From CT scans to ultrasounds, there are several ways to see inside your dog or cat’s body. Here’s how these diagnostic imaging techniques differ, and the pros and cons of each.
Along with lab work such as blood and urine testing, your dog or cat may sometimes require diagnostic imaging studies to look at the deeper tissues of his body. Depending on his condition and the suspected problem, diagnostic imaging can include radiography, ultrasonography, a CT scan, and/or MRI scan. This article examines each of these modalities along with their pros and cons.

1. Radiography

This form of diagnostic imaging uses radiation to produce energy (x-rays) that penetrate the body to show underlying structures such as bones and soft tissues (organs). It is a common imaging modality and is available in most veterinary hospitals. Radiography is one of the “standard” tests I often use to assist me in making a diagnosis and formulating a treatment plan.


  • Inexpensive compared to other imaging techniques (typically under $500).
  • Easily performed.
  • Allows for quick imaging.
  • Often gives a diagnosis for many diseases (fractures, heart failure, bladder stones, some types of cancer, etc.).
  • Minimal levels of radiation exposure.


  • Uses ionizing radiation. While generally safe, the more radiographs a dog or cat receives over his lifetime, the greater the risk of side effects, such as cancer. Also, there’s a lifetime radiation exposure level that shouldn’t be breached; however, it’s unlikely this level would ever be closely approached unless the animal receives large amounts of radiation for cancer treatment.
  • May not reveal every problem (e.g. brain tumors, prolapsed spinal disks, etc.), necessitating the need for different imaging modalities.
  • Most animals need to be sedated to minimize the number of radiographs and allow perfect positioning, and to minimize radiation exposure to veterinary staff.

2. Ultrasonography/echocardiography

Ultrasonography is a popular diagnostic imaging tool that looks inside your dog or cat’s body via the use of sound waves. Ultrasound examinations are most useful for diagnosing conditions that could be missed or not easily defined using a typical x-ray examination. This can include bladder stones, tumors of abdominal organs, and free abdominal fluid (as in the case of a bleeding tumor).

Echocardiography is an ultrasound examination of the heart. It is commonly used to look for heart-based tumors such as hemangiosarcomas and, more often, for examining the heart in an animal suspected of cardiac disease. While radiography can show heart and blood vessel enlargement (a snapshot of the heart and vessels), echocardiography shows the heart and its parts (valves) in motion (i.e. a motion picture of heart muscle movement and blood flow). In my opinion, with extremely rare exceptions, no dog or cat should be placed on cardiac medications without echocardiography being used to make a diagnosis (see below).


  • Inexpensive compared to other imaging modalities (typically under $600).
  • Like radiography, it’s easily performed, allows for quick imaging, and often provides a diagnosis for many diseases (heart failure, bladder stones, some types of cancer, etc.).
  • Uses safe sound waves.
  • Most animals do not need to be sedated.


  • May not reveal every diagnosis, especially very small tumors, necessitating the need for different imaging modalities.
  • Sedation may be needed for fractious animals.
  • Echocardiography won’t reveal pulmonary edema (fluid in the lungs), which may require separate testing such as radiology.

3. CT scan

Computerized tomography (CT scan) uses x-rays to create the image. However, instead of using a single x-ray, as in a standard radiograph, CT scans combine numerous x-rays taken from different positions, and use advanced computer technology to create more detailed images of the patient. It’s easier to see more detail of a body part when it’s viewed from multiple angles. Think of the difference between a 2D image and a 3D image, and you’re on the right track. CT scans pick up many of the same things as simple x-rays do, but in a more detailed and precise manner, making them particularly useful for detecting small tumors and internal bleeding.


  • Often gives a diagnosis for many diseases not easily visualized by traditional radiography or ultrasonography.


  • More expensive compared to other modalities (typically $1,500 to $2,500).
  • Requires referral to a specialty center.
  • Scan takes longer (one to two hours) than a traditional radiograph.
  • More radiation exposure than with traditional radiography.
  • Uses ionizing radiation.
  • May not reveal every diagnosis (e.g. brain tumors, prolapsed spinal disks, etc.), necessitating the need for an MRI.
  • All animals need to be sedated/anesthetized.

4. MRI

Magnetic resonance imaging (MRI), like ultrasonography, doesn’t use radiation to produce an image. Instead, it relies on a combination of magnetic force and radio waves.

Although MRIs are occasionally used to diagnose knee, nerve, and other issues in dogs, the vast majority are used to examine problems with the brain and spinal cord, especially if tumors or bleeding are suspected. An MRI is ideal because it’s particularly good for imaging soft tissue (brain and spinal cord) and it gives more detail than a CT scan. It does this by reading the differences in tissue density to reveal tumors and lesions that CT scans might miss.


  • Often gives a diagnosis for many diseases not easily visualized by traditional radiography or ultrasonography, or even CT scan.
  • No radiation exposure, making it a very safe imaging modality.


  • Like CT scan, MRI requires referral to a specialty center, the imaging takes one to two hours to complete, and all animals need to be sedated/anesthetized.
  • More expensive compared to other modalities (typically $2,500 to $3,500).
  • While excellent, no test can reveal every cause of disease, and even an MRI may not reveal every diagnosis.

Echocardiography — essential for diagnosing heart disease
Recently, I saw a dog that had been placed on three cardiac medications more than a year ago by another doctor who diagnosed “heart disease” just by hearing a heart murmur. No diagnostic testing had been done, and now the dog had increased kidney values on blood testing.

I performed a complete cardiac evaluation, including echocardiography, which showed two things: there was no primary heart disease, but the heart was showing negative changes due to the improperly prescribed cardiac medications. The cardiac drugs were also negatively affecting the kidneys.

Once we had the correct diagnosis and stopped the unnecessary medications, the dog improved!

Diagnostic imaging has progressed greatly in veterinary medicine, and it’s exciting to have all these modalities available for our dogs and cats. Keep in mind that the more advanced the modality, the higher the cost, so it’s wise to consider pet insurance before one of these diagnostic imaging techniques is needed. While basic radiographs are adequate for getting to the root of most medical conditions, ultrasonography, CT scans, and MRI scans can help diagnose problem early on — and that can be lifesaving in many cases.