therefore, the effects of image contrast and spatial resolution of three-dimensional heavily T2-weighted variable refocusing flip angle TSE images on ETD in fundamental and clinical settings were measured using a phantom. No significant difference was detected with regard to image contrasts. Increasing ETD reduced spatial resolution, but no significant difference was detected regarding visual evaluation in the fundamental setting. On the other hand, in some of the clinical settings, increasing ETD with phase partial Fourier (PPF) reduced spatial resolution. The study result indicates that changing ETD fitting respiratory state of individual examinee without PPF is useful for optimized acquisition time without sacrificing image contrast and spatial resolution.

Three-dimensional vessel wall MRI to characterize thrombus prior to endovascular thrombectomy for large vessel occlusion stroke.

Endovascular thrombectomy (EVT) for acute ischemic stroke (AIS) caused by large vessel occlusion requires rapid and reliable imaging of the vessel course including the clot to reduce complications and ensure success. However, no method to acquire this information has been established. Six consecutive patients with AIS caused by large vessel occlusion underwent EVT in our institute. High-resolution vessel wall MRI was performed using three-dimensional (3D) variable refocusing flip angle pulse and turbo spin-echo sequences (VRFA-TSE) with the volume isotropic turbo spin-echo acquisition (VISTA) technique. This study evaluated the effectiveness of 3D proton density-weighted (PDW) VRFA-TSE (called PDW-VISTA) compared with T2-weighted (T2W) VRFA-TSE (called T2W-VISTA) to demonstrate the cerebral vessels including the occluded invisible lesion. PDW-VISTA and T2W-VISTA were successfully performed in all cases. PDW-VISTA was more useful to visualize the anterior circulation than T2W-VISTA by clearly revealing invisible vessels, whereas PDW-VISTA and T2W-VISTA had similar findings in the posterior circulation. The vessel courses shown by 3D PDW-VISTA imaging before treatment and digital subtraction angiography after treatment showed good agreement in all cases. Furthermore, 3D PDW-VISTA imaging demonstrated the length and size of the clot. PDW-VISTA imaging was found to more clearly depict the cerebral vessels including occluded lesion than T2W-VISTA imaging. Findings of thrombus size and length were important for correctly placing the stent retriever and securing safety during the procedure.

Three-dimensional multicontrast blood imaging with a single acquisition: Simultaneous non-contrast-enhanced MRA and vessel wall imaging in the thoracic aorta.

To evaluate MRA and vessel wall imaging (VWI) image quality in the thoracic aorta using a novel method named BRIDGE (bright and dark blood images with multishot gradient-echo EPI). The BRIDGE method consists of 3D multishot gradient-echo EPI acquisition using pulse gating, navigator gating, and magnetization preparation with a T2 -preparation pulse and a nonselective inversion-recovery pulse. The BRIDGE and conventional methods (noncontrast MRA based on 3D turbo-field-echo [TFE] and VWI based on 3D turbo spin echo with variable refocusing flip angle [VRFA-TSE]) were performed in 10 healthy volunteers and 10 patients. The SNR, contrast-to-noise ratio (CNR), and sharpness in the thoracic aorta were compared for MRA evaluation. The values of SNRlumen , SNRwall , CNRwall-lumen , contrast ratio (CR)lumen-muscle , coefficient of variation, sharpness, lumen area, and wall area in the thoracic aorta were compared for VWI evaluation. Two radiologists independently performed qualitative image-analysis assessments. When MRA and VWI were acquired, the acquisition time was 26.6% to 27.8% shorter with BRIDGE than the conventional method. In the MRA evaluation, BRIDGE and TFE methods were comparable. In the VWI evaluation, BRIDGE was superior to the VRFA-TSE method in blood suppression and evaluation of the ascending aorta. Because the blood signal suppression of BRIDGE is based on the T1 value of blood, the blood signal can be suppressed more uniformly than with the VRFA-TSE method, regardless of age, blood flow velocity, or vascular anatomy. The BRIDGE method can provide both MRA, to assess vascular anatomy and luminal changes, and VWI, to assess the vessel wall and detect vulnerable plaques, in a single scan.

Development and Evaluation of Deep Learning-Accelerated Single-Breath-Hold Abdominal HASTE at 3 T Using Variable Refocusing Flip Angles.

Deep learning (DL) reconstruction enables substantial acceleration of image acquisition while maintaining diagnostic image quality. The aims of this study were to overcome the drawback of specific absorption rate (SAR)-related limitations at 3 T and to develop a DL-accelerated single-breath-hold half-Fourier acquisition single-shot turbo spin echo (HASTE) sequence for 2-dimesional T2-weighted fat-suppressed magnetic resonance imaging of the abdomen at 3 T using a variable flip angle (FA) evolution for the refocusing radiofrequency pulses, as well as to evaluate its feasibility and image quality in comparison to state-of-the-art T2-weighted fat-suppressed imaging technique (BLADE). First, a suitable FA evolution with low cardiac motion-related signal loss (CRSL) and low SAR was determined through a prospective volunteer study with 11 participants. Image quality and diagnostic confidence with 5 different FA evolutions of a HASTEDL were assessed to identify the most suitable FA evolution. Second, the identified FA evolution was implemented clinically and evaluated in 51 patients undergoing a clinically indicated liver magnetic resonance imaging at 3 T. Two radiologists assessed the HASTEDL and standard sequences regarding overall image quality, noise, contrast, sharpness, artifacts, CRSL, and diagnostic confidence using a Likert scale ranging from 1 to 4, with 4 being the best. Comparative analyses were conducted to assess the differences between HASTEDL (acquisition time, 21 seconds; single breath-hold) and the routinely used T2-weighted BLADE sequence (acquisition time, 4 minutes; respiratory triggering). From the volunteer study, the FA evolution characterized by the control points 130-90-110-130 degrees (HASTEDL) was identified as optimal among the 5 evolutions evaluated and was implemented in our clinical protocol. In all 51 patients, HASTEDL was successfully acquired at 3 T and showed excellent image quality (median, 4; interquartile range, 3-4). Although BLADE was rated significantly higher for overall image quality, noise, contrast, sharpness, artifacts, CRSL, and diagnostic confidence than HASTEDL, no differences were found concerning the number (n = 102) and measured diameter of the detected hepatic lesions between the 2 sequences BLADE and HASTEDL. The proposed single-breath-hold abdominal HASTEDL with variable refocusing FAs is feasible at 3 T within SAR limits and yields high image quality and diagnostic confidence as compared with a standard T2-weighted acquisition technique, at a 10th of the acquisition time.

Pseudo-Enhancement in Intracranial Aneurysms on Black-Blood MRI: Effects of Flow Rate, Spatial Resolution, and Additional Flow Suppression.

Vessel-wall enhancement (VWE) on black-blood MRI (BB MRI) has been proposed as an imaging marker for a higher risk of rupture and associated with wall inflammation. Whether VWE is causally linked to inflammation or rather induced by flow phenomena has been a subject of debate. To study the effects of slow flow, spatial resolution, and motion-sensitized driven equilibrium (MSDE) preparation on signal intensities in BB MRI of patient-specific aneurysm flow models. Prospective. Aneurysm flow models based on 3D rotational angiography datasets of three patients with intracranial aneurysms were 3D printed and perfused at two different flow rates, with and without Gd-containing contrast agent. Variable refocusing flip angle 3D fast-spin echo sequence at 3 T with and without MSDE with three voxel sizes ((0.5 mm)3 , (0.7 mm)3 , and (0.9 mm)3 ); time-resolved with phase-contrast velocity-encoding 3D spoiled gradient echo sequence (4D flow MRI). Three independent observers performed a qualitative visual assessment of flow patterns and signal enhancement. Quantitative analysis included voxel-wise evaluation of signal intensities and magnitude velocity distributions in the aneurysm. Kruskal-Wallis test, potential regressions. A hyperintense signal in the lumen and adjacent to the aneurysm walls on BB MRI was colocalized with slow flow. Signal intensities increased by a factor of 2.56 ± 0.68 (P < 0.01) after administering Gd contrast. After Gd contrast administration, the signal was suppressed most in conjunction with high flows and with MSDE (2.41 ± 2.07 for slow flow without MSDE, and 0.87 ± 0.99 for high flow with MSDE). A clear result was not achieved by modifying the spatial resolution . Slow-flow phenomena contribute substantially to aneurysm enhancement and vary with MRI parameters. This should be considered in the clinical setting when assessing VWE in patients with an unruptured aneurysm. 2 TECHNICAL EFFICACY: Stage 2.

Variable Refocusing Flip Angle Single-Shot Imaging for Sedation-Free Fast Brain MRI.

Conventional single-shot FSE commonly used for fast MRI may be suboptimal for brain evaluation due to poor image contrast, SNR, or image blurring. We investigated the clinical performance of variable refocusing flip angle single-shot FSE, a variation of single-shot FSE with lower radiofrequency energy deposition and potentially faster acquisition time, as an alternative approach to fast brain MR imaging. We retrospectively compared half-Fourier single-shot FSE with half- and full-Fourier variable refocusing flip angle single-shot FSE in 30 children. Three readers reviewed images for motion artifacts, image sharpness at the brain-fluid interface, and image sharpness/tissue contrast at gray-white differentiation on a modified 5-point Likert scale. Two readers also evaluated full-Fourier variable refocusing flip angle single-shot FSE against T2-FSE for brain lesion detectability in 38 children. Variable refocusing flip angle single-shot FSE sequences showed more motion artifacts (P < .001). Variable refocusing flip angle single-shot FSE sequences scored higher regarding image sharpness at brain-fluid interfaces (P < .001) and gray-white differentiation (P < .001). Acquisition times for half- and full-Fourier variable refocusing flip angle single-shot FSE were faster than for single-shot FSE (P < .001) with a 53% and 47% reduction, respectively. Intermodality agreement between full-Fourier variable refocusing flip angle single-shot FSE and T2-FSE findings was near-perfect (κ = 0.90, κ = 0.95), with an 8% discordance rate for ground truth lesion detection. Variable refocusing flip angle single-shot FSE achieved 2× faster scan times than single-shot FSE with improved image sharpness at brain-fluid interfaces and gray-white differentiation. Such improvements are likely attributed to a combination of improved contrast, spatial resolution, SNR, and reduced T2-decay associated with blurring. While variable refocusing flip angle single-shot FSE may be a useful alternative to single-shot FSE and, potentially, T2-FSE when faster scan times are desired, motion artifacts were more common in variable refocusing flip angle single-shot FSE, and, thus, they remain an important consideration before clinical implementation.

An efficient 3D stack-of-stars turbo spin echo pulse sequence for simultaneous T2-weighted imaging and T2 mapping.

To design a pulse sequence for efficient 3D T2-weighted imaging and T2 mapping. A stack-of-stars turbo spin echo pulse sequence with variable refocusing flip angles and a flexible pseudorandom view ordering is proposed for simultaneous T2-weighted imaging and T2 mapping. An analytical framework is introduced for the selection of refocusing flip angles to maximize relative tissue contrast while minimizing T2 estimation errors and maintaining low specific absorption rate. Images at different echo times are generated using a subspace constrained iterative reconstruction algorithm. T2 maps are obtained by modeling the signal evolution using the extended phase graph model. The technique is evaluated using phantoms and demonstrated in vivo for brain, knee, and carotid imaging. Numerical simulations demonstrate an improved point spread function with the proposed pseudorandom view ordering compared to golden angle view ordering. Phantom experiments show that T2 values estimated from the stack-of-stars turbo spin echo pulse sequence with variable refocusing flip angles have good concordance with spin echo reference values. In vivo results show the proposed pulse sequence can generate qualitatively comparable T2-weighted images as conventional Cartesian 3D SPACE in addition to simultaneously generating 3D T2 maps. The proposed stack-of-stars turbo spin echo pulse sequence with pseudorandom view ordering and variable refocusing flip angles allows high resolution isotropic T2 mapping in clinically acceptable scan times. The optimization framework for the selection of refocusing flip angles improves T2 estimation accuracy while generating T2-weighted contrast comparable to conventional Cartesian imaging.

Optimization of Fat Suppression Technique and Imaging Parameters for MR Neurography Using 3D Turbo Spin Echo with Variable Refocusing Flip Angle at 3.0 T: Visualization of Brachial Plexus

Magnetic resonance neurography (MRN) has been used to evaluate abnormal conditions of entire nerves and nerve bundles. A fat-suppressed 3D turbo spin echo (TSE) sequence is one of the imaging techniques for MRN, which has been widely adopted at 1.5 T. However, MRN of the brachial plexus using a 3D TSE sequence with short-term inversion recovery (STIR) reduces the effect of fat suppression at 3.0 T. Moreover, the use of spectral pre-saturation with inversion recovery (SPIR) does not result in uniform fat suppression due to the inhomogeneity of the static magnetic field. On the other hand, it is well known that the visibility of the brachial plexus using a 3D TSE sequence greatly changes with the equivalent echo time (TEequiv). Therefore, we optimized the fat suppression technique and TEequiv so that the 3D TSE sequence, using a combination of STIR with SPIR and an optimal TEequiv (from 73 to 110 ms), achieved better visualization of the brachial plexus without residual fat.

Clinical Utility of a Novel Ultrafast T2-Weighted Sequence for Spine Imaging.

TSE-based T2-weighted imaging of the spine has long scan times. This work proposes a fast imaging protocol using variable refocusing flip angles, optimized for blurring and specific absorption rate. A variable refocusing flip angle echo-train was optimized for the spine to improve the point spread function and minimize the specific absorption rate, yielding images with improved spatial resolution and SNR compared with the constant flip angle sequence. Data were acquired from 51 patients (35 lumbar, 16 whole-spine) using conventional TSE and the proposed sequence, with a single-shot variant for whole-spine. Noninferiority analysis was performed to evaluate the efficiency of the proposed technique. The proposed multishot sequence resulted in a 2× shorter scan time with a >1.5× lower specific absorption rate. The variable flip angle sequence was noninferior to the conventional TSE (P < .025) for all image-quality and clinical criteria except signal-to-noise ratio for the lumbar spine protocol. However, mean image scores for the TSE-variable refocusing flip angle were ≥4.3 for all criteria, and concordance analysis showed high agreement (>90%) with the TSE, indicating clinical equivalence. The single-shot sequence resulted in 4× shorter whole-spine scans, and image scores were ≥4.4 for all criteria, attesting to its clinical utility. We present a fast T2-weighted spine protocol using variable refocusing flip angles, including a single-shot variant. The sequences have better point spread function behavior than their constant flip angle counterparts and, being faster, should be less sensitive to patient motion, often seen in the longer TSE scans.

Retrospective multi-phase non-contrast-enhanced magnetic resonance angiography (ROMANCE MRA) for robust angiogram separation in the presence of cardiac arrhythmia.

PurposeTo develop a novel, retrospective multi‐phase non‐contrast‐enhanced MRA (ROMANCE MRA) in a single acquisition for robust angiogram separation even in the presence of cardiac arrhythmia.MethodsIn the proposed ROMANCE MRA, data were continuously acquired over all cardiac phases using retrospective, multi‐phase flow‐sensitive single‐slab 3D fast spin echo (FSE) with variable refocusing flip angles, while an external pulse oximeter was in sync with pulse repetitions in FSE to record real‐time information on cardiac cycles. Data were then sorted into k‐bin space using the real‐time cardiac information. Angiograms were reconstructed directly from k‐bin space by solving a constrained optimization problem with both subtraction‐induced sparsity and low rank priors. Peripheral MRA was performed in normal volunteers with/without caffeine consumption and a volunteer with cardiac arrhythmia using conventional fresh blood imaging (FBI) and the proposed ROMANCE MRA for comparison.ResultsThe proposed ROMANCE MRA shows superior performance in accurately delineating both major and small vessel branches with robust background suppression if compared with conventional FBI. Even in the presence of irregular heartbeats, the proposed method exhibits clear depiction of angiograms over conventional methods within clinically reasonable imaging time.ConclusionWe successfully demonstrated the feasibility of the proposed ROMANCE MRA in generating robust angiograms with background suppression.

Controlling T2 blurring in 3D RARE arterial spin labeling acquisition through optimal combination of variable flip angles and k-space filtering.

To improve the SNR efficiency and reduce the T2 blurring of 3D rapid acquisition with relaxation enhancement stack-of-spiral arterial spin labeling imaging by using variable refocusing flip angles and k-space filtering. An algorithm for determining the optimal combination of variable flip angles and filtering correction is proposed. The flip angles are designed using extended phase graph physical simulations in an analytical and global optimization framework, with an optional constraint on deposited power. Optimal designs for correcting to Hann and Fermi window functions were compared with conventional constant amplitude or variable flip angle only designs on 6 volunteers. With the Fermi window correction, the proposed optimal designs provided 39.8 and 27.3% higher SNR (P < .05) than conventional constant amplitude and variable flip angle designs. Even when power deposition was limited to 50% of the constant amplitude design, the proposed method outperformed the SNR (P < .05) of these 2 conventional approaches by 32.5 and 20.7%. The sharpness and the contrast between gray and white matter were improved with the k-space filtering correction for all of the flip angle designs. The improvements were moderate for the Hann window correction. This work demonstrates that variable flip angles can be derived as the output of an optimization problem. The combined design of variable flip angle and k-space filtering provided superior SNR to designs primarily emphasizing either approach singly.

Variable refocusing flip angle single-shot fast spin echo imaging of liver lesions: increased speed and lesion contrast.

To evaluate acquisition time and clinical image quality of a variable refocusing flip angle (vrf) single-shot fast spin echo (SSFSE) sequence in comparison with a conventional SSFSE sequence for imaging of liver lesions in patients undergoing whole-body PET/MRI for oncologic staging. A vrfSSFSE sequence was acquired in 43 patients with known pancreatic neuroendocrine tumors undergoing 68Ga-DOTA-TOC PET on a simultaneous time-of-flight 3.0T PET/MRI. Liver lesions≥1.5cm with radionucleotide uptake were analyzed. Contrast-to-noise ratios (CNRs) were measured, and four blinded radiologists assessed overall image quality. Differences in repetition time and CNR were assessed using a paired Student's t test with p<0.05 considered statistically significant. Inter-reader variability was assessed with Fleiss' kappa statistic. 53 eligible lesions in 27 patients were included for analysis. vrfSSFSE demonstrated higher mean lesion CNR compared to SSFSE (9.9±4.1 vs. 6.7±4.1, p<0.001). Mean repetition time (TR) was 679±97ms for the vrfSSFSE sequence compared to 1139±106ms for SSFSE (p<0.0001), corresponding to a 1.7-fold decrease in acquisition time. Overall quality of liver lesion and common bile duct images with the vrfSSFSE sequence was graded as superior than or equivalent to the SSFSE sequence for 59% and 67% of patients, respectively. Compared to conventional SSFSE, vrfSSFSE resulted in improved lesion contrast on simultaneous PET/MRI in patients with liver metastases. Due to decreased SAR demands, vrfSSFSE significantly decreased TR, allowing coverage of the entire liver in a single twenty-second breath hold. This may have important clinical implications in the setting of PET/MRI, where scan time is limited by the necessity of whole-body image acquisition in addition to bed specific imaging.

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.

Increased Speed and Image Quality for Pelvic Single-Shot Fast Spin-Echo Imaging with Variable Refocusing Flip Angles and Full-Fourier Acquisition.

Purpose To assess image quality and speed improvements for single-shot fast spin-echo (SSFSE) with variable refocusing flip angles and full-Fourier acquisition (vrfSSFSE) pelvic imaging via a prospective trial performed in the context of uterine leiomyoma evaluation. Materials and Methods Institutional review board approval and informed consent were obtained. vrfSSFSE and conventional SSFSE sagittal and coronal oblique acquisitions were performed in 54 consecutive female patients referred for 3-T magnetic resonance (MR) evaluation of known or suspected uterine leiomyomas. Two radiologists who were blinded to the image acquisition technique semiquantitatively scored images on a scale from -2 to 2 for noise, image contrast, sharpness, artifacts, and perceived ability to evaluate uterine, ovarian, and musculoskeletal structures. The null hypothesis of no significant difference between pulse sequences was assessed with a Wilcoxon signed rank test by using a Holm-Bonferroni correction for multiple comparisons. Results Because of reductions in specific absorption rate, vrfSSFSE imaging demonstrated significantly increased speed (more than twofold, P < .0001), with mean repetition times compared with conventional SSFSE imaging decreasing from 1358 to 613 msec for sagittal acquisitions and from 1494 to 621 msec for coronal oblique acquisitions. Almost all assessed image quality and perceived diagnostic capability parameters were significantly improved with vrfSSFSE imaging. These improvements included noise, sharpness, and ability to evaluate the junctional zone, myometrium, and musculoskeletal structures for both sagittal acquisitions (mean values of 0.56, 0.63, 0.42, 0.56, and 0.80, respectively; all P values < .0001) and coronal oblique acquisitions (mean values of 0.81, 1.09, 0.65, 0.93, and 1.12, respectively; all P values < .0001). For evaluation of artifacts, there was an insufficient number of cases with differences to allow statistical testing. Conclusion Compared with conventional SSFSE acquisition, vrfSSFSE acquisition increases 3-T imaging speed via reduced specific absorption rate and leads to significant improvements in perceived image quality and perceived diagnostic capability when evaluating pelvic structures. © RSNA, 2016 Online supplemental material is available for this article.

Fresh Blood Imaging using variable TR and variable refocusing flip angle for non-contrast peripheral MR angiography at 3T: a 7-Minute iliac to calf station run-offs scan

Fresh Blood Imaging using variable TR and variable refocusing flip angle for non-contrast peripheral MR angiography at 3T: a 7-Minute iliac to calf station run-offs scan

Usefulness of R2* maps generated by iterative decomposition of water and fat with echo asymmetry and least-squares estimation quantitation sequence for cerebral artery dissection

Acute intramural hematoma resulting from cerebral artery dissection is usually visualized as a region of intermediate signal intensity on T1-weighted images (WI). This often causes problems with distinguishing acute atheromatous lesions from surrounding parenchyma and dissection. The present study aimed to determine whether or not R2* maps generated by the iterative decomposition of water and fat with echo asymmetry and least-squares estimation quantitation sequence (IDEAL IQ) can distinguish cerebral artery dissection more effectively than three-dimensional variable refocusing flip angle TSE T1WI (T1-CUBE) and T2*WI. We reviewed data from nine patients with arterial dissection who were assessed by MR images including R2* maps, T2*WI, T1-CUBE, and 3D time-of-flight (TOF)-MRA. We visually assessed intramural hematomas in each patient as positive (clearly visible susceptibility effect reflecting intramural hematoma as hyperintensity on R2* map and hypointensity on T2*WI), negative (absent intramural hematoma), equivocal (difficult to distinguish between intramural hematoma and other paramagnetic substances such as veins, vessel wall calcification, or hemorrhage) and not evaluable (difficult to determine intramural hematoma due to susceptibility artifacts arising from skull base). Eight of nine patients were assessed during the acute phase. Lesions in all eight patients were positive for intramural hematoma corresponding to dissection sites on R2* maps, while two lesions were positive on T2*WI and three lesions showed high-intensity on T1-CUBE reflected intramural hematoma during the acute phase. R2* maps generated using IDEAL IQ can detect acute intramural hematoma associated with cerebral artery dissection more effectively than T2*WI and earlier than T1-CUBE.

T2 Relaxation time quantitation differs between pulse sequences in articular cartilage.

To compare T2 relaxation time measurements between MR pulse sequences at 3 Tesla in agar phantoms and in vivo patellar, femoral, and tibial articular cartilage. T2 relaxation times were quantified in phantoms and knee articular cartilage of eight healthy individuals using a single echo spin echo (SE) as a reference standard and five other pulse sequences: multi-echo SE (MESE), fast SE (2D-FSE), magnetization-prepared spoiled gradient echo (3D-MAPSS), three-dimensional (3D) 3D-FSE with variable refocusing flip angle schedules (3D vfl-FSE), and quantitative double echo steady state (qDESS). Cartilage was manually segmented and average regional T2 relaxation times were obtained for each sequence. A regression analysis was carried out between each sequence and the reference standard, and root-mean-square error (RMSE) was calculated. Phantom measurements from all sequences demonstrated strong fits (R(2) > 0.8; P < 0.05). For in vivo cartilage measurements, R(2) values, slope, and RMSE were: MESE: 0.25/0.42/5.0 ms, 2D-FSE: 0.64/1.31/9.3 ms, 3D-MAPSS: 0.51/0.66/3.8 ms, 3D vfl-FSE: 0.30/0.414.2 ms, qDESS: 0.60/0.90/4.6 ms. 2D-FSE, qDESS, and 3D-MAPSS demonstrated the best fits with SE measurements as well as the greatest dynamic ranges. The 3D-MAPSS, 3D vfl-FSE, and qDESS demonstrated the closest average measurements to SE. Discrepancies in T2 relaxation time quantitation between sequences suggest that care should be taken when comparing results between studies.