What are radiographs?
Radiographs are 2-D images obtained using x-rays, which allows visualization of internal organs (ie within the chest or abdominal cavities) and bones. Types of radiographs include thoracic (evaluation of the heart, lungs, ribs, diaphragm, thoracic spine, esophagus, and chest lymph nodes), abdominal (evaluation of stomach, intestines, liver, spleen, kidney, lumbar/sacral spine, bladder, and pancreas), limb (evaluation of bones that make up the front and/or hind limbs), spinal (evaluation of the vertebrae – bones that surround the spinal cord), neck (evaluation of the throat region, esophagus, and trachea), head/skull (evaluation of the bones and tissues that make up the jaw, skull, nasal cavity, and sinuses), and dental (evaluation of the teeth and bones within the oral cavity).
Overall, radiographs are helpful in that they can detect changes in the size, shape, or position of internal organs and tissues. The type of radiograph taken depends on what is going on with each individual patient. For example, a clinician will recommend thoracic radiographs for a patient that is having difficulty breathing, to rule out evidence of heart failure, fluid within the chest cavity, or abnormalities involving lung tissue that may be suggestive of cancer, inflammation, or infection (ie pneumonia). Patients suffering a traumatic incident (such as being hit by a car) may have limb radiographs to check for bone fractures) and chest radiographs to check the lungs and ribs and ensure that the diaphragm is intact. A patient that is vomiting repeatedly may have abdominal radiographs to assess for a gastrointestinal blockage or changes consistent with pancreatitis.
In some cases radiographs are utilized to monitor therapy, such as response to heart medications used to treat heart failure, chemotherapy to treat cancer affecting the lungs, or antibiotics to treat pneumonia. This diagnostic test can also be utilized to evaluate internal tissues after certain procedures (eg to ensure that feeding/chest tubes are placed properly, fractures have been fixed appropriately, or that all bladder stones have been removed after a cystotomy).
How are radiographs used for cancer patients?
Radiographs are often used as a staging tool for patients with cancer. Staging means evaluating the body for metastasis (tumor spread) or evidence that the cancer is in multiple locations. Thoracic radiographs are most commonly used (to check the lungs for metastatic disease), although limb radiographs are often utilized as well (when primary or metastatic bone tumors are suspected). Patients undergoing treatment will frequently be evaluated with thoracic radiographs every 6-12 weeks, to evaluate response to therapy (if pulmonary disease is already present) or to ensure that metastasis hasn’t developed.
How are radiographs taken and are they safe?
The position of the patient during radiographs depends on the area being x-rayed and the views needed. For chest and abdominal radiographs the patient is placed gently on his side (for the lateral view), and then on his back (for a ventrodorsal view). In many situations a third view is taken (particularly when evaluating the chest), where the patient lays down on the other side for the opposite lateral view. For patients with particular heart or respiratory diseases, radiographs are taken in sternal recumbency (meaning they lay on their chest). For most other areas (bones, skull spine) at least two (usually perpendicular) views are recommended to best evaluate the tissue or organ in question.
Once the patient is positioned appropriately, a button is pressed that allows x-rays to pass from a tube (within the radiograph machine) through the patient and onto films (either underneath the patient or on the other side of the tissue being evaluated). As the x-rays pass through the patient, different shades of gray are produced on the film creating a picture that can be seen once the film is developed. The shades of gray produced depend on the ability of x-rays to pass through different tissues (more x-rays will pass through air compared to soft tissue compared to bone – bone comes out white on radiographs, air is black, and soft tissue is grey), which ultimately relates to the density and composition of the tissues being evaluated.
Generally radiographs take about 5-20 minutes to obtain, and can usually be performed without sedation. In some cases where the patient is stressed, anxious, or painful (due to underlying disease), mild sedation is given to help the patient and more quickly complete the study. It is rare that general anesthesia is required to obtain radiographs. The procedure itself is not painful and is very safe (the radiation exposure is minimal and should not cause any issues). While your veterinarian will always evaluate the films, he may recommend sending them out in certain situations to a board certified radiologist for review (particularly in complicated cases).
What are the limitations to radiographs?
Because radiographs are 2-D and depend on the difference in “opacity” (shades of gray) between various organs/tissues, superimposition or overlapping structures may hide important details (such as the presence of a tumor that is hidden by normal organs). In addition, fluid within the chest or abdominal cavity can make evaluation of internal tissues difficult. It is also important to note that radiographs cannot detect fine details within specific organs (such as very small lung nodules, masses within the liver/spleen/kidney that do not distort the size or shape of the organ affected, or vascular abnormalities). In cases that are screened with radiographs, follow-up testing (such as ultrasound, CT scan, MRI, endoscopy, or an exploratory surgery) may be recommended if abnormalities are suspected.