Imaging equipment vendors tout innovations to reduce radiation exposure

Medical imaging may expose patients to ionizing radiation, but it also empowers physicians to view the human body with ever-increasing clarity and accuracy, according to a 28-page white paper issued April 13 by the Medical Imaging and Technology Alliance, an association of vendors.

The heavily referenced report accentuates the positive aspects of imaging devices that employ ionizing radiation to generate diagnostic images. It highlights innovations that have over the past 20 years reduced exposure from many imaging procedures by 20% to 75% without diminishing their ability to diagnose injury and disease.

Publication of the report from the former medical imaging division of the National Electrical Manufacturers Association coincided with grim news about radiation exposure from the 2007 National Council on Radiation Protection and Measurements meeting. Disclosures reported at the NCRP meeting underscored the rapid growth of CT utilization and subsequent increase in public exposure to ionizing radiation from CT and other medical imaging instruments.

The MITA report, How innovations in medical imaging have reduced radiation dosage, grew out of recent efforts at NEMA to raise public awareness about the importance of diagnostic imaging in medicine. MITA has created a glitzy website and has ratcheted up its political lobbying efforts, including broadsides against federal policies and positions the alliance opposes. MITA's 55 members account for about 90% of the medical imaging and informatics equipment sold in the U.S.

The report first places radiation exposure in context, examining the importance of imaging instruments that expose patients to ionizing radiation. It then explores innovations that have helped minimize the radiation such instruments produce.

It notes that the FDA and other federal agencies have repeatedly said that benefits from the use of radiation in medicine normally outweigh what is generally considered a small potential risk posed by such radiation. U.S. residents have about a 25% lifetime chance of cancer. Using FDA risk factors, the report estimates that a CT cardiac stress/rest perfusion study increases that risk by 0.05%.

The report cites the limitations of linear no-threshold models that use Hiroshima and Nagasaki radiation exposure data to extrapolate risk for humans exposed to far less radiation than atomic bomb blast survivors. It explains that a routine CT head scan involving 1.5 mSv of radiation is equivalent to eight months of normal background radiation from celestial sources. A cardiac stress/rest test exposes a patient to 10 mSv, the equivalent of four years of natural radiation.

The report notes that technical innovations have kept radiation exposure from imaging equipment under control:

• pulsed radiation strategies to guide interventional procedures

• dose modulation for CT that coordinates the timing of radiation exposure with the dynamic phase of data acquisition at specific points during the cardiac or respiratory cycle

• automated exposure controls that match dose to patient body size and thickness to reduce dose an estimated 10% to 30% for routine CT procedures and up to 50% for cardiac CT

• specific imaging protocols for infants and children based on patient age and weight for claimed dose reduction of up to 80% for infants and 50% for small children

• CT reconstruction techniques that decrease negative effects of scattered radiation, noise, and motion

• improved beam collimation, beam filtration, and adaptive software filtration that selectively reduce noise in uniform areas of an image while preserving the edges

• dose displays that allow the user to track effective dose during imaging

• ECG tube-current controls for CT cardiac exams to ensure that dose is delivered only during the resting phase of the ECG cycle

The report promises more effort from manufacturers to reduce dose, particularly for children. It notes that CT equipment vendors support mechanisms to capture radiation dose data for regional and national CT dose databases. To support that effort, manufacturers are committed to implementing a new DICOM standard for CT dose recording on production equipment by July 2008.

Special section: Exclusive coverage of the 2007 National Council on Radiation Protection and Measurements meeting

This year's historic NCRP meeting reveals the disturbing growth of patient exposure to ionizing radiation from medical imaging and proposes practical solutions to regulate its growth. Extended coverage from Diagnostic Imaging lays out the facts and recommendations to better protect patients, physicians, and medical staff.

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