MRI T2* imaging for assessment of liver iron overload: study of different data analysis approaches

Iron deposition in ovarian endometriosis evaluated by magnetic resonance imaging R2* correlates with ovarian function

RESEARCH QUESTION

Does iron overload in patients with endometriosis affect ovarian function? Can a method be developed to visually reflect this?

DESIGN

Magnetic resonance imaging (MRI) R2* was used to evaluate the correlation between iron deposition of ovarian and anti-Müllerian hormone (AMH) in patients with endometriosis. All patients underwent T2* MRI scanning. Serum AMH levels were measured preoperatively. The area of focal iron deposition, iron content of the cystic fluid and AMH levels between the endometriosis and control groups were compared using non-parametric tests. The effects of iron overload on AMH secretion in mouse ovarian granulosa cells were investigated by adding different concentrations of ferric citrate to the medium.

RESULTS

A significant difference was found between endometriosis and control groups in area of iron deposition (P < 0.0001), cystic fluid iron content (P < 0.0001), R2* of lesions (P < 0.0001) and R2* of the cystic fluid (P < 0.0001). Negative correlations were found between serum AMH levels and R2* of cystic lesions in patients with endometriosis aged 18-35 years (rs = -0.6484, P < 0.0001), and between serum AMH levels and R2* of cystic fluid (rs = -0.5074, P = 0.0050). Transcription level (P < 0.0005) and secretion level (P < 0.005) of AMH significantly decreased with the increase in iron exposure.

CONCLUSION

Iron deposits can impair ovarian function, which is reflected in MRI R2*. Serum AMH levels and R2* of cystic lesions or fluid in patients aged 18-35 years had a negative correlation with endometriosis. R2* can be used to reflect the changes of ovarian function caused by iron deposition.

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

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

Pancreatic iron quantification with MR imaging: a practical guide

Accurate determination of pancreatic iron status is crucial for preventing impairment of the exocrine and endocrine function of the pancreas and for prospectively stratifying the cardiac iron risk. The following article should be a sort of practical guide for radiologists interested in quantifying pancreatic iron overload by Magnetic Resonance Imaging (MRI). After a brief background on iron-deposition diseases, we will describe basic principles and relative advantages and disadvantages of the more widely used and clinically feasible MRI-based techniques for pancreatic iron assessment. These methods can be classified into signal intensity ratio (SIR) and relaxometry methods. We will examine different technical aspects representing the key for accurate and precise relaxation time measurement.

The history of magnetic resonance imaging and its reflections in Acta Radiologica

The first reports in Acta Radiologica on magnetic resonance imaging (MRI) were published in 1984, four years after the first commercial MR scanners became available. For the first two years, all MR papers originated from the USA. Nordic contributions started in 1986, and until 2020, authors from 44 different countries have published MR papers in Acta Radiologica. Papers on MRI have constituted, on average, 30%-40% of all published original articles in Acta Radiologica, with a high of 49% in 2019. The MR papers published since 1984 document tremendous progress in several areas such as magnet and coil design, motion compensation techniques, faster image acquisitions, new image contrast, contrast-enhanced MRI, functional MRI, and image analysis. In this historical review, all of these aspects of MRI are discussed and related to Acta Radiologica papers.

Evaluation of Rabbits Liver Fibrosis Using Gd-DTPA-BMA of Dynamic Contrast-Enhanced Magnetic Resonance Imaging

Objective

To evaluate the different pharmacokinetic parameters of the DCE-MRI method on diagnosing and staging of rabbits' liver fibrosis.

Methods

We had performed DCE-MRI for rabbits that had been divided into the experiment group and the control group. Then, rabbits' images were transferred to a work station to get three parameters such as K _trans, K _ep, and V _e, which had been measured to calculate. After data were analyzed, ROC analyses were performed to assess the diagnostic performance of K _trans, K _ep, and V _e to judge liver fibrosis.

Results

The distribution of the different liver fibrosis group was as follows: F1, n = 8; F2, n = 9; F3, n = 6; F4, n = 5. No fibrosis was deemed as F0, n = 6. K _ep is statistically significant (P < 0.05) for F0 and mild liver fibrosis stage, and the K _ep shows AUC of 0.814. Three parameters are statistically significant for F0 and advanced liver fibrosis stage (K _trans and K _ep, P < 0.01; V _e, P < 0.05), and the K _trans shows AUC of 0.924; the K _ep shows AUC of 0.909; the V _e shows AUC of 0.848; K _trans and K _ep are statistically significant for mild and advanced liver fibrosis stages (K _trans, P < 0.01; K _ep, P < 0.05), and the K _trans shows AUC of 0.840; the K _ep shows AUC of 0.765. Both K _trans and K _ep are negatively correlated with the liver fibrosis stage. V _e is positively correlated with the liver fibrosis stage.

Conclusion

K _trans is shown to be the best DCE parameter to distinguish the fibrotic liver from the normal liver and mild and advanced fibrosis. On the contrary, K _ep is moderate and V _e is worst. And K _ep is a good DCE parameter to differentiate mild fibrosis from the normal liver.

Hepatic gadoxetic acid uptake as a measure of diffuse liver disease: Where are we?

MRI has emerged as the most comprehensive noninvasive diagnostic tool for focal liver lesions and diffuse hepatobiliary disorders. The introduction of hepatobiliary contrast agents, most notably gadoxetic acid (GA), has expanded the role of MRI, particularly in the functional imaging of chronic liver diseases, such as nonalcoholic fatty liver disease (NAFLD). GA-enhanced MRI (GA-MRI) may help to distinguish between the two subgroups of NAFLD, simple steatosis and nonalcoholic steatohepatitis. Furthermore, GA-MRI can be used to stage fibrosis and cirrhosis, predict liver transplant graft survival, and preoperatively estimate the risk of liver failure should major resection be undertaken. The amount of GA uptake can be estimated, using static images, by the relative liver enhancement, hepatic uptake index, and relaxometry of T1-mapping during the hepatobiliary phase. On the contrary, the hepatic extraction fraction and liver perfusion can be measured on dynamic imaging. Importantly, there is currently no clear consensus as to which of these MR-derived parameters is the most suitable for assessing liver dysfunction. This review article aims to describe the current role of GA-enhanced MRI in quantifying liver function, primarily in diffuse hepatobiliary disorders.

LEVEL OF EVIDENCE

3 J. Magn. Reson. Imaging 2017;45:646-659.

Comparison of clinical MRI liver iron content measurements using signal intensity ratios, R 2 and R 2

Purpose

To compare three types of MRI liver iron content (LIC) measurement performed in daily clinical routine in a single center over a 6-year period.

Methods

Patients undergoing LIC MRI-scans (1.5T) at our center between January 1, 2008 and December 31, 2013 were retrospectively included. LIC was measured routinely with signal intensity ratio (SIR) and MR-relaxometry (R₂ and R₂*) methods. Three observers placed regions-of-interest. The success rate was the number of correctly acquired scans over the total number of scans. Interobserver agreement was assessed with intraclass correlation coefficients (ICC) and Bland–Altman analysis, correlations between LIC_SIR, R₂, R₂*, and serum values with Spearman’s rank correlation coefficient. Diagnostic accuracies of LIC_SIR, R₂ and serum transferrin, transferrin-saturation, and ferritin compared to increased R₂* (≥44 Hz) as indicator of iron overload were assessed using ROC-analysis.

Results

LIC MRI-scans were performed in 114 subjects. SIR, R₂, and R₂* data were successfully acquired in 102/114 (89%), 71/114 (62%), and 112/114 (98%) measurements, with the lowest success rate for R₂. The ICCs of SIR, R₂, and R₂* did not differ at 0.998, 0.997, and 0.999. R₂ and serum ferritin had the highest diagnostic accuracies to detect elevated R₂* as mark of iron overload.

Conclusions

SIR and R₂* are preferable over R₂ in terms of success rates. R₂*’s shorter acquisition time and wide range of measurable LIC values favor R₂* over SIR for MRI-based LIC measurement.

Electronic supplementary material

The online version of this article (doi:10.1007/s00261-016-0831-7) contains supplementary material, which is available to authorized users.