Hee Kyung Kim MD, Presenter: Nothing to Disclose

Arnold Carlson Merrow MD, Abstract Co-Author: Author for Amirsys, Inc

Suraj Serai PhD, Abstract Co-Author: Nothing to Disclose

Tal Laor MD, Abstract Co-Author: Nothing to Disclose

Brenda Wong, Abstract Co-Author: Nothing to Disclose

T2 maps have been used to quantify substantial amounts of fatty infiltration in skeletal muscle in muscular dystrophies. T2 relaxation times (T2 values) are affected by molecular tumbling (a method greatly influenced by the surrounding environment, such as fatty replacement of the muscles) can be considered an indirect method of measuring macroscopic fatty infiltration of skeletal muscles in children with a variety of muscular dystrophies. However, whether T2 values can directly reflect a minimal amount of fat is uncertain. Therefore, the purpose of our study is to validate T2 mapping for the objective measurement of microscopic fatty infiltration of normal skeletal muscles.

IRB approval and informed consent were obtained. Sixteen healthy boys were included, age range: 8-17 years, mean: 14.7 ±2.7 years. Pelvic MR exams were obtained including axial T1-weighted images (WI), axial T2-WI with fat saturation (FS), and axial T2 maps with and without FS. Fatty infiltration and inflammation of the right gluteus maximus muscle were evaluated on T1-WI and T2-WI with FS, respectively. Differences between the T2 maps with and without FS (∆ T2) of the gluteus maximus muscles were obtained and used as an index of fat of the muscles. MRS of the right gluteus maximus muscle was performed: water and lipid peaks of the right gluteus muscles were obtained, and fat ratios ((fat/water+fat) x 100) were calculated.

All 16 boys showed very minimal fatty infiltration of the gluteus maximus muscle on T1 WI, and none of the 16 boys showed inflammation on T2 WI with FS. ∆ T2 ranged from 2.8 to 21.6 msec (mean 5.4 ± 2.6 msec). Fat ratios ranged from 0.1 to 49.9 %. There was significant correlation between ∆ T2 and fat ratios (p<0.05, r2=0.72).

T2 maps can directly detect minimal fatty infiltration of normal skeletal muscles in healthy children, including microscopic amounts as validated by MRS.

T2 maps potentially can be used to enable early diagnosis of skeletal muscle diseases which result in microscopic fatty infiltration of the muscles.

Kim, H, Merrow, A, Serai, S, Laor, T, Wong, B, Objective Measurement Using T2 Relaxation Time Mapping (T2 Maps) and MR Spectroscopy (MRS) of Minimal Fat in Normal Skeletal Muscles of Healthy Children.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11010093.html