![]() Spin-echo acquisition times can be shortened by use of a multi-echo approach where multiple refocused echoes are acquired preceded by a single 90° excitation pulse (Figure 2) and this is known as turbo spin-echo (TSE), fast spin-echo (FSE) or rapid acquisition with relaxation enhancement (RARE). The main disadvantages of spin-echo sequences are their limited temporal-resolution and sensitivity to motion and flow. Generally spin-echo sequences offer a greater flexibility in obtaining different contrasts (T1-weighted, T2-weighted, or proton-density weighted) depending on the choice of TE and TR (Time of Repetition). This can be caused, for example, by main field inhomogeneities or magnetic susceptibilities. Off-resonance refers to a small deviation in the local spins' resonant frequency in relation to the nominated scanner centre frequency. Spin-echo sequences refocus the excited signal with a 180° pulse or pulses (Figure 1a) which makes them robust to off-resonance effects and able to use longer TE (Time of Echo) values than gradient-echo sequences (Figure 1b). Cardiovascular pulse sequencesīoth spin-echo and gradient-echo pulse sequences play a major role in CMR. Also, alternatives to these sections are available elsewhere such as the excellent physics articles from Ridgway and Biglands in JCMR 20. If this is the case then please jump to section Cardiovascular Magnetic Resonance Artefacts. At this point it is quite possible that some readers will not require the introductory sections describing cardiovascular pulse sequences and applications and would happily move directly to the main sections describing artefacts. The main section follows, with common examples of artefacts, accompanied with a small description of the mechanisms behind them and possible solutions and trade-offs. There is initially a brief description of the most common sequences and preparation pulses used, along with imaging techniques and typical cardiovascular applications. This article, that is designed for a clinical readership, follows previous publications on the subject. The artefacts are also specific to cardiovascular imaging, and more general artefacts related to hardware are omitted. ![]() It is therefore impossible to be completely comprehensive covering all artefacts for all sequences, thus the examples of artefact have been restricted to one or two of the most problematic or common. For this reason it is important to have an understanding of the physical principles behind the formation of such artefacts so that they can be identified and possibly avoided.Ī large range of different sequences are used for the different applications in CMR and the majority of these are still being developed to improve their accuracy and reliability. An artefact can be defined as something that is visible in an image but it is artificial, and is often detrimental to diagnosis. There are unique motion and other issues involved in Cardiovascular Magnetic Resonance (CMR) that can lead to artefacts which can obscure or easily be misinterpreted as pathology. ![]()
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