stem cell track

8/19/2019 Stem Cell Track

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STEM CELL TRACKING TECHNIQUES

SUBMITTED BY:

M.VINOTH,

MVM 09003,


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STEM CELL TRACKING TECHNIQUES

Introduction

Stem cells can be classified as embryonic stem (ES cells, ad!lt stem cells. "ein# $it%

t%e &otential of differentiation, stem cell %as been increasin#ly attracti'e in re#enerati'e

t%era&ies s!c% as t%e treatment of ar)inson*s disease, +l%eimer-s disease, myocardial

infarction, le!)emia, diabetes, and ot%er de#enerati'e disorders. +fter t%e systemic or local

trans&lantation, stem cells and &ro#enitor cells may be able to mi#rate and re&o&!late in

&at%olo#ic sites to brin# tremendo!s t%era&e!tic effect. Ho$e'er, ris) may %a&&en for t%e

misbe%a'ior follo$in# t%e stem cell trans&lantation, for eam&le, teratoma formation .

T%erefore, in vivo trac)in# t%e fate of t%e trans&lanted stem cells o'er time is a 'ital ste& in

determinin# t%e efficacy of t%e im&lant. /or a lon# time, st!dies on stem cell mobility

con'entionally re!ire %istolo#ical in'esti#ation to determine 'iable en#raftment of t%e

trans&lanted cells. Ho$e'er, t%e inability to 'is!alie cell &o&!lations in t%e same animal

o'er time %as been a ma1or bottlenec) in t%e in vivo e'al!ation of stem cell t%era&ies beca!se

#ro!&s of animals %a'e to be sacrificed at different time &oint for %istolo#y &!r&ose.

In recent years, t%e emer#in# and ad'ances of non2in'asi'e in vivo stem cell ima#in#

%as si#nificantly contrib!ted to t%e real2time trac)in# of #rafted stem cells as $ell as

monitorin# t%eir &roliferation, mi#ration and &ersistence in li'e animals .Stem cells carryin#

contrast a#ents (direct labelin# can be detected by o&tical, ma#netic resonance ima#in#

(MI or radion!clide ima#in# met%ods, s!c% as sin#le &%oton emission com&!ted

tomo#ra&%y (SE4T and &ositron emission tomo#ra&%y (ET (Norman et al .,59967

Ha$ryla) et al .,5993. In contrast to direct labelin# tec%ni!es, re&orter #ene tec%ni!es for

stem cell labelin# offer an attracti'e alternati'e beca!se ima#in# si#nals are #enerated only

from 'iable cells of interest. "y sensiti'e ima#in# de'ices s!c% as t%e o&tical co!&led de'ice,

MI, SE4T or ET, stem cells $it% t%e stably transfected ima#in# re&orter #enes can be


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detected $it% s!itable ima#in# &robes to 'is!alie t%eir distrib!tion, to lon#it!dinally monitor

t%e cell s!r'i'al and e'en to follo$ t%e s!ccessf!l differentiation of stem cells to mat!re

f!nctional cells in stem cell t%era&ies (4ao et al .,6008

Characteritic o! an Idea" I#a$in$ Techno"o$% !or Ste# Ce"" Trac&in$

Durin$ C"inica" Tria"

S!ccessf!l in 'i'o ima#in# re!ires t%at a contrast a#ent associated $it% a stem cell eert an

effect sie s!fficient for detection by ima#in# %ard$are. +lt%o!#% t%e most attracti'e

contrast a#ents for trac)in# are endo#eno!s ones (ie, normal com&onents of t%e stem cell,

t%eir effect sie is etremely small.

5. "iocom&atible, safe, and nontoic

6. No #enetic modification or &ert!rbation to t%e stem cell

3. Sin#le2cell detection at any anatomic location

:. ;!antification of cell n!mber


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T%e > c%aracteristics of an ideal ima#in# tec%nolo#y for stem cell trac)in# are &resented.

/irst, and foremost, t%e eo#eno!s contrast a#ent m!st be biocom&atible, safe, and nontoic.

T%is is es&ecially im&ortant $%en nanotec%nolo#y sol!tions to t%e trac)in# &roblem are

considered, beca!se most solid2state de'ices $ill be com&osed of materials t%at do not %a'e

&ro'en lon#2term safety in 'i'o.

+not%er consideration is t%e need for #enetic modification of t%e stem cell or &ert!rbation of

its #enetic &ro#ram by t%e contrast a#ent itself. Se'eral ima#in# tec%ni!es, s!c% as

enymatic con'ersion of an in1ected s!bstrate and rece&tor2based bindin#, re!ire stable

inte#ration of trans#enes. T%is strate#y may be combined $it% #enetic mani&!lation of stem

cell &o&!lations to en%ance t%e 'iability, differentiation, and co!&lin# of t%ese cells $it% t%e

myocardi!m. T%ese ty&es of mani&!lations add si#nificant cost, re#!latory roadbloc)s, and

t%e &otential to ind!ce #enetic abnormalities, incl!din# !ncontrolled #ro$t% and mali#nancy.

(Hacein2"ey2+bina et al .,6003 +lt%o!#% eo#eno!s #enes %a'e t%e distinct ad'anta#e of not

bein# dil!ted by cell di'ision and %a'e t%e &otential to ind!ce cell s!r'i'al or s!icide on

demand it is !nclear at &resent if t%e etra ste& of #enetic mani&!lation $ill become ro!tine in

%!man clinical stem cell trials.

Ideally, ima#in# tec%nolo#y !sed for stem cell trac)in# $o!ld %a'e sin#le2cell sensiti'ity and

$o!ld &ermit !antification of eact cell n!mbers at any anatomic location. Sin#le2cell

sensiti'ity is es&ecially im&ortant in a ne$ field s!c% as t%at of stem cells beca!se t%e &attern

of mi#ration of stem cells, e'en after local in1ection, is !n)no$n, and t%ere is a distinct

&ossibility t%at sin#le stem cells scattered diff!sely t%ro!#%o!t t%e body mi#%t be effecti'e

t%era&e!tics for certain disease states.

e#ardless of t%e le'el of sensiti'ity finally ac%ie'ed, !antification of cell n!mber can be

es&ecially diffic!lt $%en $e consider t%e effects of contrast a#ent dil!tion d!rin# cell

di'ision, t%e &ro&ensity of some contrast a#ents to be transferred to nonstem cells, and certain

tec%nical limitations . T%e criteria of !ltra2%i#% %i#% sensiti'ity, !antification, and f!ll2body

scannin# render many clinically a'ailable ima#in# modalities inade!ate at &resent.

T%e ideal ima#in# tec%nolo#y $o!ld &ermit trac)in# of in1ected stem cells for mont%s to

years beca!se clinical trials !ndo!btedly $ill re!ire lon#2term follo$2!& of tiss!e f!nction

or %ost s!r'i'al. /inally, in1ectable contrast a#ents, s!c% as enyme s!bstrates, add com&leity

and cost to stem cell trac)in# &roced!res


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I#a$in$ Moda"itie

Se'eral ima#in# modalities %a'e been !sed for t%e in'esti#ation of stem cell fates and

f!nction and a n!mber of !sef!l tools %a'e been de'elo&ed for cell fate ima#in# by eac% of

t%ese . Ima#es of bone marro$ and imm!ne cell traffic)in# %a'e been obtained by ma#netic

resonance ima#in# (MI, &ositron emission tomo#ra&%y (ET, and sin#le &%oton emission

com&!ted tomo#ra&%y (SE4T ("ennin) et al .,6009. Eac% of t%ese is !sed clinically for

dia#nostic a&&lications. In 'i'o biol!minescence ("?I and fl!orescence ima#in# may %a'e

t%eir #reatest a&&lication in t%e st!dy of small animal models, and %a'e been !sed to assess

t%e traffic)in# &atterns of cells in vivo. T%ere may be clinical a&&lications of t%ese tools, b!t

t%eir !se in small animal models $ill be in'al!able as t%ey are a&&lied to t%e st!dy of stem

cell biolo#y. T%e a'ailability of s&ecialied MI, ET, and SE4T scanners for small animal

ima#in# %as increased dramatically $it% im&ro'ed &erformance and ca&abilities. T%eir

increased !se in animal models $ill li)ely lead to translational a&&roac%es, and t%ey %old

#reat &romise for ad'ances in a n!mber of fields $%ere t%ere are clinical needs. T%ere are a

n!mber of o&tical ima#in# a&&roac%es t%at %a'e been de'elo&ed for sensin# and ima#in# in

t%e li'in# body, incl!din# diff!se o&tical tomo#ra&%y (@OT, o&tical co%erence tomo#ra&%y

(O4T, and ot%ers, b!t only in 'i'o "?I and fl!orescence %a'e been !sed to st!dy cell

traffic)in# &atterns. (Meral "e)sac, 6009

Recent ad'ance in nanotechno"o$% !or te# ce"" trac&in$


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Detection Method !or In (i'o Ste# Ce"" Trac&in$

Ma#netic esonance Ima#in#(MI

O&tical Ima#in#

o "iol!minescence ima#in#

o /l!orescence ima#in#

N!clear Ima#in#

o ositron Emission Tomo#ra&%y(ET

o Sin#le %oton Emission 4om&!ted Tomo#ra&%y (SE4T


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A2ay com&!ted microtomo#ra&%y (micro4T

La)e"

In order to be trac)ed !sin# any of t%e ima#in# modalities, cells of interest m!st be labeled

for detection. + n!mber of st!dies %a'e !sed eo#eno!s fl!orescent dyes to label cells o!tside

t%e body &rior to trans&lantation. +lt%o!#% t%ese dyes can %a'e a relati'ely intense si#nal, a

disad'anta#e of s!c% tec%ni!es is t%at t%ese dyes can be s%ort2li'ed, and as labeled cells

di'ide, t%e &ro#eny cells, de&endin# on t%e dye, may not be labeled and t%!s t%e si#nal is lost

o'er time d!e to dil!tion t%ro!#% cell di'ision. Some fl!orescent dyes do not &rod!ces!fficient si#nal to be detectable by cameras &laced o!tside t%e body, necessitatin# e!t%anasia

of t%e animal and tiss!e sam&lin# for analysis. /or t%ese reasons, t%e in 'i'o ima#in#

tec%ni!es, by and lar#e, %a'e re!ired t%e a&&lication of #enetic labels. T%ese BlabelsC are

#enes t%at m!st be introd!ced into cells and encode &roteins t%at interact $it% Bre&orter

&robes,C a&&lied s!bstrates (biol!minescence, or eo#eno!s ecitation li#%t so!rces

(fl!orescence to #enerate a si#nal t%at can be localied from o!tside t%e body.(%ao et

al .,6050


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Denetic labels %a'e been de'elo&ed for all of t%e modalities !sed in stem cell traffic)in#

st!dies.

La)e" !or *ET+S*ECT+MRI

T%e most commonly !sed #enetic label for ET ima#in# is t%e %er&es sim&le 'ir!s

t%ymidine )inase (HSV52t). +t t%e time of ima#in#, 5>/F2/H"D or 56:IF2/I+G is

administered to t%e animal as a radioacti'e re&orter &robe t%at %as s&ecificity for t%is T

enyme. T%e &robe is trans&orted into cells and is &%os&%orylated by t%e T &rotein only in

t%e #enetically labeled cells. T%e &%os&%orylated &robe becomes tra&&ed in t%e cell and

acc!m!lates t%ere, &referentially fla##in# t%e #enetically labeled cells for detection. T%e

%!man do&amine @6 rece&tor (%@6, t%e %!man somatostatin rece&tor (%SST6, and t%e

%!man transferrin rece&tor (%Tf %a'e been !sed $it% different ima#in# modalities and

f!nction sim&ly as transmembrane rece&tors t%at acti'ely trans&ort t%eir corres&ondin#

re&orter &robes into t%e #enetically labeled cells. In t%is manner, li)e HSV52t), t%ey also


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acc!m!late t%e &robe $it%in t%e labeled cells to fla# t%em for detection.

Sche#atic o'er'ie, o! #o"ecu"ar i#a$in$ ,ith re-orter $ene trate$ie. A 'ector

containin$ a DNA re-orter contruct ,ith the re-orter $ene/0 dri'en )% a -eci!ic

-ro#oter. Trancri-tion and tran"ation "ead to the e1-reion o! #RNA and re-orter

-rotein+ re-ecti'e"%. A!ter ad#initration o! a corre-ondin$ re-orter -ro)e

%te#ica""%+ the re-orter -ro)e ,i"" )e cata"%2ed )% -eci!ic ce"" that ha'e the re-orter

-rotein. The i$na" occurred in thi a#-"i!ication -roce can )e detected )% a

eniti'e i#a$in$ de'ice. E1a#-"e o! re-orter $ene and their -eci!ic re-orter -ro)e

are de"ineated )% i#a$in$ #oda"it%. 3"uc+ 3ire!"% "uci!erae4 *ET+ -oitron e#iion

to#o$ra-h%4 S*ECT+ in$"e -hoton e#iion co#-uted to#o$ra-h%4 hNIS+ hu#an


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odiu#5iodide %#-orter4 MRI+ #a$netic reonance i#a$in$4 CCD+ char$ed cou-"ed

de'ice4 BLI+ )io"u#inecence i#a$in$.

La)e" !or )io"u#inecence o-tica" i#a$in$

/l!orescence and biol!minescence o&tical ima#in# modalities re!ire t%e #eneration of li#%t

by t%e cells of interest.Denetic labels for "?I are #enes t%at encode l!ciferases.T%e Bre&orter

&robesC for t%ese &roteins are s!bstrates t%at are oidied and c%emically cons!med by t%e

l!ciferases in reactions t%at #enerate li#%t. /l!orescence ima#in# detects cells t%at e&ress

fl!orescent &roteins. "y analo#y to ET and SE4T, t%e Bre&orter &robeC t%at m!st be

deli'ered to t%ese #enetically labeled cells is eo#eno!s li#%t of t%e a&&ro&riate $a'elen#t%

to ser'e as an ecitation so!rce.

In c%oosin# a label for o&tical ima#in#, a fe$ )ey &arameters m!st be considered.

S&ecifically, absor&tion and s!bstrate biodistrib!tion si#nificantly infl!ence t%e be%a'ior of

t%e e&erimental system. In t%e intact animal, absor&tion of li#%t by tiss!e, and in &artic!lar

absor&tion by %emo#lobin, atten!ates t%e detectable si#nal #enerated by cells of interest. ed

and infrared li#%t ($a'elen#t%s 800 nm s!ffers less si#nal atten!ation in t%e body d!e to

absor&tion t%an does li#%t $it% s%orter $a'elen#t%s (J800 nm. T%is is an ad'anta#e to

firefly l!ciferase (/l!c7 deri'ed from t%e Nort% +merican /irefly %otin!s &yralis and clic)

beetle red l!ciferase (4"l!c7 deri'ed from Pyrophorus plagiophalam o'er enilla

l!ciferase (l!c7 deri'ed from t%e sea &ansy Renilla reniformisKbot% /l!c and 4"l!c

s%o$ emission &ea)s at a&&ro 860 nm at body tem&erat!re, $%ereas t%e emission &ea) of

l!c is at :>0 nm, in a re#ion $%ere absor&tion by %emo#lobin is relati'ely %i#%. T%e

biodistrib!tion of t%e administered s!bstrate is also an im&ortant consideration for

inter&retin# "?I data. To obtain !antitati'e information from "?I data, t%e s!bstrate m!st

not be limitin# in t%e oidation reaction t%at #enerates li#%t. T%erefore, &ro&er ima#in#

tec%ni!e re!ires a&&ro&riate timin# from t%e administration of s!bstrate to t%e ac!isition

of data. T%e o&timal time from administration to ac!isition de&ends !&on bot% t%e ro!te of

administration and t%e rate of clearance of t%e s!bstrate in t%e body. T%e s!bstrate for /l!c

and 4"l!c, @2l!ciferin, is relati'ely stable in t%e body and %as a relati'ely lon# circ!lation

time. In contrast, t%e s!bstrate for l!c, coelenteraine, is ra&idly cleared from t%e body and

binds to ser!m &roteins( L%ao, H et al.,600


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min!te after in1ection. @2?!ciferin can be in1ected intra&eritoneally or intra'eno!sly

("%a!mi) et al .,6006. T%e biodistrib!tion of @2l!ciferin, after intra&eritoneal in1ection,

&ea)s at 5


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In an MI mac%ine a radio fre!ency transmitter is briefly t!rned on, &rod!cin# an

electroma#netic field. T%e &%otons of t%is field %a'e 1!st t%e ri#%t ener#y, )no$n as t%e

resonance fre!ency, to fli& t%e s&in of t%e ali#ned &rotons in t%e body. +s t%e intensity and

d!ration of a&&lication of t%e field increase, more ali#ned s&ins are affected. +fter t%e field is

t!rned off, t%e &rotons decay to t%e ori#inal s&in2do$n state and t%e difference in ener#y

bet$een t%e t$o states is released as a &%oton. It is t%ese &%otons t%at &rod!ce t%e

electroma#netic si#nal t%at t%e scanner detects. T%e fre!ency t%e &rotons resonate at

de&ends on t%e stren#t% of t%e ma#netic field. T%is ca!ses t%e n!clei to &rod!ce a rotatin#

ma#netic field detectable by t%e scanner and t%is information is recorded to constr!ct an

ima#e of t%e scanned area of t%e body (S!ire ?/, No'elline + 599=

Di'en its etraordinary 32dimensional ca&abilities and %i#% safety &rofile, ma#netic

resonance ima#in# (MI is t%e ima#in# modality !sed by most researc% st!dies to trac) stem

cells in 'i'o. +t t%is &oint in time, MI ima#in# tec%ni!es can be di'ided into t%ose

#eneratin# &rimarily T5 contrast and t%ose #eneratin# &rimarily T6T6P contrast.

T6 contrat

T5 contrast a#ents are t%ose t%at !tilie t%e lant%anide #adolini!m (Dd3Q, $%ic% c%an#es t%e

relai'ity of &rotons from associated $ater molec!les and increases t%e si#nal on T52

$ei#%ted ima#es. Gnfort!nately, $it% &resently a'ailable field stren#t%s, Dd3Q2based contrast

re!ires


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MIONs can be !sed to trac) etremely small n!mbers of stem cells, on t%e order of

t%o!sands, at %i#% field stren#t%s, for !& to se'eral $ee)s. T6T6P contrast a#ents ( @aldr!&2

?in) et al 6009 and t%eir tec%nical im&ro'ements( ?e$in et al., 6000 already %a'e been

a&&lied by many #ro!&s for stem cell trac)in# in 'i'o. Most s!&er&arama#netic form!lations

a&&ear to be biocom&atible, safe, and nontoic, and some already %a'e been a&&ro'ed by t%e

GS /ood and @r!# +dministration.

In 'i'o MR i#a$e /to-0 9 da% a!ter inection o! 6.; < 6=; BMSC "a)e"ed ,ith 7 >"

M*I? 5 #" #ediu# into a rat )rain ,ith a o"id tu#or eta)"ihed a ,ee& -rior to

BMSC inection. Re$ion #ar&ed )% dahed "ine and arro, -oint to area o!

h%-ointene i$na"+ indicatin$ the -reence and #i$ration o! BMSC containin$ M*I?.

The nu#)er re!er to the che#atic dra,in$ in the inet+ ho,in$ the inection ite o!

tu#or and BMSC .


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Re-reentati'e tran#iion e"ectron #icroco-% o! BMSC "a)e"ed !or 7@ h ,ith 7 >"

M*I? 5#" #ediu#. N+ nuc"eu4 arro, indicate an iron #icro-here /Nohroudi et

al .+7=6=0

Ad'anta$e

MI scan is %armless to t%e &atient. It !ses stron# ma#netic fields and non2ioniin# radiation,

!nli)e 4T scans and traditional A2rays !se ioniin# radiation.Hi#% s&atial

resol!tion,O!tstandin# anatomic ima#in#,MI meets t%e re!irements of &enetration de&t%

and clinical a'ailability (Himmelreic% et al.,600>

Diad'anta$e

T%e &roblems $it% s!&er&arama#netic &articles incl!de dil!tion of contrast $it% cell di'ision7

diffic!lty in !antification beca!se of s!sce&tibility artifact7 and t%e &otential transfer of

contrast to non stem cells, s!c% as macro&%a#es, after stem cell deat%. (Himmelreic% et

al.,600>

+ si#nificant clinical &roblem common to all MI met%ods is t%at certain im&lantable

de'ices, s!c% as &acema)ers and defibrillators, are c!rrently contraindications to scannin#.

+lt%o!#% a recent re&ort s!##ests t%at &atients $it% &acema)ers can be scanned safely at 5.< T

(Martin et al.,600:

Ra%Baed Method

ra% co#-uted to#o$ra-h% /CT0 is a medical ima#in# met%od em&loyin# tomo#ra&%y

created by com&!ter &rocessin#. @i#ital #eometry &rocessin# is !sed to #enerate a


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t%reedimensional ima#e of t%e inside of an ob1ect from a lar#e series of t$o2dimensional A2

ray ima#es ta)en aro!nd a sin#le ais of rotation.( Herman, D. T et al.,6009

4T &rod!ces a 'ol!me of data $%ic% can be mani&!lated, t%ro!#% a &rocess )no$n as

$indo$in#, in order to demonstrate 'ario!s bodily str!ct!res based on t%eir ability to bloc)

t%e A2ray beam. +lt%o!#% %istorically t%e ima#es #enerated $ere in t%e aial or trans'erse

&lane, ort%o#onal to t%e lon# ais of t%e body, modern scanners allo$ t%is 'ol!me of data to

be reformatted in 'ario!s &lanes or e'en as 'ol!metric (3@ re&resentations of str!ct!res

lain films and com&!ted tomo#ra&%y (4T are t%e most readily a'ailable clinical ima#in#

modalities. Gnfort!nately, contrast

#eneration re!ires etremely %i#% concentrations of %i#%2density%i#%atomic n!mber materials s!c% as iodine, #adolini!m, or metals. To render a stem

cell or collection of stem cells 'isible by !sin# e'en a solid metal, t%e 'ol!me of metal

associated $it% t%e cell 'ol!me m!st be e!al to or #reater t%an t%e in'erse of its density. /or

eam&le, it $o!ld ta)e a&&roimately one ei#%t% of t%e cell 'ol!me in solid iron to #enerate a

si#nal abo'e bac)#ro!nd d!rin# 4T scannin#. S!c% contrast is diffic!lt to ac%ie'e, renderin#

2raybased met%ods !nli)ely to &lay a direct role in stem cell trac)in# at t%e &resent time.

(/ran#ioni et al.,6009

MicroCT in vivo Ce"" Trac&in$

Microtomo#ra&%y !ses 2rays to create cross2sections of a 3@2ob1ect t%at can be !sed to

recreate a 'irt!al model $it%o!t destroyin# t%e ori#inal model. T%e term micro is !sed to

indicate t%at t%e &iel sies of t%e cross2sections are in t%e micrometer ran#e.T%ese &iel

sies %a'e also res!lted in t%e terminolo#y micro2com&!ted tomo#ra&%y, micro2ct, micro2

com&!ter tomo#ra&%y, %i#% resol!tion 2ray tomo#ra&%y, and similar terminolo#ies. +ll of

t%ese names #enerally re&resent t%e same class of instr!ments.

T%is also means t%at t%e mac%ine is m!c% smaller in desi#n com&ared to t%e %!man 'ersion

and is !sed to model smaller ob1ects. In #eneral, t%ere are t$o ty&es of scanner set!&s. In one

set!&, t%e A2ray so!rce and detector are ty&ically stationary d!rin# t%e scan $%ile t%e

sam&leanimal rotates. T%e second set!&, m!c% more li)e a clinical 4T scanner, is #antry

based $%ere t%e animals&ecimen is stationary in s&ace $%ile t%e A2ray t!be and detector


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rotate aro!nd. T%ese scanners are ty&ically !sed for small animals (in-vivo scanners,

biomedical sam&les, foods, microfossils, and ot%er st!dies for $%ic% min!te detail is desired.

T%e first A2ray microtomo#ra&%y system $as concei'ed and b!ilt by im Elliott in t%e early

59>0s. T%e first &!blis%ed A2ray microtomo#ra&%ic ima#es $ere reconstr!cted slices of a

small tro&ical snail, $it% &iel sie abo!t 6 Many belie'e

t%at t%e tec%nolo#y did not really ta)e off !ntil t%e ad'ent of t%e cone beam reconstr!ction

al#orit%m ori#inally a!t%ored by ?ee /eld)am&

Micro4T is similar to con'entional 4T systems !s!ally em&loyed in medical dia#noses and

ind!strial a&&lied researc%, b!t !nli)e t%ese systems, $%ic% ty&ically %a'e a maim!m s&atial

resol!tion of abo!t 0.< mm, ad'anced micro4T is ca&able of ac%ie'in# a s&atial resol!tion !&

to 0.3 Rm, abo!t t%ree orders of ma#nit!de lo$er. Gse of sync%rotron A2rays %as se'eral

ad'anta#es com&ared to laboratory or ind!strial A2 ray so!rces, s!c% as %i#% s&atial

resol!tion and a $ide ran#e of #reyscale 'al!es (corres&ondin# to different A2ray absor&tion

coefficients $it%in and amon# datasets (+s%brid#e et al.,6003.

More recently Sync%rotron adiation (S micro4T systems $ere made a'ailable also for

ima#in# small animals in vivo, s!c% as for t%e eamination of li'in# rats or mice . T%e #reat

ad'anta#e of s!c% systems is to enable lon#it!dinal st!dies, t%!s red!cin# t%e effect of

biolo#ical 'ariability in t%e co%ort. T%e first in vivo lon#it!dinal st!dy re&orted alterations of

bone micro2arc%itect!re in t%e %ind limb loaded female rats("oyd et al .,60080. In vivo

micro4T $as also !sed to monitor microarc%itect!ral c%an#es in o'ariectomied rats at t%e

tibial meta&%yses. It is a non2in'asi'e tec%ni!e #i'in# inte#ral information abo!t t%e content

of ma#netic material alon# t%e beam direction as $ell as a relati'e local sna&s%ot of t%ema#netic nano&article distrib!tion in relation to t%e n!mber of slices . Micro4T &ro'ides %i#%

s&atial resol!tion ima#es (from 50 Rm to 5 Rm $it% %i#% si#nal2to2noise ratio. In &re'io!s

st!dy (Torrente, et al., 6009.$e s%o$ed t%at A2ray micro4T analysis is able to detect stem

cells, &re'io!sly labeled $it% nano&articles of iron oide, inside s)eletal m!scles of

dystro&%ic mice after intra2arterial trans&lantation, &ro'idin# biolo#ical insi#%ts into t%e early

&rocesses of m!scle stem cell %omin#.


17/36

T%is tec%ni!e also offers t%e &ossibility of obtainin# a !antification of t%e n!mber of cells

t%at are able to mi#rate from t%e blood stream inside t%e m!scle tiss!e, and a 3@ 'is!aliation

of t%eir distrib!tion. One #ro!& analyed nine m!sc!lar bio&sies trans&lanted $it% t%ree

different n!mbers of stem cells labeled $it% iron2oide nano&articles, at t%ree different times

after in1ection. T%e different timin# in'esti#ated did not s%o$ differences in t%e location of

stem cells, $%ile t%e 'ariation in stem cells n!mber allo$ed !s to o&timie t%e e&erimental

conditions and identify


18/36

li#%t in tiss!es, t%e red2s%ift (com&ared to t%e ot%er systems of t%is emission ma)es

detection of firefly l!ciferase m!c% more sensiti'e in vivo.

• enilla l!ciferase re!ires its s!bstrate, coelenteraine, to be in1ected as $ell. +s

o&&osed to l!ciferin, coelenteraine %as a lo$er bioa'ailability .+dditionally, t%e &ea)

emission $a'elen#t% is abo!t :>0 nm.

• "acterial l!ciferase %as an ad'anta#e in t%at t%e lux o&eron !sed to e&ress it also

encodes t%e enymes re!ired for s!bstrate biosynt%esis. Gnfort!nately, t%is system

%as not yet been ada&ted for mammalian cell e&ression .T%is l!ciferase reaction %as a

&ea) $a'elen#t% of abo!t :90 nm.

%ile t%e total amo!nt of li#%t emitted from biol!minescence is ty&ically small and not

detected by t%e %!man eye, an !ltra2sensiti'e 44@ camera can ima#e biol!minescence from

an eternal 'anta#e &oint.

"iol!minescence !tilies li#%t #enerated by t%e enyme l!ciferase to detect cells in vivo. /o!r

&!blis%ed st!dies, 3 in mice (an# A et al., 6003,Tan# et al., 6003,4ao + et al , 600:and5 in rats, (! 4 et al ., 6003!tilied biol!minescence to trac) t%e distrib!tion and

en#raftment of stem cells in vivo. Gnfort!nately, l!ciferase #enes and s!bstrates described to

date #enerate only 'isible (:00 to =00 nm li#%t, $%ic% %as 'ery %i#% absor&tion and scatter in

li'in# tiss!e. T%is &recl!des !se of t%e tec%ni!e in animals lar#er t%an rats, and e'en in mice

false2ne#ati'e scannin# can occ!r, de&endent on cell de&t%.( ice " et al ., 6005

"iol!minescence also re!ires t%e stable e&ression of non%!man #enes, and t%e in1ection of

%i#% concentrations of &otentially imm!no#enic, non%!man s!bstrates, s!c% as l!ciferin and

coelenteraine. It is t%erefore !nli)ely t%at t%is tec%ni!e $ill be !sed clinically.


19/36

Location o! )io"u#inecent !oci !o""o,in$ tran-"antation o! tran$enic "uc

he#ato-oietic te# ce"" /HSC0

3"uorecence i#a$in$

/l!orescence ima#in# !tilies or#anic (e#, #reen fl!orescent &rotein, small2molec!le

&olymet%ines or or#anicinor#anic %ybrids (e#, !ant!m dots as eo#eno!s contrast a#ents

for in 'i'o ima#in# ( /ran#ioni et al .,6003. "eca!se of %i#% &%oton absor&tion and scatter at

'isible $a'elen#t%s, only near2infrared (NI (=00 to 5000 nm fl!oro&%ores %a'e clinical

&otential. T%e ma1or &roblem $it% NI fl!orescence is t%at e'en $it% tomo#ra&%ic ima#in#

met%ods, detection is limited to only : to 50 cm of tiss!e (Ntiac%ristos et al and Se'ic)2

M!raca et al. Hence, clinical !se of NI fl!orescence li)ely $ill be limited to near2s!rface


20/36

a&&lications, s!c% as intrao&erati'e ima#in#. + ma1or ad'anta#e of NI fl!orescence is its

com&atibility $it% con'entional microsco&y, (La%eer et al .,6009 &ermittin# sin#le2cell

detection of stem cells in &at%olo#ical s&ecimens. E 'i'o %istolo#ical detection of stem cells

!ndo!btedly $ill be re!ired in clinical trials. Ma1or disad'anta#es of NI fl!orescence are

t%e dil!tion of t%e a#ent $it% eac% cell di'ision and t%e &ossibility of !&ta)e by nonstem cells

after stem cell deat%.

U"traound

"eca!se cardiolo#ists li)ely $ill cond!ct t%e ma1ority of clinical st!dies of stem cells in

cardio'asc!lar a&&lications, trac)in# by ec%ocardio#ra&%y $o!ld be etremely con'enient.

4ontrast for ec%ocardio#ra&%y is #enerated by aco!stic interfaces s!c% as $ater#as (e#,

microb!bbles, &erfl!orocarbons. +lt%o!#% a sin#le !nit of contrast is on t%e order of 0.6< to

5 Rm in diameter, t%e #enerated aco!stic &ert!rbation a&&ears m!c% lar#er. Ec%ocardio#ra&%y

t%erefore %as t%e &otential to detect a sin#le cell loaded $it% a sin#le !nit of

contrast(libano' et al .,600>.Ne'ert%eless, met%ods to acc!m!late contrast intracell!larly

are not yet rob!st, and effects on cell motility, etc, are not )no$n. +n additional &roblem is

t%at ec%o#enic contrast a#ents cast an aco!stic s%ado$ belo$ t%e first !nit of contrast

detected, t%!s &recl!din# acc!rate !antification of cell n!mber. S!c% contrast a#ents are

s!b1ect to dil!tion d!rin# cell di'ision and transfer to nonstem cells after cell deat%. /inally,

s&atial resol!tion of !ltraso!nd is limited, and many anatomic sites are inaccessible.(fran#ioni

et al .,600>

Sin$"e*hoton E#iion Co#-uted To#o$ra-h%

Sin$"e -hoton e#iion co#-uted to#o$ra-h% /S*ECT+ or "e co##on"%+ S*ET0 is a

n!clear medicine tomo#ra&%ic ima#in# tec%ni!e !sin# #amma rays. It is 'ery similar to

con'entional n!clear medicine &lanar ima#in# !sin# a #amma camera. Ho$e'er, it is able to

&ro'ide tr!e 3@ information. T%is information is ty&ically &resented as cross2sectional slices

t%ro!#% t%e &atient, b!t can be freely reformatted or mani&!lated as re!ired.

SE4T ima#in# is &erformed by !sin# a #amma camera to ac!ire m!lti&le 62@ ima#es ,

from m!lti&le an#les. + com&!ter is t%en !sed to a&&ly a tomo#ra&%ic reconstr!ction

al#orit%m to t%e m!lti&le &ro1ections, yieldin# a 32@ dataset. T%is dataset may t%en be


21/36

mani&!lated to s%o$ t%in slices alon# any c%osen ais of t%e body, similar to t%ose obtained

from ot%er tomo#ra&%ic tec%ni!es, s!c% as MI, 4T, and ET.

SE4T is similar to ET in its !se of radioacti'e tracer material and detection of #amma

rays. In contrast $it% ET, %o$e'er, t%e tracer !sed in SE4T emits #amma radiation t%at is

meas!red directly, $%ereas ET tracer emits &ositrons $%ic% anni%ilate $it% electrons !& to a

fe$ millimeters a$ay, ca!sin# t$o #amma &%otons to be emitted in o&&osite directions. +

ET scanner detects t%ese emissions coincident in time, $%ic% &ro'ides more radiation

e'ent localiation information and t%!s %i#%er resol!tion ima#es t%an SE4T ($%ic% %as

abo!t 5 cm resol!tion. SE4T scans, %o$e'er, are si#nificantly less e&ensi'e t%an ET

scans, in &art beca!se t%ey are able to !se lon#er2li'ed more easily2obtained radioisoto&es

t%an ET.

Hi#%2ener#y #amma rays emitted by radioacti'e atoms as 99mTc, 555In, and 563I are detected by

rotatin# a collimated #amma camera aro!nd t%e s!b1ect and reconstr!ctin# a 32dimensional

ima#e. T%ree strate#ies for in 'i'o stem cell detection %a'e been describedU direct loadin#

$it% a radiometal,( Dao et al .,600= enymatic con'ersion and retention of a radioacti'e

s!bstrate (re'ie$ed in Damb%ir et al, and rece&tor2mediated bindin#.

@irect loadin# is &roblematic #i'en t%e tradeoff bet$een %alf2life and lon#2term e&os!re to

ioniin# radiation and #i'en t%e &ossibility of transfer of t%e radiometal from stem cells to

nonstem cells.

Enymatic con'ersionretention %as been !sed for bot% sin#le2&%oton emission 4T (SE4T

and &ositron emission tomo#ra&%y (ET s!bstrates. T%e si#nificant ad'anta#es of t%is

strate#y incl!de t%e ability to follo$ stem cells indefinitely after stable inte#ration of t%e

trans#ene, t%e absence of mar)er dil!tion by cell di'ision, and t%e ability to destroy stem cells

by administration of a s!icide dr!# s&ecific for t%e enyme. T%e disad'anta#es of t%is strate#y

incl!de t%e need to #enetically mani&!late t%e stem cell e 'i'o and t%e need to administer a

s!bstrate intra'eno!sly for eac% ima#in# session.

ece&tor2mediated tar#etin# re!ires stable e&ression of a rece&tor not fo!nd else$%ere in

t%e body and intra'eno!s in1ection of a radioacti'e rece&tor li#and. (Simono'a et al .,6008

*oitron E#iion To#o$ra-h%


22/36

ositron emission tomo#ra&%y (ET is a n!clear medicine ima#in# tec%ni!e $%ic%

&rod!ces a t%ree2dimensional ima#e or &ict!re of f!nctional &rocesses in t%e body. T%e

system detects &airs of #amma rays emitted indirectly by a &ositron2emittin# radion!clide

(tracer, $%ic% is introd!ced into t%e body on a biolo#ically acti'e molec!le. Ima#es of tracer

concentration in 32dimensional or :2dimensional s&ace $it%in t%e body are t%en reconstr!cted

by com&!ter analysis. In modern scanners, t%is reconstr!ction is often accom&lis%ed $it% t%e

aid of a 4T A2ray scan &erformed on t%e &atient d!rin# t%e same session, in t%e same

mac%ine.

ET !tilies coincident detection of 6 anti2&arallel / c%emistry, a ET

scanner, and radiation e&os!re (albeit it intermittent to t%e stem cells and s!b1ect.

+dditional ca'eats for SE4T2 and ET2based trac)in# of stem cells incl!de nons&ecific

!&ta)e of t%e radiotracer by normal tiss!e, relati'ely lo$ efficiency of collimated SE4T

cameras, and &%oton atten!ation by tiss!e. +lt%o!#% tiss!e &%oton atten!ation can be

corrected in some cases, for eam&le by em&loyin# %ybrid n!clear medicine4T systems, it

red!ces sensiti'ity, and &re'ents acc!rate !antification of stem cell n!mber (4%in "" et

al.,6003. %et%er !sed for atten!ation correction or not, %ybrid 4T systems %a'e t%e ma1or

ad'anta#e t%at t%ey &ermit co re#istration of anatomic (4T and &%ysiolo#ical (SE4T or

ET ima#es.

+not%er (often o'erloo)ed iss!e is t%e in%erent limits of radioacti'e met%ods for stem cell

detection. + ty&ical &atient dose of 50 to 60 m4i is e!i'alent to only 3.< to =50 56

radioacti'e molec!les of contrast a#ent. In ty&ical clinical n!clear medicine ima#in#, 509

radioacti'e molec!les &er milliliter are re!ired to #enerate detectable si#nal abo'e


23/36

bac)#ro!nd (+nt%ony ar)er. To detect a sin#le stem cell, 0.05 of t%e in1ected dose $o!ld

%a'e to be concentrated inon t%e cell, $%ic% is a formidable tec%nical c%allen#e.

esol!tion in ET is less t%an t%at $%ic% can be ac%ie'ed by MI, b!t t%e cross2sectional

information and t%ree2dimensional (3@ reconstr!ction ca&ability offer t%e &otential to be

more informati'e t%an t%e ty&ical &lanar &ro1ection data obtained !sin# o&tical ima#in#

tec%ni!es (im et al.,600:

Co#-are *ET and S*ECT

SE4T is similar to ET in its !se of radioacti'e tracer material and detection of #amma

rays. In contrast $it% ET, %o$e'er, t%e tracer !sed in SE4T emits #amma radiation t%at is

meas!red directly, $%ereas ET tracer emits &ositrons $%ic% anni%ilate $it% electrons !& to a

fe$ millimeters a$ay, ca!sin# t$o #amma &%otons to be emitted in o&&osite directions. +

ET scanner detects t%ese emissions coincident in time, $%ic% &ro'ides more radiation

e'ent localiation information and t%!s %i#%er resol!tion ima#es t%an SE4T ($%ic% %as

abo!t 5 cm resol!tion. SE4T scans, %o$e'er, are si#nificantly less e&ensi'e t%an ET

scans, in &art beca!se t%ey are able to !se lon#er2li'ed more easily2obtained radioisoto&es

t%an ET.

T%e ET and SE4T radion!clide ima#ine tec%ni!es allo$ t%e ima#in# of radiolabeled

mar)ers and t%eir interaction $it% bioc%emical &rocesses in li'in# animals. @!e to t%eir

nanomolar (J5029 M sensiti'ity, ET and SE4T are able to meas!re biolo#ical &rocess at

'ery lo$ concentrations. T%e mass of radiotracer in1ected is etremely small and does not

im&act t%e biolo#ical system !nder st!dy. Tec%nolo#ical de'elo&ments of bot% ET and

SE4T %a'e led to t%e im&lementation of s&ecialied systems for small animals ima#in#,

$it% a better s&atial resol!tion (J6 mm and conse!ent ad'ancement in t%e field of cell

trac)in# in animals model in vivo.

In #eneral a radioisoto&e $it% a relati'ely lon# decay %alf life is !se to enable t%e trac)in# of

cells o'er &eriod of se'eral %o!rs, or e'en days (555In T WX 6.>days. N!mero!s cell trac)in#

e&eriments %a'e been &erformed !sin# cells labeled $it% a radioacti'e mar)ers.

555In2labeled cells %a'e been $idely !sed in %!mans in localiin# areas of inflammation by

ima#in# t%e le!)ocyte distrib!tion . /!rt%ermore, 555In2labeled cells %a'e been a&&lied in


24/36

'ario!s e&erimental settin#s in animals to determine mi#ration of dendritic cells ,

biodistrib!tion of trans&lanted %e&atocytes and e'en %omin# of in1ected mesenc%ymal stem

cells (MS4s in animal models . Micro2sin#le2&%oton2emission2com&!ted2tomo#ra&%y

(microSE4T4T small animal ima#in# system and an /@+2a&&ro'ed radiotracer (555In

oy!inoline, %as been !se to demonstrate t%at monocyte recr!itment to at%erosclerotic

lesions. it% a nonin'asi'e, dynamic, and t%ree2dimensional fas%ion in li'e animals it is

&ossible to trac) t%e monocytes recr!itment to t%e at%erosclerotic lesions in a&oli&o&rotein E2

deficient (+&oE2 2 mice. T%e lon# %alf2life of 555In (6.> days enabled t%e detection of

monocytes for !& to se'en days after ado&ti'e transfer, and t%e %i#%2resol!tion anatomical

data deri'ed from 4T allo$ed localiation of %ots&ots of monocyte infiltration in a s!b2

millimeter ran#e. Non in'asi'e radion!clide ima#in# is also $ell s!ited to dynamically trac)

t%e biodistrib!tion and traffic)in# of mesenc%ymal stem cells to bot% tar#et and non tar#et

or#ans. MS4s isolated from bone marro$ %a'e t%e ability to differentiate into m!lti&le cell

linea#es incl!din# osteocytes, c%ondrocytes, and cardiac myocytes. T%e recent ability to label

MS4s $it% radiotracers &ro'ides a met%od to serially assess t%e biodistrib!tion of t%ese stem

cells after intra'eno!s administration $it% t%e !se of radio2n!clide ima#in# as $ell as to

determine t%e %omin# &otential of MS4s to sites of in1!ry (raitc%man et al .,600

%o!rs after in1ection. /ocal and diff!se !&ta)e of MS4s in t%e infarcted myocardi!m $as

already 'isible in SE4T4T ima#es in t%e first 6: %o!rs after in1ection and &ersisted !ntil

se'en days after in1ection and $as 'alidated by tiss!e co!nts of radioacti'ity. Ne'ert%eless,

SE4T2 and ET2based trac)in# of stem cells incl!de nons&ecific !&ta)e of t%e radiotracer

by normal tiss!e, relati'ely lo$ efficiency of collimated SE4T cameras, and &%oton

atten!ation by tiss!e. T%erefore, as concerns 555In oy!inoline labelin# of %!man stem cells,

t%e effect of radiation dose on %!man cell lines need to be caref!lly obser'ed. + critical factor

is to determine $%et%er t%e 555In oy!inoline labelin# affects 'iability, f!nctionality,

mi#ration and &roliferati'e ca&acity in distinct cell &o&!lations as $ell as s&ecies.

Quantu# Dot !or La)e"in$ ?! Ste# Ce""


25/36

ecent ad'ances in nanotec%nolo#y offer some &ros&ects to combine t%e best of eac%

ima#in# tec%ni!e $it% res&ect to sensiti'ity and s&ecificity. T%ere is no$ an array of

artificial &artic!late systems !sed as dia#nostic a#ents ca&able of tar#etin# different cells in

vivo. T%ose incl!de colloidal #old, s!&er&arama#netic iron2oide crystals, dendrimers,

&olymeric micelles and li&osomes, nanot!bes, nano$ires, nanos%ells, and !ant!m dots

(;@s. ;!ant!m dots consist of semicond!ctor nanocrystals 6< nm in diameter, $%ic% %a'e

%i#%ly fa'orable fl!orescence &ro&erties (broad band absor&tion s&ectra, narro$ band

emission, and %i#% resistance to &%otobleac%in# com&ared to commonly !sed fl!oro&%ores .

/l!orescent ;@s &ossess se'eral !ni!e o&tical &ro&erties best s!ited for in vivo ima#in# .

"eca!se of !ant!m confinement effects, t%e emission color of ;@s can be &recisely t!ned

by sie from t%e !ltra'iolet to t%e near2infrared. ;@s are etremely bri#%t and &%otostable.

4ol%era toin s!b!nit " (4T"2!ant!m dots con1!#ates $ere de'elo&ed for labelin#

mammalian cells. Se'eral stem cell ty&es $ere labeled $it% 4T"2;@ con1!#ates and

!ant!m dots $ere com&letely dis&ersed t%ro!#%o!t t%e cyto&lasm in eac% cell ty&e,

&res!mably in 'esicles . Stem cells labeled a&&ear to maintain t%eir differentiation &otential

as $ell as stem cell &ro&erties .4T"2;@ labeled m!scle deri'ed stem cells maintain similar

&ercenta#e of e&ression for s!rface mar)ers indicati'e of stem cell &%enoty&e, s!c% as stem

cell anti#en 5 (sca25 and 4@3:. T%ey can also form myot!bes !nder ser!m de&ri'ation,

%ence maintainin# t%eir myo#enic &otential follo$in# labelin# $it% 4T"2;@ con1!#ates. T%e

4T"2;@ con1!#ates are li)ely to be s!itable for lon# term cell trac)in# . /!nctionalied

!ant!m dots offer se'eral ad'anta#es for trac)in# t%e motion of indi'id!al molec!les on t%e

cell s!rface, incl!din# selecti'e bindin#, &recise o&tical identification of cell s!rface

molec!les, and details eamination of t%e molec!lar motion. T%ey $ere con1!#ated $it%

inte#rin antibodies to &erform st!dies abo!t c%an#es in t%e inte#rin dynamics d!rin#

osteo#enic differentiation of %!man bone marro$ deri'ed &ro#enitors cells ("M4s . It $as

&ossible to obtain a sin#le &article trac)in#, by $%ic% it $as &ossible to monitor and

determine !ant!m dots con1!#ated inte#rin molec!les on t%e s!rface of "M4 and to

el!cidate t%e &%ysical constraints on t%e &rotein mobility at t%e cell s!rface. (Mic%alet et

al.,600


26/36

coatin# mi#%t affect t%eir cell!lar internaliation, t%eir intracell!lar concentration and,

conse!ently, t%e cytotoicity of ;@s.

Mu"ti#oda"it% Contrat A$ent

"eca!se no sin#le contrast a#entdetector &air $ill satisfy all needs of stem cell clinical trials,

d!al2 and m!ltimodality contrast a#ents, $%ic% combine t%e best feat!res of eac% tec%nolo#y,

%a'e been de'elo&ed. /l!oro&%ore2labeled MIONs &ermit in1ection of stem cells !nder

o&tical ima#e #!idance and identification of sin#le cells in &at%olo#ical s&ecimens e 'i'o.

Similar d!al o&ticalMI contrast %as been described !sin# 'isible2$a'elen#t% fl!oro&%ores

and Dd3Q

c%elators con1!#ated to %i#%2molec!lar2$ei#%t

scaffolds s!c% as detran. ?ar#enano&articles #eneratin# sim!ltaneo!s MI, !ltraso!nd, and fl!orescence contrast %a'e also

been described (re'ie$ed in ic)line and ?ana and mi#%t &ro'e !sef!l for m!ltimodality

stem cell trac)in#.


27/36

3uture Direction

Di'en t%e in%erent limitations of c!rrently a'ailable ima#in# tec%nolo#y, f!t!re researc%

s%o!ld foc!s on im&ro'in# sensiti'ity $%ile minimiin# &atient ecl!sion, st!dy cost, and

st!dy com&leity. No'el ideas $o!ld be $elcomed in t%e field. arama#netic c%emical

ec%an#e sat!ration transfer (++4EST a#ents for MI %a'e t%e &otential to im&ro'e MI

sensiti'ity by !& to 6 orders of ma#nit!de (re'ie$ed in L%an# et al. Tera%ert and ot%er


28/36

electroma#netic fre!encies offer certain ad'anta#es, alt%o!#% eo#eno!s contrast a#ents do

not yet eist. Solid2state nanotec%nolo#y sol!tions, %o$e'er remote at &resent, are

&artic!larly attracti'e beca!se t%ey co!ld &otentially &ro'ide nonin'asi'e, real2time

monitorin# of intracell!lar &H, calci!m, etc, as $ell as anatomic location, of sin#le stem cells.

3indin$ throu$h thee techniue

Trans&lantation of &redifferentiated rat%er t%an !ndifferentiated %ES cells $o!ld be more

s!ited for a'oidin# teratoma formation.(?i et al .,600> in t%is bot% MI"?I $ere

!sed.?abeled N4 are recr!ited to infarcts $it% bot% &arenc%ymal and cerebros&inal fl!id

administration, b!t %i#%er initial &%oton co!nts s!##est t%at cerebros&inal fl!id

administration is more efficient()im et al .,600: ("?I $as !sed.+fter "MS4 trans&lantationt%ro!#% intra'eno!s ro!te , 5= of inf!sed cells localied to t%e marro$ s&ace $it%in

5< %(c!i et al 600


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In concl!sion, 2ray tec%ni!es do not &ro'ide ade!ate contrast sensiti'ity for cardio'asc!lar

stem cell trac)in# in t%e clinical settin#. "iol!minescence is limited to small animal st!dies

and NI fl!orescence to near2s!rface and %istolo#ical a&&lications.

Gltraso!ndec%ocardio#ra&%y %as t%e &otential for sin#le2cell detection b!t %as limited

anatomic accessibility, resol!tion, and !antification. Hi#%2ener#y &%oton ima#in# (SE4T

or ET %as %i#% sensiti'ity, b!t for lon#2term trac)in# it re!ires #enetic mani&!lation of t%e

stem cell, stable e&ression of a trans#ene, and m!lti&le e&os!res to ioniin# radiation. MI

&ro'ides ecellent 32dimensional anatomy b!t is contraindicated for many &atients and %as

limited a'ailability at many instit!tions, and some contrast tec%ni!es %a'e lo$ sensiti'ity.

+lt%o!#% m!ltimodality contrast a#ents mi#%t im&ro'e t%e &ros&ects for stem cell trac)in#

bot% in vivo and ex vivo, no c!rrently a'ailable ima#in# tec%nolo#y is ideal.

e&orter #ene ima#in# !sin# ET is a better tec%ni!e for monitorin# lon#2term cell

'iability, deat%, and &roliferation, $%ereas M ima#in# is a better tec%ni!e for %i#%2

resol!tion detection of cell location &ost2trans&lantation (li et al .,600>. "iol!minescent

ima#in# s%o!ld be seen as t%e one t%at is &ossibly com&lementary to ot%er modalities s!c% as

MI in $%ic% %i#%er resol!tion is re!ired( )im et al .,6009. To confirm t%e fate of stem cells

in vivo, it is cr!cial to contin!e t%e de'elo&ment and f!rt%er refinement of nonin'asi'e

ima#in# tec%ni!es.

Re!erence

+s)enasy, N., /ar)as, @. ?. In 'i'o ima#in# st!dies of t%e effect of reci&ient conditionin#, donor cell

&%enoty&e and anti#en dis&arity on %omin# of %aemato&oietic cells to t%e bone marro$. Br J

aematol. 6003767=U 63>38.


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+ic%er, +., "renner, ., L!%ayra , M. et al. +ssessment of t%e tiss!e distrib!tion of trans&lanted

%!man endot%elial &ro#enitor cells by radioacti'e labelin#. "irculation. 600376=9U653:

6539.

"%a!mi), S., ?e$is, A. L., and Damb%ir, S. S. (600: O&tical ima#in# of enilla l!ciferase,

synt%etic enilla l!ciferase, and firefly l!ciferase re&orter #ene e&ression in li'in# mice. J.

Biomed. $pt. F+ 8.

"!lte, . ., @o!#las T, it$er ", 6006. Monitorin# stem cell t%era&y in 'i'o !sin#

ma#netodendrimers as a ne$ class of cell!lar M contrast a#ents. %cad Radiol.7 9, S336

S33


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4ao, . +., a#ers, +. ., "eil%ac), +. et al. S%iftin# foci of %emato&oiesis d!rin# reconstit!tion

from sin#le stem cells. Proc &atl %cad !ci ( ! %. 600:7 6=6U665668.

4ancedda, ., 4edola, +., Di!liani, +., omle', V., ?a#omarsino, S., Mastro#iacomo, M., eyrin, /.,

!stic%elli, /. "!l) and interface in'esti#ations of scaffolds and tiss!e2en#ineered bones by

A2ray microtomo#ra&%y and A2ray microdiffraction. Biomaterials 600=, 28, 6U =80=8=

@aldr!&2?in) HE, !deli!s M, Oostendor& +, et al. Tar#etin# of %emato&oietic &ro#enitor cells

$it% M contrast a#ents. Radiology. 60037 66>U=80 =8=.

Elliott, . 4 and S. @. @o'er. A2ray microtomo#ra&%y. . Microsco&y 67, 6552653, 59>6.

/er#!son, "., an#, S., Dray, @. et al. To$ards f!nctional 3@ T2ray ima#in#. Phys 'ed Biol.

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/ord, . ., ellin#, T. H., 3rd Stanley, . 4. et al. H68 and 563 "irculation

Damb%ir, S. S., Hersc%man, H. ., 4%erry, S. ., et al. Ima#in# trans#ene e&ression $it%

radion!clide ima#in# tec%nolo#ies. &eoplasia. 600077U 55> 53>.

Dao, ., @ennis, . E., M!ic, . /. et al. T%e dynamic in 'i'o distrib!tion of bone marro$2deri'ed

mesenc%ymal stem cells after inf!sion. "ells )issues $rgans . 600=7 6FU5660.

Darot, ., Gntersee%, T., Tei#er, E., et al. Ma#netic resonance ima#in# of tar#eted cat%eter2based

im&lantation of myo#enic &rec!rsor cells into infarcted left 'entric!lar myocardi!m. J %m

"oll "ardiol. 60037 @6U 5>:55>:8.

Hacein2"ey2+bina, S., Von alle, 4., Sc%midt, M., et al. ?MO62associated clonal T cell

&roliferation in t$o &atients after #ene t%era&y for S4I@2A5. !cience. 60037306U:5


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Ha$ryla), N., D%os%, ., "road!s, ., et al. N!clear ma#netic resonance (NM ima#in# of iron

oide2labeled ne!ral trans&lants. E& Ne!rol 59937 676U 5>5296.

Hinds +, Hill M, S%a&iro EM, et al. Hi#%ly efficient endosomal labelin# of &ro#enitor and stem

cells $it% lar#e ma#netic &articles allo$s ma#netic resonance ima#in# of sin#le cells. Blood.

60037506U>8= >=6.

Hill, . M., @ic), +. ., aman, V. . et al. Serial cardiac ma#netic resonance ima#in# of in1ected

mesenc%ymal stem cells. "irculation. 6003U6=U 5009 505:.

im, @. E., Sc%ellin#er%o!t @, Is%ii , et al. Ima#in# of stem cell recr!itment to isc%emic infarcts

in a m!rine model. Stro)e 600:7 3.

raitc%man, @. ?., Tats!mi, M., Dilson, . @., Is%imori, T., ediore), @., alca), ., Se#ars, .

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?i L, S!!)i , H!an# M, et al. 4om&arison of re&orter #ene and iron &article labelin# for trac)in#

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Stem 4ells 600>7 68U >8:2=3.

?e$in M, 4arlesso N, T!n# 4H, et al. Tat &e&tidederi'atied ma#netic nano&articles allo$ in 'i'o

trac)in# and reco'ery of &ro#enitor cells. &at Biotechnol. 60007 5>U :50:5:

?a!terb!r 4 (59=3. Ima#e /ormation by Ind!ced ?ocal InteractionsU Eam&les of Em&loyin#

N!clear Ma#netic esonance. &ature 7@7U 590595

?e$in M, 4arlesso N, T!n# 4H, et al. Tat &e&tide deri'atied ma#netic nano&articles allo$ in 'i'o

trac)in# and reco'ery of &ro#enitor cells. &at Biotechnol. 600075>U:50 :5:.

?i, L., S!!)i, ., H!an#, M., et al. 4om&arison of re&orter #ene and iron &article labelin# for

trac)in# fate of %!man embryonic stem cells and differentiated endot%elial cells in li'in#

s!b1ects. Stem 4ells 600>7 7U >8:2=3.

Mic%alet, A., ina!d, /. /. "entolila, ?. +., Tsay, . M., @oose, S., ?i, . ., S!ndaresan, D., !, +.

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stem cell track

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