Comment on: L. Saba and G. Mallarini. Window Settings for the Study of Calcified Carotid Plaques with Multidetector CT Angiography. AJNR Am J Neuroradiol first published on March 19, 2009 as doi: 10.3174/ajnr.A1509

In a technical note entitled “Window Settings for the Study of Calcified Carotid Plaques with Multidetector CT Angiography”, Drs. L. Saba and G. Mallarini evaluated how neuroradiologists who are reviewing CT-angiograms of the carotid arteries tend to spontaneously adjust their selection of CT window level and width, in order to accurately quantify the degree of carotid stenosis. They observed that, in the presence of calcified carotid plaques, the window width and level selected by the reviewers were not influenced by the degree of stenosis, but rather increased proportionally to the intraluminal Hounsfield unit value. Indeed, in the presence of a successful contrast bolus, the density of the intraarterial contrast comes closer to that of calcium, and a higher level and wider window are needed to decrease the “edge blur” and the “halo” artifacts, and to allow accurate quantification of the carotid stenosis.

It is interesting to note that the interobserver agreement in terms of characterizing the degree of carotid stenosis was extremely high in this study, superior to 90%. This high interobserver agreement was not the result of specific reading instructions, as the reviewers were not provided any, but were free to select their windowing and reading approach. Their experience prompted them to choose similar approaches and contributed to  their making the same measurements. This is a testament to the reliability of CT-angiography technique  in assessing carotid atherosclerotic disease in experienced hands. This technical note adds to a series of papers showing that carotid CT-angiography is accurate in quantifying carotid stenosis, (1, 2) is relevant in terms of clinical management; (3) and is a non-invasive alternative of choice to conventional angiography for screening purposes.(1) This is something that neuroradiologists want to emphasize and explain to justify the 200% increase in utilization of this technique over the past couple of years the latter raising concern on the side of the healthcare reimbursement entities, and leading them to question the validity of CT-angiography as compared to conventional angiography.

Further improvements in terms of CT assessment of carotid atherosclerotic plaques are expected with the generalization of dual-energy CT, which should allow to better characterize carotid plaque themselves, like they do for coronary arteries (4). Assessing atherosclerotic plaques themselves (rather than their mere impact on the lumen) holds great promises in terms of identifying “vulnerable” plaques associated with an increased risk of stroke, which is the Holy Grail of carotid imaging (5).

References:
1. Marja Berg, Zishu Zhang, Aki Ikonen, Petri Sipola, Reetta Kälviäinen, Hannu Manninen, and Ritva Vanninen. Multi-Detector Row CT Angiography in the Assessment of Carotid Artery Disease in Symptomatic Patients: Comparison with Rotational Angiography and Digital Subtraction Angiography. AJNR Am. J. Neuroradiol., May 2005; 26: 1022 – 1034.
2. Michael H. Lev, Javier M. Romero, Daniel N.F. Goodman, Ranjit Bagga, H. Young Kwon Kim, Neil A. Clerk, Robert H. Ackerman, and R. Gilberto Gonzalez. Total Occlusion versus Hairline Residual Lumen of the Internal Carotid Arteries: Accuracy of Single Section Helical CT Angiography. AJNR Am. J. Neuroradiol., Jun 2003; 24: 1123 – 1129.
3. T. Ohara, K. Toyoda, R. Otsubo, K. Nagatsuka, Y. Kubota, M. Yasaka, H. Naritomi, and K. Minematsu. Eccentric Stenosis of the Carotid Artery Associated with Ipsilateral Cerebrovascular Events. AJNR Am. J. Neuroradiol., Jun 2008; 29: 1200 – 1203.
4. Barreto M, Schoenhagen P, Nair A, Amatangelo S, Milite M, Obuchowski NA, Lieber ML, Halliburton SS. Potential of dual-energy computed tomography to characterize atherosclerotic plaque: ex vivo assessment of human coronary arteries in comparison to histology. J Cardiovasc Comput Tomogr. 2008 Jul-Aug;2(4):234-42. Epub 2008 Jun 12.
5. Chalela JA. Evaluating the carotid plaque: going beyond stenosis. Cerebrovasc Dis. 2009;27 Suppl 1:19-24. Epub 2009 Apr 3.