Patent Document ID: 10151814
Application ID: 15133907
Patent Status: 1

Claim One:
1. A method for improving intensity homogeneity of image data acquired using a balanced steady-state free precision (bSSFP) sequence in magnetic resonance (MR) imaging, the method comprising: performing multiple bSSFP sequences with different radio frequency (RF) phase increments by using a MR imaging apparatus, to generate multiple bSSFP image volumes with different phase offset Φ of an object to be examined, each image volume containing voxels having intensities M that are a function of a nuclear resonance signal, and wherein a position and a size of the voxel is defined by a field of view (FOV) and a desired resolution; a per-voxel fitting of a mathematical signal model onto a measured magnetization M of the FOV as a function of the phase offset Φ; determining from the fit a spin density M 0 , a relaxation time ratio Λ and a local phase offset ΔΦ for each voxel; generating a homogeneous image of the object by calculating a new signal intensity M (Φ) for each voxel, using the previously obtained spin density M 0 and the relaxation time ratio Λ, and choosing ΔΦ so that Φ−ΔΦ=0° , in order to obtain the homogeneous image of the object; and using the following mathematical signal model for fitting the measured magnetization M of the FOV as a function of the phase offset Φ: M ⁡ ( Φ ) = M 0 ⁢ 2 ⁢ ⁢ sin ⁢ ⁢ α ⁢  cos ⁡ ( Φ - Δ ⁢ ⁢ Φ 2 )  1 + cos ⁢ ⁢ α + 2 ⁢ ⁢ cos ⁡ ( Φ - Δ ⁢ ⁢ Φ ) + ( 4 ⁢ ⁢ Λ - 2 ⁢ ⁢ cos ⁡ ( Φ - Δ ⁢ ⁢ Φ ) ⁢ sin ⁡ ( α 2 ) 2 ) wherein: M 0 is the spin density of a voxel in the FOV; Λ is the relaxation time ratio T1/T2; α is the applied flip-angle of the bSSFP MR sequence; and ΔΦ is the local phase offset caused by field inhomogeneity for the voxel.