Evaluation of Superparamagnetic Iron Oxide for MR Imaging of Liver Injury: Proton Relaxation Mechanisms and Optimal MR Imaging Parameters

Abstract

Purpose: To investigate the proton relaxation mechanisms and the optimal MR imaging parameters in superparamagnetic iron oxide (SPIO)-enhanced MR imaging of liver injury.Methods: A liver injury model was created in the rat using carbon tetrachloride. The T 1 and T 2 relaxation eŠects of SPIO in normal and injured liver were estimated by ex vivo relaxometry. In vivo laser confocal microscopy of the liver was performed to simulate the distribution and clustering of SPIO particles in the hepatic macrophages. SPIO-enhanced MR imaging (1.5T) of normal and diseased rats was performed with variable parameters. The liver specimens were prepared for histopathological examination.Results: Histopathological and laser confocal microscopicˆndings showed diŠuse macrophage distribution but decreased intracellular clustering of SPIO in injured liver. Ex vivo relaxometry showed sustained T 1 and T 2 relaxation eŠects of SPIO in liver injury. On MR images obtained with moderate echo time (spin echo [SE] 2000 W 40 and gradient echo [GRE] 130 W 9.0 W 609 ), injured liver showed signiˆcantly lower decrease in signal-tonoise ratio (SNR) than the normal liver, whereas little diŠerence in SNR was found between the normal and injured liver on heavily T 2 -(SE 2000 W 80) and T 1 -weighted (SE 300 W 11 and GRE 130 W 2.0 W 909 ) MR images.Conclusion: Pulse sequences with a moderately long echo time (TE) may be more appropriate than heavily T 1 -or T 2 -weighted images for distinguishing normal and injured liver in SPIO-enhanced MR imaging because of the maintained T 1 and T 2 relaxation eŠect but decreased T 2 * relaxation eŠect of SPIO in injured liver.

Phagocytic function of Kupffer cells in mouse nonalcoholic fatty liver disease models: Evaluation with superparamagnetic iron oxide

“…First, although direct T 2 or T 2 * quantification using multiecho images at different echo times would have been more accurate for quantifying the T 2 or T 2 * shortening effect of SPIO in the liver, we used RSL values calculated using the signal intensities of the liver, as seen on single‐echo images before and after SPIO enhancement, due to the limited gradient power and long data acquisition time of our animal MR scanner. However, our imaging method has been widely used in clinical practice and for research and is also thought to be a reliable method for estimating the degree of hepatic SPIO‐enhancement . Second, in our study our NAFLD animal model did not show the very early stage of NAFLD, ie, mild hepatic steatosis without insulin resistance, as the ob/ob mice, which are genetically prone to obesity and insulin resistance, developed moderate to severe hepatic steatosis and metabolic features of NAFLD as early as 3 weeks after beginning their HFHC diet.…”

“…However, SPIO agents are not commercially available in most countries, which limits the application of our findings for daily clinical practice. In addition, for the clinical application of SPIO‐enhanced MRI for evaluating NAFLD, it should be noted that the diminished hepatic SPIO enhancement is not specific for NAFLD, but is also observed in various, diffuse liver diseases, including liver cirrhosis, chronic viral hepatitis, and hepatotoxin‐induced severe hepatic injury . In order to validate the practical value of SPIO‐enhanced MRI for the evaluation of NAFLD, further clinical studies are warranted.…”

Synthesis and Testing of Modular Dual-Modality Nanoparticles for Magnetic Resonance and Multispectral Photoacoustic Imaging

“…However, modular NP design may result in greater clustering of IO on gold NP thus increasing the magnitude of T2-weighted MR signal due to r2 increase 19, 20 . With this in mind we designed hybrid IO- gold NPs that are held together via anchoring provided by silver NPs deposited using Ag (I) reduction by aldehydes which are present in the carbohydrate coating of a typical stabilized USPIO.…”

“…A modular design approach to the synthesis of multifunctional NPs appeared to be less intuitive than the core-to-shell design approach − due to potential difficulties in controlling the resultant particle size. However, modular NP design may result in greater clustering of IO on gold NP thus increasing the magnitude of the T2-weighted MR signal due to r2 increase. , With this in mind we designed hybrid IO- gold NPs that are held together via anchoring provided by silver NPs deposited using Ag (I) reduction by aldehydes which are present in the carbohydrate coating of a typical stabilized USPIO. We then tested the obtained hybrid NPs for multiplexed PA that was enabled by linking NIR dyes, i.e., organic fluorophores with very high extinction coefficients, to the stabilizing layer of a biocompatible copolymer on the surface of hybrid NPs.…”

MRI tracking of autologous pancreatic progenitor-derived insulin-producing cells in monkeys

“…An ideal monitoring modality should permit early detection of islet damage to enable timely therapeutic intervention and protect the islet grafts from further damage. Superparamagnetic iron oxide nanoparticles are the most commonly used magnetic resonance imaging (MRI) contrast agent for biomedical imaging 13, 14 , and transplanted SPION-labeled cells can be visualized as hypointense areas by MRI 15–17 . Several previous preclinical and clinical studies have tested the feasibility and safety of SPION-based MR tracking of transplanted islets 12, 18–20 .…”