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Abdomen, Colon, Gastrointestinal tract, MR-Diffusion/Perfusion, Technical aspects, Cancer
G. C. Manikis1, K. Marias1, K. Nikiforaki1, D. M. J. Lambregts2, M. V. Heeswijk2, R. G. H. Beets-Tan2, N. Papanikolaou3; 1Heraklion/GR, 2Maastricht/NL, 3Stockholm/SE
Methods and materials
Sixteen consecutive patients with rectal adenocarcinoma underwent MRI examination before chemoradiation therapy or surgery.
Diffusion weighted imaging (DWI) using a Spin-Echo Echo Planar Imaging sequence was acquired on a Philips Ingenia 1.5T system utilizing 6 b-values (0,
1000) assymetrically sampled to acquire more data on the low b-value area were microperfusion effects are more evident.
Mono-exponential and bi-exponential diffusion models were used both in Gaussian and non-Gaussian form to fit the data and extract the relevant diffusion imaging biomarkers.
ADC was calculated based on the mono-exponential Gaussian model,
while two components were used in the bi-exponential Gaussian model,
the true Diffusion and Pseudo-Diffusion,
leading to the quantification of f (microperfusion fraction),
D* (pseudo diffusion coefficient) and D (true diffusion coefficient).
D(K) (non-Gaussian Diffusion coefficient),
and K (kurtosis) were calculated based on the mono-exponential non-Gaussian model,
while the bi-exponential non-Gaussian model was used to extract f(k),
D(K) and K.
All models were applied on multiple regions of interest including rectal tumors and their associated biomarkers were derived for every pixel in the region using non-linear fitting techniques.
Four different statistical criteria were recruited to determine which diffusion model provided more accurate fitting on the experimental data.
These statistical criteria were adjusted R-square (adj-R2) ,
root mean square (RMSE),
sum of squares due to error (SSE) and corrected Akaike information criterion (cAIC) .
Wilkoxon signed-rank and Dunn's non-parametric statistical tests were used to disclose any significant differences between all four models.