A new CT artefact - the bubble curve sign.

Since the introduction of the original singlesection computed tomography (CT) machines, and more recent spiral CT, several different types of CT artefact have been described. Recognized artefacts include motion artefact, metallic streak artefact, beam hardening, partial volume artefact and step artefact. The use of contrast-enhanced spiral CT has created many new artefacts and potential pitfalls. Imaging too early, or in a patient with poor cardiac output leads to heterogeneous appearances of the spleen and liver. Mixing of unopacified venous blood from the legs with opacified renal venous blood in the inferior vena cava (IVC) gives the false impression of thrombus. Artefacts are also prevalent in multi-detector CT coronary angiography and motion artefact can cause the appearance of an anomalous right coronary artery. Much research has been carried out to both understand and reduce these artifacts. In the present study, the authors describe a new artefact, which may be due to beam hardening acting on a moving bubble of gas in spiral CT machines. Beam-hardening artefact (cupping artefact) comes from the absorption of lower energy photons and the resultant variable linear attenuation coefficients of tissue. Its appearance is improved by beam-hardening reconstruction algorithms. On review of the literature, the authors did not find an artefact similar to that described in the present report.