Magnetic susceptibility-weighted MR phase imaging of the human brain

Abstract

Background and purpose: MR gradient echo imaging is sensitive to the magnetic susceptibility of different tissue types. The purpose of this study was to investigate the diagnostic potential of MR phase imaging of the human brain.

Methods: High-spatial-resolution, T2*-weighted, single-echo images were acquired in five volunteers and one patient with a brain tumor on a 1.5T system by applying a 3D, first-order, velocity-compensated gradient echo sequence by using a quadrature transmit-receive head coil. Phase images were reconstructed from the raw data and unwrapped by using a region-growing phase-unwrapping algorithm. Low-spatial-frequency components originating from static background susceptibility effects were removed by high-pass filtering.

Results: Phase images showed excellent image contrast and revealed anatomic structures that were not visible on the corresponding magnitude images.

Conclusion: Improved processing of susceptibility-weighted MR phase images offers a new means of contrast for neuroimaging applications.

Fig 1.

Wrapped (A) and unwrapped phase images (B–D). The sphenoid sinuses cause strong field inhomogeneities that extend far into the interior of the brain (white arrows). Parameters: TR = 67 ms, TE = 40 ms, α = 25°, FOV = 256 × 256 × 64, imaging matrix = 512 × 512 × 128.

Fig 2.

Minimum intensity projections over 4 sections of the magnitude data (A), the corresponding high-pass filtered phase images (B), and a reproduction from an anatomic atlas for comparison (C). In the phase image (B) the capsula interna, capsula externa, putamen, nucleus caudatus, corpus callosum and the claustrum are better visualized than in the magnitude image (A). Also improved is the contrast between gray and white matter. The ventricles are not easily visible in the phase images due to the fact that the magnetic susceptibility of CSF and brain tissue is very similar. TR = 67, TE = 40, α = 25°, FOV = 256 × 256 × 192 mm³, matrix = 512 × 256 × 96, w = 21. (Image C is reproduced with permission from Putz/Pabst: Sobotta, Atlas der Anatomie des Menschen, 21. Auflage 2000, Elsevier GmbH, Urban & Fischer Verlag München, Jena.)

Fig 3.

Minimum intensity projections over 4 sections of magnitude image (A), the corresponding high-pass filtered phase images (B), and a reproduction from an anatomic atlas (C). In the phase image (B) the caudate nucleus, the putamen, the globus pallidus, and the thalamus with parts of the thalamostriate veins, amongst other features, can be identified. TR = 67 ms, TE = 40 ms, α = 25°, FOV = 256 × 256 × 96 mm³, matrix = 512 × 256 × 96, w = 21. (Image C is reproduced with permission from Putz/Pabst: Sobotta, Atlas der Anatomie des Menschen, 21. Auflage 2000, Elsevier GmbH, Urban & Fischer Verlag München-Jena.)

Fig 4.

Magnitude image (A), a mIP over 5 sections from the phase images (B) and a reproduction from an anatomic atlas. The red nuclei, the substantia nigra, the crus cerebri and venous vessels are displayed well in the phase image. The medullary lamellae in the red nuclei can be clearly identified. TR = 67 ms, TE = 40 ms, α = 25°, FOV = 256 × 256 × 96 mm³, matrix = 512 × 256 × 96, w = 21. (Image C is reproduced with permission from Putz/Pabst: Sobotta, Atlas der Anatomie des Menschen, 21. Auflage 2000, Elsevier GmbH, Urban & Fischer Verlag München-Jena.)

Fig 5.

Contrast-enhanced T1-weighted MP-RAGE scan (A) (TR = 15 ms, TE = 5 ms, FOV = 224 × 256 mm², section thickness = 1.0 mm), minimum intensity projections over four sections of magnitude (B), and phase (C) of the susceptibility weighted 3D scan of a 29-year-old female patient with a glioblastoma multiforme (TR = 67 ms, TE = 40 ms, α = 25°, FOV = 169 × 256 × 64 mm³, matrix = 160 × 160 × 64, w = 23).