por Lisa Chamoff
, Contributing Reporter | October 22, 2014
From the September 2014 issue of HealthCare Business News magazine
“Is it possible to design two tubes to produce the same output when used in the same CT system and with the same mA and kV? Yes,” Denison says. “Will every tube design used in the same CT system and with the same mA and kV produce the same output? No.”
Hafner says she agrees that the X-ray output is dependent on the tube’s design, and notes that Dunlee tubes are manufactured to the exact designs as the GE originals. This includes the inherent filtration and attenuation of the X-ray beam.
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“There are actually differences from tube to tube of the exact same design,” Hafner says. “This is why the system manufacturer — in this instance GE — allows for variation of a certain percentage, published by GE as plus or minus 15 percent of the CT Dose Index. When designed identically, the Dunlee tube delivers a dose (CTDI 100) within the published GE specifications for its own GE CT scanners.”
Dunlee also measures the exposure to the patient, and has measured dose, according to GE published specifications, on Dunlee tubes in hundreds of GE systems. Hafner says that Dr. Robert Dixon, former chairman of the CT committee for the American Association of Physicists in Medicine, says the Dunlee replacement tubes for both the GE VCT scanner and the GE Lightspeed 16-slice scanners were found to deliver a radiation dose to the phantom that is indistinguishable from that of the GE tube it replaces.
Denison says GE provides in its technical reference manual and within the operating software methods for estimating the exposure to patients based on all of the imaging parameters, including the tube in use, mA, kV, filtration, collimation, and helical pitch. “These estimates are based on the physical measurements mentioned above that allow us to calibrate the software and the methods in the technical reference manual,” Denison says. “Because we do not have access to Dunlee tubes in order to make the physical measurements needed to calibrate the methods for estimating exposure, GE is unable to know what the estimated exposure is when using these tubes. As a result, we put a simple statement of this fact into the dose reports from the system.” Hafner says Denison’s response is a bit misleading.
“GE’s strategy is to instill fear and uncertainty to the user when they use the system with other than GE Glassware, Hafner says. “The GE CT systems do not measure dose. They calculate dose based on empirical evidence collected using GE tubes (their statement). They could also calculate dose based on empirical evidence from Dunlee tubes, but they chose not to do so, since this would validate a competitive part. Dunlee tubes are manufactured to the highest quality standards, and certify the output from all tubes to be within GE published specifications.”