Pitfalls

Movement may be physiological or non-physiological. Cardiac motion propagates a movement artefact in the phase direction that may obscure pathology (Figure 17.2). The artefact is accentuated after injection of paramagnetic contrast agent. Shifting the phase direction so that the artefact is projected in another direction is the usual solution. For example, when patients are imaged using a 3D sequence in the coronal plane, phase direction is set in the z-direction (i.e. along the long axis of the patient). Respiratory motion leads to anterior-posterior movement of the thorax, and to superior-inferior movement of the diaphragm (Figure 17.3). Respiratory excursion of the anterior chest wall is minimized when the examination is performed in the (usual) prone position, but may be a problem if the patient is imaged in the supine position without breast fixation. Non-physiological patient movement is usually readily recognized if a subtraction technique is used to aid lesion identification. The characteristic finding is a rim of altered signal intensity (usually high intensity) around the breast, caused by the patient moving into or out of the coil between successive imaging sequences. Recognition of this artefact should prompt careful scrutiny of the non-subtracted images, as occasionally a spurious ‘lesion’ may be produced (Figure 17.4). Movement into the coil may be the result of a tense, anxious patient relaxing during the examination. Clearly, efforts to ensure the patient is comfortably positioned within a padded coil will be repaid here (Chapter 6). It may also be helpful if the

‘dynamic’ contrast-enhanced imaging sequences that are so susceptible to patient movement are preceded by an initial sequence (for example, high-resolution T1-weighted sequence, T2-weighted sequence, short tau inversion recovery (STIR) sequence) that might help the patient to relax.