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Screen ing Pa tien ts fo r R ena lA rte ry S tenos is : V a lu e o fTh re e -D im ens iona l T im e -o f-F lig h t M RAng iog raphy

H #{149 } .# {149 } . :P ierre

D id ie r R eve lP asca l G a rc ia

A lexand ra D e ligne tteEmm anue lle C ane tP ie rre C hiro s se l

G ille s G en inM iche l Am ie l

R ece ive d Febru a ry 24 , 1 99 3 : ac ce p te d a fte r re -v is io n No vem ber 30 , 19 93 .

1 A ll a uth ors : D #{2 33 }p arte me nt d e R ad io lo gie , H #{2 44 }p i-ta l C a rd iovascu la ire e t P ne um o log iqu e L ou isP rad e l, 59 b ou leva rd P ine l, 69 003 Lyon , F ra nce .A dd re ss co r resp ond en ce to D . R eve l.0 36 1 - 80 3X /9 41 1 62 4- 08 47 Am er ica n Roen tge n R ay S oc ie ty

OB JEC T IV E . The pu rpose o f th is s tudy w as to dete rm in e th e va lu e o f th re e -d im en -s iona l tim e-o f-f lig h t M R ang iog raphy in sc re en ing pa tien ts fo r th e p re sence o f ren a la rt er y s te no se s.

S UB JEC TS AND ME THODS . F ifty -th re e pat ie n ts w ho w e re though t to have reno -v a scu la r h ype rten s ion on c lin ic a l g rounds w e re p ro spec tive ly e xam ined w ith th ree -d im ens iona l tim e -o f-f lig h t M R ang iog raphy . IV d ig ita l s ub tra c tio n ang iog ram s anddup le x sonog ram s w ere ava ilab le fo r a ll p a t ie n ts . Fo r 21 patie n ts in w hom IV ang ie -g ram s w e re o f h igh qua lity and show ed th e rena l a rte rie s to be no rm a l, as con firm edw ith dup le x sonog ram s, in tra ar te r ia l d ig ita l sub trac tio n ang iog ram s w e re no tob ta in ed fo r M R co rre la tio n . In th e o th er 32 pat ie n ts , in traa rte ria l ang iog ram s o f th eabdom ina l ao r ta w ere ob ta in ed . M R ang iog ram s w e re in te rp re ted independen tly b ytw o rad io log is ts w ho w ere unaw are o f th e f in d ings on ang iog raphy and dup lexsonography . O u r p re lim in a ry c lin ica l e xpe r ie n ce suggested th a t a s igna l lo ss in th erena l a rte r ie s on m ax im um -in ten s ity -p ro jec tio n M R ang iog ram s ind ic a ted a po ten tia ls tenos is and th a t th e deg re e o f s tenos is cou ld no t b e m easu red accu ra te ly w ith M Rang iog raphy . The sea rch fo r s tenoses w as focused on th e p ro x im a l and m idd le p a rtso f th e vesse l, as fa r a s 3 cm from the o r ig in o f th e vesse l. W e used in tra ar te ria la ng iog raphy to m easu re and g rade rena l a r te ry s tenoses . O n in traa rte r ia l a ng ie -g ram s , s tenoses th a t in vo lv ed m o re th an 50% o f th e vesse ls s ec tio n w e re cons id ereds ignif icant (n = 24) and stenoses th a t in vo lv ed 50% o r le ss o f th e sec t io n w ere cons id -e re d i ns ig n if ic an t (n = 7) . These 31 stenoses w e re found in 26 o f the 32 patie n ts w hohad in traa rte r ia l d ig ita l sub trac tio n ang iography .

R ESU LTS . A ll 24 s ign ific an t s tenoses appeared as a cu to ff o f s ig na l in ten s ity onM R ang iog ram s . R esu lts w ere fa lse -pos itiv e in 20 cases : in e igh t c ases , a rte rie s w ereo f sm all d iam e te r; in s even cases , th e s tenoses w ere in s ign ifican t; in tw o cases , th eacqu is it io n vo lum e w as in co rre c tly pos itio n ed ; in tw o cases , th ere w as a sha rp ang lein th e p ro x im a l p ar t o f th e rena l a r te ry ; and in one case , no exp lan a tio n w as found .M R ang iog raphy had a sens itiv ity o f 1 0 0% fo r d e te c tin g s tenoses in th e pro x im a l 3 cmo f th e rena l a r te ry ; s tenoses m o re th an 3 cm from the o r ig in o f th e ar te rie s cou ld no tb e d etec ted re liab ly .

C O NC LUS IO N . O u r resu lts sugges t th a t th re e -d im ens iona l tim e -o f-f lig h t M Rang iog raphy is a s im p le m ethod fo r d e te c tin g s tenoses o f th e p ro x im a l po rtio n o f them ain rena l a r te rie s . H ow eve r, m ore w o rk is n eeded be fo re w id esp read c lin ic a l u se o fsuch a techn ique is fe a s ib le .

AJ R 1994;162 : 847 - 852

Rena l a rte ry s tenos is is im p lica ted in le ss than 3% o f a ll cases o f hype rtens ion[1 , 2] . Today, in traa rte ria l d ig ita l sub tra c tion ang iog raphy and conven tiona l ang io -g raphy , wh ich en ta il som e ris k , rem a in the de fin itive m e thods o f screen ing fo rrena l a rte ry s tenos is . D e tec tion o f rena l a rte ry s tenos is in hype rtens ive pa tien ts is


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848 LO UBEYRE ET AL . A JR :16 2, A pril 1 99 4

im portan t because o f the ava ilab ility and success o f pencu ta -neous trans lum ina l ang iop la s ty and su rge ry fo r co rre c tings tenoses [3 ]. T hus , a non invas ive , sens itiv e , and spec ifics creen ing tes t is needed fo r pa tien ts w ith suspec ted nenovas-cu la r hype rtens ion . MR im ag ing has been enhanced by thein troduc tion o f te chn iques tha t perm it p ro je c tion ang iognam s,wh ich a re ana logous to conven tiona l ang iognam s [4 , 5 ]. S tud -ie s o f the use o f M R ang iognaphy to eva luate the rena l a rten -ie s , m a in ly w ith tw o -d im ens iona l (2D ) tim e -o f- flig h t andphase -con tra s t im ag ing , have been repo rted . The need fo rb rea th -ho ld ing and fo r im ag ing in seve ra l p lanes , w h ichin creases acqu is itio n tim es, and the p resence o f venousove rlap on recons tru c ted im ages have been repo rted [6 -9 ].O u r goa l w as to de te rm ine the va lue o f th ree -d im ens iona l(3D ) tim e -o f-flig h t M R ang iognaphy in sc reen ing patien ts fo rthe p resence o f rena l a rte ry s tenos is .

A cco rd ing ly , w e p rospec tive ly te s ted an asymm e tric ,sho rt-e cho, 3D tim e -o f-fl ig h t MR ang iognaph ic sequencew ith ve lo c ity com pensa tion in 53 adu lt pa tien ts w ith sus -pec ted rena l a rte ry s tenos is . T h is sequence m in im izes thee ffe c ts o f phys io log ic m o tion on im age qua lity (no b reath -ho ld ing is requ ired ) and p rov ides rap id acqu is itio n o f h igh -re so lu tion 3D MR ang iognam s o f the rena l a rte r ie s .

Sub jec ts and M e thodsS tu dy G ro up

F ifty -th ree con secu tiv e pa tie n ts w e re p ro spec tive ly e n ro lled in thes tudy be tw een M a rch 1990 and Ap ril 1 992 a fte r they had g ivenin fo rm ed consen t fo r MR ang iog raphy . T he g roup inc luded 34 m en40-7 4 years (m ean age , 55 yea rs ) a n d 1 9 w om en 45-7 8 years(m ean age , 56 yea rs ) w ho had unde rgone d ig ita l s ub tra c tionang iog raphy fo r eva lua tion o f renovascu la r hype rtens ion suspec tedon c lin ica l g rounds . S ix pa tien ts had an abdom ina l aneu ry sm . T hein te rv a l b e tw een MR ang iog ra ph y and d ig ita l su b tra c tio n ang iog ra -phy w as less than 1 w eek in a ll pa tien ts . The resea rch p ro toco l w asapp roved by the H um an Inves tiga tion C om mittee o f our in s titu tion .

M R Im ag in gIm ages we re ob ta ined w ith a 1 .5 -T w ho le -body MR im ag ing sys-

tem w ith a c irc u la rly po la r ized body co il u sed as an R F transm itte rand re ce ive r. Pe ak g rad ien t am p litu de wa s 1 0 m T /m , w ith a ram ptim e to pe ak am p litu de o f 1 m sec . Th e m eth od wa s based on 3Dfa s t im ag ing w ith s teady -s ta te p recess ion , a g rad ien t-re ca lled echosequence w ith a sm a ll f lip a ng le a nd firs t-o rde r flow com pensa tio n inth e re ado ut a nd se ctio n-se le ct d ire ctio ns .

In the firs t phase o f ou r s tudy , the M R ang iog raph ic sequence wasop tim ized to v is ua liz e rena l a rte rie s . Im ag ing pa ram ete rs w ere em pir-ica lly eva lu a ted in 1 5 hea lth y v o lun tee rs a nd five p a tien ts from asequ en ce prop ose d b y the m anu fac tu re r (30 # {1 76 }lip an g le , 3 2 /7 [TR /T E], o ne s ig na l a ve ra ge d, 300 x 30 0 m m fie ld o f v iew , 64 ax ia l s licesy ie ld in g an acqu is it io n v o lum e o f 80 -mm th ic kne ss , 2 56 x 256 a cqu is i-t ion m atrix ). S ix ty m easurem en ts w ere m ade by us ing a ll pos s ib le va l-ues o f each va riab le . O n ly one va riab le was eva lua ted du ring eachm easu rem en t. The d iffe ren t va lues fo r TR w e re 25 , 30 , 32 , 35 , and 40m sec ; fo r fie ld o f v iew , 200 x 20 0 , 25 0 x 250 , 3 00 x 300 , and 350 x350 mm ; fo r TE , 7 and 11 m sec; fo r num ber o f s igna ls ave raged , one ,two , and th ree ; fo r acqu is itio n m atrix s ize , 1 28 x 256 and 256 x 256;fo r a cqu is itio n vo lum e th ic kness , 40 , 60 , and 80 mm ; fo r num be r o fs lices , 32 and 64 ; and fo r fl ip an g le , 2 5 # {1 76 },00 , 350 an d 400 . Two van-

ab les w ere ke y in o b ta in in g op tim a l v ascu la r co n tra s t a nd in im ag in gthe leng th o f the rena l a rte rie s in a sho rt a cqu is itio n tim e : it w as nec -essa ry to a ve rag e tw o s ig n a ls in o rd e r to p rov id e an adequa te s ig na l-to -n o ise ra tio , a nd a sm all f lip an g le (2 5# {176 })a s n e ces sa ry to m in im izethe sa tu ra tio n e ffe c t w ith in th e vo lum e . A 40-m m -th ick ax ia l vo lum ew as su ffic ien t to im age the m ain rena l a rte r ie s .

Fo r the p rospec tiv e s tudy , the op tim ized 3D tim e-o f-fl ig h t sequencepa ram ete rs w ere a 25# {176 }lip ang le , a TR /TE o f 32 /11 , tw o s ig na ls a ve r-aged , 32 ax ia l s lices y ie ld ing a 40 -mm -th ick acqu is itio n vo lum e , a300 -mm 2 fie ld o f v iew , a 128 x 256 acqu is it io n m atrix , an d a 256 x256 recons truc tion m a tr ix , w h ich p rov ided an in -p lane reso lu tion o f2 .35 mm . A 900 ax ia lly o rien ted spa tia l p resa tu ra tion pu lse w asp laced in fe r io r to the im ag ing vo lum e to supp ress the s igna l fromin flow ing b loo d from th e in fe rio r ve na ca va . T he m ax im um -in te ns ity -p ro jec tion ra y -tra c in g a lg o rithm w as u sed to p ro v ide ang io g raph icp ro jec tion s from any des ire d v iew ing ang le a round th e lo n g a x is o f th ebody. F as t ax ia l scou t im ages w e re firs t ob ta ined to lo ca lize theabdom ina l ao rta , then ha lf-Fou r ie r T i -w eigh ted co rona l im ages we reob ta in ed to lo ca liz e the m a in re na l a rte rie s . T o m in im iz e th e e ffec ts o fsp in sa tu ra tion , w e p laced the im ag ing vo lum e so tha tthe o rig in o f them a in re na l a rte rie s w as in its up pe r th ird . In th ree ca ses in w h ich th em ain ren a l a rte rie s w ere loca te d a t d iffe ren t lev e ls o n T i -w e ig h te dco rona l im ages , a second vo lum e acqu is itio n w as used . MR ang io -g ram s to o k exa c tly 4 .3 mm to a cqu ire . T he to ta l a cq u is ition tim e ,inc lud ing the tim e requ ired to ob ta in lo ca liz ing im ages , ranged from 8mm in m os t cases to 1 2 m m when a secon d vo lum e acq u is ition wa snecessa ry . T o m in im ize m o tion a rtifa c ts , w e used w ebb ing to com -p re ss ea ch pa tien ts ab dom en .

Ang iog r aphyD ig ita l sub tra c tio n ang io g ra phy w as pe rfo rm ed no m ore tha n 1

week be fo re M R exam in a tion . A ll 5 3 pa tie n ts u nderw en t IV d ig ita lsub tra c tion ang iog raphy firs t, a fte r in je c tion o f 50 m l o f con tra s tm ed ium v ia an an tecub ita l ve in . In 21 cases in w h ich the IV ang io -gram s we re o f ve ry h ig h qua lity (n o ove rly in g bow e l g as , no super-im po s it ion o f th e v is ce ra l c ircu la tion on par ts o f th e re na l a rte ries ,and su ffic ien t opac ifica tion o f the rena l a rte rie s ) and bo th the IVang iog ram s and dup lex sonog ram s show ed the rena l a rte r ie s to beno rm al, in traa rte r ia l ang iog ram s we re no t ob ta ined . In these cases ,re su lts o f M R ang iog raphy w e re com pa red w ith com bined resu lts o fbo th IV ang io g ra phy and dup le x sonography .

In the o the r 32 pa tien ts , in traa rte r ia l d ig ita l s ub tra c tion ang iog ra -ph y o f th e abdom in a l ao rta in the an te ro po s te rio r v iew w as per-fo rm ed w ith 40 m l o f con tra s t m ed ium in je c ted v ia a 5 -F rench p ig ta ilca the te r pos itioned at the le ve l o f the rena l a rte rie s . In traa rte r ia l d ig -ita l s ub tra c tion ang iog raphy has a lw ays been the re fe rence m ethodfo r e va lua tin g ren a l a rte ry s te n os is . O n in traa rte r ia l d ig ita l su b trac -tio n ang iog ram s , w e used a quan tita tive app roach to g rade rena la rte ry s tenoses . F irs t, vesse l edges w e re iden tifie d w ith an au to -m atic ve sse l e dge de te c tio n a lgo rithm (a rte r ia l s te no s is quan tif ica -tio n package , G E Eu rope , P a ris ). T hen , s tenos is w as g raded w ithgeom etr ic and dens itom etric m ethods . In bo th cases , the deg ree o fs tenos is was ca lcu la ted au tom atica lly , a s a re la tive va lue in com pa r-ison w ith a no rm al re fe rence segm ent chosen by the ope ra to r. In thegeom e tric m e th od , bo th a re as (s ten o tic an d no rm a l) a re take n to bec ircu la r an d a re com pa re d . In th e dens itom e tric m e th od , th e in te g ra lo f the am p litu de va lu es o f th e d iffe re n t p ix e ls in th e s ten o sed seg -men t o f the vesse l is com pa red w ith the in teg ra l fo r the no rm a l seg -m on t. W hen th e tw o m e thod s p ro v id ed d isco rd an t m easurem en ts o fthe deg ree o f s te n os is , th e den s itom e tric m ea surem en ts w e re u sed .W e de fined s tenoses tha t in vo lved 50% or le s s o f the vesse l sec tionas in s ig n ifica n t an d ste no se s tha t invo lve d m o re th an 50% of th ev es se l s ec tio n a s s ig nific an t.


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U N orm al (D SA 1E Stenosis > 5 0%

(IA DSA )us 50 %A)

Leng th of v isua l ized r ena l a rter y by M RAF ig . 1 .-H is to g ram p lo ttin g num ber o f ve sse ls sh ow n by d ig ita l su b -

t rac tio n an g io g rap hy (D 5A ) vs le ng ths o f v isu a liz ed rena l a r te r Ies shownby th re e -d im en s io na l t im e -o f-fl igh t M R ang io g rap hy (M RA ). A ll re na l a r-te rles w ith v isu a liz ed le ng ths o f 2 .5 cm or m o re on MR ang iog ram s ap -p ea red n orm al o n d ig ita l su btra c tio n an gio gram s. (W hen a lo ca lized lo sso f s ig na l in ten sity o ccu rred w ith in a vesse l, o nly len gth v isu alized b efo res ign a l los s w as cons ide red .) IA = intraarterial .

A JR :1 62 , A pr il 1 994 SCREENING FOR RENAL ARTERY STENOSIS 849

Am ong the 32 pa tien ts exam ined w ith in tra arte ria l d ig ita l sub tra c-tio n ang iog raphy , 31 rena l a rte ry s tenoses w e re de tec ted in 26pa tie n ts . Tw en ty -o ne p a tien ts h ad un ila te ra l s ten oses , five p a t ien tshad b ila te ra l s tenoses , and s ix pa tien ts d id no t have any rena l a rte rys tenoses . S even s tenoses in vo lved 50% or le ss o f the vesse l sec-t ion and 24 s ten oses in vo lv ed m o re tha n 50% o f th e ve sse l sec tio n .

D up le x S onog ra ph yD up lex sonog ram s in a ll 53 pa tien ts w e re obta ined w ith a com -

m erc ia lly ava ilab le s canne r w ith a 3 .75 -M Hz phased -a rra y sec to rp robe . C rite ria fo r no rm al m ain rena l a rte rie s on dup lex sonog raph icwe re (1 ) no sys to lic acce le ra tion a t the s ite o f the rena l os tium (i.e ,sy sto lic p ea k fre que nc y < 3 500 H z, ra tio o f peak sys to lic ve lo c ity inthe rena l a rte ry to p eak sys to lic v e loc ity in the ao rta < 2 .5 ) an d (2 )no dem odu la tion and no b roaden ing o f d is ta l tra c ings ( i.e . , r ise tim e< O .i4 sec , re s is tiv e index 0 .5 ).

In traa rte ria l ang iog ram s and dup lex sonog ram s w ere in te rp re tedb y r ad io lo gi st s in de pe nd en tly .

E va lua tio n o f MR A ng iog ram sM ax im um -in ten s ity -p ro je c tio n M R ang io g ram s w e re in te rp re ted

by tw o rad io log is ts who w e re unawa re o f the find ings on d ig ita l sub -tra c tion ang iog raphy and dup lex sonog raphy . T he t w o r ad io lo g is tsreached a consensus on the fo llow ing in fo rm ation from each s tudy :num be r o f rena l a rte rie s v isua lized , leng th o f each rena l a rte ry , andp resence o r absence o f rena l a rte ry s tenos is .

O u r p re lim ina ry c lin ica l expe rience (unpub lished da ta ) w ith 3Dt im e-o f-fligh t M R ang iog ra ph y has sugge s ted tha t an y s ten os isw ou ld appea r as a s igna l lo ss w ith in the rena l a rte ry ju s t be fo re thes tenos is and tha t the ve ry d is ta l pa rt o f a no rm a l rena l a rte ry w ou ldno t be v isua lized because of a sa tu ra tion e ffe c t. S igna l lo ss isde fin ed a s a lo ca lize d los s in s ig na l in ten s ity w ith in a ve sse l o r acom ple te cuto ff o f the vesse l.

T he sea rch fo r s tenoses w as focused on the p rox im a l and m idd lepa rts o f the vesse l, a s fa r as 3 cm from the vesse ls o rig in , becausem ost o f the pa tien ts had c lin ic a l find ings sugges tive o f a the rosc le -ro tic le s ions . Thus , any v isua liz ed leng th le s s than 3 cm , o r anylo ca lized lo ss in s igna l in tens ity w ith in the firs t 3 cm , w as cons ide reda po ten tia l rena l a rte ry s tenos is , and an a rte ry w hose v isua lizedleng th w as g rea te r than o r equa l to 3 cm w as cons ide red a no rm a la rte ry . N o a ttem p t w a s m ade to q uan tify th e de gre e o f s te nos is w ithMR ang iog raphy

Resu l t sOn MR ang iog ram s, a rte r ie s w ith sm a ll d iam e ters (d iam e -

ten le ss than 2 mm on d ig ita l s ub tra c tion ang iog ram s) e ithe rwe re no t v isua lized on the ir v isua lized leng th was 3 cm onless . D ig ita l sub tra c tion ang iognam s show ed tha t fou rpa tien ts had tw o rena l a rte r ie s on one s ide (m u ltip le rena la rte r ie s ). In tw o o f those four pa tien ts , ne ithe r o f the m u ltip lerena l a rte rie s on one s ide w as v isua lized on M R ang io -g ram s. W e conc luded , there fo re , tha t an os tia l s tenos is o f am a in rena l a rte ry w as p resen t on the nonv isua lized s ide inthose tw o patien ts . In the othe r tw o pa tien ts , the to ta l o f fou rrena l a rte r ie s on one s ide we re v isua lized fo r 0 .5 , 2 .0 , 3 .0 ,and 3 .0 cm on M R ang iognam s. D ig ita l sub tra c tion ang iog ra -phy show ed 110 rena l a rte rie s (F ig . 1 ).

S ix ty -s ix o f 79 no rm a l rena l a rte r ie s w e re de tec ted w ithM R ang iognaphy (F ig s . 2 and 3 ). Leng ths m easu red on MR

ang iognam s w e re 3 -6 cm (m ean , 4 .6 cm ) (F ig . 2 ). The yes-se l d iam e te r was p rog ress ive ly dec reased in these no rm a la rte r ie s . In som e cases , w e no tic ed a loss o f de fin itio n o fthe edge o f the vesse l in the d is ta l pa rt o f the v isua lizedrena l a rte ry . W hen the v isua lized leng th w as m o re than 4 .5 -5 .0 cm , w h ich usua lly co rre sponds to the loca tion o f thean te rio r and pos te rio r d iv is ion , the d is ta l pa rt o f the vesse lv is ua liz ed co rresponded to one o f these rena l a rte ryb ranches (F ig . 3 ).

A ll 24 s tenoses g rea ten than 50% w ere de tec ted w ith M Rang iognaphy . The v isua lized vesse l leng ths ranged from 0 to2 cm (F ig . 1 ). In a ll cases , the s tenos is w as appa ren t on M Rang iognam s as a cu to ff in s igna l in the rena l a rte ry (F ig . 4 ).

R esu lts o f M R ang iognaphy we re fa lse pos itiv e in 20cases . R esu lts w e re cons ide red fa lse pos itive w hen thev isua liz ed leng th o f the rena l a rte ry w as le ss than 3 cm onwhen the re w as a loca lized lo ss in s igna l in tens ity in the firs t3 cm o f the rena l a rte ry on MR ang iognam s , w he reas d ig ita ls ub tra c tion ang iog ram s show ed no rm a l rena l a rte r ie s onshowed ins ign ific an t rena l a rte ry s tenos is . O f the 20 fa lse -pos itiv e resu lts , a rte r ie s w e re o f sm a ll d iam e te r in e igh tcases , the s tenoses we re in s ign ifican t in seven cases , theacqu is itio n vo lum e was incorrec tly pos itioned in tw o cases ,the re was a sha rp ang le in the p rox im a l pa rt o f the rena la rte ry in tw o cases , and no exp lana tion was found in onecase.

If one cons ide rs a ll 11 0 rena l a rte rie s v isua lized on d ig ita ls ub tra c tion ang iognam s p lus the ab ility o f M R ang iognaphy toshow stenoses o f g rea ten than 50% in the firs t 3 cm o f therena l a rte ry , 66 resu lts w e re true nega tive , 20 w e re fa lsepos itive , none we re fa lse nega tive , and 24 we re true pos i-tive . T h is y ie ld s a sens itiv ity o f 100% , a spec ific ity o f 76% , apos itive p red ic tive va lue o f 54% , and a nega tiv e p red ic tiv eva lue o f 100% .


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Dis cuss ion

85 0 LOUBEYRE E T A L. AJR :1 62 , Ap ril 1 994

F ig . 2 .-4 5 -y ea r-o lc m an w ith no rm al ren a l a rte ries .A , Maxim um -in te ns ity p ro je c t ion o f a 2O le ft o bliq ue M R an gio gram sh ow s n orm al ren al a r te rie s . S tru ctu re th at res em bles an an eu ry sm a t d is ta l p ar to f v is ua lized p ortio n o f le ft re n al a rte ry ( a r rowhead ) correspond s to su pe rim po s it ion o f to r tuo us prox im a l lob ar a rte rie s . V es se l a t rig h t pa rt o f a o rta

( a r row) is sup er io r m esen te rlc a rte ry .B, C orrespond ing IV d ig ita l s ub tra c tio n an g io g ram in an terop osterio r p ro je c tion shows non steno tic m a in ren a l a r te r ies .

F ig . 3 .-53 -ye a r-o ld m an w ith no r-m al r en al a rte rie s.

A , M ax im um -in ten s ity p ro jec t ion o fan an te rop os te rio r M R ang io g ramshow s f irs t 5 cm o f no rm al le f t ren a lar tery and f irs t 4 cm o f no rm al r igh t re -n a l a r te ry .

B, In tra arte ria l d ig ita l s ub tra ctio nang iog ram show s norm a l m ain rena larte ry .

F ig . 4 .-6 2 -ye ar -o ld w om an w ithste no s is o f r igh t re na l a rte ry .

A, Maxim um -in tens ity p ro je c tion o fM R ang iog ram show s cu to ff o f s ign a l( a r row) in r igh t ren a l os tlum .B , Correspond ing i nt ra ar te ri al d ig i-ta l sub trac tio n ang iog ram show sg re a te r than 50% sten os is in firs t cen -tim eter o f righ t re na l a rte ry .

The sens itiv ity and spec ific ity o f IV d ig ita l s ub tra c tionang iognaphy in te chn ica lly adequa te s tud ie s a re bo th le s sthan 90% [10 ]. D up lex sonognaphy requ ire s m e ticu lousa tten tion to seve ra l te chn ica l de ta ils , and the exam ina tioncan be pe rfo rm ed on ly by expe rienced pe rsonne l. In onese rie s , dup le x sonognaphy w as repo rted to have a 95% sen -sitiv ity and 97% spec ific ity fo r de tec ting s tenoses o f the m a inrena l a rte rie s , and the exam ina tion w as repo rted to requ irele ss than 30 mm [11 ].

MR ang iog raphy can show stenoses p rim a rily because o fthe phase d ispe rs ion . P hase d ispe rs ion is p roduced byh ighe r-o rder m otion and by va r ia tion in ve lo c itie s o f b loodp ro tons , bo th o f w h ich resu lt in s igna l lo s s [12 ]. Two -d im en -s iona l im ag ing is lim ited in spa tia l re so lu tion and s igna l- to -

no ise ra tio and su ffe rs from im pe rfe c t p ro file s o f ind iv idua ls lic es [6 , 7 ]. B rea th -ho ld ing is usua lly requ ired . In d iffe ren tse rie s , in te rp re ta tion was poss ib le on ly a fte r seve ra l o f theco rona l and ax ia l im ages and the ir com pos ite s we rerev iew ed [7 , 8 ]. The phase -con tra s t m e thod requ ire s 3Dda ta to be acqu ired w ith m u ltip le pe rm u ta tions o f the flow -sens itiz ing g rad ien ts ; thus , the acqu is itio n tim es a re m uchlonge r than fo r the tim e -o f-fl ig h t approach . M o reove r, phase -con tra s t ang iognaphy requ ire s m uch m o re in tens ive pos tpno -cess ing o f the da ta and is sens itiv e to a lia s ing [5 ]. U n lik et im e -o f-fligh t m e th od s , ph a se -c on tras t te ch n iqu e s a re lesss en sitive to sa tu ra tio n.

W e have assessed 3D tim e -o f-fl ig h t M R ang iognaphy. T heth in s lic e th ickness a ffo rded by the 3D acqu is itio n y ie ld s h ighspa tia l re so lu tion in the sec tion -se le c t d ire c tion and a llow sm ax im um -in tens ity pos tp rocess ing o f any v iew tha t has spa -


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A JR :16 2 , Ap ril 199 4 SCREEN ING FO R RENAL AR TERY S TENOS IS 85 1

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tia l re so lu tion s im ila r to tha t o f the s ing le 3D da ta se t [4 , 12 ].T h is te chn ique does no t requ ire coope ra tion from pa tien ts inthe fo rm o f brea th -ho ld ing m aneuve rs bu t is pe rfo rm ed w iththe pa tien t b rea th ing qu ie tly . N o venous ove rlap is p resen t,un like on 2D tim e -o f-fl ig h t o r phase -contra s t im ages [7 , 9 ].T he p rim a ry d isadvan tages o f the 3D acqu is itio n techn iquere la te to sens itiv ity to m o tion a rtifa c ts and p rog ress ive sp insa tu ra tion . M o tion a rtifa c t is reduced by the h igh num be r o fs igna ls ave raged du ring the 32 -s lice acqu is itio n and by theuse o f a ve lo c ity com pensa tion g rad ien t in the read -ou t andsec tion -se le c t d ire c tions , a sho rt TE [13 ], and abdom ina lcom p ress ion . S a tu ra tion e ffe c ts can be m in im ized by pos i-tion ing rena l a rte rie s a tthe top th ird o f the im age vo lum e [14 ].

In tw o cases , rena l a rte r ie s w e re a t d iffe ren t le ve ls (>1cm ), so a second acqu is itio n vo lum e had to be pe rfo rm ed . Ina ll o the r cases , a s ing le acqu is itio n vo lum e was su ffic ien t.Dur ing the eva lua tion p rocedu re , a 40 -mm -th ick vo lum e wasfound to be la rge enough to im age the m a in rena l a rte rie s .T h is lim ited vo lum e acqu is itio n a llow ed the num be r o f s ig -na ls ave raged to be inc reased by tw o , y ie ld ing an increasein the s igna l- to -no ise ra tio by a fac to r o f N 2 , w ithou t exceed -ing a 4 .4 -mm acqu is itio n tim e .

In a ll pub lished se rie s , d is c repanc ie s w e re found be tweenM R ang iognaphy and in traa rte ria l ang iog raphy in g rad ing theseve rity o f s tenos is [5 , 7 -9 , 1 4, 1 5]. T hese d isc repanc ie s a rep roduced by the p resence of tu rbu len t flow w ith in each pa rto f the s tenos is , w h ich resu lts in s igna l lo ss on M R ang io -g ram s tha t is no t en tire ly m ade up fo r by flow com pensa tion .T he p rob lem is a ttenua ted bu t no t e lim ina ted by the use o f ave ry sho rt TE [16 ]. In add ition , w ith the low flow ve loc itie stha t can ex is t in seve re ly s tenosed a rte r ie s and a t the edgeso f a rte r ie s , flow con tra s t is reduced by sa tu ra tion e ffe c t. S ow e d id no t try to g rade the seve rity o f s tenos is w ith M Rang iog raphy . W e used a longe r TE (11 rnsec) than the onep roposed by the m anu fac tu re r (7 m sec ), w h ich y ie ld s m o rephase d ispe rs ion in s tenosed segm en ts o f the vesse l; thus ,any vesse l na rrow ing appea red as a s igna l lo ss . In add ition ,w e have em p ir ica lly o bserved tha t a no rm al v es se l d eepw ith in the vo lum e can be v isua liz ed in som e cases when aTE o f 11 m sec is used . W e canno t exp la in th is phenom enon .R e tro spec tive ly , w e no tic ed tha t the s igna l reappea red d is ta lto wh at w e ca lled the lo ca lized s igna l lo ss , w hen in traa rte r ia ld ig ita l s ub tra c tion ang iog raphy had show n a stenos is o f 50%o r les s (F ig . 5 ). T h is phenom enon can be exp la ined by alow e r sa tu ra tion e ffe c t d is ta l to the s tenos is w hen the flow isno t g rea tly reduced , as in s tenoses le s s than 50% .

A pp rox im a te ly tw o th ird s o f s tenoses o f the rena l a rte rya re caused by athe rosc le ros is [1 7 ]. A the rosc le ro tic le s ionstyp ica lly in vo lve the p rox im a l th ird o f the vesse l [18 ].B ecause o f ou r s tudy g roup , w e focused our M R ang io -g raph ic sea rch fo r s tenoses a long the firs t 3 cm o f the rena la rte ry , w h ich co rresponds to the p rox im a l and m idd le pa rtso f the vesse l. W e had no fa lse -negative find ings in th iss tudy , bu t we cou ld have m issed a d is ta l s tenos is , such asobse rved in fib ro rnuscu la r d isease , w h ich tends to occu r inpa tien ts younge r than those w ho have a the rosc le ros is .B ecause o f sp in sa tu ra tion , w e v isua lized the ve ry d is ta l pa rto f the rena l a rte ry (> 35 mm ) in on ly 70% o f no rm a l rena la rte rie s (F ig . 1 ).

U sua lly , rena l a rte rie s tha t a re sm a ll in d iam e ter, such asm u ltip le o r accesso ry rena l a rte r ie s , w e re no t v is ua liz ed o rthe v isua liz ed leng th w as les s than 3 cm , w h ich pa rtlyexp la in s the fa lse -pos itive find ings . Th is la ck o f v isua liza tionm ay be due to the sm a ll d iam e te r o f the vesse l, w h ich m aybe be low the spa tia l re so lu tion o f the techn ique . The reportedp reva lence o f m u ltip le rena l a rte rie s has been va riab le , rang -ing up to as m uch as 44% o f the popu la tion [19 , 20 ]. K now l-edge o f the poss ib ility o f m u ltip le rena l a rte rie s is use fu l,a lthough renovascu lan hype rtens ion caused by s tenos is o f anaccesso ry a rte ry in a pa tien t w ith no rm a l m a in rena l a rte r ie sa lso m us t be cons ide red . O u r te chn ique is no t adequate tode tec t and eva lua te accesso ry a rte rie s , and th is is a lim ita tiono f M R ang iognaphy fo r sc reen ing pa tien ts fo r the p resence o frena l a rte ry s tenos is .

A no the r d raw back o f us ing M R ang iog raphy fo r de tec tingrena l a rte ry s tenos is is the p rox im a l s igna l cu to ff, c rea ted bya sha rp ang le in the p rox im a l pa rt o f the rena l arte ry , w h ichinduced phase d ispe rs ion . T he p resence o f an abdom ina lao rtic aneu rysm in s ix pa tien ts d id no t in fluence the appea r-ance o f the le s ions on M R ang iog ra rns . T h is m ay have beenbecause the aneu ry sm s w e re d is ta l to the rena l arte r ie s .

3D tim e -o f- fligh t M R angiognaphy appea rs to be an accu -ra te , non in vas ive , and ve ry sens itiv e m e thod fo r d iagnos ings te no ses o f th e firs t 3 cm o f the m a in rena l a rte ries , w h icha re obse rved m a in ly in pa tien ts w ith a the rosc le ro tic le s ions .Th is p re lim ina ry c lin ic a l e va lua tion sugges ts seve ra l advan -tages o f 3D tim e -o f- flig h t o ve r o the r MR ang iognaph ic te ch -n iques : un ique and fas t acqu is itio n and recons tru c tion o fda ta , no b rea th -ho ld ing m aneuve rs , no venous ove rlap .Im ages ob ta ined w ith th is techn ique w e re free of ghos t a rti-fa c ts and o f b lu rring a rtifa c ts from resp ira tory m o tion . Them a in lim ita tions rem a in : no v isua liz a tion o f sm a ll rena l a rte r-

F ig . 5 .-6 5 -y ea r-o ld m an w iths teno s is o f r igh t rena l a rte ry .

A , M ax im um -in ten s ity p ro je c t ion o fM R an gio gram sh ow s lo ca lized s ig na lloss ( a r row) a long f irs t cen tim ete r o frig h t rena l a rte ry . S ign a l re ap pears b e-yo nd a rea o f s igna l lo ss .

B, C o rr es p on d in g in tr aa rt er ia l d ig i -ta l su b trac tio n an g iog ram shows le ssth an 50% s teno s is in firs t 1 .5 cm ofrig ht ren al a r te ry .

screening patients for renal artery stenosis

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