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Water and fat images and PDFF maps of fat–water emulsions with different fat fractions (0%, 10%, 20%, 30%, 40%, 50%, and 60%, starting from bottom left). Consistent fat–water separation in each tube is shown.
Source publication
Purpose:
To develop an MRI method for quantifying hepatic fat content and visceral adipose tissue fatty acid composition in mice on a 7.0T preclinical system.
Methods:
MR acquisitions were performed with a multiple echo spoiled gradient echo with bipolar readout gradients. After phase correction, the number of double bounds (ndb) and the number...
Context in source publication
Context 1
... of the emulsion droplets ranged between 360 and 480 nm. The emulsions did not show any phase separation during the course of the study. Pro- ton density fat fractions were 1.1 6 0.5, 9.0 6 0.9, 18.3 6 0.9, 28.0 6 1.0, 38.7 6 1.2, 49.1 6 1.6, and 58.8 6 1.9% for the emulsions containing 0%, 10%, 20%, 30%, 40%, 50%, and 60% fat, respectively (Fig. 2). The linear regression between the PDFF measured in MRI and the theoretical fat fraction in emulsions was y ¼ 0.98 Â À0.33, (95% confidence interval: y ¼ 0.93 Â À2.0, y ¼ 1.02 Â 1.36), R 2 ¼ 0.99, P < 0.0001 (Fig. 3). Regarding the fatty acid composition in the emulsions, both hazel- nut oil ndb and nmidb were moderately overestimated. ...
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Citations
... We chose the abdominal muscle defect model for validation because this model was close to the subcutis, which was easier to observe and locate under MRI compared with deep tissues. Also, the range of the abdominal muscle defect model was in line with the resolution of the image that could be observed using 7.0-T MRI, which was more conducive for us to determine the degree of tissue repair in the MRI scans [35]. AS the purpose of animal magnetic resonance was to verify whether the signal of the MRI could reflect the degradation of the HMs in vivo, along with monitoring the regeneration of local tissues. ...
By integrating magnetic resonance-visible components with scaffold materials, hydrogel microspheres (HMs) become visible under magnetic resonance imaging(MRI), allowing for non-invasive, continuous, and dynamic monitoring of the distribution, degradation, and relationship of the HMs with local tissues. However, when these visualization components are physically blended into the HMs, it reduces their relaxation rate and specificity under MRI, weakening the efficacy of real-time dynamic monitoring. To achieve MRI-guided in vivo monitoring of HMs with tissue repair functionality, we utilized airflow control and photo-crosslinking methods to prepare alginate-gelatin-based dual-network hydrogel microspheres (G-AlgMA HMs) using gadolinium ions (Gd (III)), a paramagnetic MRI contrast agent, as the crosslinker. When the network of G-AlgMA HMs degrades, the cleavage of covalent bonds causes the release of Gd (III), continuously altering the arrangement and movement characteristics of surrounding water molecules. This change in local transverse and longitudinal relaxation times results in variations in MRI signal values, thus enabling MRI-guided in vivo monitoring of the HMs. Additionally, in vivo data show that the degradation and release of polypeptide (K2 (SL)6 K2 (KK)) from G-AlgMA HMs promote local vascular regeneration and soft tissue repair. Overall, G-AlgMA HMs enable non-invasive, dynamic in vivo monitoring of biomaterial degradation and tissue regeneration through MRI, which is significant for understanding material degradation mechanisms, evaluating biocompatibility, and optimizing material design.
Supplementary Information
The online version contains supplementary material available at 10.1186/s12951-024-02549-7.
... In the present study, we confirm these findings, with dietary saturated and monounsaturated fats being positively associated with fSFA and negatively associated with fMUFA and fPUFA, respectively, in both fat depots. These results also align well with previous murine studies, where high dietary SFAs resulted in VAT containing significantly fewer MUFA and PUFA but more SFA than a diet composed primarily of PUFAs (29). ...
Objectives: This study aimed to assess the fatty acid (FA) composition of abdominal subcutaneous (ASAT) and visceral (VAT) adipose tissue in the UK Biobank imaging cohort (N = 33,823) using magnetic resonance imaging (MRI).
Methods: We measured the fractions of saturated (fSFA), monounsaturated (fMUFA), and polyunsaturated (fPUFA) in ASAT and VAT from multi-echo MRI scans. We selected a sub-cohort that followed a vegan and an omnivore diet (N=36) to validate the effect of diet on adipose tissue. In the wider imaging cohort, we examined the relationship between adipose tissue FA composition and various traits related to disease and body size.
Results: We measured adipose tissue FA composition for over 33,000 participants, revealing higher fSFA and fPUFA and lower fMUFA in VAT (p < 0.00016). fMUFA and fPUFA were higher in ASAT and lower in VAT for women (p<0.00016). Vegans exhibited lower fSFA in both ASAT and VAT (p < 0.00016). VAT fSFA and fMUFA showed significant associations with disease as well as anthropometric variables.
Discussion: This extensive analysis revealed the relationships between adipose tissue FA composition and a range of factors in a diverse population, highlighting the importance of studying body adipose tissue beyond its quantity.
... Currently, fat-water phantoms and diffusion phantoms have been used to validate MRI-based methods in quantifying the FC [12,[29][30][31][32][33] and to measure the diffusivity of polyethylene particle suspensions or microbead impregnated gels on DWI [11,19,34,35], respectively. However, these phantoms do not enable us to clarify the impact of FC on the measure of the diffusivity of polyethylene or microbead preparations in any single phantom. ...
Background
A dual-function phantom designed to quantify the apparent diffusion coefficient (ADC) in different fat contents (FCs) and glass bead densities (GBDs) to simulate the human tissues has not been documented yet. We propose a dual-function phantom to quantify the FC and to measure the ADC at different FCs and different GBDs.
Methods
A fat-containing diffusion phantom comprised by 30 glass-bead-containing fat-water emulsions consisting of six different FCs (0, 10, 20, 30, 40, and 50%) multiplied by five different GBDs (0, 0.1, 0.25, 0.5, and 1.0 g/50 mL). The FC and ADC were measured by the “iterative decomposition of water and fat with echo asymmetry and least squares estimation-IQ,” IDEAL-IQ, and single-shot echo-planar diffusion-weighted imaging, SS-EP-DWI, sequences, respectively. Linear regression analysis was used to evaluate the relationship among the fat fraction (FF) measured by IDEAL-IQ, GBD, and ADC.
Results
The ADC was significantly, negatively, and linearly associated with the FF (the linear slope ranged from -0.005 to -0.017, R ² = 0.925 to 0.986, all p < 0.001). The slope of the linear relationship between the ADC and the FF, however, varied among different GBDs (the higher the GBD, the lower the slope). ADCs among emulsions across different GBDs and FFs were overlapped. Emulsions with low GBDs plus high FFs shared a same lower ADC range with those with median or high GBDs plus median or lower FFs.
Conclusions
A novel dual-function phantom simulating the human tissues allowed to quantify the influence of FC and GBD on ADC.
Relevance statement
The study developed an innovative dual-function MRI phantom to explore the impact of FC on ADC variation that can affect clinical results. The results revealed the superimposed effect on FF and GBD density on ADC measurements.
Key points
• A dual-function phantom made of glass bead density (GBD) and fat fraction (FF) emulsion has been developed.
• Apparent diffusion coefficient (ADC) values are determined by GBD and FF.
• The dual-function phantom showed the mutual ADC addition between FF and GBD.
Graphical Abstract
... Especially the optimal ΔTE, total readout time, and choice between a free and a constrained fat model may be different in BMAT compared with WAT. 22 All FAC imaging has previously been conducted using clinical magnetic field strengths, except for an initial feasibility study in the WAT and liver of mice at 7 T. 23 At 7 T, the increased spectral resolution is expected to be an advantage, whereas the shorter T * 2 may be a challenge. The aim of this work is to demonstrate the feasibility of BMAT FAC imaging using chemical shift-encoded MRI at 7 T. Accuracy is tested in phantoms, and a pilot in vivo experiment is conducted in the knee of healthy volunteers. ...
Purpose
To demonstrate the feasibility and accuracy of chemical shift–encoded imaging of the fatty acid composition (FAC) of human bone marrow adipose tissue at 7 T, and to determine suitable image‐acquisition parameters using simulations.
Methods
The noise performance of FAC estimation was investigated using simulations with a range of inter‐echo time, and accuracy was assessed using a phantom experiment. Furthermore, one knee of 8 knee‐healthy subjects (ages 35–54 years) was imaged, and the fractions of saturated fatty acids (SFA) and polyunsaturated fatty acids (PUFA) were mapped. Values were compared between reconstruction methods, and between anatomical regions.
Results
Based on simulations, ΔTE = 0.6 ms was chosen. The phantom experiment demonstrated high accuracy of especially SFA using a constrained reconstruction model (slope = 1.1, average bias = −0.2%). The lowest accuracy was seen for PUFA using a free model (slope = 2.0, average bias = 9.0%). For in vivo images, the constrained model resulted in lower intersubject variation compared with the free model (e.g., in the femoral shaft, the SFA percent‐point range was within 1.0% [vs. 3.0%]). Furthermore, significant regional FAC differences were detected. For example, using the constrained approach, the femoral SFA in the medial condyle was lower compared with the shaft (median [range]: 27.9% [27.1%, 28.4%] vs. 32.5% [31.8%, 32.8%]).
Conclusion
Bone marrow adipose tissue FAC quantification using chemical‐shift encoding is feasible at 7 T. Both the noise performance and accuracy of the technique are superior using a constrained signal model.
... [17][18][19] These points suggest that whereas imaging EAT volume provides one important metric describing the EAT, 20,21 imaging EAT FAC may provide additional important information regarding its inflammatory or proinflammatory state. FAC MRI techniques have recently been developed and validated in phantoms [22][23][24] and applied in the abdomen, 22,25,26 liver, 27 and bone marrow 28,29 to quantify adipose tissue FAC; however, these methods have not yet been applied to EAT. Generally, by using prior knowledge of the 1 H triglyceride spectrum, 30 the multi-echo gradient echo (GRE) signal from adipose tissue is represented using a multi-resonance signal model. ...
... 24 In visceral adipose tissue of mice fed a high-fat diet, these values were 0.37 and 2.44. 27 Compared to other fat depots, our EAT data show good agreement for SFA, but UD values in EAT were higher. This may be related to the heart's use of EAT as a reservoir of fatty acids for ATP generation with a preference toward unsaturated fatty acids. ...
Purpose
To develop an accelerated MRI method to quantify the epicardial adipose tissue (EAT) fatty acid composition (FAC) and test the hypothesis that eplerenone (EPL) shifts the EAT FAC toward unsaturation in obese mice.
Methods
Undersampled multi‐echo gradient echo imaging employing a dictionary‐based compressed‐sensing reconstruction and iterative decomposition with echo asymmetry and least‐squares–based mapping (IDEAL) was developed, validated, and used to study EAT in obese mice scanned at 7T. Fully sampled and rate 2, 2.5, 3, and 3.5 undersampled image data were acquired, reconstructed, and assessed using RMSE and structural similarity (SSIM). Two groups of mice were studied: untreated (control, n = 10) and EPL‐treated (n = 10) mice fed a high‐fat high‐sucrose diet. MRI included imaging of EAT FAC, EAT volume, and myocardial perfusion reserve.
Results
Rate 3 acceleration provided RMSE <5% and structural similarity >0.85 for FAC MRI. After 6 weeks of diet, EPL‐treated compared to untreated mice had a reduced EAT saturated fatty acid fraction (0.27 ± 0.09 vs. 0.39 ± 0.07, P < 0.05) and increased EAT unsaturation degree (4.37 ± 0.32 vs. 3.69 ± 0.58, P < 0.05). Also, EAT volume in EPL‐treated compared to untreated mice was reduced (8.1 ± 0.6 mg vs. 11.4 ± 0.7 mg, P < 0.01), and myocardial perfusion reserve was improved (1.83 ± 0.15 vs. 1.61 ± 0.17, P < 0.05).
Conclusion
Rate 3 accelerated FAC MRI enabled accurate quantification of EAT FAC in mice. EPL treatment shifted the EAT FAC toward increased unsaturation and was associated with improvement of coronary microvascular function.
... WFI with multiple gradient echoes (WFI-mGRE) is able to quantify both bone marrow fat fraction and BMAT unsaturation from the same MRI images, with fast acquisition times. Furthermore, WFI-mGRE shows good agreement with 1 H-MRS (20)(21)(22)(23)(24). ...
Bone marrow adipose tissue (BMAT) is a dynamic tissue which is associated with osteoporosis, bone metastasis, and primary bone tumors. The aim of this study is to determine region-specific variations and age- and gender-specific differences in BMAT and BMAT composition in healthy subjects. In this cross-sectional study, we included 40 healthy subjects (26 male: mean age 49 years, range 22–75 years; 14 female: mean age 50 years, range 29–71) and determined the bone marrow signal fat fraction and bone marrow unsaturation in the spine (C3-L5), pelvis, femora, and tibiae using chemical shift encoding-based water–fat imaging (WFI) with multiple gradient echoes (mGRE). Regions of interest covered the individual vertebral bodies, pelvis and proximal epimetaphysis, diaphysis, and distal epimetaphysis of the femur and tibia. The spinal fat fraction increased from cervical to lumbar vertebral bodies (mean fat fraction ( ± SD or (IQR): cervical spine 0.37 ± 0.1; thoracic spine 0.41 ± 0.08. lumbar spine 0.46 ± 0.01; p < 0.001). The femoral fat fraction increased from proximal to distal (proximal 0.78 ± 0.09; diaphysis 0.86 (0.15); distal 0.93 ± 0.02; p < 0.001), while within the tibia the fat fraction decreased from proximal to distal (proximal 0.92 ± 0.01; diaphysis 0.91 (0.02); distal 0.90 ± 0.01; p < 0.001). In female subjects, age was associated with fat fraction in the spine, pelvis, and proximal femur (ρ = 0.88 p < 0.001; ρ = 0.87 p < 0.001; ρ = 0.63 p = 0.02; ρ = 0.74 p = 0.002, respectively), while in male subjects age was only associated with spinal fat fraction (ρ = 0.40 p = 0.04). Fat fraction and unsaturation were negatively associated within the spine (r = -0.40 p = 0.01), while in the extremities fat fraction and unsaturation were positively associated (distal femur: r = 0.42 p = 0.01; proximal tibia: r = 0.47, p = 0.002; distal tibia: r = 0.35 p = 0.03), both independent of age and gender. In conclusion, we confirm the distinct, age- and gender-dependent, distribution of BMAT throughout the human skeleton and we show that, contradicting previous animal studies, bone marrow unsaturation in human subjects is highest within the axial skeleton compared to the appendicular skeleton. Furthermore, we show that BMAT unsaturation was negatively correlated with BMAT within the spine, while in the appendicular skeleton, BMAT and BMAT unsaturation were positively associated.
... Up till now, many MR scientists have already used oilin-water (o/w) emulsions for validation and comparison of various water or fat MRI-based quantification methods [8][9][10][11][12][13][14], but also to study changes in the MR signal of water in the presence of fat and vice versa [15]. In MR technology, there are a number of different approaches for determining the fat content in tissue. ...
Objective
To provide a basis for the selection of suitable emulsifiers in oil-in-water emulsions used as tissue analogs for MRI experiments. Three different emulsifiers were investigated with regard to their ability to stabilize tissue-like oil-in-water emulsions. Furthermore, MR signal properties of the emulsifiers themselves and influences on relaxation times and ADC values of the aqueous phase were investigated.
Materials and methods
Polysorbate 60, sodium dodecyl sulfate (SDS) and soy lecithin were used as emulsifiers. MR characteristics of emulsifiers were assessed in aqueous solutions and their function as a stabilizer was examined in oil-in-water emulsions of varying fat content (10, 20, 30, 40, 50%). Stability and homogeneity of the oil-in-water emulsions were evaluated with a delay of 3 h and 9 h after preparation using T 1 mapping and visual control. Signal properties of the emulsifiers were investigated by ¹ H-MRS in aqueous emulsifier solutions. Relaxometry and diffusion weighted MRI (DWI) were performed to investigate the effect of various emulsifier concentrations on relaxation times (T 1 and T 2 ) and ADC values of aqueous solutions.
Results
Emulsions stabilized by polysorbate 60 or soy lecithin were stable and homogeneous across all tested fat fractions. In contrast, emulsions with SDS showed a significantly lower stability and homogeneity. Recorded T 1 maps revealed marked creaming of oil droplets in almost all of the emulsions with SDS. The spectral analysis showed several additional signals for polysorbate and SDS. However, lecithin remained invisible in ¹ H-MRS. Relaxometry and DWI revealed different influences of the emulsifiers on water: Polysorbate and SDS showed only minor effects on relaxation times and ADC values of aqueous solutions, whereas lecithin showed a strong decrease in both relaxation times (r 1,lecithin = 0.11 wt.% ⁻¹ s ⁻¹ , r 2,lecithin = 0.57 wt.% ⁻¹ s ⁻¹ ) and ADC value (Δ(ADC) lecithin = − 0.18 × 10 –3 mm ² /s⋅wt.%) with increasing concentration.
Conclusion
Lecithin is suggested as the preferred emulsifier of oil-in-water emulsions in MRI as it shows a high stabilizing ability and remains invisible in MRI experiments. In addition, lecithin is suitable as an alternative means of adjusting relaxation times and ADC values of water.
... We have to admit that the effective liver coverage dropping to 30% in some cases is a significant drawback of our 7T configuration compared to current 3T measurements where full liver coverage is not an issue, and that appears to be the main limitation of the study. The other potential limitations are minimal echo time and echo spacing, but in fact it can be a problem especially in approaches where are estimated individual fat components [66,67]. In our case, we have the prior knowledge of fat spectral model. ...
Fat fraction quantification and assessment of its distribution in the hepatic tissue become more important with the growing epidemic of obesity, and the increasing prevalence of diabetes mellitus type 2 and non-alcoholic fatty liver disease. At 3Tesla, the multi-echo, chemical-shift-encoded magnetic resonance imaging (CSE-MRI)-based acquisition allows the measurement of proton density fat-fraction (PDFF) even in clinical protocols. Further improvements in SNR can be achieved by the use of phased array coils and increased static magnetic field. The purpose of the study is to evaluate the feasibility of PDFF imaging using a multi-echo CSE-MRI technique at ultra-high magnetic field (7Tesla). Thirteen volunteers (M/F) with a broad range of age, body mass index, and hepatic PDFF were measured at 3 and 7T by multi-gradient-echo MRI and single-voxel spectroscopy MRS. All measurements were performed in breath-hold (exhalation); the MRI protocols were optimized for a short measurement time, thus minimizing motion-related problems. 7T data were processed off-line using Matlab® (MRI:multi-gradient-echo) and jMRUI (MRS), respectively. For quantitative validation of the PDFF results, a similar protocol was performed at 3T, including on-line data processing provided by the system manufacturer, and correlation analyses between 7 and 3T data were performed off-line. The multi-echo CSE-MRI measurements at 7T with a phased-array coil configuration and an optimal post-processing yielded liver volume coverage ranging from 30 to 90% for high- and low-BMI subjects, respectively. PDFFs ranged between 1 and 20%. We found significant correlations between 7T MRI and -MRS measurements ( R ² ≅ 0.97; p < 0.005), and between MRI-PDFF at 7T and 3T fields ( R ² ≅ 0.94; p < 0.005) in the evaluated volumes. Based on the measurements and analyses performed, the multi-echo CSE-MRI method using a 32-channel coil at 7T showed its aptitude for MRI-based quantitation of PDFF in the investigated volumes. The results are the first step toward qMRI of the whole liver at 7T with further improvements in hardware.
... In another study using 3T, a maximum inter-echo time of 1.23 ms and a readout time of 14-18 ms (corresponding to 11-15 echoes) was suggested for a sequential reconstruction of ndb and nmidb with cl expressed in terms of ndb and with correction of bipolar phase errors by Schneider et al. 60 Imaging-based FAC estimation has been compared between 1.5T and 3T, 20,60 and the feasibility also at 7T has been demonstrated, using a preclinical system. 62 In oil phantoms, a bias was found between the estimates at 1.5T and 3T, 20 and a lower reproducibility was demonstrated between field strengths than between 2D and 3D acquisition protocols with a lower accuracy found at 1.5T. 60 Apart from the lower spectral resolution, an increased impact of J-coupling is also expected at the lower field strength which may motivate the choice of 3T over 1.5T. ...
... 63,64 For FAC estimation, correction of these phase errors has been suggested as the first part of sequential reconstruction approaches. 59,60,62 The data acquisition time for imaging-based FAC assessment is typically a few minutes, but may also be limited to a single breath-hold for liver applications. 6,51,59 ...
... In breast adipose tissue of healthy volunteers, Dimitrov et al 83 measured a fat composition in good agreement with the composition of subcutaneous fat in the calf, as measured in an earlier study by Ren et al. 17 MRI techniques have been used to measure the FAC in adipose tissue in diet intervention studies. 51,62,84 In mice, a high-fat diet resulted in significant changes of the visceral adipose tissue f SFA , f MUFA , and f PUFA compared to a fructose diet in mice. 62 Similarly, an overfeeding protocol in nonobese human subjects led to especially f MUFA alterations of the subcutaneous and visceral adipose tissue depots, which could be detected using MRI, but not MRS, due to a larger inter-subject variability of the latter technique. ...
Adipose tissue as well as other depots of fat (triglycerides) are increasingly being recognized as active contributors to the human function and metabolism. In addition to the fat concentration, also the fatty acid chemical composition (FAC) of the triglyceride molecules may play an important part in diseases such as obesity, insulin resistance, hepatic steatosis, osteoporosis, and cancer. MR spectroscopy and chemical‐shift‐encoded imaging (CSE‐MRI) are established methods for non‐invasive quantification of fat concentration in tissue. More recently, similar techniques have been developed for assessment also of the FAC in terms of the number of double bonds, the fraction of saturated, monounsaturated, and polyunsaturated fatty acids, or semi‐quantitative unsaturation indices. The number of papers focusing on especially CSE‐MRI‐based techniques has steadily increased during the past few years, introducing a range of acquisition protocols and reconstruction algorithms. However, a number of potential sources of bias have also been identified. Furthermore, the measures used to characterize the FAC using both MRI and MRS differ, making comparisons between different techniques difficult. The aim of this paper is to review MRS‐ and MRI‐based methods for in vivo quantification of the FAC. We describe the chemical composition of triglycerides and discuss various potential FAC measures. Furthermore, we review acquisition and reconstruction methodology and finally, some existing and potential applications are summarized. We conclude that both MRI and MRS provide feasible non‐invasive alternatives to the gold standard gas chromatography for in vivo measurements of the FAC. Although both are associated with gas chromatography, future studies are warranted.
... With the advance of imageology, MRI, as a noninvasive detection tool, has attracted more attention in qualitative and quantitative evaluation of fatty liver [21,28,29]. Compared with CT, MRI has dominant advantages based on its high resolution, use of multi-panel imaging, lack of radiation, and high accuracy with respect to hepatic fat content [18,23]. Furthermore, it can provide a dynamic looking into the pathological changes of a liver suffering from steatosis [33]. ...
... T2WI and T2WI fs in MRI are simple and reproducible in terms of operation. The value for liver fat content determined by such techniques not only server as a diagnostic index of whether fatty liver is present or not but can also indicate 18 the degree of hepatic steatosis. In this study, we utilized the FRFSE T2WI sequence with or without fat saturation to generate two different images. ...
There has been a lack of suitable fatty liver models and characterization techniques for histopathological evaluation of alcoholic fatty liver (AFL). This work aimed to exploit an MRI technique for characterizing an alcohol-induced fatty liver model established in tree shrews (Tupaia belangeri chinese). The animals were treated with 15% alcohol for two weeks instead of drinking water to induce AFL. Blood ALT, AST, alcohol, and liver MDA concentrations were determined, and the histopathology of the liver was checked by HE and Oil red O staining on day 0 and on the 4th, 7th and 14th days after alcohol feeding. MRI was used to trace the histopathological changes in the liver of tree shrews in real time. Compared with the control group, the levels of ALT, AST, and MDA significantly increased in the alcohol-induced group and were positively correlated with the induction time. HE and Oil red O staining revealed that a moderate fatty lesion occurred in the liver on the 4th day and that a serious AFL was successfully induced on the 14th day. MRI further confirmed the formation of AFL. MRI, as noninvasive examination technique, provides an alternative tool for accurate characterization of AFL in live subjects. It is comparable to HE or Oil red O staining for histopathological examination, but is more suitable by virtue of its high flexibility and compliance. The AFL model of tree shrews combined with MRI characterization can work as a platform for studying fatty liver diseases and medications for their treatment.
