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More radiation exposure when contrast medium is used with CT scans

Contrast use spikes CT radiation dose, BEric Barnes, AuntMinnie.com staff writer, May 30, 2013 –– The use of contrast media during CT scans significantly increases how much radiation patients absorb in amounts that vary by organ, researchers report in the June edition of the American Journal of Roentgenology. Radiologists should account for the expected dose increases when setting scanner protocols, they said.

Radiation dose increased for every organ scanned at CT, particularly in the most vascularized tissues, wrote researchers from the University of Messina in Italy. Average doses rose by one-fifth for the liver, one-third for the spleen and pancreas, and almost three-fourths for the kidneys.

“The results are in agreement with our previous data, confirming an increase in organ radiation dose in contrast-enhanced CT compared with unenhanced CT,” wrote Dr. Ernesto Amato and colleagues (AJR, June 2013, Vol. 200:6, pp. 1288-1293)……

Investigators have also found an increase in the frequency of cellular abnormalities in patients who underwent contrast-enhanced radiographic examinations. But the actual increase in dose for any given scan — which depends on iodine uptake; the shape, volume, and position of the organ; and the emitted x-ray energy spectrum — remains unknown, the authors wrote…….

Confirming dose increases

The results were in line with the group’s previous phantom study, and they confirmed significant radiation dose increases in contrast-enhanced CT versus unenhanced CT, Amato and colleagues wrote. The data showed average dose increases of 19% for the liver, 71% for the kidneys, 33% for the spleen and pancreas, and 41% for the thyroid.

“The kidneys showed the maximum among the average dose [increases] (71%, resulting from an attenuation increment of 139 HU),” the authors wrote.”High renal enhancement is, in fact, due to both their high vascularization because they receive 20% to 25% of the cardiac output and the passage of iodine within the renal tubules. In particular, the level of contrast medium within renal tubules can be up to 50 to 100 times higher than that in the blood because of the mechanisms of tubular concentration and secretion.”

Thyroid tissue showed the second highest dose increase (41%) after contrast injection, based on an HU increase of 87%. Also, the dose increases in the thyroid depended on tissue density on unenhanced CT, the group noted. Denser thyroids showed a lower increase in attenuation and, consequently, lower increases in dose.

Because the liver and spleen are richly vascularized, Hounsfield units increased with contrast by 49 HU and 71 HU, respectively, and average dose increased by 19% and 33%……. http://www.auntminnie.com/index.aspx?sec=ser&sub=def&pag=dis&ItemID=103565

June 1, 2013 - Posted by | radiation, Reference, USA

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