Comparison of fat quantification methods: A phantom study at 3.0T

Concurrent water T2 and fat fraction mapping of the breast using the radial gradient and spin echo (RADGRASE) pulse sequence

This work describes and evaluates an efficient radial gradient- and spin-echo (RADGRASE) pulse sequence and reconstruction algorithm for concurrent measurement of proton-density weighted fat fraction (FF) and water component T2 (T2w) within breast tissues. The ability to estimate T2w in breast tissues, where fat can be highly abundant, is demonstrated using oil/gel phantoms across a wide range of FF values (0.1-0.7). Successful T2w mapping of breast tissues is also demonstrated in vivo by comparison with fat suppressed T2 values. The sensitivity of RADGRASE to detect changes in the breast was assessed by tracking T2w in 3 healthy volunteers through their menstrual cycle, demonstrating T2w values in the late luteal phase to be 18-29 ms higher than in the follicular phase. The technique is also applied to a cohort of 68 patients taking tamoxifen for breast cancer risk reduction, where significant positive correlation between the FF parameter Frac50 and T2w (p = 0.035) was observed in premenopausal subjects (n = 20). Our findings demonstrate the ability and efficacy of RADGRASE for simultaneously mapping FF and T2w within breast tissues, and the potential utility of the technique in studying breast tissue changes in clinical applications.

Development of estimation method for T1 and T2 values using the relaxivity of contrast agent and coagulant for a magnetic resonance imaging phantom

The T1 and T2 values of magnetic resonance imaging phantoms used by researchers should be equivalent to those of the target tissue. However, this is difficult to achieve because of variations in the phantoms depending on the type and concentration of contrast agents and coagulants. The aim of this study was to elucidate the utility of a determination equation derived using the relaxivity of the contrast agent and coagulant. We prepared phantoms using 0.05-10 mmol L-1 contrast agent (Gadovist®; Bayer Yakuhin, Ltd., Osaka, Japan) and 0.1-5.0 wt% agar (agar, powder [010-15815]; Fujifilm Wako Pure Chemical Corporation, Osaka, Japan) and measured their T1 and T2 values. Determination equations for T1 and T2 values were derived using the relaxivity calculated from the T1 and T2 values of the contrast agent and coagulant. Subsequently, the determined values were compared with the measured values. The error rate of the determined T1 and T2 values were 7.66 ± 6.60% and 5.66 ± 4.05%, respectively, with correlation coefficients of 0.996 and 0.999. These results indicate that this method enables easy and highly accurate estimation of T1 and T2 values in MRI phantoms.

Understanding the impact of Achilles lipid content on tendon mechanical parameters: a cross-sectional study of people with familial hypercholesterolemia and healthy controls

BACKGROUND

Familial hypercholesterolemia (FH) is a genetic condition that affects cholesterol metabolism, resulting in life-long elevated serum levels of low-density lipoprotein cholesterol. Systemically elevated cholesterol levels are associated with the onset of tendon injury and potentially lead to impaired mechanical properties. Applying a cross-sectional design, we examined whether FH patients present with altered Achilles biomechanics compared to healthy controls and conducted correlational analyses to determine the relationship between Achilles tendon biomechanics and tendon lipid or water content.

METHODS

Patients with FH (n = 33) and healthy controls (n = 31) were recruited from the Greater Vancouver area. Achilles cross sectional area, thickness, lipid and water content was determined using Dixon method magnetic resonance imaging (3.0T). Achilles mechanical properties were determined using synchronized dynamometry, motion capture, ultrasound and electromyography during ramped maximal voluntary isometric contractions, and stiffness and Young's modulus calculated. Between group differences were assessed with independent t-tests or Mann-Whitney U tests and Pearson's r or Spearman's ρ were employed for correlational analyses. Sensitivity analysis was conducted on FH patients diagnosed with Achilles xanthoma and the remaining FH patients.

RESULTS

FH patients had significantly elevated Achilles total water content (p = 0.006), cross-sectional area (p = 0.006), and thickness (p = 0.019). No between-group differences were observed in any of the biomechanical parameters. In patients with FH there were significant positive relationships between tendon lipid or water content and tendon strain (ρ = 0.35, p = 0.046; r = 0.42, p = 0.02, respectively). No significant relationships were observed in control participants. In patients with FH, increased tendon cross-sectional area was associated with reduced stiffness (r=-0.371, p = 0.033) and increased strain (r = 0.48, p = 0.005). The presence of xanthoma was associated with increased Achilles dimensions (p < 0.05), total water content (p = 0.03), strain (p = 0.029), and decreased Young's modulus (p = 0.001).

CONCLUSION

Increased Achilles lipid and water content is associated with increased tendon strain in people with FH and the presence of xanthoma might indicate altered tendon mechanics. This study holds relevance for individuals with hypercholesteremia, as best management practices advocate for physical activity as part of a healthy lifestyle.

Supaglutide alleviates hepatic steatosis in monkeys with spontaneous MASH

BACKGROUND

Glucagon-like peptide 1 (GLP-1) is an incretin hormone and plays an important role in regulating glucose homeostasis. GLP-1 has a short half-life due to degrading enzyme dipeptidyl peptidase-IV and rapid kidney clearance, which limits its clinical application as a therapeutic agent. We demonstrated previously that supaglutide, a novel long-acting GLP-1 analog, exerted hypoglycemic, hypolipidemic, and weight loss effects in type 2 diabetic db/db mice, DIO mice, and diabetic monkeys. In the present study, we investigated supaglutide's therapeutic efficacy in rhesus monkeys with spontaneous metabolic dysfunction-associated steatohepatitis (MASH).

METHODS

15 rhesus monkeys with biopsy-confirmed MASH were divided into three groups, receiving supaglutide 50 µg/kg, supaglutide 150 µg/kg, and placebo, respectively, by weekly subcutaneous injection for 3 months. Liver fat content quantified by magnetic resonance imaging-estimated proton density fat fraction (MRI-PDFF), liver pathology, and metabolic parameters were assessed.

RESULTS

We found that once-weekly subcutaneous injections of supaglutide for 3 months significantly reduced hepatic fat accumulation, with a 40% percentage decrease in MRI-PDFF from baseline (P < 0.001 vs. Placebo). Treatment with supaglutide alleviated hepatic histological steatosis (nonalcoholic fatty liver disease activity score P < 0.001 vs. Placebo) without worsening of fibrosis, as assessed by ultrasound-guided liver biopsy. Supaglutide concomitantly ameliorated liver injury exemplified by a lowering tendency of hepatic alanine aminotransferase levels. Supaglutide also decreased body weight in a dose-dependent fashion accompanied by decreased food intake, improved lipid profile and glycemic control.

CONCLUSIONS

Supaglutide exerts beneficial effects on hepatic and metabolic outcomes in spontaneous MASH monkeys.

Assessment of calf muscle constitution in chronic Achilles tendon disease using Dixon-based MRI

OBJECTIVES

To assess calf muscle constitution in chronic Achilles tendon disease (ATD) using two-point Dixon-based MRI (2pt-MRIDIXON).

MATERIALS AND METHODS

This retrospective study analyzed 91 patients (36 females; 57.0 ± 14.4 years) with midportion or insertional chronic ATD who underwent clinical MRI of the Achilles tendon (AT), including 2pt-MRIDIXON for quantitative assessment of calf muscle fat content (MFC). Additionally, two radiologists qualitatively assessed MFC, AT quality, and co-pathologies. 2pt-MRIDIXON-derived fat fractions (FF) were related to patients' demographics and qualitative imaging findings.

RESULTS

The overall mean FF derived from 2pt-MRIDIXON of the triceps surae muscle was 11.2 ± 9.3%. Comparing midportion and insertional ATD, there was no significant difference regarding fatty muscle infiltration assessed with 2pt-MRIDIXON (P ≥ .47) or qualitative grading (P ≥ .059). More severe AT thickening (11 vs.9 mm, P < .001) and complete tears (29 vs. 9%, P = .025) were significantly more common in midportion ATD, while partial tears were significantly more frequent in insertional ATD (55 vs. 31%, P = .027). Soleus muscle edema was more prevalent in midportion than insertional ATD (40 vs. 9%, P = .002). In contrast, insertional ATD more commonly featured bone marrow edema (61 vs. 2%), Haglund's deformity (67 vs. 0%), and retrocalcaneal bursitis (82 vs. 43%) (P ≤ .002). Significant correlations (P ≤ .001) were demonstrated between FF, AT diameter, age (both in midportion and insertional ATD), and body mass index (in midportion ATD only) (ρ range = 0.53-0.61).

CONCLUSION

In chronic ATD, calf MFC was statistically equivalent (approximately 11%), irrespective of the localization of tendon damage. More severe tendon thickening and complete tears were more common in midportion ATD, and, vice versa, partial AT tears were significantly more frequent in insertional ATD.

Comparative analysis of hepatic fat quantification across 5 T, 3 T and 1.5 T: A study on consistency and feasibility

OBJECTIVES

Magnetic resonance imaging (MRI) is a critical noninvasive technique for evaluating liver steatosis, with efficient and precise fat quantification being essential for diagnosing liver diseases. This study leverages 5 T ultra-high-field MRI to demonstrate the clinical significance of liver fat quantification, and explores the consistency and accuracy of the Proton Density Fat Fraction (PDFF) in the liver across different magnetic field strengths and measurement methodologies.

METHODS

The study involved phantoms with lipid contents ranging from 0 % to 30 % and 35 participants (21 females, 14 males; average age 30.17 ± 13.98 years, body mass index 25.84 ± 4.76, waist-hip ratio 0.84 ± 0.09). PDFF measurements were conducted using chemical shift encoded (CSE) MRI at 5 T, 3 T, and 1.5 T, alongside magnetic resonance spectroscopy (MRS) at 5 T and 1.5 T for both liver and phantoms, analyzed using jMRUI software. The MRS-derived PDFF values served as the reference standard. Repeatability of 5 T MRI measurements was assessed through correlation analysis, while accuracy was evaluated using linear regression analysis against the reference standards.

RESULTS

The CSE-PDFF measurements at 5 T demonstrated strong consistency with those at 3 T and 1.5 T, showing high intraclass correlation coefficients (ICC) of 0.988 and 0.980, respectively (all p < 0.001). There was also significant consistency across ROIs within liver lobes, with ICC values ranging from 0.975 to 0.986 (all p < 0.001). MRS-PDFF measurements for both phantoms and liver at 5 T and 1.5 T exhibited substantial agreement, with ICC values of 0.996 and 0.980, respectively (all p < 0.001). Particularly, ICC values for ROIs in the liver ranged from 0.963 to 0.990 (all p < 0.001). Despite overall agreement, statistically significant differences were noted in specific ROIs within the liver lobes (p = 0.004 and 0.012). The CSE and MRS PDFF measurements at 5 T displayed strong consistency, with an ICC of 0.988 (p < 0.001), and significant agreement was also found between 5 T CSE and 1.5 T MRS PDFF measurements, with an ICC of 0.978 (p < 0.001). Agreement was significant within the ROIs of the liver lobes on the same platform at 5 T, with ICC values ranging from 0.986 to 0.991 (all p < 0.001).

CONCLUSION

PDFF measurements at 5 T MR imaging exhibited both accuracy and repeatability, indicating that 5 T imaging provides reliable quantification of liver fat content and shows substantial potential for clinical diagnostic applications.

Feasibility of omega-3 fatty acid fraction mapping using chemical shift encoding-based imaging at 3 T

PURPOSE

The aim of this work is to develop an ω-3 fatty acid fraction mapping method at 3 T based on a chemical shift encoding model, to assess its performance in a phantom and in vitro study, and to further demonstrate its feasibility in vivo.

METHODS

A signal model was heuristically derived based on spectral appearance and theoretical considerations of the corresponding molecular structures to differentiate between ω-3 and non-ω-3 fatty acid substituents in triacylglycerols in addition to the number of double bonds (ndb), the number of methylene-interrupted double bonds (nmidb), and the mean fatty acid chain length (CL). First, the signal model was validated using single-voxel spectroscopy and a time-interleaved multi-echo gradient-echo (TIMGRE) sequence in gas chromatography-mass spectrometry (GC-MS)-calibrated oil phantoms. Second, the TIMGRE-based method was validated in vitro in 21 adipose tissue samples with corresponding GC-MS measurements. Third, an in vivo feasibility study was performed for the TIMGRE-based method in the gluteal region of two healthy volunteers. Phantom and in vitro data was analyzed using a Bland-Altman analysis.

RESULTS

Compared with GC-MS, MRS showed in the phantom study significant correlations in estimating the ω-3 fraction (p < 0.001), ndb (p < 0.001), nmidb (p < 0.001), and CL (p = 0.001); MRI showed in the phantom study significant correlations (all p < 0.001) for the ω-3 fraction, ndb, and nmidb, but no correlation for CL. Also in the in vitro study, significant correlations (all p < 0.001) between MRI and GC-MS were observed for the ω-3 fraction, ndb, and nmidb, but not for CL. An exemplary ROI measurement in vivo in the gluteal subcutaneous adipose tissue yielded (mean ± standard deviation) 0.8% ± 1.9% ω-3 fraction.

CONCLUSION

The present study demonstrated strong correlations between gradient-echo imaging-based ω-3 fatty acid fraction mapping and GC-MS in the phantom and in vitro study. Furthermore, feasibility was demonstrated for characterizing adipose tissue in vivo.

Effect of particle size on liver MRI R 2 * relaxometry: Monte Carlo simulation and phantom studies

PURPOSE

To investigate the effect of particle size on liverR 2 * $$ {\mathrm{R}}_2^{\ast } $$ by Monte Carlo simulation and phantom studies at both 1.5 T and 3.0 T.

METHODS

Two kinds of particles (i.e., iron sphere and fat droplet) with varying sizes were considered separately in simulation and phantom studies. MRI signals were synthesized and analyzed for predictingR 2 * $$ {\mathrm{R}}_2^{\ast } $$ , based on simulations by incorporating virtual liver model, particle distribution, magnetic field generation, and proton movement into phase accrual. In the phantom study, iron-water and fat-water phantoms were constructed, and each phantom contained 15 separate vials with combinations of five particle concentrations and three particle sizes.R 2 * $$ {\mathrm{R}}_2^{\ast } $$ measurements in the phantom were made at both 1.5 T and 3.0 T. Finally, differences inR 2 * $$ {\mathrm{R}}_2^{\ast } $$ predictions or measurements were evaluated across varying particle sizes.

RESULTS

In the simulation study, strong linear and positively correlated relationships were observed betweenR 2 * $$ {\mathrm{R}}_2^{\ast } $$ predictions and particle concentrations across varying particle sizes and magnetic field strengths (r ≥ 0.988 $$ r\ge 0.988 $$ ). The relationships were affected by iron sphere size (p < 0.001 $$ p<0.001 $$ ), where smaller iron sphere size yielded higher predictedR 2 * $$ {\mathrm{R}}_2^{\ast } $$ , whereas fat droplet size had no effect onR 2 * $$ {\mathrm{R}}_2^{\ast } $$ predictions (p ≥ 0.617 $$ p\ge 0.617 $$ ) for constant total fat concentration. Similarly, the phantom study showed thatR 2 * $$ {\mathrm{R}}_2^{\ast } $$ measurements were relatively sensitive to iron sphere size (p ≤ 0.004 $$ p\le 0.004 $$ ) unlike fat droplet size (p ≥ 0.223 $$ p\ge 0.223 $$ ).

CONCLUSION

LiverR 2 * $$ {\mathrm{R}}_2^{\ast } $$ is affected by iron sphere size, but is relatively unaffected by fat droplet size. These findings may lead to an improved understanding of the underlying mechanisms ofR 2 * $$ {\mathrm{R}}_2^{\ast } $$ relaxometry in vivo, and enable improved quantitative MRI phantom design.

Stability and accuracy of fat quantification on photon-counting detector CT with various scan settings: A phantom study

OBJECTIVE

Fat deposition is an important marker of many metabolic diseases. As a noninvasive and convenient examination method, CT has been widely used for fat quantification. With the clinical application of photon-counting detector (PCD)-CT, we aimed to investigate the accuracy, stability, and dose level of PCD-CT using various scan settings for fat quantification.

MATERIALS AND METHODS

Eleven agar-based lipid-containing phantoms (vials with different fat fractions [FFs]; range: 0 %-100 %) were scanned using PCD-CT. Three scanning types (sequence scan, regular spiral scan with a pitch of 0.8, and high-pitch spiral scan with a pitch of 3.2), four tube voltages (90, 120, 140, and 100 kV with a tin filter), and three image quality (IQ) levels (IQ levels of 20, 40, and 80) were alternated, and each scan setting was used twice. For each scan, a 70-keV image was generated using the same reconstruction parameters. A regular spiral scan at 120 kV with IQ80 was used to transfer the CT numbers of all scans to the FF. Intraclass correlation coefficient (ICC) and Bland-Altman analysis were implemented for accuracy and agreement evaluation, and group differences were compared using analysis of variance.

RESULTS

Excellent agreement and accuracy of FF derived by PCD-CT with all scan settings was demonstrated by high ICCs (>0.9; range: 0.929-0.998, p < 0.017) and low bias (<5% range: -2.9 %-5%). The root mean square error (RMSE) between the PCD-CT-acquired FF and the reference standard ranged from 1.0 % to 5.0 %, among which the high-pitch scan at 120 kV with IQ20 accounted for the lowest RMSE (1.0 %). The spiral scan at 120 kV with IQ20 and IQ80 yielded the lowest bias (mean value: 1.19 % and 1.23 %, respectively).

CONCLUSION

Fat quantification using PCD-CT reconstructed at 70 keV was accurate and stable under various scan settings. PCD-CT has great potential for fat quantification using ultralow radiation doses.

Quantitative MRI of diffuse liver diseases: techniques and tissue-mimicking phantoms

Quantitative magnetic resonance imaging (MRI) techniques are emerging as non-invasive alternatives to biopsy for assessment of diffuse liver diseases of iron overload, steatosis and fibrosis. For testing and validating the accuracy of these techniques, phantoms are often used as stand-ins to human tissue to mimic diffuse liver pathologies. However, currently, there is no standardization in the preparation of MRI-based liver phantoms for mimicking iron overload, steatosis, fibrosis or a combination of these pathologies as various sizes and types of materials are used to mimic the same liver disease. Liver phantoms that mimic specific MR features of diffuse liver diseases observed in vivo are important for testing and calibrating new MRI techniques and for evaluating signal models to accurately quantify these features. In this study, we review the liver morphology associated with these diffuse diseases, discuss the quantitative MR techniques for assessing these liver pathologies, and comprehensively examine published liver phantom studies and discuss their benefits and limitations.

An Adapted Deep Convolutional Neural Network for Automatic Measurement of Pancreatic Fat and Pancreatic Volume in Clinical Multi-Protocol Magnetic Resonance Images: A Retrospective Study with Multi-Ethnic External Validation

Pancreatic volume and fat fraction are critical prognoses for metabolic diseases like type 2 diabetes (T2D). Magnetic Resonance Imaging (MRI) is a required non-invasive quantification method for the pancreatic fat fraction. The dramatic development of deep learning has enabled the automatic measurement of MR images. Therefore, based on MRI, we intend to develop a deep convolutional neural network (DCNN) that can accurately segment and measure pancreatic volume and fat fraction. This retrospective study involved abdominal MR images from 148 diabetic patients and 246 healthy normoglycemic participants. We randomly separated them into training and testing sets according to the proportion of 80:20. There were 2364 recognizable pancreas images labeled and pre-treated by an upgraded superpixel algorithm for a discernible pancreatic boundary. We then applied them to the novel DCNN model, mimicking the most accurate and latest manual pancreatic segmentation process. Fat phantom and erosion algorithms were employed to increase the accuracy. The results were evaluated by dice similarity coefficient (DSC). External validation datasets included 240 MR images from 10 additional patients. We assessed the pancreas and pancreatic fat volume using the DCNN and compared them with those of specialists. This DCNN employed the cutting-edge idea of manual pancreas segmentation and achieved the highest DSC (91.2%) compared with any reported models. It is the first framework to measure intra-pancreatic fat volume and fat deposition. Performance validation reflected by regression R² value between manual operation and trained DCNN segmentation on the pancreas and pancreatic fat volume were 0.9764 and 0.9675, respectively. The performance of the novel DCNN enables accurate pancreas segmentation, pancreatic fat volume, fraction measurement, and calculation. It achieves the same segmentation level of experts. With further training, it may well surpass any expert and provide accurate measurements, which may have significant clinical relevance.

Diffuse Reflectance Spectroscopy for The Assessment of Steatosis in Liver Phantom and Liver Donors - A Pilot Study

This paper reports the application of a low-cost diagnostic modality for fat analysis in a liver phantom as well as human liver donors. The device works on the principle of diffuse reflectance spectroscopy, which absorbs and/or scatters depending upon the molecules that compose a tissue. Here, we describe the development of liver phantom of varying fat concentration using saturated fat mimicking liver steatosis. Followed by a pilot study in the human liver donor setting. Later, handheld device based on Infrared-LED and Photodetector for real-time time assessment of live donor liver and fat assessment. Clinical Relevance- This device can be used in the development of an accurate and non-invasive for quantification of liver fat in the deceased donor selection process. It has an error margin of 10% in the quantification of fat which is comparable to a standard biopsy technique.

Study of lipid proton difference evaluation via 9.4T MRI analysis of fatty liver induced by exposure to methionine and choline-deficient (MCD) diet and high-fat diet (HFD) in an animal model

The selection of an animal model is based on the pathological mechanism appropriate for experimental investigation because the therapeutic effect was low depending on the pathological occurrence mechanism. The purpose of this study is to elucidate the changes in lipid proton concentration in two animal models of nonalcoholic fatty liver disease (NAFLD): methionine and choline-deficient (MCD) diet and high-fat diet (HFD). We calculated the T2 relaxation time of 7 lipid protons (LP) in the 9.4 T MRS phantom experiment. The concentrations of LPs were adjusted for T2 and T2* of MCD, HFD, and CCl₄ fatty liver animal models. Multivariate analysis and Pearson correlation were performed to analyze LP concentration, and the difference was investigated via Kendall correlation and independent t-test using LP composition ratio. The T2 relaxation time of each LP was accurately determined using phantom experiments. The in vivo magnetic resonance spectroscopy (MRS) data were obtained by quantifying the t2/t2* corrected LP concentration in the liver of the animal model. In case of MCD and HFD, there was an average difference in all LPs except 0.9 ppm LP, and the MCD and CCl₄ groups showed differences in the average of all LPs. However, there was no difference between LP of HFD and CCl₄ groups. A higher level of unsaturated fatty acids was found in the MCD fatty liver model than in HFD induced fatty liver.

Quantification of Liver Fat Content with CT and MRI: State of the Art

Hepatic steatosis is defined as pathologically elevated liver fat content and has many underlying causes. Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, with an increasing prevalence among adults and children. Abnormal liver fat accumulation has serious consequences, including cirrhosis, liver failure, and hepatocellular carcinoma. In addition, hepatic steatosis is increasingly recognized as an independent risk factor for the metabolic syndrome, type 2 diabetes, and, most important, cardiovascular mortality. During the past 2 decades, noninvasive imaging-based methods for the evaluation of hepatic steatosis have been developed and disseminated. Chemical shift-encoded MRI is now established as the most accurate and precise method for liver fat quantification. CT is important for the detection and quantification of incidental steatosis and may play an increasingly prominent role in risk stratification, particularly with the emergence of CT-based screening and artificial intelligence. Quantitative imaging methods are increasingly used for diagnostic work-up and management of steatosis, including treatment monitoring. The purpose of this state-of-the-art review is to provide an overview of recent progress and current state of the art for liver fat quantification using CT and MRI, as well as important practical considerations related to clinical implementation.

A comparison of emulsifiers for the formation of oil-in-water emulsions: stability of the emulsions within 9 h after production and MR signal properties

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 T₁ mapping and visual control. Signal properties of the emulsifiers were investigated by ¹H-MRS in aqueous emulsifier solutions. Relaxometry and diffusion weighted MRI (DWI) were performed to investigate the effect of various emulsifier concentrations on relaxation times (T₁ and T₂) 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 T₁ 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 ¹H-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 mm²/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.

Assessment of bone marrow fat fractions in the mandibular condyle head using the iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL-IQ) method

The prevalence of temporomandibular joint disorder (TMD) is gradually increasing, and magnetic resonance imaging (MRI) is becoming increasingly common as a modality used to diagnose TMD. Edema and osteonecrosis in the bone marrow of the mandibular condyle have been considered to be precursors of osteoarthritis, but these changes are not evaluated accurately and quantitatively on routine MRI. The iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL-IQ) method, as a cutting-edge MRI technique, can separate fat and water using three asymmetric echo times and the three-point Dixon method. The purpose of this study was to analyze the quantitative fat fraction (FF) in the mandibular condyle head using the IDEAL-IQ method. Seventy-nine people who underwent MRI using IDEAL-IQ were investigated and divided into 1) the control group, without TMD symptoms, and 2) the TMD group, with unilateral temporomandibular joint (TMJ) pain. In both groups, the FF of the condyle head in the TMJ was analyzed by two oral and maxillofacial radiologists. In the TMD group, 29 people underwent cone-beam computed tomography (CBCT) and the presence or absence of bony changes in the condylar head was evaluated. The FF measurements of the condyle head using IDEAL-IQ showed excellent inter-observer and intra-observer agreement. The average FF of the TMD group was significantly lower than that of the control group (p < 0.05). In the TMD group, the average FF values of joints with pain and joints with bony changes were significantly lower than those of joints without pain or bony changes, respectively (p < 0.05). The FF using IDEAL-IQ in the TMJ can be helpful for the quantitative diagnosis of TMD.

Mapping the medullar adiposity of lumbar spine in MRI: A feasibility study

PURPOSE

The bone medullar adiposity is a marker of bone quality to the point that there is a need to investigate the factors which influence or not the density and distribution of this fat in the spine, especially at the lumbar level. The purpose was to test the feasibility of a Dixon three-point technique and investigate the vertebral marrow fat distribution.

MATERIAL AND METHODS

A sagittal sequence Iterative Decomposition of Water and Fat with Echo Asymmetry and Least-squares Estimation (IDEAL) IQ was performed on the lumbar spine of 46 subjects who were not suffering from any bone disease (21 women and 25 men, aged 18-77 years). Medulla adiposity was determined directly from the measurement of the fat fraction in each vertebral body (T12 to S1) obtained on the fat cartography automatically generated by the IDEAL sequence.

RESULTS

Average vertebral fat fraction was 36.48% (SD 12.82), with a tendency to increase with age and to higher values among men. We observed a craniocaudal gradient of the fat fraction (β = 1.37; p < 0,001; SD 0.11) increasing with age in the lumbar spine from T12 to L5. Through multivariate analysis, this gradient was adjusted for sex, weight and height of the subjects.

CONCLUSION

This feasibility study shows the existence of a physiological craniocaudal gradient of vertebral medullar adiposity from T12 to L5. This gradient increases with age but it is independent of sex or BMI. The IDEAL sequence allows quick and reproducible measurement of the spine vertebral medullar adiposity.

A portable single-sided magnetic-resonance sensor for the grading of liver steatosis and fibrosis

Low-cost non-invasive diagnostic tools for staging the progression of non-alcoholic chronic liver failure from fatty liver disease to steatohepatitis are unavailable. Here, we describe the development and performance of a portable single-sided magnetic-resonance sensor for grading liver steatosis and fibrosis using diffusion-weighted multicomponent T2 relaxometry. In a diet-induced mouse model of non-alcoholic fatty liver disease, the sensor achieved overall accuracies of 92% (Cohen's kappa, κ = 0.89) and 86% (κ = 0.78) in the ex vivo grading of steatosis and fibrosis, respectively. Localization of the measurements in living mice through frequency-dependent spatial encoding led to an overall accuracy of 87% (κ = 0.81) for the grading of steatosis. In human liver samples, the sensor graded steatosis with an overall accuracy of 93% (κ = 0.88). The use of T2 relaxometry as a sensitive measure in fully automated low-cost magnetic-resonance devices at the point of care would alleviate the accessibility and cost limits of magnetic-resonance imaging for diagnosing liver disease and assessing liver health before liver transplantation.

Advanced Quantitative Spine Imaging

Although advanced quantitative imaging may not be currently used to any degree in the routine reporting of spinal examinations, this situation will change in the not too distant future. Advanced quantitative imaging has already allowed us to understand a great deal more regarding spinal development, marrow physiology, and disease pathogenesis. Radiologists are ideally suited to drive this research forward. To speed up this process and optimize the impact of studies reporting spine quantitative data, we should work toward universal standards on the acquisition of spine data that will allow quantitative studies to be more easily compared, contrasted, and amalgamated.

Design and evaluation of quantitative MRI phantoms to mimic the simultaneous presence of fat, iron, and fibrosis in the liver

PURPOSE

To design, construct, and evaluate quantitative MR phantoms that mimic MRI signals from the liver with simultaneous control of three parameters: proton-density fat fraction (PDFF), R 2 ∗ , and T₁ . These parameters are established biomarkers of hepatic steatosis, iron overload, and fibrosis/inflammation, respectively, which can occur simultaneously in the liver.

METHODS

Phantoms including multiple vials were constructed. Peanut oil was used to modulate PDFF, MnCl₂ and iron microspheres were used to modulate R 2 ∗ , and NiCl₂ was used to modulate the T₁ of water (T_1,water ). Phantoms were evaluated at both 1.5 T and 3 T using stimulated-echo acquisition-mode MRS and chemical shift-encoded MRI. Stimulated-echo acquisition-mode MRS data were processed to estimate T_1,water , T_1,fat , R 2 , water ∗ , and R 2 , fat ∗ for each vial. Chemical shift-encoded MRI data were processed to generate PDFF and R 2 ∗ maps, and measurements were obtained in each vial. Measurements were evaluated using linear regression and Bland-Altman analysis.

RESULTS

High-quality PDFF and R 2 ∗ maps were obtained with homogeneous values throughout each vial. High correlation was observed between imaging PDFF with target PDFF (slope = 0.94-0.97, R² = 0.994-0.997) and imaging R 2 ∗ with target R 2 ∗ (slope = 0.84-0.88, R² = 0.935-0.943) at both 1.5 T and 3 T. The values of R 2 , fat ∗ and R 2 , water ∗ were highly correlated with slope close to 1.0 at both 1.5 T (slope = 0.90, R² = 0.988) and 3 T (slope = 0.99, R² = 0.959), similar to the behavior observed in vivo. The value of T_1,water (500-1200 ms) was controlled with varying NiCl₂ concentration, while T_1,fat (300 ms) was independent of NiCl₂ concentration.

CONCLUSION

Novel quantitative MRI phantoms that mimic the simultaneous presence of fat, iron, and fibrosis in the liver were successfully developed and validated.

BONE PERFUSION AND ADIPOSITY BEYOND THE NECROTIC ZONE IN FEMORAL HEAD OSTEONECROSIS: A QUANTITATIVE MRI STUDY

PURPOSE

To describe bone perfusion and adiposity beyond the necrotic zone with quantitative MRI techniques in osteonecrosis of the femoral head (ONFH).

METHOD

In this cross-sectional multicentre study, we recruited patients suffering from late-stage ONFH or hip osteoarthritis. Hip MRI included quantitative MRI sequences: chemical-shift imaging and dynamic contrast-enhanced MRI. We drew regions of interest inside the necrotic zone (inner necrosis and its border) and outside (femoral head, neck and greater trochanter) in ONFH. In the control group, regions of interest were drawn in the femoral head, femoral neck and the greater trochanter. For each region of interest, we measured fat fraction, and calculated semi-quantitative (area under the curve, initial slope) and pharmacokinetic perfusion parameters (K_trans and K_ep).

RESULTS

Thirty-two male adults (mean age 58 ± 9 years, range 38-74 years) were included. Sixteen patients formed the ONFH group and fifteen the control group; one was excluded. In the normal-appearing non-necrotic part of the femoral head, fat fraction was not significantly different in comparison with controls (p = 1), but _Ktrans was significantly lower than in controls (0.012 ± 0.018 vs. 0.027 ± 0.045; p = 0.05). This perfusion parameter reflects exchanges between blood microvessels and bone marrow.

CONCLUSIONS

Our results question the concept of adipose toxicity on the macroscopic scale, and bring up the concept of regional ischemic penumbra that goes beyond the visible necrotic zone. Further studies are required to test these hypotheses in larger populations and earlier disease states.

Quantifying bone marrow fat using standard T1-weighted magnetic resonance images in children with typical development and in children with cerebral palsy

Excess bone marrow adiposity may have a negative effect on bone growth and development. The aim of this study was to determine whether a procedure using standard T1-weighted magnetic resonance images provides an accurate estimate of bone marrow fat in children with typical development and in children with mild spastic cerebral palsy (CP; n = 15/group; 4-11 y). Magnetic resonance imaging was used to acquire T1-weighted images. It was also used to acquire fat and water images using an iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) technique. Bone marrow fat volume and fat fraction in the middle-third of the tibia were determined using the standard T1-weighted images (BMFV_T1 and BMFF_T1, respectively) and the fat and water images (BMFV_IDEAL and BMFF_IDEAL, respectively). In both groups, BMFV_T1 was highly correlated with (both r > 0.99, p < 0.001) and not different from (both p > 0.05) BMFV_IDEAL. In both groups, BMFF_T1 was moderately correlated with (both r = 0.71, p < 0.01) and not different from (both p > 0.05) BMFF_IDEAL. There was no group difference in BMFV_T1 or BMFV_IDEAL (both p > 0.05). BMFF_IDEAL was higher in children with CP (p < 0.05), but there was no group difference in BMFF_T1 (p > 0.05). We conclude that a procedure using standard T1-weighted magnetic resonance images can produce estimates of bone marrow fat volume similar to estimates from the IDEAL technique in children. However, it is less sensitive to variation in the bone marrow fat fraction.

Assessment of magnetic resonance imaging derived fat fraction as a sensitive and reliable predictor of myosteatosis in liver transplant recipients

BACKGROUND

Measures of skeletal muscle abnormalities are rapidly emerging as independent predictors of outcomes after liver transplantation (LT). We describe a simple, novel assessment of myosteatosis acquired prior to liver transplantation using Magnetic Resonance Imaging (MRI) derived fat fraction.

METHODS

A retrospective longitudinal cohort study included clinical and biochemical data from patients who underwent liver transplantation at our institution between Feb 2008 and Aug 2014. Patients transplanted for a diagnosis of hepatocellular carcinoma were excluded from the study. The fat fraction of erector spinae muscles was estimated using MRI at the level where muscle volume was highest, with myosteatosis defined at a cut-off value of 0.8.

RESULTS

180 patients were included. At baseline, those with myosteatosis were, on average, older, more likely to be female, and more likely to receive a multi-organ transplant (p < 0.05). Patients with pre-transplant myosteatosis, as delineated by MRI derived fat fraction, also had increased length of hospital stay.

CONCLUSION

This preliminary study suggests myosteatosis, as measured by fat fraction on MRI prior to LT, may be associated with increased graft loss and mortality after transplant.

Chemical-shift encoding-based water-fat separation with multifrequency fat spectrum modeling in spin-lock MRI

PURPOSE

Chemical exchange saturation transfer is used commonly to generate MRI contrast based on the chemical exchange effect. The spin-lock techniques can also be used to probe the chemical exchange and other molecular motion processes in tissues. The presence of fat can cause errors in spin-lock MRI. Signals from fat are typically suppressed based on spectral selectivity or T₁ nulling approaches in spin-lock imaging. However, these methods cannot be used to suppress fat signals from multiple fat peaks. To address this problem, we report chemical-shift encoding-based water-fat separation approaches with multifrequency fat spectrum modeling.

METHODS

Both the conventional spin-lock and the adiabatic continuous-wave constant-amplitude spin lock (ACCSL) with multi-echo acquisitions are investigated for chemical-shift encoding-based water-fat separation in spin-lock imaging. A comparison is made of reconstructions based on 3 models: a single-peak fat spectrum model, a standard precalibrated proton density 6-peak fat spectrum model, and the self-calibrated relaxation-dependent 3-peak fat spectrum model. Comparisons were performed using Bloch simulations, phantom, and in vivo experiments at 3 T.

RESULTS

Conventional spin-lock acquisitions cannot be used for reliable water-fat separation with a multipeak fat spectrum model. Water-fat separation based on ACCSL acquisitions achieves superior performance compared with the use of conventional spin-lock acquisitions. The best result is achieved from ACCSL acquisition with self-calibrated relaxation-dependent multipeak fat spectrum modeling.

CONCLUSION

The ACCSL acquisition can be used for chemical-shift encoding-based water-fat separation with multipeak fat spectrum modeling. This approach has the potential to improve quantitative analysis using spin-lock MRI for assessing the biochemical properties of tissues.

MR fingerprinting for water T1 and fat fraction quantification in fat infiltrated skeletal muscles

PURPOSE

To develop a fast MR fingerprinting (MRF) sequence for simultaneous estimation of water T1 (T1_H2O ) and fat fraction (FF) in fat infiltrated skeletal muscles.

METHODS

The MRF sequence for T1_H2O and FF quantification (MRF T1-FF) comprises a 1400 radial spokes echo train, following nonselective inversion, with varying echo and repetition time, as well as prescribed flip angle. Undersampled frames were reconstructed at different acquisition time-points by nonuniform Fourier transform, and a bi-component model based on Bloch simulations applied to adjust the signal evolution and extract T1_H2O and FF. The sequence was validated on a multi-vial phantom, in three healthy volunteers and five patients with neuromuscular diseases. We evaluated the agreement between MRF T1-FF parameters and reference values and confounding effects due to B0 and B1 inhomogeneities.

RESULTS

In phantom, T1_H2O and FF were highly correlated with references values measured with multi-inversion time inversion recovery-stimulated echo acquisition mode and Dixon, respectively (R² > 0.99). In vivo, T1_H2O and FF determined by the MRF T1-FF sequence were also correlated with reference values (R² = 0.98 and 0.97, respectively). The precision on T1_H2O was better than 5% for muscles where FF was less than 0.4. Both T1_H2O and FF values were not confounded by B0 nor B1 inhomogeneities.

CONCLUSION

The MRF T1-FF sequence derived T1_H2O and FF values in voxels containing a mixture of water and fat protons. This method can be used to comprehend and characterize the effects of tissue water compartmentation and distribution on muscle T1 values in patients affected by chronic fat infiltration.

Hepatic steatosis in patients undergoing resection of colorectal liver metastases: A target for prehabilitation? A narrative review

The prevalence of elevated intra-hepatic fat (IHF) is increasing in the Western world, either alone as hepatic steatosis (HS) or in conjunction with inflammation (steatohepatitis). These changes to the hepatic parenchyma are an independent risk factor for post-operative morbidity following liver resection for colorectal liver metastases (CRLM). As elevated IHF and colorectal malignancy share similar risk factors for development it is unsurprisingly frequent in this cohort. In patients undergoing resection IHF may be elevated due to excess adiposity or its elevation may be induced by neoadjuvant chemotherapy, termed chemotherapy associated steatosis (CAS). Additionally, chemotherapy is implicated in the development of inflammation termed chemotherapy associated steatohepatitis (CASH). Following cessation of chemotherapy, patients awaiting resection have a 4-6 week washout period prior to resection that is a window for prehabilitation prior to surgery. In patients with NAFLD dietary and pharmacological interventions can reduce IHF within this timeframe but this approach to modifying IHF is untested in this population. In this review, the aetiology of CAS and CASH is reviewed with recommendations to identify those at risk. We also focus on the post-chemotherapy washout period, reviewing dietary interventions applied to the metabolic population and suggest this window may be used as an opportunity to optimise IHF with such a regime as part of a pre-operative prehabilitation programme to produce improved patient outcomes.

Repeatability of Dixon magnetic resonance imaging and magnetic resonance spectroscopy for quantitative muscle fat assessments in the thigh

BACKGROUND

Changes in muscle fat composition as for example observed in sarcopenia or muscular dystrophy affect physical performance and muscular function, like strength and power. The purpose of the present study is to measure the repeatability of Dixon magnetic resonance imaging (MRI) for assessing muscle volume and fat in the thigh. Furthermore, repeatability of magnetic resonance spectroscopy (MRS) for assessing muscle fat is determined.

METHODS

A prototype 6-point Dixon MRI method was used to measure muscle volume and muscle proton density fat fraction (PDFF) in the left thigh. PDFF was measured in musculus semitendinosus of the left thigh with a T2-corrected multi-echo MRS method. For the determination of short-term repeatability (consecutive examinations), the root mean square coefficients of variation of Dixon MRI and MRS data of 23 young and healthy (29 ± 5 years) and 24 elderly men with sarcopenia (78 ± 5 years) were calculated. For the estimation of the long-term repeatability (13 weeks between examinations), the root mean square coefficients of variation of MRI data of seven young and healthy (31 ± 7 years) and 23 elderly sarcopenic men (76 ± 5 years) were calculated. Long-term repeatability of MRS was not determined.

RESULTS

Short-term errors of Dixon MRI volume measurement were between 1.2% and 1.5%, between 2.1% and 1.6% for Dixon MRI PDFF measurement, and between 9.0% and 15.3% for MRS. Because of the high short-term repeatability errors of MRS, long-term errors were not determined. Long-term errors of MRI volume measurement were between 1.9% and 4.0% and of Dixon MRI PDFF measurement between 2.1% and 4.2%.

CONCLUSIONS

The high degree of repeatability of volume and PDFF Dixon MRI supports its use to predict future mobility impairment and measures the success of therapeutic interventions, for example, in sarcopenia in aging populations and muscular dystrophy. Because of possible inhomogeneity of fat infiltration in muscle tissue, the application of MRS for PDFF measurements in muscle is more problematic because this may result in high repeatability errors. In addition, the tissue composition within the MRS voxel may not be representative for the whole muscle.

Effect of laterality, gender, age and body mass index on the fat fraction of salivary glands in healthy volunteers: assessed using iterative decomposition of water and fat with echo asymmetry and least-squares estimation method

OBJECTIVES:

To evaluate the effect of laterality, gender, age and body mass index (BMI) on fat fraction (FF) measurements of both parotid glands (PGs) and submandibular glands (SMGs) by using: Iterative decomposition of water and fat with echo asymmetry and least-squares estimation method (IDEAL-IQ).

METHODS:

A total of 87 healthy participants were enrolled in our study. IDEAL-IQ image was scanned using a 3.0 T scanner. Paired t test was performed to compare the difference on FF of both PGs and SMGs between left and right side. The FF of two glands between male and female healthy participants were compared using an unpaired t-test. The correlation between the FF of two glands and participant age or BMI were analyzed by Pearson's correlation.

RESULTS:

Excellent inter- and intrareader agreements were obtained during the measurements of FF by IDEAL-IQ method (ICC, 0.952-0.981). FF values correlated positively with the age and BMI in both left and right PGs and SMGs (p < 0.05). No significant difference was found on FF between left and right PGs and SMGs (p > 0.05). There was also no difference on FF between male and female healthy participants (p > 0.05).

CONCLUSIONS:

FFs of PGs and SMGs were age- and BMI- dependent, but not laterality- and gender-dependent. The effect of age and BMI need to be considered in further studies using Ideal-IQ technology to evaluate FFs of salivary gland diseases.

Fat-Water Phantoms for Magnetic Resonance Imaging Validation: A Flexible and Scalable Protocol

As new techniques are developed to image adipose tissue, methods to validate such protocols are becoming increasingly important. Phantoms, experimental replicas of a tissue or organ of interest, provide a low cost, flexible solution. However, without access to expensive and specialized equipment, constructing stable phantoms with high fat fractions (e.g., >50% fat fraction levels such as those seen in brown adipose tissue) can be difficult due to the hydrophobic nature of lipids. This work presents a detailed, low cost protocol for creating 5x 100 mL phantoms with fat fractions of 0%, 25%, 50%, 75%, and 100% using basic lab supplies (hotplate, beakers, etc.) and easily accessible components (distilled water, agar, water-soluble surfactant, sodium benzoate, gadolinium-diethylenetriaminepentacetate (DTPA) contrast agent, peanut oil, and oil-soluble surfactant). The protocol was designed to be flexible; it can be used to create phantoms with different fat fractions and a wide range of volumes. Phantoms created with this technique were evaluated in the feasibility study that compared the fat fraction values from fat-water magnetic resonance imaging to the target values in the constructed phantoms. This study yielded a concordance correlation coefficient of 0.998 (95% confidence interval: 0.972-1.00). In summary, these studies demonstrate the utility of fat phantoms for validating adipose tissue imaging techniques across a range of clinically relevant tissues and organs.

Fat fraction mapping using magnetic resonance imaging: insight into pathophysiology

Adipose cells have traditionally been viewed as a simple, passive energy storage depot for triglycerides. However, in recent years it has become clear that adipose cells are highly physiologically active and have a multitude of endocrine, metabolic, haematological and immune functions. Changes in the number or size of adipose cells may be directly implicated in disease (e.g. in the metabolic syndrome), but may also be linked to other pathological processes such as inflammation, malignant infiltration or infarction. MRI is ideally suited to the quantification of fat, since most of the acquired signal comes from water and fat protons. Fat fraction (FF, the proportion of the acquired signal derived from fat protons) has, therefore, emerged as an objective, image-based biomarker of disease. Methods for FF quantification are becoming increasingly available in both research and clinical settings, but these methods vary depending on the scanner, manufacturer, imaging sequence and reconstruction software being used. Careful selection of the imaging method-and correct interpretation-can improve the accuracy of FF measurements, minimize potential confounding factors and maximize clinical utility. Here, we review methods for fat quantification and their strengths and weaknesses, before considering how they can be tailored to specific applications, particularly in the gastrointestinal and musculoskeletal systems. FF quantification is becoming established as a clinical and research tool, and understanding the underlying principles will be helpful to both imaging scientists and clinicians.

Quantification and visualization of lipid landscape in glioma using in -and opposed-phase imaging

Objectives

This study maps the lipid distributions based on magnetic resonance imaging (MRI) in-and opposed-phase (IOP) sequence and correlates the findings generated from lipid map to histological grading of glioma.

Methods

Forty histologically proven glioma patients underwent a standard MRI tumour protocol with the addition of IOP sequence. The regions of tumour (solid enhancing, solid non-enhancing, and cystic regions) were delineated using snake model (ITK-SNAP) with reference to structural and diffusion MRI images. The lipid distribution map was constructed based on signal loss ratio (SLR) obtained from the IOP imaging. The mean SLR values of the regions were computed and compared across the different glioma grades.

Results

The solid enhancing region of glioma had the highest SLR for both Grade II and III. The mean SLR of solid non-enhancing region of tumour demonstrated statistically significant difference between the WHO grades (grades II, III & IV) (mean SLR_II = 0.04, mean SLR_III = 0.06, mean SLR_IV = 0.08, & p < .01). A strong positive correlation was seen between WHO grades with mean SLR on lipid map of solid non-enhancing (ρ=0.68, p < .01).

Conclusion

Lipid quantification via lipid map provides useful information on lipid landscape in tumour heterogeneity characterisation of glioma. This technique adds to the surgical diagnostic yield by identifying biopsy targets. It can also be used as an adjunct grading tool for glioma as well as to provide information about lipidomics landscape in glioma development.

•

In- and opposed-phase imaging is useful in gliomas characterisation and grading.

•

Signal loss ratio in the solid non-enhancing region is a potential imaging marker for discriminating between the WHO grades.

•

Lipid quantification via lipid distribution mapping provides useful information on lipid landscape in tumour heterogeneity.

Reliable quantification of marrow fat content and unsaturation level using in vivo MR spectroscopy

PURPOSE

To develop a novel technique for reliable quantification of bone marrow fat content and composition using in vivo MR spectroscopy (MRS).

METHODS

An MRS quantification method combining both advantages of Voigt line shape model and time-domain analysis was developed. The proposed method was tested using computer-simulated data and in vivo data acquired at lumbar vertebral bodies of 23 subjects (age, 83.8 ± 3.7 y; male, n = 13; female, n = 10) from L1 to L4. Reliability and reproducibility were calculated for the quantification results. Comparisons between the proposed method and some conventional methods were conducted.

RESULTS

Low mean absolute percentage errors and low mean coefficients of variation for computer simulations suggest that the proposed method is accurate and precise. By using this method, marrow fat content can be quantified reliably, even for data with low spectral resolution and low signal-to-noise ratio (SNR). Unsaturation level can be reliably quantified for data with moderate spectral resolution and moderate SNR. Results obtained from in vivo data using the proposed method demonstrated better model fit than conventional methods.

CONCLUSION

The method proposed in this study has better performance than conventional methods in the quantification of bone marrow MRS data and has great potential for wide applications of studying marrow fat content and composition. Magn Reson Med 79:1722-1729, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Achilles Tendon Xanthomas: Fat-Water Separation at Baseline and after Treatment

Purpose To investigate the fat-water content of Achilles tendon xanthomas at baseline and after treatment and to compare this assessment with that of ultrasonography (US) and other magnetic resonance (MR) imaging-based parameters. Materials and Methods Forty-eight Achilles tendons with clinically apparent xanthomas in 24 patients with familial hypercholesterolemia (FH) (six men, 18 women; mean age ± standard deviation, 58 years ± 9) were compared with 20 Achilles tendons in 10 control subjects without FH (two men, eight women; mean age, 62 years ± 7). US imaging measurements (thickness, width, cross-sectional area, echogenicity) and 3.0-T MR imaging measurements (thickness, width, cross-sectional area, volume, and fat-water separation) of the Achilles tendons were obtained at baseline and in patients with FH at 3 and 6 months after treatment with probucol, a cholesterol-lowering agent. Nonparametric tests compared baseline data, whereas repeated-measures analyses assessed treatment change. Results At baseline, all US and MR imaging-based parameters were higher in xanthoma tendons compared with those in control tendons (all P < .05). The mean relative water content per unit volume was 71% higher (42.0% ± 6.7) in xanthoma tendons than in control tendons (24.5% 6 5.8; P < .001). After 6 months of cholesterol-lowering treatment, only MR imaging measurements of tendon volume (P = .007), relative fat (P = .041), and relative water content (P < .001) showed significant changes. As relative tendon fat content decreased with treatment, relative water content increased. Conclusion Most of the enlargement of Achilles tendon xanthomas is due to an increase in water content rather than fat. For depicting treatment change, relative tendon water content was the most sensitive parameter, followed by tendon volume and relative tendon fat content. ^© RSNA, 2017 Online supplemental material is available for this article.

Quantifying fat replacement of muscle by quantitative MRI in muscular dystrophy

The muscular dystrophies are rare orphan diseases, characterized by progressive muscle weakness: the most common and well known is Duchenne muscular dystrophy which affects young boys and progresses quickly during childhood. However, over 70 distinct variants have been identified to date, with different rates of progression, implications for morbidity, mortality, and quality of life. There are presently no curative therapies for these diseases, but a range of potential therapies are presently reaching the stage of multi-centre, multi-national first-in-man clinical trials. There is a need for sensitive, objective end-points to assess the efficacy of the proposed therapies. Present clinical measurements are often too dependent on patient effort or motivation, and lack sensitivity to small changes, or are invasive. Quantitative MRI to measure the fat replacement of skeletal muscle by either chemical shift imaging methods (Dixon or IDEAL) or spectroscopy has been demonstrated to provide such a sensitive, objective end-point in a number of studies. This review considers the importance of the outcome measures, discusses the considerations required to make robust measurements and appropriate quality assurance measures, and draws together the existing literature for cross-sectional and longitudinal cohort studies using these methods in muscular dystrophy.

Correlation distance dependence of the resonance frequency of intermolecular zero quantum coherences and its implication for MR thermometry

PURPOSE

Because the resonance frequency of water-fat intermolecular zero-quantum coherences (iZQCs) reflects the water-fat frequency separation at the microscopic scale, these frequencies have been proposed and used as a mean to obtain more accurate temperature information. The purpose of this work was to investigate the dependence of the water-fat iZQC resonance frequency on sample microstructure and on the specific choice of the correlation distance.

METHODS

The effect of water-fat susceptibility gradients on the water-methylene iZQC resonance frequency was first computed and then measured for different water-fat emulsions and for a mixture of porcine muscle and fat. Similar measurements were also performed for mixed heteronuclear spin systems.

RESULTS

A strong dependence of the iZQC resonance frequency on the sample microstructure and on the specific choice of the correlation distance was found for spin systems like water and fat that do not mix, but not for spin systems that mix at the molecular level.

CONCLUSIONS

Because water and fat spins do not mix at the molecular level, the water-fat iZQC resonance frequency and its temperature coefficient are not only affected by sample microstructure but also by the specific choice of the correlation distance. Magn Reson Med 79:1429-1438, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Magnetic resonance spin-spin relaxation time estimation in a rat model of fatty liver disease

PURPOSE

To compare mono- and bi-exponential relaxation model equations to discriminate between normal and fatty liver disease.

MATERIALS AND METHODS

Six rats on a choline deficient amino acid modified (CDAA) diet and six on normal chow were studied. Multiple spin echo images with increasing echo times (TEs) were collected at 9.4T. Pixel-wise T₂ maps were generated using mono-exponential decay function to calculate T_2M , and a bi-exponential to calculate, short T₂ component (T_2S ), long T₂ component (T_2L ), and fractions of these components (ρ_S , ρ_L ), respectively. Statistical F-tests and Akaike's information criterion (AIC) were used to assess the relative performance of the two models.

RESULTS

F-test and AIC showed that in the CDAA group, T₂ bi-exponential model described the signal of T₂ weighted imaging of the liver better than the mono-exponential model. Controls were best described by the mono-exponential model. Mean values for T_2M , T_2L , T_2S , ρ_S , ρ_L were 31.2 ± 0.7 ms, 72.8 ± 3.3 ms, 8.2 ± 0.6 ms,71.2 ± 2.1%, 30.4 ± 1.3%, respectively, in CDAA rats, compared with 18.8 ± 0.5 ms, 32.3 ± 0.7 ms, 9.2 ± 1.8 ms, 79 ± 2%, 21.0 ± 1.1% in controls.

CONCLUSION

In the fatty liver of CDAA rats we have shown that T₂ weighted images fit the bi-exponential model better than mono-exponential decays thus providing a better description of the data.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:468-476.

Simultaneous Quantification of Bone Edema/Adiposity and Structure in Inflamed Bone Using Chemical Shift-Encoded MRI in Spondyloarthritis

Purpose

To evaluate proton density fat fraction (PDFF) and R2* as markers of bone marrow composition and structure in inflamed bone in patients with spondyloarthritis.

Methods

Phantoms containing fat, water, and trabecular bone were constructed with proton density fat fraction (PDFF) and bone mineral density (BMD) values matching those expected in healthy bone marrow and disease states, and scanned using chemical shift‐encoded MRI (CSE‐MRI) at 3T. Measured PDFF and R2* values in phantoms were compared with reference FF and BMD values. Eight spondyloarthritis patients and 10 controls underwent CSE‐MRI of the sacroiliac joints. PDFF and R2* in areas of inflamed bone and fat metaplasia in patients were compared with normal bone marrow in controls.

Results

In phantoms, PDFF measurements were accurate over the full range of PDFF and BMD values. R2* measurements were positively associated with BMD but also were influenced by variations in PDFF. In patients, PDFF was reduced in areas of inflammation and increased in fat metaplasia compared to normal marrow. R2* measurements were significantly reduced in areas of fat metaplasia.

Conclusion

PDFF measurements reflect changes in marrow composition in areas of active inflammation and structural damage and could be used for disease monitoring in spondyloarthritis. R2* measurements may provide additional information bone mineral density but also are influenced by fat content. Magn Reson Med 79:1031–1042, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Magnetic resonance spectroscopic analysis of multifidus muscles lipid content and association with spinopelvic malalignment in chronic low back pain

OBJECTIVE

To analyze intramyocellular lipids (IMCLs) and extramyocellular lipids (EMCLs) of the multifidus muscle (Mm) using MR spectroscopy in chronic low back pain (CLBP) and control groups and to identify correlations with spinopelvic alignment.

METHODS

40 patients (16 males, 24 females; mean age, 62.9 ± 1.9 years) whose visual analogue scale scores were >30 mm for CLBP were included. Furthermore, 40 control participants matched with the CLBP group subjects by sample size, gender and age (17 males, 23 females; mean age, 65.0 ± 1.2 years) were included. We compared the body mass index, physical workload, leisure time physical activity level, spinopelvic parameters, and IMCLs and EMCLs of the Mm between the groups. We also evaluated possible correlations of spinopelvic parameters with IMCLs and EMCLs of the Mm in the groups.

RESULTS

There were no statistically significant differences in body mass index, physical workload, exercise intensity level, spinopelvic parameters and EMCLs between the groups. The IMCLs were significantly higher in the CLBP group than in the control group (p < 0.01). In the CLBP group, there was a significantly negative correlation between IMCLs and lumbar lordosis (r = -0.64, p < 0.01) and a significantly positive correlation between IMCLs and sagittal vertical axis (r = 0.43, p < 0.01).

CONCLUSION

The measurement of IMCLs might be a characteristic finding of CLBP as well as a precursor to spinal deformity. Advances in knowledge: IMCLs of the Mm may be a useful prognostic marker in rehabilitation strategies for patients with CLBP.

A pilot study on the correlation between fat fraction values and glucose uptake values in supraclavicular fat by simultaneous PET/MRI

PURPOSE

To assess the spatial correlation between MRI and 18F-fludeoxyglucose positron emission tomography (FDG-PET) maps of human brown adipose tissue (BAT) and to measure differences in fat fraction (FF) between glucose avid and non-avid regions of the supraclavicular fat depot using a hybrid FDG-PET/MR scanner.

METHODS

In 16 healthy volunteers, mean age of 30 and body mass index of 26, FF, R2*, and FDG uptake maps were acquired simultaneously using a hybrid PET/MR system while employing an individualized cooling protocol to maximally stimulate BAT.

RESULTS

Fourteen of the 16 volunteers reported BAT-positive FDG-PET scans. MR FF maps of BAT correlate well with combined FDG-PET/MR maps of BAT only in subjects with intense glucose uptake. The results indicate that the extent of the spatial correlation positively correlates with maximum FDG uptake in the supraclavicular fat depot. No consistent, significant differences were found in FF or R2* between FDG avid and non-avid supraclavicular fat regions. In a few FDG-positive subjects, a small but significant linear decrease in BAT FF was observed during BAT stimulation.

CONCLUSION

MR FF, when used in conjunction with FDG uptake maps, can be seen as a valuable, radiation-free alternative to CT and can be used to measure tissue hydration and lipid consumption in some subjects. Magn Reson Med 78:1922-1932, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Cortical bone deficit and fat infiltration of bone marrow and skeletal muscle in ambulatory children with mild spastic cerebral palsy

INTRODUCTION

Nonambulatory children with severe cerebral palsy (CP) have underdeveloped bone architecture, low bone strength and a high degree of fat infiltration in the lower extremity musculature. The present study aims to determine if such a profile exists in ambulatory children with mild CP and if excess fat infiltration extends into the bone marrow.

MATERIALS AND METHODS

Ambulatory children with mild spastic CP and typically developing children (4 to 11years; 12/group) were compared. Magnetic resonance imaging was used to estimate cortical bone, bone marrow and total bone volume and width, bone strength [i.e., section modulus (Z) and polar moment of inertia (J)], and bone marrow fat concentration in the midtibia, and muscle volume, intermuscular, subfascial, and subcutaneous adipose tissue (AT) volume and intramuscular fat concentration in the midleg. Accelerometer-based activity monitors worn on the ankle were used to assess physical activity.

RESULTS

There were no group differences in age, height, body mass, body mass percentile, BMI, BMI percentile or tibia length, but children with CP had lower height percentile (19th vs. 50th percentile) and total physical activity counts (44%) than controls (both p<0.05). Children with CP also had lower cortical bone volume (30%), cortical bone width in the posterior (16%) and medial (32%) portions of the shaft, total bone width in the medial-lateral direction (15%), Z in the medial-lateral direction (34%), J (39%) and muscle volume (39%), and higher bone marrow fat concentration (82.1±1.8% vs. 80.5±1.9%), subfascial AT volume (3.3 fold) and intramuscular fat concentration (25.0±8.0% vs. 16.1±3.3%) than controls (all p<0.05). When tibia length was statistically controlled, all group differences in bone architecture, bone strength, muscle volume and fat infiltration estimates, except posterior cortical bone width, were still present (all p<0.05). Furthermore, a higher intermuscular AT volume in children with CP compared to controls emerged (p<0.05).

CONCLUSIONS

Ambulatory children with mild spastic CP exhibit an underdeveloped bone architecture and low bone strength in the midtibia and a greater infiltration of fat in the bone marrow and surrounding musculature compared to typically developing children. Whether the deficit in the musculoskeletal system of children with CP is associated with higher chronic disease risk and whether the deficit can be mitigated requires further investigation.

Quantifying disease activity in fatty-infiltrated skeletal muscle by IDEAL-CPMG in Duchenne muscular dystrophy

The purpose of this study was to explore the use of iterative decomposition of water and fat with echo asymmetry and least-squares estimation Carr-Purcell-Meiboom-Gill (IDEAL-CPMG) to simultaneously measure skeletal muscle apparent fat fraction and water T₂ (T_2,w) in patients with Duchenne muscular dystrophy (DMD). In twenty healthy volunteer boys and thirteen subjects with DMD, thigh muscle apparent fat fraction was measured by Dixon and IDEAL-CPMG, with the IDEAL-CPMG also providing T_2,w as a measure of muscle inflammatory activity. A subset of subjects with DMD was followed up during a 48-week clinical study. The study was in compliance with the Patient Privacy Act and approved by the Institutional Review Board. Apparent fat fraction in the thigh muscles of subjects with DMD was significantly increased compared to healthy volunteer boys (p <0.001). There was a strong correlation between Dixon and IDEAL-CPMG apparent fat fraction. Muscle T_2,w measured by IDEAL-CPMG was independent of changes in apparent fat fraction. Muscle T_2,w was higher in the biceps femoris and vastus lateralis muscles of subjects with DMD (p <0.05). There was a strong correlation (p <0.004) between apparent fat fraction in all thigh muscles and six-minute walk distance (6MWD) in subjects with DMD. IDEAL-CPMG allowed independent and simultaneous quantification of skeletal muscle fatty degeneration and disease activity in DMD. IDEAL-CPMG apparent fat fraction and T_2,w may be useful as biomarkers in clinical trials of DMD as the technique disentangles two competing biological processes.

Quantification of bone marrow fat content using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL): reproducibility, site variation and correlation with age and menopause

OBJECTIVE

To determine the reproducibility of the quantitative chemical shift-based water-fat separation method with a multiecho gradient echo sequence [iteraterative decomposition of water and fat with echo asymmetry and least-squares estimation quantitation sequence (IDEAL-IQ)] for assessing bone marrow fat fraction (FF); to evaluate variation of FF at different bone sites; and to investigate its association with age and menopause.

METHODS

31 consecutive females who underwent pelvic iterative decomposition of water and fat with echo asymmetry and least-squares estimation at 3-T MRI were included in this study. Quantitative FF using IDEAL-IQ of four bone sites were analyzed. The coefficients of variance (CV) on each site were evaluated repeatedly 10 times to assess the reproducibility. Correlations between FF and age were evaluated on each site, and the FFs between pre- and post-menopausal groups were compared.

RESULTS

The CV in the quantification of marrow FF ranged from 0.69% to 1.70%. A statistically significant correlation was established between the FF and the age in lumbar vertebral body, ilium and intertrochanteric region of the femur (p < 0.001). The average FF of post-menopausal females was significantly higher than that of pre-menopausal females in these sites (p < 0.05). In the greater trochanter of the femur, there was no significant correlation between FF and age.

CONCLUSION

In vivo IDEAL-IQ would provide reliable quantification of bone marrow fat.

ADVANCES IN KNOWLEDGE

IDEAL-IQ is simple to perform in a short time and may be practical for providing information on bone quality in clinical settings.