Region Expansion of Background Field Removal with Local Spherical Harmonics Approximation for Whole-brain Quantitative Susceptibility Mapping

Abstract

Purpose: Quantitative susceptibility mapping (QSM) is useful for obtaining biological information. To calculate susceptibility distribution, it is necessary to calculate the local field caused by the differences of susceptibility between the tissues. The local field can be obtained by removing a background field from a total field acquired by MR phase image. Conventional approaches based on spherical mean value (SMV) filtering, which are widely used for background field calculations, fail to calculate the background field of the brain surface region corresponding to the radius of the SMV kernel, and consequently cannot calculate the QSM of the brain surface region. Accordingly, a new method calculating the local field by expansively removing the background field is proposed for whole brain QSM. Methods:The proposed method consists of two steps. First, the background field of the brain surface is calculated from the total field using a locally polynomial approximation of spherical harmonics. Second, the whole brain local field is calculated by SMV filtering with a constraint term of the background field of the brain surface. The parameters of the approximation were optimized to reduce calculation errors through simulations using both a numerical phantom and a measured human brain. Performance of the proposed method with the optimized parameters was quantitatively and visually compared with conventional methods in an experiment of five healthy volunteers. Results:The proposed method showed the accurate local field over the expanded brain region in the simulation studies. It also showed consistent QSM with conventional methods inside of the brain surface and showed clear vein structures on the brain surface. Conclusion:The proposed method enables accurate calculation of whole brain QSM without eroding the brain surface region while maintaining same values inside of the brain surface as the conventional methods.

Pulvinar quantitative susceptibility mapping predicts visual hallucinations post‐deep brain stimulation in Parkinson's disease

“…The pulse sequence for QSM was a gradient-echo SWI sequence using the following param- susceptibility map in k-space before and after filtering. This process was described in previous reports (Shirai et al, 2022(Shirai et al, , 2015. The pulse sequence for the T1-weighted image (T1WI) was a three-dimensional fast field-echo technique using the following parameters: TR, 8.2 ms; TE, 4.6 ms; flip angles, 10; FOV, 260 mm; matrix size, 288 × 288; slice thickness, 0.9 mm; 200 slices; and acquisition time, 4 min and 42 s.…”

“…This software method consists of three steps: (I) iterative least square minimization, (II) adaptive edge‐preserving filtering to the susceptibility map in the minimization process, and (III) weighted addition of the susceptibility map in k‐space before and after filtering. This process was described in previous reports (Shirai et al., 2022, 2015). The pulse sequence for the T1‐weighted image (T1WI) was a three‐dimensional fast field‐echo technique using the following parameters: TR, 8.2 ms; TE, 4.6 ms; flip angles, 10; FOV, 260 mm; matrix size, 288 × 288; slice thickness, 0.9 mm; 200 slices; and acquisition time, 4 min and 42 s.…”

Simultaneous Arterial and Venous Imaging Using 3D Quantitative Parameter Mapping

“…The brain surface was removed when calculating magnetic susceptibility, so it could not be visualized. Methods have been proposed for calculating magnetic susceptibility with brain surface corrections, 16 , 17 and it is thought that these methods will also make it possible to visualize veins on the surface of the brain.…”

“…8,9 Quantitative susceptibility mapping (QSM) is a method for acquiring quantitative parameters other than relaxation time. [10][11][12][13][14][15][16][17] Since QSM can perform iron deposition and oxygen extraction fraction measurements, 12,13 it is expected to be useful for diagnosing cerebral iron deposition in tissues and cerebrovascular diseases. We previously proposed quantitative parameter mapping (QPM) as a method for acquiring T1, T2*, PD, and magnetic susceptibility simultaneously.…”

Three-dimensional Multi-parameter Mapping of Relaxation Times and Susceptibility Using Partially RF-spoiled Gradient Echo

“…T 1 and T 2 * values for WM and GM estimated using QPM were evaluated through comparison with reference values. 13 , 14 To evaluate the QSM obtained using QPM, we examined the correlation with QSM acquired at the same spatial resolution as QPM and the same imaging conditions as in the reference: FA = 15 degrees, TR = 35 ms, and TE = (7.0, 11.6, 16.2, 20.8, 25.4, and 30.0) ms. 15 …”