The Power of Imaging - by Dr. John Farrelly

As a radiation oncologist, I get to look at a lot of images – CT scans, radiographs, ultrasound images, MRIs, nuclear medicine scans and now PET scans.  What always impresses me is how imaging can add so much information to what we know about our patients, as long as we pick the right imaging test based on our patient’s history and physical exam.

For example, as veterinarians, we look at thoracic radiographs almost daily.  For patients with cancer, we are usually trying to rule out the possibility of metastasis.  Finding metastases can often mean the difference between an animal with a good or excellent prognosis and one who may have a worse prognosis, one that we might want to consider palliative treatment options for.  Thoracic radiographs are a powerful tool to help figure this out.  However, CT of the lungs has been shown in recent studies to be much more sensitive in finding metastases.  With CT we are able to detect lung nodules as small as 2 mm. 

Figure 1 Chest radiograph showing small nodule that is barely visible (red arrow)  

Figure 2 CT scan showing that same nodule clearly showing its size and location in the lung (red arrow)

Another great example is CT scan of the neck.  Palpation of the neck can often be difficult and dogs or cats with enlarged retropharyngeal nodes can feel normal on palpation.  However, imaging tests like a CT scan or an MRI can tell you exactly how large those nodes are, which can often give an idea of whether the tumor has metastasized there.

Figuer 3 CT scan of the neck of a dog showing the normal retropharyngeal lymph node (red arrow) and an enlarged node (yellow arrow)

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For me, this is sometimes the most important information that I can give to a pet owner…have we done all that we can to rule out spread of their tumor?

Dr. John Farrelly