Human Subjects in fMRI ResearchHuman Subjects in fMRI ResearchCredits:Credits:Robert Savoy,Robert Savoy, Ph Ph.D..D.Franz Franz SchmittSchmitt, , PhPh.D..D.OutlineOutlineOutline• General Information for Use of Human Subjects• fMRI Specific Information for Use of Human Subjects• Static B0 fields• RF B1 fields- tissue heating• Switched gradient fields- peripheral nerve stimulation• Acoustic Noise• Practicing Safe Imaging• Minimizing Distress in the MR EnvironmentSafety is Your ResponsibilitySafety is Your ResponsibilitySafety is Your Responsibility• Become familiar with the material posted on yourinstitution’s Human Subjects web site• e.g. http://hms.harvard.edu/integrity• Read• Belmont Report• Title 45 Code of Federal Regulations Part 46 Protection ofHuman Subject• Review NIH presentation from the Office ofHuman Research Protection• http://ohrp.osophs.dhhs.gov/humansubjects/assurance/sbirsttr/requirements.htmHuman Subject ConsiderationsHuman Subject ConsiderationsHuman Subject Considerations• Informed Consent• Risk/Benefit ConsiderationsStatic B0 FieldsStatic BStatic B00 Fields Fields• No established adverse health effects• Projectile accidents• Metallic object screening• Magnetohydrodynamic effectsStatic B0 fields- Projectile AccidentsStatic BStatic B00 fields- Projectile Accidents fields- Projectile Accidents45 y.o. male 2+ years s/p altercation45 y.o. male 2+ years s/p altercationAGS / MGHAGS / MGHRF B1 Fields- Tissue HeatingRF BRF B11 Fields- Tissue Heating Fields- Tissue Heating• Ohmic heating of patient tissue is due to resistivelosses from induced electric fields• Greatest effect at periphery or surface• Described in terms of Specific Absorption Rate(SAR)• Scanner determinants: RF frequency, type of RFpulse, TR and type of RF coil• Body determinants: thermoregulatory function• Electrical BurnsSwitched Gradient FieldsSwitched Gradient FieldsSwitched Gradient Fields• Peripheral Nerve Stimulation• Metallic Taste• Magnetophosphenes• Skeletal Muscle Contractions• By Faraday’s Law of Induction exposure ofconductive tissue to time-varying magnetic fieldswill induce an electric field.Peripheral Nerve StimulationPeripheral Nerve StimulationPeripheral Nerve StimulationZ - gradientZ - gradientzzBBmaxzzOOFOVFOVLLFOVFOVSSzzOO11 / Gradient-tutorial.pptF. Schmitt, MGHStimulation Aspects(I)Stimulation Aspects(I)Stimulation Aspects(I)#pulsesGTh(#pulse)1N• Stimulation thresholds vary• linearly with rise time• ramp shape• fct (#pulses)TRise GTh(TRise)12 / Gradient-tutorial.pptF. Schmitt, MGHHow to Place the Gradient Coil Performance?How to Place the Gradient Coil Performance?How to Place the Gradient Coil Performance?• GPA performanceTRGmaxGTh(TR)Gradient strength limits: IGradient strength limits: ImaxmaxSR limits: VmaxAllowed gradient switchingstimulationsstimulationsStimulation ThresholdGCGCLLg Peripheral Nerve/Muscle Stimulation13 / Gradient-tutorial.pptF. Schmitt, MGHHow to Place the Gradient Coil Performance?How to Place the Gradient Coil Performance?How to Place the Gradient Coil Performance?• GPA performanceTRGmaxGTh(TR)Gradient strength limits: IGradient strength limits: ImaxmaxSR limits: VmaxGCGCSSstimulationsstimulationsAllowed gradient switchingStimulation ThresholdGCGCLL• Peripheral Nerve/Muscle Stimulation14 / Gradient-tutorial.pptF. Schmitt, MGHFaster & Stronger Gradients Faster & Stronger Gradients Faster & Stronger Gradients • “shorten” the gradient coil typically results in• higher stimulation thresholds, when expressed in mT/m• lower inductance• i.e. higher SR, Gmax• but more geometricimage distortionsZ - gradientZ - gradientBzzzzOOBmaxFOVFOVSSFOVFOVLLSR150 SR20015 / Gradient-tutorial.pptF. Schmitt, MGHWhy does EPI make so MUCH noise?Why does EPI make so MUCH noise?Strong, Static Magnetic FieldStrong, Static Magnetic FieldCurrent pulseCurrent pulseto createto creategradientgradientfieldsfieldsTogether, theseTogether, theseproduce mechanicalproduce mechanicalforces on the coilsforces on the coilsthat create the that create the gradient fields; gradient fields; so the coils move.so the coils move.The result is The result is acoustic noise.acoustic noise.Acoustic Noise .. and how to avoid?Acoustic Noise .. and how to avoid?Acoustic Noise .. and how to avoid?• passive damping ~ 10 - 15 dB• acoustic insulation• more mass & stiffer• encapsulation & vacuum ~ 20 - 30 dB• cooling• MRI system becomes longer• “active” damping ~ 20 dB• avoid mechanical / acoustical resonancef/HzS( )~l do not allow that sequence peak coincides with acoustic modesl change TR, echo spacing, ...17 / Gradient-tutorial.pptF. Schmitt, MGHCurrent FDA Criteria for Non-significant RiskCurrent FDA Criteria for Non-significant RiskCurrent FDA Criteria for Non-significant Risk• Field strength < 4T• SAR < 3 W/kg averaged over 10 minutes in head• SAR < 8 W/Kg in any 1 cc of tissue in headaveraged over 5 minutes• Acoustic Noise <140 dB peak and 99 dB averagewith ear protection• No painful or severe peripheral nerve stimulationSubjective Distress in the MRI EnvironmentSubjective Distress in the MRI EnvironmentSubjective Distress in the MRI Environment• Incidence of distress among clinical MRI is high• Distress can be caused by may factors including:confined space, noise, restriction of movement• Distress can range from mild anxiety to full blownpanic attack• Distress can result in subject motion and disruptimage qualityMinimizing Subjective DistressMinimizing Subjective DistressMinimizing Subjective Distress• Careful screening• Complete explanations• Make them comfortable in the scanner• Maintain verbal contact• Give them the panic