Tumour size measurement in a mouse model using high resolution MRI

2D and 3D T2-weighted RARE images of tumour bearing mice were acquired in vivo using a 7？T dedicated animal MR system. For the 3D images the acquired image resolution was varied. The images were exported to a PC workstation where the tumour mass was determined assuming a density of 1？g/cm3, using an in-house developed tool for segmentation and delineation. The resulting data were compared to the weight of the resected tumours after sacrifice of the animal using regression analysis.Strong correlations were demonstrated between MRI- and necropsy determined masses. In general, 3D acquisition was not a prerequisite for high accuracy. However, it was slightly more accurate than 2D when small (<0.2？g) tumours were assessed for inter- and intraobserver variation. In 3D images, the voxel sizes could be increased from 1603？μm3 to 2403？μm3 without affecting the results significantly, thus reducing acquisition time substantially.2D MRI was sufficient for accurate tumour size measurement, except for small tumours (<0.2？g) where 3D acquisition was necessary to reduce interobserver variation. Acquisition times between 15 and 50 minutes, depending on tumour size, were sufficient for accurate tumour volume measurement. Hence, it is possible to include further MR investigations of the tumour, such as tissue perfusion, diffusion or metabolic composition in the same MR session.