A. Landi et al., Accuracy of stereotactic localisation with magnetic resonance compared to CT scan: Experimental findings, ACT NEUROCH, 143(6), 2001, pp. 593-601
Background. Stereotactic localisation of proper targets can be obtained wit
h Magnetic Resonance imaging (MRI). pending correction of the well-known in
accuracy of MRI in reproducing exact geometrical dimension. The aim of the
experimental work was to determine the real extent of the MRI distortion an
d to correct it.
Methods. PVC phantoms and fixed human brains were used as target simulators
; stereotactic targeting was obtained with CT and MRI: the results were com
pared and, finally. the real stereotactic values were measured on a commerc
ial stereotactic device. To optimise MRI targeting it was necessary to abat
e the "chemical-shift", to modify the head-coil receiver (tuning the "off-r
esonance" frequencies) and to correct the targeting directly on the images
(especially for the Y axis values). careful quality control and environment
al tests were also necessary to maintain good performances along the time.
Results. 172 measurements were carried out using both CT, plain X-ray and M
RI on PVC phantom. The values obtained from CT were considered as reference
. Significant geometrical accuracy was found with CT targeting, except for
the Z co-ordinate, due to the slice thickness. Mean value differences betwe
en the targets on MRI and their real geometric position are about 1 mm on X
and Z axises and about 2 mm on Y axis. Similar results were obtained on fi
xed brains, where absolute values of X and Y co-ordinates of the simulators
were measured using a millimetre grid placed over the brain slice.
Interpretation. Experimental findings concerning stereotactic targeting wit
h MRI suggest accuracy adequate for clinical practice. even when extreme ge
ometrical precision is required. such as in radiosurgery or functional ster
eotaxy. Careful quality control and intensive experimental setting of the M
RT device are mandatory to obtain satisfactory results.