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Contrast-enhanced Coronary MR Angiography [letter]

Department of Radiology, Charité, Medical School of the Humboldt-Universität zu Berlin, Schumannstrasse 20/21, PO Box 10098, 10117 Berlin, Germany. e-mail: marc.dewey@charite.de

Editor:

In their article on coronary magnetic resonance (MR) angiography published in the June 2003 issue of Radiology, Dr Dirksen and colleagues (1) reported a contrast-to-noise ratio (CNR) (signal difference–to-noise ratio) of about 8 by using the blood pool contrast medium P792 (Guerbet Research, Aulnay Sous Bois, France) together with both breath-hold and navigator MR imaging techniques. They concluded that this CNR is twofold the value achieved in our study, in which we used P792 for coronary MR angiography (2). However, Dr Dirksen and colleagues calculated the CNR as follows, where SI indicates signal intensity:

In contrast, in our study, the CNR was calculated in a much more common way:

This calculation necessarily results in much lower CNR values than those obtained with the formula Dr Dirksen and colleagues used in their study. Therefore, the higher CNR in the study of Dr Dirksen and colleagues is almost entirely attributable to the difference in calculating the CNR.

REFERENCES

1. Dirksen MS, Lamb HJ, Kunz P, Robert P, Corot C, de Roos A. Improved MR coronary angiography with use of a new rapid clearance blood pool contrast agent in pigs. Radiology 2003; 227:802-808.[Abstract/Free Full Text]
2. Taupitz M, Schnorr J, Wagner S, et al. Coronary magnetic resonance angiography: experimental evaluation of the new rapid clearance blood pool contrast medium P792. Magn Reson Med 2001; 46:932-938.[CrossRef][Medline]

Dr Dirksen and colleagues respond:

Department of Radiology, Leiden University Medical Center, Albinusdreef 2, C2-S, Leiden 2333 ZA, the Netherlands. e-mail: m.s.dirksen@lumc.nl

We thank Dr Dewey and colleagues for their interest in our study. Reference is made to their initial study (1) and our study (2) for calculation of CNR. Apparently, there are some differences in the approach of the calculation of this measurement. We agree that the reported differences in CNR in both studies can be explained at least in part by the differences in CNR calculation. However, this methodologic difference does not interfere with the conclusions from both articles that the blood pool contrast medium P792 is well suited for MR coronary angiography.

REFERENCES

1. Taupitz M, Schnorr J, Wagner S, et al. Coronary magnetic resonance angiography: experimental evaluation of the new rapid clearance blood pool contrast medium P792. Magn Reson Med 2001; 46:932-938.
2. Dirksen MS, Lamb HJ, Kunz P, Robert P, Corot C, de Roos A. Improved MR coronary angiography with use of a new rapid clearance blood pool contrast agent in pigs. Radiology 2003; 227:802-808.

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