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EJNMMI Res. 2019 Feb 22;9(1):21. doi: 10.1186/s13550-019-0489-6.

Diffusion-weighted magnetic resonance imaging using a preclinical 1 T PET/MRI in healthy and tumor-bearing rats.

Author information

1
Department of Nuclear Medicine, Charité - Universitätsmedizin Berlin, Augustenburger Platz 1, 13353, Berlin, Germany. jakob.albrecht@charite.de.
2
German Cancer Consortium (DKTK), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany. jakob.albrecht@charite.de.
3
German Cancer Research Center (DKFZ) Heidelberg, Im Neuenheimer Feld 280, 69120, Heidelberg, Germany. jakob.albrecht@charite.de.
4
Department of Surgery, Campus Charité Mitte, Luisenstraße 64, 10117, Berlin, Germany.
5
Department of Surgery, Campus Virchow Klinikum, Charité - Universitätsmedizin Berlin, Mittelallee 4, 13353, Berlin, Germany.
6
iPATH.Berlin - Immunopathology for Experimental Models, Charité - Universitätsmedizin Berlin, Berlin Institute of Health, Core Unit, Hindenburgdamm 30, 12203, Berlin, Germany.
7
Department of Nuclear Medicine, Charité - Universitätsmedizin Berlin, Augustenburger Platz 1, 13353, Berlin, Germany.
8
Mediso Medical Imaging Systems, Laborc utca 3, Budapest, 1037, Hungary.
9
Berlin Experimental Radionuclide Imaging Center (BERIC), Charité - Universitätsmedizin Berlin, Südstraße 3, 13353, Berlin, Germany.
10
German Cancer Consortium (DKTK), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany.
11
German Cancer Research Center (DKFZ) Heidelberg, Im Neuenheimer Feld 280, 69120, Heidelberg, Germany.

Abstract

BACKGROUND:

Hybrid positron emission tomography and magnetic resonance imaging (PET/MRI) scanners are increasingly used for both clinical and preclinical imaging. Especially functional MRI sequences such as diffusion-weighted imaging (DWI) are of great interest as they provide information on a molecular level, thus, can be used as surrogate biomarkers. Due to technical restrictions, MR sequences need to be adapted for each system to perform reliable imaging. There is, to our knowledge, no suitable DWI protocol for 1 Tesla PET/MRI scanners. We aimed to establish such DWI protocol with focus on the choice of b values, suitable for longitudinal monitoring of tumor characteristics in a rat liver tumor model.

MATERIAL AND METHODS:

DWI was first performed in 18 healthy rat livers using the scanner-dependent maximum of 4 b values (0, 100, 200, 300 s/mm2). Apparent diffusion coefficients (ADC) were calculated from different b value combinations and compared to the reference measurement with four b values. T2-weighted MRI and optimized DWI with best agreement between accuracy, scanning time, and system performance stability were used to monitor orthotopic hepatocellular carcinomas (HCC) in five rats of which three underwent additional 2-deoxy-2-(18F)fluoro-D-glucose(FDG)-PET imaging. ADCs were calculated for the tumor and the surrounding liver parenchyma and verified by histopathological analysis.

RESULTS:

Compared to the reference measurements, the combination b = 0, 200, 300 s/mm2 showed the highest correlation coefficient (rs = 0.92) and agreement while reducing the acquisition time. However, measurements with less than four b values yielded significantly higher ADCs (p < 0.001). When monitoring the HCC, an expected drop of the ADC was observed over time. These findings were paralleled by FDG-PET showing both an increase in tumor size and uptake heterogeneity. Interestingly, surrounding liver parenchyma also showed a change in ADC values revealing varying levels of inflammation by immunohistochemistry.

CONCLUSION:

We established a respiratory-gated DWI protocol for a preclinical 1 T PET/MRI scanner allowing to monitor growth-related changes in ADC values of orthotopic HCC liver tumors. By monitoring the changes in tumor ADCs over time, different cellular stages were described. However, each study needs to adapt the protocol further according to their question to generate best possible results.

KEYWORDS:

1 Tesla; ADC; DWI; Hepatocellular carcinoma; PET/MRI; Preclinical; Rats; Tumor microenvironment

PMID:
30796555
DOI:
10.1186/s13550-019-0489-6
Free PMC Article

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