Projection names

Names of projections are always given as representations of the direction of beam, so that this gives the radiographer information on the initial patient position. This is in preference to a system which uses names for some projections that reflect the original describer of the projection (e.g. Towne’s’, ‘Waters’) but gives little or no information on the position. The UK system has for many years avoided overuse of named projections, and the use of position descriptors for projection titles is less confusing, making it unnecessary for the radiographer to learn eponymous titles. As a matter of interest, the editors of this text searched for all named projections in use, most popularly used in the US; the total number found was 200 (projections for all body areas, not exclusively relating to the head). Confusion caused by a lack of consistency in projection names/descriptors is further discussed in the chapter on facial bones, as it is a particularly relevant topic for that area.

In reality, one or two eponymous titles are still considered mainstream and heard in use by radiographers in the clinical setting; when such a name is very commonly used in everyday practice, the alternative will be given in brackets after the projection title.

Patient preparation

For all examinations, patient preparation should always include:

Image recording (CR cassettes and digital plates)

With the current situation of image recording, where there is a choice of computed radiography (CR), digital radiography (DR) and film/screen systems for use, it has been difficult to select a method of description that accurately embraces the use of all of these methods. It must be said that, in the UK, use of film/screen radiography is now almost obsolete. As CR uses cassettes similar in appearance to conventional film/screen systems, there would appear to be little change from film/screen methods for image receptor (IR) use; however, some notable differences regarding DR exist. It has therefore been decided that the term ‘image receptor’ will be used as an umbrella term. This is intended to include any of the recording systems that may be used by the radiographer. It should also be noted that use of lead rubber for masking is not advisable for CR and DR systems, although some of the positioning images do demonstrate this on a film/screen cassette.

Since the last edition of this book was published there have been significant developments in DR plates and increased use of these. Wireless plates are now widely available, which further improves the flexibility and range of uses for digital plates, with some manufacturers developing DR support units which are flexible in their positioning rather than being fixed vertically or horizontally. DR plates vary slightly in size and are usually square in shape, but generally do not come in the wider range of sizes found with film/screen or CR plates. They can be fixed under a stand or table surface, independent (wired or wireless), in a tray used under the table-top or pulled from the side of the table-top for extremity work.

As a result of the range of possibilities for receptor arrangement, the IR position will simply be referred to as horizontal or vertical and no IR sizes will be given.

DR plates do not require the centre of the body part to be placed coincident with the middle, unlike CR cassette radiography. For this reason, the positioning descriptors provided in this book assume that the radiographer will always ensure that the body part lies within the IR, or within an unexposed section if the IR is used for more than one projection. At times it will be necessary to centre the body part to the middle of the DR plate, e.g. when that body part is large (as in chest or abdomen radiography), and this will be advised in descriptors for some sections, in order to ensure that the whole of the body part is included in the image.

Another point to raise is the use of an antiscatter device (grid), which should be used in conjunction with the IR if scatter reduction is relevant. Their use will be indicated in descriptors when necessary.

Change in terminology for focus film and object film distances

With the disappearance of film/screen radiography it has become necessary to reconsider these radiographic terms in order to ensure accuracy of reference. It has been noted that different terminologies have been introduced in recent years in an attempt to address this issue, and US texts initiated the use of the terms ‘source image distance’ and ‘object image distance’ as long ago as 2005² in an attempt to use more appropriate terms that did not include the word ‘film’. However, one must question the use of the word ‘source’: it is true that the tube target is a source of radiation but use of the word ‘source’ in a radiation environment does imply ‘radioactive source’, simply because ‘source’ is used more routinely when referring to radioactive materials (although it is not inaccurate to refer to electrically produced X radiation as a source of radiation). In addition, use of the word ‘image’ can be considered inaccurate, as the image is latent until digitally processed and displayed. As a result it has been decided to use the terms focus receptor distance (FRD) and object receptor distance (ORD) in this edition; we feel that these are more appropriate, especially as the terms only include one changed word from old terminology, making them more easy to adopt.

Anatomical markers

It is assumed that anatomical markers will always be placed within the field of primary beam, clear of the essential area of interest. Therefore, instruction for this will not be included for every description of projections. Unless otherwise specified, it will be assumed that AP (anteroposterior) markers will be applied. Use of posteroanterior (PA) markers will be referred to but the authors do acknowledge that some imaging departments do not use PA markers. Anatomical markers do not always appear in positioning images as often they are too small to reproduce on a small photograph.

It will also be assumed that the radiographer will always check accuracy of anatomical markers on the resulting images as this is an important medicolegal requirement; therefore the image quality criteria will not refer specifically to this requirement.

Image identification

Correct identification of the image will be assumed to be an area that the radiographer need not be reminded to assess during image quality assessment, since this is a vital medicolegal requirement. This is therefore not included in the image evaluation lists in the text.

Exposure factors – evaluation of images

As digital radiography has brought the possibility of image manipulation, the image submitted for reporting is not always exactly as produced at the point of exposure, as it was with film/screen radiography. It is still possible to state required evaluation criteria for exposure factors in the way used in the first edition of this book, but recognition of faults, and suggested correction, may be less relevant if manipulation of images can successfully bring appearances in line with required standards stated. It is clear, though, that the possibility of manipulation is no excuse for poor attention to exposure factor selection, and balancing dose minimisation with high-quality appearance is of paramount importance.

Dose reduction methods

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