3D RECONSTRUCTION OF THE TEMPORAL BONE IN COCHLEAR IMPLANT SURGERY M.C. Dhm, H.L. Seldon, B.C. Pymn nd G.M. Clrk Humn Communiction Reserch Centre, Deprtment o/otolryngology, University 0/ Melbourne, The Royl ViclOrin Eye nd Er Hospitl, 32 Gisborne Street, Est Melbourne 3002, ViclOri, Austrli Introduction In the preopertive evlution of prospective cochler implnt ptients high resolution computed tomogrphy (CT) is routinely performed l. 2. Sectionl imges of the temporl bones in the xil or coronl plne cn give essentil informtion bout cochler or mstoid pthology tht will enble the surgeon to select side for opertion nd lert him to surgicl obstcles he might encounter l. 4. Even with the help of seril CTs it hs lwys been very difficult to visulize the complicted ntomy of the norml temporl bone. In prticulr, in ptient with mlformtion or previous opertion, even n experienced otologic surgeon cnnot lwys void unwelcome surprises. In nlyzing the CT films he must still try to form 3-dimensionl imge in his mind by looking through lrge number of different pictures s. Consequently, to mke it esier to understnd, lot of effort hs been put into the development of 3-dimensionl (3D) imging of the object. A vriety of 3D grphics systems tht provide multi-ngled surfce renderings from seril CT imges hve become vilble in recent yers nd proved to be useful in crniofcil reconstructive, orthopedic nd neurosurgicl plnning 6. S. We pplied our own imge nlysis technique to produce three-dimensionl reconstructions of temporl bones in ptients nd in isoltion on personl computer 9 We focused on the use of this method for the preopertive exmintion nd surgicl plnning for cochler implnttion s well s for our reserch purposes. This system nd the results re presented here. Methods Input for the reconstructions cn be ny series of CT scns. The imges re usully stored on X-ry films or cn be sved onto mgnetic tpes or floppy disks. In most cses we use CT imges sved on tpe. On our own VAX computer these files re converted into stndrd formt (GIF) nd cn be-trnsferred to personl computer on floppy disk. Alterntively the films cn be viewed on light-box with video cmer. These video imges re digitized nd stored on the personl computer. By trnsferring the imge dt onto our independent work-sttion we overcome the problem of blocking vluble scnning time on the CT-scnner computer. The sme system cn lso be used for the reconstruction of histologicl sections. In first step the progrm displys the CT imges on the screen by color coding the different gry levels pproximtely representing the density (Hounsfield Units). Depending on the resolution nd the intervls of the consecutive "originl" CT-scn imges, vrible number of slices cn be interpolted between them. The progrm llows now for either utomtic, interctive or mnul edge detection in the CT imges. By using the originl imge dt, there is bsolutely no loss of resolution in the reconstruction. The user cn select certin regions of interest in the surfces s boxes nd store them s seprte fetures or objects. This mens, tht ny feture detected on prticulr scn cn be esily recognised in the following 3D recon- This work ws supported by the NIH Contrct NO I-DC-7-2342 Studies on Peditric AudilOry Prostheses Implnts nd the Deulsche Forschungsgemeinschft DFG D 232/1-2. Trnsplnts nd Implnts in Otology II, pp. 271-275 Proceedings of the Second Interntionl Symposium on Trnsplnts nd Implnts in Otology Mtsuym, Ehime, Jpn, April 1-5,1991 edited by N. Yngihr nd J. Suzuki 1992 Kugler Publictions, Amsterdm/New York
272 M.e. Dhm et l. ~-.----------------------------------, ọ.. 8 D DD Ig : 8... ' B, 0+---,----,,---,-----,----,----,,---,-----,----,-----1 S 0 Fig. I The distnces of ntomicl points of interest yielded fter 3D reconstruction re correlted with direct clliper mesurements fter ntomicl dissection of the sme specimen. The correltion coefficient for 574 mesurements is 0.9452, the slope is 0.867 with n intercept t 1.38. T(572)= 69.25. Fig. 2. Photogrph of the lterl spect of temporl bone (ge 17 yers).
3D reconstruction of the tem orl bone 273 struction. For instnce the ossicles, the round window, the fcil recess etc. cn lter be highlighted by being plotted lone or in different color thn the surrounding bone. Within the disply mode of the reconstruction progrm the user cn rotte the object round ll xes, zoom nd move it, cut off section t ny level, or "drill" hole to disply otherwise hidden structures. The imges cn be lbeled nd stored for documenttion. By defining points of interest with the computer mouse, distnces nd ngles cn be clculted even fter dditionl rott ions, mgnifictions, drilling etc.. To enhnce the 3D ppernce of the object shding cn be dded with virtul light source from ny ngle nd t ny intensity. The most plstic 3D ppernce imge however cn be chieved by producing video imitting rottion of the object. In ddition to its use in exmining the temporl bone in ptients nd 10 determine the ccurcy of our 3D reconstruction system the CT-scn imges of six cdver temporl bones from children rnging from three months to 18 yers were recorded, digitized nd trnsferred onto our microcomputer. We selected severl ntomicl nd surgicl lndmrks relevnt for cochler implnt surgery in children, including the round nd ovl windows, the promontory. the lterl semicirculr cnl, the foss incudis, the mstoid tip, the sinudurl ngle nd others. The distnces between these points were mesured using our reconstruction progrm nd compred to those yielded by direct clliper mesurements fter ntomicl dissection of the sme bone. Results The correltion between the two sets of dt ws very good nd yielded regression coefficient of 0.9452 (Fig. I). Exmples of the 3D reconstructions from these temporl bones re shown in Figs. 2 nd 3. FiR 3 The sme temporl bone s in Fig. 2 fter reconstruction using the originl CT dt.
274 M.e. Dhm et l. Fig. 4. Reconslructed imge of seven-yer-old girl with bilterl Mondini's syndrome fter implnttion of Cochler 22 multichnnel implnt. The led-wire of the implnt cn be seen in the msloid cvity. forming loop to ccommodte expected skull growth. Fig. 5. The sme child s in Fig. 4. Only the cochler implnt nd the ossicles re plotled, displying lhe orienttion of the eleclrode rry in the inner nd middle er.
3D reconstruction of the tem orl bone 275 On ptient with bilterl Mondini's mlformtion of the inner er postopertive CT scn ws performed nd the imges used for reconstruction (Figs. 4 nd 5). By only displying the electrode rry, the ossicles nd the inner er spces, the orienttion of the Nucleus Mini 22 multichnnel cochler implnt inside the inner nd middle er becomes obvious. The intrcochler prt of the electrode follows the bsl turn of the rudimentry cochle. Even the thin pltinum wire we use for the fixtion of the electrode rry t the foss incudis in children is visible. Discussion The presented concept with its bility to visulize the complicted ntomy of the er nd 10 mke ccurte mesurements of the vrious structures in it cn provide importnt informtion for the surgeon plnning the cochler implnt opertion. For instnce, the reltionship of bulging sigmoid sinus to the fcil recess cn be ssessed more ccurtely nd, by detecting the crnil sutures in child prior to the opertion, the surgeon cn try to void the plcement of the pckge cross these sutures. For reserch purposes, we re exmining the growth pttern of the temporl bone during erly childhood in order to mke the cochler implnt vilble for smll children. Cdver lemporl bones from children re not esy to come by. On the other hnd, CT scns re performed routinely on ll our cochler implnt cndidtes including the incresing number of smll children. So now these CT-scn series re used for our mesurements. By its nture the 3D reconstruction cn only detect fetures lredy present on the plin two-dimensionl CT scn. But it fcilittes significntly the conceptuliztion of the complicted ntomy of the er nd is supplementing plin CT scns. With the present progrm we believe we hve chieved reltively chep nd effective system, providing the surgeon nd resercher with rpid nd ccurte method to exmine ptient's temporl bone. Therefore we will continue to use the 3D reconstruction for the preopertive evlution in cochler implnt surgery nd for the collection of dl on the growth pttern of the temporl bone. References I. Pymn BC, Brown AM. Dowell RC. Clrk GM: Preopertive evlution nd selection of dults. In: Cochler Prostheses. (Eds) Clrk GM, Tong yc. Ptrick JF. Edinburgh: Churchill LivingslOne, 1990 2. Phelps PD. Annis JAD. Robinson PJ: Imging for cochler implnts. Br J RdioI63:512-516. 1990 3. Hrnsberger HR. Drt OJ. Prkin JL. Smoker WRK. Osborn AG: Cochler implnt cndidtes: ssessment with CT nd MR imging. Rdiology J64:53-57, 1987 4. Mueller DP. Doln KD. Gntz BJ: Temporl bone computed tomogrphy in the preopertive evlution for cochler implnttion. Ann 0101 Rhinol LryngoI98:.146-349, 1989 5. LRouere MJ, Niprko JK, Gebrski SS, Kemink JL: Three-dimensionl X-ry computed tomogrphy of the temporl bone s n id to surgicl plnning. Otolryngol Hed & Neck Surg 103:740-747, 1990 6. Zinreich SJ. Mttox DE. Kennedy OW et l: 3-D CT for crnil fcil nd lryngel surgery. Lryngoscope 98:1212-1219,1988 7. Zinreich SJ. Rosenbum AE. Wng H et l: The criticl role of 3-D CT reconstruction for defining spinl disese. Act Rdiol 369:699-702, 1986 8. Burk DL. Mers DC, Kennedy WHo Cooperstein LA, Herbert DL: Three dimensionl computed tomogrphy of cetbulr frctures. Rdiology 155: 183-186, 1985 9. Seldon HL: Three-dimensionl reconstruction of temporl bone from CTscns on personl computer. Arch Otolryngol Hed Neck Surg 117: I J58-1161, 1991
Minerv Access is the Institutionl Repository of The University of Melbourne Author/s: Dhm, M. C.; Seldon, H. L.; Pymn, B. C.; Clrk, Greme M. Title: 3D reconstruction of the temporl bone in cochler implnt surgery Dte: 1992 Cittion: Dhm, M. C., Seldon, H. L., Pymn, B. C., & Clrk, G. M. (1992). 3D reconstruction of the temporl bone in cochler implnt surgery. In Trnsplnts nd Implnts in Otology II, Mtsuym, Ehime (Jpn). Persistent Link: http://hdl.hndle.net/11343/26872 File Description: 3D reconstruction of the temporl bone in cochler implnt surgery Terms nd Conditions: Terms nd Conditions: Copyright in works deposited in Minerv Access is retined by the copyright owner. The work my not be ltered without permission from the copyright owner. Reders my only downlod, print nd sve electronic copies of whole works for their own personl non-commercil use. Any use tht exceeds these limits requires permission from the copyright owner. Attribution is essentil when quoting or prphrsing from these works.