T1 independent,T2* corrected MRI with accurate spectral modeling for quantification of fat: Validation in a fat‐water‐SPIO phantom

Purpose:

To validate a T₁‐independent, T₂*‐corrected fat quantification technique that uses accurate spectral modeling of fat using a homogeneous fat‐water‐SPIO phantom over physiologically expected ranges of fat percentage and T₂* decay in the presence of iron overload.

Materials and Methods:

A homogeneous gel phantom consisting of vials with known fat‐fractions and iron concentrations is described. Fat‐fraction imaging was performed using a multiecho chemical shift‐based fat‐water separation method (IDEAL), and various reconstructions were performed to determine the impact of T₂* correction and accurate spectral modeling. Conventional two‐point Dixon (in‐phase/out‐of‐phase) imaging and MR spectroscopy were performed for comparison with known fat‐fractions.

Results:

The best agreement with known fat‐fractions over the full range of iron concentrations was found when T₂* correction and accurate spectral modeling were used. Conventional two‐point Dixon imaging grossly underestimated fat‐fraction for all T₂* values, but particularly at higher iron concentrations.

Conclusion:

This work demonstrates the necessity of T₂* correction and accurate spectral modeling of fat to accurately quantify fat using MRI. J. Magn. Reson. Imaging 2009;30:1215–1222. © 2009 Wiley‐Liss, Inc.     

T1‐corrected fat quantification using chemical shift‐based water/fat separation: Application to skeletal muscle

Chemical shift‐based water/fat separation, like iterative decomposition of water and fat with echo asymmetry and least‐squares estimation, has been proposed for quantifying intermuscular adipose tissue. An important confounding factor in iterative decomposition of water and fat with echo asymmetry and least‐squares estimation‐based intermuscular adipose tissue quantification is the large difference in T₁ between muscle and fat, which can cause significant overestimation in the fat fraction. This T₁ bias effect is usually reduced by using small flip angles. T₁‐correction can be performed by using at least two different flip angles and fitting for T₁ of water and fat. In this work, a novel approach for the water/fat separation problem in a dual flip angle experiment is introduced and a new approach for the selection of the two flip angles, labeled as the unequal small flip angle approach, is developed, aiming to improve the noise efficiency of the T₁‐correction step relative to existing approaches. It is shown that the use of flip angles, selected such the muscle water signal is assumed to be T₁‐independent for the first flip angle and the fat signal is assumed to be T₁‐independent for the second flip angle, has superior noise performance to the use of equal small flip angles (no T₁ estimation required) and the use of large flip angles (T₁ estimation required). Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

Independent estimation of T*2 for water and fat for improved accuracy of fat quantification

Noninvasive biomarkers of intracellular accumulation of fat within the liver (hepatic steatosis) are urgently needed for detection and quantitative grading of nonalcoholic fatty liver disease, the most common cause of chronic liver disease in the United States. Accurate quantification of fat with MRI is challenging due the presence of several confounding factors, including T*₂ decay. The specific purpose of this work is to quantify the impact of T*₂ decay and develop a multiexponential T*₂ correction method for improved accuracy of fat quantification, relaxing assumptions made by previous T*₂ correction methods. A modified Gauss‐Newton algorithm is used to estimate the T*₂ for water and fat independently. Improved quantification of fat is demonstrated, with independent estimation of T*₂ for water and fat using phantom experiments. The tradeoffs in algorithm stability and accuracy between multiexponential and single exponential techniques are discussed. Magn Reson Med 63:849–857, 2010. © 2010 Wiley‐Liss, Inc.     

Simultaneous T2 and lipid quantitation using IDEAL‐CPMG

Muscle damage, edema, and fat infiltration are hallmarks of a range of neuromuscular diseases. The T₂ 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 T₂ 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 T₂‐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 T₂‐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. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

Improved fat suppression using multipeak reconstruction for IDEAL chemical shift fat‐water separation: Application with fast spin echo imaging

Purpose

To evaluate and quantify improvements in the quality of fat suppression for fast spin‐echo imaging of the knee using multipeak fat spectral modeling and IDEAL fat‐water separation.

Materials and Methods

T₁‐weighted and T₂‐weighted fast spin‐echo sequences with IDEAL fat‐water separation and two frequency‐selective fat‐saturation methods (fat‐selective saturation and fat‐selective partial inversion) were performed on 10 knees of five asymptomatic volunteers. The IDEAL images were reconstructed using a conventional single‐peak method and precalibrated and self‐calibrated multipeak methods that more accurately model the NMR spectrum of fat. The signal‐to‐noise ratio (SNR) was measured in various tissues for all sequences. Student t‐tests were used to compare SNR values.

Results

Precalibrated and self‐calibrated multipeak IDEAL had significantly greater suppression of signal (P < 0.05) within subcutaneous fat and bone marrow than fat‐selective saturation, fat‐selective partial inversion, and single‐peak IDEAL for both T₁‐weighted and T₂‐weighted fast spin‐echo sequences. For T₁‐weighted fast spin‐echo sequences, the improvement in the suppression of signal within subcutaneous fat and bone marrow for multipeak IDEAL ranged between 65% when compared to fat‐selective partial inversion to 86% when compared to fat‐selectivesaturation. For T2‐weighted fast spin‐echo sequences, the improvement for multipeak IDEAL ranged between 21% when compared to fat‐selective partial inversion to 81% when compared to fat‐selective saturation.

Conclusion

Multipeak IDEAL fat‐water separation provides improved fat suppression for T₁‐weighted and T₂‐weighted fast spin‐echo imaging of the knee when compared to single‐peak IDEAL and two widely used frequency‐selected fat‐saturation methods. J. Magn. Reson. Imaging 2009;29:436–442. © 2009 Wiley‐Liss, Inc.     

Spectrally selective B1‐insensitive T2 magnetization preparation sequence

A T₂ magnetization‐preparation (T₂ Prep) sequence is proposed that is insensitive to B₁ field variations and simultaneously provides fat suppression without any further increase in specific absorption rate (SAR). Increased B₁ inhomogeneity at higher magnetic field strength (B₀ ≥ 3T) necessitates a preparation sequence that is less sensitive to B₁ variations. For the proposed technique, T₂ weighting in the image is achieved using a segmented B₁‐insensitive rotation (BIR‐4) adiabatic pulse by inserting two equally long delays, one after the initial reverse adiabatic half passage (AHP), and the other before the final AHP segment of a BIR‐4 pulse. This sequence yields T₂ weighting with both B₁ and B₀ insensitivity. To simultaneously suppress fat signal (at the cost of B₀ insensitivity), the second delay is prolonged so that fat accumulates additional phase due to its chemical shift. Numerical simulations as well as phantom and in vivo image acquisitions were performed to show the efficacy of the proposed technique. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Fat‐water separated delayed hyperenhanced myocardial infarct imaging

Fat deposition associated with myocardial infarction (MI) has been reported as a commonly occurring phenomenon. Magnetic resonance imaging (MRI) has the ability to efficiently detect MI using T₁‐sensitive contrast‐enhanced sequences and fat via its resonant frequency shift. In this work, the feasibility of fat‐water separation applied to the conventional delayed hyperenhanced (DHE) MI imaging technique is demonstrated. A three‐point Dixon acquisition and reconstruction was combined with an inversion recovery gradient‐echo pulse sequence. This allowed fat‐water separation along with T₁ sensitive imaging after injection of a gadolinium contrast agent. The technique is demonstrated in phantom experiments and three subjects with chronic MI. Areas of infarction were well defined as conventional hyperenhancement in water images. In two cases, fatty deposition was detected in fat images and confirmed by precontrast opposed‐phase imaging. Magn Reson Med 60:503–509, 2008. © 2008 Wiley‐Liss, Inc.     

Change in the proton T1 of fat and water in mixture

This work describes observed changes in the proton T₁ relaxation time of both water and lipid when they are in relatively homogeneous mixtures. Results obtained from vegetable oil–water emulsions, pork kidney and lard mixtures, and excised samples of white and brown adipose tissues are presented to demonstrate this change in T₁ as a function of mixture fat fraction. As an initial proof of concept, a simpler acetone‐water experiment was performed to take advantage of complete miscibility between acetone and water and both components' single chemical shift peaks. Single‐voxel MR spectroscopy was used to measure the T₁ of predominant methylene spins in fat and the T₁ of water spins in each setup. In the vegetable oil–water emulsions, the T₁ of fat varied by as much as 3‐fold when water was the dominant mixture component. The T₁ of pure lard increased by 170 msec (+37%) when it was blended with lean kidney tissue in a 16% fatty mixture. The fat T₁ of lipid‐rich white adipose tissue was 312 msec. In contrast, the fat T₁ of leaner brown adipose tissue (fat fraction 53%) was 460 msec. A change in the water T₁ from that of pure water was also observed in the experiments. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.     

k‐space water‐fat decomposition with T2* estimation and multifrequency fat spectrum modeling for ultrashort echo time imaging

Purpose:

To demonstrate the feasibility of combining a chemical shift‐based water‐fat separation method (IDEAL) with a 2D ultrashort echo time (UTE) sequence for imaging and quantification of the short T₂ tissues with robust fat suppression.

Materials and Methods:

A 2D multislice UTE data acquisition scheme was combined with IDEAL processing, including T₂* estimation, chemical shift artifacts correction, and multifrequency modeling of the fat spectrum to image short T₂ tissues such as the Achilles tendon and meniscus both in vitro and in vivo. The integration of an advanced field map estimation technique into this combined method, such as region growing (RG), is also investigated.

Results:

The combination of IDEAL with UTE imaging is feasible and excellent water‐fat separation can be achieved for the Achilles tendon and meniscus with simultaneous T₂* estimation and chemical shift artifact correction. Multifrequency modeling of the fat spectrum yields more complete water‐fat separation with more accurate correction for chemical shift artifacts. The RG scheme helps to avoid water‐fat swapping.

Conclusion:

The combination of UTE data acquisition with IDEAL has potential applications in imaging and quantifying short T₂ tissues, eliminating the necessity for fat suppression pulses that may directly suppress the short T₂ signals. J. Magn. Reson. Imaging 2010;31:1027–1034. ©2010 Wiley‐Liss, Inc.     

T(1) independent, T(2) (*) corrected chemical shift based fat-water separation with multi-peak fat spectral modeling is an accurate and precise measure of hepatic steatosis

Purpose:

To determine the precision and accuracy of hepatic fat‐fraction measured with a chemical shift‐based MRI fat‐water separation method, using single‐voxel MR spectroscopy (MRS) as a reference standard.

Materials and Methods:

In 42 patients, two repeated measurements were made using a T₁‐independent, T‐corrected chemical shift‐based fat‐water separation method with multi‐peak spectral modeling of fat, and T₂‐corrected single voxel MR spectroscopy. Precision was assessed through calculation of Bland‐Altman plots and concordance correlation intervals. Accuracy was assessed through linear regression between MRI and MRS. Sensitivity and specificity of MRI fat‐fractions for diagnosis of steatosis using MRS as a reference standard were also calculated.

Results:

Statistical analysis demonstrated excellent precision of MRI and MRS fat‐fractions, indicated by 95% confidence intervals (units of absolute percent) of [?2.66%,2.64%] for single MRI ROI measurements, [?0.81%,0.80%] for averaged MRI ROI, and [?2.70%,2.87%] for single‐voxel MRS. Linear regression between MRI and MRS indicated that the MRI method is highly accurate. Sensitivity and specificity for detection of steatosis using averaged MRI ROI were 100% and 94%, respectively. The relationship between hepatic fat‐fraction and body mass index was examined.

Conclusion:

Fat‐fraction measured with T₁‐independent T‐corrected MRI and multi‐peak spectral modeling of fat is a highly precise and accurate method of quantifying hepatic steatosis. J. Magn. Reson. Imaging 2011;33:873–881. © 2011 Wiley‐Liss, Inc.

     

Myocardial fat quantification in humans: Evaluation by two‐point water‐fat imaging and localized proton spectroscopy

Proton MR spectroscopy (¹H‐MRS) has been used for in vivo quantification of intracellular triglycerides within the sarcolemma. The purpose of this study was to assess whether breath‐hold dual‐echo in‐ and out‐of‐phase MRI at 3.0 T can quantify the fat content of the myocardium. Biases, including T₁, T*₂, and noise, that confound the calculation of the fat fraction were carefully corrected. Thirty‐four of 46 participants had both MRI and MRS data. The fat fractions from MRI showed a strong correlation with fat fractions from MRS (r = 0.78; P < 0.05). The mean myocardial fat fraction for all 34 subjects was 0.7 ± 0.5% (range: 0.11–3%) assessed with MRS and 1.04 ± 0.4% (range: 0.32–2.44%) assessed with in‐ and out‐of‐phase MRI (P < 0.05). Scanning times were less than 15 sec for Dixon imaging, plus an additional minute for the acquisition used for T*₂ calculation, and 15‐20 min for MRS. The average postprocessing time for MRS was 3 min and 5 min for MRI including T*₂ measurement. We conclude that the dual echo method provides a rapid means to detect and quantifying myocardial fat content in vivo. Correction/adjustment for field inhomogeneity using three or more echoes seems crucial for the dual echo approach. Magn Reson Med 63:892–901, 2010. © 2010 Wiley‐Liss, Inc.     

Automated method for accurate abdominal fat quantification on water-saturated magnetic resonance images

PURPOSE: To introduce and evaluate the performance of an automated fat quantification method for water-saturated magnetic resonance images. MATERIALS AND METHODS: A fat distribution model is proposed for fat quantification on water saturated magnetic resonance images. Fat from both full- and partial-volume voxels are accounted for in this model based on image intensity histogram analysis. An automated threshold method is therefore proposed to accurately quantify total fat. This method is compared to a traditional full-volume-fat-only method in phantom and human studies. In the phantom study, fat quantification was performed on MR images obtained from a human abdomen oil phantom and was compared with the true oil volumes. In the human study, results of the two fat quantification methods of six subjects were compared on abdominal images with different spatial resolutions. RESULTS: In the phantom study, the proposed method provided significantly more accurate estimations of true oil volumes compared to the reference method (P < 0.0001). In human studies, fat quantification using the proposed method gave much more consistent results on images with different spatial resolutions, and on regions with different degrees of partial volume averaging. CONCLUSION: The proposed automated method is simple, rapid, and accurate for fat quantification on water-saturated MR images.     

Multiple-echo proton spectroscopic imaging using time domain parametric spectral analysis

A multiple-echo MR spectroscopic imaging (MRSI) method is presented that enables improved metabolite imaging in the presence of local field inhomogeneities and measurement of transverse relaxation parameters. Short echo spacing is used to maximize signal energy from inhomogeneously line-broadened resonances, and time domain parametric spectral analysis of the entire echo train is used to obtain sufficient spectral resolution from the shortened sampling periods. Optimal sequence parameters for ¹H MRSI are determined by computer simulation, and performance is compared with conventional single-echo acquisition using phantom studies at a field strength of 4.7 T. A preliminary example for use at 1.5 T is also presented using phantom and human brain MRSI studies. This technique is shown to offer improved performance relative to single-echo MRSI for imaging of metabolites with shortened T₂* values due to the presence of local field inhomogeneities. Additional advantages are the intrinsic measurement of metabolite T₂ values and determination of metabolite integrals without T₂ weighting, thereby facilitating quantitative metabolite imaging.     

Peritumoral Fat Content Correlates with Histological Prognostic Factors in Breast Carcinoma: A Study Using Iterative Decomposition of Water and Fat with Echo Asymmetry and Least-squares Estimation (IDEAL)

Purpose:To correlate peritumoral fat content using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) with histologic prognostic factors in breast carcinoma.Methods:This study consisted of 100 patients who were diagnosed with invasive carcinoma of breast and underwent breast MRI including IDEAL before surgery. The scan time of IDEAL fat fraction (FF) map imaging was 33 s. Four regions of interests (ROIs), which are a distance of 5 mm from the tumor edge, and one ROI in the mammary fat of the healthy side were set on the FF map. Then average peritumoral FF values (FFt), average FF values in the healthy side (FFh), and peritumoral fat ratio (pTFR: defined as FFt/FFh) were calculated. Histologically, the presence of lymph node metastasis and the MIB-1 index were evaluated.Results:FFt and pTFR for breast carcinoma with lymph node metastasis (79.27 ± 10.36 and 0.897 ± 0.078) were significantly lower than those without (86.23 ± 4.53 and 0.945 ± 0.032) (P < 0.001 and P = 0.005). Spearman rank correlation suggested that the FFt correlated with the MIB-1 index (r = −340, P = 0.001).Conclusion:Quantification of peritumoral fat using IDEAL-iron quantification is associated with the histologic prognostic factors, and may be a practical tool for therapeutic strategy of breast carcinoma.     

Multiecho water‐fat separation and simultaneous R estimation with multifrequency fat spectrum modeling

Multiecho chemical shift–based water‐fat separation methods are seeing increasing clinical use due to their ability to estimate and correct for field inhomogeneities. Previous chemical shift‐based water‐fat separation methods used a relatively simple signal model that assumes both water and fat have a single resonant frequency. However, it is well known that fat has several spectral peaks. This inaccuracy in the signal model results in two undesired effects. First, water and fat are incompletely separated. Second, methods designed to estimate T in the presence of fat incorrectly estimate the T decay in tissues containing fat. In this work, a more accurate multifrequency model of fat is included in the iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (IDEAL) water‐fat separation and simultaneous T estimation techniques. The fat spectrum can be assumed to be constant in all subjects and measured a priori using MR spectroscopy. Alternatively, the fat spectrum can be estimated directly from the data using novel spectrum self‐calibration algorithms. The improvement in water‐fat separation and T estimation is demonstrated in a variety of in vivo applications, including knee, ankle, spine, breast, and abdominal scans. Magn Reson Med 60:1122–1134, 2008. © 2008 Wiley‐Liss, Inc.     

Double-echo three-point-dixon method for fat suppression MRI

A double-echo two-excitation pulse sequence encoding fat and water signals for a phase-sensitive three-point Dixon-type analysis (DE-3PD) was developed and implemented on a 1.5 T MR imager. Data processing was performed using a previously developed two-dimensional (2D) region-growing algorithm, adapted to use double-echo data. Density-, T₁, and T₂-weighted fat suppression images were obtained from six volunteers using the new fat suppression method. The images were compared with corresponding images obtained using frequency-selective excitation fat suppression (FAT-SAT) and a single-echo three-point-Dixon method (SE-3PD). The results demonstrate that the DE-3PD sequence shortens the imaging time by one-third compared with the SE-3PD method, without loss in image quality. The data also show that a 2D region-growing algorithm effectively unwraps the phase of DE-3PD data sets, and that results of DE-3PD fat signal suppression are consistently better than those obtained using a standard FATSAT method. The authors conclude that the double-echo sequence provides density-, T₁, and T₂-weighted images that appear to be promising for routine clinical applications.     

Reproducibility of hepatic fat fraction measurement by magnetic resonance imaging

Purpose:

To evaluate the reproducibility of magnetic resonance imaging (MRI)‐determined hepatic fat fraction (%) across imaging sites with different magnet types and field strength. Reproducibility among MRI platforms is unclear, even though evaluating hepatic fat fractions (FFs) using MRI‐based methods is accurate against MR spectroscopy.

Materials and Methods:

Overweight subjects were recruited to undergo eight MRI examinations at five imaging centers with a range of magnet manufacturers and field strengths (1.5 and 3 T). FFs were estimated in liver and in fat‐emulsion phantoms using three methods: 1) dual‐echo images without correction (nominally out‐of‐phase [OP] and in‐phase [IP]); 2) dual‐dual‐echo images (two sequences) with T2* correction (nominally OP/IP and IP/IP); and 3) six‐echo images with spectral model and T2* correction, at sequential alternating OP and IP echo times (Methods 1, 2, and 3, respectively).

Results:

Ten subjects were recruited. For Methods 1, 2, and 3, respectively, hepatic FF ranged from ?2.5 to 27.0, 1.9 to 29.6, and 1.3 to 34.4%. Intraclass correlation coefficients were 0.85, 0.89, and 0.91 for each method, and within‐subject coefficients of variation were 18.5, 9.9, and 10.3%, respectively. Mean phantom FFs derived by Methods 2 and 3 were comparable to the known FF for each phantom. Method 1 underestimated phantom FF.

Conclusion:

Methods 2 and 3 accurately assess FF. Strong reproducibility across magnet type and strength render them suitable for use in multicenter trials and longitudinal assessments. J. Magn. Reson. Imaging 2013;37:1359–1370. © 2012 Wiley Periodicals, Inc.

     

T2 measurement in articular cartilage: Impact of the fitting method on accuracy and precision at low SNR

T₂ relaxation time is a promising MRI parameter for the detection of cartilage degeneration in osteoarthritis. However, the accuracy and precision of the measured T₂ may be substantially impaired by the low signal‐to‐noise ratio of images available from clinical examinations. The purpose of this work was to assess the accuracy and precision of the traditional fit methods (linear least‐squares regression and nonlinear fit to an exponential) and two new noise‐corrected fit methods: fit to a noise‐corrected exponential and fit of the noise‐corrected squared signal intensity to an exponential. Accuracy and precision have been analyzed in simulations, in phantom measurements, and in seven repetitive acquisitions of the patellar cartilage in six healthy volunteers. Traditional fit methods lead to a poor accuracy for low T₂, with overestimations of the exact T₂ up to 500%. The noise‐corrected fit methods demonstrate a very good accuracy for all T₂ values and signal‐to‐noise ratio. Even more, the fit to a noise‐corrected exponential results in precisions comparable to the best achievable precisions (Cramér‐Rao lower bound). For in vivo images, the traditional fit methods considerably overestimate T₂ near the bone‐cartilage interface. Therefore, using an adequate fit method may substantially improve the sensitivity of T₂ to detect pathology in cartilage and change in T₂ follow‐up examinations. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.     

T2‐weighted 3D fast spin echo imaging with water–fat separation in a single acquisition

Purpose:

To develop a robust 3D fast spin echo (FSE) T₂‐weighted imaging method with uniform water and fat separation in a single acquisition, amenable to high‐quality multiplanar reformations.

Materials and Methods:

The Iterative Decomposition of water and fat with Echo Asymmetry and Least squares estimation (IDEAL) method was integrated with modulated refocusing flip angle 3D‐FSE. Echoes required for IDEAL processing were acquired by shifting the readout gradient with respect to the Carr‐Purcell‐Meiboom‐Gill echo. To reduce the scan time, an alternative data acquisition using two gradient echoes per repetition was implemented. Using the latter approach, a total of four gradient echoes were acquired in two repetitions and used in the modified IDEAL reconstruction.

Results:

3D‐FSE T₂‐weighted images with uniform water–fat separation were successfully acquired in various anatomies including breast, abdomen, knee, and ankle in clinically feasible scan times, ranging from 5:30–8:30 minutes. Using water‐only and fat‐only images, in‐phase and out‐of‐phase images were reconstructed.

Conclusion:

3D‐FSE‐IDEAL provides volumetric T₂‐weighted images with uniform water and fat separation in a single acquisition. High‐resolution images with multiple contrasts can be reformatted to any orientation from a single acquisition. This could potentially replace 2D‐FSE acquisitions with and without fat suppression and in multiple planes, thus improving overall imaging efficiency. J. Magn. Reson. Imaging 2010;32:745–751. © 2010 Wiley‐Liss, Inc.     

MR spectroscopy of liver in overweight children and adolescents: investigation of ¹H T₂ relaxation times at 3T

Objective

The objective was to investigate T₂ relaxation values and to optimize hepatic fat quantification using proton MR spectroscopy (¹H MRS) at 3 T in overweight and obese children and adolescents.

Subjects

The study included 123 consecutive children and adolescents with a body mass index above the 97th percentile according to age and sex.¹H MR spectroscopy was performed at 3.0 T using point resolved spectroscopy sequence with series TE. T₂ relaxation values and hepatic fat content corrected for the T₂ relaxation effects were calculated.

Results

T₂ values for water ranged from 22 ms to 42 ms (mean value 28 ms) and T₂ values for fat ranged from 36 ms to 99 ms (mean value 64 ms).Poor correlation was observed: (1) between T₂ relaxation times of fat and T₂ relaxation times of water (correlation coefficient r = 0.038, P = 0.79); (2) between T₂ relaxation times of fat and fat content (r = 0.057, P = 0.69); (3) between T₂ relaxation times of water and fat content (r = 0.160, P = 0.26).Correlation between fat peak content and the T₂ corrected fat content decreased with increasing echo time TE: r = 0.97 for TE = 45, r = 0.93 for TE = 75, r = 0.89 for TE = 105, P < 0.0001.

Conclusion

¹H MRS at 3 T is an effective technique for measuring hepatic fat content in overweight and obese children and adolescents. It is necessary to measure T₂ relaxation values and to correct the spectra for the T₂ relaxation effects in order to obtain an accurate estimate of the hepatic fat content.