NMR in Biomedicine最新文献

Solitary fibrous tumor (SFT), formerly known as hemangiopericytoma, is an uncommon brain tumor often confused with meningioma on MRI. Unlike meningiomas, SFTs exhibit a myoinositol peak on magnetic resonance spectroscopy (MRS). This study aimed to develop automated classifiers to distinguish SFT from meningioma grades using MRS data from a 26-year patient cohort. Four classification tasks were performed on short echo (SE), long echo (LE) time, and concatenated SE + LE spectra, with datasets split into 80% training and 20% testing sets. Sequential forward feature selection and linear discriminant analysis identified features to distinguish between meningioma Grade 1 (Men-1), meningioma grade 2 (Men-2), meningioma grade 3 (Men-3), and SFT (the 4-class classifier); Men-1 from Men-2 + 3 + SFT; meningioma (all) from SFT; and Men-1 from Men-2 + 3 and SFT. The best classifier was defined by the smallest balanced error rate (BER) in the testing phase. A total of 136 SE cases and 149 LE cases were analyzed. The best features in the 4-class classifier were myoinositol and alanine at SE, and myoinositol, glutamate, and glutamine at LE. Myoinositol alone distinguished SFT from meningiomas. Differentiating Men-1 from Men-2 was not possible with MRS, and combining higher meningioma grades did not improve distinction from Men-1. Notably, combining short and long echo times (TE) enhances classification performance, particularly in challenging outlier cases. Furthermore, the robust classifier demonstrates efficacy even when dealing with spectra of suboptimal quality. The resulting classifier is available as Supporting Information of the publication. Extensive documentation is provided, and the software is free and open to all users without a login requirement.

Cerebral imaging is crucial in the diagnosis and treatment algorithm of acute stroke to determine salvageable brain tissue. While diffusion MRI is commonly used to define the ischemic core, it cannot reliably distinguish irreversibly damaged from salvageable tissue. We investigated the added value of ²³Na MRI to define irreversible necrotic tissue after a stroke. Fifteen patients with acute stroke involving medial cerebral artery occlusion were longitudinally explored with conventional and ²³Na MRI within 24 h, 70 h following stroke and at 3 months to characterize the necrotic area. Time-courses of sodium accumulations were observed within regions presenting with or spared by cytotoxic/ionic edema and converting or not to necrosis. Dynamics of sodium accumulations were very different across subjects. At the group level, time-courses of sodium signal in cytotoxic edema showed a non-linear increase with an upper asymptote of 59 ± 6%% relative to the contralateral hemisphere. Regions with a larger early increase in ²³Na signal (ionic edema) showed a non-linear accumulation during the first 70 h and were associated with subsequent necrosis at month 3. Some of the regions with no ionic edema during the first 70 h became necrotic at month 3, showing that pejorative pathophysiological processes could worsen after 70 h following attack. Final necrotic volume was well predicted by the cytotoxic volume (ADC decrease) during the first 24 h, and by the volume of ionic edema during the subacute period (25-70 h) following attack. The regions showing ionic edema showed a non-linear increase of ²³Na signal during the first 70 h, with larger sodium accumulations in regions converting to necrosis at month 3. It may be of interest to consider the role of ionic edema imaging in the 70 h after stroke and reperfusion, with a view to better understand stroke pathophysiology. Sodium MRI could add complementary information about the fate of cell necrosis within low ADC signal regions.

Nuclear Overhauser effect (NOE) MRI has been used for in vivo brain imaging to assess lipid and protein composition and benefits from 7 T field strengths due to the larger chemical shift dispersion. However, a continuing challenge is signal drop off observed in regions such as the medial temporal lobes due to "standing wave" effects from shorter radiofrequency (RF) wavelengths at ultra-high fields. 2D periodic unit cell metasurfaces have been a promising approach for providing improvements in anatomical imaging but have not yet been evaluated in chemical exchange saturation transfer (CEST)-based sequences. Here, we report the use of metasurfaces for enhancement of NOE imaging as well as for improvement of Lorentzian line fitting of full Z-spectrum data. 3D NOE image data, B₁ ⁺ maps, and B₀ maps were acquired on five healthy volunteers using a 7 T MRI system with and without metasurfaces positioned near the temporal lobes. A frequency offset range of -5 to +5 ppm with additional separate acquisitions of ±20 and ±100 ppm offset images. A five-pool Lorentzian line fitting model was employed to fit and quantitatively compared magnetization transfer (MT), amide proton transfer (APT), amine, and relayed NOE (rNOE) metabolite pools. NOE_MTR-weighted contrast maps were also calculated via Z-spectrum asymmetry analysis. The metasurfaces globally enhanced the transmit efficiency within the imaging slab by approximately 9.6% and reduced B₁ ⁺ inhomogeneity by approximately 16.6% and increased transmit efficiency by 55.8% in the temporal lobes. Amplitude fit maps showed decreases in contrast magnitude ranging from 1 to 16% and changes in image uniformity ranging from a 4.3 decrease to a 34.7% increase, while NOE_MTR-weighted contrast maps demonstrated similar changes. The results presented here demonstrate that metasurfaces can enhance CEST-based techniques complementing previously reported benefits in anatomical imaging.

The noninvasive, in vivo measurement of postexercise phosphocreatine (PCr) recovery kinetics using 31-phosphorus magnetic resonance spectroscopy (³¹P-MRS) is a highly prevalent method for assessing skeletal muscle energetics. However, ³¹P-MRS methodology is notoriously laboratory-specific, leading to uncertainty about the normal range of PCr recovery kinetics among healthy individuals, as well as relationships with disease and demographic factors. This systematic review and meta-analysis characterized the normal range of PCr recovery kinetics from ³¹P-MRS in human skeletal muscles across the lifespan, differences between healthy and those with muscle-related diseases, and relationships between intermuscular PCr recovery measurements and demographic factors. PubMed, Web of Science, Cochrane, and Google Scholar databases were searched for PCr recovery studies, which resulted in a final set of 128 studies eligible for meta-analysis. Studies were categorized into three muscle groups (forearm, upper leg, and lower leg) and further subdivided into three groups: diseased, control (the comparator group in studies of disease), and healthy (those recruited into studies that lacked a disease group). Only English-language studies were included. All statistical analysis was performed using Stata 17 software. Forest plots showed significant heterogeneity across PCr recovery time estimates and outlier study removal significantly reduced this heterogeneity. Greater age was associated with longer PCr recovery in upper leg muscles among both healthy (ρ = 0.387, p < 0.05) and diseased (ρ = 0.733, p < 0.05) individuals. Additionally, longer PCr recovery time was correlated with more acidic end-of-exercise pH in all three muscle groups among healthy individuals. In conclusion, skeletal muscle energetics as indexed by ³¹P-MRS-based PCr recovery time is similar across three different skeletal muscle groups among healthy people. Common diseases significantly prolong PCr recovery times. Methodological heterogeneity has a significant impact on PCr recovery time measurements in this literature. Greater age and more acidic pH increase PCr recovery time among healthy people.

Muscle twitch dynamics and fatigability change in response to muscle disease. In this study, we developed an imaging paradigm to measure muscle twitch dynamics, and the response of the muscle to voluntary fatiguing contractions. We used a novel imaging technique called motor unit magnetic resonance imaging (MUMRI). MUMRI allows visualisation of muscle and motor unit activity by combining in-scanner electrical stimulation with dynamic pulsed gradient spin echo (twitch dynamics, PGSE-MUMRI) and phase contrast (fatigue, PC-MUMRI) imaging. In Part I of this study, we scanned 10 healthy controls, we measured the muscle rise (T_rise), contraction (T_contract) and half-relaxation time (T_half-relax) of the tibialis anterior (TA) muscle on a voxel-wise basis using PGSE-MUMRI. Five controls were scanned twice to assess reproducibility; PGSE-MUMRI demonstrated reproducible results, with low variation between scans 3.4% for T_rise, 6.4% for T_contract and 7.1% for T_half-relax. We then developed a PC-MUMRI paradigm to measure the recovery of the TA in response to a fatiguing voluntary exercise. In Part II of the study, we applied these two novel imaging paradigms in a cohort study of nine patients with single large-scale mtDNA deletion primary mitochondrial myopathy (PMM). Patients underwent a 12-week resistance exercise programme and baseline, and follow-up MRI was performed. PGSE-MUMRI detected a significantly longer muscle contraction time between baseline and follow-up in PMM patients 108.7 ± 7.9 vs. post-119.3 ± 10.4 ms; p = 0.018. There was no statistical difference in the recovery half maximum measured using PC-MUMRI in PMM patients between baseline and follow-up 254 ± 109 vs. 137 ± 41 s; p = 0.074. In conclusion, PGSE-MUMRI has detected differences in muscle twitch dynamics between controls and PMM following an exercise programme, and we can visualise differences in twitch dynamics subregions of muscle using this technique. The PC-MUMRI technique has shown promise as a novel measure of muscle fatigue.

T1 mapping is essential for detecting myocardial changes, but standard methods like the MOLLI sequence are limited by heart rate dependency and sensitivity to motion artifacts. This study introduces the multiflip angle (MFA) sequence as a novel alternative, aiming to provide frequency-independent and robust T1 mapping, particularly in challenging cardiac conditions. The novel MFA sequence was validated using nickel (II) chloride phantoms and systematically compared with the standard MOLLI sequence in 20 healthy volunteers using a 1.5 Tesla Philips Achieva MRI system. T1 values were assessed at rest and under mild physical exertion to evaluate frequency dependency, measurement precision, and robustness to motion artifacts. The MFA sequence demonstrated robust frequency independence, with T1 values remaining stable across varying heart rates, unlike MOLLI, which exhibited a significant correlation between T1 values and heart rate (R = 0.52, p < 0.001), and sex (3% higher values in females; p = 0.044). Although both sequences showed no statistically significant age-related differences, MOLLI yielded more precise T1 measurements with lower variability compared to MFA. Additionally, MFA exhibited reduced susceptibility to motion artifacts, maintaining consistent values across myocardial regions and physiological conditions, particularly in basal segments where MOLLI showed greater variability. The MFA sequence offers a frequency-independent and motion-robust alternative to the MOLLI sequence for myocardial T1 mapping. Although the MOLLI sequence provides higher precision, MFA's stability across varying heart rates and resistance to motion artifacts positions it as a promising option, particularly for patients with arrhythmias or during stress testing. Further investigation is warranted to refine its clinical applications.

Many different transmit (Tx) coil concepts and designs for 7-T magnetic resonance imaging of the head have been proposed. Most of them are placed close to the head and in combination with the receive coils creating a helmet-like structure. This limits the space for additional equipment for external stimuli. A large diameter transmit coil can increase the ease using supplementary measurement devices. Therefore, this study systematically evaluated nine different Tx elements regarding their performance within a large diameter transmit coil with a diameter $>$  350 mm. Each Tx element was examined regarding its power and specific absorption rate (SAR) efficiencies, its loading dependence, intrinsic decoupling, and its radio frequency (RF) shimming capability. Additionally, an experimental validation of $\left|B_{\text{1}}^{\text{+}}\right|$ -maps was performed. The loop-based Tx elements (circular and rectangular loop) provided the highest power and SAR efficiency with at least 15.5% and 21.2% higher efficiencies for a single channel and 22.1% and 18.0% for the eight-channel array, respectively. In terms of voxel-wise power efficiency, the circular loop was the superior Tx element type within most of the head. Looking at the voxel-wise SAR efficiency, the loop-based elements manifest themselves as the most efficient type within most of the central brain. The mutual coupling was lowest for the passively fed dipole ( $-$ 31.23 dB). The highest RF shimming capability in terms of sum of normalized singular values was calculated for the rectangular (4.21) and the circular loop (4.36), whereby the L-curve results showed that the arrays have only minor $\left|B_{\text{1}}^{\text{+}}\right|$ shimming performance differences for the transversal slice. For the hippocampus, the meander element provided the highest overall homogeneity with a minimal coefficient of variation (CoV) of 5.1%. This work provides extensive and unique data for single and eight-channel Tx elements applying common performance benchmarks and enables further discourse on multi-channel evaluations towards large diameter Tx coils at 7-T head imaging. On the bases of the provided results, the preferable Tx element type for this specific application is loop-based.

Thermal and mechanical tissue stimulation is widely utilized in various medical contexts, particularly to enhance local circulation, alleviate pain, and restore movement. Techniques to objectively quantify the physiological effects of these interventions support therapeutic efficacy and explain clinical benefits. Here we conducted a pilot trial to evaluate the feasibility of magnetic resonance imaging (MRI) technology to provide an objective assessment of acute treatment effects in enhancing blood flow. Subjects ( $n=10$ ) received an MRI flow quantification scan of the abdominal aorta before and immediately after undergoing a 20-min thermo-mechanical massage delivered to the lumbar spine by a commercial automated device. We report a significant increase of 27% in the peak velocity of blood flow following treatment. There were no significant changes in the volume of the imaged vessel, in mean heart rate, or heart rate variability (HRV), which is consistent with direct local effects of therapy on circulation. These findings are consistent with the potential utility of MRI in detecting and quantifying regional increases in blood flow following thermo-mechanical stimulation.

This study investigated the potential of combining multiple MR parameters to enhance the characterization of myelin in the mouse brain. We collected ex vivo multiparametric MR data at 7 T from control and Gli1^-/- mice; the latter exhibit enhanced myelination at Postnatal Day 10 (P10) in the corpus callosum and cortex. The MR data included relaxivity, magnetization transfer, and diffusion measurements, each targeting distinct myelin properties. This analysis was followed by and compared to myelin basic protein (MBP) staining of the same samples. Although a majority of the MR parameters included in this study showed significant differences in the corpus callosum between the control and Gli1^-/- mice, only T₂, T₁/T₂, and radial diffusivity (RD) demonstrated a significant correlation with MBP values. Based on data from the corpus callosum, partial least square regression suggested that combining T₂, T₁/T₂, and inhomogeneous magnetization transfer ratio could explain approximately 80% of the variance in the MBP values. Myelin predictions based on these three parameters yielded stronger correlations with the MBP values in the P10 mouse brain corpus callosum than any single MR parameter. In the motor cortex, combining T₂, T₁/T₂, and radial kurtosis could explain over 90% of the variance in the MBP values at P10. This study demonstrates the utility of multiparametric MRI in improving the detection of myelin changes in the mouse brain.

Previous work indicates evidence that cerebrospinal fluid (CSF) plays a crucial role in brain waste clearance processes and that altered flow patterns are associated with various diseases of the central nervous system. In this study, we investigate the potential of deep learning to predict the distribution in human brain of a gadolinium-based CSF contrast agent (tracer) administered intrathecal. For this, T1-weighted magnetic resonance imaging (MRI) scans taken at multiple time points before and after injection were utilized. We propose a U-net-based supervised learning model to predict pixel-wise signal increase at its peak after 24 h. Performance is evaluated based on different tracer distribution stages provided during training, including predictions from baseline scans taken before injection. Our findings show that training with imaging data from only the first 2-h postinjection yields tracer flow predictions comparable to models trained with additional later-stage scans. Validation against ventricular reflux gradings from neuroradiologists confirmed alignment with expert evaluations. These results demonstrate that deep learning-based methods for CSF flow prediction deserve more attention, as minimizing MR imaging without compromising clinical analysis could enhance efficiency, improve patient well-being and lower healthcare costs.