Improved intravoxel incoherent motion analysis of diffusion weighted imaging by data driven Bayesian modeling

In addition to the diffusion coefficient, fitting the intravoxel incoherent motion model to multiple b‐value diffusion‐weighted MR data gives pseudo‐diffusion measures associated with rapid signal attenuation at low b‐values that are of use in the assessment of a number of pathologies. When summary measures are required, such as the average parameter for a region of interest, least‐squares based methods give adequate estimation accuracy. However, using least‐squares methods for pixel‐wise fitting typically gives noisy estimates, especially for the pseudo‐diffusion parameters, which limits the applicability of the approach for assessing spatial features and heterogeneity. In this article, a Bayesian approach using a shrinkage prior model is proposed and is shown to substantially reduce estimation uncertainty so that spatial features in the parameters maps are more clearly apparent. The Bayesian approach has no user‐defined parameters, so measures of parameter variation (heterogeneity) over regions of interest are determined by the data alone, whereas it is shown that for the least‐squares estimates, measures of variation are essentially determined by user‐defined constraints on the parameters. Use of a Bayesian shrinkage prior approach is, therefore, recommended for intravoxel incoherent motion modeling. Magn Reson Med 71:411–420, 2014. © 2013 Wiley Periodicals, Inc.     

IVIM-DWI技术在肝脏弥漫性病变中的研究进展

在生物组织中体素内不相干运动(IVIM)包括体素内水分子扩散和微循环灌注,IVIM双指数模型可以精确描述DWI信号衰减与b值的关系,分别获取反映组织水分子扩散和微循环灌注的参数。近年来,IVIM成像在肝脏弥漫性病变的检测与分级中应用越来越多。主要阐述肝脏IVIM成像的原理、影响因素及可重复性以及在弥漫性病变中的诊断价值。     

Enhancing pancreatic adenocarcinoma delineation in diffusion derived intravoxel incoherent motion f‐maps through automatic vessel and duct segmentation

Diffusion‐based intravoxel incoherent motion imaging has recently gained interest as a method to detect and characterize pancreatic lesions, especially as it could provide a radiation‐ and contrast agent‐free alternative to existing diagnostic methods. However, tumor delineation on intravoxel incoherent motion‐derived parameter maps is impeded by poor lesion‐to‐pancreatic duct contrast in the f‐maps and poor lesion‐to‐vessel contrast in the D‐maps. The distribution of the diffusion and perfusion parameters within vessels, ducts, and tumors were extracted from a group of 42 patients with pancreatic adenocarcinoma. Clearly separable combinations of f and D were observed, and receiver operating characteristic analysis was used to determine the optimal cutoff values for an automated segmentation of vessels and ducts to improve lesion detection and delineation on the individual intravoxel incoherent motion‐derived maps. Receiver operating characteristic analysis identified f = 0.28 as the cutoff for vessels (Area under the curve (AUC) = 0.901) versus tumor/duct and D = 1.85 μm²/ms for separating duct from tumor tissue (AUC = 0.988). These values were incorporated in an automatic segmentation algorithm and then applied to 42 patients. This yielded clearly improved tumor delineation compared to individual intravoxel incoherent motion‐derived maps. Furthermore, previous findings that indicated that the f value in pancreatic cancer is strongly reduced compared to healthy pancreatic tissue were reconfirmed. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

Intravoxel incoherent motion diffusion imaging of the liver: Optimal b-value subsampling and impact on parameter precision and reproducibility

PurposeTo increase diffusion sampling efficiency in intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) of the liver by reducing the number of diffusion weightings (b-values).Materials and methodsIn this IRB approved HIPAA compliant prospective study, 53 subjects (M/F 38/15, mean age 52 ± 13 y) underwent IVIM DWI at 1.5 T using 16 b-values (0–800 s/mm²), with 14 subjects having repeat exams to assess IVIM parameter reproducibility. A biexponential diffusion model was used to quantify IVIM hepatic parameters (PF: perfusion fraction, D: true diffusion and D*: pseudo diffusion). All possible subsets of the 16 b-values were probed, with number of b values ranging from 4 to 15, and corresponding parameters were quantified for each subset. For each b-value subset, global parameter estimation error was computed against the parameters obtained with all 16 b-values and the subsets providing the lowest error were selected. Interscan estimation error was also evaluated between repeat exams to assess reproducibility of the IVIM technique in the liver. The optimal b-values distribution was selected such that the number of b-values was minimal while keeping parameter estimation error below interscan reproducibility error.ResultsAs the number of b-values decreased, the estimation error increased for all parameters, reflecting decreased precision of IVIM metrics. Using an optimal set of 4 b-values (0, 15, 150 and 800 s/mm²), the errors were 6.5, 22.8 and 66.1% for D, PF and D* respectively. These values lie within the range of test–retest reproducibility for the corresponding parameters, with errors of 12.0, 32.3 and 193.8% for D, PF and D* respectively.ConclusionA set of 4 optimized b-values can be used to estimate IVIM parameters in the liver with significantly shorter acquisition time (up to 75%), without substantial degradation of IVIM parameter precision and reproducibility compared to the 16 b-value acquisition used as the reference.     

同时多层成像技术联合肝脏MR扩散成像的应用及展望

同时多层（SMS）成像技术与多种MRI序列联合应用可明显缩短成像时间。MR扩散成像,如常规扩散加权成像（DWI）、体素内不相干运动成像（IVIM）、扩散张量成像（DTI）和扩散峰度成像（DKI）能反映组织内水分子扩散、血流灌注、组织结构复杂性等微观特征,在肝脏病变检测和辅助定性中有重要价值。SMS与MR扩散成像联合后可明显缩短成像时间,利于各种MR扩散成像在肝脏中的广泛应用。综述SMS对肝脏扩散成像扫描速度的提升效率、对影像质量和定量参数的影响,以期推动SMS成像技术在临床中的广泛应用。     

Applications of the intravoxel coherent motion technique to the central nervous system

Phase difference images, obtained by comparing data from motion-sensitized and -unsensitized spin-echo sequences, can be used to study intravoxel coherent motions. The resulting images, which have been routinely used to study fast flowing blood, may potentially yield information about perfused flows and bulk tissue motion. The likely limitations and potential of this technique applied to the central nervous system are reviewed with reference to parallel studies of intravoxel incoherent motion.     

Intravoxel incoherent motion imaging of tumor microenvironment in locally advanced breast cancer

Diffusion‐weighted imaging plays important roles in cancer diagnosis, monitoring, and treatment. Although most applications measure restricted diffusion by tumor cellularity, diffusion‐weighted imaging is also sensitive to vascularity through the intravoxel incoherent motion effect. Hypervascularity can confound apparent diffusion coefficient measurements in breast cancer. We acquired multiple b‐value diffusion‐weighted imaging at 3 T in a cohort of breast cancer patients and performed biexponential intravoxel incoherent motion analysis to extract tissue diffusivity (D_t), perfusion fraction (f_p), and pseudodiffusivity (D_p). Results indicated significant differences between normal fibroglandular tissue and malignant lesions in apparent diffusion coefficient mean (±standard deviation) values (2.44 ± 0.30 vs. 1.34 ± 0.39 μm²/msec, P < 0.01) and D_t (2.36 ± 0.38 vs. 1.15 ± 0.35 μm²/msec, P < 0.01). Lesion diffusion‐weighted imaging signals demonstrated biexponential character in comparison to monoexponential normal tissue. There is some differentiation of lesion subtypes (invasive ductal carcinoma vs. other malignant lesions) with f_p (10.5 ± 5.0% vs. 6.9 ± 2.9%, P = 0.06), but less so with D_t (1.14 ± 0.32 μm²/msec vs. 1.18 ± 0.52 μm²/msec, P = 0.88) and D_p (14.9 ± 11.4 μm²/msec vs. 16.1 ± 5.7 μm²/msec, P = 0.75). Comparison of intravoxel incoherent motion biomarkers with contrast enhancement suggests moderate correlations. These results suggest the potential of intravoxel incoherent motion vascular and cellular biomarkers for initial grading, progression monitoring, or treatment assessment of breast tumors. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

腹部IVIM-DWI应用研究及进展

体素内不均一运动(IVIM)是指MR扩散加权成像(DWI)上体素内信号衰减同时包括真性水分子扩散和毛细血管网中随机血流微循环灌注,导致表观扩散系数(ADC)值反映的信息有限。采用多b值可获取系列DWI影像,根据双指数模型拟合,可同时获得组织的扩散和灌注信息,更全面地分析组织扩散成像数据。IVIM-DWI目前已广泛应用于肝脏、胰腺、肾脏、前列腺等脏器,就该技术在腹部MR成像中的应用研究现状及进展予以综述。     

On the use of bayesian probability theory for analysis of exponential decay date: An example taken from intravoxel incoherent motion experiments

Traditionally, the method of nonlinear least squares (NLLS) analysis has been used to estimate the parameters obtained from exponential decay data. In this study, we evaluated the use of Bayesian probability theory to analyze such data; specifically, that resulting from intravoxel incoherent motion NMR experiments. Analysis was done both on simulated data to which different amounts of Gaussian noise had been added and on actual data derived from rat brain. On simulated data, Bayesian analysis performed substantially better than NLLS under conditions of relatively low signal-to-noise ratio. Bayesian probability theory also offers the advantages of: a) not requiring initial parameter estimates and hence not being susceptible to errors due to incorrect starting values and b) providing a much better representation of the uncertainty in the parameter estimates in the form of the probability density function. Bayesian analysis of rat brain data was used to demonstrate the shape of the probability density function from data sets of different quality.     

Intravoxel incoherent motion in body diffusion-weighted MRI: reality and challenges

OBJECTIVE: Diffusion-weighted MRI is increasingly applied in the body. It has been recognized for some time, on the basis of scientific experiments and studies in the brain, that the calculation of apparent diffusion coefficient by simple monoexponential relationship between MRI signal and b value does not fully account for tissue behavior. However, appreciation of this fact in body diffusion MRI is relatively new, because technologic advancements have only recently enabled high-quality body diffusion-weighted images to be acquired using multiple b values. There is now increasing interest in the radiologic community to apply more sophisticated analytic approaches, such as those based on the principles of intravoxel incoherent motion, which allows quantitative parameters that reflect tissue microcapillary perfusion and tissue diffusivity to be derived. CONCLUSION: In this review, we discuss the principles of intravoxel incoherent motion as applied to body diffusion-weighted MRI. The evidence for the technique in measuring tissue perfusion is presented and the emerging clinical utility surveyed. The requisites and challenges of quantitative evaluation beyond simple monoexponential relationships are highlighted.     

不同定量测量参数对子宫肌瘤IVIM扩散和灌注特点显示的差异

目的 研究用直方图计算的不同定量测量参数对子宫肌瘤体素内不相干运动(IVIM)扩散和灌注特点显示的差异.方法 63例患者80个子宫肌瘤,进行了MR 3D T2WI和IVIM成像,根据肌瘤T2WI信号将肌瘤分为Funaki 1型、2型、3型.分别用直方图计算3种类型肌瘤的IVIM扩散系数(D)、灌注系数(D*)和灌注分数(f)的平均值、位于直方图左侧第25%(D25、D*25、f25)、50%(D50、D*50、f50)、75%(D75、D*75、f75)位置的数值.使用方差分析对3种肌瘤的IVIM定量测量参数进行比较.结果 80个肌瘤中Funaki分型1型肌瘤44个,2型肌瘤24个,3型肌瘤12个,3种肌瘤间D的直方图计算值和均值都有显著性差异(P<0.05),但灌注参数只有D*75有显著性差异(P<0.05).3种肌瘤的f不论是直方图计算值还是均值都无显著性差异.结论 用直方图计算子宫肌瘤IVIM的扩散参数没有比均值提供更多的信息,但直方图计算灌注参数D*75较均值更能反映不同类型肌瘤的灌注特点.     

Renal artery stenosis: in vivo perfusion MR imaging

The intravoxel incoherent motion (IVIM) model of perfusion and diffusion imaging was applied to an in vivo canine model of unilateral renal artery stenosis and was compared with relative renal blood flow determination with radioactive microspheres. The percentage relative renal blood flow as determined with radioactive microspheres correlated closely with the percentage apparent diffusion coefficient. If this method can be adapted to human imaging, it may provide a noninvasive means for detecting renal artery stenosis.     

肝脏多b值扩散心率因素的评价

目的:评价心电门控技术心率因素对肝脏体素内不相干运动成像(IVIM)图像质量及参数值的影响.方法:选取20名接受心电门控IVIM DWI序列扫描的志愿者,设定6个b值(范围0,50,100,150,300,600s/mm2),按受检者心率分为2组,每组10例,实验组受检者心率≤70次/分,对照组受检者心率≥80次/分.由两名从事腹部MR影像诊断5年以上的高年资医师对所得MR图像进行分析,测量并分析图像SNR、ADC、IVIM各参数值,并对IVIM-DWI图像质量进行评价.结果:实验组所得图像伪影最少,解剖结构清晰,图像质量较高,不同b值时实验组SNR值均大于对照组,两组间差异有统计学意义(P＜0.05).两组ADC、D、D*、f值中,仅肝左叶的ADC值[实验组(1.432±0.299)×10-3mm2/s;对照组(1.945±0.543)×10-3 mm2/s]和D值[实验组(1.372±0.378)×10-3mm2/s;对照组(1.617±0.361)×10-3mm2/s]在两组间的差异有统计学意义(P值分别为0.000、0.013).结论:肝脏IVIM心电门控成像技术具有重要的临床价值,低心率心电门控IVIM DWI成像可得到较好的图像质量和稳定可靠的参数值.     

Measurement reproducibility of perfusion fraction and pseudodiffusion coefficient derived by intravoxel incoherent motion diffusion-weighted MR imaging in normal liver and metastases

Objective

To determine the measurement reproducibility of perfusion fraction f, pseudodiffusion coefficient D ^* and diffusion coefficient D in colorectal liver metastases and normal liver.

Methods

Fourteen patients with known colorectal liver metastases were examined twice using respiratory-triggered echo-planar DW-MRI with eight b values (0 to 900 s/mm²) 1 h apart. Regions of interests were drawn around target metastasis and normal liver in each patient to derive ADC (all b values), ADC_high (b values ≥100 s/mm²) and intravoxel incoherent motion (IVIM) parameters f, D ^* and D by least squares data fitting. Short-term measurement reproducibility of median ADC, ADC_high, f, D ^* and D values were derived from Bland–Altman analysis.

Results

The measurement reproducibility for ADC, ADC_high and D was worst in colorectal liver metastases (?21 % to +25 %) compared with liver parenchyma (?6 % to +8 %). Poor measurement reproducibility was observed for the perfusion-sensitive parameters of f (?75 % to +241 %) and D ^* (?89 % to +2,120 %) in metastases, and to a lesser extent the f (?24 % to +25 %) and D* (?31 % to +59 %) of liver.

Conclusions

Estimates of f and D ^* derived from the widely used least squares IVIM fitting showed poor measurement reproducibility. Efforts should be made to improve the measurement reproducibility of perfusion-sensitive IVIM parameters.

Key Points

? Quantitative diffusion-weighted MRI parameters are increasingly used for clinical management decisions. ? However perfusion-sensitive intravoxel incoherent motion (IVIM) parameters showed poor measurement reproducibility. ? Measurement reproducibility of IVIM parameters was worse in metastases than normal liver. ? Efforts to improve measurement reproducibility of IVIM parameters should be explored.     

Diffusion imaging with prospective motion correction and reacquisition

A major source of artifacts in diffusion‐weighted imaging is subject motion. Slow bulk subject motion causes misalignment of data when more than one average or diffusion gradient direction is acquired. Fast bulk subject motion can cause signal dropout artifacts in diffusion‐weighted images and results in erroneous derived maps, e.g., fractional anisotropy maps. To address both types of artifacts, a fully automatic method is presented that combines prospective motion correction with a reacquisition scheme. Motion correction is based on the prospective acquisition correction method modified to work with diffusion‐weighted data. The images to reacquire are determined automatically during the acquisition from the imaging data, i.e., no extra reference scan, navigators, or external devices are necessary. The number of reacquired images, i.e., the additional scan duration can be adjusted freely. Diffusion‐weighted prospective acquisition correction corrects slow bulk motion well and reduces misalignment artifacts like image blurring. Mean absolute residual values for translation and rotation were <0.6 mm and 0.5°. Reacquisition of images affected by signal dropout artifacts results in diffusion maps and fiber tracking free of artifacts. The presented method allows the reduction of two types of common motion related artifacts at the cost of slightly increased acquisition time. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Quantitative magnetic resonance imaging for focal liver lesions: bridging the gap between research and clinical practice

Magnetic resonance imaging (MRI) is highly important for the detection, characterization, and follow-up of focal liver lesions. Several quantitative MRI-based methods have been proposed in addition to qualitative imaging interpretation to improve the diagnostic work-up and prognostics in patients with focal liver lesions. This includes DWI with apparent diffusion coefficient measurements, intravoxel incoherent motion, perfusion imaging, MR elastography, and radiomics. Multiple research studies have reported promising results with quantitative MRI methods in various clinical settings. Nevertheless, applications in everyday clinical practice are limited. This review describes the basic principles of quantitative MRI-based techniques and discusses the main current applications and limitations for the assessment of focal liver lesions.     

Magnetic resonance diffusion/perfusion phantom experiments

Recently, several models for determining microcirculatory parameters using magnetic resonance imaging have been proposed. These include the intravoxel incoherent motion (IVIM) model, the intravoxel coherent motion (IVCM) model, and various tracer models. In order to evaluate these models before extension into physiological systems, phantom studies were used to assess model assumptions, measurement uncertainties, and sensitivity to changes in perfusion. Emphasis is placed on the IVIM model, but the techniques discussed could be extended to evaluation of other models as well. An overview of considerations in pulse sequence development, phantom design, and data interpretation is presented for a variety of phantoms ranging in complexity from stationary volumes of fluid and mechanically pumped phantoms to isolated animal kidneys and finally to an in vivo animal model.     

Extension of the intravoxel incoherent motion model to non‐gaussian diffusion in head and neck cancer

Purpose:

To extend the intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) model to restricted diffusion and to simultaneously quantify the perfusion and restricted diffusion parameters in neck nodal metastases.

Materials and Methods:

The non‐Gaussian (NG)‐IVIM model was developed and tested on diffusion‐weighted MRI data collected on a 1.5‐Tesla MRI scanner from eight patients with head and neck cancer. Voxel‐wise parameter quantification was performed by using a noise‐rectified least‐square fitting method. The NG‐IVIM, IVIM, Kurtosis, and ADC (apparent diffusion coefficient) models were used for comparison. For each voxel, within the metastatic node, the optimal model was determined using the Bayesian Information Criterion. The voxel percentage preferred by each model was calculated and the optimal model map was generated. Monte Carlo simulations were performed to evaluate the accuracy and precision dependency of the new model.

Results:

For the eight neck nodes, the range of voxel percentage preferred by the NG‐IVIM model was 2.3–79.3%. The optimal modal maps showed heterogeneities within the tumors. The Monte Carlo simulations demonstrated that the accuracy and precision of the NG‐IVIM model improved by increasing signal‐to‐noise ratio and b value.

Conclusion:

The NG‐IVIM model characterizes perfusion and restricted diffusion simultaneously in neck nodal metastases. J. Magn. Reson. Imaging 2012;36:1088–1096. © 2012 Wiley Periodicals, Inc.     

Utility of Intravoxel Incoherent Motion MR Imaging for Distinguishing Recurrent Metastatic Tumor from Treatment Effect following Gamma Knife Radiosurgery: Initial Experience

BACKGROUND AND PURPOSE:Intravoxel incoherent motion MR imaging can simultaneously measure the diffusion and perfusion characteristics of brain tumors. Our aim was to determine the utility of intravoxel incoherent motion–derived perfusion and diffusion parameters for assessing the treatment response of metastatic brain tumor following gamma knife radiosurgery.MATERIALS AND METHODS:Ninety-one consecutive patients with metastatic brain tumor treated with gamma knife radiosurgery were assessed by using intravoxel incoherent motion imaging. Two readers independently calculated the 90th percentile and the 10th percentile histogram cutoffs for perfusion, normalized CBV, diffusion, and ADC. Areas under the receiver operating characteristic curve and interreader agreement were assessed.RESULTS:With the combination of the 90th percentile histogram cutoff for perfusion and the 10th percentile histogram cutoff for diffusion, the sensitivity and specificity for differentiating recurrent tumor and treatment were 79.5% and 92.3% for reader 1 and 84.6% and 94.2% for reader 2, respectively. With the combination of the 90th percentile histogram cutoff for normalized CBV and the 10th percentile histogram cutoff for ADC, the sensitivity and specificity for differentiating recurrent tumor and treatment were 69.2% and 100.0% for reader 1 and 74.3% and 100.0% for reader 2, respectively. Compared with the combination of 90th percentile histogram cutoff for normalized CBV and the 10th percentile histogram cutoff for ADC, adding intravoxel incoherent motion to 90th percentile histogram cutoff for normalized CBV substantially improved the diagnostic accuracy for differentiating recurrent tumor and treatment from 86.8% to 92.3% for reader 1 and from 89.0% to 93.4% for reader 2, respectively. The intraclass correlation coefficients between readers were higher for perfusion parameters (intraclass correlation coefficient range, 0.84–0.89) than for diffusion parameters (intraclass correlation coefficient range, 0.68–0.79).CONCLUSIONS:Following gamma knife radiosurgery, intravoxel incoherent motion MR imaging can be used as a noninvasive imaging biomarker for differentiating recurrent tumor from treatment effect in patients with metastatic brain tumor.

Perfusion MR imaging techniques have significantly advanced and can now provide information regarding tumor physiology. There are several reports suggesting the usefulness of dynamic susceptibility contrast-enhanced perfusion MR imaging for differentiating recurrent metastatic brain tumor from stereotactic radiosurgery–induced radiation necrosis.^1–3 However, quantitative brain perfusion measurement remains a challenge for currently available MR perfusion methods. DSC and dynamic contrast-enhanced MR imaging are inhibited by their signal nonlinearity, and arterial spin-labeling exhibits, in addition to a low signal-to-noise ratio, a strong dependence on the transit time.Le Bihan et al⁴ defined intravoxel incoherent motion (IVIM) as the microscopic translational motion occurring in each image voxel in MR imaging. In biologic tissue, this incoherent motion includes molecular diffusion of water and microcirculation of blood in the capillary network, referred to as “perfusion.” These 2 phenomena account for the biexponential decay of the signal intensity on DWI when different diffusion b-values are applied. With the IVIM theory, both true molecular diffusion and water molecule motion in the capillary network can be estimated by using a single diffusion imaging-acquisition technique. As opposed to DSC, dynamic contrast-enhanced imaging, and arterial spin-labeling, IVIM has a unique capillary dependence that is not sensitive to the coherent laminar flow of arteries and veins. The measurement of IVIM is intrinsically local (ie, the encoding and readout are performed at the same location).⁵In our clinical experience, the major advantage of IVIM MR imaging is that because it allows the simultaneous acquisition of diffusion and perfusion parameters, it can provide both measures within corresponding solid lesions without the requirement for a further coregistration processing step. In the current study, we attempted to validate the IVIM-derived perfusion and diffusion parameters by using the clinicoradiologic correlation in patients with post-gamma knife radiosurgery (GKRS) metastatic brain tumor. We also assessed the diagnostic accuracy and added value of the IVIM method for differentiating recurrent tumor from treatment effect, compared with the combination of DSC perfusion MR imaging and DWI, which has commonly been used as a parameter for brain tumor imaging.Our hypothesis was that the difference in vascularity between recurrent tumor and the treatment effect can be assessed by using an IVIM-derived perfusion fraction (f); and the combination of f and the true diffusion parameter (D) would show diagnostic performance comparable with the combination of normalized CBV (nCBV) and the ADC. The purpose of this study was to determine the utility of IVIM-derived perfusion and diffusion parameters for assessing the treatment response of metastatic brain tumor following GKRS.     

Value of magnetic resonance imaging in diffuse liver diseases

CLINICAL PROBLEM: Diffuse liver diseases show an increasing prevalence. The diagnostic gold standard of liver biopsy has several disadvantages. There is a clinical demand for non-invasive imaging-based techniques to qualitatively and quantitatively evaluate the entire liver. STANDARD RADIOLOGICAL METHODS: Ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI) are routinely used. METHODICAL INNOVATIONS: Steatosis: chemical shift and frequency selective imaging, MR spectroscopy (MRS). Hemochromatosis: MR-based iron quantification. Fibrosis: MR elastography, diffusion, intravoxel incoherent motion (IVIM) and MR perfusion. PERFORMANCE/ACHIEVEMENTS/PRACTICAL RECOMMENDATIONS: T1-weighted in and opposed phase imaging is the clinically most frequently used MR technique to noninvasively detect and quantify steatosis. New methods for quantification that are not influenced by confounders like iron overload are under investigation. The most sensitive method to measure the fat content of the liver is MRS. As data acquisition and analysis remain complex and there is no whole organ coverage, MRS of the liver is not a routine method. With an optimized protocol incorporating T2* sequences, MRI is the modality of choice to quantify iron overload in hemochromatosis. Standard MR sequences cannot depict early stages of liver fibrosis. Advanced MR techniques (e.g. elastography, diffusion, IVIM and perfusion) for noninvasive assessment of liver fibrosis appear promising but their role has to be further investigated.