Measurements of MRI R2* Relaxation Rate in Liver and Muscle: Animal Model

Authors: Chiung-Yun Chang, Po-Chou Chen, Jiun-Shiang Tzeng, Ka-Wai Mac, Chia-Chi Hsiao, Jo-Chi Jao

Abstract:

This study was aimed to measure effective transverse relaxation rates (R2*) in the liver and muscle of normal New Zealand White (NZW) rabbits. R2* relaxation rate has been widely used in various hepatic diseases for iron overload by quantifying iron contents in liver. R2* relaxation rate is defined as the reciprocal of T2* relaxation time and mainly depends on the constituents of tissue. Different tissues would have different R2* relaxation rates. The signal intensity decay in Magnetic resonance imaging (MRI) may be characterized by R2* relaxation rates. In this study, a 1.5T GE Signa HDxt whole body MR scanner equipped with an 8-channel high resolution knee coil was used to observe R2* values in NZW rabbit’s liver and muscle. Eight healthy NZW rabbits weighted 2 ~ 2.5 kg were recruited. After anesthesia using Zoletil 50 and Rompun 2% mixture, the abdomen of rabbit was landmarked at the center of knee coil to perform 3-plane localizer scan using fast spoiled gradient echo (FSPGR) pulse sequence. Afterwards, multi-planar fast gradient echo (MFGR) scans were performed with 8 various echo times (TEs) to acquire images for R2* measurements. Regions of interest (ROIs) at liver and muscle were measured using Advantage workstation. Finally, the R2* was obtained by a linear regression of ln(sı) on TE. The results showed that the longer the echo time, the smaller the signal intensity. The R2* values of liver and muscle were 44.8 ± 10.9 s-1 and 37.4 ± 9.5 s-1, respectively. It implies that the iron concentration of liver is higher than that of muscle. In conclusion, the more the iron contents in tissue, the higher the R2*. The correlations between R2* and iron content in NZW rabbits might be valuable for further exploration.

Keywords: Liver, MRI, multi-planar fast gradient echo, muscle, R2* relaxation rate.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1110147

References:

[1] R. P. Lim, K. Tuvia, C. H. Hajdu, M. Losada, R. Gupta, T. Parikh, J. S. Babb, B. Taouli, “ Quantification of hepatic iron deposition in patients with liver disease: comparison of chemical shift imaging with single echo T2*-weighted imaging,” AJR Am J Roentgenol, vol. 194, no. 5, 1288-1295, May 2010.
[2] E. Szurowska, K. Sikorska, E. Izycka-Swieszewska, T. Nowicki, T. Romanowski, K. P. Bielawski, M. Studniarek, “ The role of MR imaging in detection of hepatic iron overload in patients with cirrhosis of different origins,” BMC Gastroenterol, vol. 10, 13, 2010.
[3] P. Storey, A. A. Thompson, C. L. Carqueville, J. C. Wood, R. A. de Freitas, C. K.. Rigsby, “R2* imaging of transfusional iron burden at 3T and comparison with 1.5T,” Magn Reson Imaging, vol. 25, no. 3, pp. 540-547, Mar. 2007.
[4] M. Barry, S. Sherlock, “Measurement of liver-iron concentration in needle-biopsy specimens,” Lancet, vol. 1, no. 7690, pp. 100–103, Jan. 1971.
[5] G. M. Brittenham, D. E. Farrell, J. W. Harris, E. S. Feldman, E. H. Danish, W. A. Muir, J. H. Tripp, E. M. Bellon, “Magnetic-susceptibility measurement of human iron stores,” N Engl J Med, vol. 307, pp. 1671– 1675, Dec. 1982.
[6] E. Angelucci, G. Barosi, C. Camaschella, M. D. Cappellini, M. Cazzola, R. Galanello, M. Marchetti, A. Piga, S. Tura, “Italian Society of Hematology practice guidelines for the management of iron overload in thalassemia major and related disorders,” Haematologica, vol. 93, no. 5, pp. 741-752, May. 2008.
[7] M. Ulla, J.M. Bonny, L. Ouchchane, I. Rieu, B. Claise, F. Durif, “ Is R2* a new MRI biomarker for the progression of Parkinson's disease? A longitudinal follow-up,” PLoS One, vol. 8, no. 3,pp. e57904, Mar. 2013.
[8] J. C. Wood, C. Enriquez, N. Ghugre, J. M. Tyzka, S. Carson, M. D. Nelson, T. D. Coates, “MRI R2 and R2* mapping accurately estimates hepatic iron concentration in transfusion-dependent thalassemia and sickle cell disease patients,” Blood, vol. 106, no. 4, pp. 1460–1465, Aug. 2005.
[9] J. Ma, F.W. Wehrli, “Method for image-based measurement of the reversible and irreversible contribution to the transverse-relaxation rate,” J Magn Reson B, vol. 111,no. 1, pp. 61-69, Apr. 1996.