Quantitative susceptibility mapping (QSM) is a rather novel MRI approach that reveals the magnetic susceptibility χ of tissue [1-4]. It is based on solving a mathematically challenging inverse problem (Fig. 1). One of its appealing properties is that the data acquisition relies on standard gradient recalled MR sequences. With these, it is possible to measure the field disturbances that are caused by spatially varying χ-distributions. The determination of the χ-distribution is called quantitative susceptibility mapping (QSM). Based on extensive research efforts, it is nowadays possible to perform QSM with decent quality (Fig. 2).
Figure 1. The challenges that need to be addressed in a QSM reconstruction.
The magnetic susceptibility χ generates field distortions B, which can be measured with standard gradient recalled echo sequences. Challenges include phase jumps in the measured phase maps, the presence of roots of the B kernel, the presence of background fields, missing image information outside the body, and the instable deconvolution problem that must be solved.
Figure 2. A susceptibility map of the human brain measured at 7 Tesla.
We are working on several aspects of QSM:
Figure 3. A susceptibility map of the mouse brain measured at 7 Tesla (ex vivo).
 Deistung A, Schweser F, Reichenbach JR.
Overview of quantitative susceptibility mapping.
NMR Biomed 2017;30(4).
 Hanspach J, Dwyer MG, Bergsland NP, Feng X, Hagemeier J, Bertolino N, Polak P, Reichenbach JR, Zivadinov R, Schweser F.
Methods for the computation of templates from quantitative magnetic susceptibility maps (QSM): Toward improved atlas- and voxel-based analyses (VBA).
J Magn Reson Imaging. 2017 Nov;46(5):1474-1484.
 Straub S, Schneider TM, Emmerich J, Freitag MT, Ziener CH, Schlemmer HP, Ladd ME, Laun FB.
Suitable reference tissues for quantitative susceptibility mapping of the brain.
Magn Reson Med. 2017 Jul;78(1):204-214.
 Straub S, Emmerich J, Schlemmer HP, Maier-Hein KH, Ladd ME, Röthke MC, Bonekamp D, Laun FB.
Mask-Adapted Background Field Removal for Artifact Reduction in Quantitative Susceptibility Mapping of the Prostate.
Tomography. 2017 Jun;3(2):96-100.
 Straub S, Laun FB, Emmerich J, Jobke B, Hauswald H, Katayama S, Herfarth K, Schlemmer HP, Ladd ME, Ziener CH, Bonekamp D, Röthke MC.
Potential of quantitative susceptibility mapping for detection of prostatic calcifications.
J Magn Reson Imaging. 2017 Mar;45(3):889-898.