Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Patent
1994-11-28
1996-01-16
O'Shea, Sandra L.
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
324309, G01V 314
Patent
active
054850851
ABSTRACT:
Disclosed is a method to correct the geometric distortion caused by field inhomogeneity in MR images such as images of patients wearing MR-compatible stereotaxic frames. A previous distortion correction method derives patient-dependent error maps by computing the phase-difference of 3D images acquired at different T.sub.E 's. The time difference (.DELTA.T.sub.E =4.9 ms at 1.5 T) is chosen such that the water and fat signals are in phase. However, .DELTA.T.sub.E is long enough to permit phase wraps in the difference images for frequency offsets greater than 205 Hz. Phase unwrapping techniques resolve these only for connected structures; therefore the phase difference for fiducial rods may be off by multiples of 2 .pi. relative to the head. This uncertainty is removed by using an additional single 2D phase-difference image with .DELTA.T.sub.E =1 ms (during which time no phase-wraps are typically expected) to determine the correct multiple of 2 .pi. for each rod. The method was tested in a cadaver and in a patient using CT as a reference. Targets in the frame coordinates were chosen from CT and compared to their locations in MR. Localizing errors were as large as 3.7 mm before correction and were reduced to less than 1.11 mm after correction.
REFERENCES:
patent: 5005578 (1991-04-01), Greer et al.
patent: 5351006 (1994-09-01), Sumanaweera et al.
Sumanaweera, et al., Characterization of Spatial Distortion in Magnetic Resonance Imaging and its Implications for Stereotactic Surgery, Neurosurgery, vol. 35, No. 4, Oct. 1994, p. 696.
Suamanaweera, et al., MR Susceptibility Misregistration Correction, IEEE Trans. on Medical Imaging, vol. 12, No. 2, Jun. 1993, p. 251.
Adler, Jr. John R.
Glover Gary H.
Napel Sandy A.
Sumanaweera Thilaka
Board of Trustees of the Leland Stanford Junior University
Haynes Mack
O'Shea Sandra L.
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