Gradient Echo Pulse Sequence Research Articles

Comparison of Free-Breathing 3D Phase-Resolved Functional Lung (PREFUL) MRI With Dynamic 19F Ventilation MRI in Patients With Obstructive Lung Disease and Healthy Volunteers.

Non-contrast-enhanced 1H magnetic resonance imaging (MRI) with full lung coverage shows promise for assessment of regional lung ventilation but a comparison with direct ventilation measurement using 19F MRI is lacking. To compare ventilation parameters calculated using 3D phase-resolved functional lung (PREFUL) MRI with 19F MRI. Prospective. Fifteen patients with asthma, 14 patients with chronic obstructive lung disease, and 13 healthy volunteers. A 3D gradient-echo pulse sequence with golden-angle increment and stack-of-stars encoding at 1.5 T. All participants underwent 3D PREFUL MRI and 19F MRI. For 3D PREFUL, static regional ventilation (RVent) and dynamic flow-volume cross-correlation metric (FVL-CM) were calculated. For both parameters, ventilation defect percentage (VDP) values and ventilation defect (VD) maps (including a combination of both parameters [VDPCombined]) were determined. For 19F MRI, images from eight consecutive breaths under volume-controlled inhalation of perfluoropropane were acquired. Time-to-fill (TTF) and wash-in (WI) parameters were extracted. For all 19F parameters, a VD map was generated and the corresponding VDP values were calculated. For all parameters, the relationship between the two techniques was assessed using a Spearman correlation (r). Differences between VDP values were compared using Bland-Altman analysis. For regional comparison of VD maps, spatial overlap and Sørensen-Dice coefficients were computed. 3D PREFUL VDP values were significantly correlated to VDP measures by 19F (r range: 0.59-0.70). For VDPRVent, no significant bias was observed with VDP of the third and fourth breath (bias range = -6.8:7.7%, P range = 0.25:0.30). For VDPFVL-CM, no significant bias was found with VDP values of fourth-eighth breaths (bias range = -2.0:12.5%, P range = 0.12:0.75). The overall spatial overlap of all VD maps increased with each breath, ranging from 61% to 81%, stabilizing at the fourth breath. 3D PREFUL MRI parameters showed moderate to strong correlation with 19F MRI. Depending on the 3D PREFUL VD map, the best regional agreement was found to 19F VD maps of third-fifth breath. 3 TECHNICAL EFFICACY: Stage 2.

In-vitro Detection of Intramammary-like Macrocalcifications Using Susceptibility-weighted MR Imaging Techniques at 1.5T.

The aim of our study was to investigate the technical accuracy of susceptibility-weighted imaging (SWI) and quantitative susceptibility mapping (QSM) created to detect intramammary-like calcifications depending on different TEs, volume, and type of calcification samples at 1.5T. Jello-embedded particles of blackboard chalk and ostrich eggshell ranging in size from 4 to 25 mm2 were used to simulate intramammary calcifications after testing different base substances and calcifications for their suitability to be used in breast phantoms. Breast phantoms were systematically examined using CT and an optimized 3D multi-echo gradient echo pulse sequence with following parameters: TR/TE, 22/1.88-15.52 ms in 1.24 ms increments; reconstructed voxel, 0.5 × 0.5 × 1.1 mm3; receiver bandwidth, 1120 Hz/Px; flip angle, 15°; integrated parallel imaging technique with a GeneRalized Autocalibrating Partial Parallel Acquisition (GRAPPA) factor of 2/24; and a total acquisition time of 3:00 min. A qualitative evaluation of the dependence of the visualization of calcification samples on volume and TE value was followed by a calculation of the SNR, the contrast-to-noise ratio (CNR) and the creation of SWI and QSM in the sense of a (semi)-quantitative analysis of the images. Jello proved to be a suitable base substance for preparing breast phantoms for SW MRI. Blackboard chalk and ostrich eggshell proved to be suitable for mimicking intramammary-like calcifications. The decrease in the median SNR of the blackboard chalk samples was significantly higher than the corresponding value of the ostrich eggshell samples over the entire TE range (47.5 to 17.0 vs. 16.0 to 6.56, P < 0.0001). The increase in the median CNR of the blackboard chalk samples was significantly higher than the corresponding value of the ostrich eggshell samples over the entire TE range (2.46 to 35.0 vs. 20.2 to 36.8, P = 0.007). With increasing TE value, the signal void volume of the calcification particle increases in the magnitude images as well as in SWI and QSM. Due to the blooming effect, the median gradients of the TE-based changes in signal void volumes were higher in SWI than in magnitude images and in QSM, regardless of the type of calcification particle examined. The maximum magnetic susceptibility of ostrich eggshell samples varied in a TE range of 1.88 to 15.52 ms from -7.2 to -2.51 ppm and that of blackboard chalk from -2.0 to -1.7 ppm. Compared to the manually measured volumes of the calcification particles, both MR-based measurements and CT examinations overestimated the actual sample size. The (non)-significant overestimation in the MRI-data is dependent on the set TE. The CT-based hyperdense volumes were overestimated compared to the corresponding manually measured sample volumes in a range of 109.8%-315.2% for ostrich eggshell samples (P = 0.016) and in a range of 39.9%-156.4% for blackboard chalk samples (P = 0.69). Our systematic in-vitro investigation of magnitude images, SWI, and QSM revealed that various set TE values, different volumes, and compositions of calcifications have a significant impact on visualizing intramammary(-like) calcifications.

Collaborative Learning for Annotation-Efficient Volumetric MR Image Segmentation.

Deep learning has presented great potential in accurate MR image segmentation when enough labeled data are provided for network optimization. However, manually annotating three-dimensional (3D) MR images is tedious and time-consuming, requiring experts with rich domain knowledge and experience. To build a deep learning method exploring sparse annotations, namely only a single two-dimensional slice label for each 3D training MR image. Retrospective. Three-dimensional MR images of 150 subjects from two publicly available datasets were included. Among them, 50 (1377 image slices) are for prostate segmentation. The other 100 (8800 image slices) are for left atrium segmentation. Five-fold cross-validation experiments were carried out utilizing the first dataset. For the second dataset, 80 subjects were used for training and 20 were used for testing. 1.5 T and 3.0 T; axial T2-weighted and late gadolinium-enhanced, 3D respiratory navigated, inversion recovery prepared gradient echo pulse sequence. A collaborative learning method by integrating the strengths of semi-supervised and self-supervised learning schemes was developed. The method was trained using labeled central slices and unlabeled noncentral slices. Segmentation performance on testing set was reported quantitatively and qualitatively. Quantitative evaluation metrics including boundary intersection-over-union (B-IoU), Dice similarity coefficient, average symmetric surface distance, and relative absolute volume difference were calculated. Paired t test was performed, and P < 0.05 was considered statistically significant. Compared to fully supervised training with only the labeled central slice, mean teacher, uncertainty-aware mean teacher, deep co-training, interpolation consistency training (ICT), and ambiguity-consensus mean teacher, the proposed method achieved a substantial improvement in segmentation accuracy, increasing the mean B-IoU significantly by more than 10.0% for prostate segmentation (proposed method B-IoU: 70.3% ± 7.6% vs. ICT B-IoU: 60.3% ± 11.2%) and by more than 6.0% for left atrium segmentation (proposed method B-IoU: 66.1% ± 6.8% vs. ICT B-IoU: 60.1% ± 7.1%). A collaborative learning method trained using sparse annotations can segment prostate and left atrium with high accuracy. 0 TECHNICAL EFFICACY: Stage 1.

MR Assessed Changes of Renal Sinus Fat in Response to Glucose Regulation in West European and South Asian Patients With Type 2 Diabetes.

Ethnic differences in the progression and outcome of diabetic kidney disease (DKD) remain to be elucidated. MRI-quantified renal sinus fat volume could be a potential biomarker to help investigate the changes of DKD risk in response to glucose regulation. To evaluate whether the effect of glucose-lowering treatment on renal sinus fat volume differed in West Europeans (WE) compared to South Asians (SA), and whether ethnic-related difference exists regarding the effect of liraglutide on renal sinus fat. Retrospective. Ninety-three patients with type 2 diabetes mellitus, including 47 WE (27 males) aged 59.3 ± 6.5 years, and 46 SA (19 males) aged 54.4 ± 9.8 years. 3.0 T dual-echo fast gradient-echo pulse sequence using two-point Dixon technique with a phase-correction algorithm. Changes of renal sinus fat volume were measured by a radiologist (LL) with 4-years' experience, and were compared between the two ethnic groups, together with glycemic level, metabolic risk factors and renal function. The effects of liraglutide were assessed. Normality of the data was visually evaluated by histograms and Q-Q plots. Within-group and between-group differences were analyzed using paired t-tests and analysis of covariance. Associations were analyzed by person's correlation and multiple linear regression models. Renal sinus fat decreased in SA patients (Δ% = -7.6% ± 14.8%), but increased in WE patients (Δ% = 5.0% ± 13.1%), with a significant difference between the two ethnic groups. In the WE group, the increase of sinus fat volume was significant in the placebo subgroup (Δ% = 6.8% ± 12.5%), in contrast to the nonsignificant increase in the liraglutide subgroup (Δ% = 3.0% ± 13.8%, P = 0.444). Renal sinus fat accumulation responds differently to glucose regulation, showing a reduction in SA patients in contrast to a persistent accumulation in WE patients. A trend of less accumulation of sinus fat in WE patients receiving liraglutide has been observed. 4 TECHNICAL EFFICACY: Stage 4.

Pituitary and Pancreatic Iron Is Present at an Early Age in Transfused Patients with Alpha Thalassemia Major

Introduction Alpha thalassemia major is generally fatal in utero or shortly after birth without aggressive red cell transfusion therapy both pre- and postnatally. The Society for Maternal-Fetal Medicine has released evidence-based practice guidelines for the diagnosis and management of fetal anemia, largely focused on red cell alloimmunization, with intrauterine transfusion typically starting at 18 weeks gestational age.((SMFM) et al., 2015) Early initiation of intrauterine transfusion allows quick correction of anemia and a prolonged reduction of hemoglobin Bart's concentration leading up to birth.(Chmait, Baskin, Carson, Randolph, &amp; Hamilton, 2015) Long-term transfusion regimens postnatally invariably lead to iron overload, which can lead to organ dysfunction.(Taher &amp; Saliba, 2017) Minimal data is currently available regarding the pattern of iron overload in young patients with alpha thalassemia major given the rarity of the disease itself and variations in iron overload monitoring. Methods We reviewed patients with alpha thalassemia major treated at our center who had iron overload evaluations prior to 10 years of age. Diagnoses were confirmed by genetic testing. Iron deposition measurements were collected using multiple gradient echo pulse sequences on 1.5 Tesla magnets. Results Six subjects were included in the study. All but one subject received several intrauterine transfusions and were delivered at term. The last subject did not receive any intrauterine transfusions and was born at 24 weeks gestational age. Subjects were routinely transfused postnatally to keep fast migrating hemoglobin below 10%. Initial MRI was done prior to 4 years of age and as early as 1.5 years. All subjects had moderate to severe iron overload based on liver iron concentration (LIC) by R2* MRI, which decreased significantly after starting chelation in the four subjects who had subsequent MRI assessments (Figure 1A). Pancreatic iron was also elevated in all subjects, and none had cardiac siderosis. All but one subject had pituitary R2 by Z-score for age and sex greater than 2 in the coronal and sagittal planes, indicating pituitary siderosis, but none had pituitary volume loss (Figure 2B). Discussion This study shows significant extrahepatic iron deposition (pancreas, pituitary) at a very young age indicating exposure to toxic reactive ferrous iron (Fe 2+). The pancreas is known to load temporally before the heart.(Noetzli, Papudesi, Coates, &amp; Wood, 2009) None of the subjects in this study had cardiac iron by MRI, probably reflecting slower cardiac loading and lowering of Fe 2+ by chelation. It is very rare to have cardiac loading from transfusion in patients less than 2 years old.(Berdoukas et al., 2013) It is reassuring that none of the patients had pituitary volume loss, which has been associated with pituitary dysfunction,(Noetzli et al., 2012) although we know very little about pituitary function and iron in very young children. Our observation that some subjects had loading at 1.5 years old suggests there is significant circulating Fe 2+ in this population and the pituitary may be at risk. Chelation is rarely started prior to 2 years of age due to concerns about theoretical effects of chelation on neurodevelopment.(Coates, 2019) Despite significant levels of iron overload seen in initial assessments, hepatic iron rapidly improved with chelation despite aggressive red cell transfusion in this cohort. There are many unknowns here, including effects of prenatal iron exposure from transfusion, the extent to which iron seen by MRI signifies organ damage, and response of extrahepatic iron to chelation. However, the effects of iron deficiency on brain development are well documented(Idjradinata &amp; Pollitt, 1993; Lozoff et al., 2013) and the possible effects of chelators on the newborn/infant brain could be serious. Long-term pituitary iron data are still needed to support earlier implementation of iron chelation in this population.

Myocardial Blood Flow Determination From Contrast-Free Magnetic Resonance Imaging Quantification of Coronary Sinus Flow.

Determination of myocardial blood flow (MBF) with MRI is usually performed with dynamic contrast enhanced imaging (MBFDCE ). MBF can also be determined from coronary sinus blood flow (MBFCS ), which has the advantage of being a noncontrast technique. However, comparative studies of MBFDCE and MBFCS in large cohorts are lacking. To compare MBFCS and MBFDCE in a large cohort. Prospective, sequence-comparison study. 147 patients with type 2 diabetes mellitus (age: 56+/-12 years; 106 male; diabetes duration: 12.9+/-8.1 years), and 25 age-matched controls. 1.5 Tesla scanner. Saturation recovery sequence for MBFDCE vs. phase-contrast gradient-echo pulse sequence (free-breathing) for MBFCS . MBFDCE and MBFCS were determined at rest and during coronary dilatation achieved by administration of adenosine at 140 μg/kg/min. Myocardial perfusion reserve (MPR) was calculated as the stress/rest ratio of MBF values. Coronary sinus flow was determined twice in the same imaging session for repeatability assessment. Agreement between MBFDCE and MBFCS was assessed with Bland and Altman's technique. Repeatability was determined from single-rater random intraclass and repeatability coefficients. Rest and stress flows, including both MBFDCE and MBFCS values, ranged from 33 to 146 mL/min/100 g and 92 to 501 mL/min/100 g, respectively. Intraclass and repeatability coefficients for MBFCS were 0.95 (CI 0.90; 0.95) and 5 mL/min/100 g. In Bland-Altman analysis, mean bias at rest was -1.1 mL/min/100 g (CI -3.1; 0.9) with limits of agreement of -27 and 24.8 mL/min/100 g. Mean bias at stress was 6.3 mL/min/100 g (CI -1.1; 14.1) with limits of agreement of -86.9 and 99.9. Mean bias of MPR was 0.11 (CI: -0.02; 0.23) with limits of agreement of -1.43 and 1.64. MBF may be determined from coronary sinus blood flow, with acceptable bias, but relatively large limits of agreement, against the reference of MBFDCE . 1 TECHNICAL EFFICACY STAGE: 2.

Dynamic Magnetic Resonance Vascular Fingerprinting During Hypercapnia for Quantitative and Multiparametric Cerebrovascular Reactivity Measures.

Magnetic resonance fingerprinting (MRF) represents a potential paradigm shift in MR image acquisition, reconstruction, and analysis using computational biophysical modelling in parallel to image acquisition. Its flexibility allows for examination of cerebrovascular metrics through MR vascular fingerprinting (MRvF), and this has been extended even further to produce quantitative cerebral blood volume (CBV), microvascular vessel radius, and tissue oxygen saturation (SO2) maps of the whole brain simultaneously every few seconds. This allows for observation of rapid physiological changes like cerebrovascular reactivity (CVR), which is the ability of vessels to dilate in response to a vasoactive stimulus. Here we demonstrated a novel protocol in which a rapid, spin- and gradient-echo pulse sequence allowed for dynamic, and simultaneous acquisition of MRvF and blood oxygen level dependent (BOLD) measures. By combining this with a tailored hypercapnic (5% CO2) breathing paradigm we were able to show how these quantitative CBV, radius, and SO2 parameters changed in response to a stimulus and directly compare those to a colocalized, traditionally used BOLD CVR. We also compared these measures to another traditionally utilized technique in cerebral blood flow CVR from an arterial spin labelling sequence. These imaging, processing, and analysis techniques will allow for further investigation into the magnitude and rate of CVR based on BOLD and MRvF-based metrics and enable investigations to better understand vascular function in healthy aging and cerebrovascular diseases.Clinical Relevance- The development of dynamic magnetic resonance vascular fingerprinting has the potential to enable rapid, quantitative, and multiparametric functional imaging biomarkers of cerebrovascular diseases like vascular cognitive impairment, dementia, and Alzheimer's disease.

Development of cardiac phantom which mimics the heart function using a 4.7t preclinical MRI system for cardiac imaging

Cardiac MRI was one of the first MRI applications in the 1980s, which helps in the human study of different cardiovascular diseases. MRI is a noninvasive imaging technique that can be used for diagnosis and has advantages over other imaging techniques since it does not rely on radiation like X-rays, PET, and SPECT. Modern clinical methods do not require much scanning time, it revels good contrast between tissues and can compensate for patient movement during the scan. The scanner used is a 300mm internal diameter superconducting magnet (Magnex Uk) 4.7T preclinical MRI system, in the Biomedical Physics building at the University of Aberdeen. The cardiac phantom is made of a balloon filled with water, connected via a nylon T-piece to two 5 m lengths of rigid pvc tubing of 3 mm internal diameter to a 12 V water pump and solenoid valve located outside the 4.7 T MRI system’s 5 Gauss stray field contour. The balloon part of the phantom was fixed on the 4.7 T MRI system’s animal bed, directly over a 30mm diameter surface coil normally used to image the rat heart. The flow system was primed with water to mimic blood and the bed was loaded into the MRI magnet for imaging. The cardiac phantom has successfully been developed using a small balloon to represent a heart chamber and imaged in a 4.7T preclinical MRI scanner. Images acquired with gradient echo pulse sequence with shorter TE of 5 ms and using surface coil displayed improved image contrast and have useful signal-to-noise ratio as compared to images acquired with birdcage coil which show ghosting artifact.

Improved accuracy and precision of fat-suppressed isotropic 3D T2 mapping MRI of the knee with dictionary fitting and patch-based denoising

PurposeTo develop an isotropic three-dimensional (3D) T2 mapping technique for the quantitative assessment of the composition of knee cartilage with high accuracy and precision.MethodsA T2-prepared water-selective isotropic 3D gradient-echo pulse sequence was used to generate four images at 3 T. These were used for three T2 map reconstructions: standard images with an analytical T2 fit (AnT2Fit); standard images with a dictionary-based T2 fit (DictT2Fit); and patch-based-denoised images with a dictionary-based T2 fit (DenDictT2Fit). The accuracy of the three techniques was first optimized in a phantom study against spin-echo imaging, after which knee cartilage T2 values and coefficients of variation (CoV) were assessed in ten subjects in order to establish accuracy and precision in vivo. Data given as mean ± standard deviation.ResultsAfter optimization in the phantom, whole-knee cartilage T2 values of the healthy volunteers were 26.6 ± 1.6 ms (AnT2Fit), 42.8 ± 1.8 ms (DictT2Fit, p < 0.001 versus AnT2Fit), and 40.4 ± 1.7 ms (DenDictT2Fit, p = 0.009 versus DictT2Fit). The whole-knee T2 CoV reduced from 51.5% ± 5.6% to 30.5 ± 2.4 and finally to 13.1 ± 1.3%, respectively (p < 0.001 between all). The DictT2Fit improved the data reconstruction time: 48.7 ± 11.3 min (AnT2Fit) versus 7.3 ± 0.7 min (DictT2Fit, p < 0.001). Very small focal lesions were observed in maps generated with DenDictT2Fit.ConclusionsImproved accuracy and precision for isotropic 3D T2 mapping of knee cartilage were demonstrated by using patch-based image denoising and dictionary-based reconstruction.Key points• Dictionary T2 fitting improves the accuracy of three-dimensional (3D) knee T2 mapping.• Patch-based denoising results in high precision in 3D knee T2 mapping.• Isotropic 3D knee T2 mapping enables the visualization of small anatomical details.

Evaluated the Correlation Between Serum Ferritin and Iron Overload of Liver, Spleen and Heart in β-Thalassemia Major Patients by MRI T2&amp;lt;sup&amp;gt;*&amp;lt;/sup&amp;gt; Method

β-Thalassemia major often results in an excess of iron in the body due to frequent blood transfusions and enhanced absorption of iron in the gastrointestinal tract. Early detection of this condition and administering sufficient iron chelator therapy can significantly decrease the risk of complications and fatalities resulting from iron overload. MRI (Magnetic Resonance Imaging) T2^* is an accurate non-invasive method for assessing organ iron overload in β-Thalassaemia major patients. This study evaluated the correlation between serum ferritin and iron overload of liver, spleen, and heart in β -Thalassaemia major patients by MRI T2^* method. The design was a cross-section, descriptive study. We used MRI-T2^* to evaluate the correlation between serum ferritin and iron overload of liver, spleen, and heart in 24 Thalassaemia major patients admitted in Cho Ray hospital from 10/2013 to 1/2014, using a 1.5T MRI system (Siemens) with a body coil. T2^* measurements were taken in the liver, spleen, and myocardium using different gradient echo pulse sequences. T2^* values were calculated within homogeneous regions of interest (ROI) in the liver avoiding major blood vessels, spleen, and the entire thickness of the interventricular septum in the myocardium. Pearson correlation coefficient was used to evaluate correlations in the study with a significance threshold of p < 0.05 using SPSS 16.0 software. As results, moderate negative correlation between serum ferritin and liver, spleen MRI T2^* relaxation time (r = 0.57 and 0.755) and a weak negative correlation between serum ferritin and heart MRI T2^* relaxation time (r = 0.303). Liver and heart MRI T2^* readings were poorly correlated (r = 0.28). In conclusion, MRI T2^* is useful to evaluate the iron overload status in β thalassemia patients.

Multi-echo gradient echo pulse sequences: which is best for PRFS MR thermometry guided hyperthermia?

Purpose MR thermometry (MRT) enables noninvasive temperature monitoring during hyperthermia treatments. MRT is already clinically applied for hyperthermia treatments in the abdomen and extremities, and devices for the head are under development. In order to optimally exploit MRT in all anatomical regions, the best sequence setup and post-processing must be selected, and the accuracy needs to be demonstrated. Methods MRT performance of the traditionally used double-echo gradient-echo sequence (DE-GRE, 2 echoes, 2D) was compared to multi-echo sequences: a 2D fast gradient-echo (ME-FGRE, 11 echoes) and a 3D fast gradient-echo sequence (3D-ME-FGRE, 11 echoes). The different methods were assessed on a 1.5 T MR scanner (GE Healthcare) using a phantom cooling down from 59 °C to 34 °C and unheated brains of 10 volunteers. In-plane motion of volunteers was compensated by rigid body image registration. For the ME sequences, the off-resonance frequency was calculated using a multi-peak fitting tool. To correct for B0 drift, the internal body fat was selected automatically using water/fat density maps. Results The accuracy of the best performing 3D-ME-FGRE sequence was 0.20 °C in phantom (in the clinical temperature range) and 0.75 °C in volunteers, compared to DE-GRE values of 0.37 °C and 1.96 °C, respectively. Conclusion For hyperthermia applications, where accuracy is more important than resolution or scan-time, the 3D-ME-FGRE sequence is deemed the most promising candidate. Beyond its convincing MRT performance, the ME nature enables automatic selection of internal body fat for B0 drift correction, an important feature for clinical application.

LARO: Learned acquisition and reconstruction optimization to accelerate quantitative susceptibility mapping

Quantitative susceptibility mapping (QSM) involves acquisition and reconstruction of a series of images at multi-echo time points to estimate tissue field, which prolongs scan time and requires specific reconstruction technique. In this paper, we present our new framework, called Learned Acquisition and Reconstruction Optimization (LARO), which aims to accelerate the multi-echo gradient echo (mGRE) pulse sequence for QSM. Our approach involves optimizing a Cartesian multi-echo k-space sampling pattern with a deep reconstruction network. Next, this optimized sampling pattern was implemented in an mGRE sequence using Cartesian fan-beam k-space segmenting and ordering for prospective scans. Furthermore, we propose to insert a recurrent temporal feature fusion module into the reconstruction network to capture signal redundancies along echo time. Our ablation studies show that both the optimized sampling pattern and proposed reconstruction strategy help improve the quality of the multi-echo image reconstructions. Generalization experiments show that LARO is robust on the test data with new pathologies and different sequence parameters. Our code is available at https://github.com/Jinwei1209/LARO-QSM.git.

Magnetic Resonance Imaging Evaluation of a Hearing Protector Device Designed for Neonatal Patients

BackgroundHearing protection for neonates that can be effectively used during magnetic resonance imaging (MRI) examinations is limited. Because MRI-related acoustic noise poses a serious risk to this patient population, a viable option for hearing protection is needed. A new hearing protector device was recently developed specifically for neonates. Because of safety concerns for products used in the MRI setting, the objective of this investigation was to evaluate MRI-related issues for this hearing protector device. In addition, patient tolerance and responses were observed and reported from in a small group of neonates. MethodsThe neonatal hearing protector device (DREAMIES T-M, NEATCap Medical, LLC, Bethlehem, Pennsylvania) was evaluated for magnetic field interactions (translational attraction and torque; 3-Tesla), MRI-related heating (1.5-Tesla/64-MHz and 3-Tesla/128-MHz), and in vitro testing of artifacts (T1-weighed spin echo and gradient echo pulse sequences obtained at 3-Tesla) using standardized test procedures. In addition, seven study subjects wearing the neonatal hearing protector device underwent MRI of the brain. ResultsThere was no translation attraction, no torque, no heating at 1.5-Tesla/64-MHz and 3-Tesla/128-MHz, and no artifacts were observed for the neonatal hearing protector device in the in vitro and study subject observations. The device was easy to apply, stayed in place for the duration of the MRI examination, and was tolerated well by the neonates evaluated. ConclusionsBecause of the benign findings for the MRI tests, along with the materials used to make this device (i.e., nonmetallic and nonconducting), this new neonatal hearing protector device is designated “MR Safe”, which is a medical device that poses no known hazards resulting from exposure to any MRI environment. In the limited number of subjects evaluated during the observational period, the device provided sufficient noise protection enabling neonates to remain undisturbed throughout their scans, resulting in images with little or no motion artifacts and diagnostically acceptable MRI examinations.

Volume-Controlled 19 F MR Ventilation Imaging of Fluorinated Gas.

19 F MRI of inhaled gas tracers has developed into a promising tool for pulmonary diagnostics. Prior to clinical use, the intersession repeatability of acquired ventilation parameters must be quantified and maximized. To evaluate repeatability of static and dynamic 19 F ventilation parameters and correlation with predicted forced expiratory volume in 1 second (FEV1 %pred) with and without inspiratory volume control. Prospective. A total of 30 healthy subjects and 26 patients with chronic obstructive pulmonary disease (COPD). Three-dimensional (3D) gradient echo pulse sequence with golden-angle stack-of-stars k-space encoding at 1.5T. All study participants underwent 19 F ventilation MRI over eight breaths with inspiratory volume control (w VC) and without inspiratory volume control (w/o VC), which was repeated within 1 week. Ventilated volume percentage (VVP), fractional ventilation (FV), and wash-in time (WI) were computed. Lung function testing was conducted on the first visit. Correlation between imaging and FEV1 %pred was measured using Pearson correlation coefficient (r). Differences in imaging parameters between first and second visit were analyzed using paired t-test. Repeatability was quantified using intraclass correlation coefficient (ICC) and coefficient of variation (CoV). Minimum detectable effect size (MDES) was calculated with a power analysis for study size n=30 and a power of 0.8. All hypotheses were tested with a significance level of 5% two sided. Strong and moderate linear correlations with FEV1 %pred for COPD patients were found in almost all imaging parameters. The ICC w VC exceeds the ICC w/o VC for all imaging parameters. CoV was significantly lower w VC for initial VVP in COPD patients, FV, CoV FV, WI and standard deviation (SD) of WI. MDES of all imaging parameters were smaller w VC. 19 F gas wash-in MRI with inspiratory volume control increases the correlation and repeatability of imaging parameters with lung function testing. 2 TECHNICAL EFFICACY: Stage 2.

Age-dependent microstructure alterations in 5xFAD mice by high-resolution diffusion tensor imaging.

PurposeTo evaluate the age-dependent microstructure changes in 5xFAD mice using high-resolution diffusion tensor imaging (DTI).MethodsThe 5xFAD mice at 4, 7.5, and 12 months and the wild-type controls at 4 months were scanned at 9.4T using a 3D echo-planar imaging (EPI) pulse sequence with the isotropic spatial resolution of 100 μm. The b-value was 3000 s/mm2 for all the diffusion MRI scans. The samples were also acquired with a gradient echo pulse sequence at 50 μm isotropic resolution. The microstructure changes were quantified with DTI metrics, including fractional anisotropy (FA) and mean diffusivity (MD). The conventional histology was performed to validate with MRI findings.ResultsThe FA values (p = 0.028) showed significant differences in the cortex between wild-type (WT) and 5xFAD mice at 4 months, while hippocampus, anterior commissure, corpus callosum, and fornix showed no significant differences for either FA and MD. FA values of 5xFAD mice gradually decreased in cortex (0.140 ± 0.007 at 4 months, 0.132 ± 0.008 at 7.5 months, 0.126 ± 0.013 at 12 months) and fornix (0.140 ± 0.007 at 4 months, 0.132 ± 0.008 at 7.5 months, 0.126 ± 0.013 at 12 months) with aging. Both FA (p = 0.029) and MD (p = 0.037) demonstrated significant differences in corpus callosum between 4 and 12 months age old. FA and MD were not significantly different in the hippocampus or anterior commissure. The age-dependent microstructure alterations were better captured by FA when compared to MD.ConclusionFA showed higher sensitivity to monitor amyloid deposition in 5xFAD mice. DTI may be utilized as a sensitive biomarker to monitor beta-amyloid progression for preclinical studies.

Analysis of Signal and Noise Characteristics of Brain T2-Weighted Image with Gradient-Echo Pulse Sequence by Changing Echo Time Based on MRiLab Simulation: Pilot Study

Analysis of Signal and Noise Characteristics of Brain T2-Weighted Image with Gradient-Echo Pulse Sequence by Changing Echo Time Based on MRiLab Simulation: Pilot Study

SNR and total acquisition time analysis of multi-echo FLASH pulse sequence for current density imaging

Magnetic Resonance Current Density Imaging (MRCDI) is an imaging modality providing cross-sectional current density (J¯) information inside the body. The clinical applicability of MRCDI is highly dependent on the sensitivity of the acquired noisy current-induced magnetic flux density (B∼z) distributions.Here, a novel analysis is developed to investigate the combined effect of relevant parameters of the RF spoiled gradient echo (FLASH) pulse sequence on the SNR level and the total acquisition time (TAT) of the acquired B∼z images. The proposed analysis then is expanded for a multi-echo FLASH (ME-FLASH) pulse sequence to take advantage of combining the multiple echoes to achieve B∼zcomb distribution with a higher SNR than the one achievable with a single echo acquisition.The optimized sequence parameters to acquire a B∼z distribution with the highest possible SNR for a given acquisition time or the desired SNR in the shortest scan time are estimated using the proposed analysis. The analysis also provides different sets of sequence parameters to acquire B∼z distributions with the same SNR at almost the same TAT. Furthermore, the effects of intensive utilization of the gradients and the magnetohydrodynamic (MHD) flow velocity on the acquired B∼z distribution in MRCDI experiments is investigated.The analytical results of the proposed analysis are validated experimentally using an imaging phantom having the conductivity and the relaxation parameters of the brain white matter tissue.

Seeking a Widely Adoptable Practical Standard to Estimate Signal-to-Noise Ratio in Magnetic Resonance Imaging for Multiple-Coil Reconstructions.

Signal-to-noise ratio (SNR) is used to evaluate the performance of magnetic resonance (MR) imaging systems. Accurate and consistent estimations are needed to routinely use SNR to assess coils and image reconstruction techniques. To identify a reliable and practical method for SNR estimation in multiple-coil reconstructions. Technical evaluation and comparison. A uniform phantom and four healthy volunteers: 35, 38, 39 y/o males, 25 y/o female. Two-dimensional multislice gradient-echo pulse sequence at 3 T and 7 T. Reference-standard SNR was calculated from 100 multiple replicas. Six SNR methods were compared against it: difference image (DI), analytic array combination (AC), pseudo-multiple-replica (PMR), generalized pseudo-replica (GPR), smoothed image subtraction (SIS), and DI with temporal instability correction (TIC). The assessment was repeated for different multiple-coil reconstructions. SNR methods were evaluated in terms of relative deviation (RD) and normalized mutual information (NMI) with respect to the reference-standard, using a linear regression (0.05 significance level) to assess how different factors affect accuracy. Average RD (phantom) for DI, AC, PMR, GPR, SIS, and TIC was 7.9%, 6%, 6.7%, 10.1%, 40%, and 14.6%, respectively. RD increased with acceleration. SNR maps with AC were the most similar to the reference standard (NMI=0.358). Considering all brain regions of interest, average RD for all SNR methods varied 96% among volunteers but remained approximately 10% for AC, PMR, and GPR, whereas it was more than 30% for DI, SIS, and TIC. RD was mainly affected by image reconstruction (beta=12) for AC and SNR entropy for SIS (beta=19). AC provided accurate and robust SNR estimation. PMR and GPR are more generally applicable than AC. DI and TIC should be used only at low acceleration factors, when an additional noise-only scan cannot be acquired. SIS is a single-acquisition alternative to DI for generalized autocalibrating partial parallel acquisition (GRAPPA) reconstructions. 1 TECHNICAL EFFICACY: Stage 1.

Fast 3D MR elastography of the whole brain using spiral staircase: Data acquisition, image reconstruction, and joint deblurring.

To address the need for a method to acquire 3D data for MR elastography (MRE) of the whole brain with substantially improved spatial resolution, high SNR, and reduced acquisition time compared with conventional methods. We combined a novel 3D spiral staircase data-acquisition method with a spoiled gradient-echo pulse sequence and MRE motion-encoding gradients (MEGs). The spiral-out acquisition permitted use of longer-duration motion-encoding gradients (ie, over two full oscillatory cycles) to enhance displacement SNR, while still maintaining a reasonably short TE for good phase-SNR. Through-plane parallel imaging with low noise penalties was implemented to accelerate acquisition along the slice direction. Shared anatomical information was exploited in the deblurring procedure to further boost SNR for stiffness inversion. In vivo and phantom experiments demonstrated the feasibility of the proposed method in producing brain MRE results comparable to the spin-echo-based approaches, both qualitatively and quantitatively. High-resolution (2-mm isotropic) brain MRE data were acquired in 5 minutes using our method with good SNR. Joint deblurring with shared anatomical information produced SNR-enhanced images, leading to upward stiffness estimation. A novel 3D gradient-echo-based approach has been designed and implemented, and shown to have promising potential for fast and high-resolution in vivo MRE of the whole brain.

Improving the sensitivity of spin-echo fMRI at 3T by highly accelerated acquisitions.

Spin-echo (SE) functional MRI (fMRI) can be highly advantageous compared to gradient-echo (GE) fMRI with respect to magnetic field-inhomogeneity artifacts. However, at 3T, the majority of blood oxygenation level-dependent (BOLD) fMRI experiments are performed using -weighted GE sequences because of their superior sensitivity compared to SE-fMRI. The presented SE implementation of a highly accelerated GE pulse sequence therefore aims to improve the sensitivity of SE-fMRI while profiting from a reduction of susceptibility-induced signal dropout. Spin-echo MR encephalography (SE-MREG) is compared with the more conventionally used spin-echo echo-planar imaging (SE-EPI) and spin-echo simultaneous multislice (SE-SMS) at 3T in terms of capability to detect neuronal activations and resting-state functional connectivity. For activation analysis, healthy subjects underwent consecutive SE-MREG (pulse repetition time [TR] = 0.25 seconds), SE-SMS (TR = 1.3 seconds), and SE-EPI (TR = 4.4 seconds) scans in pseudorandomized order applied to a visual block design paradigm for generation of t-statistics maps. For the investigation of functional connectivity, additional resting-state data were acquired for 5 minutes and a seed-based correlation analysis using Stanford's FIND (Functional Imaging in Neuropsychiatric Disorders) atlas was performed. The increased sampling rate of SE-MREG relative to SE-SMS and SE-EPI improves the sensitivity to detect BOLD activation by 33% and 54%, respectively, and increases the capability to extract resting-state networks. Compared with a brain region that is not affected by magnetic field inhomogeneities, SE-MREG shows 2.5 times higher relative signal strength than GE-MREG in mesial temporal structures. SE-MREG offers a viable possibility for whole-brain fMRI with consideration of brain regions that are affected by strong susceptibility-induced magnetic field gradients.