Takeshi Yoshikawa1, Yoshiharu Ohno2, Masao Yui3, Yoshimori Kassai3, Tatsuya Ohkubo3, Shinichiro Seki4, Katsusuke Kyotani5, and Yuji Kishida6
1Kobe University Graduate School of Medicine, Kobe, Japan, 2Fujita Health University School of Medicine, Toyoake, Japan, 3Canon Medical Systems Corporation, Otawara, Japan, 4Hyogo Prefectural Tamba Medical Center, Tamba, Japan, 5Kobe University Hospital, Kobe, Japan, 6Konan Medical Center, Kobe, Japan
Synopsis
Stretched-exponential model
enables diffusion analysis considering diffusion varieties in each voxel on
abdominal DWI. Our study showed stretched-exponential
model has a potential to increase diagnostic performance of liver DWI. Alpha
has a potential to be used for malignant lesion differentiation.
Backgrounds & Purpose
Backgrounds-
To measure water diffusion in tissue more precisely compared to
conventional ADC (mono-exponential model), several non-mono-exponential models
have been proposed and evaluated.
-
One of them is stretched-exponential model.
-
It can estimate heterogeneity of water diffusion as well as
microstructures in the tissue and express them with only two parameters.
-
Distributed diffusion coefficients (DDC)
-
Water molecular diffusion heterogeneity index (Alpha, α)
α=1: pure homogenous intravoxel signal decay
α=0: high degree of multi-exponential
signal decay
Equation
: Sb/S0 = exp{-(b×DDC)
α} cf. Sb/S0 = exp(-b×ADC)
Purpose- The purpose of this study was to assess DWI with
stretched-exponential model in evaluation of focal liver lesions
Methods and Materials
Patients
& Lesion- 76 patients (53 men and 22 women, mean: 66.9 years), who were suspected
to have hepatic malignancy and underwent 3T-MRI, were chosen and
retrospectively analyzed.
-
78 malignant (HCC: 43, metastasis: 27, CCC: 3, combined HCC & CCC:
5) and 30 benign (hepatic cyst: 18, hepatic hemangioma: 12) lesions were
confirmed and evaluated.
Imaging
Technique, Post-Processing, & ROI placement-
All patients underwent MRI at a 3T scanner (Vantage Titan 3T; Canon
Medical Systems, Otawara, Japan).
-
Source DWIs were obtained with
SE-EPI sequence (TR/TE/FA = 3000-6000/66/90, b values: 0, 500, 1000, matrix: 96
×128, thickness: 7mm, NEX: 2, scan time: 10-12min, PASTA+SPAIR, PI: 2, MPG: x,
y, z) as
one of routine sequences in our institution.
-
ADC, DDC, Alpha images were
calculated by using mono-exponential and stretched-exponential models on a
workstation (OleaSphere, Olea Medical).
-
Oval ROIs were placed in the liver
and focal lesions and mean ADC, DDC, and Alpha were measured.
Quantitative
Analysis-
Mean values of malignant and benign lesions were compared for each
parameter.
-
Correlations coefficients among the three parameters were assessed in
the liver and focal lesions.
- Lesion-to-liver contrasts (=(lesion-liver) / (lesion+liver)) were calculated and compared
among the parameters.
-
Lesion characterization was compared using ROC among the parameters and
their combinations.
-
Mean values of HCC, metastasis, and other primary cancers were compared
for evaluation of lesion differentiation capability.
Results
-
Malignant lesion ADC and DDC were significantly lower than benign ones (p<0.0001, fig. 1).
- DDCs showed the trends similar to ADCs in the liver and focal lesion
and were significantly correlated. Correlations of lesion ADCs and DDCs were significantly lower than
hepatic ones (fig. 2).
-
Malignant lesion contrast was significantly higher on DDC than on ADC (p=0.019, fig. 3).
-
For lesion characterization, no significant difference was found between ADC and DDC, and Az had non-significant trend toward highest at ADC+Alpha and ADC+DDC+Alpha sets (Az: 0.996, fig. 4).
-
In malignant lesion
differentiation, significant difference was found between HCC and metastasis on ADC (1.18 vs 1.39, p=0.009) and Alpha (0.71 vs 0.80, p=0.011), and between HCC and other primary cancers on Alpha (0.71 vs 0.92, p=0.0003) (fig. 5).
- Representative cases are shown in figures 6 & 7.
Summary & Conclusion
Summary- Stretched-exponential model enables diffusion analysis considering diffusion
varieties in each voxel and has a potential to increase diagnostic performance
of liver DWI.
-
DDC can be used as an alternative to ADC.
-
Alpha has a potential to be used for malignant lesion differentiation.
Conclusion- Stretched-exponential
model has a potential to increase diagnostic performance of liver DWI.
- Alpha
has a potential to be used for malignant lesion differentiation.
Acknowledgements
No acknowledgement found.References
Previous reports for liver tumors and fibrosis
-
Kim
HC, et
al. Eur
Radiol 2019.
Alpha indicated degree of
necrosis in treated colon ca metastasis.
-
Hu Y,
et
al.
Cancer Med 2018.
Alpha: malignant <
benign lesion
-
Seo N,
et al. Eur
Radiol 2018.
Alpha: F0-1 > F2 >
F4