CT scans can cause medical device malfunction
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The FDA has received a few reports of adverse events in which CT scans interfered with electronic implants or externally worn drug infusion pumps
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Now more patients have implanted or externally worn electronic medical devices
Higher dose rates from the new generation of CT scanners may be a reason
— Photo: K.R. Deepak
Operator’s responsibility: The CT operator must initially use CT scout views, which use only minimum dose, to see for any implanted medical devices in the patient.
The United States Food and Drug Administration (FDA) alerted health professionals in U.S. to the possibility that x-rays used during CT examinations may cause implanted and external electronic medical devices to malfunction (FDA, July 14, 2008)
FDA assured that most patients with electronic medical devices undergo CT scans without any adverse consequences. It has received a few reports of adverse events in which CT scans may have interfered with electronic devices such as pacemakers, defibrillators, neurostimulators and implanted or externally worn drug infusion pumps.
More extensive usage
Institutions use CT scans more extensively now; healthcare professionals have started noticing the few incidents. Higher dose rates from the new generation of CT scanners may be another reason. Now more patients have implanted or externally worn electronic medical devices. FDA continues to investigate this issue with the cooperation of manufacturers. Reports to the FDA indicated unintended “shocks” (stimuli) from neurostimulators, malfunctions of insulin infusion pumps, transient changes in pacemaker output pulse rates caused by x-rays from CT scans.
No deaths reported
Till now, FDA has not received any reports of deaths from CT scanning of medical devices. In one study, researchers found transient malfunctioning of pacemakers due to CT examinations in six out of 11 patients as indicated by their ECGs during the CT examinations. They examined the effect of CT on a pacemaker in a human body model with and without shielding by rubber or lead. X-rays from CT equipment caused the malfunctioning as they could show that lead shielding prevented it (Circulation Journal, 2006). In another study, researchers exposed 21 devices to X rays from CT scanners.
They found malfunctioning in 20 out of 21 devices at maximum dose levels and in 17 out of 21 at typical dose levels. Two devices inhibited for more than 4 seconds in spiral mode at clinical dose levels (Radiology, 2007). Effects occurred only if the x-ray beam passed directly over the device.
In another investigation, an implanted neurostimulator unit give the patient a shock when he was scanned (CT) in that area (Health Services, 2007).
Millions of Americans are now fitted with devices which use electrical currents to help various organs overcome functional deficits (chicagotribune.com. July 14, 2008). We do not have any data on the availability of such devices in India. But it is better to be cautious about them. If patients are fitted with any device, they must bring it to the notice of the CT operator.
FDA recommended that the CT operator must initially use CT scout views to see for any implanted or externally worn medical devices, if any, in the patient. CT scout views use minimum dose.
Precautionary steps
If it is present, they must identify its location relative to the area to be scanned. They must determine the type of the device; if possible, they may remove the external device out of the scan range. They may ask patients with neurostimulators to switch them off temporarily while the scan is done.
The x-ray operator must minimize x-ray exposure to the device by using the minimum tube current consistent with image quality.
They must make sure that the x-ray beam must not dwell over the device for more than a few seconds (FD, 2008).
“For CT procedures that require scanning over the medical device continuously for more than a few seconds, as with CT perfusion studies or interventional exams, attending staff should be ready to take emergency measures to treat adverse reactions if they occur”, FDA cautioned
What is issued now is a Preliminary Public Health Notification when the available information and the agency’s understanding of the issue are still evolving. FDA will revise the Notification, as new information emerges (FDA, July14, 2008).
K.S. PARTHASARATHY
Former Secretary, AERB
( ksparth@yahoo.co.uk
)
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