Abstracts

RATIONALE: Volumetric studies of the entorhinal cortex (ERC) depend upon the correct visualization of the anatomic landmarks. The objectives of this study are: 1) to verify whether differences of image quality induce differences in quantification of the ERC, 2) to compare the morphometric study of the ERC performed on 3D images of 1, 2 and 3mm thick slices and single plane 3mm thick coronal slices.
METHODS: We studied 16 healthy subjects who underwent our MRI protocol. Images were acquired in a 2T scanner. We used coronal slices oriented perpendicularly to hippocampal long axis for manual delineation of regions of interest. We used the same anatomic protocol for the segmentation of all subjects either for the single plane based analysis or for the three-dimensional analysis. This protocol was based on previously described methods for the entorhinal segmentation (Insausti et al Am J Neuroradiol 1998; 19(4):659-671). A T1-IR 3mm single plane acquisition was used for quantification of ERC volumes by NIH Image program, using TIFF format. A T1 gradient echo three dimensional sagittal acquisition was used for multiplanar reconstruction of 1, 2 and 3mm thick slices volumetric converted into MINC format and were analysed using the software DISPLAY. For statistical analysis we used student[ssquote]s t test and ANOVA.
RESULTS: We studied 16 healthy subjects (3 men) with mean age of 31 years (ranging from 21 to 53). The 1mm three-dimensional DISPLAY analysis (TDISPLAY) showed mean volumes of 895 [plusminus] 143mm3 (703 to 1098) for the right ERC and 968 [plusminus] 186mm3 (673 to 1317) for the left ERC . The 2mm TDISPLAY showed a mean volume of 1299 [plusminus] 182mm3 (943 to 1686) for the right ERC and a mean volume of 1317 [plusminus] 151mm3 (1105 to 1592) for the left ERC. The 3mm TDISPLAY reconstructed images showed a mean volume of 1609 [plusminus] 187mm3 (1259 to 1896) for the right ERC and a mean volume of 1722 [plusminus] 179 mm3 (1463 to 2016) for the left ERC. The 3mm NIH analysis showed a mean volume of 1905 [plusminus] 264 mm3 (1602 to 2439) on the right and 1903[plusminus] 226 mm3 (1530 to 2339) on the left. There was no influence of age, gender or side on the volumes observed in TDISPLAY segmentation. Female subjects exhibited a larger entorhinal cortex, when the analysis was performed on NIH (p[lt]0.05). ANOVA revealed difference between the volumes obtained from the three-dimensional analysis with 1mm, 2mm and 3mm and the coronal based 3mm analysis (p[lt]0.001). Tukey post-hoc comparison revealed difference between all groups (p[lt]0.001)
CONCLUSIONS: Morphometric analysis of the ERC performed with different slice thickness yield different results. Thick slices are sometimes used because it is time saving, but volumes obtained are linearly incremented according to increased slice thickness, and false estimates may then supervene.
[Supported by: FAPESP, S[atilde]o Paulo, Brazil]