What are imaging exams for dogs?
Imaging is a technique, using various types of radiation, to obtain images of different parts of the body. The imaging techniques used for dogs are essentially the same as those for humans.
However, some human tests can be performed without anaesthesia. This is sometimes not the case with dogs.
There are several types of imaging uses for the canine organism.
- Gammagraphy or scintigraphy
This is a radiographic examination that provides a good view of the entire spinal canal and its contents. An iodinated contrast agent is injected into the subarachnoid space via the suboccipital or lumbar route.
This is a simple and inexpensive technique that is somewhat less accurate than MRI or CT scanning.
The injected product makes it possible to clearly visualize the contour of the spinal cord, to evaluate spinal cord distortions and locate lesions present in the spinal region. The injection can be done at tail level (lower route) or near the skull (upper route), depending on the case.
The dog is put under general anesthesia. A cerebrospinal fluid sample is often taken at the same time to allow for additional tests if necessary.
Although they are rather rare, some complications may occur during such an examination. When the puncture is carried out near the dog’s skull, it may cause respiratory arrest or paralysis.
When the animal wakes up, seizures may be observed in some specimens that can occur up to 12 hours after the examination. Since the examination is done under general anesthesia, the usual risks related to anesthesia are also present.
Gammagraphy or scintigraphy
This is a verification technique on beam accuracy related to the irradiation of a tumor in dogs. By printing on an X-ray film, it is possible to control the volume of tissue irradiated in the dog under treatment.
It therefore allows to determine precisely the extent of a tumour in the body and can be complementary to a CT or MRI scan. Scintigraphy, unlike CT and MRI, can only study one organ at a time.
This method artificially reproduces certain markers of the organ concerned by fixing them to a radioactive substance which can then be detected with a gamma-ray camera.
To carry out the examination, a radioactive substance is injected into the dog’s body, positioned in camera range. The organ can then be studied according to the stains produced by the radioactive substance. It is then possible to evaluate the performance of the organ and assess the extent of the tumour and its metastases.
In veterinary medicine, scintigraphy is generally used for searching for bone metastases, exploring the thyroid gland or searching for a cause of limping in animals.
Scintigraphy is not always offered in private clinics but can usually be performed in a veterinary hospital. The dose of radioactive material used to perform the radiography is very low and generally safe for the dog.
MRI (Nuclear Magnetic Resonance Imaging)
This is a very sophisticated medical imaging method that is increasingly being used.
Since it is based on the phenomenon of magnetic resonance, it is much less traumatic than some other forms of radiography, such as myelography, for example, while providing tomographic images of the distribution of atomic elements (hydrogen) in the body.
This method does not use contrast products or ionising radiation and allows for original and adjustable contrasts between healthy and pathological tissues of the canine organism.
Anatomical images are reconstructed using detectable magnetic properties of neutrons or protons contained in atomic nuclei.
Molecular structures can be studied following the analysis of magnetic resonance phenomena of intermolecular bonds and atoms. The images obtained can be in situ, in vivo, in real time, in two or three dimensions. MRI allows to visualize the whole body of the dog but in sections.
The principle of MRI is a bit complex. A tissue subjected to an intense magnetic field causes the protons in its hydrogen molecules to all point in the same direction. This is the nuclear part.
As each proton reacts like a small magnet (magnetic part), the electromagnetic wave of the radio wave frequency excites it and allows it to enter in resonance with the produced wave. The direction of its magnetic field then changes at a certain angle.
When the radio wave is interrupted, the initial angle is picked up by the protons. This reaction then forms the electromagnetic resonance wave which is picked up by receivers and transmitted to a computer. Each point is given a color value by the computer, resulting in a colored dot on the screen. Performed section per section, the operation produces an image that can be viewed in 3D.
Typically, the veterinarian will suggest an MRI when an abnormality in the spinal cord, brain or soft tissue is suspected. When ultrasound, CT scan or X-ray is not sufficient to determine the exact cause of the problem in the dog, MRI can greatly assist the veterinarian in making an accurate diagnosis.
The MRI is done under anesthesia. Usually two veterinarians are present during the examination, one supervising the anesthesia while the other takes care of the imaging part. There are no risks associated with MRI except the classic risks of anesthesia.
No preparation is necessary except for the removal of all metal objects from the dog. The animal is anesthetized for an examination that can last between 15 and 60 minutes.
Also for diagnostic purposes, ultrasound is the entire medical imaging department with the material resources necessary to produce and interpret images obtained by means of ultrasound echoes on the internal tissues of the dog’s body.
The frequency of the ultrasound is determined by the type of tissue to be explored by the veterinarian. The images generated are recorded on photographs and on a screen allowing to view increasingly precise images due to sophisticated equipment of the latest generations.
There is no danger for the dog. Positioned on a table, the veterinarian will move a probe with gel (acting as a conductor) on the dog’s skin, allowing him to visualize on the screen what is in the path of the ultrasound.
It is an instrument or device for medical imaging by scanning a defined field. Scanning consists of detecting or measuring the emitted waves in order to produce a medical image of the chosen area.
Because organs absorb the x-ray beam differently depending on their particular composition, the scanner works the same way as conventional radiography by emitting x-rays through the dog’s body.
However, instead of the conventional X-ray plate, they are digital sensors that transmit the collected data to a computer, which then displays the captured images.
The veterinarian places the dog, usually anesthetized, in a narrow tunnel where the x-ray beam revolves around the animal. The computer then collects all the necessary data and gives a very clear picture of the anatomical parts being examined.
The study of tumors, soft tissues, abdomen, trunk organs and brain are very often targeted by veterinary CT scans.
It is a method of examination using flexible devices (fibroscope) made of glass fibres used as light conductors to visually explore the inside of different cavities and ducts of the dog’s body.
Fibroscopes, being equipped with a channel allowing the insertion of fine instruments, are twice as useful, allowing the veterinarian to visualize the targeted interior and at the same time to proceed if necessary to a sampling of the selected zone. The veterinarian may also proceed with the cleaning of the zone by injecting products using the fibre-optic scope.
Fibroscopy is generally used to evaluate the stomach, esophagus, duodenum, respiratory tract, nasal cavities, bladder and urethra.
This is a conventional method using X-rays to obtain medical images of the inside of the dog’s body through a plate containing an X-ray sensitive film.
The X-ray beam passes through the dog’s body, hitting the nuclei of molecules and electrons to produce a print on the film in the plate behind the dog.
Today’s irradiation is very low. As the absorption of the targeted zones is different according to the particular molecules of each zone, the contrast appears differently on the plate allowing the veterinarian to visualize certain anomalies. There are different types of X-rays.
Radiography with a contrast medium
- Blood vessels
- Digestive tract
- Spinal cord
The digitized radiograph
The computer processing of the resulting images increases the sharpness of the image and can be used with standard or contrast radiography.
Complications are rather rare after a dog has an X-ray. The irradiation being very low, the risks of complications are practically nil.
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