Plain film abdominal radiographs are one of the most commonly performed radiographic series. We often forget how much information can be gleaned from a correctly exposed and positioned set of images.
Standard views should include both right lateral and ventrodorsal, with consideration given to the addition of a left lateral if you are interested in the stomach (particularly the pylorus), large and small intestines. Failure to perform at least two views can lead to missed pathology.
The following are some of the most commonly encountered issues when performing abdominal radiographs.
Motion on an abdominal radiograph can be caused by either respiratory motion or generalised patient movement.
Ensuring you expose your radiograph at the end of expiration can help reduce respiratory motion, and correct chemical restraint of a patient with sedation or general anaesthesia will reduce (and hopefully eliminate) generalised patient motion.
Mild respiratory artifact is always more noticeable on the cranial aspect of the abdominal radiograph.
This image demonstrates good exposure, but the patient is poorly positioned and slightly rotated. There is respiratory artifact present and the image is incorrectly orientated and requires flipping to ensure the right-side marker is to the left of the image
Ensuring good positioning can reduce superimposition of structures and improve identification of abdominal contents, e.g. patient rotation can lead to elongation of organs and poor representation of kidneys.
It is vital to fully extend the pelvic limbs caudally when taking lateral images, as this reduces the soft tissue superimposition of muscle overlaying the caudal abdomen (see image 2).
Padding or foam positioning aids placed under a patient’s sternum can help reduce rotation, and for very muscular dogs, placing one between the pelvic limbs can help improve positioning of the pelvis and pelvic limbs.
Rotation of the ventrodorsal (VD) projection can cause the kidneys to appear uneven in size and shape. When assessing the dorsal spinous processes (DSPs), these should appear in the centre of the vertebrae. A helpful tip for identifying the correct direction to rotate the patient, in order to correct poor positioning of DSPs in a VD projection, is to assess which side they are closer too (left or right). Then simply rotate the patient towards that direction.
This image demonstrates poor positioning of the pelvic limbs. Extending the limbs caudally ensures the associated soft tissue does not obscure other soft tissue structures like the bladder. There is also a greater than necessary quantity of thorax included in the image (and an elbow). Improved centring would result in the pelvic portion of the abdomen more readily visible. A slight respiratory artifact can also be seen.
To maximise intra-abdominal contrast, a low kV technique should be used. Depending on the generator used and size of the patient, this is usually in the range of 50-60kV for a cat and 50-75 kV for dogs. This should then be coupled with use of a high mAs. This can be problematic if using a low powered generator as they often work at a low mA with longer exposure times, which may increase the incidence of motion artifact.
When imaging a patient where the depth of tissue is greater than 10cm, an anti-scatter grid should be used in order to reduce internal scatter. Grids become even more important when imaging overweight patients. If a grid is to be used, then compensatory alteration of the exposure factors is vital. This is usually achieved by doubling or tripling the mAs, taking into consideration the radiation absorbed by the anti-scatter grid.
Please remember, just because you are using a digital radiography system does not mean grids are no longer required!
Often abdominal imaging requires a multimodality approach. For example, if looking for a linear foreign body ultrasound can be a valuable second modality. If available, CT can provide additional information when imaging the abdomen of large breed dogs.
This image quality is reduced due to exposure using a low mAs, along with an excess of scattered radiation. By adding an anti-scatter grid and increasing the mAs, image quality will dramatically improve and abdominal organs will be more easily identified.
When imaging large breeds, it can be difficult to include the entire abdomen in a single image, even with a 35x43cm cassette. It may therefore be necessary to perform two views to ensure all organs are identified.
A view incorporating the cranial abdomen including diaphragm, in addition to a collimated view of the pelvic region, can be useful for larger patients. If looking for calculi, it is vital to include the entire of the route of the urethra, stones can be hidden in the strangest locations especially in exotic patients.
Although this image generally demonstrates good positioning and exposure, the cranial abdomen has not been included. Absence of the diaphragm may be due to a large dog, but looking at the relative size of the marker, this appears to be due to small cassette size. A larger cassette may have allowed for inclusion of the diaphragm in this case. Lastly, the marker should not be positioned so that it masks the anatomy.It should be placed safely within the primary beam on the plate itself.
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