Role of diffusion MRI in characterizing benign and malignant breast lesions

Aims: The aim of this study was to evaluate the role of MRI based diffusion-weighted imaging (DWI) and the apparent diffusion coefﬁ cient (ADC) for characterizing breast lesions in Indian patients. Materials and Methods : This prospective analysis was performed between October 2006 and June 2008. It includes 200 patients between the ages of 16 and 80 years with solid breast lesions greater than 1 cm in diameter. Of these 200 patients, 80 underwent breast MRI with contrast and DWI. One hundred and twenty patients had only DWI as they had come only for sonomammography. A total of 280 lesions were detected. ADC values were calculated for all the lesions and the highest and lowest values of ADC for benign and malignant lesions were identiﬁ ed. Finally, we compared our ﬁ ndings with those of previous studies. Results : Two hundred and eight lesions were categorized as benign and 72 lesions were categorized as malignant based on the ADC values. Based on previous data, lesions with ADC values from 1.3 to 1.5 mm 2 /s were considered benign where as lesions with ADC values ranging between 0.85 and1.1 mm 2 /s were considered malignant. Two lesions whose ADC values were in the benign range were proven to be malignant tumors after surgery. This method of using ADC values for the detection of malignant lesions showed a sensitivity of 97.22% and a speciﬁ city of 100%. The positive predictive value was 100%. Conclusion : DWI is a useful technique for characterizing breast tumors, especially for lesions that cannot be adequately characterized by ultrasonography and routine magnetic resonance imaging.


Introduction
Diff usion-weighted MRI imaging (DWI) is widely used, especially for the evaluation of acute cerebral infarction.It has recently been used to evaluate other organs such as the liver, prostate, ovaries, pancreas, and the breast. [1]Some studies have found that DWI has the ability to diff erentiate benign from malignant lesions. [1]Our study was also performed to evaluate the role of DWI in diff erentiating benign from malignant breast lesions.

Materials and Methods
This study includes a total of 200 patients (199 female patients and one male patient) between the ages of 16 and 80 years who had come for imaging between October 2006 and June 2008.Those patients who had come for breast MRI examinations and were detected to have lesions greater than 1 cm in size were included in the study and DWI was performed aft er obtaining prior consent.Patients who were referred for mammography and sonomammography and who were detected to have solid lesions greater than 1 cm were also included in this study aft er obtaining prior consent; diff usion-weighted sequences were performed for these patients only to characterize the lesions detected on mammography and sonomammography.Purely cystic lesions, even those that were later proven to be malignant, show no significant restriction within the lesion and therefore were not included in this study.There were two such lesions.Lesions greater than 1 cm in size were selected for this study because only such lesions are clearly identiÞ able on the DWI images for the placement of a region of interest (ROI) entirely within the lesion.

Abstract
Aims: The aim of this study was to evaluate the role of MRI based diffusion-weighted imaging (DWI) and the apparent diffusion coeffi cient (ADC) for characterizing breast lesions in Indian patients.Materials and Methods: This prospective analysis was performed between October 2006 and June 2008.It includes 200 patients between the ages of 16 and 80 years with solid breast lesions greater than 1 cm in diameter.Of these 200 patients, 80 underwent breast MRI with contrast and DWI.One hundred and twenty patients had only DWI as they had come only for sonomammography.A total of 280 lesions were detected.ADC values were calculated for all the lesions and the highest and lowest values of ADC for benign and malignant lesions were identifi ed.Finally, we compared our fi ndings with those of previous studies.Results: Two hundred and eight lesions were categorized as benign and 72 lesions were categorized as malignant based on the ADC values.Based on previous data, lesions with ADC values from 1.3 to 1.5 mm 2 /s were considered benign where as lesions with ADC values ranging between 0.85 and1.1 mm 2 /s were considered malignant.Two lesions whose ADC values were in the benign range were proven to be malignant tumors after surgery.This method of using ADC values for the detection of malignant lesions showed a sensitivity of 97.22% and a specifi city of 100%.The positive predictive value was 100%.Conclusion: DWI is a useful technique for characterizing breast tumors, especially for lesions that cannot be adequately characterized by ultrasonography and routine magnetic resonance imaging.
Axial DWI with single-shot echo-planar imaging (EPI) was performed at b values = 0, 500, and 1000, TR/TE: 1800/75, FOV: 350 mm, and slice thickness: 3 mm.Diff usion imaging was performed at b values of 0, 500, and 1000.The apparent diffusion coefficient (ADC) values were automatically calculated by placing the ROI well within the conÞ nes of the lesion.Fatt y glandular parenchyma, which shows homogeneous signal intensity on the ADC map, was used as a reference.The ADC values were automatically measured by drawing ROIs.The size of the ROI was 0.03 cm 2 .The scanner soft ware provides the mean value within the ROI, which equals the ADC value (multiplied by 10 −3 ).

Results
Two hundred and eighty breast lesions were detected in our sample of 200 patients.Based on previous experience, lesions with ADC values in the range of 0.89 ± 0.18 x 10 -3 mm 2 /s were called malignant [Figure 1] and those between 1.41 ± 0.56 x 10 -3 mm 2 /s were called benign [2] [Figure 2].For normal breast parenchyma, the ADC values were between 1.59 and 1.7 x 10 -3 mm 2 /s.Of the 280 lesions, 208 lesions were categorized as benign and 72 lesions were categorized as malignant using these ADC values.Two lesions whose ADC values were in the benign range turned out to be malignant aft er surgery [Figure 3].Both these lesions also showed type 2 curves on the dynamic contrast-enhanced study.According to this study, the sensitivity of ADC values for the detection of malignant lesions was 97.22% and the speciÞ city was 100% and the positive predictive value was 100% and the negative predictive value was 99%.

Discussion
DWI provides important biological information about the composition of tissues, their physical properties, their microstructure, and their architectural organization. [3]This information is available noninvasively and without contrast administration.DWI generates images that are based on the molecular motion of water, which is altered by disease. [4]I is based on the principle of Fick's Law of concentration gradients and the Brownian movement of molecules.Malignant lesions, in general, have more tightly packed cells with a more compact architecture and, consequently, have lower ADC values as compared with benign lesions.There is inhibition of eff ective movement of water molecules and restricted diff usion in dense malignant lesions.The higher ADC values of cystic or necrotic areas reß ect a lack of signiÞ cant restriction of diff usion of water. [5]False-negative values can be obtained in cystic/necrotic malignancies. [5] have found that using cut-off ADC ranges of 1.3-1.5 x 10 -3 mm 2 /s for benign lesions and 0.85-1.1 x 10 -3 mm 2 /s for malignant lesions allows diff erentiation of benign from malignant lesions with a high sensitivity and speciÞ city.They were two false negatives for malignancy.Both these lesions had small cystic components, which were included in the ROI, leading to high ADC values.
In the study conducted by Zhang et al. on 57 breast lesions, the threshold ADC value at b-1000 was 1.20 ± 0.25 x 10 -3 mm 2 /s. [6]They found that ADC values of malignant lesions were statistically much lower than benign lesions and peritumoral tissues. [6]The usefulness of contrast MRI in detecting breast malignancy was studied by Drew et al. in 334 women. [7]The sensitivity and speciÞ city of dynamic contrast MRI in their study were 100% and 86% respectively for detecting malignant lesions. [7]In a study performed by Yabuuchi et al. to assess the utility of a combination of dynamic contrast MRI and DWI in lesion characterization, the sensitivity was found to be 92% and the speciÞ city was found to be 86% for diff erentiating benign from malignant lesions. [8]e results in our study are better than other studies probably because all the lesions were above 1 cm and therefore the ROI was placed well within the lesion, reducing the possibility of false sampling from adjacent tissues.All our cases, except one, were completely solid lesions and hence there was no cystic component in the ROI, which would otherwise have altered the ADC values.

Conclusion
Based on our preliminary data, we have found that DWI for breast lesions can diff erentiate benign from malignant lesions with a high sensitivity and speciÞ city.The usefulness of this technique needs to be further evaluated with larger double-blind studies.

Figure 1 (
Figure 1 (A,B): Invasive ductal carcinoma.Diffusion-weighted image (A) at a b value of 1000 shows a malignant mass (arrow).Apparent diffusion coeffi cient (ADC) mapping (B) reveals restricted diffusion in the mass (arrow).The ADC value was 0.95 mm 2 /s

Figure 2 (
Figure 2 (A,B): Fibroadenoma.Diffusion-weighted image (A) at a b value of 1000 shows bilateral breast fi broadenomas (arrows) Apparent diffusion coeffi cient (ADC) mapping (B) reveals no restricted diffusion in the lesions (arrowheads).ADC values are 1.3 and 1.34 mm 2 /s in the left and right breast lesions, respectively

Figure 3 (
Figure 3 (A,B): False-negative result in a patient with invasive ductal carcinoma.Diffusion-weighted image (A) at a b value of 1000 shows a left breast mass (arrow) with solid and cystic components.This lesion was proven to be malignant after surgery.Apparent diffusion coeffi cient (ADC) mapping (B) reveals restricted diffusion (arrow) in the solid component of the mass.The region of interest containing the solid and cystic component reveals an ADC value of 1.5 mm 2 /s