An image correction protocol to reduce distortion for 3-T stereotactic MRI.
BACKGROUND
Image distortion limits application of direct 3-T magnetic resonance imaging for stereotactic functional neurosurgery.


OBJECTIVE
To test the application of a method to correct and curtail image distortion of 3-T magnetic resonance images.


METHODS
We used a phantom head model mounted on a platform with the dimensions and features of a stereotactic frame. The phantom was scanned within the head coil of a Philips Achieva 3T X series (Philips Medical Systems, Eindhoven, the Netherlands). For each scan, 2 images were obtained-the normal and the reversed images. We applied the inverted gradient correction protocol to produce a corrected x, y, and z coordinates. We applied the Cronbach test or coefficient of reliability to assess the internal consistency of the data.


RESULTS
For all analyzed data, the P value was >.05, indicating that the differences among the observers were not statistically significant. Moreover, the data rectification proved to be effective, as the average distortion after correction was 1.05 mm. The distortion varied between 0.7 mm and 3.7 mm, depending on the target location.


CONCLUSIONS
This study examined a rectifying technique for correcting geometric distortion encountered in magnetic resonance images related to static field inhomogeneities (resonance offsets), and the technique proved to be highly successful in producing consistently accurate stereotactic target registration. The technique is applicable to all routinely used spin-echo MRI.
*Division of Functional Neurosurgery, Institute of Neurology, University of São Paulo, São Paulo, Brazil; ‡Department of Radiology, Institute of Radiology, University of São Paulo, São Paulo, Brazil; §Hospital Israelita Albert Einstein, São Paulo, Brazil.
Wagner Malagó
WM
Tavares
Francisco
F
Tustumi
Claudia
C
da Costa Leite
Lionel Fernel
LF
Gamarra
Edson
E
Amaro
Manoel Jacobsen
MJ
Teixeira
Erich Talamoni
ET
Fonoff
D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging; D019047:Phantoms, Imaging