synopsis devesh

8/4/2019 Synopsis DEVESH

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A

SEMINAR REPORT

ON

MAGNETIC RESSONANCE IMAGING

BY

DEVESH SHUKLA

DEPARTEMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

N I E T Gr NOIDA


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CERTIFICATE

THIS IS TO CERTIFY THAT A SEMINAR ENTITLED MAGNETIC RESSONANCE IMAGING

HAS BEEN CARRIED OUT BY DEVESH SHUKLA UNDER MY GUIDANCE IN PARTIAL

FULFILLMENT OF THE DEGREE OF BACHELOR OF ENGINEERING IN ELECTRICAL AND

ELECTRONICS ENGINEERING OF NOIDA INSTITUTE OF ENGINEERING AND

TECHNOLOGY, GREATER NOID A DURING THE ACEDAMIC YEAR 2010-2011(SEMESTER-

VI) .

DATE:

PLACE: GREATER NOIDA

GUIDE HEAD, E N DEPARTMENT

(MR S.VIKRM SINGH) (DR S GAIROLA)


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ACKNOWLEDGEMENT

I take this opportunity to express my gratitude to my faculties,colleagues and seniors who have contributed a lot in completionof this seminar project. First of all I would like to give my heartythanks to HOD of our branch Mr SANJAY GAIROLA for hissupervision and guidance without which it would not have beenpossible to complete this report. I also acknowledge the kind

support of my faculties Mrs AKANSHA RAJPUT andMr S. VIKRM SINGH for their valuable contribution in completionof this report. It will be worth mentioning that these facultieswere always there for our help in whatsoever ways possible.

Last but not least I would like to thank mycolleagues specially my roommate PRAVEEN PATEL forproviding appropriate environment which was essential for me

to complete the project.

DEVESH SHUKLA


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CONTENTSTopic Page No.

y Abstract y In troductio n 7 y M ag ne tic prop e rti e s of matt e r 10 y Atomic structur e a n d N MR t e ch n ology 12 y U s e s of MR I (N MR) t e ch n ology 24


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ABSTRACT

Magnetic resonance imaging (MRI) formally known as nuclear magnetic

resonance (NMR) is being extensively used in many industrial and non-

industrial applications . Medical field can be considered as one of the most

important field in which MRI is being extensively used for diagnosis of many

diseases.

MRI scanners uses the magnetic properties of magnetically

active nuclei and its interaction with both a large external magnetic field

and radio-waves to produce highly detailed images of the body being

scanned. These images are used for the further study and diagnosis of the

body or sample under study. This technology of magnetic resonance imaging

has been detailed by me in this report .A due emphasis is made on the

application of this technologies and various new areas in which this

technology can be applied has been brought out.


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MAGNETIC RESSONANCE

IMAGING

INTRODUCTION

Clinical Magnetic Resonance Imaging (MRI) uses the magnetic

properties of hydrogen and its interaction with both a large external

magnetic field and radio-waves to produce highly detailed images of

the human body. In this first module, we will discuss some basic

principles of magnetism, the magnetic properties of the hydrogen

nucleus, and its interaction with the externally applied magnetic field(B0).

In its early days, MRI was known as NMR. This stands for Nuclear

Magnetic Resonance. Although the name has changed (primarily due

to the negative connotation of the word nuclear), the basic principles

are the same. We derive our images from the magnetic resonance

properties of nuclear particles (specifically hydrogen).

In order to perform MRI, we first need a strong magnetic field. The field

strength of the magnets used for MR is measured in units of Tesla. One

(1) Tesla is equal to 10,000 Gauss. The magnetic field of the earth is

approximately 0.5 Gauss. Given that relationship, a 1.0 T magnet has a

magnetic field approximately 20,000 times stronger than that of the

earth. The type of magnets used for MR imaging usually belongs to one

of three types; permanent, resistive, and superconductive.

A permanent magnet is sometimes referred to as a vertical field

magnet.

These magnets are constructed of two magnets (one at each pole).

The patient lies on a scanning table between these two plates.


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As previously mentioned, some vertical field systems are based on

resistive magnets. The main advantages of these types of magnets are:

1) No liquid cryogen,

2) The ability to turn off the magnetic field,

)Relatively small fringe field .

Superconducting magnets are the most common. They are made

fromcoils of wire (as are resistive magnets) and thus produce a

hori ontal field. They use liquid helium to keep the magnet wire at

degrees Kelvin where there is no resistance. The current flows through

the wire without having to be connected to an external power source.

The main advantage of superconducting magnets is their ability toattain field strengths of up to Tesla for clinical imagers and up to 10

Tesla or more for small bore spectroscopy magnets.


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Magne ti P er ti es f Ma tt er Magne ti i a f ndamen ta l er t f ma tter . e t ree t es f

magne ti roper ties are : d iamagne ti , paramagne ti , and

f erromagne ti .ese t ree proper ties are ill s tra ted in figure 3 shown on the nex t

page .

uts ide a magne ti fie ld , d iamagne ti subs tances exh ib it no magne ticproper ties . hen p laced in a magne tic fie ld , diamagneticsubs tances will exh ib it a nega ti e interac tion with the ex terna l magne tic fie ld .

In o ther words they are no t a ttrac ted to , bu t ra ther s ligh tly repe lled by

the magne tic fie ld . hese subs tances are sa id to have a negative

magneticsusceptibility .

Paramagnetic subs tances a lso exh ib it no magne tic proper ties ou ts ide

a magne tic fie ld . hen p laced in a magne tic fie ld , however , t hese


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subs tances exh ib it a s ligh t pos itive in terac tion with the ex terna l

magne tic fie ld and are s ligh tly a ttrac ted . he magne tic fie ld is

in tens ified with in the samp le caus ing an increase in the loca l magne tic

fie ld . hese subs tances are sa id to have a positive magnetic

susceptibility .

Ferromagnetic subs tances are u ite d iff eren t. hen p laced in a

magne tic fie ld they exh ib it an ex t reme ly s trong a ttrac tion to the

magne tic fie ld . he loca l magne tic fie ld in the cen tre o f the subs tance is

grea tly increased . hese subs tances such as iron) re ta in magne tic

proper ties when removed f rom the magne tic fie ld . bjec ts made o f f erromagne tic subs tances shou ld no t be brough t into the scan room as

they can become projec tiles ; be ing pu lled a t grea t speed toward the

cen tre o f the MR imager . A n objec t t ha t has become permanen tly

magne tized is re f erred to as a permanen t magne t.

A permanen t magne t, such as a bar magne t, has two po les and is

re f erred to as a d ipo le


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OTHER MAG ET I ALLY A TIVE

LEI

13 arbon

19F Fluorine31P Phosphorus

23 a Sodium

Hydrogen has a s ign ifican t magne tic momen t and is near ly %

abundan t in the human body . F or these reasons , we use on ly the

hydrogen pro ton in rou tine c linica l imag ing , and tha t is where we will

f ocus our a tten tion f rom here on .

The nuc leus o f the hydrogen a tom con ta ins a s ing le pro ton . B ecause o f

this , as prev ious ly men tioned , it possesses a s ign ifican t magne tic

momen t.

The pro ton will behave as a tiny bar magne t figure 6 ).


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Because o f the sp in charac ter is tics o f the pro ton , if it is p laced in a

largeex terna l magne tic fie ld , it will assume one o f two poss ib le

pos itions . It willa lign a t a s ligh t ang le) in e ither a para lle l or an ti para lle l

with thed irec tion o f the magne tic fie ld as shown in the figure 7) on the

nex t page .

In add ition to a lign ing with B , t he pro ton will precess a t some

f requency .

The f requency a t wh ich the pro ton precesses is g iven by the

Larmor Equa tion figure 8 ).

The Larmor Equa tion te lls us tha t t he precess iona l f requency is equa l

to the s treng th o f the ex terna l s ta tic magne tic fie ld B ) mu ltip lied by

the gyro-magne tic ra tio g) . Increas ing B will increase the precess iona l


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f requency and converse ly, decreas ing B will decrease the precess iona l

f requency . This is ana logous to a sp inn ing top . It will precess due to the

f orce o f grav ity.If the grav ity were to be decreased-(as it is on themoon)

then the top wou ld precess s lower .

Pl ac ing many pro tons in a magne tic fie ld , we find tha t some a lign an ti-

para lle l and a s ligh t major ity a ligns para lle l. P ro tons a ligned in the

para lle l or ien ta tion are sa id to be in a low energy s ta te . P ro tons in the

an ti-para lle l or ien ta tion are sa id to be in a high-energy s ta te as shown

in (figure 9) on the nex t page .

The energy d iff eren tia l be tween the h igh and low energy s ta tes

ispropor tiona l to the s treng th o f the ex terna lly app lied magne tic fie ld

B .

The grea ter the s treng th o f the ex terna l fie ld the grea ter the energy

d iff eren tia l be tween the two sp in s ta tes (figure ).Also re la ted to the

s treng th o f B is the number o f sp ins in the low energy s ta te . The

h igher the B , t he grea ter the number o f sp ins a ligned in the low-energy

s ta te . The number o f sp ins in the low energy s ta te inexcess o f the

number in the high-energy s ta te is re f erred to as the sp inexcess .


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nce the tissue has become magne tized , t ha t is the sp ins are in

e ither the high or low energy s ta te , a cond ition is reached nown as

therma l equ ilibr ium . It shou ld be no ted tha t a t equ ilibr ium , t he ind ividua l

sp ins crea ting the ne t magne tiza tion do no t precess in phase . This is

because o f s ligh t d iff erences in precess iona l f requenc ies caused by ,

among o ther th ings , magne tic fie ld inhomogen ities and d iff erences in

sma ll loca l magne tic fie lds genera ted w ithin each par ticu lar mo lecu le .

As a resu lt, the ne t magne tiza tion is a ligned para lle l with B bu t does

no t precess (figure12) .

Hydrogen ex is ts in many mo lecu les in the body . a ter (cons is ting o f

two hydrogen a toms and one oxygen) compr ises up to 7 % o f body

we igh t. H ydrogen is a lso presen t in f a t and mos t o ther tissues in the

body . Thevary ing mo lecu lar s truc tures and the amoun t o f hydrogen in var ious tissues e ff ec t how the pro tons behave in the ex terna l fie ld . As

one examp le , because o f the to ta l amoun t o f hydrogen in wa ter , it has

one o fthe s tronges t ne t magne tiza tion vec tors re la tive to o ther tissues .


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O thers truc tures and tissues within the body have less hydrogen

concen tra tionand become magne tized to a lesser ex ten t. I n o ther

words , t he ir ne tmagne tiza tion is less intense (figure 13 ).

The amoun t o f mob ile hydrogen pro tons tha t a g iven tissue possesses

re la tive to wa ter (spec ifica lly SF ), is re f erred to as its sp in

dens ity(pro ton dens ity) .This is the bas is with wh ich we beg in to

produce images us ing Magne ticResonance . The hydrogen nuc leus

con ta ins one pro ton and possesses as ign ifican t magne tic momen t. In add ition , hydrogen is very abundan t inthe human body . B y p lac ing the

pa tien t in a large ex terna l magne tic fie ld ,we magne tize the tissue

(hydrogen) , prepar ing it f or the MR imag ingprocess . In the nex t sec tion ,

we will look a t how this magne tiza tionbehaves in the presence o f an R F

fie ld . rea ting an MR Si gna lA rad io wave is ac tua lly an osc illa ting

e lec tromagne tic fie ld . The R F fie ld isa lso re f erred to as the B1 fie ld . It is

or ien ted perpend icu lar to the ma inmagne tic fie ld (B ). If we app ly a

pu lse o f R F energy in to the tissue a t the Larmor f requency , we firs t find

the ind ividua l sp ins beg in to precess inphase , as will the ne t

magne tiza tion vec tor . A s the R F pu lse con tinues ,some o f the sp ins in


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the lower energy s ta te absorb energy f rom the RFfie ld and make a

trans ition into the higher energy s ta te . Th is has thee ff ec t o f tipp ing the

ne t magne tiza tion toward the transverse p lane .F or the purpose o f this

exp lana tion , we will assume su ffic ien t energy isapp lied to produce a

9 -degree flip o f the ne t magne tiza tion . In such an examp le , it is sa id

tha t a 9 -degree flip ang le or a 9 -degree pu lsehas been app lied

(figure 14 ).

O r ien ted perpend icu lar to B is a rece iver co il. As the magne tiza tion

(nowre f erred to as transverse magne tiza tion , or Mxy)precesses through

therece iver co il, a curren t or s igna l is induced in the co il. The

pr inc ip lebeh ind th is s igna l induc tion is Faradays Law o f Induc tion . This

s ta tes tha tif a magne tic fie ld is moved through a conduc tor , a curren t

will beproduced in the conduc tor . If we increase the s ize o f the

magne tic fie ld ,or increase the speed with wh ich it moves , we will

increase the s ize o f thes igna l (curren t) induced in the conduc tor (figure

15) .


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In order to de tec t the s igna l produced in the co il, the transm itter mus tbe turned o ff. hen the RF pu lse is d iscon tinued , t he s igna l in the co il

beg ins a t g iven amp litude (de term ined by the amoun t o f

magne tiza tionprecesss ing in the transverse p lane and the precess iona l

f requency) and f ades rap id ly away .


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This initia l s igna l is re f erred to as the F ree Induc tionDecay or FID

(figure 16 ).

The s igna l f ades as the ind ividua l sp ins con tr ibu ting to the

ne tmagne tiza tion lose the ir phase coherence , mak ing the vec tor sum

equa lto zero (figure 17 overhead view o f the x-y p lane) .


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The FID decays a t a ra te g iven by the tissue re laxa tion parame ter

known as T2* (T2-s tar) .At t he same time , bu t independen tly, some o f

the sp ins tha t had moved in to the h igher energy s ta te g ive o ff the ir

energy to the ir la ttice and re turn to the lower energy s ta te , caus ing the

ne t magne tiza tion to regrow a long the z ax is . This regrow th occurs a t a

ra te g iven by the tissue re laxa tion parame ter known as T1 (figure 18).


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US ES O N ETIC R ESSON NC E I IN

N -m i l li i f N R

C I i l li i li R

The applications in industry are widespread. Routine analysis of

chemicals is probably the most common use but the NMR technique is

sufficiently flexible to be used for example to measure the water/fat

ratio in foods, monitor the flow of corrosive fluids in pipes, or to study

the structure of catalysts.

Industrial applications can be divided into chemical, biological,

paramedical, data processing, and non-destructive testing. This

overview is not exhaustive, but it gives some highlights of the possible

applications. It underlines the difficulties, challenges, and possibilities of

interdisciplinary research and teaching.

C mi l li i

l R m k

Hydrogen-1 (1 H) and carbon-1 (1 C) NMR spectroscopy of solutions

of chemicals are indispensible to the organic chemist in identifying the

products of the latest reaction. The analysis is quick and simple and

does not require an especially pure sample. This type of work is

probably the most common type of NMR work done throughout the

world and will continue to be so for many years. Yet, it does not begin

to hint at the enormous versatility of the NMR technique and the wide

range of information which can be obtained from different systems.


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O il a d C al al sis of low molecular weight fractions of oils can be

done by NMR, although other techniques do exist. The higher

molecular weight fractions which are very viscous or even solid are

more difficult to analy e but solid-state NMR techniques can be very

useful. Solid-state 1 C NMR has been performed on kerogens (an

immature type of coal). The information obtained when used in

con junction with other types of analysis can be used to predict if the

kerogen comes from a site which is gas-forming or oil-forming. Such

information is extremely valuable when planning an exploration and

drilling program. Among the possible new applications in this area is

the development of a transportable MRI/MRS system which can beflown into a potential drilling region.

Pl i P l m

Some samples are mainly of interest as solids. Important examples are

found in polymer science where it is the properties of the solid which

are important and not the individual subunits which go to make up the

solid. Solid-state NMR is used to study how plastics are put together, to

relate their chemistry with their known physical properties. This

information can be used to help improve the plastics and develop new

ones. There are very few alternatives to NMR for getting this type of

information from polymers.

Liq i C l

Liquid crystals are used in watches, calculators, and television and

computer screens. They are also very difficult to study by other means

than NMR. Just like the plastics, information about the packing of the


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molecules shows how structure relates to functional properties and so

can help in creating new products.

C m C

The study of the hydration process in cement is of great interest to the

industry. Increasing the speed of hydration and the degree of hydration

are both highly desirable since they increase the speed of setting and

the strength of the concrete. However, both processes were rather

difficult to quantify until it was shown that they can clearly be seen in

solid-state 2 Si spectra of cement. Changes in the concrete can be

followed over periods of 0 days or more and thereby one cancharacteri e the effect of different additives on the curing process.

Exp l i

Whilst it is not possible (or at least not safe) to examine explosives

directly it is possible to study chemical analogues of explosive s like

acetyl cellulose to improve understanding of the chemical structure of

such materials. By relating chemical structure with functional properties

one can help in the designing of safer and more efficient explosives.

Im i f S li i l

Imaging of solids is in its infancy. Like medical imaging the nucleus

being observed is 1 H, but unlike medical imaging where the signal is

relatively sharp and long lived, the signal from the proton in solidmaterials is generally rather difficult to detect since it is a very broad

signal which lasts for a relatively short time. The purpose of such

experiments would be to test non-destructively the various plastics and

polymers used increasingly in modern manufacturing.


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At present most published images are typically of a block of a solid

material with holes of varying si e drilled in it to demonstrate the

resolution of the technique. There is one recent example of the use of

MRI to observe solid rocket fuel prior to combustion. The packing of the

solid fuel can have a large impact upon the burning properties.

Conventional analytical techniques would either disturb the packing or

prevent the sample being used in an ignition experiment. By the use of

solid-state MRI it was possible to image samples before ignition tests

and so directly correlates the effect of packing on burning properties.

However, it was hardly more than twenty years ago that people were

publishing MRI cross-sections of lemons and other fruits. MRI is nowused routinely in hospitals throughout the world, and MRI of solids will

probably make substantial progress in the next ten years.

B i l i l pp li i

Water content and fat/water ratio are two important parameters in manymanufactured foodstuffs. Control of product quality may depend

critically on them, but the traditional chemical methods of

measurements may take between a few hours to a day to complete.

NMR methods exist to make such measurements in less than a minute

which is fast enough to help in the control of the production line. Some

companies already use spectrometers dedicated to this sort of work,

but there is still room for a huge expansion in the market.

A ma jor problem is that whilst the routine analysis is a totally trivial task,

it may take many weeks for a research scientist and a line manager to


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develop a suitable method for each particular analytical task, and the

number of suitably trained scientists is very small.

Another area of routine analysis is that of wine. The European

Community is currently developing an NMR test for the quality of wine,

particularly to detect glycol adulteration. A routine method for

determining the alcohol content in fermentation vats in two-three

minutes has recently been published. NMR is also useful as a research

tool in food science.

Agr i l re, restry, Env iro n m e n t

NMR techniques have only recently begun to be applied to plant

systems but one ma jor area already established is the phosphorus and

nitrogen nutrition of plants. Basic research in this area can hopefully

lead to a more efficient use of fertili ers and thereby lead to reduced

pollution of rivers, lakes, and the seas.

MR imaging of p la s s ms is even younger than spectroscopy but

in one study of frost damage in pot grown pine and spruce seedlings it

was possible to detect damaged and dead root systems weeks before

the shoots showed any sign of damage.

Co m pu ter App li tio n s nd P tter n Recog n itio n Tech n iq u es

With manifold tissue parameters, magnetic resonance imaging (MRI)

has a great variety of image contrast and substantial theoreticalpotential for tissue discrimination and even characteri ation in different

organs. This, on the one hand, is a ma jor advantage of MRI compared

with other imaging modalities; on the other hand, it may prove to be

disadvantageous because several series of images with different


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parameter weighting (i.e. proton density-, T1, and T2-weighting, pre-

and post-contrast) of the same region of the body have to be acquired.

This leads to several do en images per examination which have to be

read by the radiologist. Image reading and interpretation is basically

done as (a) analysis of morphology, and (b) analysis of signal behavior.

In general, MRI is a qualitative and sub jective examination with a high

level of uncertainty.

For routine clinical imaging, a simplification of the diagnostic procedure

would be advantageous. This would both cut down time and costs, as

well as diagnostic uncertainty. In addition, pattern recognition

techniques could lead to a preliminary diagnosis before images are

read and increase diagnostic performance. Tissue discrimination and

characteri ation on the basis of relaxation time calculations has been

shown to be unfeasible. Thus, other methods have to be considered.

Basic considerations must include: (a) MRI possesses several physical

parameters; (b) there are difficulties in computing and exploiting these

parameters; and (c) there is the possibility to devise a multivariate test(pattern recognition techniques), which will decrease the level of

uncertainty in the diagnosis and increase the diagnostic performance.

In general, MR images are crude and it is inappropriate to process

them by pattern recognition techniques, mainly because of geometrical

distortion, intensity distortion, and noise. However, first results have

demonstrated that computers can recogni e certain normal structures

and distinguish them from pathology. These methods could also be

applied to industrial use of MRI or other imaging techniques, e.g. for

quality assurance programs.


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No n -Destr u ct ive Test in g

Some applications of NMR in non-destructive testing have been

described before, e.g. the examination of plastic and ceramic

components. Here, a broad range of applications has been developed,

but the spectrum of possible new applications is wide. Space

technology will exploit the possibilities of NMR to assess the influence

of microgravity, acceleration, and vibration upon materials and their

possible degradation. Monitoring could be performed before and after

space flights, and with suitable equipment even in space. Quality

assurance programs with NMR include also measurement and control

of other techniques such as chromatography. Small, robust NMR

machines are already available, and machines for particular

applications custom-tailored for specific technical solutions can be

developed at competitive prices.


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BIBLIOGRAPHY

[1]. Wm Fulkner Basic Principles of MRI.

[2] Carr Herman (200 ). " Letter: Field Gradients in Early MRI". Physics

Today 57 ( ):

[3] Wikipedia www.wickipedia.org .

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