Diffusion-weighted MR imaging is sensitive to microscopic motion that can be quantified by means of an apparent diffusion coefficient (ADC). In biologic tissues, the microscopic motions include molecular diffusion of water and microcirculation of blood in the capillary network (perfusion). The ADC is equal to the diffusion coefficient when diffusion is the only type of motion present. But ADCs in biologic tissues are often higher than expected because they are affected by both diffusion and perfusion.
Diffusion-weighted imaging has been primarily limited to the CNS because many technical problems, mostly related to gross physiologic motion, affect diffusion-weighted imaging. Recently, an echoplanar imaging technique has been developed, and diffusion-weighted imaging of the abdomen with an echoplanar sequence has become possible because its fast imaging capability minimizes the effect of gross physiologic motion.
In summary, our results show that measurement of ADC by diffusion-weighted MR imaging has good potential for characterizing liver lesions, but the measured ADCs could be affected by the magnitude of the maximum b value, and imaging quality needs to be improved for clinically routine use by diminishing the distortion artifact resulting from a single-shot echoplanar sequence. It has been reported that a combined use of moderately (TE, 60-120) and heavily (TE, >140) T2-weighted MR images improves differentiation of benign hepafic lesions from malignant lesions. A combined use of diffusion-weighted MR imaging and moderately and heavily T2-weighted MR imaging may further improve the differentiation and may result in financial savings by reducing the necessity for gadolinium-enhanced MR imaging.
Value of apparent diffusion coefficient measurement for discrimination of focal benign and malignant hepatic masses
Bayramoglu, E Inciand T Cimilli
The purpose of our study was to investigate the value of diffusion-weighted magnetic resonance imaging (DW-MRI) to discriminate benign and malignant focal lesions of the liver using parallel imaging technique. A total of 77 patients and 65 healthy controls were enrolled in the study. DW-MRI was performed with b-factors of 0, 500 and 1000 s/mm2, and the apparent diffusion coefficients (ADC) values of the normal liver and the lesions were calculated. The mean ADC value of the focal liver lesions were as follows: simple cysts (3.16 ± 0.18 × 10−3 mm2/s), hydatid cysts (2.58 ± 0.53 × 10−3 mm2/s), hemangiomas (1.97 ± 0.49 × 10−3 mm2/s), metastases (1.14 ± 0.41 × 10−3 mm2/s) and hepatocellular carcinomas (HCC) (1.15 ± 0.36 × 10−3 mm2/s). The mean ADC values of all the disease groups were statistically significant when compared with the mean ADC value of the normal liver (1.56 ± 0.14 × 10−3 mm2/s), (P < 0.01). There were also statistically significant differences among the ADC values of hemangiomas and HCC metastases (P < 0.01), and simple and hydatid cysts (P < 0.008). However, there was no statistically significant difference between HCC and metastases. The present study showed that ADC measurement has the potential to differentiate benign and malignant focal hepatic lesions. We propose to add DW sequence in the MR protocol for the detection and quantitative discrimination of hepatic pathologies.
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