This article is the first in a series of articles

Transcription

1 Tody s Technicin Peer reviewed Imging Essentils Series Smll Animl ThorAcic rdiogrphy Dnielle Murgis, CVT, nd Clifford R. erry, DVM, Diplomte ACVR RdiOgRphy LingO node: n electriclly positive terminl of rdiogrphic tube tht emits x-rys from the point of impct of the electron strem from the cthode. Cthode: The negtive side of the rdiogrphic tube where electrons re emitted; it consists of the focusing cup nd filments. Cssette/detector plte: light-proof housing for rdiology film, contining front nd bck intensifying screens between which the film is plced. Collimtion: This term refers to the process of djusting n opticl instrument so tht the x-ry imge includes the re of interest. Millimpere second (ms): describes the exposure setting of rdiology mchine nd determines the rdiogrphic density. ms is clculted by: ma (sttion number setting) x time (setting) = mas (eg, 100 ma 0.10 sec = 10 mas) pek kilovoltge (kvp): The mximum voltge pplied cross n rdiogrphic tube, which controls the x-ry penetrtion of the subject being imged. pek inspirtion: exposing film t pek inspirtion mximizes the ir in the lungs nd the subject contrst within the thorx. This rticle is the first in series of rticles tht will discuss vrious rdiogrphic positions nd techniques. The veterinry technicin plys criticl role in the development nd mintennce of rdiogrphic progrm t veterinry prctice. Thus, it is the responsibility of the technicin to be fmilir with the bsics of: Antomy nd positioning Technique nd imge formtion Qulity control of imges mde within the rdiogrphic suite. The purpose of this rticle is to review the 3 bsic components of creting highqulity thorcic rdiogrphs of the dog nd ct, including positioning, technique, nd qulity control of the finl imges. With dvnces in imging technology (computed nd digitl rdiogrphy), errors in technique re less common; however, if ntomy is not ppropritely collimted nd positioning is indequte, ll imging studies cn be rendered nondignostic. A routine thorcic rdiogrphic study includes 3 projections: right nd left lterl imges nd ventrodorsl (VD) or dorsoventrl (DV) imge. September/October 2011 Tody s Veterinry Prctice 45

2 Tody s Technicin Figure 1. (A) Dog in right lterl recumbency with thorcic limbs pulled crnilly. See text for ntomic boundries of collimted thorx. () Right lterl thorcic rdiogrph of dog in Figure 2A; notice the crnil loction of the thorcic limbs reltive to the thorcic inlet. Figure 2. (A) Dog in left lterl recumbency with thorcic limbs pulled crnilly. See text for ntomic boundries of collimted thorx. () Left lterl thorcic rdiogrph of the dog in Figure 2A; notice the crnil loction of the thorcic limbs reltive to the thorcic inlet. MEOw MEETS Rk: differences ETwEEn CTS & dogs even though the sme ntomic lndmrks re used in the dog nd ct, there re some key differences when it comes to qulity control of the thorcic imge. In the ct, the cudl dorsl lung mrgins (diphrgmtic crur) will extend beyond the 13th thorcic vertebr, which will not be true in the dog (T10-11). In ddition, while the thorcic limbs in the ct re esier to pull forwrd, cts my resent lterl recumbency positioning. Tke your time nd llow the ptient to clm down rther thn rushing through study. 46 Tody s Veterinry Prctice September/October 2011 ThORCiC RdiOgRphiC ExpOSuRE From technicl stndpoint, thorcic rdiogrphic exposure should be obtined using high pek kilovoltge (kvp) ( kvp) nd low millimpere second (mas) (1 5 mas) technique. This technique llows for ltitude (long gry scle) imges, which re importnt when evluting the structures of the thorx. Severl exmples would include: 82 kvp t 2 mas for 15-cm dog for nlog film (400 speed system) or 80 kvp t 5 mas for 15-cm dog for digitl plte rdiogrphic system. For ny dog mesuring 15 cm or greter (mesured t the liver or thickest prt of the thorx), grid (8:1, 110 lines per inch) should be used. Grids re vilble from most rdiology mnufcturers nd grid try comes with ll rdiology units. For lmost ll rdiology units, grid is sold with the rdiogrphic mchine nd tble. The rotor for the node nd the low-voltge circuit for the focusing cup/electrons of the cthode should be coupled to foot or hnd switch so tht ccurte timing of the exposure t pek inspirtion cn be mde (Tble).

3 Tble. how to determine Whether Rdiogrph Ws Tken t Pek inspirtion Ptient Size Lterl Ventrodorsl/Dorsoventrl Smll-breed dogs (hrdest to consistently ctch on pek inspirtion) diphrgmtic crur t level of T10 costophrenic ngle (Figure 4) t level of Medium-breed dogs Lrge-breed dogs Cts diphrgmtic crur t T12 T13 (cts, (minimum); preferbly t T12 cupul t T8 My see overlp between the borders of the crdic silhouette nd diphrgm T1 l1) cupul t T10 seprtion of hert nd diphrgm ROutine ViewS Lterl imges Positioning For right nd left lterl imge, the ptient is positioned on the tble with the dependent side down nd mrked with led mrker to indicte the dependent side in the collimted re s right (R) or left (L). 1. The thorcic limbs should be tped together evenly nd pulled crnilly so tht the elbows nd tissues of the triceps muscle re not superimposed over the crnil thorx (Figures 1 nd 2). 2. To determine whether or not ptient is ligned in lterl position nd prllel to the tble, use n imginry plne through the sternum nd dorslly through the spinous processes of the thorcic vertebre. 3. A fom wedge my be plced under the elbows in order to mintin lterlity of the ptient (sternum nd vertebre re equidistnt to the tble). 4. In order to keep the ptient in true lterl position, the pelvic limbs re lso tped nd pulled cudlly. A Collimtion To set the collimtion for the thorcic ntomic boundries of lterl imge (right or left): Verticl Line of the Collimtion Light: Plpte the cudl border of the scpul dorslly nd plce the verticl line t this point. This llows for the crdic silhouette to be in the center of the imge, giving true representtion of the crdic size nd shpe. Horizontl Line of the Collimtion Light: The horizontl line should be plced in n imginry plne so s to bisect the thorcic cvity even- 10th rib (minimum); preferbly t 12th rib diphrgmtic cupul (center) t T8 costophrenic ngle locted t T10 T11 diphrgmtic cupul t T10 seprtion of hert nd diphrgm ly between dorsl nd ventrl. Plpte the mnubrium nd plce the crnil edge of the collimtion bem t the crnil edge of the mnubrium; this plces the cudl edge of the bem t the level of the 13th rib hed nd T13. Remember to lwys include the sternum of the ptient so s not to exclude vitl ntomy: In lrge-breed dogs, it my be necessry to exclude the spinous processes. A seprte imge might be necessry if indicted. In deep-chested breeds, such s Gret Dnes, Dobermn pinschers, or mstiffs, the cssette/ detector plte my be turned verticlly to encompss the entire thorcic cvity in the dorsl nd ventrl plne. Turning the cssette/detector plte verticlly does not llow for the entire thorx to be included; therefore, crnil nd cudl views need to be tken, for completeness. Figure 3. (A) Dog in ventrodorsl recumbency with thorcic limbs tped nd pulled crnilly. The light mrks the crnil border of the imge tht is collimted to the level just crnil to the thorcic inlet. () Ventrodorsl lterl thorcic rdiogrph of the dog in Figure 3A; notice the crnil loction of the thorcic limbs reltive to the thorcic inlet. September/October 2011 Tody s Veterinry Prctice 47 smll niml Thorcic Rdiogrphy Tody s Technicin

4 Tody s Technicin Figure 4. (A) Dog in dorsoventrl recumbency with thorcic limbs tped nd pulled crnilly. The light mrks the crnil border of the imge tht is collimted to the level just crnil to the thorcic inlet. () Dorsoventrl thorcic rdiogrph of the dog in Figure 4A; notice the crnil loction of the thorcic limbs reltive to the thorcic inlet. Ventrodorsl imges Positioning For the ventrodorsl view, the ptient should be plced in dorsl recumbency. 1. Using V-trough helps keep the ptient s spine nd sternum ligned. 2. The thorcic limbs re tped together evenly nd pulled forwrd with the ptient s muzzle plced between the limbs (Figure 3, pge 47). 3. The pelvic limbs re pulled cudlly nd secured. The technique described in Step 2 does not work well for: rchycephlic breeds, such s English bulldogs or pugs, tht might hve issues with upper irwy disese or obstruction Figure 5. A conventionl ventrodorsl projection (with the legs pulled forwrd); notice tht the cudl portion of the scpule re superimposed over the crnil lung fields. Chondrodystrophic breeds, such s dchshunds or bsset hounds, becuse they re physiclly unble to do so. When presented with these types of ptients ensure tht the hed nd neck re stright out in front of the body nd not obliqued to the left or right. Collimtion To set collimtion for the ventrodorsl view, the lndmrks re the sme s the lterl projection: Verticl Line of the Collimtor Light: Plce the verticl line t the cudl border of the scpul. This llows the crdic silhouette to be in the center of the imge. Figure 6. (A) Dog in ventrodorsl recumbency with the thorcic limbs tped in the humnoid position, down long the dog s side. This position results in the scpule rotting externlly nd crnilly insted of being superimposed over the crnil lung lobes. The light mrks the crnil border of the imge tht is collimted to the level just crnil to the thorcic inlet. () Ventrodorsl thorcic rdiogrph corresponding to the dog in Figure 6A; notice the externlly rotted scpule (rrows) nd lck of superimposition over the crnil lung fields (compred with Figure 5). 48 Tody s Veterinry Prctice September/October 2011

5 Figure 7. Dog in ventrl recumbency with the rdiogrph cssette (detector plte) plced long the lterl thorx. This view will help differentite fluid (remins ventrl on exposure) nd ir ccumultion (remins dorsl on exposure) in the pleurl spce, pulmonry prenchym, or medistinum. Horizontl Line of the Collimtor Light: The horizontl line should be plced directly over the sternum so s to bisect the thorcic cvity from left nd right lterl. Plpte nd plce the edge of the collimtion bem t the crnil edge of the mnubrium; this plces the cudl edge of the bem to the 13th rib hed t the level of the thorcic spine. In lrge-breed dogs (eg, Gret Dne), it will be necessry to tke crnil nd cudl projection. dorsoventrl imges Positioning & Collimtion The dorsoventrl rdiogrph is one of the hrdest rdiogrphs to position consistently. The dorsoventrl imge best visulizes lesions in the cudodorsl lung lobes. 1. The dog is either in: Ventrl recumbency without the legs tped, resulting in sphinx position (Figure 4) or A frog-leg position (pelvic limbs). The comfort of the ptient is of utmost importnce. 2. The thorcic limbs re pulled crnil nd bducted. 3. The ntomic lndmrks re the sme s for ventrodorsl imge. dditionl ViEwS humnoid projection In conventionl ventrodorsl projection (with the thorcic limbs pulled crnil), the cudl portion of the scpule re superimposed over the crnil lung fields (Figure 5). The humnoid projection obtins no summtion of the scpul with the crnil lung fields. Tody s Technicin 1. The ptient is plced dorslly nd the thorcic limbs re tped seprtely nd pulled cudlly to lie djcent to the lterl body wll (Figure 6). 2. The lndmrks will be the sme s the ventrodorsl view. horizontl em projections Horizontl bem sternl or dorsl projections re used for ssessing the crnil medistinum or fluid/ir distribution within the thorcic cvity. These views re dependent on the bility of the rdiology mchine tube to be mnipulted in 90 ngle. In ddition, using positioning trough mkes these views esier to obtin. 1. To determine fluid or free ir distribution, position the ptient s if performing ventrodorsl view (ie, dorsl recumbency). 2. To visulize the crnil medistinum, position the ptient s if performing dorsoventrl view. 3. Plce the cssette/detector ginst the lterl body wll, mking sure to mrk the dependent side L or R. 4. The lndmrks re the sme s the lterl projection (Figure 7). QuLiTy COnTROL For qulity control of ny dignostic imge, keep simple 4-step pproch in mind: 1. Determine if the technique is pproprite. 2. Ascertin if the pproprite ntomy is present within the imge. 3. Check the positioning for lterlity nd strightness. 4. Determine if projection ws tken t pek of inspirtion. positioning VETERinRy ptients The following positioning devices cn be used to help position ptients nd reduce stff members exposure to rdition: Elstic tpe Plstic tongs Positioning trough (fom or plstic) Rope nd clets long the side of the tble Sndbgs (prticulrly long snke-like snd bgs) Ptient in lterl recumbency showing correct use of tpe nd sndbgs; the dog is muzzled due to its history of biting (see Dog ites: Protecting Your Stff & Clients, pge 66) smll niml Thorcic Rdiogrphy September/October 2011 Tody s Veterinry Prctice 49

6 Tody s Technicin Technique & ntomy Given tht the desired technique hs been ttined, mke sure tht the pproprite ntomy is included. The lterls, ventrodorsl, dorsoventrl, humnoid, nd horizontl bem projections should: Extend from the crnil mrgin of the mnubrium to the cudodorsl mrgin of the lung mrgin/diphrgmtic crus. Not exclude the sternum on the lterl or lterl spect of the ribs on the ventrodorsl view. positioning If the technique exceeds qulity stndrds nd the correct ntomy is present, check ptient positioning. For the lterl projection, use superimposition of the rib heds throughout the thorcic spine to determine if ptient is in true lterl position (Figures 1 nd 2). Dnielle Murgis, CVT, is rdiology technicin in the Dignostic Imging Service t University of Florid College of Veterinry Medicine. Her responsibilities include performing rdiogrphy, computed tomogrphy, nd nucler medicine studies; ssisting with ultrsonogrphy; nd teching physics, techniques, nd qulity control of rdiology to veterinry students. Ms. Murgis couthored the hndbook of Rdiogrphic Positioning for Veterinry Technicins nd ws contributing uthor for Principles nd Prctice of Veterinry Technology. She ws lso the recipient of the Florid Veterinry Medicl Assocition s 2011 Certified Veterinry Technicin of the Yer Awrd. Ms. Murgis received her ssocite s degree in veterinry technology from St. Petersburg College in Lrgo, Florid. Clifford R. erry, DVM, Diplomte ACVR, is professor in dignostic imging t the University of Florid College of Veterinry Medicine. His reserch interests include crosssectionl imging of the thorx, nucler medicine pplictions in veterinry medicine, nd biomedicl pplictions of imging in humn nd veterinry medicine. Dr. erry hs been fculty member t North Crolin Stte University nd the University of Missouri. He received his DVM from University of Florid nd completed rdiology residency t University of Cliforni Dvis. For the ventrodorsl projection, ech thorcic spinous process is viewed end-on nd hs distinct dimond or ter-dropped shpe without the bility to see the sternum nd the thorcic vertebre s seprte structures. For the dorsoventrl projection, positioning is similr to the ventrodorsl in tht the thorcic spinous process is viewed end-on nd hs distinct dimond or ter-dropped shpe without the bility to see the sternum nd the thorcic vertebre s seprte structures. pek inspirtion for imge cquisition Finlly, determine if the projection ws tken t the pek of inspirtion: For the lterl view, the cudl spect of the crdic silhouette will not be superimposed over the diphrgm nd there is n upside down tringle tht is visulized using the cudl ven cv, diphrgm, nd cudl border of the hert s the mrgins. For the ventrodorsl view, the cupol or centrl portion of the diphrgm will be seprted from the cudl border of the crdic silhouette. The lterl mrgins of the diphrgmtic crur will come to the 11th or 12th intercostl spce nd the right nd left crnil lung lobes will extend to the level of the thorcic inlet. The exception to these rules is the extremely obese ptient tht cnnot tke deep inspirtory breth. SuMMRy Thorcic rdiogrphs re often used s first-line test for possible intrthorcic disese. High-qulity, correctly positioned rdiogrphs re required in order to provide s ccurte n ssessment s possible. In ddition, 3-view thorx (right lterl, left lterl, nd dorsoventrl or ventrodorsl view) is considered the stndrd of cre in veterinry medicine. Following consistent, repetble pttern for obtining thorcic rdiogrphs ensures tht the qulity of the imges will lwys be dignostic. kvp = pek kilovoltge; ms = millimpere second Suggested Reding urk rl, Feeney da. Smll Animl Rdiology nd Ultrsonogrphy: A Dignostic Atls nd Text, 3rd ed. Phildelphi: Sunders elsevier, KeelyJK, McAllister h, Grhm JP. Dignostic Rdiology nd Ultrsonogrphy of the Dog nd Ct, 5th ed. Phildelphi: Sunders elsevier, Sirois M, Anthony e, Murgis d. Hndbook of Rdiogrphic Positioning for Veterinry Technicins. clifton Prk, New York: delmr cengge Lerning, Suter PF, Gomez JA. Diseses of the Thorx Rdiogrphic Dignosis. Ames, iow: iow Stte University Press, Thrll de (ed). Textbook of Veterinry Rdiology, 5th ed. Phildelphi: Sunders elsevier, Thrll de, robertson id. Atls of Norml Rdiogrphic Antomy nd Antomic Vrints in the Dog nd Ct. Phildelphi: elsevier Sunders, Tody s Veterinry Prctice September/October 2011