Calcifications represent one component of pathology in many brain diseases. With MRI, they are most often detected by exploiting negative contrast in magnitude images. Calcifications are more diamagnetic than tissue, leading to a magnetic field disturbance that can be seen in phase MR images. Most phase imaging studies use gradient recalled echo based pulse sequences. Here, the phase component of SWIFT, a virtually zero acquisition delay sequence, was used to detect calcifications ex vivo and in vivo in rat models of status epilepticus and traumatic brain injury. Calcifications were detected in phase and imaginary SWIFT images based on their dipole like magnetic field disturbances. In magnitude SWIFT images, calcifications were distinguished as hypointense and hyperintense. Hypointense calcifications showed large crystallized granules with few surrounding inflammatory cells, while hyperintense calcifications contained small granules with the presence of more inflammatory cells. The size of the calcifications in SWIFT magnitude images correlated with that in Alizarin stained histological sections. Our data indicate that SWIFT is likely to better preserve signal in the proximity of a calcification or other field perturber in comparison to gradient echo due to its short acquisition delay and broad excitation bandwidth. Furthermore, a quantitative description for the phase contrast near dipole magnetic field inhomogeneities for the SWIFT pulse sequence is given. In vivo detection of calcifications provides a tool to probe the progression of pathology in neurodegenerative diseases. In particular, it appears to provide a surrogate marker for inflammatory cells around the calcifications after brain injury.
Bibliographical noteFunding Information:
We thank Maarit Pulkkinen for her invaluable help in handling the histology, Jarmo Hartikainen for his help with the disease models, and Ryan Chamberlain and Rajesh Venkataraman for the use of high performance gridding code for image reconstruction. We would also like to thank Doctoral Program in Molecular Medicine at University of Eastern Finland, Emil Aaltonen Foundation, Academy of Finland and the strategic funding of the University of Eastern Finland (UEF-Brain). Additional funds were provided by NIH grants, P41 RR008079 , P30 NS057091 , R21 CA139688 , and S10 RR023730 .
- Brain calcification
- Phase contrast
- Ultra short echo-time