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* P re se n ted on M ay 23 1 9 6 8 to th e W iscon sin M e d ica l A lu m n i, M a d iso n , W isc on sin ; an d on A u gu st 30, 19 68 to T he S c an d in av ianN eu rosu rg ica l S ocie ty , A h r u s, D en m ark .

F r om th e D ep a rtm en t of R ad io lo gy a n d D e p ar tm en t o f S u rge ry (D ivis ion of N eu r osu rge ry), U n ive rs ity of F lor id a , C olle ge o f M e d -icin e , G ain e sville, F lo rid a .

F E B R U A R Y , 1 9 6 9

2 .60

P R E C IS E A L IG N M E N T O F X -R A Y B E A M S F O RS T E R E O T A C T IC S U R G E R Y *

y PA U L C . H O D G E S , M .D ., an d F R A N C IS C O G A R C IA -B E N G O C H E A , M .D .G A IN E S V IL L E , F L O R ID A

A 7IT H at lea s t o ne im po rta n t e x ce p - tio & the X -ra y gu id an ce o f n eu ro -

su rg ica l in s tru m e n ts u sua lly h as b e en do neat tub e-fi lm d is ta nc e s o f 2 me te rs , 3 me te rs ,o r m ore , a lig nm en t be in g ac co m p lish ed bym ea ns o f lig h t b ea m s attac he d to th e h ou s-in gs o f th e X -ra y tu be s . T im e is sa ve d ,co s t red uc ed an d ac c u ra cy im p rov ed iftub e-film d is ta nc e is re du ce d to i me te ran d align m e n t is d on e w ith th e X -ra ybe am s the m selv es (F ig . 7 ; 8 , 1 an d B ; an d 1 an d B ). W e ha ve d e v ise d a n a p pa ratu sof th is so rt fo r th alam ec to m y a nd ha veuse d it su c ce ssfu lly in o ve r 20 ope ra t ions .T he c on s truc tio n , a lig nm en t a nd su rg ic alem ploy m e n t o f th e a ppa ra tu s are d esc ribe din th e tex t o f th is a rtic le a nd the le ge n ds fo rit s 12 figures .

G E O M E T R Y O F S T E R E O T A X ISW h e n the p atien ts h ea d ha s b ee n fix ed

in a n ins tru m e n t-gu ida nc e sys te m , o rien te dso th at its g eo m etric c en te r c o inc ide s w ithth e cro ss in g o f fro n ta l a n d la te ra l X -ra yb ea m s, p re lim in ary roe n tg en og ram s arem ad e . In the la te ra l fi lm the im ag e o f thea na to m ic ta rge t o n the th alam us is co m -p u te d from th e lo ca tio n o f the im ag e o f th eju nc tio n o f th e m id d le a nd p os te rio r th ird so f the in te rco m m issu ra l line , a nd in th efro n ta l film by m e asu re m en t fro m the m id -line o f th e b ra in . A lm ost inv ariab ly th efirst f i lm s w ill sh ow th e im ag e o f th e targ etd isp lac ed m ore o r le ss from th e ce n te r o f th egu ida nc e sys te m , bu t b ec a use o f th e fa c tth at X -ray s d ive rge from the ir sou rce , them a gn itu de o f th at d isp la ce m e n t w ill b eg re ate r th a n the d isp lac e m e n t o f th e a n -a tom ic ta rge t itse lf . F igu re 2 sh ow s thege om e try fo r th e fron ta l be am a n d film ,

b u t th e m ath e m a tic s are the sa m e fo r th eo th er p la n e. T h e m a gn itu de o f d isp lac e -m e n t o f th e an ato m ic ta rge t (T ) from th elon g itud ina l a x is o f the fron ta l film (L ) isd es ig na te d 0 (ob je ct) a nd th e d isp lac e -m e n t o f its im a ge (I.T .) is de s ign ated I(im ag e ). W he n the m ea su re d v a lue s o f 0 a n d I are su bs titu te d in the fa m ilia req ua tio ns fo r th e d iv erg en t d isto rtio n c o r-rec tio n fa c to r an d its re cip roc a l, w e a cq u ireto o ls fo r c om pu tin g th e loc ation o f th eim a ge o f the tha la m ic ta rge t re la tive to th em id lin e o f the b ra in a nd fo r de te rm in in gth e ne t am o un ts b y w hic h he ad an d be a m -re tic le a sse m bly m u st be sh ifte d to b ringthe ta rge t to th e ge om etric c e n te r o f th e in -s tru m e n t-gu ida nc e sys te m (F ig . ii, ii an dB ; an d I 2, ii an d B ). R e ga rd le ss o f th em ag n itud e o f tu be -film d istan ce the se co m -p u ta tio ns m u st b e m a de , an d th e fa ct tha tw ith lo ng er d is tan ce s the c o rre c tion fa cto rbe co m es m o re n ea rly 1.0 ha s no p ra c tic a lad va n tag e. L on g d ista n ce s , ho w ev er, ha v ese riou s m e ch an ic al d isad va n tag es p lu s thed isad va n ta ge o f req u iring m uc h he av ie rX -ra y tub e lo ad ing .

A P P A R A T U SW e em plo y a m o d ifica tio n o f the T od d-

W e lls h ea d -h o ld er, in s trum en t-g u id an cesy stem 5 (F ig . 3 ; a nd 5 ) m oun te d on theo p tic a l be d (F ig . 6 ) o f a b ea m align ing u n ito f o u r o w n de s ign (F ig . i). T w o sm a ll X -ra y ge ne ra to rs are c arrie d on a s tu rd ytu bu lar s tee l b rid ge run n ing o n p re c ise lya lig ne d op tica l ra ils so tha t it ca n b e ro lle dou t o f the su rg ic al fie ld e xc e p t fo r thepe rio d o f fi lm ex po su re . A b rac ke t o n theb ridg e c arrie s a fe eler ga ug e a nd w he n theX -ra y be a m s a re to be b ro ug h t in to p os i-

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I

* G en era tor a n d c on trol a re th e g re atly ap p r ec iated gift o f afrien d w h o p re fers to r em a in an on ym ou s.

\oi. i o N o . 2 X -R ay B ea m s fo r S te re o ta ct ic S u rge ry 26 1

F IG . 1 . G en e ral v iew of ap p ar atu s. i. B ridge ; 2.B racke t ; 3. Fro n tal X -ray genera to r and its co lli-m ato r; 4 . L a te ra l g en erato r and its co llim a to r; O ptical b ed ; 6 . U pper op tical ra il; 7 . L o w er op ticalra il (the re a re 2 sim ila r ra ils at the o th er S ide);8 . C on tro l fo r la te ra l genera to r;* Plas tic re tic lessu pp lied by m an ufac tu re r o f head ho lder. W e sub-stitu te m agn es ium re tic les (see F ig . 4).

W heeled base , b ridge , X -ray gen erato rs andth e ir co llim ato rs and con tro ls co nstitu te a un itw h ich can be m ov ed th rough stand ard ho sp ita ldoo rs in clu d ing e leva to r doors . B e tw een periodsof se rv ice it can be draped w ith a pro tec tive coverand s to red in corr id o rs o r ap para tus sto rag e room s.T h e ins trum en t gu idance system , inc lud ing headho lder and fa r retic le , is w rap ped in c lo th andgas ste rilized and w hen un w rapp ed in th e opera tingroom is p laced dow n o n the op tica l bed reg is -te red in p lace by m eans of 2 dow els (see F ig . 6 ).T h e un it is n o t sa fe fo r use w ith exp los ive anes th e t-ic s, bu t our su rgeons and anesthes io lo g ists a recontent to work only with the nonexplosive va-riety.

W ith a ph an to m head in pos ition and the fro n ta ltube opera ting a t 8o kv ., 10 m a., the d ose a t 2m eters is on ly 0.2 m r/m m . and fo r the la te ra l tubeop era ting a t 7 5 kv . and 12 m a., the dose is 1.0.

tion fo r film ing , the su rg eo n h as m e rely tosee to it th at th e t ip o f th e ga ug e tou c he sthe ba c k o f th e h o rse sh oe o f th e in stru -m e n t gu ida nc e sy s tem in o rde r to assu retha t th e c ross ing o f the 2 be am s lie s a t thege om e tric c en ter o f th e h ea d -h o ld er a s-sem bly . T he retic le , a s ilv er-filled g ra tingru le d in to a sh ee t o f m a gn es iu m (F ig . 4), ispe rm an en tly m o un te d o n th e he a d -h o ld erso tha t its ce n ter po in t lie s on the trans-verse ax is exac tly oppos ite th e ge om etricce n te r o f th e g u ida nc e sys te m w h e n theb rid ge is in film in g po s itio n . A silve r-fille dlin e in th e m a gn es iu m h o ld e r fo r th e fron ta lfilm de fin es the lon g itud ina l ax is o f th at filman d is c e n te red ex ac tly be n ea th the c en terof th e f ron ta l X -ray beam .

T he c om ple te ap pa ratu s h a s ov er-a lld im en s ion s o f o n ly 2 4 X 6 0 X 7 4 inc he s inhe igh t. I t is ca rrie d on rub be r tire d c as te rs ,w ill pa ss th ro ug h s ta nd ard h osp ita l do o rsan d c a n b e w he e led in to w h ate ve r o pe ra tingro om is a va ila b le to th e su rg eo n . It is no tsafe for u se n ea r e xp lo siv e gasses , b u t o fc ou r se e xp lo sive a ne s the tic s a re n o t ne ce s-sary fo r th is ty pe o f su rge ry .

S U R G IC A L D E T A IL S

T o b e u se d , the a pp ara tu s is w he eledin to po si tion at the e nd of a s ta nd a rdope ra ting tab le , c lam p ed to it , a nd flo o rloc ks set (F ig . 10) . T h e s teril ize d a sse m blyof b a se , ho rizo n ta l a rc , 2 film h o lde rs an dfixe d re tic le o f the he a d -h o ld er gu id an cesy s tem are p lac ed on the op tica l b ed , be in gp re cise ly lo ca te d the re by 2 do w els (F ig . 6 ).F ina lly , the pa tie n ts he ad is a nc h o re d toth e h ead -h old er.

V E N T R I C U L O G R A P H YF or the ro en tge no log ic ide n tifica tio n o f

la n dm ark s w e u se a m o d ifica tio n o f th e

These very iow doses are accomplished by closeco llim a tio n of b o th beam s and lead back ing onb o th casse tte ho lders . S ince ind iv id ua l film s re -qu ire exp osu res o f o n ly 3- 5 seco nds, it is m erelynecessary fo r doc to rs , nu rses an d techn ic ian s tos tep back to a d istance of 2 m eters fro m the pa-tie n ts h ea d in o rder to w ork sa fe ly w ith ou t lead eda pr on s g lo ve s o r p ro te ct iv e s cr ee ns .

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V O L . 1 0 5 , No . 2 X -R ay B ea m s fo r S tere o ta c tic S u rge ry 26 3

in strum en t in troduced th rou gh a ho le in a r id erw ill lie w ith its tip exac tly a t tha t ta rge t.

F I G . T od d-W ells h ead ho lder an d instru m en tgu ide . i. H orsesh oe ; 2. B ase lock ; 3. Instrumentgu ide arcs; 4 . In strum ent g u id e rid ers ; C r o w n fo r im m obiliz ing pa tien ts head ; 6 . S u pp orts fo rim m obiliz ing p ins ; 7 . S upp ort in w hich cro w nis c lam ped ; 8 . P in io n fo r m ov in g pa tien ts h eadven tra lly o r do rsa lly ; Lock to arrest su ch m ove-m e n t ; 10 . L ate ra l casse tte ho lder; II. Fron ta lcasse tte ho lder; 12 . B ase of T odd-W ells dev ice ;13 . O ptical b ed of our appara tus; I4 . B racke t onbr idge ; 15 . F ee le r gauge on bracke t. T he tip o fthe g auge is in co n tact w ith the h orseshoe as itm us t be w h en film s are to be exposed ; i6 . N earre ticle , so -ca lled because it lie s neares t to thesource of rad ia tion . T h is o rig ina l re ticle o f c lea rp lastic has inheren t d isad van tag es an d w e h av erep laced it w ith one m ad e o f sheet m agnes iu m (seeF ig . 2); 17 . F ar retic le o f c lea r p lastic . T h is tooh as been rep laced by shee t m ag nesium (see F ig . 2) .

F or all po sitions of arc and ride r a freez ing in -stru m en t in trodu ced th ro ugh a h o le in th e ride rand advanced un til its tip is 13 5 m m . beyon d theb ack of the r id er w ill lie w ith its tip a t the m id-p o in t o f an im ag inary lin e jo in ing th e cen te rs o f the2 la te ra l re tic les an d d irectly over the long itud ina lax is o f the fron ta l film .

The objective of all the maneuvers presently tob e d esc ribed is to iden tify an an ato m ic ta rg et inthe bra in and bring it exac tly to the geom etriccen te r o f th e g u idance sys tem so tha t a f reez ing

[::_ ._ -F I G . 4. M agnesiu m re tic les . i. H orseshoe ; 2. B ase ;

3 . O ptica l bed ; 4. B racke t ; F ee ler gau ge; 6 .F ar re tic le o f 1 / 3 2 inch sheet m agnes iu m ;7 . S treng then ing rib at ed ge , ou tside the fie ld o fex am ina tion ; 8 . H oles fo r sc rew s tha t h o ld jigd uring op tica l a lignm ent o f fron ta l X -ray beam(see F ig . 7 ); 9. N ear retic le (used on ly du rin gp re lim inary op tica l a lignm ent o f the 2 X-raybeam s) is 1 / 3 2 inch shee t m ag nesium cem ented toa shee t o f 1/4 in ch a lum inum for rig id ity ; 10 .S crew s w hich a ttach re tic le to ho rseshoe ;I I . I 1/4 inch open in g th roug h a lum inu m at s ite o freticle; 12 . L ate ra l casse tte ho lder w ith bu ilt-ins ta tionary g rid ; 13 . l ron tal casse tte ho lder w ithbu ilt-in g rid . A line engraved in the m agn es iumfron t and filled w ith s ilve r* defines the lon g itu -d ina l ax is o f the 8X io inch fron ta l film .

T he orig ina l p las tic re tic les w ere so m ew hat un-s tab le d im ens io na lly and the re in fo rced m arg insshow ed on film s and som etim es obscured land-m arks . B o th had to be used fo r each exam ina tio nand beam alignm ent h ad to be checked fro m tim eto tim e du ring the course of exam ina tions . \V ithour appara tus and our m odifica tion s of the h eadho lder and ins trum en t gu idance sy stem th e farre tic le rem ains in p osition a t a ll tim es and thenear one is unused on ce beam align m ent hasb ee n a cc om plis he d.

T h is part o f the gu idance sy stem is c lam ped toth e b ed of a m illing m ach in e an d befo re the re tic lesa re engrav ed th eir cen te rs a re lo ca ted . T hese cen-te rs lie on an im ag inary lin e perpend icu la r to thela te ra l film an d w ith its m id po in t perpend icu la rlyabove the long itud ina l ax is o f the fron ta l film . Asim ilar tech n ique (see F ig . 7) is em ployed fo rlo cating th e sho t and silve r f illed line in the m ag-n es ium jig fo r a lignm ent o f th e fron ta l beam .

* E cc obo nd S ilve r-Ep oxy E a sy M ix #s7-C P aste. E m e rso n &C u m in g, In c. , C an ton , M assa ch u setts .

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26 4 P a u l C . H o dg es a nd F ran cisc o G a rcia-B e ng oc he a F E B R U A R Y , 1 969

lic,. {231}. th er m odifica tion s of T odd -W ells dev ice .i. S crew for transv erse m ovem ent o f pa tien tshead ; 2. S ca le fo r transverse m ovem ent; 3. Sca lefo r ven tra l-dorsa l m ovem ent o f head ; Pin ionfo r sh ifting ho rseshoe and a ttach ed F ar re tic letow ard vertex or tow ard feet; L ock for such m o -tio n ; 6 . S cale fo r such m otion .

T he orig ina l sca les w ere engrav ed in m eta l andhard to read . O urs a re eas ily readab le b ein g en-g rav ed o n b lack p las tic lam ina ted on w hite b ack -in g . T ra nsverse sh ift ing of the he ad form e rly w asd one b y p ush in g or ham m ering the b ase of th e yokea long its w ays . W e accom plish th is m otion w ith asc rew . S h iftin g of re tic le and h orseshoe assem blytow ard fee t o r tow ard vertex w e do b y m eans o f arack and p in ion ra the r than by push ing or h am -m ering . In the locks fo r the slo tted w ay s in base ,ho rseshoe an d g u idance arcs (see F ig . 3) th e sm allrec tangu la r clam ping m em bers a t th e en ds of lock-ing sc rew s w ere free to ro ta te u n til they had beenlodg ed w ith in the ir s lo ts. A s a resu lt a su rg ica lassistan t, in ste rile attire , a ssem bling the ste rilizedparts o f the gu id an ce sys tem w asted m uch tim em aneuv er in g the rec tan g les in to the ir s lo ts. T hed ifficu lty ha s be en c orrected b y f ix in g sm a ll p insin the clamps. These p ins ride in free fitting h o lesin th e b lo ck s in to w hich the s cr ew s a re t ap pe d pre -ven ting the rec tan g les fro m ro ta tin g ou t o f a lign -m en t w ith th eir respective slo ts.

m ethod of pos itive p ressu re ven tricu logra -ph y d esc ribe d by C a lv in a nd C o e.2 W em a ke th e b u rr h o le o n the d ay of th e stere o -tac tic p r oce d u r e, after the pa tie n t ha s be e nfix ed in the h o ld in g an d g u id ing a pp ara tu s ,a nd p la ce th e ho le on th e c o rona l su tu re , 3c m . from the m id lin e . U su ally no flu id isrem o ved excep t fo r the fe w dro ps lo s t ina sce rta in in g tha t the v en tric le ha s b e enen tere d , an d in c on ne ct ing rub be r tu b in gto the b rain c a nn u la . F o r a du lts w itho u tin c re ase d in tra cr an ia l p re ssu r e 15 cc . o f a ir

is in jec te d g en tly in 40 to 6o sec o nds a ndthe firs t f ilm s (la te ra l an d an tero po s terio r)ar e exposed (F ig . ii, 4 a nd B ; an d 12 , 4

an d B ). If th e film s rev ea l tha t m o re a ir isne e de d , it is a dd ed in sm a ll in c r e me n t sa c co rd in g to e s tim ates ba se d on p r e ssu r elev els a nd th e d eg re e o f ve n tricu la r fi llin ga lre ad y o b ta ine d . F o r th a lam e cto m ies ad e-q ua te v isu a liza tio n of th e th ird v en tric lea n d ro s tra aq ue du c t o f S y lv iu s usu ally isa ch ie ve d w ith v o lum es o f a ir ran g in g from20 to 30 c c . In so m e c ase s it m a y be n ec es-sa ry to rem ov e so m e flu id an d in jec t la rge ram o u n ts o f a ir , the o p tim u m vo lum e o f airse em in g to b e re la ted to a trop hy a nd v e n -tric u la r s iz e . D urin g the in jec tio n o f air

F I G . 6. O p tic al b ed . i. B e d ; 2. Pads; 3. Dowels;4. Bracket; 5. Feeler gauge; 6. Slots to receivebrackets on operating table; 7. Locks to anchoropera ting tab le to appara tus ; 8 . L ocks to fix b ridgeto op tica l rails .

T h e bed is 8 inch in shee t a lu m inum bolted tothe s teel tab le top , the la tte r hav in g been m ach inedto be fla t and as n early as possib le perpend icu la rto the 2 m ach in ed s id es w hich carry the supp ortsfo r the o p tica l ra ils . T o fu rthe r inc rease accuracythe head ho lder rests no t on the a lum inum top b u tra the r on brass pads w h ich are th readed in tothe a lum inum an d pro jec t th rough the sh eet p lasticw hich is cem en ted to it. B y m eans of su rface g au gesthese pads are ra ised and low ered un til they arew i th in 3 thousand ths o f an in ch of defin ing a p laneperpend icu la r to the p lanes of the o p tica l rails .W hen the head h o lder has been p laced dow n o n thedow els, the long itud ina l ax is o f the fro n ta l filmw ill lie d irec tly benea th the so urce of the fron ta lX -ray b e am for a ll pos ition s of the bridg e, andw h en the fee le r gauge m a k e s co n tact w ith theh orseshoe bo th beam s w ill in te rsec t a t the geo-m etric cen te r o f the ins tru m en t gu idance syst e m.

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A B

Sa 2

R L

V O L . 105, N o. X -R ay B ea m s fo r S te re o ta ct ic S u rg ery 26 5

* E x ce p t fo r com puta tion of lo ca tion of im ag e o f targ et infr o nta l film (see F ig . ii).

F I G . 7 . A lig nm ent o f X -ray beam s. A shee t o f i/inch m agnesium (I) 6 in ches w ide , 12 8 incheslong and w ith a 5 8 c ircu lar cu t ou t in the cen te rfo rm s a jig fo r the a lignm ent o f the fron ta l beam .W ith the ho lder c lam ped to th e bed o f a m illingm ach ine (see leg en d F ig . the jig is lined up w iththe cen te rs o f th e 2 re tic les. A t the upper ed ge asm all ho le is d rilled ex ac tly over the long itu d ina lax is o f th e fron ta l film an d in the low er edge a sh ortg roove is m illed ou t ex actly p aralle l w ith the im ag-ina ry line co nnec tin g the 2 re tic le cen te rs an dperpen d icu la rly b eneath the h o le in the upp er edge .A sm all sho t (ac tua lly a ba ll bear in g ) is p ressedin to the ho le in the up per edge of th e jig an d silve r-epo xy p as te app lied to th e g roove , thus prov id ingtw o landm ark s fo r op tica l a lignm ent o f the fron ta lX -ray beam (see F ig . 8 ); (2 ) is the con tro l fo r thefron ta l genera to r, (3 ) the bracke t w hich su pportsthe fee le r gaug e (in th is v iew co ncealed by the jig ),( is the fron ta l g en erato r , ( the la te ra l gen era-to r and (6 ) the tubu la r s tee l b ridge o n w hich thetw o genera to rs a re m oun ted . A lignm ent o f thela te ra l beam is desc rib ed in the legend fo r F igu re 8 .W hen b o th a lignm ents have been m ade th e 2genera to rs are lo cked in pos ition an d the jigand n ear re tic le a re rem oved and no t usedaga in .

T he short tub e- film dis tan ce o f i m eter in ev eryw ay im p roves an d in n o respec t d ecreases theaccu racy of ins trum en t gu idance . B ecause a t im eter an ex posure of o m as. su f fices , th e genera -to rs m ay be sm all and of ligh t w eigh t so tha t th eycan be carried on a tubu la r stee l b ridg e w h ich al-low s n o sign ifican t sag . O nce a lignm ent has beenacco m plished no th ing short o f a se rious m echan ica lacciden t w ill d istu rb it. T he fac t tha t d ive rg en td isto r tion of im ages is g rea te r than it is a t g rea terD s improves accuracy by m agn ify in g theam ount by w hich an ana to m ic targ e t fa ils to liea t the geo m etric cen ter o f the gu idance sys tem .E rro rs in d and in the sim p le a rithm etic re -qu ired h av e no effec t o n accuracy and can m ere lyinc rease so m ew hat the n um ber of tes t f ilm s tha tm us t b e m ade . O nce a ta rge t lies a t the g eom etr iccen ter all o the r fac to rs h ave b een elim ina ted and

L RF IG . 8 . O ptica l a lignm ent o f fron ta l X -ray beam .

i. Im age o f silve r filled line in fron ta l casse tteh o lder ind ica ting lo ng itud ina l ax is o f fro n ta l film ;2. Im age o f sho rt, transverse , s ilve r-filled line a tlow er edg e of jig ; 3. Im age of sm all sho t im bedd edin upp er edge of jig . (A ) T h is d raw ing fro m a filmear ly in a ser ies o f tes ts show s the sho t d isp lacedsligh tly abov e and to th e le ft o f the cen tra l cross ingo f film ax is and transverse line . (B ) Follow ing ates t se ries, w ith approp riate sh ift o f f ron ta l tu beb e tw een tes ts , the sho t is foun d to lie p rec ise ly a tthe cen tra l c rossing o f transverse line and film ax is.T he prec ision of th is type o f a lignm ent is m uchgrea te r than the best tha t co u ld b e accom plishedw ith ligh t beam s an d o nce su ch a lignm ent h asbeen do ne it need n eve i be don e aga in .

In the f ilm s them se lves the im ag es o f sho t andtran sverse line , even thoug h su perim posed on them agnes ium fo rm in g the u pper an d low er portionsof the cu t-ou t in the jig , co u ld b e w ell seen bytran sm itted ligh t. B ecause such film s do n o t lendthem se lves w ell to rep rodu ction w e have em ploy edfo r th is figu re no t film repro duc tio ns bu t an artistsd raw ing m ad e from the film s.

beam alignm ent a lone affec ts accuracy .* T o b e truethe d iam ete r o f the im ag e of the ta rge t w ill bela rger than th e ta rge t itse lf bu t since w e are d ea lingw ith the cen te r o f tha t im ag e its ac tua l d iam ete r iso f n o im p ortance w hatever.

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jun ction o f the po s terio r a n d m id d le th ird so f the in te rco m m issu ra l line . W he n thefirs t fi lm s (la tera l an d fron ta l) ha ve b ee nexposed fo llo w ing th e in jec tio n o f air , the w o rk -u p be g ins a n d c on tinu es th ro ughsu bse que n t film s u n til th e targ et h a s be e nb ro ug h t to th e lo ng itud ina l a x is o f thefron ta l film an d th e c en te r o f the re tic le inthe la te ra l film . W h e n the se tw o ob je ctive s

26 6 P au l C . H o dg es a nd F ran cisc o G a rcia-B e ng oc he a F E B R U A R Y , 1969

A B

l i O p tica l a lignm ent o f la te ra l X -ray beam .B y m eans of sk illfu l and pa ins tak in g m ach in ew o rk (see lig . and 7) th e cen te rs o f th e 2 reticlesar e m ad e to lie so tha t an im ag inary lin e c on ne ct-in g them is exac tly para lle l w ith the fron ta l filmand perpend icu la r to the la te ra l film . W hen th ish as been don e and the la te ra l tub e arranged w ithits ta rge t ap prox im ate ly in line w ith th e 2 reticlecen te rs , fu rthe r tub e alignm en t is acco m plished byop tical m eans. T he fa r re tic le has silve r-filledv er tica l an d tran sverse lines each w ith fou r trans-v erse s trokes. T h e near retic le cons is ts o f as ilv e r-filled c irc le w ith strok es a t IX , X II, III andV I oc lock . (A ) T he near re tic le is d isp laced dow n-w ard and to the le ft rela tive to the fa r re tic leind ica tin g tha t the ta rge t o f th e la te ra l tube is inno t q u ite perfec t a lig nm ent. (B ) A fte r repea tedtests , w ith sh ift o f X -ray tu be be tw een them , th e2 re ticles co inc id e. T he tube is now locked in pos i-tion and th e near re tic le rem o ved . It is usedm ere ly fo r th is p re lim inary a lignm ent an d c lin ica lw ork em ploys m ere ly the fa r re ticle w h ich re -m ains perm anen tly in p lace. T he beam alignm entillu s tra ted here an d in F igure 8 assu res tha t th e 2beam s m eet a t the geom etric cen te r o f the ins tru -m en t g u idance sy stem .

and the m a kin g of ro en tge n ogra m s, ca re istak en to p re v en t lo ss o f p re ssu re a nd toa vo id in tro du cing un ne ce ssa ry a ir in to th efou rth ventric le .

S E L E C T IO N O F A N A T O M IC A L T A R G E T SA N D B R IN G IN G T H E M T O IH E C E N T E R

O F IN ST RU ME NTG U ID A N C E S Y S T E M

S ubject to subsequen t c o rre c tion ba sedon p hy sio lo g ic respo nse , th e a na tom icta rge t is as su m ed to lie 13.6 m m . to therig h t o r left o f th e m id lin e an d at a p o in ti m m . rostra an d 3 m m . do rsal to th e

F i G . io . A p para tus a ttached to opera ting tab le .1. B racke t on op erating tab le en te rs recep tac le onour app aratus ; 2. L ock h o lds tab le b racke t inp lace ; 3. Fron ta l X -ray genera to r; 4. L ate ra l X -raygenera to r ; B ridge .

Th e 2 b eam s are c lo se ly co llim a ted so tha t theycover a m ere 6 inch c ircle a t the film s and bo thcasse tte h o lders are backed w ith lead . A s a resu lt, theo u tpu t o f sca tte red rad iation is so lo w th at doc to rs ,n u rses , techn ic ians and o thers w ork ing in theo pera tin g ro om do no t n eed apro ns o r g loves (seeF ig . I).

A t our ins titu tion surg eo ns and an es thesio log is tshave ag reed to u se o n ly no nexp los ive anes th etic s,w henev er su rgery requ ires the em ploy m en t o f X -rays . A ccord ing ly th is appara tus, like a ll th e rest o fou r X -ray appara tus, ca rrie s a s ign sta tin g tha t itis no t sa fe fo r u se in exp los iv e a tm ospheres .

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\o i . 105, No . 2 X -1 B eam s fo r S tereo tac tic S urge ry 26 7

A B

J I G . ii. Work-up of frontal film. In th e av era ge adu lt it has been found that the anatomic target in the tha la -m us lies 13 .6 mm. lateral to the mid-line of the brain. Multiplying 13. 6 by the rec ip ro cal facto r 1.25 ( seeF ig . 2) we obtain the value i m. as the location of the image of that target lateral to the mid-line of thebrain. This value remains the same throughout the film series an d we trea t a m ark m ad e on the film 17 mm .la te ra l to the m id -lin e of the brain as th ough it w ere the im age o f a v isib le s truc tu re . lo r exam p le , if in aparticu la r film tha t m ark is foun d to lie 10 m m . to the le ft of the ax is o f the fro n ta l f ilm , w e m ultip ly th atva lue by the correc tion fac to r o .8 o b ta in in g 8 .o m m . as the am oun t b y w hich th e p atien ts head shou ld besh ifted to w ard th e righ t.

I. A ir-filled la te ra l ven tric les; 2. Sep tum pelluc idum ; 3. L ongitud ina l ax is o f fron ta l film ; 4. M ark p lacedon film ind ica ting co m puted location of ana tom ic ta rg et; 5. C an nu la fo r in jec tion o f a ir; 6 . F reezing ins tru -m e n t .

(A ) T he ta rge t ( lie s sligh tly to th e le ft o f the long itud ina l ax is . (B ) A fte r severa l film ex posures, w ithtransverse sh ift o f p atien ts head b e tw een them , the targe t (4) lie s squ arely on the long itud in al ax is andthe tip o f the freez ing in strum en t (6 ) co inc ides w ith it.

N o te: It m u st be ad m itted th at the abil ity to c om p ute the loc atio n o f the im age ( invo lves a cc urate kn ow le dge of (d) and of th ere cipro cal fa ctor (se e F ig . a) bu t c lin ic al re su lts in m o re than 20 ope ratio ns ind ica te th e sou ndne ss of th e a ssu m ption s in volve d (see F ig .7) .

ha ve be e n ac c om plish ed , th e ta rge t w il lha ve be e n b rou gh t to th e ce n ter o f th ein strum en t-g u idance system . F o r de tails o fw ork in g -up fron ta l an d la te ra l film s se eth e legends for F ig u re s ii an d 12 .

P h ys io log ic te s ting is ca rried ou t b y c on -v en tion al m e an s a nd , if n ec essa ry , fin als lig h t a d ju s tm e n ts are m a de in the p os itiono f h ead an d tu be -retic le a ssem b ly . T h ere m ain in g step s o f th e th alam ec to m y fo llo w

te ch n ique s w h ich ha v e b ee n d esc ribe d b yo the rs an d need no t be rep ea ted he re .

D I S C U S S I O NO bjectio n h as b een ra ised tha t any sys-

tem requ ir ing fixa tion o f the p atien ts h eadin th e b ro w -u p po s itio n (a s in th e T o dd -\V ells he ad -ho lde r) p re ve n ts a de qu ate d is -tr ibu tion o f co n tras t m e d ia , e ith er liq u idor gaseo u s, by m a k ing it im po ss ib le to

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V.3 .3

P P

26 8 P au l C . H o d g e s and F ranc isco G arcia -B en go ch ea F E B R U A R Y , 1 9 6 9

F I G . 12 . W ork-up of la te ra l film . (A ) T h e an a to m ic ta rge t ( lie s pos te rio rly and tow ard the p atien ts fee tre la tive to the cen te r o f the fa r re tic le (i). (B ) A fte r severa l tria l film exp osu res, be tw een w h ich p atien tshead w as sh ifted an te rio r ly and the re tic le -beam assem bly to w ard h is fee t, the ta rge t (3 ) lie s a t the cen tero f the re tic le assu ring tha t it is a t th e geom etric cen te r o f the ins trum en t g u idance sys tem . T h e freez in gins t rumen t ( lie s w ith its tip a t the ta rg et, bu t befo re destruc tive freez ing is don e there m us t still bephys io log ic tes ting fo r fu rthe r re finem en t o f p osition ing .

T he m ean s of iden tify ing th e in te rcom m issu ra l line and loca ting the ta rge t i m m . rostra l and 3 m m. do rsa lto the ju nc tio n of th e m id d le and po ste rio r th irds o f tha t line a re exp la ined in th e tex t.

mo v e th e h ea d . E v en pre v io us to the de -v elo p m en t o f ou r n e w e q u ip m en t, h ow eve r,w e w er e co n v in c ed th a t the e m p loy m en to f po si tive p ressu re pe rm itte d co ns is te n tv isua liz a tion o f th e th ird ve n tric le a nda q u e d u ct of Sy lv ius w ithou t mo v i n g th eh ea d fro m the b ro w -u p po sit ion . W e a gre ew ith C alv in an d C oe2 th at w ith the irp os itiv e p re ssu re m e th od the re are fe w e rs id e e ffe cts tha n w ith stan da rd v e n tric -u lo g rap hy and pn eu m oen cep h a log raphy ,an d w e find it s im p le r tha n th e m e th odde scribe d by C la rk et a l. C on tra ry to th esug ge s tion b y W altz an d C oo pe r6 w e be lie vetha t the tip o f th e c a nn u la n ee d no t bep la c ed c a uda l to th e fo ra m e n o f M onro ino rd er to ob ta in c ons is te n t v isua liz a tion o fth e posterior th i rd ve n tr icle , aq u ed u ct ,p a rts of b o th the fou rth ventricle a nd ba sal

cis terns in pa tien ts w ith pa ten t ven tr icu la ran d su ba rac hn o id sys te m s.

W e a tte m p t to p re v en t sp re ad o f airbeyon d the ro stra fou rth ven tr ic le , no ton ly to redu ce sid e e ffec ts bu t a lso to avo idpo ss ib le ob scu rat ion o f the th ird ventricleand aqu ed uc t o f S y lv ius by po ck ets o f air inth e su ba rac hn o id spa c e, bu t w h ile w e a ren o t a lw a ys suc ce ssfu l in th is a tte m p t a nda ir freq ue n tly is see n in the c is tern s , in n ocase has it in te rfered w ith v isu aliza tion ofc r itica l s truc tu re s .

S U M M A R Y

i. A lign m e n t o f th e X -ra y be a m s use d inster eotact ic su rg er y is b es t d on e w ithth ose be a m s the m se lv es ra th er tha n w ithlig h t beam s attached to the X -ray tub eh o u s i n g s .

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V O L . 1 0 5 , No . 2 X -R ay B ea m s fo r S te re o ta ct ic S u rge ry 2 69

2. A tu be -film d is ta nc e o f i m ete r isp re fe rab le to 2 o r 3 m eters or m o re, th esho rte r d is tan c e im pro v in g rath er tha nd im in ish in g the ac cu rac y o f lo ca liz a tion o fb rain ta rge ts in tha la m e ctom y .3. In a d d itio n to im pro ve d a cc u ra c y , th esh o rt tu be -film d istan ce m a ke s po ss ib le th euse o f sm a ll X -ra y ge ne ra to rs inc o rp o ra te din a self-c on ta ine d un it w h ic h ca n bew h ee le d in to a ny o pe rating roo m th ath ap pe ns to be av ailab le to the ne u ro -su rg eo n at th e m om en t.

4 . B e ca use the X -ra y b ea m s h av e b ee np erm a ne n tly al ign ed in the m ac h in e sh op ,th e t im e fo r stere ota ctic su rg er y is r e-ma r k a b l y sh o rte n ed w ith resu ltin g d i-m in ishe d d isc o m fo rt to th e p at ien t.

{231} .T h e construct ion, c a lib ra tio n an dsu rg ica l e m p loy m e n t o f su c h a n ap pa ratu sa re d es cr ib ed .

6 . P o s itiv e p re ssu re v en tric u lo g ra ph ya llo w s v isu al iza tio n o f th e th ird ve n tric lea nd th e a qu ed uc t o f S y lv iu s in th e re -c um b en t p a tien t.

Pau l C . H o d g e s , M . D .D e p ar tm en t o f R ad io logyUn iv er sit y o f F lo ri daC ollege o f M ed ic ineGainesville Florida 32601

R E F E R E N C E S

1. B A I L E Y , P . C ha irm an , S ym po sium on Ste reo tac ticSu rgery , D e tro it, A pril 26 , 1 9 5 7 . 7 . N eurosurg . ,1958, 15 239-280.

2 . C A L V IN , T . H ., J R . , and C O E , J. E . P ositive p res-su re ven tricu log raphy fo r ste reo tax ic su rgery .7. N eurosurg . , 1967 26 548 552 .

3. C L A R K , L. , M O S E R , D ., and B R A C K E T T , C . C on-tro lled sm a ll vo lum e ven tr icu log raph y . 7 .N eurosurg . , 1966 24 777-778 .

4 . D OB B E N , G . D ., M U L L A N , S. and M O 5 E L E Y , R .D. JR . New biplane neuroradiologic localizingin s t rumen t . R adio logy , 1967, 89 , 329- 33 .

T O D D , E . M . M anua l o f S te reo tax ic Pro ced ures.Privately pu b lish e d b y M ec ha n ic al D evelop-m en ts C o m pany , S ou th G ate, C alifo rn ia, 1967.

6. W A L T Z , J. M ., and C O O P E R , I. S . C om para tiv estudy o f ven tricu log raph y and pneum oencep h-a lography for roen tg en ograph ic land m arksd ur in g c ry ot ha la me ct om y. AM . J. R O E N T -G E N O L ., R A D . T H E R A P Y & N U C L E A R M E D .,1 9 6 6 , 97 583-587 .