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.