Neuroradiology 2 2007

Neuroradiology Comparing modalities Graduate Entry Medicine Programme Daniel Bulte Objectives  Review imaging modalities  Understand their features  Learn their limitations  See how they can complement each other  Ask more questions Phrenology Gall and Spurzheim (1810) Functional localization Brodmann’s anatomical  areas Important point  We do not only use 10% of our brains! Functional Localisation  Brain injury and surgical cases  Direct electrode stimulation/recording  PET ­ blood flow and metabolism  EEG ­ scalp potentials from neuronal firing  fMRI ­ blood oxygenation  MEG ­ magnetic field from neuronal firing Measurement         X­Rays CT Scans MRI/MRS  Ultrasound/Sonography PET/SPECT EEG MEG NIRS Early X­Ray Advanced CT Imaging Positron Emission  Tomography  PET PET  Quantifies metabolism  Technically indirect, but much more direct  than MRI  Requires administration of radioactive  compounds  Requires a harm/benefit analysis  Poor spatial resolution  Very expensive, not readily available  Frightens people Near Infrared  Spectroscopy  Measurement of the spectroscopic changes in the absorption and scattering properties of the human cerebral cortex when exposed to near-infrared (NIR) radiation  The wavelength region is known as the ‘therapeutic optical window’ due to the relative transparency of biological tissue at these wavelengths that allows the radiation to penetrate several centimeters (35cm) into the tissue before re-emerging NIRS Very safe Non­invasive Portable Cheap Excellent temporal resolution Poor spatial  resolution/penetration  Direct and indirect measures  (cytochrome oxidase/Hb)       Combining Techniques  PET/CT  MRI/EEG  MRI/TCD  MRI/TMS  PET/MRI  MRI/MRS Combining Techniques Functional MRI Functional MRI Tutorials  Functional MRI  MRI image formation Missed something?  www.fmrib.ox.ac.uk/~bulte Fourier Transforms Time Frequency Fourier Transforms ... 0 10 10 10 21 0 21 0 21 0 10 10 10 10 10 10 10 21 0 21 0 21 0 10 10 10 10 10 10 10 21 0 21 0 21 0 10 10 10 10 0 10 10 10 0 0 0 10 10 10 0 0 10 10 10 21 0 21 0 21 0 10 10 10 10 10 10 10 21 0 21 0 21 0 10 10 10... 0 0 10 10 10 0 0 10 10 10 21 0 21 0 21 0 10 10 10 10 10 10 10 21 0 21 0 21 0 10 10 10 10 10 10 10 21 0 21 0 21 0 10 10 10 10 0 10 10 10 0 0 Magnetic Resonance  Imaging          Good spatial resolution... Can be used with or without contrast agents Best with soft tissues Magnetic Resonance  Spectroscopy MRS  Looks at signals other than H2  A chemical profile of the voxel  Poor spatial resolution  Very poor temporal resolution 