functional MRI everything you always wanted to know, but never dared to MD PhD

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1 functional MRI everything you always wanted to know, but never dared to MD PhD Associate Professor of Neuroradiology Dept. of Radiology, Erasmus MC, Rotterdam (NL) Honorary Consultant and Reader UCLH National Hospital for Neurology and Neurosurgery, London (UK)

2 functional MRI = visualising the brain at work

3 why fmri?

4 fmri in clinical practice Presurgical evaluation of eloquent brain regions complex motor motor sensation comprehension phonology audition source: vision

5 fmri in clinical practice Presurgical evaluation of eloquent brain regions motor function motor cortex. complex motor motor sensation comprehension phonology audition source: vision

6 fmri in clinical practice Presurgical evaluation of eloquent brain regions motor function motor cortex. language function complex motor motor sensation comprehension hemispheric dominance. phonology audition source: vision

7 fmri in clinical practice Presurgical evaluation of eloquent brain regions motor function motor cortex. language function complex motor motor sensation comprehension hemispheric dominance. vision visual cortex. phonology audition source: vision

8 Lacroix et al. J Neurosurg 2001;95:190 Survival of glioma patients patient clinical condition extent of resection

9 without fmri Clinical value of presurgical fmri with presurgical fmri no awake GA no awake GA Petrella et al. Radiology 2006:793

10 without fmri Clinical value of presurgical fmri with presurgical fmri no awake GA no awake GA /17 patients are operable Petrella et al. Radiology 2006:793

11 Outline Neurophysiology fmri basics Localising eloquent brain regions Motor function Language function Pitfalls & limitations Conclusions

12 Neurophysiology FMRI BASICS

13 neurovascular coupling FMRI BASICS fmri neurophysiology neuronal activity local energy consumption local oxygen demand local perfusion

14 FMRI BASICS fmri neurophysiology Most commonly used fmri-technique: BOLD-imaging. BOLD: Blood Oxygenation Level Dependent. Pauling (1936) oxygenised haemoglobin (oxyhb): diamagnetic (no magnetic field disturbance). deoxygenised haemoglobin (desoxyhb): paramagnetic (magnetic field disturbance). Ogawa (1990) hypoxia leads to signal loss on T2*w imaging.

15 FMRI BASICS fmri neurophysiology neuronal activity oxygen demand local perfusion oxyhb/desoxyhb signal T2*w sequence

16 FMRI BASICS BOLD response delayed and prolonged response peak after 6-8s return to baseline > 12s

17 FMRI BASICS The fmri experiment BOLD signal change maximum 3-5%. Many measurements required (>100). Relative, compared with baseline perfusion. Task consists of alternating active and baseline conditions. Task based fmri (most common)

18 FMRI BASICS fmri experiment finger tapping rest rest fast (<3s/scan) whole brain scans (T2*w) many acquisitions (typically > 100 scans) required to obtain sufficient statistical power

19 FMRI BASICS fmri analysis active rest - =

20 FMRI BASICS fmri analysis: general linear model paradigm

21 FMRI BASICS fmri: presenting results project statistical maps on high resolution scan

22 FMRI BASICS Summary fmri technique Delayed and prolonged signal Very small signal Indirect signal Statistical maps projected on high-resolution image but it works!

23 complex motor motor sensation comprehension phonology Mapping eloquent brain regions audition FUNCTIONAL ANATOMY vision source: healthandpuzzles.com

24 FUNCTIONAL NEUROANATOMY

25 MOTOR SYSTEM fmri of the motor system Good correlation with electrocortical mapping. Primary motor cortex precentral gyrus. Somatotopic organisation.

26 MOTOR SYSTEM Primary motor cortex: foot 36 y.o. female: oligodendroglioma

27 MOTOR SYSTEM Primary motor cortex: hand 59 y.o. male: AV-malformation

28 MOTOR SYSTEM Primary motor cortex: lip 36 y.o. male: glioma

29 LANGUAGE SYSTEM Classical model of language Frontal expressive Broca s area Arcuate fasciculus Posterior receptive Wernicke s area

30 LANGUAGE SYSTEM Language Hemispheric dominance based on functional language representation. Cortical language representation in the brain is left-lateralised in 95% of right-handed people in 70% of left-handed people. In the remaining 30% of left-handers 15% symmetrical only 15% right-sided.

31 LANGUAGE SYSTEM Task: verb to noun generation book TV ball chair chair water 3 s watc h throw eat sit swim read what would you do with it? Smits et al. Radiographics 2006;26:S145

32 LANGUAGE SYSTEM Left-handed patient strong language activation in the right hemisphere R R

33 LANGUAGE SYSTEM Localising language areas with fmri Good accuracy of fmri for mapping the motor cortex. NOT for language localisation!! POOR correlation with electrocortical mapping. Low sensitivity (22-100%) eloquent language areas are not visualised. Low specificity (61-100%) activation does not necessarily indicate eloquence. Language fmri primarily for assessment of hemispheric dominance. Bizzi et al. Radiology 2008;248:579

34 Limitations of fmri PITFALLS source:

35 PITFALLS & LIMITATIONS Mass effect and/or presence of tumour failure to demonstrate left-hemispheric language activation in a right-handed patient

36 PITFALLS & LIMITATIONS Word repetition Story Listening Steal-effect with AVM Before embolization After embolization right-handed patient Slide courtesy of Stéphane Lehéricy

37 PITFALLS & LIMITATIONS Reduced vascular reserve in ICA stenosis failure to assess language dominance in a left-handed patient left ICA right ICA Smits et al. J Neuroimaging 2011;21:e162

38 PITFALLS & LIMITATIONS Task performance fmri activation entirely depends on task performance Proper patient preparation is essential. Monitor task performance in-scanner visual assessment (mirror, camera) response buttons real-time data analysis. Eliminate unwanted processes/motion eyes closed head fixation. Adapt task to patient ability. Smits et al. Arch Phys Med Rehabil 2012;93:S1

39 Take Home Messages CONCLUSIONS

40 Concluding remarks fmri has great value in specialist clinical practice presurgical localisation of eloquent brain regions. BOLD fmri is a perfusion imaging technique any perfusion abnormality will potentially affect fmri signal. fmri activation maps are statistical maps derived from low resolution, susceptibility weighted images projected on high resolution anatomical images. Absence of fmri signal absence of neuronal activity. Proper task performance is essential.

41 fmri & DTI in clinical practice 7-9 May 2015, Basel/CH source: