CT Users Group

P Doyle¹, P Ball², P Donnelly³

1. Radiological Sciences & Imaging, Forster Green Hospital

2. Department of Radiology, Ulster Hospital

3. Department of Cardiology, Ulster Hospital

Abstract

Each year one in five deaths in Europe is related to cardiac disease, about every second victim dies of an acute coronary event without even making it to hospital. Invasive Coronary Angiography (CA) is the gold standard for diagnosing coronary artery disease (CAD). 2.5 million CA examinations are performed per year in the EU, >40% of which are not followed by interventional or surgical therapy and are conducted only to rule out CAD. There is evidence to suggest that the majority of acute coronary events occur at the site of angiographically non-significant lesions.

Since the advent of 64 slice CT scanning, coronary CT angiography (CTA) has been widely used to rule out CAD, particularly in patients with atypical chest pain, low-to-intermediate risk and a questionable stress test. Several investigations have been made on the accuracy of CTA - all compare detection rates of luminal obstruction > 50% with CTA and CA. The real strength of CTA was demonstrated in the modalities ability to provide negative predictive values ranging from 95% to 97%. The predicted future growth rate for CTA is substantial. It is recommended as the modality of choice for patients with calcium scores < 400 in the current NICE guidelines draft, due for publication in 2010.

The present study is focused on estimating effective doses for a range of protocols in CTA and assessing the efficacy of available dose reduction options for cardiac CT. A generalised dose reduction strategy is proposed, followed by specific CTA considerations. In particular, the use of in-plane bismuth shielding is investigated both in terms of dosimetry and clinical image quality.

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