Please note: Media Relations is unable to answer questions about pet health problems. Contact your veterinarian.  

CT, MRI and radiation therapy

If your veterinarian recommends a CT scan, an MRI or radiation therapy for your pet, you may have some questions. Below are answers to some commonly asked questions.

A new $1 million renovation to the radiology section at the Veterinary Medical Teaching Hospital in Kansas State University's College of Veterinary Medicine showcases advanced in-house technology that is rarely seen in veterinary teaching hospitals.

The three-room suite features premier computed tomography -- CT -- for small animals and horses as well as magnetic resonance imaging -- MRI -- capabilities for small animals. The equipment, which is rarely available for large animals, offers the same specialized medical care used for human patients.

The CT scanner is used to assimilate multiple X-ray images into a two-dimensional, cross-sectional image. MRI scans, which are superior to traditional X-ray images, are used to examine internal structures of the body, particularly the soft tissues of the brain, spinal cord, joints and abdomen. MRI is typically used for detecting and monitoring cancers.

ANSWERS TO COMMONLY ASKED QUESTIONS ABOUT CT AND MRI

Why does my pet need CT or MRI?

Some areas of the body are difficult to image with conventional radiographs (X-rays) or ultrasound. Because of complex anatomy or overlying structures, tomographic (or slice) images must be used to evaluate the area. CT and MRI also both have the advantage of displaying images digitally, which can emphasize differences between normal and abnormal tissues making problems easier to detect, and the margins easier to recognize.

Is it safe?

Magnetic resonance imaging uses radio-frequency energy to excite molecules in your pet -- similar to that which a radio or TV station emits. No ionizing radiation is used. Low magnetic fields have not been demonstrated to be harmful to animals or people. Caution must be taken in animals or people that have been implanted with pacemakers or metal clips in certain areas. Because pets cannot move during the MRI scan, they must be anesthetized during the procedure. While there are some risks inherent to anesthesia, at the KSU VMTH, anesthesia is supervised by board certified (American College of Veterinary Anesthesiology) specialists who carefully assess each patient prior to the procedure. While CT scanning uses ionizing radiation, the dose received by the patient is similar to that of conventional radiographs (X-rays) and less than that for a human receiving a similar procedure. CT should be avoided in breeding animals during the first trimester of pregnancy. Pets are usually anesthetized for CT scans. These procedures are relatively quick (15 - 30 minutes), further minimizing the risks.

Why does my pet need to be anesthetized or sedated for the procedure?

Both CT and MRI require the patient to hold still during the scanning procedure. Even small movements result in artifacts which degrade the scan quality.

Why does the procedure cost more than conventional (radiographs) X-rays?

Equipment costs and maintenance costs are much higher for CT and MRI equipment. A CT scanner will cost 10 – 20 times as much as a conventional X-ray unit. An MRI unit costs 20 – 50 times as much.

How does CT work?

CT units produce a very thin fan of x-rays which are directed through the patient and strike a row of radiation detectors. The amount of radiation going through a specific part of the patient, and therefore reaching the detector is related to the density of the body part. A CT scanner takes numerous views of each part, and reconstructs an image based on the density of different areas.

How does MRI work?

When a patient is put in a strong magnet, some of the atoms become aligned with the magnetic field. If a carefully tuned radio-frequency (RF) pulse is sent into the patient, those atoms can be tipped over. As the atoms realign themselves with the magnetic field, they give off an RF pulse that can be detected by the MRI scanner. The amount of RF signal given off, and the time at which it is released are characteristic for certain tissues. RF signal changes can differentiate normal from abnormal tissues such as those affected by cancer, infection or trauma.

What are the indications for CT?

CT is particularly useful for looking at complex bony structures such as the skull, spine or joints. It is also useful for detecting and characterizing lung disease. Both CT and MRI are excellent for assessing blood flow to an organ or region.

What are the indications for MRI?

MRI is useful for looking at soft tissue structures which have low contrast on conventional radiographs (x-rays) and complex soft tissue structures. The largest indications are in imaging the brain, spinal cord, and soft tissues of the musculoskeletal system.

COMMONLY ASKED QUESTIONS ABOUT RADIATION THERAPY

How does radiation therapy work?

The linear accelerator can be programmed to produce photons or electrons to treat deep or superficial tumors, respectively. These energy beams can be directed to specific sites on the body to treat the patient. Radiation therapy works by sterilizing cells, which keeps them from being able to undergo successful division. This means a large tumor may not shrink immediately with RT. The cells will be sterilized, and will live out their natural life span. When they attempt to divide, they will be unable to do so and will die resulting in tumor shrinkage.

Why does my pet need radiation therapy?

Radiation therapy is used to treat inoperable tumors that have not spread to other sites in the body. Like, surgery, this offers a potential cure for localized tumors. It may be combined with surgery or it may be combined with chemotherapy to address both local and systemic disease. Certain chemotherapy drugs act as radiation sensitizers and are used for their ability to enhance the effects of radiotherapy.

How often is radiation therapy administered?

RT can be used with curative or palliative intent (relieving clinical signs). When administered with curative intent RT is given in small fractions over three to four weeks. For palliative effects, RT is given in large fractions once weekly for three weeks.

What types of side effects can happen with radiation therapy?

Radiation therapy in dogs and cat does NOT cause systemic side effects (tiredness, loss of appetite, nausea). Side effects of RT occur more often with curative attempts, and can be categorized in to acute and chronic problems. Acute injuries begin during or shortly after the completion of therapy. They arise in tissues within the RT field that are growing and dividing rapidly; the most common acute effects are skin problems that mimic a severe sunburn. Acute side effects will resolve with minimal nursing care and they are not considered to be does limiting. Chronic side effects arise from damage to tissues within the RT field that are slowly renewing populations (i.e. bone, retina, brain). Clinical syndromes include the formation of bony sequestra, retinal lesions, brain cataracts and neurologic signs. Chronic side effects are dose limiting, veterinary protocols are designed to minimize long term problems.

Why does my pet need to be anesthetized or sedated for the procedure?

Because pets cannot move during the radiation therapy, they must be anesthetized during the procedure. While there are some risks inherent to anesthesia, at the KSU VMTH, anesthesia is supervised by board certified (American College of Veterinary Anesthesiology) specialists who carefully assess each patient before the procedure. Each treatment is very short, animals are anesthetized for 10-15 minutes daily.

Facts about K-State's Linear Accelerator

The Linear Accelerator is a refurbished Siemens 67.40 model. It is housed in a special room, commonly referred to as a vault. The walls and ceilings are lined with 2-inch-thick lead bricks and there is a lead-lined automatic door. The system is fully-integrated with state-of-the-art override systems to prevent accidental exposure. In additional to daily quality assurance testing, the linear accelerator is evaluated by a medical physicist on a monthly basis. The facility is also inspected and certified by the State of Kansas.

* Table will hold up to 300 pounds.

* The gantry can rotate 360 degrees in order to treat from a variety of angles.

* The LA has the ability to produce both high (photon) and low (electron) energy beams to treat deep and superficial tumors, respectively.

June 2002

---

Kansas State University is a comprehensive, research, land-grant institution first serving students and the people of Kansas, and also the nation and the world.