Differentiation of pancreas carcinoma from healthy pancreatic tissue using multiple b-values: comparison of apparent diffusion coefficient and intravoxel incoherent motion derived parameters.

OBJECTIVES: To evaluate in detail the diagnostic performance of diffusion-weighted imaging (DWI) to differentiate pancreas carcinoma from healthy pancreas using the apparent diffusion coefficient (ADC) and parameters derived from the intravoxel incoherent motion (IVIM) theory.
MATERIALS AND METHODS: Twenty-three patients with pancreas carcinoma and 14 volunteers with healthy pancreas were examined at 1.5 Tesla using a single-shot echo-planar imaging DWI pulse sequence. Eleven b-values ranging from 0 to 800 s/mm2 were used. The acquisition was separated into blocks (b0, b25), (b0, b50),...(b0, b800) and each block was acquired in a single expirational breath-hold (TA = 26 seconds) to avoid motion artifacts. The ADC was calculated for all b-values using linear regression yielding ADC(tot). By applying the IVIM model, which allows for the estimation of perfusion effects in DWI, the perfusion fraction f and the perfusion free diffusion parameter D were calculated. The diagnostic performance of ADC, f and D as a measure for the differentiation between healthy pancreas and pancreatic carcinoma was evaluated with receiver operating characteristics analysis.
RESULTS: In the healthy control group, the ADC(tot) ranged from 1.53 to 2.01 microm2/ms with a mean value of 1.71 +/- 0.19 microm2/ms, the perfusion fraction f ranged from 18.5% to 40.4% with a mean value of 25.0 +/- 6.2%, and the diffusion coefficient D from 0.94 to 1.28 microm2/ms with a mean value of 1.13 +/- 0.15 microm2/ms. In patients with pancreas carcinoma, the ADC(tot) ranged from 0.98 to 1.81 microm2/ms with a mean value of 1.31 +/- 0.24 microm2/ms, the perfusion fraction f ranged from 0% to 20.4% with a mean value of 8.59 +/- 4.6% and the diffusion coefficient D from 0.74 to 1.60 microm2/ms with a mean value of 1.15 +/- 0.22 microm2/ms. In comparison to healthy pancreatic tissue, a significant reduction of the perfusion fraction f and of ADC(tot) was found in pancreatic carcinoma (P < 0.00001, 0.0002, respectively). The f value showed more than a 10-fold higher significance level in distinguishing cancerous from normal tissue when compared with the ADC(tot) value. No significant difference in the diffusion coefficient D was observed between the 2 groups (P > 0.5). In the receiver operating characteristic-analyses, the area under curve for f was 0.991 and significantly larger than ADC(tot) (P < 0.05). f had the highest sensitivity, specificity, negative predictive value, and positive predictive value with 95.7%, 100%, 93.3%, and 100%, respectively.
CONCLUSIONS: Using the IVIM-approach, the f value proved to be the best parameter for the differentiation between healthy pancreas and pancreatic cancer. The acquisition of several b-values strongly improved the stability of the parameter estimation thus increasing the sensitivity and specificity to 95.7% and 100% respectively. The proposed method may hold great promise for the non invasive, noncontrast-enhanced imaging of pancreas lesions and may eventually become a screening tool for pancreatic cancer.