Optimizing image quality of cerebrovascular CT angiography

Analysis by V. Matarese

 

Introduction
For patients with symptoms suggestive of cerebral aneurysm, the gold-standard diagnostic test is digital subtraction angiography (DSA). As DSA is an invasive procedure, numerous studies have investigated the possibility of diagnosing aneurysms with CT angiography. A meta-analysis published in 2011 reviewed the diagnostic accuracy of this minimally invasive examination by combining the results of 45 studies comprising altogether 3643 patients [ 1]. The analysis found that, overall, CT angiography had high sensitivity for detecting aneurysms and high specificity for ruling them out (both >95% for per-patient and per-aneurysm calculations). Diagnostic accuracy was significantly greater with 16- and 64-detector scanners than with 4- or single-detector scanners, especially for small aneurysms (≤4 mm).
Notwithstanding these excellent results, the small possibility of false negatives (missed aneurysms) implies that further improvements in diagnostic accuracy are needed if CT angiography is to replace DSA as the reference standard. Diagnostic improvements may come from advances in scanner technology (in fact, no study included in the meta-analysis used scanners with 128 detector rows or more) or from refinements in scanning protocols. Regarding the latter, a new study published in Acta Radiologica [ 2] investigated how adjustments in the tube voltage and the iodine concentration of the contrast medium influence the quality of intracranial artery images obtained with CT angiography.

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