[ RadSafe ] What's wrong with this story?

Geo>K0FF GEOelectronics at netscape.com
Wed Dec 1 18:01:29 CST 2010

Original press release/article
"Nov. 26 (Bloomberg) -- FedEx Corp. located a missing shipment of low-level radioactive rods used by hospitals to calibrate CT scanning equipment.

A cylinder containing the rods, which had been missing since Nov. 23, was found at a FedEx facility in Knoxville, Tennessee, the package's destination city, Sandra Munoz, a spokeswoman, said today in an e-mail. The package was sent by plane Nov. 22 from Fargo, North Dakota, Munoz said.

"It was always in our custody," she said, hours after Memphis, Tennessee-based FedEx confirmed that it couldn't account for the shipment..

The cylinder was one of three, each packaged separately, in a box that got wet, possibly during a rainstorm in Memphis, where the shipment was transferred for the last leg of its journey to Knoxville, Munoz said. After delivery on Nov. 23, the box had water damage and one cylinder was missing.

FedEx retrieved the cylinder today in Knoxville, Munoz said.

"My guess, and we are looking into this, was as they were doing the sort, they came across a box with no label on it, they set it aside," Munoz said. "They knew we were looking for a cylinder, but they never opened that box until today."

The recovered cylinder, about 10 inches long and weighing 20 pounds, held four rods of germanium-68. They are used in CT, or computerized tomography, scans in which X-rays from a variety of angles produce cross-sectional images of patients' bodies.

Total radioactivity for the rods is 684 megabecquerels, the equivalent of about 18 microcuries, said David McIntyre, a spokesman for the U.S. Nuclear Regulatory Commission. The rods aren't considered significant sources of radiation, according to the International Atomic Energy Agency.

If someone had opened the canister, "it would take like 1,000 hours of exposure to get a skin blister," Munoz said.

She declined to identify the final destination of the package. FedEx is the second-largest U.S. package-shipping company after United Parcel Service Inc.

--Editors: Ed Dufner, Elizabeth Wollman

To contact the reporter on this story: Will Daley in New York at wdaley2 at bloomberg.net

To contact the editor responsible for this story: Ed Dufner at edufner at bloomberg.net"

What's wrong with this story?

" rods used by hospitals to calibrate CT scanning equipment."
"held four rods of germanium-68. They are used in CT, or computerized 
tomography, scans in which X-rays from a variety of angles produce 
cross-sectional images of patients' bodies."

Ge-68/Ga-68 would be the calibration isotope used in PET (Positron Emission Tomography), not CT scanners (my guess based on reading- corrections welcome.  
One such test is called a "Pairs Transmission Test", and utilizes three rods spaced at 120 degrees. Since the 
three rods cost in the tens of thousands of dollars, most facilities probably get it done under maintenance contract 
by the machine's manufacturer Ge-68 yields one daughter, short lived Ga-68 which provides positron emission via electron capture decay.

"Total radioactivity for the rods is 684 megabecquerels, the equivalent of about 18 microcuries,"

Actually, 684 MBq is equal to about 18.5 milliCuries, not microCuries. I notified the editor who bounced it back to the NRC, who subsequently re issues the corrected press release.

CT or CAT scanning involves the use of an external X-Ray source ( X-Ray tube e.g. 70-140 keV) ganged to 
an X-Ray detector. The tube/detector are ganged and rotate around the subject providing "slices" for computer 
analysis during the diagnosis cycle.

PET scans on the other hand use an external fixed circular array of detectors , but the radiation source is 
from inside the subject, not external. This source is provided with a tracer isotope such as F-18 attached to 
a biologically active molecule ( ie glucose). 
The isotope is injected into the subject where it decays via electron Capture, providing  
Positron Emission. The resultant positrons are immediately absorbed by free electrons within the subject, 
decaying into a pair of 511 keV photons which eject from the subject simultaneously and at (almost) exactly 
180 degrees from one another. The detector portion of the machine that I am most familiar with consists of an 
array of heavy element scintillators, such as BGO. These BGO crystals are arranged in groups of 8, with 
interconnecting optical windows between the various crystal, A set of 4 photomultiplier tubes ( actually two 
dual PMTs) provide signals to the computer that allow software to predict the exact angle from which the 
511 photon derives. On the opposite side of the array, another probe will receive an identical but opposite 
photon at the exact same time. With both these signals identified by the software (coincidence detection  
called LOR), an accurate 3D estimation is calculated as to the position of the originating nuclear decay. 

PET-CT is a combination machine using both technologies sequentially on the same subject. With 
both technologies, biological activity as well as physical information is provided (anatomical plus metabolic)

George Dowell
New London Nucleonics Lab

GEOelectronics at netscape.com

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