Magnetic resonance image registration and subtraction in the assessment of minor changes in low grade glioma volume.

The purpose of this study was to apply image registration and subtraction to standard T2-weighted (T2-W) and FLAIR magnetic resonance imaging (MRI) protocols in an attempt to improve the detection of minor changes in low grade glioma volume. Thirteen patients with low grade glial tumours and minimal or no apparent change on serial MRI scans were prospectively recruited for the study. Forty-two pairs of images were compared (T2-W sequences in 27/27 and FLAIR sequences in 15/27). The image pairs were registered, subtracted and randomised. Three independent raters assigned non-parametric ratings according to the dominant volume change for unregistered, registered and subtracted image sets. There was a statistically significant improvement in the detection of tumour volume change using T2-W registration and T2-W and FLAIR registration/subtraction relative to unregistered images. The reproducibility and increased sensitivity of FLAIR images relative to T2-W images were most apparent when registration was applied. Smaller degrees of low grade glioma tumour volume change are detectable using image registration and subtraction techniques that can be applied successfully to images acquired with standard clinical protocols.