Abstract
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.
Highlights
Introduction and technical partMagnetic resonance imaging (MRI) data are collected in the k-space which is mathematically related to imageInsights Imaging (2018) 9:1107–1115Both methods, namely compressed sensing and sensitivity encoding (SENSE), rely on different ancillary information and may be combined to further reduce scan time [4], a technique hereafter referred to as Compressed SENSE by Philips Healthcare [5]
We present special image artefacts occurring in Compressed SENSE technique combining compressed sensing and SENSE in neuroradiological and musculoskeletal MRI examinations based on our 6 monthsexperience with this technique
Motion artefacts appeared in phase direction as semi-circular rings on images acquired without compressed SENSE (Fig. 1c, d) or with compressed SENSE (Fig. 1e-h) after slight (Fig. 1d, e) or severe (Fig. 1g, h) head movements from left to right if compared to images obtained without head movement (Fig. 1a, b)
Summary
Magnetic resonance imaging (MRI) data are collected in the k-space which is mathematically related to image Both methods, namely compressed sensing and SENSE, rely on different ancillary information and may be combined to further reduce scan time [4], a technique hereafter referred to as Compressed SENSE by Philips Healthcare [5]. Undersampling in general can be performed randomly, radially or by a variable density incoherent scheme, where more data are sampled in the centre of the k-space than in the periphery [1, 5]. In all these non-uniform data sampling methods, noise-like incoherent artefacts distributed in a nonuniform pattern on the image may occur [5], leading to noiseenhancement with noisy and blurred images and to semicircular ringing artefacts [1, 6]. The undersampling method performed dictates the kind of artefacts that may occur in the final image
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