Sunday, January 15, 2012

CT scans

CT scanners have been installed in veterinary facilities and zoos as a diagnostic tool for everything from aardvarks (1st image, "Bernaard" from the Brookfield Zoo near Chicago being scanned for an infected tooth in 2011) to - presumably - zebras. They are used routinely to scan domesticated dogs (4th image, an undated photo of a dog undergoing a CT scan at the Ohio State University Veterinary Medical Center) and wildcats (2nd image, a 16-year-old leopard named "Meili" scanned at the Taipei Zoo in 2010 to visualize a 40cm tumor in her chest before it was removed). Housecats (3rd image, a pet cat being scanned at the Animal Medical Center of New York in 2010) have been sent through the machine, and so have tortoises big (6th image, a Galapagos tortoise named "Arizona" positioned for a CT scan at Cornell University Veterinary Specialists in Stamford in 2011 to determine why one of its rear legs was not functioning) and turtles little (5th image, a Kemp's ridley sea turtle known as #57 with severe pneumonia scanned at Tufts Cummings School of Veterinary Medicine in 2010 to determine how best to treat the infection). Even gorillas (7th image, "Rafiki", a 25-year-old silverback lowland gorilla monitored during a CT scan at the Cheyenne Mountain Zoo in Colorado Springs in 2009 prior to ear surgery) and horses (8th image, an 8-year-old gelding named "Sydney" being sent through the CT scanner at Massey University in Palmerston, New Zealand, in 2010 to diagnose his hoof problem) have been positioned and sent through the scanner.

But animals put in compromised positions do not experience the embarrassment and outrage that heavy human patients suffer at the hands of unequipped medical personnel - and insensitive newspaper editors - when they are referred to the zoo for medical imaging. Of 407lb Jennifer Walters, the American College of Radiology writes, "Aware that the New York City woman was too large to squeeze into an MRI scanner, the physician reasoned that if the nearby Bronx Zoo could image hippopotami, elephants, rhinos, and other large animals, surely it could accommodate her." At 275lbs, Carolyn Ragan says, “I thought, I know I’m big, but I’m not as big as an elephant." Recently revisited in the weird news, the issue is legitimate, as obesity increases and even open MRI scanners cannot accommodate those too overweight to fit far enough through the gantry without dissipating the magnetic field. When heavy patients do fit in the machines - which typically have a gantry diameter of 27.6" and a table capacity of 450lbs - the images are often of poor quality. But Chicago's Lincoln Park Zoo veterinary technician Joel Pond, executive director of the Association of Zoo Veterinary Technicians, calls the search for super-sized scanners at zoos an urban legend. In an open letter to radiographers and their instructors, he writes:
"Very few zoos own a CT machine — only one of which is known to me — and none own MRIs. And that one zoo, along with veterinary specialty practices that do have this larger equipment, obtained them from the human side. Zoos do not have any special imaging equipment for large animals that is not already available in the human field. Our 400lb gorillas are imaged with standard radiograph machines and would not fit into any CT or MRI we could currently use. No matter how you slice it (pun intended), a 40"-wide ape will not fit through a 27" opening in a CT scanner."
An assessment by Harvard University Medical School of U.S. hospital emergency rooms showed that 10% or less were outfitted with large weight-capacity CT or MRI equipment, but that most of the animal facilities that are equipped are not licensed as alternate sources of imaging for human patients. Until the design changes that some manufacturers have implemented become standard, doctors will have to continue to rely on traditional radiography, ultrasound, and fluoroscopy.

1 comment:

  1. Chris,
    I appreciate your quoting my open letter to the radiologists here in the US. It is important to note, the table maximum load is the limiting factor in the use of most of these CT's. The manufacturers could make a table that could support a thousand pound person or animal, but that would require all the testing and verification of a new instrument. In other words, it is not currently economical for them to do that. And as Harvard correctly pointed out, veterinary devices cannot be used on humans, even though human devices can be used on animals.
    Joel Pond, Certified (Zoo) Veterinary Technician
    Immediate Past Executive Director, AZVT.


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