NDT

Editor's Note: Computed Tomography-The CAT's Meow

August 2, 2011
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There is no doubt that just about everyone in the field is familiar with computed tomography as a nondestructive technology. Most everyone else is familiar with it as it pertains to health care, having at the least heard of a CT scan, sometimes referred to as a CAT scan.

Recently, Newswise reported that researchers from UCLA and the University of California completed a 10-year clinical study of 53,000 current or heavy smokers that concluded that those who were screened with low-dose spiral CT scanning had a 20% reduction in deaths from lung cancer apposed to those who were screened by chest X-ray.

According to the reporting, the study-called the National Lung Screening Trial (NLST)-was conducted among this high-risk group to compare the differences in death rates for lung cancer between those who were screened annually with low-dose helical (or spiral) CT versus the conventional chest X-ray. The study was published in the June 29th online edition of the New England Journal of Medicine.

Dr. Denise R. Aberle, a principal investigator for the NLST and a researcher with UCLA’s Jonsson Comprehensive Cancer Center, said the publication of the study offers further definitive evidence of a significant mortality benefit from CT screening.

“These findings confirm that low dose CT screening can decrease deaths from lung cancer, which is expected to kill more than 150,000 Americans this year alone,” said Aberle, who serves as vice chair for research in the Department of Radiological Sciences. “This study also will provide us with a road map for public policy development in terms of lung cancer screening in the years to come.”

Aberle also commented that while the study cannot answer all the questions regarding implementation, “the NLST data can be used to develop mathematical models to determine how long screening should be performed and how often” and “can be used to determine whether other groups at risk of lung cancer, such as light smokers, those with family histories of lung cancer or individuals with lung diseases like emphysema, would benefit from screening with spiral CT scanning.”

CT technology in the medical field can be traced back to the early 1900s with Italian radiologist Alessandro Vallebona’s method for representing a single slice of the body on the radiographic film known as tomography. It is based on projective geometry-“moving synchronously and in opposite directions the X-ray tube and the film, which are connected together by a rod whose pivot point is the focus; the image created by the points on the focal plane appears sharper, while the images of the other points annihilate as noise.

In the late 1970s, “minicomputers” and of the transverse axial scanning method developed by Godfrey Hounsfield and Allan McLeod Cormack moved the technology to “computed” tomography. This improved method took 180 separate readings every 1° with each scan taking a little more than five minutes. A large computer then reconstructs the images using algebraic equations…just like my 10th-grade math teacher warned me.

While its success in the medical community is credited with saving countless lives, its benefits in the nondestructive technology field are also well established. Gain a better understanding of the rules of X-ray micro CT, not only opens the door to production cost savings and productivity improvement, but also knowing when to break them can provide even further process flexibility in this month’s feature article, “The Rules of X-Ray Micro CT (and When to Break Them),” by Andrew Ramsey.

Enjoy and thanks for reading!

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