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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
#his information changes rapidly ;ee your
handout for this class for the latestinformation
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