Determinants of MR relaxation rates in jaw cysts: implications for diagnostic values of the relaxation times.

ABSTRACT

OBJECTIVES: The MRI signal intensities and the relaxation times (T1 and T2) have already been used for comparisons among various types of cysts. The signal intensities (or T1 and T2) were suggested to be related to cyst content. However, such a relationship between the relaxation rates (1/T1 and 1/T2) and the aspirated content of jaw cysts was not given. Therefore, an investigation on the determinants of the relaxation rates in the jaw cysts may be helpful in elucidating the biological basis for the differences in relaxation rates among the categories of jaw cysts. METHODS: The aspirated contents of 23 cysts (16 radicular and 7 haemorrhagic) were scanned using an MR imager operating at 1 T magnetic field strength. The viscosities and the dry-weight-to-water-weight ratios (Ms/Mw) were determined. Also, the mean values of cyst categories were compared using statistical analysis. RESULTS: The 1/T1 had a moderate correlation with viscosity (0.66) and Ms/Mw (0.56), while the 1/T2 had a good correlation with viscosity (0.87) and Ms/Mw (0.82). The mean values of viscosity, Ms/Mw and relaxation rates in radicular cysts were significantly lower (P < 0.05) than those of haemorrhagic cysts. CONCLUSIONS: The present data suggest that similarities and differences between relaxation rates of radicular and haemorrhagic cysts can be explained by the solid content and viscosity of cysts.