Ultrashort Echo Time Research Articles

Automated Electrodes Detection During Simultaneous EEG/fMRI

The coupling of EEG/fMRI allows measuring brain activity at high spatio-temporal resolution. The localisation of EEG sources depends on several parameters including the position of the electrodes on the scalp. An accurate knowledge about this information is important for source reconstruction. Currently, when acquiring EEG/fMRI together, the position of the electrodes is generally estimated according to fiducial points by using a template. In the context of simultaneous EEG/fMRI acquisition, a natural idea is to use MR images to localise EEG electrodes. However, MR compatible electrodes are built to be almost invisible on MR Images. Taking advantage of a recently proposed Ultra-Short Echo Time (UTE) sequence, we introduce a fully automatic method to detect and label those electrodes in MR images. Our method was tested on 8 subjects wearing a 64-channel EEG cap. This automated method showed an average detection accuracy of 94% and the average position error was 3.1 mm. These results suggest that the proposed method has potential for determining the position of the electrodes during simultaneous EEG/fMRI acquisition.

Dynamic [18F]FET-PET/MRI using standard MRI-based attenuation correction methods

AimTo assess if tumour grading based on dynamic [18F]FET positron emission tomography/magnetic resonance imaging (PET/MRI) studies is affected by different MRI-based attenuation correction (AC) methods.MethodsTwenty-four patients with suspected brain tumours underwent dynamic [18F]FET-PET/MRI examinations and subsequent low-dose computed tomography (CT) scans of the head. The dynamic PET data was reconstructed using the following AC methods: standard Dixon-based AC and ultra-short echo time MRI-based AC (MR-AC) and a model-based AC approach. All data were reconstructed also using CT-based AC (reference). For all lesions and reconstructions, time-activity curves (TACs) and time to peak (TTP) were extracted using different region-of-interest (ROI) and volume-of-interest (VOI) definitions. According to the most common evaluation approaches, TACs were categorised into two or three distinct curve patterns. Changes in TTP and TAC patterns compared to PET using CT-based AC were reported.ResultsIn the majority of cases, TAC patterns did not change. However, TAC pattern changes as well as changes in TTP were observed in up to 8% and 17% of the cases when using different MR-AC methods and ROI/VOI definitions, respectively. However, these changes in TTP and TAC pattern were attributed to different delineations of the ROIs/VOIs in PET corrected with different AC methods.ConclusionPET/MRI using different MR-AC methods can be used for the assessment of TAC patterns in dynamic [18F]FET studies, as long as a meaningful delineation of the area of interest within the tumour is ensured.Key Points• PET/MRI using different MR-AC methods can be used for dynamic [18F]FET studies.• A meaningful segmentation of the area of interest needs to be ensured, mandating a visual validation of the delineation by an experienced reader.

The role of imaging in diagnosing and managing tendinopathy

Tendons were first imaged in the late 1980’s, where it was apparent that tendon pathology was highly associated with tendon pain, normal tendons on imaging almost never gave rise to symptoms. As larger cohorts were imaged in the early 2000’s it became apparent that tendon pathology existed in tendons that were not currently symptomatic, and that never developed symptoms. This questioned the role of imaging in diagnosing the tendon as the source of pain, as there are no imaging criteria that indicate if the tendon is painful. Pathology of imaging is also not predictive of symptoms, again there is no indication on imaging to determine the likelihood of a tendon becoming symptomatic. Degenerative tendon pathology does not heal, so serial imaging of tendon during rehabilitation will indicate little or no change, often despite improvements in pain and function. The role of imaging in the management if tendon pathology is limited to diagnosis the early stage of pathology (reactive tendon pathology) where strategies to decrease load are best practice. Ultrasound imaging provides the best clinical information about tendons, as it can indicate tendon fascicle continuity, the level of vascularity and an indication or proteoglycan infiltration. Magnetic resonance imaging (MRI) can also indicate levels of proteoglycan and vascular infiltration but with less clarity. Currently, neither of these modalities improve clinical diagnosis and amnagement, and are limited in providing a differential diagniosis of pain. Newer outputs from ultrasound such as elastography, as well as enhanced ultrasound imaging (ultrasound tissue characterisation) and specialised sequences on MRI (diffusion tensor imaging, ultrashort echo time) may improve clinical diagnosis and prognosis, however the inability of the tendon to heal and the inability of imaging to diagnose pain suggest that tendons will remain and enigma to imaging in the short to long term.

Morphologic Evaluation of Primary Non-Small Cell Lung Cancer by 3 Tesla MRI with Free-Breathing Ultrashort Echo Time and Radial T1-Weighted Gradient Echo Sequences: A Comparison with CT Analysis

Morphologic Evaluation of Primary Non-Small Cell Lung Cancer by 3 Tesla MRI with Free-Breathing Ultrashort Echo Time and Radial T1-Weighted Gradient Echo Sequences: A Comparison with CT Analysis

Ultrashort Echo Time MRI (UTE-MRI) Quantifications of Cortical Bone Varied Significantly at Body Temperature Compared with Room Temperature

Ultrashort Echo Time MRI (UTE-MRI) Quantifications of Cortical Bone Varied Significantly at Body Temperature Compared with Room Temperature

Comparison of Influence of Susceptibility Artifact due to Metallic Embolic Material in MRA Image

To identify the influence of susceptibility artifact caused by commonly used trans-catheter embolic devices for vascular lesions in the body on the images of various magnetic resonance angiography (MRA) techniques as an aid to patient screening after endovascular embolization. We constructed vascular phantoms in which three embolic materials; platinum coil, Inconel coil, and vascular plug, were placed. Each phantom was imaged with three types of MRA techniques as follows: ultra-short echo time magnetic resonance imaging (UTE), three-dimensional fast advanced spin echo (3D-FASE), time-resolved contrast MRA with key hole technique (Key hole). For each embolic material, four reviewers compared the visual capabilities of the vessel lumen and surrounding area of each MRA technique by using a four-point visual scoring system. The quantitative values of susceptibility artifacts generated from each embolic material were compared between each MRA technique. For all MRA techniques, the platinum coil showed the highest visual score (median=four-point) among all the embolic materials (p<0.05). In the platinum coil, the MR signal in the coil was clearly depicted in UTE. For all MRA technique, the quantitative values of the susceptibility artifacts were the lowest in platinum coil among all the embolic materials (p<0.05). UTE is less susceptible to susceptibility artifact of embolic materials.

Three‐dimensional ultrashort echo time (3D UTE) MRI of Achilles tendon at 4.7T MRI with comparison to conventional sequences in an experimental murine model of spondyloarthropathy

Due to the very short T2 of its components, the normal anatomy of Achilles enthesis is impossible to define with "conventional" long echo time (TE) T2 sequences. However, this is a common site affected by rheumatologic disease. Early abnormalities related to inflammatory processes are impossible to detect in this location. To assess the feasibility of a 3D-UTE (ultrashort echo time) sequence to evaluate normal and pathological Achilles entheses, determining both anterior fibrocartilaginous and posterior collagenic portions at 4.7T, in a rat model of spondyloarthropathy (SpA) with histological correlation. To assess whether this sequence detects SpA enthesopathy prior to long TE T2 sequences, enabling disease monitoring. Prospective case-control study. Twelve immunocompetent Wistar male rats imaged before (controls); the model was induced in eight rats (16 tendons) imaged at day 6, day 13, and day 21 with regular sacrifice for ex vivo imaging and histological correlation. 4.7T Bruker Biospec Systems. 3D balanced steady-state free precession (bSSFP) and 3D-UTE sequences, performed at baseline (day 0, n = 12 animals / 24 tendons), day 6 (n = 8/16), 13 (n = 4/8), and day 21 (n = 2/4). Visual analysis and signal intensity measurements (signal to noise ratio, SNR) of both bSSFP and UTE images were performed by two independent musculoskeletal radiologists at different locations of the Achilles enthesis and preinsertional area. Normal and pathological rat values were compared by Wilcoxon signed-rank tests, as well as interobserver differences. MRI findings were compared against histological data. The 3D-UTE sequence identified the anterior fibrocartilage and posterior collagenic areas of Achilles entheses in all cases. Visual analysis and signal intensity measurements distinguished SpA-affected entheses from healthy ones at days 6 and 13 (P = 0.002 and P = 0.006, respectively). Neither the normal anatomy of the enthesis nor its pathological pattern could be identified on T2 bSSFP sequences. Unlike bSSFP T2 sequences, 3D-UTE sequences enable visualization of normal enthesis anatomy and early detection of abnormalities in pathological conditions. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:127-135.

Rapid dual-RF, dual-echo, 3D ultrashort echo time craniofacial imaging: A feasibility study.

To develop a dual-radiofrequency (RF), dual-echo, 3D ultrashort echo-time (UTE) pulse sequence and bone-selective image reconstruction for rapid high-resolution craniofacial MRI. The proposed pulse sequence builds on recently introduced dual-RF UTE imaging. While yielding enhanced bone specificity by exploiting high sensitivity of short T2 signals to variable RF pulse widths, the parent technique exacts a 2-fold scan time penalty relative to standard dual-echo UTE. In the proposed method, the parent sequence's dual-RF scheme was incorporated into dual-echo acquisitions while radial view angles are varied every pulse-to-pulse repetition period. The resulting 4 echoes (2 for each RF) were combined by view-sharing to construct 2 sets of k-space data sets, corresponding to short and long TEs, respectively, leading to a 2-fold increase in imaging efficiency. Furthermore, by exploiting the sparsity of bone signals in echo-difference images, acceleration was achieved by solving a bone-sparsity constrained image reconstruction problem. In vivo studies were performed to evaluate the effectiveness of the proposed acceleration approaches in comparison to the parent method. The proposed technique achieves 1.1-mm isotropic skull imaging in 3 minutes without visual loss of image quality, compared to the parent technique (scan time = 12 minutes). Bone-specific images and corresponding 3D renderings of the skull were found to depict the expected craniofacial anatomy over the entire head. The proposed method is able to achieve high-resolution volumetric craniofacial images in a clinically practical imaging time, and thus may prove useful as a potential alternative to computed tomography.

Fast high-resolution brain metabolite mapping on a clinical 3T MRI by accelerated H-FID-MRSI and low-rank constrained reconstruction.

Epitomizing the advantages of ultra short echo time and no chemical shift displacement error, high-resolution-free induction decay magnetic resonance spectroscopic imaging (FID-MRSI) sequences have proven to be highly effective in providing unbiased characterizations of metabolite distributions. However, its merits are often overshadowed in high-resolution settings by reduced signal-to-noise ratios resulting from the smaller voxel volumes procured by extensive phase encoding and the related acquisition times. To address these limitations, we here propose an acquisition and reconstruction scheme that offers both implicit dataset denoising and acquisition acceleration. Specifically, a slice selective high-resolution FID-MRSI sequence was implemented. Spectroscopic datasets were processed to remove fat contamination, and then reconstructed using a total generalized variation (TGV) regularized low-rank model. We further measured reconstruction performance for random undersampled data to assess feasibility of a compressed-sensing SENSE acceleration scheme. Performance of the lipid suppression was assessed using an ad hoc phantom, while that of the low-rank TGV reconstruction model was benchmarked using simulated MRSI data. To assess real-world performance, 2D FID-MRSI acquisitions of the brain in healthy volunteers were reconstructed using the proposed framework. Results from the phantom and simulated data demonstrate that skull lipid contamination is effectively removed and that data reconstruction quality is improved with the low-rank TGV model. Also, we demonstrated that the presented acquisition and reconstruction methods are compatible with a compressed-sensing SENSE acceleration scheme. An original reconstruction pipeline for 2D H-FID-MRSI datasets was presented that places high-resolution metabolite mapping on 3T MR scanners within clinically feasible limits.

Collagen proton fraction from ultrashort echo time magnetization transfer (UTE-MT) MRI modelling correlates significantly with cortical bone porosity measured with micro-computed tomography (μCT).

Intracortical bone porosity is a key microstructural parameter that determines bone mechanical properties. While clinical MRI visualizes the cortical bone with a signal void, ultrashort echo time (UTE) MRI can acquire high signal from cortical bone, thus enabling quantitative assessments. Magnetization transfer (MT) imaging combined with UTE-MRI can indirectly assess protons in the bone collagenous matrix, which are inversely related to porosity. This study aimed to examine UTE-MT MRI techniques to evaluate intracortical bone porosity. Eighteen human cortical bone specimens from the tibial and fibular midshafts were scanned using UTE-MT sequences on a clinical 3T MRI scanner and on a high-resolution micro-computed tomography (μCT) scanner. A series of MT pulse saturation powers (500°, 1000°, 1500°) and frequency offsets (2, 5, 10, 20, 50kHz) were used to measure the macromolecular fraction (MMF) and macromolecular T2 (T2MM ) using a two-pool MT model. The measurements were made on 136 different regions of interest (ROIs). ROIs were selected at three cortical bone layers (from endosteum to periosteum) and four anatomical sites (anterior, mid-medial, mid-lateral, and posterior) to provide a wide range of porosity. MMF showed moderate to strong correlations with intracortical bone porosity (R=-0.67 to -0.73, p<0.01) and bone mineral density (BMD) (R=+0.46 to +0.70, p<0.01). Comparing the average MMF between cortical bone layers revealed a significant increase from the endosteum towards the periosteum. Such a pattern was in agreement with porosity reduction and BMD increase towards the periosteum. These results suggest that the two-pool UTE-MT technique can potentially serve as a novel and accurate tool to assess intracortical bone porosity.

Protein aggregation linked to Alzheimer's disease revealed by saturation transfer MRI

The goal of this study was to develop a molecular biomarker for the detection of protein aggregation involved in Alzheimer's disease (AD) by exploiting the features of the water saturation transfer spectrum (Z-spectrum), the CEST signal of which is sensitive to the molecular configuration of proteins. A radial-sampling steady-state sequence based ultrashort echo time (UTE) readout was implemented to image the Z-spectrum in the mouse brain, especially the contributions from mobile proteins at the frequency offsets for the composite protein amide proton (+3.6 ppm) and aliphatic proton (−3.6 ppm) signals. Using a relatively weak radiofrequency (RF) saturation amplitude, contributions due to strong magnetization transfer contrast (MTC) from solid-like macromolecules and direct water saturation (DS) were minimized. For practical measure of the changes in the mobile protein configuration, we defined a saturation transfer difference (ΔST) by subtracting the Z-spectral signals at ±3.6 ppm from a control signal at 8 ppm. Phantom studies of glutamate solution, protein (egg white) and hair conditioner show the capability of the proposed scheme to minimize the contributions from amine protons, DS, and MTC, respectively. The ST signal at ±3.6 ppm of the cross-linked bovine serum albumin (BSA) solutions demonstrated that the ΔST signal can be used to monitor the aggregation process of the mobile proteins. High-resolution ΔST images of AD mouse brains at ±3.6 ppm of mouse brains showed significantly reduced ΔST (-3.6) signal compared to the age-matched wild-type (WT) mice. Thus, this signal has potential to serve as a molecular biomarker for monitoring protein aggregation in AD.

Ultra-short echo time imaging with multiple echo refocusing for porous media T2 mapping.

T2 relaxation time measurement is a powerful tool to distinguish signal components in porous media. As T2 weighting is generally achieved by spin-echo based methods, it is very challenging to capture very short T2 relaxation time components, approximately 1 ms, with high resolution spatial encoding. It is especially challenging when T2 relaxation times of the other signal components are not known a priori. We propose a method, combining ultrashort echo time (UTE) imaging with multiple spin echo refocusing, to generate a series of images with T2 weighting. The T2 decay curves for each image voxel were extracted, and multiple T2 relaxation components were quantitatively evaluated. The method has been applied to a fast relaxation system, namely, moisture content in wood samples to differentiate cell wall (bound) water and cell cavity (lumen) water.

Evaluation of normal cadaveric Achilles tendon and enthesis with ultrashort echo time (UTE) magnetic resonance imaging and indentation testing.

Entheses are regions where tendons and ligaments attach to bone, and are the primary target in seronegative and other diseases of the musculoskeletal (MSK) system. MRI has been widely used for visualizing features of inflammatory and degenerative MSK disease; however, normal tendons and entheses have short transverse relaxation times (T2 ), and show little or no signal with conventional clinical MRI pulse sequences, making it difficult to investigate their MR properties. In this study we examined the normal MR morphology of the cadaveric Achilles tendon and enthesis at 3T using novel three-dimensional ultrashort echo time (3D UTE) Cones sequences, and at 11.7T using conventional MRI sequences. We also studied the MR properties of the Achilles tendon and enthesis including T2 *, T1 , and magnetization transfer ratio (MTR). In addition, MT modeling of macromolecular proton fractions was investigated using 3D UTE Cones sequences at 3T. Indentation testing was performed to investigate the mechanical properties of the tendons and entheses, and this was followed by histological examination. In total five specimens (<50years) were investigated. On average, tendons and entheses respectively had T2 * values of 0.93±0.48ms and 2.77±0.79ms, T1 values of 644±22ms and 780±55ms, MTRs of 0.373±0.03 and 0.244±0.009 with an MT power of 1000° and frequency offset of 2kHz, and macromolecular proton fractions of 18.0±2.2% and 13.9±1.9%. Compared with the tendon, the enthesis generally had a longer T2 *, a longer T1 , a lower MTR, and a lower macromolecular proton fraction as well as both a higher Young's modulus and stiffness. Results from this study are likely to provide a useful baseline for identifying deviations from the normal in seronegative arthritis and other disease of the entheses.

Whole knee joint T1 values measured in vivo at 3T by combined 3D ultrashort echo time cones actual flip angle and variable flip angle methods.

To measure T1 relaxations for the major tissues in whole knee joints on a clinical 3T scanner. The 3D UTE-Cones actual flip angle imaging (AFI) method was used to map the transmission radiofrequency field (B1 ) in both short and long T2 tissues, which was then used to correct the 3D UTE-Cones variable flip angle (VFA) fitting to generate accurate T1 maps. Numerical simulation was carried out to investigate the accuracy of T1 measurement for a range of T2 values, excitation pulse durations, and B1 errors. Then, the 3D UTE-Cones AFI-VFA method was applied to healthy volunteers (N = 16) to quantify the T1 of knee tissues including cartilage, meniscus, quadriceps tendon, patellar tendon, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), marrow, and muscles at 3T. Numerical simulation showed that the 3D UTE-Cones AFI-VFA technique can provide accurate T1 measurements (error <1%) when the tissue T2 is longer than 1 ms and a 150 μs excitation RF pulse is used and therefore is suitable for most knee joint tissues. The proposed 3D UTE-Cones AFI-VFA method showed an average T1 of 1098 ± 67 ms for cartilage, 833 ± 47 ms for meniscus, 800 ± 66 ms for quadriceps tendon, 656 ± 43 ms for patellar tendon, 873 ± 38 ms for ACL, 832 ± 49 ms for PCL, 379 ± 18 ms for marrow, and 1393 ± 46 ms for muscles. The 3D UTE-Cones AFI-VFA method allows volumetric T1 measurement of the major tissues in whole knee joints on a clinical 3T scanner.

Neonatal Pulmonary Magnetic Resonance Imaging of Bronchopulmonary Dysplasia Predicts Short-Term Clinical Outcomes.

Bronchopulmonary dysplasia (BPD) is a serious neonatal pulmonary condition associated with premature birth, but the underlying parenchymal disease and trajectory are poorly characterized. The current National Institute of Child Health and Human Development (NICHD)/NHLBI definition of BPD severity is based on degree of prematurity and extent of oxygen requirement. However, no clear link exists between initial diagnosis and clinical outcomes. We hypothesized that magnetic resonance imaging (MRI) of structural parenchymal abnormalities will correlate with NICHD-defined BPD disease severity and predict short-term respiratory outcomes. A total of 42 neonates (20 severe BPD, 6 moderate, 7 mild, 9 non-BPD control subjects; 40 ± 3-wk postmenstrual age) underwent quiet-breathing structural pulmonary MRI (ultrashort echo time and gradient echo) in a neonatal ICU-sited, neonatal-sized 1.5 T scanner, without sedation or respiratory support unless already clinically prescribed. Disease severity was scored independently by two radiologists. Mean scores were compared with clinical severity and short-term respiratory outcomes. Outcomes were predicted using univariate and multivariable models, including clinical data and scores. MRI scores significantly correlated with severities and predicted respiratory support at neonatal ICU discharge (P < 0.0001). In multivariable models, MRI scores were by far the strongest predictor of respiratory support duration over clinical data, including birth weight and gestational age. Notably, NICHD severity level was not predictive of discharge support. Quiet-breathing neonatal pulmonary MRI can independently assess structural abnormalities of BPD, describe disease severity, and predict short-term outcomes more accurately than any individual standard clinical measure. Importantly, this nonionizing technique can be implemented to phenotype disease, and has potential to serially assess efficacy of individualized therapies.

Artifact Properties of Dental Ceramic and Titanium Implants in MRI.

Assessment of the visualization of titanium and ceramic dental implants using various isotropic three-dimensional magnetic resonance imaging (MRI) methods. 21 dental implants (7 ceramic, 14 titanium) were scanned in vitro with a spatially isotropically resolved three-dimensional gradient echo (FFE), a turbo spin echo (SE) and an ultra-short-echo time (UTE) imaging technique. The resulting absolute volumes of the implants were quantified and the relative error to the theoretical volume was calculated. Ceramic implants and their periphery could be displayed well in all cases. The observed mean relative error results were 5.4 ± 2.3 % (UTE) to 6.5 ± 4.3 % (FFE). No significant difference was observed between the investigated MRI methods. The transition between implant and surrounding agarose could be shown in all cases without artifacts. Titanium implants resulted in mean relative errors between 1314 ± 350 % (FFE) and 2157 ± 810 % (SE). Here, significant differences were observed between the FFE and the SE and between the UTE and the SE sequence. The periphery of the implants could not be displayed in any case. Use of the MRI technique for the diagnosis of peri-implantitis, the assessment of anatomical structures and planning of dental implantation is currently very limited but could be used more frequently, provided there are no disturbing or imaging-disturbing materials in the region of interest. MRI technology is not suitable in case of titanium implants. When using ceramic implants, MRI technology is an option. · MRI allows the artifact-free depiction of dental ceramic implants.. · Titanium implants cause the greatest relative errors in SE techniques.. · The UTE technique shows no significant improvements with respect to artifact behavior over the FFE technique.. · Geibel M, Gelißen B, Bracher A et al. Artefakt-Verhalten von dentalen Keramik- und Titanimplantaten im MRT. Fortschr Röntgenstr 2019; 191: 433 - 441.

Accurate hybrid template\u2013based and MR-based attenuation correction using UTE images for simultaneous PET/MR brain imaging applications

BackgroundAttenuation correction is one of the most crucial correction factors for accurate PET data quantitation in hybrid PET/MR scanners, and computing accurate attenuation coefficient maps from MR brain acquisitions is challenging. Here, we develop a method for accurate bone and air segmentation using MR ultrashort echo time (UTE) images.MethodsMR UTE images from simultaneous MR and PET imaging of five healthy volunteers was used to generate a whole head, bone and air template image for inclusion into an improved MR derived attenuation correction map, and applied to PET image data for quantitative analysis. Bone, air and soft tissue were segmented based on Gaussian Mixture Models with probabilistic tissue maps as a priori information. We present results for two approaches for bone attenuation coefficient assignments: one using a constant attenuation correction value; and another using an estimated continuous attenuation value based on a calibration fit. Quantitative comparisons were performed to evaluate the accuracy of the reconstructed PET images, with respect to a reference image reconstructed with manually segmented attenuation maps.ResultsThe DICE coefficient analysis for the air and bone regions in the images demonstrated improvements compared to the UTE approach, and other state-of-the-art techniques. The most accurate whole brain and regional brain analyses were obtained using constant bone attenuation coefficient values.ConclusionsA novel attenuation correction method for PET data reconstruction is proposed. Analyses show improvements in the quantitative accuracy of the reconstructed PET images compared to other state-of-the-art AC methods for simultaneous PET/MR scanners. Further evaluation is needed with radiopharmaceuticals other than FDG, and in larger cohorts of participants.

A Simulation Study on the Fat Caused Chemical Shift Effects on the Magnetic Susceptibility Measurement of IONPs With Ultra-Short TEs

To study how the fat affects the quantification of magnetic susceptibility of iron oxide nanoparticles (IONPs) according to the chemical shift effects, especially at ultra-short echo times, simulation experiments were carried out in this paper. Numerical phantom of IONPs solutions with six different concentrations was designed. Magnetic resonance imaging signals with different fat fractions (ffs) were generated according to a multi-peak chemical shift model. Quantitative susceptibility mapping (QSM) was calculated, and the relationship between the QSM value and ff, as well as echo selection, is evaluated. The results show that streaking artifacts become more and more severe when ff increases, which makes QSM value overestimated. Shortened echo spacing time can reduce streaking artifacts with the same ff. These findings will benefit future clinical evaluations for quantification of iron in vivo.

Quantitative Gd-DOTA-based aerosol deposition mapping in the lungs of asthmatic rats using 3D UTE-MRI.

Asthma is a chronic respiratory disease, commonly treated with inhaled therapy. Better understanding of the mechanisms of aerosol deposition is required to improve inhaled drug delivery. Three-dimensional ultrashort echo time (UTE) MRI acquisitions at 1.5T were combined with spontaneous nose-only inhalation of aerosolized gadolinium (Gd) to map the aerosol deposition and to characterize signal enhancement in asthmatic rat lungs. The rats were sensitized to ovalbumin (OVA) to develop asthmatic models and challenged before imaging by nebulization of OVA to trigger asthmatic symptoms. The negative controls were not sensitized or challenged by nebulization of saline. The animal lungs were imaged before and after administration of Gd-based aerosol in freely breathing rats, by using a T1 -weighted 3D UTE sequence. A contrast-enhanced quantitative analysis was performed to assess regional concentration. OVA-sensitized rats had lower signal enhancement and lower deposited aerosol concentration. Their enhancement dynamics showed large inter-subject variability. The signal intensity was homogeneously enhanced for controls while OVA-sensitized rats showed heterogeneous enhancement. Contrast-enhanced 3D UTE was applied with aerosolized Gd to efficiently measure spatially resolved deposition in asthmatic lungs. The small administered dose (around 1μmol/kg body weight) and the use of standard clinical MRI suggest a potential application for the exploration of asthma.

Dynamic 23Na MRI - A non-invasive window on neuroglial-vascular mechanisms underlying brain function

A novel magnetic resonance imaging (MRI) acquisition and reconstruction method for obtaining a series of dynamic sodium 23Na-MRI acquisitions was designed to non-invasively assess the signal variations of brain sodium during a hand motor task in 14 healthy human volunteers on an ultra high field (7T) MR scanner. Regions undergoing activation and deactivation were identified with reference to conventional task-related BOLD functional MRI (fMRI). Activation observed in the left central regions, the supplementary motor areas and the left cerebellum induced an increase in the sodium signal observed at ultra short echo time and a decrease in the 23Na signal observed at long echo time. Based on a simple model of two distinct sodium pools (namely, restricted and mobile sodium), the ultra short echo time measures the totality of sodium whereas the long echo time is mainly sensitive to mobile sodium. This activation pattern is consistent with previously described processes related to an influx of Na+ into the intracellular compartments and a moderate increase in the cerebral blood volume (CBV). In contrast, deactivation observed in the right central regions ipsilateral to the movement, the precuneus and the left cerebellum induced a slight decrease in sodium signal at ultra short echo time and an increase of sodium signal at longer echo times. This inhibitory pattern is compatible with a slight decrease in CBV and an efflux of intracellular Na+ to the extracellular compartments that may reflect neural dendritic spine and astrocytic shrinkage, and an increase of sodium in the extracellular fraction. In conclusion, cerebral dynamic 23Na MRI experiments can provide access to the ionic transients following a functional task occurring within the neuro-glial-vascular ensemble. This has the potential to open up a novel non-invasive window on the mechanisms underlying brain function.