Robert Wujek^{1}, Mona Al-Gizawiy^{1}, Kathleen Schmainda^{1}, and Rodney Willoughby^{2}

MR imaging is commonly used in the diagnosis and monitoring of cerebral abscess, especially diffusion weighted imaging. However, the use of advanced diffusion models has yet to be seen with respect to this type of brain mass. The stretched-exponential, intra-voxel incoherent, and kurtosis diffusion models not only generate diffusivity coefficients, but also other parameters that may prove valuable in properly understanding the structure and progression of such lesions.

1. Muzumdar D, Jhawar S, Goel A. Brain abscess: An overview. Int J Surg. 2011;9:136–44

2. Bakan, Selim et al. “Perianal Fistula With and Without Abscess: Assessment of Fistula Activity Using Diffusion-Weighted Magnetic Resonance Imaging.” Iranian Journal of Radiology 12.4 (2015): e29084. PMC. Web. 9 Nov. 2017.

3. Bennett, K. M., Schmainda, K. M., Bennett (Tong), R., Rowe, D. B., Lu, H. and Hyde, J. S. (2003), Characterization of continuously distributed cortical water diffusion rates with a stretched-exponential model. Magn. Reson. Med., 50: 727–734. doi:10.1002/mrm.10581

4. Separation of diffusion and perfusion in intravoxel incoherent motion MR imaging.D Le Bihan, E Breton, D Lallemand, M L Aubin, J Vignaud, and M Laval-JeantetRadiology 1988 168:2, 497-505

5. Jensen, J. H., Helpern, J. A., Ramani, A., Lu, H. and Kaczynski, K. (2005), Diffusional kurtosis imaging: The quantification of non-gaussian water diffusion by means of magnetic resonance imaging. Magn. Reson. Med., 53: 1432–1440. doi:10.1002/mrm.20508

Advanced Diffusion
Models. The mono-exponential model is the widely-accepted standard. The other
models have been studied in relation to other fields such as neuro-oncology^{3,4,5}.

In vivo cerebral abscess structure as represented by different imaging parameters. The Delta T1 (A) and T2 (B) maps at best show the formation of the capsule, but provide little information regarding changes within the core or surrounding tissue. The standard ADC map (C) highlights some of the surrounding edema. DDC, Dt, and Dk (D, E, and F) display varying degrees of contrast, with DDC and Dk being the best.

P-values from ANOVA test
comparing diffusion parameters between abscess ROIs and NAGM. Green indicates
that the parameter was statistically different in the ROI when compared to
NAGM. ADC and Dt generated similar trends in reduced diffusivity within the
core and elevated diffusivity in the edema. DDC and Dk at the capsule and in
the edema were significantly high. Alpha was lower in all 3 regions. Kurtosis
within the abscess core was elevated. fp was statistically greater at the
capsule and edema ROIs. There was no statistical difference in Dp between ROIs.

P-values from ANOVA
test comparing diffusion coefficients of advanced models and ADC from the standard
mono-exponential model. Green indicates coefficients that significantly differed
from ADC and significantly differed within abscess regions to a higher degree
than ADC. Yellow indicates parameters statistically differed from ADC, but
provide less contrast compared to NAGM. DDC matches ADC within the core, and
offers superior contrast outside the core. Dp matches ADC closely. Dt only performs
better within the core. Dk generates less contrast within the core, but more
contrast outside the core when compared to ADC.