Magnetic Resonance Data Acquisition Research Articles

Rapid nuclear magnetic resonance data acquisition with improved resolution and sensitivity for high-throughput metabolomic analysis.

Nuclear magnetic resonance (NMR)-based metabolomics has witnessed rapid advancements in recent years with the continuous development of new methods to enhance the sensitivity, resolution, and speed of data acquisition. Some of the approaches were earlier used for peptide and protein resonance assignments and have now been adapted to metabolomics. At the same time, new NMR methods involving novel data acquisition techniques, suited particularly for high-throughput analysis in metabolomics, have been developed. In this review, we focus on the different sampling strategies or data acquisition methods that have been developed in our laboratory and other groups to acquire NMR spectra rapidly with high sensitivity and resolution for metabolomics. In particular, we focus on the use of multiple receivers, phase modulation NMR spectroscopy, and fast-pulsing methods for identification and assignments of metabolites.

MR biomarkers predict clinical function in Duchenne muscular dystrophy.

To investigate the potential of lower extremity magnetic resonance (MR) biomarkers to serve as endpoints in clinical trials of therapeutics for Duchenne muscular dystrophy (DMD) by characterizing the longitudinal progression of MR biomarkers over 48 months and assessing their relationship to changes in ambulatory clinical function. One hundred sixty participants with DMD were enrolled in this longitudinal, natural history study and underwent MR data acquisition of the lower extremity muscles to determine muscle fat fraction (FF) and MRI T2 biomarkers of disease progression. In addition, 4 tests of ambulatory function were performed. Participants returned for follow-up data collection at 12, 24, 36, and 48 months. Longitudinal analysis of the MR biomarkers revealed that vastus lateralis FF, vastus lateralis MRI T2, and biceps femoris long head MRI T2 biomarkers were the fastest progressing biomarkers over time in this primarily ambulatory cohort. Biomarker values tended to demonstrate a nonlinear, sigmoidal trajectory over time. The lower extremity biomarkers predicted functional performance 12 and 24 months later, and the magnitude of change in an MR biomarker over time was related to the magnitude of change in function. Vastus lateralis FF, soleus FF, vastus lateralis MRI T2, and biceps femoris long head MRI T2 were the strongest predictors of future loss of function, including loss of ambulation. This study supports the strong relationship between lower extremity MR biomarkers and measures of clinical function, as well as the ability of MR biomarkers, particularly those from proximal muscles, to predict future ambulatory function and important clinical milestones. NCT01484678.

A Reconfigurable Platform for Magnetic Resonance Data Acquisition and Processing.

Developments in magnetic resonance imaging (MRI) in the last decades show a trend towards a growing number of array coils and an increasing use of a wide variety of sensors. Associated cabling and safety issues have been addressed by moving data acquisition closer to the coil. However, with the increasing number of radio-frequency (RF) channels and trend towards higher acquisition duty-cycles, the data amount is growing, which poses challenges for throughput and data handling. As it is becoming a limitation, early compression and preprocessing is becoming ever more important. Additionally, sensors deliver diverse data, which require distinct and often low-latency processing for run-time updates of scanner operation. To address these challenges, we propose the transition to reconfigurable hardware with an application tailored assembly of interfaces and real-time processing resources. We present an integrated solution based on a system-on-chip (SoC), which offers sufficient throughput and hardware-based parallel processing power for very challenging applications. It is equipped with fiber-optical modules serving as versatile interfaces for modular systems with in-field operation. We demonstrate the utility of the platform on the example of concurrent imaging and field sensing with hardware-based coil compression and trajectory extraction. The preprocessed data are then used in expanded encoding model based image reconstruction of single-shot and segmented spirals as used in time-series and anatomical imaging respectively.

Evolving role of magnetic resonance techniques in primary sclerosing cholangitis.

Development of non-invasive methods to risk-stratify patients and predict clinical endpoints have been identified as one of the key research priorities in primary sclerosing cholangitis (PSC). In addition to serum and histological biomarkers, there has been much recent interest in developing imaging biomarkers that can predict disease course and clinical outcomes in PSC. Magnetic resonance imaging/magnetic resonance cholangiopancreatography (MRI/MRCP) continue to play a central role in the diagnosis and follow-up of PSC patients. Magnetic resonance (MR) techniques have undergone significant advancement over the last three decades both in MR data acquisition and interpretation. The progression from a qualitative to quantitative approach in MR acquisition techniques and data interpretation, offers the opportunity for the development of objective and reproducible imaging biomarkers that can potentially be incorporated as an additional endpoint in clinical trials. This review article will discuss how the role of MR techniques have evolved over the last three decades from emerging as an alternative diagnostic tool to endoscopic retrograde cholangiopancreatography, to being instrumental in the ongoing search for imaging biomarker of disease stage, progression and prognosis in PSC.

Sparsity Promoting Adaptive Regularization for Compressed Sensing Parallel MRI

Low sampling density and reduced signal-to-noise ratio resulting from accelerated magnetic resonance data acquisition calls for sparsity promoting regularization for improved reconstruction. The simplest optimization strategy relies on thresholded Landweber algorithm that results in reconstructions with slow rate of convergence. A varying threshold can accelerate the rate of convergence, but does not guarantee low steady-state errors. In this paper, we propose a statistical approach to optimize the tradeoff between steady-state reconstruction error and speed of convergence, by iteratively adapting the regularization parameter. Analogous to the generalized discrepancy principle that implicates the nonnegativity of discrepancy level (absolute difference between $l_{2}$ -norms of consistency and perturbation errors) as provided by regularized reconstruction, the proposed method of adaptation entails reduction of the discrepancy level in $l_{1}$ -norm of the consistency and sparse approximation errors. In discrete form, this is deduced from the convergence properties of Landweber updates soft thresholded using monotonically decreasing thresholds. With very large number of iterations, the thresholds approach a lower bound determined by the noise level and adaptation function. Further improvements in image quality can be achieved by separately adapting the thresholds in each wavelet subband. Application of adaptive regularization combined with over-relaxation to parallel MRI shows significant improvements in both speed and image quality.

Spatially Resolved MR-Compatible Doppler Ultrasound: Proof of Concept for Triggering of Diagnostic Quality Cardiovascular MRI for Function and Flow Quantification at 3T.

We demonstrate the use of a magnetic-resonance (MR)-compatible ultrasound (US) imaging probe using spatially resolved Doppler for diagnostic quality cardiovascular MR imaging (MRI) as an initial step toward hybrid US/MR fetal imaging. A newly developed technology for a dedicated MR-compatible phased array ultrasound-imaging probe acquired pulsed color Doppler carotid images, which were converted in near-real time to a trigger signal for cardiac cine and flow quantification MRI. Ultrasound and MR data acquired simultaneously were interference free. Conventional electrocardiogram (ECG) and the proposed spatially resolved Doppler triggering were compared in 10 healthy volunteers. A synthetic "false-triggered" image was retrospectively processed using metric optimized gating (MOG). Images were scored by expert readers, and sharpness, cardiac function and aortic flow were quantified. Four-dimensional (4-D) flow (two volunteers) showed feasibility of Doppler triggering over a long acquisition time. Imaging modalities were compatible. US probe positioning was stable and comfortable. Image quality scores and quantified sharpness were statistically equal for Doppler- and ECG-triggering (p ). ECG-, Doppler-triggered, and MOG ejection fractions were equivalent (p ), with false-triggered values significantly lower (p < 0.0005). Aortic flow showed no difference between ECG- and Doppler-triggered and MOG (p > 0.05). 4-D flow quantification gave consistent results between ECG and Doppler triggering. We report interference-free pulsed color Doppler ultrasound during MR data acquisition. Cardiovascular MRI of diagnostic quality was successfully obtained with pulsed color Doppler triggering. The hardware platform could further enable advanced free-breathing cardiac imaging. Doppler ultrasound triggering is applicable where ECG is compromised due to pathology or interference at higher magnetic fields, and where direct ECG is impossible, i.e., fetal imaging.

Neural correlates of childhood language disorder: a systematic review.

The neurobiological contributions of childhood language disorder are not well understood. Yet there is increasing evidence that language disorder is associated with differences in brain structure and/or function in core language regions. A key hypothesis has been that children with language disorder do not show the same degree of leftward asymmetry of these regions as observed in typically developing children. We aimed to systematically review structural and functional magnetic resonance imaging (fMRI) studies to examine brain commonalities and differences between children with language disorder and typically developing controls; and differences in leftward asymmetry between these groups. A systematic review was conducted using MeSH terms synonymous with childhood language disorder and brain MRI methods. The search identified 1443 papers, and 18 articles met the criteria and were appraised for level and quality of evidence. Atypical brain structure and function was reported within traditionally recognized language regions across studies, including the inferior frontal gyrus, posterior superior temporal gyrus, and caudate nucleus. The direction of difference (e.g. increased/decreased) was variable, however, likely because of differences in language disorder groups examined and magnetic resonance data acquisition and analysis approaches. As regards asymmetry, there was some evidence of reduction of the anticipated structural and functional leftward asymmetry in frontal language regions in language disorder groups. Mounting evidence suggests that children with language disorder have atypical brain structure and function within neural regions integral to language. There is limited support for the hypothesis that children with language disorder show a reduction of leftward structural and/or functional asymmetry in frontal language regions. Interpretation is limited, however, by a high degree of variability in language disorder assessment and phenotype, and in magnetic resonance methodologies. A large-scale magnetic resonance study of brain structure and function is required in a well-defined language disorder population cohort, with replication, to provide confirmatory data on the neural correlates of childhood language disorder.

Quadrature birdcage coil with distributed capacitors for 7.0 T magnetic resonance data acquisition of small animals

ABSTRACTHigh static magnetic field magnetic resonance imaging (MRI) is commonly used for preclinical studies in rodents. In this context, minimization of coil losses is mandatory to scan samples that are small compared to the radiofrequency wavelength in the medium. In this study we construct a radiofrequency (RF) birdcage probe with distributed capacitors, operating in quadrature, tailored for 7.0T 1H MRI of small animals. The design eliminates the need for extra electrical components on the probe structure and affords a high SNR, a uniform field (homogeneity of 93% in the axial plain of the phantom) and a coil sensitivity of 9.8 . Feasibility experiments of mouse imaging are conducted and the competitive capability of a 7.0 T human system equipped with the proposed coil is demonstrated in both body and brain preclinical imaging. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 44B: 83–88, 2015

PET-MR bei Patienten mit Glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and most aggressive primary tumor of the brain. In recent years newer therapeutic approaches have been developed. To allow for an optimized treatment planning it is important to precisely delineate necrotic tissue, edema and vital tumor tissue and to identify the most aggressive parts of the GBM. The magnetic resonance (MR) portion of an MR-positron emission tomography (PET) examination in patients with GBM should consist of both structural and functional sequences including diffusion-weighted and perfusion sequences. The use of (18)F-fluorodeoxyglucose ((18)F-FDG) is limited in patients with gliomas as glucose metabolism is already physiologically high in parts of the brain but (18)F-FDG is nevertheless a commonly used radiopharmaceutical for neuro-oncological questions. (18)F-fluorothymidine reflects the cellular activity of thymidine kinase 1 and correlates with the expression of KI-67 as an index of mitotic activity. The nitroimidazole derivatives (18)F-fluoromisonidazole and (18)F-fluoroazomycin arabinoside ((18)F-FAZA) allow the detection of hypoxic areas within the tumor. In recent years amino acid tracers, such as (18)F-fluoroethyltyrosine are increasingly being used in the diagnosis of gliomas. The simultaneous PET-MR image acquisition allows new approaches, e.g. motion correction by the simultaneous acquisition of MR data with a high temporal resolution and an improved quantification of the PET signal by integrating the results of functional MR sequences. Moreover, the simultaneous acquisition of these two time-consuming methods leads to reduced imaging times for this, often severely ill patient group.

Optimizing Positron Emission Tomography Image Acquisition Protocols in Integrated Positron Emission Tomography/Magnetic Resonance Imaging

In integrated positron emission tomography (PET)/magnetic resonance imaging (MRI), the PET data acquisition is performed simultaneously to the magnetic resonance data acquisition, leaving latitude for the duration of PET acquisition time. This establishes emission time as an important parameter in forthcoming PET/MRI protocols because it is one of the key factors determining PET image quality. Thus, the purpose of the current study was to identify optimal duration of PET acquisition time in PET/MRI. A total of 22 consecutive patients (7 men, 15 women) underwent fluorine-18-labeled fluorodeoxyglucose (18[F]FDG) PET/MRI after clinical PET/computed tomography. Positron emission tomography/magnetic resonance scans were acquired for 8 minutes per bed position (mpb). Positron emission tomography was extracted to reconstruct images with 2, 4, 6, and 8 mpb for each patient. Visual and quantitative approaches were used to assess image quality and lesion detectability for each image. For image quality, (a) 3 readers independently scored subjective image quality on a 4-point scale and (b) a region-of-interest approach was used to obtain a quantitative estimate of image quality in terms of noise. For lesion detectability, (a) the readers independently counted the number of hypermetabolic lesions and (b) signal-to-noise ratio and contrast-to-noise ratio were computed in a region-of-interest approach. Moreover, the mean and maximal standardized uptake value (SUV mean and SUV max, respectively) of the hypermetabolic lesions was compared across all acquisition times. For image quality, subjective image quality significantly declined from 8 to 2 mpb (P <; 0.05), with the exception of the difference between 6 and 8 mpb. Image noise increased with shorter imaging duration, ranging from 13% on average in the 8-mpb scans to 23% in the 2-mpb scans (differences were statistically significant for 2 vs 6 mpb, 2 vs 8 mpb, and 4 vs 8 mpb; P <; 0.05). For lesion detectability, 39 hypermetabolic lesions were identified by consensus. There was no difference in detected lesions across all acquisition times. Signal-to-noise ratio and contrast-to-noise ratio were constantly high and did not differ significantly across the acquisition times. The SUV mean and SUV max did not differ significantly across all acquisition times. Positron emission tomography acquisition times on integrated PET/MRI do not need to exceed usual acquisition times on current PET/computed tomography scanners: Although the PET image quality suffers from short acquisition times, even a duration of 2 mpb permits sufficient lesion detection. Moreover, quantitative measures of tracer uptake are also reasonably precise at short acquisition times.

A simple 5-DoF MR-compatible motion signal measurement system

The purpose of this study was to develop a simple motion measurement system with magnetic resonance (MR) compatibility and safety. The motion measurement system proposed here can measure 5-DoF motion signals without deteriorating the MR images, and it has no effect on the intense and homogeneous main magnetic field, the temporal-gradient magnetic field (which varies rapidly with time), the transceiver radio frequency (RF) coil, and the RF pulse during MR data acquisition. A three-axis accelerometer and a two-axis gyroscope were used to measure 5-DoF motion signals, and Velcro was used to attach a sensor module to a finger or wrist. To minimize the interference between the MR imaging system and the motion measurement system, nonmagnetic materials were used for all electric circuit components in an MR shield room. To remove the effect of RF pulse, an amplifier, modulation circuit, and power supply were located in a shielded case, which was made of copper and aluminum. The motion signal was modulated to an optic signal using pulse width modulation, and the modulated optic signal was transmitted outside the MR shield room using a high-intensity light-emitting diode and an optic cable. The motion signal was recorded on a PC by demodulating the transmitted optic signal into an electric signal. Various kinematic variables, such as angle, acceleration, velocity, and jerk, can be measured or calculated by using the motion measurement system developed here. This system also enables motion tracking by extracting the position information from the motion signals. It was verified that MR images and motion signals could reliably be measured simultaneously.

Combining magnetic resonance imaging and ultrawideband radar: A new concept for multimodal biomedical imaging

Due to the recent advances in ultrawideband (UWB) radar technologies, there has been widespread interest in the medical applications of this technology. We propose the multimodal combination of magnetic resonance (MR) and UWB radar for improved functional diagnosis and imaging. A demonstrator was established to prove the feasibility of the simultaneous acquisition of physiological events by magnetic resonance imaging and UWB radar. Furthermore, first in vivo experiments have been carried out, utilizing this new approach. Correlating the reconstructed UWB signals with physiological signatures acquired by simultaneous MR measurements, representing respiratory and myocardial displacements, gave encouraging results which can be improved by optimization of the MR data acquisition technique or the use of UWB antenna arrays to localize the motion in a focused area.

Application of Magnetic Resonance Virtual Endoscopy as a Presurgical Procedure Before Sialoendoscopy

The objectives of this study were to investigate the feasibility of clinical application of magnetic resonance (MR) virtual endoscopy as a presurgical procedure before sialoendoscopy and to evaluate its value in the diagnosis of obstructive salivary gland diseases and preoperative visualization of endoluminal views. This study presents our initial experience to use MR virtual endoscopy for the presurgical visualization of salivary duct lumen and ductal pathologies in comparison to the sialoendoscopy findings in a feasibility study. Six consecutive patients with suspected obstructive salivary gland diseases underwent MR sialography with a three-dimensional fast imaging using steady-state acquisition. The three-dimensional MR data were transferred to an independent workstation and were postprocessed with navigator software to generate three-dimensional reconstruction and virtual endoscopic images. The fly-through mode was used to imitate the sialoendoscopic exploratory procedure. Then the patients underwent sialoendoscopy and the endoscopic findings were compared with the preoperative virtual endoscopic images. The MR data acquisition and postprocessing protocol were feasible. The virtual endoscopy created clear endoluminal views of salivary duct and the ductal pathologies. The diagnoses were all confirmed by surgical sialoendoscopy. The virtual endoscopic images showed close resemblance to the sialoendoscopic findings. MR virtual endoscopy is an effective and noninvasive diagnostic method for evaluating the endoluminal anatomy and pathologies of the salivary duct. The clinical application of MR virtual endoscopy as a presurgical procedure before sialoendoscopy is a valuable and promising approach, which can provide surgeons useful morphologic and pathologic information.

Noninvasive detection of coronary artery stenosis using contrast-enhanced three-dimensional breath-hold magnetic resonance coronary angiography

OBJECTIVESThe purpose of this study was to evaluate a contrast-enhanced three-dimensional (3D) breath-hold magnetic resonance (MR) technique for detection of coronary artery stenoses.BACKGROUNDThe accuracy of previously published MR coronary angiography protocols varies widely. Recently, coronary artery imaging using T1-shortening contrast agent has become possible, but so far there are no data concerning its clinical application.METHODSMagnetic resonance coronary angiography was performed in 50 patients with suspected coronary artery disease. Magnetic resonance data acquisition using an ultrafast 3D gradient-echo sequence lasted over 32 heartbeats within one single breath-hold. Twenty milliliters of gadopentetate dimeglumine was injected at a flow rate of 1 ml/s for two successive studies covering the main coronary arteries in single-oblique planes. Stenosis assessment by MR was compared with significant (diameter stenosis > 50%) stenoses on X-ray angiography. Evaluation was limited to the proximal and mid-coronary artery segments.RESULTSTwo hundred sixty-eight of 350 artery segments (76.6%) could be evaluated. Left circumflex coronary artery was only evaluable in 50% of cases by MR. In the evaluable segments, 48 of 56 stenoses and 193 of 212 nonstenotic segments were correctly classified by MR. On a patient basis, MR correctly identified 34 of 36 patients with and 8 of 14 patients without significant coronary stenoses as demonstrated by X-ray angiography (sensitivity 94.4%, specificity 57.1%).CONCLUSIONSOblique projection contrast-enhanced MR coronary angiograms obtained within one single breath-hold permit identification of patients with coronary stenoses in the proximal and mid segments of the major coronary arteries with satisfactory accuracy.

Low-cost MR-compatible moving heart phantom.

For the development and evaluation of cardiac magnetic resonance (MR) imaging sequences and methodologies, the availability of a periodically moving phantom to model respiratory and cardiac motion would be of substantial benefit. Given the specific physical boundary conditions in an MR environment, the choice of materials and power source of such phantoms is heavily restricted. Sophisticated commercial solutions are available; however, they are often relatively costly and user-specific modifications may not easily be implemented. We therefore sought to construct a low-cost MR-compatible motion phantom that could be easily reproduced and had design flexibility. A commercially available K'NEX construction set (Hyper Space Training Tower, K'NEX Industries, Inc., Hatfield, PA) was used to construct a periodically moving phantom head. The phantom head performs a translation with a superimposed rotation, driven by a motor over a 2-m rigid rod. To synchronize the MR data acquisition with phantom motion (without introducing radiofrequency-related image artifacts), a fiberoptic control unit generates periodic trigger pulses synchronized to the phantom motion. Total material costs of the phantom are US$ < 200.00, and a total of 80 man-hours were required to design and construct the original phantom. With schematics of the present solution, the phantom reproduction may be achieved in approximately 15 man-hours. The presented MR-compatible periodically moving phantom can easily be reproduced, and user-specific modifications may be implemented. Such an approach allows a detailed investigation of motion-related phenomena in MR images.

Projection reconstruction MR imaging for the reduction of artifacts caused by interview motion

Projection reconstruction (PR) magnetic resonance (MR) imaging is considered. The purpose of the authors' study was to develop a new PR method which allows to minimize the influence of rigid motion on the quality of MR images. As a first step of the method, motion during the MR data acquisition is detected with a time resolution of one repetition time. Next, the authors correct for both translational and rotational motion separately, by tracking the motion of the object's center of mass, and by estimating object rotations, respectively. Besides, an alternative PR imaging sequence is proposed. In this sequence, the raw-data is acquired in an interleaved way. The authors' method does not require any a priori information concerning the motion, which is an important advantage compared with other methods for the correction of motion artifacts. Experiments show that the authors' method is very efficient for correcting rigid-motion artifacts, especially in the case of brain imaging.

5117187 Localized multi-region magnetic resonance data acquisition

5117187 Localized multi-region magnetic resonance data acquisition

A microcomputer-based data acquisition system for an NMR pulse spectrometer

A data acquisition card is designed and constructed for the Amstrad PC 1512, a low-cost IBM compatible microcomputer. This card is installed in the expansion slot of the microcomputer and the software necessary for nuclear magnetic resonance data acquisition and analysis is developed. This system generates the pulse sequences necessary for a nuclear magnetic resonance pulse spectrometer and acquires data from the free-induction-decay signal for further analysis. The generation of the timing pulses and the capturing of the free-induction-decay signal are done with the help of an assembly language source program.