Safari has added a CAT scan machine to our arsenal of tools to fully evaluate each patient’s individual case. CAT stands for Computer Axial Tomography. CT is the more current abbreviation meaning Computed Tomography. Few diagnostic modalities can rival the advancements of CT technology over the past 25 years.
Early CT scans would rotate around the patient, creating multiple angles of view that were digitally sewn together to form a slice – think of a loaf of bread that is sliced and you are then able to see the cut surface. Today’s CT scans for pet animals, however, use multiple simultaneous detectors, making the slice more of a spiral – think of a spiral cut ham instead of individual slices.
This spiral effect creates three dimensional cubes of visual data that can be examined from any direction. This means we are now able to see CT images from any angle, like turning a Rubik’s cube from the red side to the green side and then over to the yellow side and seeing every angle in between.
In addition, the traditional shades of grey are replaced with color to give a colorful three-dimensional view of the animal. These 3-D cubes are called voxels and can be as small as 1mm on a side. This level of resolution has never been possible in a traditional pet CT scan much less a radiograph.
The color is important because our eyes can only see 50 shades of grey, yet we can discern about 10 million different colors. The current pet CT scanner at Safari computes about 2000 different shades of grey, and each shade can be assigned a different color. These shades are then numbered and even though our eyes cannot see the differences, the computer can help us discern those differences through this color coding.
The following is an example of a case where a pet is paralyzed and has had an MRI image of the spinal cord. This image shows some change to the center of the spinal cord, meaning the neurons – nerves – contain increased water. They are swollen. But from the MRI scan we cannot see the reason for the damage. A Dog CT scan with color assignments made to different cartilage densities allows us to see much more. The following series of images illustrates this concept.
Figure 1 is a cross section of the spinal canal at the area of spinal cord damage. The red and green lines cross inside the spinal cord that in turn is inside the bony vertebrae. At the junction of the lines is the number 139. This number is a density value that represents the density of cartilage. The surrounding density values are 30 to 50 representing normal spinal cord. The density of the bone of the vertebral body is 900. The cartilage should not be present but would not have been see had it not been for the advanced capabilities of the newer veterinary CT scanners.
Figure 2 shows three color filters that are designed to show cartilage density as a different color spectrum than the spinal cord. The first one colors the spinal cord that has increased water in it (swelling) as blue and cartilage is the black hole. Figure 3 shows the spinal cord tissue as gold with the cartilage as being yellow.
Finally, there are two blue neuro filters that eliminate the bone and other tissues showing only the cartilage and the swelling of the spinal cord. If we go one vertebra up the spine to a more normal, non-damaged area there is nothing within the spinal cord. This pet had surgery and the bits of cartilage were removed from the spinal cord. The cartilage came from a ruptured intervertebral disc.
The final image shows another pet where the disc encroaches on the spinal cord but not explosively like the one above.
The digital voxels of certain densities can be instructed by the software to disappear so that the underlying tissues can be seen. This is helpful in showing the skeleton absent the muscles. It is also helpful in showing the blood vessels when they have a dye in them or the elements of the urinary system absent the intestinal tissues that surround it.
Techniques for seeing deep into tissues using the three-dimensional technology like cutting a “hole” in the skull to see the brain inside come in handy when trying to see the lungs of a turtle with emphysema or eggs.
Some animals are critical or exotic or both and scanning them without sedation is another feature of the Safari pet CT scanner. An exotic pet can be placed in a Plexiglas box and the entire box scanned in just a few seconds to get very quick but precise diagnostic images as this lemur, prairie dog, and parrot demonstrate.