4836209 NMR imaging of moving material using variable spatially selected excitation

Abstract

A method of imaging material flowing through a slab in a body using magnetic resonance techniques includes placing the body in a magnetic field including a first magnetic (z) gradient for slab thickness selection. A first rf pulse (180°) is applied to the body at a frequency band and of sufficient strength to flip nuclear spins located essentially in the slab. After allowing moving material in the slab to flow from the slab, a second rf (90°) pulse is applied to the body at a frequency band of sufficient strength to flip the nuclear spins in the slab for generating a signal. First image date in an X-Z plane is obtained from the nuclear spins flipped by the second 90° rf pulse. Thereafter, a third 180° rf pulse is applied to the body. In one embodiment the third rf pulse is non-selective and is of sufficient strength to flip nuclear spins in the body including but not limited to the slab. Moving material is again allowed to flow from the slab, and a fourth 90° rf pulse is then applied to the body at a frequency band and of sufficient strength to flip nuclear spins in the slab. Second image data in an X-Z plane is obtained from nuclear spins flipped by the fourth 90° rf pulse. The first image data is subtracted from the second image data to obtain third image data of moving material through the slab. Alternatively, the first image data and the second image data can be gated to different portions of a cardiac cycle whereby the flow of moving material differs in obtaining the first image data from the flow of moving material in obtaining the second image data. Direction sensitivity can be obtained by selective spatial excitation of portions of the body.