Slide 1OutlineStatic B0 FieldsStatic B0 fields- Projectile Accidents45 y.o. male 2+ years s/p altercationSlide 6RF B1 Fields- Tissue HeatingSwitched Gradient FieldsPeripheral Nerve StimulationStimulation Aspects(I)Faster & Stronger GradientsWhy does EPI make so MUCH noise?Acoustic Noise .. and how to avoid?Current FDA Criteria for Non-significant RiskSubjective Distress in the MRI EnvironmentMinimizing Subjective DistressSafety is Your ResponsibilityHuman Subject ConsiderationsSlide 19Human Subjects in fMRI ResearchHuman Subjects in fMRI ResearchCredits:Credits:Robert Savoy, Ph.D.Robert Savoy, Ph.D.Franz Schmitt, Ph.D.Franz Schmitt, Ph.D.OutlineOutlineOutlineOutline fMRI Risks to Human SubjectsStatic B0 fieldsRF B1 fields- tissue heatingSwitched gradient fields- peripheral nerve stimulationAcoustic NoisePracticing Safe Imaging- minimize risksMinimizing Distress in the MR EnvironmentEthical Conduct of fMRI Research involving Human SubjectsStatic BStatic B00 Fields FieldsStatic BStatic B00 Fields FieldsNo established adverse health effectsProjectile accidentsMetallic object screeningMagnetohydrodynamic effectsStatic BStatic B00 fields- Projectile Accidents 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 BRF B11 Fields- Tissue Heating Fields- Tissue HeatingRF BRF B11 Fields- Tissue Heating Fields- Tissue HeatingOhmic heating of patient tissue is due to resistive losses from induced electric fieldsGreatest effect at periphery or surfaceDescribed in terms of Specific Absorption Rate (SAR)Scanner determinants: RF frequency, type of RF pulse, TR and type of RF coilBody determinants: thermoregulatory functionElectrical BurnsSwitched Gradient FieldsSwitched Gradient FieldsSwitched Gradient FieldsSwitched Gradient FieldsPeripheral Nerve StimulationMetallic TasteMagnetophosphenesSkeletal Muscle ContractionsBy Faraday’s Law of Induction exposure of conductive tissue to time-varying magnetic fields will induce an electric field.Peripheral Nerve Peripheral Nerve StimulationStimulationPeripheral Nerve Peripheral Nerve StimulationStimulationZ - gradientZ - gradientzzBBmaxzzOOFOVFOVLLFOVFOVSSzzOO9 / Gradient-tutorial.pptF. Schmitt, MGHStimulation Aspects(I)Stimulation 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)10 / Gradient-tutorial.pptF. Schmitt, MGHFaster & Stronger Gradients Faster & 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 SR20011 / 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 pulse Current pulse to create to create gradient gradient fieldsfieldsTogether, 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?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()~ do not allow that sequence peak coincides with acoustic modes change TR, echo spacing, ...13 / Gradient-tutorial.pptF. Schmitt, MGHCurrent FDA Criteria for Non-significant RiskCurrent 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 head averaged over 5 minutesAcoustic Noise <140 dB peak and 99 dB average with ear protectionNo painful or severe peripheral nerve stimulationSubjective Distress in the MRI EnvironmentSubjective 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 blown panic attackDistress can result in subject motion and disrupt image qualityMinimizing Subjective DistressMinimizing Subjective DistressMinimizing Subjective DistressMinimizing Subjective DistressCareful screeningComplete explanationsMake them comfortable in the scannerMaintain verbal contactGive them the panic buttonSafety is Your ResponsibilitySafety is Your ResponsibilitySafety is Your ResponsibilitySafety is Your ResponsibilityBecome familiar with the material posted on your institution’s Human Subjects web siteRead Belmont ReportTitle 45 Code of Federal Regulations Part 46 Protection of Human Subject Review NIH presentation from the Office of Human Research ProtectionHuman Subject ConsiderationsHuman Subject ConsiderationsHuman Subject ConsiderationsHuman Subject ConsiderationsInformed ConsentRisk/Benefit