Arrays of surface receiver coils in magnetic resonance imaging (MRI) have several advantages over volume coils such as TEM or birdcage coils. The most important advantage is an improvement in the signal-to-noise ratio (SNR) which is due to the ability to bring surface coils closer to the subject's body, leading to a stronger MRI signal. Surface coils' intrinsically lower sensitivity to noise from the body also contributes to an enhanced SNR, which can be used to improve image quality, reduce scan times, or to implement parallel imaging techniques such as sensitivity encoding (SENSE).
Optimal SNR performance is achieved by covering the imaging region on the subject as completely as possible and with a large number of coils. In practice, this requires having arrays of mechanically individual coils of a number of different sizes and shapes to cover as many imaging situations and patient sizes as possible. Positioning such individual coils, however, becomes challenging for the MRI staff, and stressful and uncomfortable for the patient. Furthermore, this procedure would need to be repeated for each patient leading to an inefficient use of time and resources.
In order to overcome this problem, it was proposed in WO 2005/124380 A2 to use an arrangement comprising a plurality of coils attached to a flexible and stretchable item of clothing. The individual coils are relatively movable with respect to one another responsive to stretching of the item of clothing.
However, a disadvantage of the arrangement disclosed in WO 2005/124380 A2 is the inability of the conductors to return to their original configuration even after just a few stretching cycles. For example, in the embodiment shown in FIG. 6 of WO 2005/124380 A2, the coils are formed by individual flexible conductive wires that are embedded or intertwined in a multilayered fabric. Although such a coil arrangement exhibits good flexibility, it suffers from a lack of stretchability and stability. This is due to the fact that the conductive wires form a wave-like structure within a plane that is substantially perpendicular to the principal plane of the multilayered fabric. Stretching the fabric in a direction within its principal plane and along the conductive wires initially reduces the amplitude of the wavelike structure until the conductive wires are substantially straight. Beyond this comparatively small extension range that is primarily determined by the initial amplitude and hence by the layer thickness, any further stretching of the fabric would require an extension of the conductive wires, which is generally an inelastic process and hence is irreversible.