Abdomen

Chapter 24 Abdomen

Plain radiography of the abdomen is often used for assessment of gross anatomical deviation, such as displacement of organs in the case of abdominal tumours or obstruction of the alimentary tract. Information on the urinary system can be provided by the plain abdominal image, preceding other imaging procedures, also providing information on gross anatomical deviation within the urinary system. The appearance of radio-opaque calculi will be demonstrated on the image but urography, ultrasound, radionuclide imaging or computed tomography (CT) will be required to provide information on renal function, site of urinary obstruction or extent of obstruction. The role of these imaging methods in genitourinary investigations is considered in Chapter 31.

Supine abdomen (Fig. 24.1)

Image receptor (IR) is horizontal, used with antiscatter grid

Figure 24.1 Supine abdomen.

Comments on centring, collimation and area of interest

It has been stated that the 11th thoracic vertebra should be included in the collimated field as it lies above the renal outlines and at the tip of the right lower lobe of liver and spleen.¹ It is noted that in most adults this would not usually allow for the inclusion of all the upper abdominal contents; however, with the exception of examination of the upper gastrointestinal tract, ultrasound is the most appropriate imaging modality for the upper abdomen. This would negate the necessity for the inclusion of abdominal tissue immediately below the diaphragm. When the supine abdomen position is used to demonstrate the kidneys, ureter and bladder, and additional abdominal information is not required, lateral collimation can be made to the ASIS on each side to more effectively reduce radiation dose.

Traditionally a specific centring point has been given when describing the anteroposterior (AP) supine abdomen. This has usually been stated as level with the iliac crests in the midline, as in centring (a), above.² Unfortunately, the continuing trend for an increase in average height, noted especially in Europe and the Western world and estimated to be increasing by between 10 and 30 mm per decade,³ affects the amount of body tissue that can now realistically be included on the image. Although the iliac crests do appear midway between the diaphragm and symphysis pubis on the image, centring point (a) will only be useful in smaller patients, i.e. those whose abdominal tissue will actually ‘fit’ within the maximum receptor length. Selection of the centring point/positioning method will therefore depend upon the radiographer’s assessment of the patient’s size.

An additional complication occurs with larger patients, whose adipose tissue will cause further elevation of the symphysis pubis above the table-top; this increases the effect of magnification, potentially adding to the risk of the image of the symphysis being projected below the lower border of the IR. Using the suggested method (b) of centring will reduce the risk of projecting the symphysis pubis off the lower end of the image in these cases.

Only gold members can continue reading. Log In or Register to continue