Single-scan R2⁎ measurement with macroscopic field inhomogeneity correction

Nam, Yoonho; Han, Dong Woo; Kim, Dong Hyun

doi:10.1016/j.neuroimage.2012.08.062

Cited by 10 publications

(27 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The red arrows in R 2 * maps indicate regions where the effect of G z compensation is prominent. Note that the retrieved G z map is similar to previously reported G z maps . Figure B shows sagittal views of the multi‐slice data set.…”

Section: Resultssupporting

confidence: 82%

“…In typical 2D T 2 * measurements using a multi‐echo gradient echo (GRE), it is assumed that background field varies prominently across the slice direction because in general the slice thickness is larger than in‐plane resolution. Several methods to compensate for the background field inhomogeneity by approximating it as a linear variation (G z ) have been introduced . Among these methods, the post‐processing approaches have limitations in recovering T 2 * values in brain regions such as near the sinus or ear canals where the signal drops rapidly because of severe field inhomogeneity.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Simultaneous estimation of PD, T₁, T₂, T₂^*, and ∆B₀ using magnetic resonance fingerprinting with background gradient compensation

Hong

Han

Kim

2018

Magnetic Resonance in Med

Self Cite

View full text Add to dashboard Cite

Purpose This study aims to estimate PD, T1, T2, T2*, and normalΔB0 simultaneously using magnetic resonance fingerprinting (MRF) with compensation of the linearly varying background field. Methods MRF based on fast imaging with steady‐state precession (FISP) and multi‐echo spoiled gradient (SPGR) schemes are alternatively used, which encode T2 and T2*, respectively. Simulations are performed to determine the appropriate ratio of the FISP and SPGR sections with respect to the T2 and T2* accuracy. Additionally, background field inhomogeneity (Gz) compensation using z‐shim gradients are incorporated into the SPGR section and the dictionary. The background field compensation is tested in the phantom experiment under well‐shimmed and poor‐shimmed conditions. An in vivo experiment is performed and the estimated parameters are compared before and after Gz compensation. Results The T1, T2, and T2* values from the phantom results are in good agreement with the reference methods under well‐shimmed condition. The underestimated T2 and T2* values under poor‐shimmed condition are recovered by Gz compensation and the parameters are also in good agreement with the reference methods. In the human brain, T2 and T2* values are restored by Gz compensation in regions where the magnetic field is particularly inhomogeneous, such as near the sinus and ear canals. Conclusions The proposed FISP and SPGR combined MRF provides a simultaneous estimation of PD, T1, T2, T2*, and normalΔB0. By incorporating field inhomogeneity as a gradient term into both the sequence and dictionary, T2 and T2* values can be restored where field inhomogeneity exists.

show abstract

Section: Resultssupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Simultaneous estimation of PD, T₁, T₂, T₂^*, and ∆B₀ using magnetic resonance fingerprinting with background gradient compensation

Hong

Han

Kim

2018

Magnetic Resonance in Med

Self Cite

View full text Add to dashboard Cite

show abstract

“…Multiple methods have been proposed to compensate for the macroscopic B 0 field inhomogeneity in mGRE (Han et al, 2015;Hernando et al, 2012;Nam et al, 2012;Oh et al, 2014;Yablonskiy et al, 2013). However, many of them require a longer minimum TE and may lose a significant portion of fast decaying myelin water signal.…”

Section: Discussionmentioning

confidence: 99%

Improved estimation of myelin water fraction using complex model fitting

et al. 2015

Self Cite

View full text Add to dashboard Cite

“…Before acquiring the third echo, a field compensation gradient is applied to compensate for the field inhomogeneity across the slice. The size of the field compensation gradient ( G c = −1.75 G/cm and t c = 0.98 ms) is similar to the optimal compensation gradient suggested in the head , considering slice thickness difference. This gradient is positioned immediately after the second echo and is followed by the third echo to minimize the increase in repetition time (TR) over conventional SWI.…”

Section: Methodsmentioning

confidence: 69%

“…Only through‐plane directional field inhomogeneity is assumed and corrected because SWI is often acquired in a lower through‐plane resolution compared with in‐plane resolution. The signal in a given voxel ( z 0 ) is modeled as follows :

S (T E_{n}; z_{0}) = M_{0} \cdot exp (‐ T E_{n} \cdot R_{2}^{*}) \cdot A (G_{z} \cdot T E_{n}; z_{0})

where A = \int_{‐ z_{s l} / 2}^{z_{s l} / 2} e^{j 2 π γ G_{z} (z ‐ z_{0}) T E_{n}} \cdot P (z ‐ z_{0}) d z

P (z) = \frac{s i n c (\frac{z}{Δ z})}{s i n c (\frac{z}{z_{s l}})}

where n is echo number ( n = 1, 2, and 3), M 0 is an equilibrium magnetization, G z is field inhomogeneity gradient in slice, z sl is a 3D slab thickness, P ( z ) is a slice profile , and Δz is the slice thickness. In the first and second echoes, G z is the same as through‐plane background field inhomogeneity ( G z,bg ).…”

Section: Methodsmentioning

confidence: 99%

Improved susceptibility weighted imaging method using multi‐echo acquisition

Nam

et al. 2013

Magnetic Resonance in Med

Self Cite

View full text Add to dashboard Cite

Purpose To introduce novel acquisition and post-processing approaches for susceptibility weighted imaging (SWI) to remove background field inhomogeneity artifacts in both magnitude and phase data. Method The proposed method acquires three echoes in a 3D gradient echo (GRE) sequence, with a field compensation gradient (z-shim gradient) applied to the third echo. The artifacts in the magnitude data are compensated by signal estimation from all three echoes. The artifacts in phase signals are removed by modeling the background phase distortions using Gaussians. The method was applied in vivo and compared with conventional SWI. Results The method successfully compensates for background field inhomogeneity artifacts in magnitude and phase images, and demonstrated improved SWI images. In particular, vessels in frontal lobe, which were not observed in conventional SWI, were identified in the proposed method. Conclusion The new method improves image quality in SWI by restoring signal in the frontal and temporal regions.

show abstract

Single-scan R2⁎ measurement with macroscopic field inhomogeneity correction

Cited by 10 publications

References 37 publications

Simultaneous estimation of PD, T₁, T₂, T₂^*, and ∆B₀ using magnetic resonance fingerprinting with background gradient compensation

Simultaneous estimation of PD, T₁, T₂, T₂^*, and ∆B₀ using magnetic resonance fingerprinting with background gradient compensation

Improved estimation of myelin water fraction using complex model fitting

Improved susceptibility weighted imaging method using multi‐echo acquisition

Contact Info

Product

Resources

About

Single-scan R2⁎ measurement with macroscopic field inhomogeneity correction

Cited by 10 publications

References 37 publications

Simultaneous estimation of PD, T1, T2, T2*, and ∆B0 using magnetic resonance fingerprinting with background gradient compensation

Simultaneous estimation of PD, T1, T2, T2*, and ∆B0 using magnetic resonance fingerprinting with background gradient compensation

Improved estimation of myelin water fraction using complex model fitting

Improved susceptibility weighted imaging method using multi‐echo acquisition

Contact Info

Product

Resources

About

Simultaneous estimation of PD, T₁, T₂, T₂^*, and ∆B₀ using magnetic resonance fingerprinting with background gradient compensation

Simultaneous estimation of PD, T₁, T₂, T₂^*, and ∆B₀ using magnetic resonance fingerprinting with background gradient compensation