Published in:
01-06-2015 | Hepatobiliary-Pancreas
Intravoxel incoherent motion diffusion-weighted imaging in the liver: comparison of mono-, bi- and tri-exponential modelling at 3.0-T
Published in: European Radiology | Issue 6/2015
Login to get accessAbstract
Purpose
To determine whether a mono-, bi- or tri-exponential model best fits the intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) signal of normal livers.
Materials and methods
The pilot and validation studies were conducted in 38 and 36 patients with normal livers, respectively. The DWI sequence was performed using single-shot echoplanar imaging with 11 (pilot study) and 16 (validation study) b values. In each study, data from all patients were used to model the IVIM signal of normal liver.
Diffusion coefficients (Di ± standard deviations) and their fractions (fi ± standard deviations) were determined from each model. The models were compared using the extra sum-of-squares test and information criteria.
Results
The tri-exponential model provided a better fit than both the bi- and mono-exponential models. The tri-exponential IVIM model determined three diffusion compartments: a slow (D1 = 1.35 ± 0.03 × 10-3 mm2/s; f1 = 72.7 ± 0.9 %), a fast (D2 = 26.50 ± 2.49 × 10-3 mm2/s; f2 = 13.7 ± 0.6 %) and a very fast (D3 = 404.00 ± 43.7 × 10-3 mm2/s; f3 = 13.5 ± 0.8 %) diffusion compartment [results from the validation study]. The very fast compartment contributed to the IVIM signal only for b values ≤15 s/mm2
Conclusion
The tri-exponential model provided the best fit for IVIM signal decay in the liver over the 0-800 s/mm2 range. In IVIM analysis of normal liver, a third very fast (pseudo)diffusion component might be relevant.
Key Points
• For normal liver, tri-exponential IVIM model might be superior to bi-exponential
• A very fast compartment (D = 404.00 ± 43.7 × 10
-3
mm
2
/s; f = 13.5 ± 0.8 %) is determined from the tri-exponential model
• The compartment contributes to the IVIM signal only for b ≤ 15 s/mm
2