Cancer in Dogs and Cats: Staging with CT scan and MRI

It is essential to know where cancer exists before knowing how best to treat the disease.  TheCancer in Dogs and Cats: Staging with CT scan and MRI process of determining where that cancer exists in the patient is called staging of cancer and involves various diagnostic tools to evaluate the patient.  Computerized tomography (CT) and magnetic resonance imaging (MRI) are two procedures used to stage cancer in dogs and cats.  They are used less commonly than plain radiographs and ultrasound and generally after those procedures have been performed.  Information obtained from CT or MRI is more precise at imaging cancer and allows for more detailed information to aid in treatment planning.

Use of computerized tomography (CT) in the staging of cancer in pets

Computerized tomography (CT) is becoming more commonly used in veterinary medicine, but is more expensive than other commonly used procedures and requires general anesthesia.  CT scanning involves an x-ray tube that rotates around the patient while a computer collects the information and creates an image called a slice.  Slices can be evaluated individually, or placed together to create a 3-dimensional image of the patient. X-rays are used to create multiple images in a transverse plane that can be reconstructed to produce images in other planes (sagittal and dorsal planes).  In doing so, CT allows for a 3-dimensional imaging of the patient.

A CT scan is more sensitive than thoracic (chest) radiographs at detecting the presence of lung metastasis and is the best means of screening the thoracic (chest) cavity.  It is particularly useful at looking at cancers involving the head region, such as oral (mouth) tumors, nasal tumors, and bone tumors of the skull.  It is also helpful and determining the extent of invasion of tumors of soft tissue structures.  It is used extensively and is very important in the treatment planning for patients receiving radiation therapy.

Use of magnetic resonance imaging (MRI) in the staging of cancer in pets

Magnetic resonance imaging (MRI) is less available than other imaging techniques.  Like CT, MRI is more expensive than other commonly used procedures and requires general anesthesia.  MRI creates images in multiple planes (transverse, sagittal, and dorsal planes) allowing for true 3-dimensional imaging of the patient.  Instead of using x-rays, MRI uses magnets and radiofrequency waves to create images.  MRI generates images through the properties of hydrogen atoms in the body when placed in a magnetic and radiofrequency field.

MRI is most useful for evaluating the nervous system for brain tumors and spinal cord lesions.  It is more sensitive at evaluating the extent of invasion of soft tissue tumors than CT.   It is useful for evaluating joints, tendons, and muscles.  One limitation of MRI is that the information from the study cannot be imported into program software used commonly to plan treatment of radiation therapy in dogs and cats.

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Dr Stephen Atwater

Stephen W. Atwater, DVM, MS, Diplomate ACVIM (oncology) is a board-certified veterinary oncology specialist. His professional interests include utilizing emerging therapies for difficult to treat cancers.

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