Terminology for Radio Graphic Projections Br Heart J

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Editorial Br Heart Jf 1981; 45: 109-11 Terminology for radiographic projections R G GRAINGER From X-ray Department, Royal Hallamshire Hospital, Glossop Road, Sheffield Every scientific discipline must agree its terminology and conventions. If this self-discipline is not exercised, confusion is inevitable and meaningful communication becomes impossible. In the past few years, laxity in terminology with regard to radiographic projections has resulted in considerable confusion in the cardiac radi
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  Editorial Br Heart Jf 1981; 45: 109-11 Terminology for radiographic projections R G GRAINGER From X-ray Department, Royal Hallamshire Hospital, Glossop Road, Sheffield Every scientific discipline must agree its terminology and conventions. If this self-discipline is not exer- cised, confusion is inevitable and meaningful communicationbecomes impossible. In the past few years, laxity in terminologywith regard to radiographic projections has resulted in considerable confusion in the cardiacradiological laboratory and the published reports. This is be- cause long established and universally agreedterminology and conventions have not been con- sistently applied to oblique cardiac radiographic projections which are now being increasingly used, especiallyforcine angiography, both in congenital heartdisease and coronary artery visualisation. It is the purposeof this editorial to urge the universal application ofthe two internationally approved,long standingconventions for describing any radiographic projection. These conventions are logical and very simple to apply, and it is hoped that they will be utilised whenever oblique cardiacprojections are described-in the radiological suite, in academic reports, and in manufacturers' in- structions or descriptions. Convention I The radiographic projection is labelled by the name of thatpart of the body next to the imaging device (radiographic cassette or image intensifier). Thisconvention is readilyapplied whether the patient is stationary on thex-ray table and thex-ray tube andimaging device are moved in a transverse plane around him (Fig.la) as in most cine installations, or whether the patient lies in a cradle which is rotated along its long axis with thex-ray tube and imaging device remaining static (Fig.lb), as with most full- sized serial film changer installations. If the right posterior aspect of the chest is next to the imaging device (Fig. lb), then the projection is labelled rightposterior oblique (RPO). If the left anterior aspect of the chest is next to the imaging device, then the projection is labelled left anterior oblique (LAO) (Fig. la). NB-All Figures viewedfromhead of patient, looking towards the feet. L ci la lb Fig. 1 (a) Undercouch x-ray tube (usual cine installation). Patientsupine on table. Tube and image intensifier rotated so that left anterioraspect of the patient is next to image intensifier. Left anterior obliqueprojection.(b) Overcouch x-ray tube (usual AOT installation). Patient in a rotating cradle which is rotated so that the rightposterior aspect of the patient is next to AOT filmchanger. Right posterior oblique projection. Both Fig. la and b provide very similar views as thecentral x-ray beammakes the same angle a , with the sagittal plane of thepatient. The central x-ray beam will therefore traverse the same diameter of the patient and produce virtually identical radiographs. L.1., image intensifier; A.O. T., full-sized serial filmchanger. 109  Grainger As RPO and LAO aspects ofthe chest are dia- metrically opposed to each other, thex-ray beam passes through the same diameter of thechest in both projections, and the imageproduced is very similar in the two techniques. Convention II The radiographic projection is identified by the direction of thex-ray beam. The situation of thex-ray tube is first specified, followed by the situation of the imaging device. Thus theusual radiograph ofthe chest is takenwith thex-ray tube posterior to the patient and the cassette in front of him-the pro- jection is therefore called posteroanterior . Thisconvention is best applied to those projec-tions in which the x-ray beam is tilted in the long axis of the patient, that is axial tilts. It is essential to specify whether thex-ray tube lies behind or in front of the patient. Thus, in theusual cine installa-tion, the patient lies supine on thehorizontalx-ray table with thex-ray tube beneath the table and the image intesifier above the table. If the tube is dis- placed towards the feet of the patient and tilted in order todirect the beam towards the headend ofthe patient (Fig. 2a), the projection is called caudo- cranial posteroanterior. In a minorityof cardiac radiographic installations, the fluoroscopic or cine x-ray tube is situated above the patient (and the table), with the imaging device below the table. With this typeof installation, thecraniocaudal anteroposterior projection (Fig. 2b), will provide virtually the same image as the caudo- cranial posteroanterior projection with an under- 2a 3 Fig. 2 Axial projections. (a) Undercouch x-ray tube (usual cine installation). X-ray tube angled towards head of patient so that x-ray beam travelsin caudocranial direction. Caudocranial, posteroanterior projection. (b) Overcouch x-ray tube (unusual cine installation). X-ray tube angled towards feet of patient so that x-ray beam travelsin craniocaudal direction. Craniocaudal, anteroposteriorprojection. Fig. 3 Undercouch x-ray tube (usual cine installation). The x-ray tube is angled towards the feet of the patient so that the x-ray beam travelsin craniocaudal direction. Craniocaudal, posteroanterior projection. (See also footnote to Fig. 2.) Projection in Fig. 3 will provide a completely different view from Fig. 2a and b. The terms craniocaudal and caudocranial shouldbe used to indicatethe pathway of the x-ray beam emanating from the x-ray tube. These terms craniocaudal and caudocranial should be qualified by indicating whether the x-ray tube is below thetable (as is conventional for cine recording) or whether the x-ray tube is above thetable (as is essential forfull-sized film radiographs). .I., image intensifier, to which is fitted thecine camera, which is not shown on the diagrams. 110 I (t 1. - 2b  Terminology forradiographic projections couch fluoroscopic tube (Fig.2a),as the x-ray beam traverses the same plane of the patient in the two different circumstances. It is therefore important for bothauthor and reader to know whether thex-ray tube is situated below the table (as is usual in cine installations), or above the table (an uncommon arrangement forcine angiography). Confusion has arisen because some investigators andequipment manufacturers' technicalreports and brochures erroneously call the under-table tube caudocranial view- craniocaudal projection . The true craniocaudal projection with undercouch fluoroscopiccine x-ray tube (Fig. 3) is of course a completely different projection. Compound oblique projections with rotations in both axial (or sagittal) and transverse planes are being more frequently used both for cardiac chamberand coronary arterycine visualisation. These projectionsare complex, and, unless the above conventions are clearly understood and always used, there will inevitably be confusion between the cardiologist, radiologist, and radiographer. Unqualified termssuch as cranial or caudal tilts are very confusing and unreliablefor they will not be interpreted in the same way by different people. Axial tilt is best used to describea tilt in the sagittal plane but it doesnot identify the direction of tilt. Use of thc abovetwo conventions is absolutely necessary to avoid confusion. In the usual cine installation (patient supine on the horizontal table, undercouch x-ray tube), the four-chamber view is both left anterior oblique (this projects the interventricular septum per- pendicular to the film) and caudocranial (this projects the x-ray beam through the atrioventricular rings). The terms four-chamberview or, pre- ferably, left anterior oblique, caudocranial should be applied to this important projection. Universal application of the twosimple conven- tions explained above will be a major advance in the cardiac radiological laboratory,for it will permit the greater understanding and collaboration between technical, clinical, and radiological staff, which is so essential. It is also important to adopt these uni- versally agreedconventions in the academic and in the technicalreports,for much confusion exists at present becauseof inappropriate terminology. This Journal requeststhat these two simple and universally approved conventions beadopted in any papersubmitted for publication. Requests for reprints to Dr Ronald G Grainger, Department ofRadiology, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF. ill
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