CALCIFICATION CALL SHORTEN T2, BUT NOT T1, AT MAGNETIC-RESONANCE-IMAGING FIELDS - RESULTS OF A RELAXOMETRY STUDY OF CALCIFIED HUMAN MENINGIOMAS

RATIONALE AND OBJECTIVES. Water content and water-proton relaxation ra tes are reported for fresh, histologically characterized, surgical spe cimens of calcified human intracranial meningiomas and compared with r esults for noncalcified meningiomas from an earlier study and with cal cium hydroxyapatite (CaHA) suspensions to elucidate the influence of c alcification on magnetic resonance imaging (MRI) signal intensity of c alcified meningiomas. METHODS. The magnetic field dependence of 1/T1 o f water protons (nuclear magnetic relaxation dispersion profile) and d ry weights are reported for 38 calcified nonhemorrhagic and 3 hemorrha gic specimens of known histologic subtype, a subset of the 67 specimen s measured earlier, Calcification was considered mild or heavy when th e dry weight was within or above the range for noncalcified meningioma s, Preliminary 1/T1 profiles for pure CaHA and a single high-field 1/T 2 value also are reported. RESULTS. The ranges of dry weights and of l ow-field 1/T1 values were twice as large for calcified as for noncalci fied meningiomas, No correlation was found between low-field 1/T1 and either histologic subtype or dry weight, Mild calcification produced t he highest low-field 1/T1 values; the most heavily calcified tumor had slightly increased low-field 1/TI, Calcium hydroxyapatite increases l ow-field 1/TI significantly but not high-field 1/T1; high-field 1/T2 i s large, For calcified hemorrhagic meningiomas, increases in both low- field and high-field 1/T1 were seen. CONCLUSION. For mild calcificatio n, MRI signal voids result from an increased high-field 1/T2; for heav ier calcification, reduced proton density (from excluded water) become s of increasing importance, Cellular CaHA appears to brighten the sign al in T1-weighted MRI in the presence of hemorrhage.