Osteosarcoma: Correlation of T1 Map and Histology Map

Suh, Jin Suck; Yun, Mi Jin; Jeong, Eun Kee; Shin, Kyoo Ho; Yang, Woo Ick

Abstract

PURPOSE: To determine whether T1 mapping shows regional differences between viable and necrotic regions of osteosarcomas after anticancer chemotherapy and to assess whether this mapping is able to express the characteristics of various intramural tissue components. MATERIALS AND METHODS: Eleven of 20 osteosarcomas were included in this study, while the remaining nine were excluded because the tumor site was inappropriate for comparison of T1 map and tumor macrosection. All patients underwent MR imaging for the purpose of T1 mapping, followed by pre-operative chemotherapy and subsequentl limb-salvage surgery. Spin echo pulse sequencing was used with varying TR (100, 200, 400, 800, 1600, and 2400 msec) and a constant TE of 20 msec. Using a C-language software program, T1 relaxation time was calculated on a pixel-by-pixel basis and then a T1 map was generated by using a post-processing program, NIH Image. We attempted correlation of the T1 map and histologic findings, particularly in regions of interest(ROI) if certain areas were different from other regions on either the T1 or histologic map. Value was expressed as an average of the ratio of T1 of ROI and T1 of fat tissue, and this was used as an internal reference for normalization of the measurement. RESULTS: Tumor necrosis was 100%(Grade IV) in six specimens, and over 90 % (Grade III) in five. Viable tumor cells were found mostly in regions with chondroid matrix and seldom in regions with osteoid matrix. Regardless of cell viability, values ranged from 0.9 to 9.87(mean, 4.02) in tumor necrotic area with osteoid matrices, and from 3.04 to 3.9(mean, 3.55) in areas with chondroid matrices. Other regions with fibrous tissue proliferation, hemorrhage, and fatty necrosis showed values of 2.92-9.83(mean, 7.20), 2.65 -5.96(mean, 3.59), and 1.43 -3.11(mean, 2.68) respectively. The values of various tissues overlapped. No statistically significant difference was found between regions in which tumors were viable and those with tumor necrosis. CONCLUSION: Although we hypothesized that areas of necrotic tumor would show an increased water component(proton number) and would have a longer T1 value than viable tumor tissues, our results were otherwise. Necrotic osteosarcoma tissves showed a wide range of T1 values according to the prevailing tissue components.