accuracy, reliability and limitations of functional and structural imaging data daniela seixas dept....
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Accuracy, reliability and limitations of functional and structural imaging data
Daniela Seixas
Dept. of Imaging, Centro Hospitalar de Vila Nova de GaiaFaculty of Medicine of Porto University
Portugal
• The accuracy, reliability and limitations of neuroimaging depend on the purpose of its use
• Neuroscience research• Medical• Marketing• Law• Military
Structural vs Functional brain imaging
• Structural brain imaging– Anatomy– Volume– Area– Thickness– Spatial resolution
• 1x1x1 mm3
• Functional brain imaging– Brain function
• fMRI• Perfusion imaging• Diffusion imaging• Molecular imaging
– MR spectroscopy– SPECT– PET
• Spatial and temporal resolution
Structural imaging
Structural imaging
• Knowledge of– Techniques
– Neuroanatomy
– Pathology• Meaning of disease?
Technical knowledge
Meaning of disease
• Newborn male diagnosed with a brain tumour before birth with fetal MRI
Meaning of disease
• Should pregnancy be interrupted?
– What is the effect of the disease on the brain development and function?
We don’t know!
Born 1932 Born 1932
Who has dementia?
Structural imaging
• Incidental findings– A brain aneurism is found incidentally in a non
clinical scan• High risk of rupture• The patient has surgery:
• Informed consent• Should all scans be read by a radiologist?
– Costs?
DiesSurvives
Survives with brain damage
Functional imaging
Acoplamento
neurovascular
Acoplamento
neurovascular
StimuluStimulussStimuluStimuluss
Neuronal Neuronal activityactivityNeuronal Neuronal activityactivity
Hemodynamic Hemodynamic responseresponse
Hemodynamic Hemodynamic responseresponse
BOLD BOLD fMRIfMRIBOLD BOLD fMRIfMRI
SensorySensoryCognitiveCognitive
MotorMotor……
Indirect measure of brain activity
Limitations and validity of fMRI• Theory behind the study & nature of the research
question
• Design and logistics of experiment
• Reliability of task
• Subject’s collaboration– Head movement– Task performance
• Field strength of the MRI scanner (and other hardware)
• Due to the nature of research questions, planning fMRI tasks and logistics can become challenging
“Castle” design; each sequential block represents increasing bladder water volume and correspondent visceral sensations
Positive linear trend of brain areas active during filling of the bladder
Hyper scanning
• Allows subjects in different fMRI scanners to interact in real time– Hardware and software that link scanners through
the internet– Behavioral experiments in which participants
interact with each other while fMRI is acquired in synchrony in both scanners (neuroeconomics)
Montague R, et al. Neuroimage 2002;16:1159-64
Subject collaboration
• Paraplegic patient (unable to move both legs) due to spine trauma– Investigate location of cortical motor areas for
right inferior limb
– Patient could not collaborate in motor task• Passive movement of right inferior limb
Limitations and validity of fMRI• Number of subjects
• Software– Registration
• Statistics– Smoothing– Type of test– False positives & false negatives– Thresholding– Region-of-interest analysis– Inferences to the population
Number of subjects
Seixas D, Ayres M, Andersson J. Neuroradiology 2009;51(S1):S93-94
Clinical settingForensic useMarketing
ResearchMarketing
Single subject Group
The effect of the number of participants
Increasing spatial extent of clusters with increasing n
Thresholding
• Several techniques can be used– Bonferroni correction– Permutation thresholding– Random field theory– False discovery rate
Designed to control for type 1 error‘To make sure that we don’t say
there is an activation when there isn’t one
Type 2 error is important when n=1!‘To make sure that we don’t say there isn’t an activation when in fact there is
one’
Seixas D, Ayres M, Andersson J. Neuroradiology 2009;51(S1):S93-94
• Prediction techniques– Multivariate analysis– Exploratory analysis
MIT Sloan Management Review 2009;50:32-34
Independent component analysis
Visual
Independent component analysis
Cognitive
Independent component analysis
Auditory & sensoriomotor
Limitations and validity of fMRI• Interpretation of data
– The activation of a certain brain area does not mean it is essential to the process, but that is is part of it
– Culture– Context– Beliefs
• No standardised tasks or normative data– What is normal or abnormal?
• Secondary use of brain images
• Quality of brain imaging research depends on the evolution of the field– Vision AND fMRI
• 3478 results
– Taste AND fMRI• 261 results
– Marketing AND fMRI (and yes, Marketing is a MeSH word in PubMed)
• 71 results
To think
• Brain imaging is already being used in numerous fields, from Neuroscience to Marketing or Military
• It is an ongoing process that cannot be stopped but should instead be supported by those who know its technical, ethical and legal limits
Seixas D, Ayres Basto M. Clin Neuroradiol 2008;18:79-87
References• Andersson J, Hutton C, Ashburner J, Turner R, Frinston K (2001). Modeling
geometric deformations in EPI time series. Neuroimage 13:903-19• Kirschen MP, Jaworska A, lles J (2006). Subjects’ expectations in
neuroimaging research. J Magn Reson Imaging 23:205-209• Nichols TE, Holmes AP (2002). Nonparametric permutation tests for
functional neuroimaging: a primer with examples. Hum Brain Mapp 15:1-25
• Seixas D, Ayres Basto M (2008). Ethics in fMRI studies: A review of the EMBASE and MEDLINE literature. Clin Neuroradiol 18:79-87
• Steinke EE (2004). Research ethics, informed consent, and participant recruitment. Clin Nurse Spec 18:88-95
• Zijlmans M, Buskens E, Hersevoort M, Huiskamp G, van Huffelen AC, Leijten FS (2008). Should we reconsider epilepsy surgery? The motivation of patients once rejected. Seizure 17:374-377