Comparing Radiography (X-Ray) And Ultrasonography

By Dr Chua Hui Li
Mount Pleasant Animal Medical Centre (Clementi)

Radiography, or commonly known as X-Ray, along with ultrasonography are two most common diagnostic imaging tools vets use to help reach a diagnosis of your pet’s problems. So what exactly is radiography and ultrasonography, and how are they different from each other in their uses?

main differences between radiography and ultrasonography

The main difference between radiography and ultrasonography lies in the different technology used to acquire the images that we see. They also have different advantages and disadvantages in their use to diagnose a problem. Different disease conditions may also require different imaging modalities for diagnosis or further investigation.

when do we use radiography?

Radiography uses ionising electromagnetic waves (radiation or “X-Rays”) to produce a still shadow image of the internal body parts including bones. Radiography allows the vet to assess the entire animal in a single image.

On a radiograph, bone & other very dense structures appear white, soft tissues such as fluid & organs show up in shades of grey, while air appears black. If your cat is vomiting, your vet may take X-rays to check for intestinal obstruction or foreign bodies. If your dog is limping, X-rays can reveal causes such as bone fractures, degeneration or dislocations.

We use radiography to help diagnose:

  • bone fractures or abnormal growths from bones
  • bone diseases, arthritis or other joint problems
  • slipped discs and certain spinal problems such as Wobblers
  • lung diseases
  • enlarged hearts
  • certain tumours and their spread to the lungs or bones in particular
  • diaphragmatic hernias
  • certain foreign objects in the body
  • bladder or kidney stones
  • late pregnancies
  • dental disease
  • middle ear disease
  • problems relating to the stomach or intestines

Some body parts such as the brain, nasal sinuses, blood vessels, the reproductive tract and gall bladder cannot be seen on radiographs. Radiography may allow us to see the shape, size and location of these body parts but does not provide information on the appearance of these organs, their internal structures or movement as well as blood flow.

when do we use ultrasonography?

Ultrasonography uses ultrasound waves (transmitted into the body via a probe/transducer) to produce real-time images of the internal organs on a screen, with details of their structure and function.

For an abdominal ultrasound, the fur on the abdomen will be clipped. A conducive gel is placed on the probe/transducer that is attached to the ultrasound machine. The procedure is painless & non-invasive.

Ultrasonography allows us to:

  • capture movement and internal structure of the certain organs such as the heart, making it possible for us to assess how well it is functioning.
  • detect early pregnancies, predicting when the foetuses are due as well as the viability of the foetuses.
  • assess the appearance of internal organs such as liver and spleen to determine if they are abnormal looking due to infection, inflammation or growths.
  • look at the bladder in greater detail where the bladder wall and its contents are seen and evaluated for stones and masses.

Other common uses, just to name a few, include the detection of pyometra (uterine infection), fluid accumulation in body cavities, smaller tumours not visible on radiographs, origins of tumours seen on radiographs, and certain kidney diseases such as renal cysts or kidney blockage.

Ultrasonography, cannot evaluate the skeletal system or lungs as bone and air reflect most of the ultrasound waves to produce a black shadow image.

Despite their differences, radiography and ultrasound may be used as complementary tests for the same section of the body. Depending on the animal’s case and circumstances, one may be chosen over the other.


other types of veterinary diagnostic imaging
  • Computed Tomography (CT) 
    Combines the use of X-Rays with the latest computer technology to show different levels of tissue density, produce cross-sectional images of the body part being scanned and provide more detailed information than X-Rays. CT scans are often used to detect structural changes deep within an animal’s body, e.g. tumours, fractures, lung and chest problems.

Sedation is not required for animals undergoing X-rays or ultrasound, unless the animal is anxious, boisterous or in pain. However, general anaesthesia is required for CT scans as the animal must be kept still for several minutes inside the scanner. CT scans can be performed at Mount Pleasant Vet Centre (Gelenggang).

  • Magnetic Resonance Imaging (MRI)
    Commonly used to evaluate tissue disease or injury of the brain and spinal cord. Animals have to be under general anaesthesia because they have to remain still during the procedure. MRI uses a powerful magnetic field and pulses of radio waves to create detailed anatomic images of the body part being scanned.
  • Fluoroscopy
    Uses a continuous series of X-Ray beams to capture real-time images on a monitor. With the “X-Ray movie”, we see the inside of a body in motion. In orthopaedic surgery, fluoroscopy allows us to see bones in numerous angles and improves the accuracy of incision, aids in the positioning of plates and minimises tissue trauma.

    Fluoroscopy allows Dr Patrick Maguire, Mount Pleasant (Gelenggang), to operate on Brownie’s fractured leg using less invasive surgical techniques so that there is minimal trauma to the tissues & Brownie can recover faster.

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