Search

Purpose: Chemical shift‐encoded magnetic resonance imaging enables accurate quantification of liver fat content though estimation of proton density fat‐fraction (PDFF). Computed tomography (CT) is capable of quantifying fat, based on decreased attenuation with increased fat concentration. Current quantitative fat phantoms do not accurately mimic the CT number of human liver. The purpose of this work was to develop and validate an optimized phantom that simultaneously mimics the MRI and CT signals of fatty liver. Methods: An agar‐based phantom containing 12 vials doped with iodinated contrast, and with a granular range of fat fractions was designed and constructed within a novel CT and MR compatible spherical housing design. A four‐site, three‐vendor validation study was performed. MRI (1.5T and 3T) and CT images were obtained using each vendor's PDFF and CT reconstruction, respectively. An ROI centered in each vial was placed to measure MRI‐PDFF (%) and CT number (HU). Mixed‐effects model, linear regression, and Bland‐Altman analysis were used for statistical analysis. Results: MRI‐PDFF agreed closely with nominal PDFF values across both field strengths and all MRI vendors. A linear relationship (slope = −0.54 ± 0.01%/HU, intercept = 37.15 ± 0.03%) with an R2 of 0.999 was observed between MRI‐PDFF and CT number, replicating established in vivo signal behavior. Excellent test‐retest repeatability across vendors (MRI: mean = −0.04%, 95% limits of agreement = [−0.24%, 0.16%]; CT: mean = 0.16 HU, 95% limits of agreement = [−0.15HU, 0.47HU]) and good reproducibility using GE scanners (MRI: mean = −0.21%, 95% limits of agreement = [−1.47%, 1.06%]; CT: mean = −0.18HU, 95% limits of agreement = [−1.96HU, 1.6HU]) were demonstrated. Conclusions: The proposed fat phantom successfully mimicked quantitative liver signal for both MRI and CT. The proposed fat phantom in this study may facilitate broader application and harmonization of liver fat quantification techniques using MRI and CT across institutions, vendors and imaging platforms. [ABSTRACT FROM AUTHOR]

Purpose: Chemical shift-encoded MRI (CSE-MRI) is well-established to quantify proton density fat fraction (PDFF) as a quantitative biomarker of hepatic steatosis. However, temperature is known to bias PDFF estimation in phantom studies. In this study, strategies were developed and evaluated to correct for the effects of temperature on PDFF estimation through simulations, temperature-controlled experiments, and a multi-center, multi-vendor phantom study. Theory and Methods: A technical solution that assumes and automatically estimates a uniform, global temperature throughout the phantom is proposed. Computer simulations modeled the effect of temperature on PDFF estimation using magnitude-, complex-, and hybrid-based CSE-MRI methods. Phantom experiments were performed to assess the temperature correction on PDFF estimation at controlled phantom temperatures. To assess the temperature correction method on a larger scale, the proposed method was applied to data acquired as part of a nine-site multi-vendor phantom study and compared to temperature-corrected PDFF estimation using an a priori guess for ambient room temperature. Results: Simulations and temperature-controlled experiments show that as temperature deviates further from the assumed temperature, PDFF bias increases. Using the proposed correction method and a reasonable a priori guess for ambient temperature, PDFF bias and variability were reduced using magnitude-based CSE-MRI, across MRI systems, field strengths, protocols, and varying phantom temperature. Complex and hybrid methods showed little PDFF bias and variability both before and after correction. Conclusion: Correction for temperature reduces temperature-related PDFF bias and variability in phantoms across MRI vendors, sites, field strengths, and protocols for magnitude-based CSE-MRI, even without a priori information about the temperature. [ABSTRACT FROM AUTHOR]

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), R2∗, 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 R2∗, and NiCl2 was used to modulate the T1 of water (T1,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 T1,water, T1,fat, R2,water∗, and R2,fat∗ for each vial. Chemical shift–encoded MRI data were processed to generate PDFF and R2∗ maps, and measurements were obtained in each vial. Measurements were evaluated using linear regression and Bland‐Altman analysis. Results: High‐quality PDFF and R2∗ 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 R2∗ with target R2∗ (slope = 0.84‐0.88, R2 = 0.935‐0.943) at both 1.5 T and 3 T. The values of R2,fat∗ and R2,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 T1,water (500‐1200 ms) was controlled with varying NiCl2 concentration, while T1,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. [ABSTRACT FROM AUTHOR]

Patient motion is a common challenge in the clinical setting and fast spin echo longitudinal relaxation time fluid attenuating inversion recovery imaging method with motion correction would be highly desirable. The motion correction provided by transverse relaxation time- and diffusion-weighted periodically rotated overlapping parallel lines with enhanced reconstruction methods has seen significant clinical adoption. However, periodically rotated overlapping parallel lines with enhanced reconstruction with fast spin echo longitudinal relaxation time fluid attenuating inversion recovery-weighting has proved challenging since motion correction requires wide blades that are difficult to acquire while also maintaining short echo train lengths that are optimal for longitudinal relaxation time fluid attenuating inversion recovery-weighting. Parallel imaging provides an opportunity to increase the effective blade width for a given echo train lengths. Coil-by-coil data-driven autocalibrated parallel imaging methods provide greater robustness in the event of motion compared to techniques relying on accurate coil sensitivity maps. However, conventional internally calibrated data-driven parallel imaging methods limit the effective acceleration possible for each blade. We present a method to share a single calibration dataset over all imaging blades on a slice by slice basis using the APPEAR non-Cartesian parallel imaging method providing an effective blade width increase of 2.45×, enabling robust motion correction. Results comparing the proposed technique to conventional Cartesian and periodically rotated overlapping parallel lines with enhanced reconstruction methods demonstrate a significant improvement during subject motion and maintaining high image quality when no motion is present in normal and clinical volunteers. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose: To determine optimal delay times and flip angles for T1-weighted hepatobiliary imaging at 1.5 Tesla (T) with gadoxetic acid and to demonstrate the feasibility of using a high-resolution navigated optimized T1-weighted pulse sequence to evaluate biliary disease. Materials and Methods: Eight healthy volunteers were scanned at 1.5T using a T1-weighted three-dimensional (3D)-SPGR pulse sequence following the administration of 0.05 mmol/kg of gadoxetic acid. Navigator-gating enabled acquisition of high spatial resolution (1.2 × 1.4 × 1.8 mm3, interpolated to 0.7 × 0.7 × 0.9 mm3) images in approximately 5 min of free-breathing. Multiple breath-held acquisitions were performed at flip angles between 15° and 45° to optimize T1 weighting. To evaluate the performance of this optimized sequence in the setting of biliary disease, the image quality and biliary excretion of 51 consecutive clinical scans performed to assess primary sclerosing cholangitis (PSC) were evaluated. Results: Optimal hepatobiliary imaging occurs at 15-25 min, using a 40° flip angle. The image quality and visualization of biliary excretion in the PSC scans were excellent, despite the decreased liver function in some patients. Visualization of reduced excretion often provided diagnostic information that was unavailable by conventional magnetic resonance cholangiopancreatography (MRCP). Conclusion: High-resolution navigated 3D-SPGR hepatobiliary imaging using gadoxetic acid and optimized scan parameters is technically feasible and can be clinically useful, even in patients with decreased hepatobiliary function. J. Magn. Reson. Imaging 2012;36:890-899. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

MRI imaging of hepatic iron overload can be achieved by estimating T2* values using multiple-echo sequences. The purpose of this work is to develop and clinically evaluate a weighted least squares algorithm based on T2* Iterative Decomposition of water and fat with Echo Asymmetry and Least-squares estimation (IDEAL) technique for volumetric estimation of hepatic T2* in the setting of iron overload. The weighted least squares T2* IDEAL technique improves T2* estimation by automatically decreasing the impact of later, noise-dominated echoes. The technique was evaluated in 37 patients with iron overload. Each patient underwent (i) a standard 2D multiple-echo gradient echo sequence for T2* assessment with nonlinear exponential fitting, and (ii) a 3D T2* IDEAL technique, with and without a weighted least squares fit. Regression and Bland-Altman analysis demonstrated strong correlation between conventional 2D and T2* IDEAL estimation. In cases of severe iron overload, T2* IDEAL without weighted least squares reconstruction resulted in a relative overestimation of T2* compared with weighted least squares. Magn Reson Med, 2011. © 2011 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]