Asymmetric radio frequency coils for magnetic resonance

Apparatus for use in a magnetic resonance system for transmitting a radio frequency field, receiving a magnetic resonance signal, or transmitting a radio frequency field and receiving a magnetic resonance signal, said apparatus and said magnetic resonance imaging system having a common longitudinal axis, said apparatus comprising:

• (a) a support member which defines a bore having first and second open ends which are spaced from one another along the longitudinal axis by a distance L;
• and
• (b) a plurality of inductive elements and a plurality of capacitive elements associated with the support member;
• wherein if used as a transmitter, the apparatus has the following characteristics:
• (i) the apparatus produces a radio frequency field which has a radial magnetic component which has a spatially-varying peak magnitude whose average value is Ar-avg;
• (ii) the apparatus has a homogenous volume within the bore over which the spatially-varying peak magnitude of the radio frequency field has a maximum deviation from Ar-avg which is less than or equal to 15%;
• (iii) the homogeneous volume defines a midpoint M which is on the longitudinal axis, is closer to the first end than to the second end, and is spaced from the first end by a distance D such that the ratio D/L is less than or equal to 0.4;
• and
• (iv) at least one of said inductive elements comprises a discrete conductor which follows a sinuous path such that during use of the apparatus current flows through a first part of the conductor in a first direction that has both longitudinal and azimuthal components and through a second part of the conductor in a second direction that has both longitudinal and azimuthal components, said first and second directions being different.