Comparison of the diagnostic performances of diffusion parameters in diffusion weighted imaging and diffusion tensor imaging of breast lesions
Introduction
Mammography and ultrasound are the basic imaging tools for breast radiology. The relatively low sensitivity of these tools resulted in demand for new imaging modalities. Dynamic contrast enhanced MRI with its high contrast resolution provided high sensitivity (90%) in the detection of breast cancer, however due to the low specificity (72%), it is still challenged to discriminate cancer from benign lesions [1].
Utilizing a new contrast mechanism, diffusion weighted imaging (DWI) provides a high sensitivity in the detection of changes in the microscopic cellular environment without the need for contrast injection [2]. DWI also offers a quantitative analysis, with the use of apparent diffusion coefficients (ADC). This quantifies Brownian Motion by reflecting the tissue cellularity and integrity of cell membranes. DWI has been used as a complementary technique to dynamic contrast enhanced MRI, which improved the diagnostic accuracy [2], [3].
Diffusion tensor imaging (DTI) is a new technique that uses additional gradients to detect the degree of diffusion in multiple directions (at least six). It measures the full diffusion tensor describing the degree of anisotropic water diffusion in the tissue, quantified with the parameters mean diffusivity (MD) and fractional anisotropy (FA). Similar to the ADC, MD reflects the average anisotropy, and FA describes the degree of anisotropy [4].
Numerous studies have been performed to assess the diagnostic performance of DWI in differentiating benign and malignant breast lesions. ADC's in malignant tumors were found to be significantly lower than those of benign lesions and adding DWI increased the diagnostic accuracy of conventional MRI [3], [5], [6], [7], [8]. More recently, a few studies with DTI have been performed to assess the efficacy of DTI parameters, MD and FA, in the normal breast tissue and lesions. MD's in malignant tumors were found to be significantly lower than that of benign lesions, whereas FA showed controversial results [9], [10]. Only a few previous DTI studies with 3 Tesla imaging analysing the normal breast [11] and breast lesions [12] were reported. Higher magnetic field imaging has the advantages of higher signal-to-noise ratio (SNR) which allows higher temporal and spatial resolution [2].
The aim of our study was to analyze DWI and DTI parameters in the normal breast tissue and breast lesions with a 3T imager. To our knowledge this is the first study to compare the diagnostic performances of the parameters in DWI and DTI in the differentiation of malignant from benign breast tumors.
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Patients
The study was approved by the institutional review board. In addition to a blanket consent-that is routinely obtained from all patients in our institution for the use of their findings for research and education purposes, with the patient privacy secured-, an informed content was obtained for each biopsy procedure.
Eighty-four consecutive women referred to our MR unit for breast MRI from September 2012 to February 2013 were enrolled in this prospective study. Pediatric age group and patients
Diffusion parameters of the normal breast parenchyma
No calculation was done from the parenchyme of 6 patients who had predominantly fatty parenchyma. Mean ADC, MD and FA values of the normal breast parenchyma measured with ROI's placed on the contralateral breast fibroglandular tissue were given in Table 1. Mean ADC and MD were lower in postmenopausal women without statistical significance (p > 0.05).
Diffusion parameters of the lesions
Mean ADC, MD and FA values of the lesions and the normal parenchyma were shown in Table 2. ADC and MD values of the malignant lesions were
Discussion
Numerous studies have been performed with quantitative DWI of the breast for the last decade. In these studies, it was assumed that the water diffusion in the breast tissue was isotropic. However the organization of the ducts toward the nipple, suggested the idea of the presence of anisotropic water diffusion in the normal breast tissue which can be evaluated by DTI [9]. The majority of published DWI breast studies and DTI studies have been conducted with 1.5 T. Three T field strength provides
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