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Chapter 7

Medical Imaging

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Medical Ultrasonography

Ultrasound: Acoustical waves above the range of human hearing

< 20 ! Infrasonic20 ! " 20 #! Audible

$ 20 #! Ultrasonic

% M! &deep organ' " %( M! &surface' is used for medical ultrasound

)ominal fre*uenc+ is ,-( M!

.ound wave behaves li#e light wave/eflection

/efraction

iffraction

1ie!oelectric transducer: Mechanical vibrations are produced when electricvoltage is applied along specified direction- Converse is also true-

uart!

3ead !irconate titanate &145'

.odium 1otassium titrate &/ochelle salt'

Ammonium dih+drogen phosphate4inc o6ide etc

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Basics of USG

5ransmission velocit+ of ultrasound is different in different organ

8aves encounter regions of non9homogeneities and partiall+ reflected &echo'-/eflected waves provide information on the internal structural details of the medium

&organ'-

Material ensit+

&gmcm,'

;elocit+

&ms'

Acoustic Impedance

%0&/a+l'

Air 0-00% ,,0 0-000=

>one %-?( ,,0 7-?0

Muscle %-0 %(70 %-70

@at 0-, %=?0 %-=0

>lood %-00 %(0 %-(0

8ater "0-7 %=0 %-=?

.oft tissue " 0-? %(00 %-0

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Scanning Modes

A .can: amplitude of the signal

> .can:brightness for signal amplitudeModified > .cantransducer is fi6ed arra+ed source is moved bac# and forth

M .can: Motional obBects &heart'- A scan with successive loo#s at the target createdb+ scanning the time base verticall+- ispla+s as brightness-

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Magnetic Resonance Imaging

MRI units use relatively strong magnetic fields to determine the

distribution of hydrogen nuclei in human body to visualizeanatomic structure of organ

Images in slices of 2 " %0 mm thic# in transverse sagittal and coronal planes

M/I depends on magnetic spin properties of atomic nuclei )uclei with even number of nuclei &e: 212) C: 1)' have spin

moment I D 0E individual spin and magnetic moments cancel each other )uclei with even mass but odd charge &odd 1 odd )' have I D integral of

basic moment

)uclei with odd mass &odd 1 even )' have I D F basic moment &% %,C,%1 have I D F 2,)a ,(Cl ,G have I D F ,'

5hird categor+ of materials behave li#e tin+ bar magnets under the influence of

magnetic filed- )uclei get oriented parallel or anti parallel to the direction of

magnetic field- 5he resultant magnetic vector lies along the a6is of precession-

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MRI

Magnetic moments has 2 states:

state: M!" #$ state: M!" % #

+drogen nuclei is most suitable due to high concentration in the bod+

Hnerg+ of interaction between applied magnetic filed &>0' and nuclear magnetic

moment &' is

H D 9 >0D 9 JhM%>02K

Jnuclear g+romagnetic ratio

)uclear transitions occur for resonance absorption at resonant fre*uenc+ &called

3armor fre*uenc+'

L0D J>0

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MRI

Instrumentation

Image &roduction

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uestions

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