Enhanced surface-coil spatial localization with an inhomogeneous surface gradient

Some observations of the design of rf coils for human internal use

“…In this paper, while most of these items are touched on to some extent, there is no discussion of points (5) and ( 6 ) and most of the work is concentrated on points (1) and (2). tender tissue…”

“…The large sensitivity variations which cause images obtained using surface coils to be dominated by signals from close to their planes cannot be eliminated simply, but can be controlled by the use of dephasing windings around the probe, as envisaged by Crowley and Ackerman (2). Various designs of these were examined, but although we show later an image taken using one form (a cage of four wires around the main winding), our studies suggested that their advantages were inadequate to offset the convenience of having no connections to the probe.…”

“…[ l ] and [2] can be used to calculate il and hence the gain due to the parasitic loop (as shown by the characteristics shown in Fig. 3b).…”

“…[I] and [2] with and without the parasitic loop, allowing the gain due to the parasitic loop to be expressed (in dB) and this is plotted in the graphs in Figs. l b and lc.…”

“…The sensitivity of a surface coil is high near its plane, but falls rapidly, so that windowing of the resultant images to see subtle tissue changes is difficult. Use of dephasing windings, along the lines proposed by Crowley and Ackerman (2), is a potential solution to the problem. Conveniently these are fed with gradient pulses like those used in slice selection and spatial encoding.…”