MR detection of intracranial calcification: a phantom study.

To make a comparative analysis of calcium detection between MR and CT, anhydrous, insoluble calcium carbonate spheres varying in size from 1.5-7.0 mm were embedded in three physiologic tissue phantoms: low-protein gelatin (3 gm%), high-protein gelatin (6 gm%), and heavy mineral oil. The calcium-containing phantoms were scanned by CT and MR, using both T1- and T2-weighted sequences, with a slice thickness varying from 5-7 mm. Partial volume artifacts were determined by abutting phantoms with and without calcium and by varying the slice position to include different proportions of the calcium- and noncalcium-containing phantoms. Contrast-detail curves, expressed as a ratio of contrast to noise, were determined for varying sizes of calcification and degrees of partial voluming. As expected, the CT conspicuity of calcification (positive contrast) markedly surpasses that of MR (negative contrast). The difference was two orders of magnitude. When the calcification filled more than half the slice on MR, the conspicuity depended on the contrast of the matrix material; i.e., increased matrix intensity caused increased conspicuity. However, as the size of the calcification decreased, partial volume effects increased; i.e., increased matrix intensity caused decreased conspicuity. Conspicuity of small calcifications is independent of matrix material, since contrast and partial volume effects balance. We conclude that CT is clearly the method of choice for identifying small foci of calcification.