An improved intravascular (IV) and interstitial (IS) prototype magnetic resonance (MR) imaging coil design offers dramatic gains in signal-to-noise ratio (SNR) and imaging volume. A multi-turn rectangular solenoid was wound inside catheters with 1.7 mm (IV) and 3.0 mm (IS) diameters. A factor of 200 in peak SNR gain over the standard birdcage head coil was observed, with the region of improved SNR persisting for a radial distance of 10 and 15 mm respectively. Very high resolution ex-vivo intravascular images and very high sensitivity MR spectroscopy (MRS) are demonstrated. This coil design offers interesting performance options in SNR and imaging volume compared to existing FDA-approved catheter coil designs.