A novel topical probe for MRI: the flat, truncated line probe

The construction and imaging characteristics of flat, truncated line probes (FTLPs) are described here. These probes illustrate a novel design of local probes for magnetic resonance imaging, with four major differences from conventional loop surface probes: (1) The B1 fields are directed perpendicular to the usual loop probes' direction. (2) The RF fringe electric fields are inherently shielded, which allows reduced loading from electrically lossy samples. (3) The homogeneity across the plane of the probe can be adjusted locally. And (4) when not used with tuning and matching circuits, a probe's local impedance can be set to match the RF line impedance. The probes are, in essence, a single loop significantly flattened with the outside conductor (away from the imaged object) wider than the inside conductor (against the imaged object). The probes are shaped so as to provide a homogeneous signal across the plane area of the probe. The signal intensity drops off faster than a loop of the same size. With a minimally loading phantom, along the midline normal to the surface, the S/N at the surface region is approximately 20% greater than a commercial probe (Phillips R2) of the same area dimensions, while at 5 cm depth, the S/N is lower. However, when used for imaging a body--again along the midline normal to the probe--the S/N at 5 cm depth is equal, and rises to approximately twice that of the Philips R2 probe at the surface.