Claims
- 1. A method for measuring velocities in phase contrast magnetic resonance imaging in the presence of magnetic field gradient field inhomogeneities comprising the steps of:
a) encoding velocity information in at least three different encoding directions and measuring phase differences (ΔΦ(r)) in each direction, b) deriving actual first moments along the encoding directions using a magnetic field deviation matrix (Λ(r)), c) providing an (N×3) encoding matrix, Ω, where N is the number of encoding directions, based on the ideal first moments along the N directions, and d) computing true velocities as a function of the gyromagnetic ratio, γ, magnetic field deviation matrix (Λ(r)), encoding matrix, Ω, and a phase difference vector (ΔΦ(r)).
- 2. The method as defined by claim 1 wherein true velocity, v(r), is computed as follows:
- 3. The method as defined by claim 2 wherein the magnetic field gradients are produced using gradient coils, and the magnetic field deviation matrix is given by
- 4. The method as defined by claim 2 wherein the encoding matrix, Ω, is given by:
- 5. The method as defined by claim 4 wherein velocity sensitivities ΔM are identical along all encoding directions and the true velocity is given by:
- 6. A method for computing velocities (v⊥(r)) in phase contrast magnetic resonance imaging in the presence of magnetic gradient field inhomogeneities comprising the steps of:
a) measuring velocity information including phase difference Δφ1(r) along an encoding direction and the absolute gradient deviation ∥Λ(r)n∥ in that direction, b) calculating flow encoding strength, 19Δ M1,ideal(1)∑j=13[∑i=13niΛji(r)]2based on relative magnetic field gradient deviations and first moment difference, ΔM1,ideal(1), and c) computing the velocity using gyromagnetic ratio, γ, as: 20v⊥(r)=Δφ1(r)γΔ M1,ideal∑j=13[∑i=13niΛji(r)]2.
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This patent application is a continuation in part of co-pending U.S. patent application No. 10/317,516 filed Dec. 11, 2002, for “Correction of the Effects of Spatial Gradient Field Distortions in Diffusion-Weighted Imaging,” (Atty. Dkt. No. STFUP096/S02-166), which is incorporated herein by reference for all purposes.
GOVERNMENT RIGHTS
[0002] The U.S. Government has rights in this invention pursuant to NIH Grant No. P41RRO9784 to Stanford University.
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
10317516 |
Dec 2002 |
US |
Child |
10463741 |
Jun 2003 |
US |