Fat Fraction Maps Research Articles

Modeling of T2* decay in vertebral bone marrow fat quantification.

Bone marrow fat fraction mapping using chemical shift encoding-based water-fat separation is becoming a useful tool in investigating the association between bone marrow adiposity and bone health and in assessing cancer treatment-induced bone marrow damage. Vertebral bone marrow is characterized by short T2* relaxation times, which are in general different for the water and fat components and can confound fat quantification. The purpose of the present study is to compare different approaches to T2* correction in chemical shift encoding-based water-fat imaging of vertebral bone marrow using single-voxel MRS as reference. Eight-echo gradient-echo imaging and single-voxel MRS measurements were made on the spine (L3-L5) of 25 healthy volunteers. Different approaches were evaluated for correction of T2* effects: (a) single-T2* correction, (b) dual-T2* correction, (c) T2' correction using the a priori-known T2 from the MRS at each vertebral body and (d) T2' correction using the a priori-known T2 equal to previously measured average values. Dual-T2* correction resulted in noisier imaging fat fraction maps than single-T2* correction or T2' correction using a priori-known T2. Linear regression analysis between imaging and MRS fat fraction showed a slope significantly different from 1 when using single-T2* correction (R(2) = 0.96) or dual-T2* correction (R(2) = 0.87). T2' correction using the a priori-known T2 resulted in a slope not significantly different from 1, an intercept significantly different from 0 (between 2.4% and 3%) and R(2) = 0.96. Therefore, a T2' correction using a priori-known T2 can remove the fat fraction bias induced by the difference in T2* between water and fat components without degrading noise performance in fat fraction mapping of vertebral bone marrow.

Accelerating MR Imaging Liver Steatosis Measurement Using Combined Compressed Sensing and Parallel Imaging: A Quantitative Evaluation.

To determine the limits of agreement of hepatic fat fraction and R2* relaxation rate quantified with accelerated magnetic resonance (MR) imaging reconstructed with combined compressed sensing and parallel imaging compared with conventional fully sampled acquisitions. Eleven subjects with type 2 diabetes and a healthy control subject were recruited with the approval of the Newcastle and North Tyneside 2 ethics committee and written consent. Undersampled data at ratios of 2.6×, 2.9×, 3.8×, and 4.8× were prospectively acquired in addition to fully sampled data by using five gradient echoes per repetition time at 3.0 T. Fat fraction maps were calculated by using combined compressed sensing and parallel imaging (CS-PI) reconstruction and Bland-Altman analysis performed to assess bias and 95% limits of agreement. Inter- and intrarater analysis was performed for quantitative fat fraction and R2* relaxation rate, and image quality was assessed with a four-point scale by two independent observers. The fat fractions from the accelerated acquisitions had 95% limits of agreement of 1.2%, 1.2%, 1.1%, and 1.5%, respectively, with no bias. When compared with the intra- and interrater 95% limits of agreement (0.7% and 0.8%), acceleration of up to 3.8× did not greatly degrade the fat fraction measurements. No or minimal artifact was detected at 2.6× and 2.9× accelerations, moderate artifact was detected at 3.8× acceleration, and substantial artifact was detected at 4.8× acceleration. Prospective undersampling and CS-PI reconstruction of liver fat fractions can be used to accelerate liver fat fraction measurements. The fat fractions and image quality produced were acceptable up to a factor of 3.8×, thereby shortening the required breath-hold duration from 17.7 seconds to 4.7 seconds.

Qualitative and quantitative evaluation of skeletal muscle fatty degenerative changes using whole-body Dixon nuclear magnetic resonance imaging for an important reduction of the acquisition time

In recent years, MRI has proven its usefulness for the diagnostic workup of patients with musculo-skeletal diseases, and also shown great promise as a non-invasive, quantitative outcome measure in clinical studies. The characterization of patterns of fatty degenerative lesions, which now plays an important part in the diagnosis of some diseases, is typically performed by the radiologist on routine T1-weighted images. We propose to rationalize acquisitions and reduce patients' time in the scanner by allowing radiologists to perform the qualitative grading of the muscles on images derived from fat/water acquisitions. These maps are color-coded, where the different colors correspond to classes of fatty infiltration degree. This allows a quick visual assessment of the muscles, equivalent to the standard method. Using the weighted Kappa agreement test, the agreement between the proposed method and the traditional one, as well as the reproducibility of the results with two raters, was measured on twenty patients suffering from various neuromuscular pathologies. The presented comparisons show that the use of color coded fat fraction maps is statistically equivalent to using the traditional T1-weighted images when performing visual assessment of degenerative lesions with fatty infiltrations in patients with neuromuscular disorders.

Magnetic resonance rotator cuff fat fraction and its relationship with tendon tear severity and subject characteristics

Compared with the Goutallier classification, chemical shift-based magnetic resonance (MR) fat quantification has superior reliability and accuracy in evaluation of muscle fatty infiltration. We used this method to assess the relationship between rotator cuff (RC) muscle fat fractions, tendon disease severity, and subject characteristics. In total, 182 subjects with shoulder symptoms underwent shoulder MR imaging including additional sequences for fat quantitation. Then, fat fraction maps were manually segmented, and custom software was used to compute the fat fraction. Goutallier scores were also obtained. The relationship between fat fraction and tendon tear severity and subject characteristics was assessed with descriptive statistics, analysis of variance, Student t test of different subgroups, and simple and multiple linear regression analysis. Statistically higher supraspinatus fat fractions were observed in subgroups with tendon tears >3cm, retraction >1cm, age >50years, body mass index (BMI) >30, higher Goutallier score, female gender, and longer symptom duration. A significant linear relationship was seen between RC fat fraction and tendon disease severity, age, and BMI but not symptom duration. Multiple regression models with fat fraction and tendon disease, age, BMI, and gender were significant for all 4 muscles (P<.001). The slope of fatty infiltration increase with age was reduced after adjustment for tendon disease, BMI, and gender. RC fat fraction assessed by chemical shift MR demonstrated a significant linear relationship with tendon tear severity, age, BMI, and gender but not with symptom duration.

Assessment of whole spine vertebral bone marrow fat using chemical shift-encoding based water-fat MRI.

The assessment of bone marrow composition has recently gained significant attention due to its association with bone loss pathophysiology and cancer therapy-induced bone marrow damage. The purpose of our study was to investigate the anatomical variation of the vertebral bone marrow fat using chemical shift-encoding based water-fat MRI and to assess the repeatability of these measurements. Chemical shift-encoding based water-fat MRI of the whole spine was performed in 28 young, healthy subjects (17 males, 11 females, 26 ± 4 years). Six subjects were scanned three times with repositioning to assess the repeatability of these measurements. Proton density fat fraction (PDFF) maps were computed and manually segmented to obtain PDFF of C3-L5. Mean PDFF of all subjects significantly increased from C3 to L5 (P < 0.05) with r = 0.88 (P < 0.05). PDFF averaged over C3-7, T1-6, T7-12, and L1-5 of males and females amounted to 31.7 ± 7.9% and 23.0 ± 7.8% (P = 0.002), 33.8 ± 6.8% and 24.6 ± 8.8% (P = 0.005), 33.8 ± 6.4% and 26.1 ± 6.4% (P = 0.023), and 38.8 ± 7.6% and 31.5 ± 12.4% (P = 0.063), respectively. The repeatability for PDFF measurements expressed as absolute precision error was 1.7% averaged over C3-L5. Whole spine vertebral bone marrow fat could be reproducibly assessed by using chemical shift-encoding based water-fat MRI and showed anatomical variations.

Method for B0 off-resonance mapping by non-iterative correction of phase-errors (B0-NICE).

To develop and evaluate a multiecho phase-unwrapping-based B0 mapping method. The proposed method estimates a B0 map by Non-Iterative Correction of phase-Errors (B0-NICE). The B0-NICE method generates an initial B0 map from a "pseudo in-phase" data set by introducing a bias frequency shift to the multipeak fat model, followed by correcting the phase errors using both phase and magnitude information. The performance of the B0-NICE method was evaluated with all data cases from the 2012 ISMRM Challenge. The B0 field estimates from B0-NICE were compared with those generated by GlObally Optimal Surface Estimation (GOOSE). In the presence of large B0 inhomogeneity, the B0-NICE method was able to generate more realistic B0 maps from multiecho data, compared with GOOSE. Accurate estimation of fat-fraction (FF) map was also achieved using the proposed algorithm. The primary finding of the present study is that accurate FF and B0 maps are achievable if magnitude data is processed independently and used to correct phase errors existing in B0 maps generated by phase unwrapping. The B0-NICE software is freely available to the scientific community.

G.P.119: Skeletal muscle fatty degenerative changes can be evaluated both qualitatively and quantitatively from whole-body Dixon NMR images with an important gain in acquisition time

Fatty infiltration of muscles is a marker of disease progression in many neuromuscular disorders. Muscle MRI is capable of revealing patterns of muscles involvement that are disease specific and facilitates the diagnostic workup of patients. Although routine T1-weighted (T1w) imaging can give an indication of the presence or absence of muscular fat infiltration, it is difficult to extract quantitative data from these images. On the contrary, Dixon methods provide quantitative measure of fat fraction. Usually, whole-body (WB) exams consist in the acquisition of T1w images, followed by Dixon acquisitions on targeted regions to quantitatively assess fat infiltration. With the aim of improving and accelerating the qualitative assessment of neuromuscular disorders, we propose to avoid the T1w acquisition altogether, by allowing to perform the visual diagnosis workup on a WB Dixon imaging. 20 patients underwent WB MRI at 3T. WB T1w images were acquired with a 2D TSE sequence (resolution = 1.1 × 1.1 mm2, slice thickness = 6 mm, Tacq = 5 min 40 s). WB Dixon acquisition consisted in a 3D VIBE sequence with 3 echoes (resolution = 1 × 1 × 5 mm3, Tacq = 14 min 5 s). Quantitative fat fraction maps were derived using a standard 3-points Dixon reconstruction method. A customed lookup table was embedded in the DICOM file to provide a colored lecture of fat fraction maps corresponding to the Mercuri’s scale. Our results show that the acquisition of a high resolution WB Dixon imaging is possible in less than 15 min using an optimized VIBE sequence. This provides quantitative data that are more suitable than T1w images for longitudinal natural history studies, or therapeutic clinical trials. Moreover, the color representation renders the visual grading of the muscles more convenient and less operator dependent as it is based on actual fat fraction measurements. WB Dixon might then overcome the use of WB T1w images for diagnostic of neuromuscular disorders. Fatty infiltration of muscles is a marker of disease progression in many neuromuscular disorders. Muscle MRI is capable of revealing patterns of muscles involvement that are disease specific and facilitates the diagnostic workup of patients. Although routine T1-weighted (T1w) imaging can give an indication of the presence or absence of muscular fat infiltration, it is difficult to extract quantitative data from these images. On the contrary, Dixon methods provide quantitative measure of fat fraction. Usually, whole-body (WB) exams consist in the acquisition of T1w images, followed by Dixon acquisitions on targeted regions to quantitatively assess fat infiltration. With the aim of improving and accelerating the qualitative assessment of neuromuscular disorders, we propose to avoid the T1w acquisition altogether, by allowing to perform the visual diagnosis workup on a WB Dixon imaging. 20 patients underwent WB MRI at 3T. WB T1w images were acquired with a 2D TSE sequence (resolution = 1.1 × 1.1 mm2, slice thickness = 6 mm, Tacq = 5 min 40 s). WB Dixon acquisition consisted in a 3D VIBE sequence with 3 echoes (resolution = 1 × 1 × 5 mm3, Tacq = 14 min 5 s). Quantitative fat fraction maps were derived using a standard 3-points Dixon reconstruction method. A customed lookup table was embedded in the DICOM file to provide a colored lecture of fat fraction maps corresponding to the Mercuri’s scale. Our results show that the acquisition of a high resolution WB Dixon imaging is possible in less than 15 min using an optimized VIBE sequence. This provides quantitative data that are more suitable than T1w images for longitudinal natural history studies, or therapeutic clinical trials. Moreover, the color representation renders the visual grading of the muscles more convenient and less operator dependent as it is based on actual fat fraction measurements. WB Dixon might then overcome the use of WB T1w images for diagnostic of neuromuscular disorders.

Atlas-based liver segmentation and hepatic fat-fraction assessment for clinical trials

Automated assessment of hepatic fat-fraction is clinically important. A robust and precise segmentation would enable accurate, objective and consistent measurement of hepatic fat-fraction for disease quantification, therapy monitoring and drug development. However, segmenting the liver in clinical trials is a challenging task due to the variability of liver anatomy as well as the diverse sources the images were acquired from. In this paper, we propose an automated and robust framework for liver segmentation and assessment. It uses single statistical atlas registration to initialize a robust deformable model to obtain fine segmentation. Fat-fraction map is computed by using chemical shift based method in the delineated region of liver. This proposed method is validated on 14 abdominal magnetic resonance (MR) volumetric scans. The qualitative and quantitative comparisons show that our proposed method can achieve better segmentation accuracy with less variance comparing with two other atlas-based methods. Experimental results demonstrate the promises of our assessment framework.

MR Quantification of the Fatty Fraction from T2*-corrected Dixon Fat/Water Separation Volume-interpolated Breathhold Examination (VIBE) in the Assessment of Muscle Atrophy in Rotator Cuff Tears

To assess the usefulness of T2*-corrected fat fraction (FF) map from volume-interpolated breathhold examination (VIBE) magnetic resonance (MR) sequence in patients with the rotator cuff pathology. The phantom study was performed to validate the FF maps. Eighty-nine shoulder MR arthrographies were analyzed: (1) divided into three groups namely tendinopathy/normal tendons, partial-thickness tears, and full-thickness tears, and (2) occupation ratio (OR) was measured for muscular atrophy. Uncorrected and T2*-corrected FF maps were reconstructed from the VIBE images. The Pearson correlation test was used to correlate the FFs with ORs. The FF and the OR were compared between groups using the Student t test. T2*-corrected FF maps could provide a higher correlation than uncorrected FF maps. There were significantly negative correlations between the ORs and the FFs (P < .01). In the normal and the partial-thickness tear group, the OR did not show a significant difference, although the FF maps showed a significant difference (P < .01). This quantitative assessment of the T2*-corrected FF in the rotator cuff muscles was found to be reliable and correlated well with the ORs. The T2*-corrected FF maps could be used for more sophisticated assessments of the fat even in the partial-thickness tear.

Hepatic fat during fasting and refeeding by MRI fat quantification

To explore the sensitivity of high-field small animal magnetic resonance imaging to dynamic changes in fat content in the liver and to characterize the effect of prandial state on imaging studies of hepatic fat. A total of three timepoints were acquired using asymmetric spin-echo acquisitions for 12 mice with 24-hour spacing. After the first scan, half of the cohort was placed on a water-only diet. The second half of the cohort continued to have access to their high-fat chow. The scans were repeated after 24 hours. All animals were then returned to the high-fat diet, and the scans were again repeated after 24 hours. Fat fraction maps were computed using previously described methods. Regions of interests were manually drawn in the livers and the patterns of the two groups over time were compared. Five out of six of the animals in the starved group showed an increase in hepatic fat fraction during the fasting period (average increase 0.54 ± 0.48), which decreased on refeeding. Analysis of variance indicated that the results significantly depended on both the group and the timepoint (P = 0.003). Fat-water imaging methods are able to measure hepatic fat changes caused by short-term dietary perturbations.

Quantification of the fat fraction in the liver using dual-energy computed tomography and multimaterial decomposition.

The objective of this study was to evaluate the feasibility and accuracy of postcontrast, dual-energy computed tomography (DECT) using multimaterial decomposition (MMD) for quantification of the hepatic fat fraction (HFF). Various degrees of fatty liver were produced in 16 rabbits divided into 4 groups, by feeding them a high-fat, high-cholesterol diet. After 6 weeks, precontrast, single-energy computed tomography (SECT) and postcontrast DECT were performed, and HFF maps were obtained from the DECT using MMD. T2*-corrected, multiecho, chemical-shift imaging for obtaining the proton density fat fraction (PDFF) map and histologic assessment of the hepatic steatosis were also performed. The Pearson correlations coefficients were calculated, and Bland-Altman analysis was performed of the fat fractions determined by DECT, magnetic resonance imaging (MRI), and pathology. Receiver operating characteristic curve analysis was performed to detect 5% hepatic steatosis or greater. The histologic HFF was used as the reference standard, and PDFFs determined by chemical-shift imaging as the technical standard. The HFFs calculated by MMD of postcontrast DECT scans were strongly correlated with those of pathology as well as the PDFFs of MRI (P < 0.05), and the mean differences of the Bland-Altman plots between the HFFs of DECT with MMD and the PDFFs of MRI were close to zero. The diagnostic performance of postcontrast DECT with MMD for detecting 5% hepatic steatosis or greater was comparable to that of the attenuation value of precontrast SECT and the PDFFs of MRI (P = 0.17-0.82). Quantification of the HFF using postcontrast DECT with MMD was feasible and showed comparable sensitivity and specificity to the precontrast SECT for the detection of hepatic steatosis.

Investigating the quantitative fidelity of prospectively undersampled chemical shift imaging in muscular dystrophy with compressed sensing and parallel imaging reconstruction

Fat fraction measurement in muscular dystrophy has an important role to play in future therapy trials. Undersampled data acquisition reconstructed by combined compressed sensing and parallel imaging (CS-PI) can potentially reduce trial cost and improve compliance. These benefits are only gained from prospectively undersampled acquisitions. Eight patients with Becker muscular dystrophy were recruited and prospectively undersampled data at ratios of 3.65×, 4.94×, and 6.42× were acquired in addition to fully sampled data: equivalent coherent undersamplings were acquired for reconstruction with parallel imaging alone (PI). Fat fraction maps and maps of total signal were created using a combined compressed sensing/parallel imaging (CS-PI) reconstruction. The CS-PI reconstructions are of sufficient quality to allow muscle delineation at 3.65× and 4.94× undersampling but some muscles were obscured at 6.42×. When plotted against the fat fractions derived from fully sampled data, non-significant bias and 95% limits of agreement of 1.58%, 2.17% and 2.41% were found for the three CS-PI reconstructions, while a 3.36× PI reconstruction yields 2.78%, 1.8 times worse than the equivalent CS-PI reconstruction. Prospective undersampling and CS-PI reconstruction of muscle fat fraction mapping can be used to accelerate muscle fat fraction measurement in muscular dystrophy.

MR Fat Fraction Mapping: A Simple Biomarker for Liver Steatosis Quantification in Nonalcoholic Fatty Liver Disease Patients

To assess the performance, postprocessing time, and intra- and interobserver agreement of a simple magnetic resonance-based mapping technique to quantify liver fat.This prospective, single-center study included 26 patients who were overweight with type 2 diabetes and at risk for nonalcoholic fatty liver disease. Mapping of the liver was based on a triple echo gradient-echo sequence, and (1)H magnetic resonance spectroscopy was used as the reference standard. The nonparametric Spearman correlation coefficient and the Wilcoxon test were used for comparisons between mapping and spectroscopy. The mapping was assessed for its predictive performance using the area under the curve of a receiver operating characteristic curve. Intraclass correlation coefficients were used to calculate intra- and interobserver's agreement for mapping measurements.Patients had a mean fat percentage of 11.7% (range, 2-35.4%). A strong correlation was seen between mapping and spectroscopy (r = 0.89, P < .0001). A cutoff of 6.9% for fat fraction mapping was found to diagnose steatosis with 93% sensitivity and 100% specificity with an area under the curve of 0.99. Mapping of the liver had shorter acquisition and post-processing times than spectroscopy (5 min vs. 38 min; P < .0001). Mapping measurements had an intra- and interobserver agreement of 0.98 and 0.99, respectively.The magnetic resonance-based liver mapping can accurately quantify liver fat with a cutoff value of 6.9% and excellent intra- and interobserver agreement. This mapping technique, with its simple methodology and short postprocessing time, has the potential to be included in routine abdominal protocols.

Fat-Corrected T2 Measurement as a Marker of Active Muscle Disease in Inflammatory Myopathy

We sought to improve the utility of T2 measurement as a marker of active muscle disease in patients with idiopathic inflammatory myopathy by correcting for T2 prolongations caused by fatty replacement of muscle that accompnaies chronic muscle damage. Twenty-one patients with idiopathic inflammatory myopathy underwent a standardized MRI evaluation of the thighs. Fat fraction maps were calculated from dual-echo gradient-echo images. Fat-corrected T2 maps were generated from multiecho spin-echo images on the basis of a biexponential model that incorporated voxelwise fat fraction estimates. Semiautomated summaries of conventional and fat-corrected muscle T2 values were compared with one another and with standardized visual scores of muscle disease based on T1-weighted spin-echo and STIR images. Fat-corrected muscle T2 maps showed lower mean values and greater histogram entropy than conventional T2 maps, as analyzed over a standardized portion of the thigh muscles. Conventional and fat-corrected T2 values correlated with visual scores of active muscle disease on STIR images and with the varying intensity of disease depicted with STIR in focal muscle regions. MRI T2 maps of muscle can be corrected for varying fat content by combining the information from chemical shift-sensitive gradient-echo and multiecho spin-echo images. Use of this strategy may prove useful in the study of idiopathic inflammatory myopathy and other diseases characterized by both muscle inflammation and atrophy.

Validation of MRI biomarkers of hepatic steatosis in the presence of iron overload in the ob/ob mouse

To validate the utility and performance of a T 2 correction method for hepatic fat quantification in an animal model of both steatosis and iron overload. Mice with low (n = 6), medium (n = 6), and high (n = 8) levels of steatosis were sedated and imaged using a chemical shift-based fat-water separation method to obtain magnetic resonance imaging (MRI) fat-fraction measurements. Imaging was performed before and after each of two superparamagnetic iron oxide (SPIO) injections to create hepatic iron overload. Fat-fraction maps were reconstructed with and without T 2 correction. Fat-fraction with and without T 2 correction and T 2 measurements were compared after each injection. Liver tissue was harvested and imaging results were compared to triglyceride extraction and histology grading. Excellent correlation was seen between MRI fat-fraction and tissue-based fat quantification. Injections of SPIOs led to increases in R 2 (=1/T 2). Measured fat-fraction was unaffected by the presence of iron when T 2 correction was used, whereas measured fat-fraction dramatically increased without T 2 correction. Hepatic fat-fraction measured using a T 2-corrected chemical shift-based fat-water separation method was validated in an animal model of steatosis and iron overload. T 2 correction enables robust fat-fraction estimation in both the presence and absence of iron, and is necessary for accurate hepatic fat quantification.

Muscle fat-fraction and mapping in Duchenne muscular dystrophy: evaluation of disease distribution and correlation with clinical assessments

To examine the usefulness of dual-echo dual-flip angle spoiled gradient recalled (SPGR) magnetic resonance imaging (MRI) technique in quantifying muscle fat fraction (MFF) of pelvic and thighs muscles as a marker of disease severity in boys with Duchenne muscular dystrophy (DMD), by correlating MFF calculation with clinical assessments. We also tried to identify characteristic patterns of disease distribution. Twenty consecutive boys (mean age, 8.6years ± 2.3 [standard deviation, SD]; age range, 5-15years; median age, 9years;) with DMD were evaluated using a dual-echo dual-flip angle SPGR MRI technique, calculating muscle fat fraction (MFF) of eight muscles in the pelvic girdle and thigh (gluteus maximus, adductor magnus, rectus femoris, vastus lateralis, vastus medialis, biceps femoris, semitendinosus, and gracilis). Color-coded parametric maps of MFF were also obtained. A neurologist who was blinded to the MRI findings performed the clinical assessments (patient age, Medical Research Council score, timed Gower score, time to run 10m). The relationships between mean MFF and clinical assessments were investigated using Spearman's rho coefficient. Positive and negative correlations were evaluated and considered significant if the P value was < 0.05. The highest mean MFF was found in the gluteus maximus (mean, 46.3 % ± 24.5 SD), whereas the lowest was found in the gracilis muscle (mean, 2.7 % ± 4.7 SD). Mean MFF of the gluteus maximus was significantly higher than that of the other muscles (P < 0.01), except for the adductor magnus and biceps muscles. A significant positive correlation was found between the mean MFF of all muscles and the patients age (20 patients; P < 0.005), Medical Research Council score (19 patients; P < 0.001), timed Gower score (17 patients; P < 0.03), and time to run 10m (20 patients; P < 0.001). A positive correlation was also found between the mean MFF of the gluteus maximus muscle and the timed Gower score. Color-coded maps provided an efficient visual assessment of muscle fat content and its heterogeneous distribution. Muscle fat fraction calculation and mapping using the dual-echo dual-flip angle SPGR MRI technique are useful markers of disease severity and permit patterns of disease distribution to be identified in patients with DMD.

Simultaneous T2 and lipid quantitation using IDEAL‐CPMG

Muscle damage, edema, and fat infiltration are hallmarks of a range of neuromuscular diseases. The T(2) of water, T(2,w) , in muscle lengthens with both myocellular damage and inflammation and is typically measured using multiple spin-echo or Carr-Purcell-Meiboom-Gill acquisitions. However, microscopic fat infiltration in neuromuscular diseases prevents accurate T(2,w) quantitation as the longer T(2) of fat, T(2,f) , masks underlying changes in the water component. Fat saturation can be inconsistent across the imaging volume and removes valuable physiological fat information. A new method is presented that combines iterative decomposition of water and fat with echo asymmetry and least squares estimation with a Carr-Purcell-Meiboom-Gill-sequence. The sequence results in water and fat separated images at each echo time for use in T(2,w) and T(2,f) quantification. With knowledge of the T(2,w) and T(2,f) , a T(2) -corrected fat fraction map can also be calculated. Monte-Carlo simulations and measurements in phantoms, volunteers, and a patient with inclusion body myositis are demonstrated. In healthy volunteers, uniform T(2,w) and T(2) -corrected fat fraction maps are present within all muscle groups. However, muscle-specific patterns of fat infiltration and edema are evident in inclusion body myositis, which demonstrates the power of separating and quantifying the fat and water components.