Radiography of the Skull

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August 8 , 1996 NJO / SKULL ISO PENDO TECHNIQUE 1998 .doc 1

Radiography of The Skull

By N.J.Oldnall

Tameside General Hospital.


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Basic Osteology, Revision

Basic Anatomy: The skull encloses and prot ect s t he brain and it s relat ed st ruct ures. It is a solid bony box wit h a backconsist ing of t he occipit al and pariet al bones; a t op consist ing of t he front al bone and t wo pariet al bones

joined by t he sagit t al sut ure; right and left sides consist ing of t he pariet al and squamous t emporal bones, a

front consist ing of t he fr ont al bone and facial st ruct ures and a floor consist ing of t he occipit al bone, pet roust emporal and sphenoid bones.

The cranium is made up of 8 bones and t he facial skelet on of 14 bones, wit h t he except ion of t he mandible allare immovable and joined by sut ures. The most complex par t is t he base which cont ains numerous f oramina fort he passage of ar t eries veins and cranial nerves.

Lateral Skull Anatomy

Key.Key.1. Front al Bone

2. Mandible3. Maxilla4. Zygoma5. Great er wing of sphenoid6 . Pariet al bone7. Squamous t emporal bone8 . Zygomat ic arch9. Mast oid process of t emporal bone10 . Occiput .


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Frontal Aspect of Skull,

Key.Key.1. Front al bone2. Mandible3. Maxilla4. Zygoma5. Great er wing of sphenoid6 . Inferior orbit al fissure7. Superior orbit al fissure8. Nasal bone


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Major Landmarks used for skull radiography:

1. Ver t ex1. Ver t ex 2. Ext er nal Occipit al Pr ot uber ance (E.O.P.)2. Ext ernal Occipit al Prot ubera nce (E.O.P.)3 . Ext ernal Audit ory3 . Ext ernal Audit ory Meat usMeat us 4 . Out er4. Out er Cant hus Of Eye.Cant hus Of Eye.5. Infr a-orbit al point5 . Inf r a- or bit al point 6 .6 . NasionNasion7.7. GlabellaGlabella

Baselines, Body Planes and Major Landmarks Accurat e locat ion of t hese lines, planes and point s is essent ial t o ensure accurat e and reproducibleposit ioning necessary for high qualit y imaging of t he skull and facial bones. Tradit ionally t he planes and point shave fr equent ly used peoples names E.g. Reids Baseline but convent ion is now regarded as being as follows.

Major body planes used in Skull radiography

Median Sagit t al Auricular Ant hropological

The Median Sagit t al plane.The Median Sagit t al plane.A vert ical plane dividing t he skull int o 2 symmet rical r ight and left halves when viewed from t he ant erioraspect .

The Ant hropological plane,The Ant hropological plane,This plane split s t he skull int o upper and lower halves passing along t he ant hropological baseline lines.

The Auricular plane.The Auricular plane.

This plane divides t he skull int o ant erior and post erior compart ment s along t he Auricular lines.


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Major Baselines used in Skull Radiography

Ant hropologicalAnt hr opological Or bit alOrbit al Meat alMeat al Int er pupillar yInt erpupillary

The Ant hropological lineThe Ant hropological lineThe Isomet ric Baseline which runs fr om t he inferior orbit al margin t o t he upper border of t he ext ernalaudit ory meat us (EAM)

The Orbit al-The Orbit al-Meat al LineMeat al LineThe original Baseline which runs fr om t he Nasion t hrough t he out er cant hus of t he eye t o t he cent re of t heext ernal audit ory meat us.

TheThe Int erpupillary lineInt erpupillary lineThe line connect s t he cent res of t he orbit s and is at 90 degree t o t he median sagit t al plane.

The Auricular Line (No Diagram)The Auricular Line (No Diagram)This line passes at 90 degrees t o t he ant hropological line t hrough t he cent re of t he ext ernal audit ory meat us.

Not e:Not e: t here is a difference of 10 t o 15 degrees bet ween t he Orbit al-Meat al line and t he ant hropological line.


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Indications, Royal College of Radiologists GuidelinesTaken from The Royal College Of Radiologist s Publicat ion Making The Best Of A Depart ment Of Radiology,Guidelines For Doct ors November 1993.

CIRCUMSTANCECIRCUMSTANCE GUIDELINESGUIDELINES EXCEPTIONSEXCEPTIONSCerebral sympt oms wit h focal

signs or sympt oms,

Lateral only in most cases Localisat ion of calcificat ions

Cerebral sympt oms wit houtfocal signs or sympt oms

Not recommended rout inely

Head Injury Not recommended rout inely Select ive radiography ofpat ient s wit h t he presence ofany of t he followingSuspect ed penet rat ing injuryCSF or blood loss via t he noseBlood discharge fr om t he earLoss of consciousnessHead injury + major t raumaPossible head injury wit hdifficult pat ient , st roke seizureor ment al handicap.

Head injury wit h alcoholicint oxicat ion which may preventproper clinical examinat ion.

X-Ray may be helpful if t hepat ient s condit ion allows t het aking of diagnost ic qualit yfilms.

Epilepsy (Children) Not r ecommended rout inely

Head injur y childr en Not r ecommended r out inely Select ive use as per adult s

Sinusit is Sinuses are poorly developedunder 6 -9 years , radiographyof limit ed use in t his agegroup.

Contra Indications: There are few if any cont ra indicat ions ot her t han t hat alt ernat ive forms of imaging may be preferable or t hefact t hat X-Ray imaging may be considered inappropriat e in some cases where t reat ment will not be aff ect edby t he result of X-Ray examinat ion.

A cont ra indicat ion t o t he use of ionising radiat ion is t he use of imaging in order t o reduce t he possibilit y ofmedico legal lit igat ion and for psychological reassurance of t he pat ient .


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Radiological Diagnostic features

Radiological signs of Cranial and Intra-cranial Abnormalities.

Head Injuries

Types of Fract ureTypes of Fr act ur e Radiological Feat ur esRadiological Feat uresLinear # Sharp t ranslucent line, may be st raight or

angled, may cross vascular grooves and causesut ural widening.

Depressed # May have curvilinear dense edges, more serioust han simple # , t angent ial project ions may berequired.

Base of skull # Suggest ed by air fluid (blood) level in sphenoidsinus, CSF rhinorr hoea and or bleeding fr om t heear.


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Radiological Diagnostic features cont.

Abnormalities of the Skull and Facial Bones CauseCause Radiological Feat ur esRadiological Feat uresEnlargement of S kull VaultEnlargement of S kull VaultChildrenChildren

Hydrocephalus Sut ural diast asis, increased convolut edmarkings, copper beat en skull

Raised int ra cranial pressure Bulging of font anelle in infancy.Adul t sAdul t sAcromegaly Enlarged front al sinuses and mandible, erosion

and enlargement of sella t urcicaPaget s disease Thickened skull vault , increased densit y of vault

and facial bones.Increased Densit yIncreased Densit yLocalised

Hyperost osis front alis Symmet rical t hickening of t he inner t able ofskull vault , usually in women, of no signif icance.

Meningioma Area of localised sclerosis, possible enlargedgroove of feeding ar t ery.

Fibrous displasia Asymmet rical, affect ing t he facial bones maxillaand base of skull.

Generalised Paget s disease Irregular sclerosis wit h t hickened vault .Secondary deposit s. e.g. prost at e & breast Irregular sclerosis, t hickened vault.Lyt ic lesionsLyt ic lesionsChildhoodChildhoodSecondary deposit s, neuroblast oma, leukaemia Variable appearances, Sut ural deposit s may

mimic sut ural diast asis.Eos inic gr anuloma, Hist i ocyt osis X Tr ans radient def ect wit h bevelled edges .Adul t sAdul t sMyelomat osis Rounded t ranslucent (2-10 mm) mult iple holesSecondary deposit s Generally ill defined t ranslucent pat ches.Hyperparat hyroidism Mot t led appearance of pepper pot skull.Paget s Sharply defined zones affect ing large areas of

t he vault .


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Radiological Diagnostic features cont.

Radiological signs of Cranial and Intra-cranial Abnormalities. Cont.

Pathological Intracranial Calicification Increased Densit yIncreased Densit y

VascularVascular Radiological feat ur esRadiological f eat uresAt heroma Curvilinear calcificat ions in t he carot id syphon.Aneurysm Relat ed t o main art eries.Angioma Any sit e bot h spot t y and curvilinearTumoursTumoursMeningioma Dense calcificat ions in t he t umour, may produce

localised sclerosis.Craniopharyngioma Deformed sella t urcica wit h calcificat ion int ra

or supra sella.


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Patients Preparation: Basic psychological preparat ion wit h reassurance and explanat ion of t echnique.

Normal pat ient examinat ion int erview. Ref.: Radiography of t he Head by Pamela Kimber. Churchill Livingst one,198 3

Pat ient s r eferr ed for skull radiography may be worried and anxious about t he out come. Many, but not all suchpat ient s, are diff icult t o handle and need special care. Some will be ment ally dist urbed, Pat ient s Preparat ion:

unconscious or unable t o co-operat e; t he assist ance of a nurse or ot her compet ent person may be required.An underst anding and t olerant at t it ude exhibit ed by t he radiographer always helps.

Time t aken t o explain t he t est t o t he pat ient is never wast ed.

Before st art ing any examinat ion, t he ident it y of t he pat ient must be checked by t he radiographer; a pat ientmay answer t o a name not his/her own and t his is part icularly t rue for some disorient at ed pat ient s at t endingfor skull imaging.

All det achable foreign opacit ies such as jewellery chains, spect acles, hearing aids, earrings, wigs and falsehairpieces and false eyes must be removed from t he head and neck. It is not usually necessary t o remove

false t eet h.It is import ant t o remember t he dignit y of t he pat ient , and essent ial t o have clean hands and a cleant able/buck t op and clean immobilisat ion aids at all t imes.

Immobilisation: Full immobilisat ion is essent ial for high qualit y diagnost ic imaging, t he use of velcro binders and pads willassist in immobilising t he pat ient in most cases.

Accessories:

Fine and st andard/ regular r esolut ion, film speed screen combinat ions in an assor t ment of sizes.Pads and immobilisat ion aids.Cones and Plat es t o fit equipment being used.Hard surf ace disinfect ant for bucky board or head support .

Radiation Protection: Radiat ion prot ect ion in line wit h local and nat ional guidelines in par t icular t he NRPB publicat ions regardingdose reduct ion. The most radiosensit ive organs involved are t he eyes and t hyroid gland, t he use of beamlimit ing cones and diaphragms is adequat e in most cases, direct lead r ubber gonad prot ect ion when t hecent ral r ay is direct ed t owards t he gonads is probably not necessar y but may be considered good pract ice.

The most effect ive met hod of dose reduct ion is careful t echnique t o avoid t he need for r epeat radiographs.

Films Screen and Grids: St at ionary fine line grids wit h a rat ion of 10 or 12 t o 1are found in most Isocent ric unit s.

The CRT4 unit has an 8 :1moving grid.

General purpose film screen combinat ions (Speed 40 0 t o 80 0 ) ar e t he best compromise of dose and imagequalit y.


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Baselines and Angles The descript ions of posit ioning which follow will use t he following convent ions.

1. Basic Skull and facial Bone Project ions 1-8 will be described using t he Film Cent red approach2. The Baseline used is t heOrbit alOrbit al Meat al Line (OML)Meat al Line (OML)3 . Angles will be described as Cranial or Caudal4. Angles will be quot ed in reference t o t he Baselinenotnot t he film plane.

5. All project ions will be described for t he Erect t echnique

I. Isocent ric posit ions 1-8Isocent ric posit ions 1-8 will be described using t he object cent red approach.II. The Baseline used is t he Ant hropological baseline (APB)III. Angles will be described as Cranial or CaudalIV. Angles will be quot ed in reference t o t he St art Zeroposit ionposit ionV. All project ions will be described for t he Supine t echnique

Respirat ion.Respirat ion.In order t o help minimise movement unsharpness exposure should be made on suspended respirat ion wherepossible.


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Common Positioning Errors Rot at ion and t ilt are t wo of t he most common posit ioning errors.

A.A. Rot at ion occurs when t he median Sagit t a l p lane is not parallel t o t he f i lm.Rot at ion occurs when t he median Sagit t al plane is not parallel t o t he film.

B.B. Tilt occurs when t heTilt occurs when t he int erpupillary line is not at 9 0int erpupillary line is not at 9 0 t o t he film.t o t he film.

Causes of Posit ioning Err orsCauses of Posit ioning Err orsWhen posit ioning a pat ient s head, it is necessary t o look at various facial feat ures and palpat e variousanat omical landmarks in order t o place cert ain planes precisely in relat ion t o t he film plane. Alt hough t hehuman body is supposed t o be symmet rical t his is not always t rue.

The ears nose and jaw being t he not able except ions. Bony part s such as t he mast oid t ips and t he orbit almargins are usually more accurat e landmarks, for example whilst posit ioning it is oft en more accurat e t o uset he eyes rat her t han t he nose as posit ioning aids.


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Equipment choice

Genera t or and TubeGenera t or and TubeA medium / high powered medium fr equency generat or mat ched t o t he t ube rat ing is t he opt imum choice forminimum exposure t imes coupled wit h t he use of a t ube wit h a focus of 0 .3mm.

Equipment ChoiceEquipment ChoiceIn order of decreasing suit abilit y for maximum image qualit y.Dedicat ed Isocent ric skull radiography is t he equipment of choice.Dedicat ed Lysholm skull unit ,General purpose generat or and erect buckyGeneral purpose generat or and grid casset t es.


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Film Centred Radiography

The Lysholm Skull Apparatus.

Film Plane Cent red Radiogr aphyFilm Plane Cent red Radiogr aphyThe original Elma - Sch enander Skull t able was f irst made in 1934 and cont inued t o be made and sold up

unt il t he lat e 1970 s when it generally became superseded by Isomet ric equipment and t he int roduct ion ofclinical Comput er Tomography around 1974 which spelt t he end procedures like air encephalography. Howevermany unit s ar e st ill in place and in use, t hese unit s ar e st ill able t o provide high qualit y images of t he craniumand it s associat ed st ruct ures, in use t he t echniques used are very similar t o t he t echniques using a normalX-Ray t ube and bucky arrangement .

The unit consist s of a small object t able made of clear perspex, which includes a removable casset t e t ray andgrid mechanism, t he largest casset t e size pract icable is a 24cm x 30 cm t hough a 35cm x 35 cm casset t ewill fit in t he mechanism t he narr ow focal spot angle will not permit full coverage.

The grid is able t o be rot at ed t hrough 36 0 degrees t o ensure t hat t he cent ral ray is parallel t o t he slat

direct ion in all possible t ube / t able posit ions.The object t able is mount ed on a vert ical column on which is free t o t ravel up and down (10 0 cm).

The object t able is also able t o rot at e round a cent ral boss fr om being flat at 90 degrees t o t he column t oupright parallel t o t he column.

The X-Ray t ube is mount ed on a count erbalanced arc cent red t o t he same cent ral boss as t he t able, wit h afocus t able dist ance of 9 0 cm. The t ube arc is also moveable in an arc across t he t able t op t he t ube movingt owards (max. 30 ) and away from t he t ube column (max. 8 0 ), also cent red around t he cent ral boss.

It is also possible t o make small angular adjust ment s at t he t ube port posit ion.

The use of a cent ral boss t o all t he rot at ions ensures t hat t he cent ral ray of t he X-Ray beam is alwaysdirect ed t o t he cent re of t he object t able, as t hough t he X-Ray t ube is on t he surface of a sphere which hast he cent re of t he object t able at t he cent re of t he sphere.

There is a syst em of mirrors and cross light s t o enable accurat e posit ioning as t here is no light beamdiaphragm arr angement , beam collimat ion being achieved using a series of cones and plat es.

The object t able is able t o fit a range of accessories including a fixat ion band t o limit movement , rails forangiographic film changers et c.

The Lysholm equipment is used in a similar manner t o a normal t ube / Bucky arrangement wit h t he object t o beimaged placed at t he cent re of any t ube angulat ion as close t o t he film as possible.

Diagram t o Illust rat e,Lysholm equipment principles.


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The Lysholm Skull Apparatus.


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AppendicesBasic Posit ioning Skull and facial bones.

Film Cent red TechniqueFilm Cent red Technique

Skull:Skull:Occipit al Front alOccipit al Front al 20

Front o Occipit al 30

Lat eralSMV

Facial bones and S inusesFacial bones and S inusesOccipit al ment alOccipit al ment al 30

Lat eral

Pat ient Cent red TechniquePat ient Cent red TechniqueThe Isocent ric equivalent s of t he above t echniques Basic Skull Project ions


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Basic Skull Projections

Fronto Occipital 0

Maxillary Sinus

Anat omy Demonst rat edAnat omy Demonst rat edFront al bone, crist a galli, int ernal audit ory canals, front al and et hmoid sinuses, pet rous ridges, great er andlesser wings of sphenoid.

Pat ient Posit ionPat ient Posit ionPat ient sit s erect facing t he erect bucky.Rest pat ient s noise and forehead against t he bucky.Align midsagit t al plane perpendicular t o and in line wit h t he midline of bucky and cent ral ray.

Tuck chin in t o bring t he OML 90

t o film.Cent re bucky t o Glabella

Cent ra l RayCent ra l RayCent re t he horizont al cent ral ray t o exit t hrough t he Glabella.

Exposure / Project ion Det ails (Typical)Exposure / Project ion Det ails (Typical)

Project ion Kv mAS FocusF/B

GridY/N

Sizecm

FFDcm.

CR

CR

OMBL

OMBL

Front o Occipit al 8 0 Fine Y 24x30 10 0 0 0 0 0

Image Evaluat ion Crit eria,Image Evaluat ion Crit eria,Pet rous pyramids f ill t he orbit s. (Cent ral Ray t o R.B.L. angle)

Dist ance from orbit al line t o t he lat eral margin of t he skull equal on bot h sides. (Rot at ion)

Dorsum sella and ant erior clinoids are visualised superior t o t he et hmoid sinuses. (Cent ral Ray t o R.B.L. angle)

Int erpupillary line parallel t o film edge. (Tilt )

Sufficient penet rat ion and exposure t o visualise front al bone and pet rous pyramids.


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30 Fronto Occipital

Anat omy Demonst rat edAnat omy Demonst rat edOccipit al bone, pet rous pyramids, foramen magnum, dorsum sellae and post erior clinoids.

Pat ient Posit ionPat ient Posit ionPat ient sit s erect A.P. against t he erect bucky

Align midsagit t al plane perpendicular t o and in line wit h t he midline of bucky and cent ral ray.Tuck chin in t o bring t he OML 90 t o film.

Cent ra l RayCent ra l Ray30 Caudad angled cent ral r ay t o a point 6 cm above t he Nasion in t he midline.

Exposure / Project ion Det ails (Typical)Exposure / Project ion Det ails (Typical)


GridY/N

Sizecm

FFDcm.

CR

CR

OMBL

OMBL

Front o Occipit al30 (Townes)

8 5 Fine Y 24x30 10 0 30 0 0

Image Evaluat ion Crit eria, Posit ioning.Image Evaluat ion Crit eria, Posit ioning.Equal dist ance fr om foramen magnum t o lat eral margin of skull on each side. (Rot at ion)

Dorsum sella and post erior clinoids are project ed int o t he foramen magnum. (Cent ral Ray t o R.B.L. angle)

Pet rous ridges are symmet rical (Rot at ion) and superior t o t he mast oids. (Cent ral Ray t o R.B.L. angle)

Tips of pet rous r idges parallel t o film edge. (Tilt )


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Lateral

Anat omy Demonst rat edAnat omy Demonst rat edLat eral aspect of cranium nearest t o t he film, dorsum sella, ant erior and post erior clinoids, great er and lesserwings of sphenoid bone.

Pat ient Posit ionPat ient Posit ionPat ient sit s erect facing t he bucky, t he head is t hen rot at ed t o t he side in quest ion, t o bring t he medianSaggit al plane parallel t o t he film.

The angle of t he OMB is adjust ed for maximum pat ient comfort .The Int erpupillary line should be parallel t o t he floor.

Cent ra l RayCent ra l RayThe horizont al cent ral ray is cent red t o a point 5cm superior t o t he EAM.

Alt ernat ive, midway bet ween t he Glabella and EOP

Exposure Det ails (Typical)Exposure Det ails (Typical)


GridY/N

Sizecm

FFDcm.

CR

CR

OMBL

OMBL

Lat eral Skull 75 Fine Y 24x30 10 0 0 0 0 0

Image Evaluat ion Crit eria, Posit ioningImage Evaluat ion Crit eria, Posit ioningMandibular r ami, orbit al roofs, E.A.M.s and wings of sphenoid bone superimposed.Mis alignment one above t he ot her = Tilt , M.S.P. not parallel t o film planeMis alignment one ant erior t o t he ot her = Rot at ion.Sella t urcica seen in profile.


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Sub Mento Vertical (SMV)

Anat omy Demonst rat edAnat omy Demonst rat edForamen magnum, foramen ovale and spinosum, mandible, sphenoid and et hmoid sinuses, pet rous ridge, hardpalat e and occipit al bone.

Pat ient Posit ionPat ient Posit ionCare must be t aken during posit ioning as t he pat ient may feint wit h t he neck in hyper ext ension so pract iceand speed ar e essent ial, it may be safer t o use t he supine posit ioning t echnique part icularly in t he elderly.

Pat ient sit s erect wit h t he dorsal aspect against t he bucky, t he shoulders may need support ing on a pad forcomfort . The pat ient s neck is hyper ext ended unt il t he OMB is parallel t o t he film plane.

Wit h t he CRT4 skull unit t his may be enabled by angling t he film plane so t he lower border is moved backwardsaway from t he pat ient . The int erpupillary line should be parallel t o t he floor.

Cent ra l RayCent ra l RayThe horizont al cent ral ray (or at 9 0 t o OMB) is d irect ed in t he midline t o a point midway bet ween t hemandibular angles.



GridY/N

Sizecm

FFDcm.

CR

CR

OMBL

OMBL

SMV 90 Fine Y 24x30 10 0 0 0 90 0

Image Evaluat ion Crit eria, Posit ioningImage Evaluat ion Crit eria, Posit ioningEnt ire facial skelet on visualised, symmet rical wit h no rot at ion.Mandibular symphysis superimposed on ant erior fr ont al bone.Symmet rical st ruct ures project ed evenly eit her s ide of t he mid Saggit al plane.Mandibular condydles project ed evenly ant erior t o pet rous bones.

Visualisat ion of foramen spinosum and ovale.


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Basic Facial Bones Projections

Occipito-Mental

Anat omy Demonst rat edAnat omy Demonst rat edMaxillary sinuses, fr ont al sinuses, inferior orbit al rim, maxillae, zygomat ic arches, zygoma bones, nasal sept um,ant erior nasal spine and floors of orbit s.

Pat ient Posit ionPat ient Posit ionThe pat ient sit s erect facing (PA) t he erect bucky midsagit t al plane in line wit h t he cent re of t he bucky.

The chin is raised so t hat t he orbit al meat al line is 45 t o t he film plane.

If it is required t o visualise t he sphenoid sinuses t he exposure is made wit h t he mout h open.

Cent ra l RayCent ra l RayThe horizont al cent ral r ay is cent red in t he midline t o exit at t he level of t he lower orbit al margins.



GridY/N

Sizecm

FFDcm.

CR

CR

OMBL

OMBL

Occipit o ment al 8 0 Fine Y 24x30 10 0 0 0 45

Image Evaluat ion Crit eria, Posit ioningImage Evaluat ion Crit eria, Posit ioningThe ent ire facial skelet on must be visualised.The pet rous bone must be project ed below t he lower borders of t he maxillary s inuses.St ruct ures must be project ed equally eit her s ide of t he midline.Int erpupillary line horizont al unless t ilt is deliberat ely applied t o examine fluid levels in t he maxillary sinuses.


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Basic Facial Bones Projections

Occipito-Mental 30

Anat omy Demonst rat edAnat omy Demonst rat edInferior orbit al margins and floors of orbit s.

Pat ient Posit ionPat ient Posit ionThe pat ient sit s erect facing (PA) t he erect bucky midsagit t al plane in line wit h t he cent re of t he bucky.

The chin is raised so t hat t he orbit al meat al line is 45 t o t he film plane.

If it is required t o visualise t he sphenoid sinuses t he exposure is made wit h t he mout h open.

Cent ra l RayCent ra l RayThe cent ral ray is angled 30 caudal t o make an angle of 10 5 t o t he orbit al meat al line in t he midline t o exit

at t he level of t he inferior orbit al margins.

Exposur e Det ails (Typical)Exposur e Det ails (Typical)


GridY/N

Sizecm

FFDcm.

CR

CR

OMBL

OMBL

Occipit o ment al 8 0 Fine Y 24x30 10 0 0 30 45

Image Evaluat ion Crit eria, Posit ioningImage Evaluat ion Crit eria, Posit ioning

The ent ire facial skelet on must be visualised.The inferior orbit al margins must be project ed in out line.St ruct ures must be project ed equally eit her s ide of t he midline.Int erpupillary line horizont al unless t ilt is deliberat ely applied t o examine fluid levels in t he maxillary sinuses.


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Bas ic Facial Bones Project ionsBas ic Facial Bones Project ions

Lat eralLat eral

Anat omy Demonst rat edAnat omy Demonst rat edSuperimposed facial bones, great er wings of sphenoid, orbit al roofs , sella t urcica, zygoma, mandible and t hefacial air sinuses.

Pat ient Posit ionPat ient Posit ionPat ient sit s erect facing t he bucky, t he head is t hen rot at ed t o t he side in quest ion, t o bring t he medianSaggit al plane paralel t o t he film.

The angle of t he OMB is adjust ed for maximum pat ient comfort .The int erpupillary line should be parallel t o t he floor.

Cent ra l RayCent ra l RayThe horizont al cent ral r ay is cent red t o a point half way bet ween t he out er cant hus of t he eye and t he EAM

Exposure Det ails (Typical)Exposure Det ails (Typical)Project ion Kv mAS Focus

F/BGridY/N

Sizecm

FFDcm.

CR

CR

OMBL

OMBL

Lat eral Facial 6 5 Fine Y 24x30 10 0 0 0 0 0

Image Evaluat ion Crit eria, Posit ioningImage Evaluat ion Crit eria, Posit ioningThe zygomat ic bones ar e superimposed vert ically (Tilt ) and ar e in ant erior / post erior alignment (Rot at ion).


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Isocentred Radiography or Object Centred RadiographyThe Orbix(Siemens), Sa t ella X, Pendo Diagst at ((Phillips).

The Isocent ric t echnique produces similar images t o t he Lysholm t echnique wit h t he benefit of all project ionsmay be t aken in t he P.A. posit ions reducing radiat ion dose t o t he eyes, and wit h t he cent ral r ay at 90 degreest o t he film reducing geomet ric dist ort ion.

The principal of Isocent ric Skull Imaging equipment is t o simplify pat ient posit ioning making it more easilyreproducible, accurat e and simple t o carry out . First described in 1956 by a man named Dulac it was not unt il1971when t he fir st commercial equipment was produced and market ed.

Whereas using t he Lysholm t echnique t he X-Ray t ube is rot at ed around t he cent re of t he film t he Isocent rict echnique relies on t he part of t he skull t o be imaged lying at t he cent re of t he sphere over which t he opposedt ube and casset t e t ravel around. Hence t he Isocent re of t he rot at ion is t he object and t he cent ral rayremains at 90 degrees t o t he film at all t imes.

Diagrams t o Illust rat e,Isocent ric equipment principles. (L Posit ion)Isocent ric equipment principles. (L Posit ion)

Ceiling SuspensionAngle fr om 'M'osit ion (R or L

Cent re ArmAngle fr om L Posit ion.(Cranial / Caudal)

Vert ical Arm

Tube Holder

Beam Collimat or

Horizont al AxisVert ical Axis

Tube & Casset t e Arm Casset t e Holder


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Isocentric Equipment & Principals There are curr ent ly t hree models of Isocent ric skull unit s in t he region, t hey are t he Sat ella X, Pendo Diagst atand t he Orbix. Of t hese t he Pendo Diagst at may be considered t he odd one out as one of t he rot at ions isproduced by rot at ing t he pat ient t able round t he cent ral axis rat her t han t he t ube / casset t e support .However all t hree models rely on t he Isocent ric pr incipal, t his handbook will describe det ailed project ions usingt he Orbix as t his is t he most fr equent ly used Isocent ric skull unit

The Orbix is a ceiling mount ed device wit h a cent ral pivot point enabling 36 0 degree rot at ion round t he vert icalaxis, (A 3 6 0 degree rot at ion when seen in plan view).

The X-Ray t ube and casset t e holder are mount ed on vert ical arm wit h a cent ral pivot enabling 36 0 degreerot at ion round t he horizont al axis arm. (A 36 0 degree rot at ion when seen fr om t he side) The cent ral ray iskept at 90 degrees t o t he casset t e at all t imes. The column has mot orised vert ical movement s, and t hefocus f ilm dist ance can be varied bet ween 70 and 130 cm.

The equipment is normally equipped wit h a fixed height pat ient t able which enables t he head t o be posit ionedover t he casset t e holder, using horizont al and crosswise float at ion. All or some of t he movement s maymot orised and are calibrat ed in degrees or millimet res depending on whet her t he movement is r ot at ional or

linear.The X-Ray t ube is equipped wit h a st andard light beam collimat or wit h accessor y rails for a select ion of beamlimit ing cones.

As well as t he light beam collimat or accurat e posit ioning is aided by t hree cross light s posit ioned t o align t heequipment in each of t he t hree planes which movement s is moved, one cross light indicat es t he vert ical heightof t he Isocent re, t he second t he horizont al posit ion and a t hird t he crosswise posit ion.

Immobilisat ion of t he pat ient s head is achieved using Velcro st raps round t he head and t he chin.

The X-Ray t ube generally is a bifocal t ube wit h a 0 .3mm and a 0 .6mm focus, t he equipment may be connect edt o a variet y of generat ors and wit h modern f ast film screen combinat ions a 40 kW medium frequency

generat or will be adequat e in most sit uat ions.

Summary of the basic Features of the Isocentric technique 1.,The pat ient is always supine.2. The posit ion of t he pat ient s head is always t he same except for t he SMV projection.3. The spat ial co-ordinat es are det ermined in t hree const ant skull planes.A) t he auricular plane.B) The median sagit t al plane.C) The Inf raor bit a l plane.4. All measurement s of dist ance are in millimet res mm.

5. There are t hree manipulations required t o posit ion the patient6 . The posit ion of t he t ube is defined by the t wo angles around t wo rot at ion axis of t he t ube st and.7. There is no geomet r ic posit ional dis tor t ion8 . Most project ions are in t he P.A. posit ion wit h t he t ube below t he pat ient and film above.


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The M and L Start positions Lat eral posit ion of t he t ube column LThe t ube column is posit ioned lat eral t o t he pat ient s head, (using t he ceiling suspension angle adjust ment ) sot hat angulat ion t he cent ral ray can be cranial or caudalMedial posit ion of t he Tube column M.

The t ube column is posit ioned adjacent t o t he vert ex of t he head (using t he ceiling suspension angleadjust ment ) so t hat t ube angulat ion causes t he cent ral ray t o be direct ed t o eit her side of t he head.

Plan View of Orbix in a) L position b) M Position

Bed Bed

Ceilng Suspension

Tube Arm

Note:

When describing t he t able movement s moving t he t able in t he direct ion of t he feet causes t he Isocent re t omove in t he Cranial direct ion.When describing t ube angulat ion t he angles will be described as caudal when t he cent ral r ay is direct edt owards t he feet .This descript ion of t he t ube angulat ion is in cont rast t o t he inst ruct ion book supplied wit h t he Orbix but followsNormal radiographic convent ion.

Base Reference Posit ion forBas e Reference Posit ion for Isocent ric Posit ioningIsocent ric Posit ioning

Not e: The Orbit al Auricular line is vert ical.The pat ient is posit ioned supine wit h t he head rest ing on a small pad for support and comfort . The mediansagit t al plane is vert ical, The ant hropological plane is vert ical. The auricular plane is horizont al.The cranio caudal and t he cross wise t able posit ion is such t hat t he cent re light s cross midway bet ween andat t he level of t he ext ernal audit ory meat i.


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Basic Skull Projections Occipito Frontal (Pineal projection)

Tube ColumnTube ColumnThe Lat eral (L) posit ion wit h t he t ube posit ioned beneat h t he pat ient s head is used.

Pat ient Posit ionPat ient Posit ionThe pat ient is moved 40 mm caudal from t he st art posit ion.

Cent ra l RayCent ra l RayThe cent ral ray is angled 15 cranial so t hat it ent ers t he head 2cm above t he ext ernal occipit al prot uberanceand exit s 4cm above t he glabella.

SummarySummary

Posit ionPosit ion St ar t Posit ionSt ar t Posi t ionM/ LM/ L

Ant hropologicaAnt hropological planel planeBasic or

Tube ArmTube ArmRot at ionRot at ion

Cranial / CaudalRight or Left mm.

TableTableDisplacementDisplacementCranial. Or Caudalmm.

OFOF LL BasicBasic 1515 CranialCranial 40 mm Caudal40 mm Caudal


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Basic Skull Projections Occipito Frontal 10

Tube ColumnTube Column

The Lat eral (L) posit ion wit h t he t ube posit ioned beneat h t he pat ient s head is used.


Cent ra l RayCent ra l RayThe cent ral ray is angled 10 caudal and ent ers in t he midline bet ween t he pariet al bones and exit s t hrought he nasion.

SummarySummary






OF 10OF 10 LL BasicBasic 10 Caudal10 Caudal 40 mm Caudal40 mm Caudal


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Basic Skull Projections Occipito Frontal 40 (Townes)

Tube ColumnTube ColumnThe Lat eral (L) posit ion wit h t he t ube posit ioned beneat h t he pat ient s head is used.


Cent ra l RayCent ra l RayThe cent ral ray is angled 40 cranial and ent ers in t he midline t hrough t he foramen magnum and exit s 6 cmabove t he glabella

SummarySummary






OF 40OF 40 LL BasicBasic 4040 CranialCranial 50 mm Caudal5 0 mm Caudal


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Basic Skull Projections Lateral

Side ViewSide View

Tube ColumnTube ColumnThe Medial (M) posit ion wit h t he t ube posit ioned t o t he side of head is used.


Cent ra l RayCent ra l Ray

The horizont al cent ral ray ent ers t he head at a point 40 mm superior t o t he upper border of t he EAM.

SummarySummary






Lat eralLat eral MM BasicBasic 9 0 Lef t / 90 Lef t / RightRight

40mm40mm


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Sub-Mento Vertical (Full Axial) SMV

Tube Column Tube Column

The Lat eral (L) posit ion wit h t he t ube posit ioned beneat h t he pat ient s head is used, and t he t ube posit ionedA.P.

Pat ient Posit ion Pat ient Posit ion

The pat ient s head is adjust ed chin up t o bring t he Ant hropological line 40 up from t he basic st art posit ion.

Cent ral Ray Cent ral Ray

The cent ral ray is angled 55 cranialy, t o ent er midway bet ween t he angles of t he mandible and exit t hrought he vert ex of t he skull.

Summary Summary






SMVSMV LL 4545 5555 CranialCr anial 0 - 5mm Caudal0 -5 mm Caudal


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Basic Facial Bone Projections

Occipto Mental 30


The Lat eral (L) posit ion wit h t he t ube posit ioned beneat h t he pat ient s head is used, and t he t ube posit ionedPA.


The chin is raised t o bring t he ant hropological baseline 35 up from t he basic st art posit ion.


The t ube arm is raised 60 mm and t he t able moved 40 mm caudal, t he cent ral r ay angled 30 caudal ent erst hrough t he occiput in t he midline and exit s in t he midline t hrough t he upper cent ral incisors.

Summary Summary



Tube ArmTube ArmRot at ionRot at ion / / Raised/ Raised/ LoweredLoweredCranial / CaudalRight or Left mm.


OM 3 0OM 30 FacialFacialBonesBones

LL 3 53 5 3 03 0

6 0 m m6 0 m m

40 mm Caudad40mm Caudad


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Basic Facial Bone Projections

Lateral


The Medial (M) posit ion wit h t he t ube posit ioned t o t he Left or Right t he pat ient s head is used.


The Pat ient is in t he basic st art posit ion


The t ube arm is raised 50 mm, t he horizont al cent ral ray ent ers and exit s t hrough opposit e point s on t het emporal bone.

Summary Summary






Lat eral facialLat eral facial MM BasicBasic R / L 9 0R / L 9 0 50 mm Cranial50 mm Cranial

Documents

Radiography of the Skull