Common artefacts encountered on images acquired with combined compressed sensing and SENSE.

Various techniques have been proposed which aim at scan time reduction and/or at improved image quality by increasing the spatial resolution. Compressed sensing (CS) takes advantage of the fact that MR images are usually sparse in some transform domains and recovers this sparse representation from undersampled data. CS may be combined with parallel imaging such as sensitivity encoding (SENSE), hereafter referred to as Compressed SENSE, to further accelerate image acquisition since both techniques rely on different ancillary information. In practice, Compressed SENSE may reduce scan times of two-dimensional (2D) and three-dimensional (3D) scans by up to 50% depending on the sequence acquired and it works on 1.5-T or 3-T scanners. Compressed SENSE may be applied to 2D and 3D sequences in various anatomies and image contrasts. Image artefacts (i.e. motion, metal and flow artefacts, susceptibility artefacts) frequently appear on magnetic resonance images. The Compressed SENSE technique may cause special artefacts, which might influence image assessment if they go undetected by imaging readers. Our institution has been using Compressed SENSE for over half a year, both in a neuroradiological setting and for musculoskeletal examinations. So far, three special image artefacts-called the wax-layer artefact, the streaky-linear artefact and the starry-sky artefact-have been encountered and we aim to review these main artefacts appearing in sequences acquired with Compressed SENSE. TEACHING POINTS: • Compressed SENSE combines compressed sensing and SENSE technique. • Compressed SENSE permits scan time reduction and increases spatial image resolution. • Images acquired with Compressed SENSE may present with special artefacts. • Knowledge of artefacts is necessary for reliable image assessment.