Reliability of stereotactic coordinates of 1.5-tesla and 3-tesla MRI in radiosurgery and functional neurosurgery

Abstract

Objective: The aims of this study are to identify interpersonal differences in defining coordinates and to figure out the degree of distortion of the MRI and compare the accuracy between CT, 1.5-tesla (T) and 3.0T MRI.

Methods: We compared coordinates in the CT images defined by 2 neurosurgeons. We also calculated the errors of 1.5T MRI and those of 3.0T. We compared the errors of the 1.5T with those of the 3.0T. In addition, we compared the errors in each sequence and in each axis.

Results: The mean difference in the CT images between the two neurosurgeons was 0.48±0.22 mm. The mean errors of the 1.5T were 1.55±0.48 mm (T1), 0.75±0.38 (T2), and 1.07±0.57 (FLAIR) and those of the 3.0T were 2.35±0.53 (T1), 2.18±0.76 (T2), and 2.16±0.77 (FLAIR). The smallest mean errors out of all the axes were in the x axis : 0.28-0.34 (1.5T) and 0.31-0.52 (3.0T). The smallest errors out of all the MRI sequences were in the T2 : 0.29-0.58 (1.5T) and 0.31-1.85 (3.0T).

Conclusion: There was no interpersonal difference in running the Gamma Plan® to define coordinates. The errors of the 3.0T were greater than those of the 1.5T, and these errors were not of an acceptable level. The x coordinate error was the smallest and the z coordinate error was the greatest regardless of the MRI sequence. The T2 sequence was the most accurate sequence.

Keywords: Functional neurosurgery; MRI; Stereotactic radiosurgery.

Fig. 1

The Elekta magnetic resonance imaging phantom was used in this study (Elekta). The phantom was equipped with the three-dimensional inlay grid shown on the right.

Fig. 2

The 3-dimensional coordinates were defined with maximal magnification in the Gamma Plan® workstation. A and B : The phantom images transferred to the Gamma Plan® workstation. C : The defining coordinates with maximal magnification (arrows).

Fig. 3

A : The errors (Δx, Δy, Δz, and Δr) in the T1 sequence of the 1.5T and 3.0T MRIs. B : The errors in T2. C : The errors in fluid attenuated inversion recovery. All p-values are corrected by Bonferroni's method.

Fig. 4

The errors in the central area are shown in each MRI sequence. The difference between the 1.5T and 3.0T MRIs is statistically significant in all MRI sequences. All p-values are corrected by Bonferroni's method.

Fig. 5

The errors of all the axes are shown in each MRI sequence. The error in the x axis is the smallest regardless of the MRI sequence.

Fig. 6

The errors of all the MRI sequences are shown in each axis. The error in the T2 sequence is the smallest in the y and z axes. There is no difference in the x axis.