Author: Max_Wintermark

Max Wintermark • UVA

Open letter in response to NYT article from July 31, 2010 “The Radiation Boom After Stroke Scans, Patients Face Serious Health Risks” By WALT BOGDANICH

posted by Michael H. Lev and Max Wintermark

Every year in the United States, more than three quarters of a million people have a stroke, and approximately every 3 minutes someone dies from a stroke. A significant portion of stroke victims are young, and left with a devastating handicap for the rest of their lives. The monetary and societal costs of stroke represent a major economic challenge to the healthcare system.  With stroke – as with heart attack – rapid treatment is essential to limit the extent of irreversible brain injury (“time-is-brain”), and rapid determination of the cause and degree of existing brain injury can be critical in deciding treatment.

CT perfusion imaging is a quick, widely available test that displays information about blood flow to the brain that can help diagnose, treat, and predict outcome in stroke patients.  When MRI is not readily available or contraindicated, CT perfusion imaging provides the best possible estimate of brain tissue likely to die without urgent, advanced therapies, including arterial “clot busting” drugs and blood clot retrieval devices.  CT perfusion imaging can also help classify reversible brain injury (“transient ischemic attacks”) that – like cardiac angina – may not require such immediate, aggressive treatment, as well as evaluate brain injury caused by arterial spasm due to bleeding from aneurysm rupture.

Published protocols for performing CT perfusion imaging at “as low a radiation dose as reasonably achievable” – a principle endorsed by the American College of Radiology and American Society of Neuroradiology – have circulated in the medical community for over a decade.  Strict protocol rules and oversight radiation protection personnel at most medical centers ensure that optimal image quality is maintained with a total radiation exposure often considerably lower than the current FDA recommended maximum dose.  Indeed, in an early, highly quoted study …

Window Setting for Calcified Carotid Plaques on CTA

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 …