Enhancing quality and speed in database-free neural network reconstructions of undersampled MRI with SCAMPI.

PURPOSE: We present SCAMPI (Sparsity Constrained Application of deep Magnetic resonance Priors for Image reconstruction), an untrained deep Neural Network for MRI reconstruction without previous training on datasets. It expands the Deep Image Prior approach with a multidomain, sparsity-enforcing loss function to achieve higher image quality at a faster convergence speed than previously reported methods. METHODS: Two-dimensional MRI data from the FastMRI dataset with Cartesian undersampling in phase-encoding direction were reconstructed for different acceleration rates for single coil and multicoil data. RESULTS: The performance of our architecture was compared to state-of-the-art Compressed Sensing methods and ConvDecoder, another untrained Neural Network for two-dimensional MRI reconstruction. SCAMPI outperforms these by better reducing undersampling artifacts and yielding lower error metrics in multicoil imaging. In comparison to ConvDecoder, the U-Net architecture combined with an elaborated loss-function allows for much faster convergence at higher image quality. SCAMPI can reconstruct multicoil data without explicit knowledge of coil sensitivity profiles. Moreover, it is a novel tool for reconstructing undersampled single coil k-space data. CONCLUSION: Our approach avoids overfitting to dataset features, that can occur in Neural Networks trained on databases, because the network parameters are tuned only on the reconstruction data. It allows better results and faster reconstruction than the baseline untrained Neural Network approach.

Seeing plants as never before.

Imaging has long supported our ability to understand the inner life of plants, their development, and response to a dynamic environment. While optical microscopy remains the core tool for imaging, a suite of novel technologies is now beginning to make a significant contribution to visualize plant metabolism. The purpose of this review was to provide the scientific community with an overview of current imaging methods, which rely variously on either nuclear magnetic resonance (NMR), mass spectrometry (MS) or infrared (IR) spectroscopy, and to present some examples of their application in order to illustrate their utility. In addition to providing a description of the basic principles underlying these technologies, the review discusses their various advantages and limitations, reveals the current state of the art, and suggests their potential application to experimental practice. Finally, a view is presented as to how the technologies will likely develop, how these developments may encourage the formulation of novel experimental strategies, and how the enormous potential of these technologies can contribute to progress in plant science.

Iterative training of robust k-space interpolation networks for improved image reconstruction with limited scan specific training samples.

PURPOSE: To evaluate an iterative learning approach for enhanced performance of robust artificial-neural-networks for k-space interpolation (RAKI), when only a limited amount of training data (auto-calibration signals [ACS]) are available for accelerated standard 2D imaging. METHODS: In a first step, the RAKI model was tailored for the case of limited training data amount. In the iterative learning approach (termed iterative RAKI [iRAKI]), the tailored RAKI model is initially trained using original and augmented ACS obtained from a linear parallel imaging reconstruction. Subsequently, the RAKI convolution filters are refined iteratively using original and augmented ACS extracted from the previous RAKI reconstruction. Evaluation was carried out on 200 retrospectively undersampled in vivo datasets from the fastMRI neuro database with different contrast settings. RESULTS: For limited training data (18 and 22 ACS lines for R = 4 and R = 5, respectively), iRAKI outperforms standard RAKI by reducing residual artifacts and yields better noise suppression when compared to standard parallel imaging, underlined by quantitative reconstruction quality metrics. Additionally, iRAKI shows better performance than both GRAPPA and standard RAKI in case of pre-scan calibration with varying contrast between training- and undersampled data. CONCLUSION: RAKI benefits from the iterative learning approach, which preserves the noise suppression feature, but requires less original training data for the accurate reconstruction of standard 2D images thereby improving net acceleration.

Quantitative monitoring of paramagnetic contrast agents and their allocation in plant tissues via DCE-MRI.

BACKGROUND: Studying dynamic processes in living organisms with MRI is one of the most promising research areas. The use of paramagnetic compounds as contrast agents (CA), has proven key to such studies, but so far, the lack of appropriate techniques limits the application of CA-technologies in experimental plant biology. The presented proof-of-principle aims to support method and knowledge transfer from medical research to plant science. RESULTS: In this study, we designed and tested a new approach for plant Dynamic Contrast Enhanced Magnetic Resonance Imaging (pDCE-MRI). The new approach has been applied in situ to a cereal crop (Hordeum vulgare). The pDCE-MRI allows non-invasive investigation of CA allocation within plant tissues. In our experiments, gadolinium-DTPA, the most commonly used contrast agent in medical MRI, was employed. By acquiring dynamic T1-maps, a new approach visualizes an alteration of a tissue-specific MRI parameter T1 (longitudinal relaxation time) in response to the CA. Both, the measurement of local CA concentration and the monitoring of translocation in low velocity ranges (cm/h) was possible using this CA-enhanced method. CONCLUSIONS: A novel pDCE-MRI method is presented for non-invasive investigation of paramagnetic CA allocation in living plants. The temporal resolution of the T1-mapping has been significantly improved to enable the dynamic in vivo analysis of transport processes at low-velocity ranges, which are common in plants. The newly developed procedure allows to identify vascular regions and to estimate their involvement in CA allocation. Therefore, the presented technique opens a perspective for further development of CA-aided MRI experiments in plant biology.

Serotonin transporter genotype modulates resting state and predator stress-induced amygdala perfusion in mice in a sex-dependent manner.

The serotonin transporter (5-HTT) is a key molecule of serotoninergic neurotransmission and target of many anxiolytics and antidepressants. In humans, 5-HTT gene variants resulting in lower expression levels are associated with behavioral traits of anxiety. Furthermore, functional magnetic resonance imaging (fMRI) studies reported increased cerebral blood flow (CBF) during resting state (RS) and amygdala hyperreactivity. 5-HTT deficient mice as an established animal model for anxiety disorders seem to be well suited for investigating amygdala (re-)activity in an fMRI study. We investigated wildtype (5-HTT+/+), heterozygous (5-HTT+/-), and homozygous 5-HTT-knockout mice (5-HTT-/-) of both sexes in an ultra-high-field 17.6 Tesla magnetic resonance scanner. CBF was measured with continuous arterial spin labeling during RS, stimulation state (SS; with odor of rats as aversive stimulus), and post-stimulation state (PS). Subsequently, post mortem c-Fos immunohistochemistry elucidated neural activation on cellular level. The results showed that in reaction to the aversive odor CBF in total brain and amygdala of all mice significantly increased. In male 5-HTT+/+ mice amygdala RS CBF levels were found to be significantly lower than in 5-HTT+/- mice. From RS to SS 5-HTT+/+ amygdala perfusion significantly increased compared to both 5-HTT+/- and 5-HTT-/- mice. Perfusion level changes of male mice correlated with the density of c-Fos-immunoreactive cells in the amygdaloid nuclei. In female mice the perfusion was not modulated by the 5-Htt-genotype, but by estrous cycle stages. We conclude that amygdala reactivity is modulated by the 5-Htt genotype in males. In females, gonadal hormones have an impact which might have obscured genotype effects. Furthermore, our results demonstrate experimental support for the tonic model of 5-HTTLPR function.

Balanced spin-lock preparation for B1 -insensitive and B0 -insensitive quantification of the rotating frame relaxation time T1ρ.

PURPOSE: Accurate and artifact-free T1ρ quantification is still a major challenge due to a susceptibility of the spin-locking module to B0 and/or B1 field inhomogeneities. In this study, we present a novel spin-lock preparation module (B-SL) that enables an almost full compensation of both types of inhomogeneities. METHODS: The new B-SL module contains a second 180° refocusing pulse to compensate each pulse in the preparation block by a corresponding pulse with opposite phase. For evaluation and validation of B-SL, extensive simulations as well as phantom measurements were performed. Furthermore, the new module was compared to three common established compensation methods. RESULTS: Both simulations and measurements demonstrate a much lower susceptibility to artifacts for the B-SL module, therefore providing an improved accuracy in T1ρ quantification. In the presence of field inhomogeneities, measurements revealed an increased banding compensation by 79% compared with the frequently used composite module. The goodness of the mono-exponential T1ρ fitting procedure was improved by 58%. CONCLUSION: The B-SL preparation enables the generation of accurate relaxation maps with significantly reduced artifacts, even in the case of large field imperfections. Therefore, the B-SL module is suggested to be highly beneficial for in vivo T1ρ quantification.

Simultaneous T1 and T2 measurements using inversion recovery TrueFISP with principle component-based reconstruction, off-resonance correction, and multicomponent analysis.

PURPOSE: To improve the reconstruction quality for quantitative T1 and T2 measurements using the inversion recovery (IR) TrueFISP sequence and to demonstrate the potential for multicomponent analysis. METHODS: The iterative reconstruction method takes advantage of the high redundancy in the smooth exponential signals using principle component analysis (PCA). Multicomponent information is preserved and allows voxel-by-voxel computation of relaxation time spectra with an inverse Laplace transform. Off-resonance effects are analytically and numerically investigated and a correction approach is presented. RESULTS: Single-shot IR TrueFISP in vivo measurements on healthy volunteers demonstrate the improved reconstruction performance compared to a view sharing (k-space weighted image contrast [KWIC]) reconstruction. Especially, tissue components with short apparent relaxation times T1 * are not filtered out and can be identified in the relaxation time spectra. These components include myelin in the human brain (T1 * ≈ 130 ms) and extra cranial subcutaneous fat. CONCLUSION: The PCA-based reconstruction method improves the temporal accuracy and preserves multicomponent information. Spatially resolved relaxation time spectra can be obtained and allow the identification of tissue types with short, apparent relaxation times.

Improved compressed sensing reconstruction for [Formula: see text]F magnetic resonance imaging.

OBJECTIVE: In magnetic resonance imaging (MRI), compressed sensing (CS) enables the reconstruction of undersampled sparse data sets. Thus, partial acquisition of the underlying k-space data is sufficient, which significantly reduces measurement time. While 19F MRI data sets are spatially sparse, they often suffer from low SNR. This can lead to artifacts in CS reconstructions that reduce the image quality. We present a method to improve the image quality of undersampled, reconstructed CS data sets. MATERIALS AND METHODS: Two resampling strategies in combination with CS reconstructions are presented. Numerical simulations are performed for low-SNR spatially sparse data obtained from 19F chemical-shift imaging measurements. Different parameter settings for undersampling factors and SNR values are tested and the error is quantified in terms of the root-mean-square error. RESULTS: An improvement in overall image quality compared to conventional CS reconstructions was observed for both strategies. Specifically spike artifacts in the background were suppressed, while the changes in signal pixels remained small. DISCUSSION: The proposed methods improve the quality of CS reconstructions. Furthermore, because resampling is applied during post-processing, no additional measurement time is required. This allows easy incorporation into existing protocols and application to already measured data.

Real-time Triggered RAdial Single-Shot Inversion recovery for arrhythmia-insensitive myocardial T1 mapping: motion phantom validation and in vivo comparison.

PURPOSE: Cardiac T1 mapping has become an increasingly important imaging technique, contributing novel diagnostic options. However, currently utilized methods are often associated with accuracy problems because of heart rate variations and cardiac arrhythmia, limiting their value in clinical routine. This study aimed to introduce an improved arrhythmia-related robust T1 mapping sequence called RT-TRASSI (real-time Triggered RAdial Single-Shot Inversion recovery). METHODS: All measurements were performed on a 3.0T whole-body imaging system. A real-time feedback algorithm for arrhythmia detection was implemented into the previously described pulse sequence. A programmable motion phantom was constructed and measurements with different simulated arrhythmias arranged. T1 mapping accuracy and susceptibility to artifacts were analyzed. In addition, in vivo measurements and comparisons with 3 prevailing T1 mapping sequences (MOLLI, ShMOLLI, and SASHA) were carried out to investigate the occurrence of artifacts. RESULTS: In the motion phantom measurements, RT-TRASSI showed excellent agreement with predetermined reference T1 values. Percentage scattering of the T1 values ranged from -0.6% to +1.9% in sinus rhythm and -1.0% to +3.1% for high-grade arrhythmias. In vivo, RT-TRASSI showed diagnostic image quality with only 6% of the acquired T1 maps including image artifacts. In contrast, more than 40% of the T1 maps acquired with MOLLI, ShMOLLI, or SASHA included motion artifacts. CONCLUSION: Accuracy issues because of heart rate variability and arrhythmia are a prevailing problem in current cardiac T1 mapping techniques. With RT-TRASSI, artifacts can be minimized because of the short acquisition time and effective real-time feedback, avoiding potential data acquisition during systolic heart phase.

Towards quantitative perfusion MRI of the lung in COPD: The problem of short-term repeatability.

PURPOSE: 4D perfusion magnetic resonance imaging (MRI) with intravenous injection of contrast agent allows for a radiation-free assessment of regional lung function. It is therefore a valuable method to monitor response to treatment in patients with chronic obstructive pulmonary disease (COPD). This study was designed to evaluate its potential for monitoring short-term response to hyperoxia in COPD patients. MATERIALS AND METHODS: 19 prospectively enrolled COPD patients (median age 66y) underwent paired dynamic contrast-enhanced 4D perfusion MRI within 35min, first breathing 100% oxygen (injection 1, O2) and then room air (injection 2, RA), which was repeated on two consecutive days (day 1 and 2). Post-processing software was employed to calculate mean transit time (MTT), pulmonary blood volume (PBV) and pulmonary blood flow (PBF), based on the indicator dilution theory, for the automatically segmented whole lung and 12 regions of equal volume. RESULTS: Comparing O2 with RA conditions, PBF and PBV were found to be significantly lower at O2, consistently on both days (p<10-8). Comparing day 2 to day 1, MTT was shorter by 0.59±0.63 s (p<10-8), PBF was higher by 22±80 ml/min/100ml (p<3·10-4), and PBV tended to be lower by 0.2±7.2 ml/100ml (p = 0.159) at both, RA and O2, conditions. CONCLUSION: The second injection (RA) yielded higher PBF and PBV, which apparently contradicts the established hypothesis that hyperoxia increases lung perfusion. Quantification of 4D perfusion MRI by current software approaches may thus be limited by residual circulating contrast agent in the short-term and even the next day.

Stable and efficient retrospective 4D-MRI using non-uniformly distributed quasi-random numbers.

The purpose of this work is the development of a robust and reliable three-dimensional (3D) Cartesian imaging technique for fast and flexible retrospective 4D abdominal MRI during free breathing. To this end, a non-uniform quasi random (NU-QR) reordering of the phase encoding (k y -k z ) lines was incorporated into 3D Cartesian acquisition. The proposed sampling scheme allocates more phase encoding points near the k-space origin while reducing the sampling density in the outer part of the k-space. Respiratory self-gating in combination with SPIRiT-reconstruction is used for the reconstruction of abdominal data sets in different respiratory phases (4D-MRI). Six volunteers and three patients were examined at 1.5 T during free breathing. Additionally, data sets with conventional two-dimensional (2D) linear and 2D quasi random phase encoding order were acquired for the volunteers for comparison. A quantitative evaluation of image quality versus scan times (from 70 s to 626 s) for the given sampling schemes was obtained by calculating the normalized mutual information (NMI) for all volunteers. Motion estimation was accomplished by calculating the maximum derivative of a signal intensity profile of a transition (e.g. tumor or diaphragm). The 2D non-uniform quasi-random distribution of phase encoding lines in Cartesian 3D MRI yields more efficient undersampling patterns for parallel imaging compared to conventional uniform quasi-random and linear sampling. Median NMI values of NU-QR sampling are the highest for all scan times. Therefore, within the same scan time 4D imaging could be performed with improved image quality. The proposed method allows for the reconstruction of motion artifact reduced 4D data sets with isotropic spatial resolution of 2.1 × 2.1 × 2.1 mm3 in a short scan time, e.g. 10 respiratory phases in only 3 min. Cranio-caudal tumor displacements between 23 and 46 mm could be observed. NU-QR sampling enables for stable 4D-MRI with high temporal and spatial resolution within short scan time for visualization of organ or tumor motion during free breathing. Further studies, e.g. the application of the method for radiotherapy planning are needed to investigate the clinical applicability and diagnostic value of the approach.

Functional lung MRI for regional monitoring of patients with cystic fibrosis.

PURPOSE: To test quantitative functional lung MRI techniques in young adults with cystic fibrosis (CF) compared to healthy volunteers and to monitor immediate treatment effects of a single inhalation of hypertonic saline in comparison to clinical routine pulmonary function tests. MATERIALS AND METHODS: Sixteen clinically stable CF patients and 12 healthy volunteers prospectively underwent two functional lung MRI scans and pulmonary function tests before and 2h after a single treatment of inhaled hypertonic saline or without any treatment. MRI-derived oxygen enhanced T1 relaxation measurements, fractional ventilation, first-pass perfusion parameters and a morpho-functional CF-MRI score were acquired. RESULTS: Compared to healthy controls functional lung MRI detected and quantified significantly increased ventilation heterogeneity in CF patients. Regional functional lung MRI measures of ventilation and perfusion as well as the CF-MRI score and pulmonary function tests could not detect a significant treatment effect two hours after a single treatment with hypertonic saline in young adults with CF (p>0.05). CONCLUSION: This study shows the feasibility of functional lung MRI as a non-invasive, radiation-free tool for monitoring patients with CF.

Calcium fluoride based multifunctional nanoparticles for multimodal imaging.

New multifunctional nanoparticles (NPs) that can be used as contrast agents (CA) in different imaging techniques, such as photoluminescence (PL) microscopy and magnetic resonance imaging (MRI), open new possibilities for medical imaging, e.g., in the fields of diagnostics or tissue characterization in regenerative medicine. The focus of this study is on the synthesis and characterization of CaF2:(Tb3+,Gd3+) NPs. Fabricated in a wet-chemical procedure, the spherical NPs with a diameter of 5-10 nm show a crystalline structure. Simultaneous doping of the NPs with different lanthanide ions, leading to paramagnetism and fluorescence, makes them suitable for MR and PL imaging. Owing to the Gd3+ ions on the surface, the NPs reduce the MR T1 relaxation time constant as a function of their concentration. Thus, the NPs can be used as a MRI CA with a mean relaxivity of about r = 0.471 mL·mg-1·s-1. Repeated MRI examinations of four different batches prove the reproducibility of the NP synthesis and determine the long-term stability of the CAs. No cytotoxicity of NP concentrations between 0.5 and 1 mg·mL-1 was observed after exposure to human dermal fibroblasts over 24 h. Overall this study shows, that the CaF2:(Tb3+,Gd3+) NPs are suitable for medical imaging.

A functional imaging study of germinating oilseed rape seed.

Germination, the process whereby a dry, quiescent seed springs to life, has been a focus of plant biologist for many years, yet the early events following water uptake, during which metabolism of the embryo is restarted, remain enigmatic. Here, the nature of the cues required for this restarting in oilseed rape (Brassica napus) seed has been investigated. A holistic in vivo approach was designed to display the link between the entry and allocation of water, metabolic events and structural changes occurring during germination. For this, we combined functional magnetic resonance imaging with Fourier transform infrared microscopy, fluorescence-based respiration mapping, computer-aided seed modeling and biochemical tools. We uncovered an endospermal lipid gap, which channels water to the radicle tip, from whence it is distributed via embryonic vasculature toward cotyledon tissues. The resumption of respiration is initiated first in the endosperm, only later spreading to the embryo. Sugar metabolism and lipid utilization are linked to the spatiotemporal sequence of tissue rehydration. Together, this imaging study provides insights into the spatial aspects of key events in oilseed rape seeds leading to germination. It demonstrates how seed architecture predetermines the pattern of water intake, which sets the stage for the orchestrated restart of life.

In vivo T2* weighted MRI visualizes cardiac lesions in murine models of acute and chronic viral myocarditis.

OBJECTIVE: Acute and chronic forms of myocarditis are mainly induced by virus infections. As a consequence of myocardial damage and inflammation dilated cardiomyopathy and chronic heart failure may develop. The gold standard for the diagnosis of myocarditis is endomyocardial biopsies which are required to determine the etiopathogenesis of cardiac inflammatory processes. However, new non-invasive MRI techniques hold great potential in visualizing cardiac non-ischemic inflammatory lesions at high spatial resolution, which could improve the investigation of the pathophysiology of viral myocarditis. RESULTS: Here we present the discovery of a novel endogenous T2* MRI contrast of myocardial lesions in murine models of acute and chronic CVB3 myocarditis. The evaluation of infected hearts ex vivo and in vivo by 3D T2w and T2*w MRI allowed direct localization of virus-induced myocardial lesions without any MRI tracer or contrast agent. T2*w weighted MRI is able to detect both small cardiac lesions of acute myocarditis and larger necrotic areas at later stages of chronic myocarditis, which was confirmed by spatial correlation of MRI hypointensity in myocardium with myocardial lesions histologically. Additional in vivo and ex vivo MRI analysis proved that the contrast mechanism was due to a strong paramagnetic tissue alteration in the vicinity of myocardial lesions, effectively pointing towards iron deposits as the primary contributor of contrast. The evaluation of the biological origin of the MR contrast by specific histological staining and transmission electron microscopy revealed that impaired iron metabolism primarily in mitochondria caused iron deposits within necrotic myocytes, which induces strong magnetic susceptibility in myocardial lesions and results in strong T2* contrast. CONCLUSION: This T2*w MRI technique provides a fast and sensitive diagnostic tool to determine the patterns and the severity of acute and chronic enteroviral myocarditis and the precise localization of tissue damage free of MR contrast agents.

Local versus global aortic pulse wave velocity in early atherosclerosis: An animal study in ApoE-/--mice using ultrahigh field MRI.

Increased aortic stiffness is known to be associated with atherosclerosis and has a predictive value for cardiovascular events. This study aims to investigate the local distribution of early arterial stiffening due to initial atherosclerotic lesions. Therefore, global and local pulse wave velocity (PWV) were measured in ApoE-/- and wild type (WT) mice using ultrahigh field MRI. For quantification of global aortic stiffness, a new multi-point transit-time (TT) method was implemented and validated to determine the global PWV in the murine aorta. Local aortic stiffness was measured by assessing the local PWV in the upper abdominal aorta, using the flow/area (QA) method. Significant differences between age matched ApoE-/- and WT mice were determined for global and local PWV measurements (global PWV: ApoE-/-: 2.7±0.2m/s vs WT: 2.1±0.2m/s, P<0.03; local PWV: ApoE-/-: 2.9±0.2m/s vs WT: 2.2±0.2m/s, P<0.03). Within the WT mouse group, the global PWV correlated well with the local PWV in the upper abdominal aorta (R2 = 0.75, P<0.01), implying a widely uniform arterial elasticity. In ApoE-/- animals, however, no significant correlation between individual local and global PWV was present (R2 = 0.07, P = 0.53), implying a heterogeneous distribution of vascular stiffening in early atherosclerosis. The assessment of global PWV using the new multi-point TT measurement technique was validated against a pressure wire measurement in a vessel phantom and showed excellent agreement. The experimental results demonstrate that vascular stiffening caused by early atherosclerosis is unequally distributed over the length of large vessels. This finding implies that assessing heterogeneity of arterial stiffness by multiple local measurements of PWV might be more sensitive than global PWV to identify early atherosclerotic lesions.

Reproducibility and comparison of oxygen-enhanced T1 quantification in COPD and asthma patients.

T1 maps have been shown to yield useful diagnostic information on lung function in patients with chronic obstructive pulmonary disease (COPD) and asthma, both for native T1 and ΔT1, the relative reduction while breathing pure oxygen. As parameter quantification is particularly interesting for longitudinal studies, the purpose of this work was both to examine the reproducibility of lung T1 mapping and to compare T1 found in COPD and asthma patients using IRSnapShotFLASH embedded in a full MRI protocol. 12 asthma and 12 COPD patients (site 1) and further 15 COPD patients (site 2) were examined on two consecutive days. In each patient, T1 maps were acquired in 8 single breath-hold slices, breathing first room air, then pure oxygen. Maps were partitioned into 12 regions each to calculate average values. In asthma patients, the average T1,RA = 1206ms (room air) was reduced to T1,O2 = 1141ms under oxygen conditions (ΔT1 = 5.3%, p < 5⋅10-4), while in COPD patients both native T1,RA = 1125ms was significantly shorter (p < 10-3) and the relative reduction to T1,O2 = 1081ms on average ΔT1 = 4.2%(p < 10-5). On the second day, with T1,RA = 1186ms in asthma and T1,RA = 1097ms in COPD, observed values were slightly shorter on average in all patient groups. ΔT1 reduction was the least repeatable parameter and varied from day to day by up to 23% in individual asthma and 30% in COPD patients. While for both patient groups T1 was below the values reported for healthy subjects, the T1 and ΔT1 found in asthmatics lies between that of the COPD group and reported values for healthy subjects, suggesting a higher blood volume fraction and better ventilation. However, it could be demonstrated that lung T1 quantification is subject to notable inter-examination variability, which here can be attributed both to remaining contrast agent from the previous day and the increased dependency of lung T1 on perfusion and thus current lung state.

Desynchronization of Cartesian k-space sampling and periodic motion for improved retrospectively self-gated 3D lung MRI using quasi-random numbers.

PURPOSE: To demonstrate that desynchronization between Cartesian k-space sampling and periodic motion in free-breathing lung MRI improves the robustness and efficiency of retrospective respiratory self-gating. METHODS: Desynchronization was accomplished by reordering the phase (ky ) and partition (kz ) encoding of a three-dimensional FLASH sequence according to two-dimensional, quasi-random (QR) numbers. For retrospective respiratory self-gating, the k-space center signal (DC signal) was acquired separately after each encoded k-space line. QR sampling results in a uniform distribution of k-space lines after gating. Missing lines resulting from the gating process were reconstructed using iterative GRAPPA. Volunteer measurements were performed to compare quasi-random with conventional sampling. Patient measurements were performed to demonstrate the feasibility of QR sampling in a clinical setting. RESULTS: The uniformly sampled k-space after retrospective gating allows for a more stable iterative GRAPPA reconstruction and improved ghost artifact reduction compared with conventional sampling. It is shown that this stability can either be used to reduce the total scan time or to reconstruct artifact-free data sets in different respiratory phases, both resulting in an improved efficiency of retrospective respiratory self-gating. CONCLUSION: QR sampling leads to desynchronization between repeated data acquisition and periodic respiratory motion. This results in an improved motion artifact reduction in shorter scan time. Magn Reson Med 77:787-793, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

The potential of nuclear magnetic resonance to track lipids in planta.

Nuclear Magnetic Resonance (NMR) provides a highly flexible platform for non invasive analysis and imaging biological samples, since the manipulation of nuclear spin allows the tailoring of experiments to maximize the informativeness of the data. MRI is capable of visualizing a holistic picture of the lipid storage in living plant/seed. This review has sought to explain how the technology can be used to acquire functional and physiological data from plant samples, and how to exploit it to characterize lipid deposition in vivo. At the same time, we have referred to the current limitations of NMR technology as applied to plants, and in particular of the difficulty of transferring methodologies optimized for animal/medical subjects to plant ones. A forward look into likely developments in the field is included, anticipating its key future role in the study of living plant.

Design of a mobile, homogeneous, and efficient electromagnet with a large field of view for neonatal low-field MRI.

OBJECTIVE: In this work, a prototype of an effective electromagnet with a field-of-view (FoV) of 140 mm for neonatal head imaging is presented. The efficient implementation succeeded by exploiting the use of steel plates as a housing system. We achieved a compromise between large sample volumes, high homogeneity, high B0 field, low power consumption, light weight, simple fabrication, and conserved mobility without the necessity of a dedicated water cooling system. MATERIALS AND METHODS: The entire magnetic resonance imaging (MRI) system (electromagnet, gradient system, transmit/receive coil, control system) is introduced and its unique features discussed. Furthermore, simulations using a numerical optimization algorithm for magnet and gradient system are presented. RESULTS: Functionality and quality of this low-field scanner operating at 23 mT (generated with 500 W) is illustrated using spin-echo imaging (in-plane resolution 1.6 mm × 1.6 mm, slice thickness 5 mm, and signal-to-noise ratio (SNR) of 23 with a acquisition time of 29 min). B0 field-mapping measurements are presented to characterize the homogeneity of the magnet, and the B0 field limitations of 80 mT of the system are fully discussed. CONCLUSION: The cryogen-free system presented here demonstrates that this electromagnet with a ferromagnetic housing can be optimized for MRI with an enhanced and homogeneous magnetic field. It offers an alternative to prepolarized MRI designs in both readout field strength and power use. There are multiple indications for the clinical medical application of such low-field devices.