Correction of diffusion-weighted magnetic resonance imaging for brachytherapy of locally advanced cervical cancer

<div><p></p><p><b>Background</b>. Geometrical distortion is a major obstacle for the use of echo planar diffusion-weighted magnetic resonance imaging (DW-MRI) in planning of radiotherapy. This study compares geometrical distortion correction methods of DW-MRI at time of brachytherapy (BT) in locally advanced cervical cancer patients.</p><p><b>Material and methods.</b> In total 21 examinations comprising DW-MRI, dual gradient echo (GRE) for B₀ field map calculation and T2-weighted (T2W) fat-saturated MRI of eight patients with locally advanced cervical cancer were acquired during BT with a plastic tandem and ring applicator in situ. The ability of B₀ field map correction (B₀M) and deformable image registration (DIR) to correct DW-MRI geometric image distortion was compared to the non-corrected DW-MRI including evaluation of apparent diffusion coefficient (ADC) for the gross tumor volume (GTV).</p><p><b>Results.</b> Geometrical distortion correction decreased tandem displacement from 3.3 ± 0.9 mm (non-corrected) to 2.9 ± 1.0 mm (B₀M) and 1.9 ± 0.6 mm (DIR), increased mean normalized cross-correlation from 0.69 ± 0.1 (non- corrected) to 0.70 ± 0.10 (B₀M) and 0.77 ± 0.1 (DIR), and increased the Jaccard similarity coefficient from 0.72 ± 0.1 (non-corrected) to 0.73 ± 0.06 (B₀M) and 0.77 ± 0.1 (DIR). For all parameters only DIR corrections were significant (p < 0.05). ADC of the GTV did not change significantly with either correction method.</p><p><b>Conclusion.</b> DIR significantly improved geometrical accuracy of DW-MRI, with remaining residual uncertainties of less than 2 mm, while no significant improvement was seen using B₀ field map correction</p></div

Normalized hippocampal modeled neurite density in stressed and control groups of rats.

<p>All values are mean ± standard deviation of the subregion (n = 4 for both groups). Subregion abbreviations are: stratum oriens (SO), pyramidal cell layer (CL), stratum radiatum (SR), stratum lacunosum moleculare layer (LM), granule cell layer (GL), molecular layer (ML).</p><p>*Significant difference between stressed and control group (Wilcoxon rank sum test P<0.05 uncorrected for multiple comparisons).</p

Neurite density maps of stressed and control rat hippocampi.

<p>(<b>A</b>) stressed rats, (<b>B</b>) control rats. The color bar shows the normalized neurite density. Note: the highest red intensity on the color bar refers to lowest neurite density.</p

CA3 and CA1 normalized neurite density of stratum oriens (SO), cell layer (CL), stratum radiatum (SR) and stratum lacunosum moleculare layer (LM).

<p>Individual data from controls rats (green dots) and stressed rats (red) are shown in conjunction with the mean values and standard deviation (black). ^*P<0.05.</p

DG normalized neurite density of granule cell layer (GL) and molecular layer (ML).

<p>Individual data from controls rats (green dots) and stressed rats (red) are shown in conjunction with the mean values and standard deviation (black). <b>^*</b>P<0.05.</p

Stroke infarct volume estimation in fixed tissue: Comparison of diffusion kurtosis imaging to diffusion weighted imaging and histology in a rodent MCAO model

<div><p>Diffusion kurtosis imaging (DKI) is a new promising MRI technique with microstructural sensitivity superior to conventional diffusion tensor (DTI) based methods. In stroke, considerable mismatch exists between the infarct lesion outline obtained from the two methods, kurtosis and diffusion tensor derived metrics. We aim to investigate if this mismatch can be examined in fixed tissue. Our investigation is based on estimates of mean diffusivity (MD) and mean (of the) kurtosis tensor (MKT) obtained using recent fast DKI methods requiring only 19 images. At 24 hours post stroke, rat brains were fixed and prepared. The infarct was clearly visible in both MD and MKT maps. The MKT lesion volume was roughly 31% larger than the MD lesion volume. Subsequent histological analysis (hematoxylin) revealed similar lesion volumes to MD. Our study shows that structural components underlying the MD/MKT mismatch can be investigated in fixed tissue and therefore allows a more direct comparison between lesion volumes from MRI and histology. Additionally, the larger MKT infarct lesion indicates that MKT do provide increased sensitivity to microstructural changes in the lesion area compared to MD.</p></div

Whole brain volumes.

<p>The whole brain volumes measured by MD and hematoxylin stain. (n = 7). Data are represented as a scatter plot. MD: Mean diffusivity.</p

Example of the H- and MAP2-stained post-hoc brains.

<p>Infarcted area on an additional post-hoc brain depicted by A) Hematoxylin stain B) MAP2-stain.</p

Example of difference in visualization.

<p>Infarcted area depicted by A) MD B) MKT C) Anatomical RARE image and D) Hematoxylin stain to illustrate the difference in resolution and contrast. MD: Mean diffusivity. MKT: Mean Kurtosis Tensor.</p

The intra- and inter-variability.

<p>The intra- and inter-variability obtained from all three infarct visualization methods. MD: Mean diffusivity. MK: Mean Kurtosis Tensor.</p