Volumetry of the Pituitary Gland: An Initial in vitro and in vivo MR Study

Purpose: We have attempted to evaluate the reliability of a new volumetric technique for MR imaging applied on measurements of phantoms with defined volumes and the normal pituitary gland (PG) of healthy individuals. Methods: In nine males without a clinical history of pituitary abnormalities and in a phantom study we performed triplicate MRI measurements before and after repositioning for volumetry of the PG or the phantoms, respectively. Using a standard head coil on a 1.5 T scanner, a tilted sagittal T₁w 3D magnetization-prepared rapid gradient-echo sequence was applied with TR/TE/alpha=15/5ms/30, 256×256 matrix, 192 slices, 1mm thickness and an isovoxel size of 1×1×1mm³. For interactive segmentation, a semi-automated 3D-watershed transform was applied to the gradient image. Each segmentation took approx. 4 minutes. Volume was assessed by voxel counting. Results: Mean volume of the nine pituitary glands was 0.62ml (SD:0.02ml) with variation coefficients (VC) between 2.68% and 6.32%, respectively. Furthermore, the intraobserver variability with four repeated volume analyses of an identical MRI measurement ranged from 1.44% to 3.67%. After intravenous administration of contrast medium, the volume calculation showed an overestimation because of reduced demarcation of PG. Reliable and precise results could be ensured up to a slice thickness of 1.8mm, preferably by coronal scanning. The VC from the phantom volume measurements (0.3, 0.5, 0.9, 1.0 and 1.6ml) only ranged from 0.49% (SD:0.006ml) to 1.98% (0.005ml). Conclusion: Our initial results demonstrate a high reliability without a significant difference of volumetric measurement for our in vitro and in vivo studies. This method provides a precise volume estimation of PG up to a slice thickness of 1.8mm and can improve the monitoring of PG volume in follow-up-studies after surgical or conservative treatment.