mri bioeffects and safety

8/20/2019 MRI Bioeffects and Safety

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MRI Bioefects andMRI Bioefects and

SaetySaetyDr. Peterson


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History and BackgroundHistory and Background

Bloch (Stanford) & Purcell (Harvard) - 1946

o!el Pri"e - 19#$ - %iscovery of

Sectroscoy

'ayond %aadian 'at *uor 19+4 ,over of Science

Paul auter!ur .ater iage - 19+/

0din!urgh rou2Peter 3anseld


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e5 %iagnostic 3odalitye5 %iagnostic 3odality

,oared to -rays (179#8)

3ore ,oara!le to ltrasound(19#:;s)

eed to understand hysics for safety


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Basic Magnetic FieldBasic Magnetic Field

ConceptsConceptsnits of


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nits of a> *he ?ersted) 3easures the 0arth@s # )

*he *esla 3easures the 3'


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3agnetic %oains3agnetic %oains

0aleC Heoglo!in

ron atos


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The Static Field and theThe Static Field and the

EnvironmentEnvironment

0Gects of the 0nvironent on the Static


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0Gects of the 0nvironent0Gects of the 0nvironent

on the Static


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0Gects of the 0nvironent0Gects of the 0nvironent

on the Static


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0Gects of the Static


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0Gects of the Static


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Bioefects o StaticBioefects o Static

Magnetic FieldsMagnetic Fields,ell


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,ell


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Bone ro5th and HealingBone ro5th and Healing

*here is uch controversy on the

eGects of agnetic elds on thegro5th and healing of !one> oconclusions yet>


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*hro!olysis *hro!olysis

ndeterinate eerients on rats

and guinea igs> ,an;t tell>


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erve


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,ardiovascular 0Gects,ardiovascular 0Gects

Sall increases in BP have !een

reorted>

Flso a slight leukoenia>


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3agnetohydrodynaic3agnetohydrodynaic

0Gect0Gect

Blood is a conductor Io5ing

through the agnetic eld>

*his usually results in an increasein *- 5ave alitude>


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*eerature *eerature

'eorts go !oth 5aysJ the !est

studies say static elds don;t aGect!ody teerature>

%on;t confuse this 5ith '< eGects>


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3agnetohoshenes3agnetohoshenes


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Static


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Bioefects o TimeBioefects o Time

!ariant Fields!ariant Fields

"#radients$"#radients$

3echanis

erve23uscle Stiulation

erves and 0P

3agnetohoshenesFuditory ,onsiderations

?ther Biological 0Gects


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Gradient Bioeffects MechanismGradient Bioeffects Mechanism

,hanging agnetic eld over tie (dB2dt)induces voltage and current in conductors>

E%ample: Peak gradient of 1 2cE rise tie D#:: µsec /: c fro the isocenter> *his is$E::: 2sec × /: cE or 6:E::: 2secE or 6

*2sec>

*he induced current is 1 µF2c$ for this

gradient>

Biological eGects usually occur !eyond /µF2c$


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erve23uscle Stiulationerve23uscle Stiulation

0ale gradient induced acurrent of 1 µF2c$>

eed 1# to 1:: µF2c$ for tetaniccontractions of !reathing uscles>

eed :>$ to 1>: µF2c$ to roduce!rillation>


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erves and 0Perves and 0P

*5itching occurs !eyond 6: *2sec


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3agnetohoshenes3agnetohoshenes

one at 1+ µF2c$ in 1>9# *

systes>

ots at 4 * and any gradient>


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Fuditory ,onsiderations>Fuditory ,onsiderations>

%iscussed later under Fuditory

0Gects>


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?ther Biological 0Gects>?ther Biological 0Gects>

'educed eGects of annitolE fentanyl

and orhine-induced analgesia>

o eGect on ahi!ian

e!ryogenesisE urine cellcytotoicityE and litter nu!er orgro5th rates of regnant ice>


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radient 3agnetradient 3agnet

BioeGects ,onclusionsBioeGects ,onclusions

o eGects at 6 *2sec>

erve stiulation at $: *2sec>

%on;t go a!ove $: *2sec>

Kee an eye on 0P in the future>


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&uenches&uenches

*he Pro!le 5ith the


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*he Pro!le 5ith the


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*he ?ford Pig *he ?ford Pig

F ig 5as laced in the !ore>

1>6* agnet Luenched at 1>+6 *

'esultsC *he ig 5as startled>


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Muench ,onclusionsMuench ,onclusions

Muenches have haened several

ties 5ith atients in the !ore ?nce it haened 5ith the ,hief *ech

in the !ore (in MueenslandE Fustralia)8

o deleterious eGects have !eenreortedE ecet for startle reIe>


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Radiore'uencyRadiore'uency

BioefectsBioefects

'< %ened

BioeGects

*eerature-sensitive organs

Muantifying BioeGects

Limits


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'< %ened'< %ened

on-ioni"ing electroagnetic

radiation


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The ElectromagneticThe Electromagnetic

SpectrumSpectrum


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BioeGectsBioeGects

nclude visualE auditoryE endocrineE cardio-vascularE iune systeE reroductiveE and

develoental functions>

Simpli(ed: t heats the tissues>

,ardiac outut & !lood Io5 increase

S5eat secretion & evaoration increase


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*eerature-sensitive *eerature-sensitive

organsorgans

*he testes

*he eyes

)imits: 1: .2kg for ore than 1:inutes


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Muantify !ioeGects usingCMuantify !ioeGects usingC

SF'C Secic F!sortion 'ate 'ate at 5hich '< energy is couled into

tissues>

nitsC .atts er kilogra (.2kg)

SF' - *ie Product nitsC .-in2kg or .-hr2kg

*eerature (N,)


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FDA SAR LimitsFDA SAR Limits


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4 .2kg

Peak for any gra of tissue of 7>:.2kg

Head average of />$ .2kg


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FDA Temperature LimitsFDA Temperature Limits


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*regnancy*regnancy


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BioeGects of the StaticEBioeGects of the StaticE

radient and '<


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Health ,are .orkersHealth ,are .orkers

F survey of $E::: feale 3' oeratorsreorted 14$1 regnanciesJ $7: 5ere 3'techs or nursesJ 794 5orked at another Oo!E #4

5ere studentsE 19/ 5ere hoeakers> *here5ere no statistically signicant diGerences!et5een 3' oerator regnancies and thegrou !efore it 5orked in 3'> Sontaneousa!ortion rateE re-ter delivery rateE lo5 !irth

5eightE infertility and oGsring gender 5ereanaly"ed> FdOustents for aternal ageEsokingE and alcohol use didn;t change theresults>


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Pregnancy onclusionsPregnancy onclusions

“MR imaging may be used in pregnant women if other non-ionizing forms of diagnostic imaging are inadequate or if theexamination provides important information that would otherwise

require exposure to ionizing radiation (eg! fluoroscopy! "#!etc$ %t is recommended that pregnant patients be informed that!to date! there has been no indication that the use of clinical MRduring pregnancy has produced deleterious effects &owever! asnoted by the ')! the safety of MR during pregnancy has not

been proved*

-SMRI Safety Committee


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BioeGects of ,ontrastBioeGects of ,ontrast

3edia3ediaadoliniu is toic !ut is caged !y a

chelate (%*PF)>

*he chelate ay !e dissolved !y thekidneysE releasing the gadoliniu>Soe = contrast agents cross the

lacentaE are s5allo5ed !y the fetusE

ltered and ecreted !y the kidneys asurineE s5allo5edJ and the cycle thenreeats any ties> *he end result ofthis cyclic rocess is not kno5n>


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ryogenicsryogenics

+ecessary for superconductivity

, +iobium-titanium metal used for wires

, ecomes superconducting at ./ 0elvins

Liquid helium boils at 12 0elvins

Liquid nitrogen boils at 33 0elvins

#his classroom is at 245 0elvins


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ryogensryogens

Liquid Boils at:

666666 66666666666666666

)ir 78 0 -.739 " -:/59 '

+itrogen 33 0 -.489 " -:2.9 '

&elium 12 0 -2849 " -1529 '


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ryogensryogens

&elium is lighter than air

+itrogen is heavier than air

#hey will drive the air out of the magnet

room if released into it

oth are incredibly cold and will burn

flesh on contact


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+uditory Efects+uditory Efects

radient agnet sounds Protection or %istraction

0ar lugs2Headsets

oise cancellation devices

'< sounds ,licksE !u""esE chirs or knocks

Sees to coe fro the !ack of the head

sually asked !y gradient noise

,ryogen release sounds (think hurricane8)


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)aser *ositioning)aser *ositioning

SystemsSystems

Possi!ility of eye daage

one has ever !een reorted

3ost anufacturers no5 useincandescent las instead of lasers


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Bibliography and LinksBibliography and Links

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