Imaging: MRS/MRI/PET/SPECT: Summary
Leigh PN., Simmons A., Williams S., Williams V., Turner M., Brooks D.
1. Quantitative neuroimaging in ALS is still at an early stage of development. Advances in hardware and software are likely to improve the sensitivity of techniques such as 1 H-MRS, DTI, and fMRI. 2. In 1 H-MRS (probably the most widely available MR research tool) there is a need for studies on reproducibility, for studies using identical protocols in different centres, and for studies using carefully matched patients. 3. DTI may also provide a useful approach to measuring tract damage in ALS. 4. The place of fMRI is currently less clear, but combined with multi-voxel MRS, it could be a powerful method to identify NAA changes in a functionally defined region such as the primary motor cortex. 5. Automated volumetric MRI will almost certainly be used alongside other techniques to assess tissue change over time. 6. A combined (multi-modal) approach with appropriate statistical analysis may help to separate ALS subjects from controls. Thus 1 H-MRS combined with automated volumetric analysis and DTI should have the potential to detect cortical and tract damage in ALS subjects, whereas each technique alone would have little if any prospect of doing so. 7. PET has the potential to provide a powerful, sensitive and potentially specific marker for neuronal damage in ALS, but currently available markers do not meet these requirements. PET could thus have both the sensitivity and diagnostic specificity that MRI is unlikely to provide. 8. The strength of MRI will lie in sensitivity (ability to detect and quantify pathology), safety, and access rather than diagnostic specificity. 9. There is an urgent need for techniques that have the sensitivity to assess neuronal damage in the spinal cord. DTI may be useful in this respect. Neuroimaging offers great potential for quantitative assessment of disease progression in ALS, and a co-ordinated, collaborative approach to dealing with technical and data analysis issues is urgently needed.