Diffusion Weighted Imaging in Breast MRI

Rationale and Objectives

Comparison of two different diffusion weighted (DW) sequences in breast MRI regarding the differentiation between benign and malignant lesions.

Materials and Methods

Breast MRI including two different DW sequences was performed in 165 consecutive women. Inclusion criteria for DW imaging and ADC evaluation were histologically proven focal mass lesions with a diameter of more than 5 mm in dynamic contrast-enhanced MRI. The DW sequences were pre-contrast echo-planar imaging with spectral fat saturation (EPI fs) and DW EPI with inversion recovery (EPI STIR) (b-values: 50, 400, and 800). Lesions were analyzed regarding visibility in DW sequences and ADC values.

Results

Inclusion criteria were fulfilled in 56 women with 69 lesions. Five lesions could not be evaluated for different reasons. Finally, DW sequences were evaluated in 51 women with 64 focal mass lesions (15 benign, 49 malignant). The visibility of the lesions was significantly better in the EPI fs sequence ( P <0.05). The ADC values (10 −3 mm 2 /s) in the EPI fs were 1.76, 2.58, and 1.21 (mean, maximum, minimum, respectively) for benign lesions and 0.90, 1.19, and 0.34 for malignant lesions. Respective values in the EPI STIR sequence were 1.92, 3.20, 1.10, and 0.91, 1.43, 0.35. Only in the EPI fs sequence there was no overlap in ADC values between benign and malignant lesions.

Conclusion

The DW MRI of the breast with EPI fs and EPI STIR sequences has a high potential to differentiate between benign and malignant breast lesions. Due to better lesion visibility and selectivity, the EPI fs sequence should be preferred.

Breast magnetic resonance imaging (MRI) is an accepted method in detecting primary or recurrent breast cancer in addition to mammography and breast ultrasound. Additionally, it improves preoperative local staging, which is useful for surgical planning ( ). Image analysis is based on the enhancement pattern of lesions in dynamic breast MRI and morphologic changes ( ). With these two criteria, breast MRI has a sensitivity of about 85% to 99% in detecting malignant breast lesions ( ). However, there is an overlap of these criteria with benign lesions, which leads to a reported specificity of about 40% to 80% ( ). In recently published studies, the specificity of breast MRI could be increased using diffusion weighted (DW) sequences ( ). DW MRI is based on the principle that random motion of molecules during the interval of excitation and signal measurement reduces the amplitude of the resulting signal. The application of appropriate pulse sequences (using, e.g., bipolar gradient pulses in one or several directions) allows the measurement of the signal cancellation due to diffusion in the given direction. While normal tissue exhibits gross signal loss, areas with restricted motion of molecules like densely packed tumor cells show less signal loss and become bright in DW images. The value of the diffusion of water in tissue is called the apparent diffusion coefficient (ADC). On basis of the DW images an ADC map can be calculated, which shows the ADC value of each voxel in every slice. Restricted water movement in tumors with high cellularity leads to smaller ADC values ( ). Although this technique is well known in brain imaging, it has not become a routine method in breast MRI. One reason for this may be the high content of fatty tissue in the breast, which makes fat saturation techniques necessary to identify the lesions in the DW images. There are two main possibilities for fat saturation: spectral fat saturation (fs) and a 180° prepulse with a short inversion time (STIR). To our knowledge there is no published study that compares both fat saturation techniques in DW breast MRI in terms of lesion detection and lesion characterization according to the ADC value.

Methods and materials

Patients

From March to November 2006, we performed 233 breast MRI examinations. Patients who took part in another study (n = 54) and patients who refused DW sequences (n = 14) were excluded. All other patients (n = 165) gave informed consent to apply the DW sequences additionally to our normal breast MRI protocol. The study was approved by the local ethics committee.

MRI

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Image Analysis

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Statistical Analysis

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Results

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Table 1

Histology of 69 Lesions with DW Sequences

Histology (N = 69) IDC ILC DCIS Rare FA FD BP Total Evaluated 39 6 1 3 8 6 1 64 Not evaluated 2 2 0 1 0 0 0 5

IDC, invasive ductal carcinoma; ILC, invasive lobular carcinoma; DCIS, ductal carcinoma in situ; Rare, rare malignant tumors (medullary, tubular carcinoma, carcinosarcoma, angiosarcoma); FA, fibroadenoma; FD, fibrocystic disease; BP, benign phylloides tumor.

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Lesion Delineation in the DW Images

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Table 2

Lesion Delineation in DW EPI STIR and DW EPI fs

Delineation DW EPI STIR DW EPI fs b m b m 1 6 27 7 38 2 4 21 5 11 3 5 1 3 0 4 0 0 0 0 Σ 15 49 15 49

Delineation of all lesions (n = 64; 15 benign, 49 malignant) in a four point scale (1 = good; 2 = moderate; 3 = poor; 4 = not visible) in both diffusion weighted (DW) pulse sequences.

EPI STIR, echo-planar imaging with short time inversion recovery; EPI fs, echo-planar imaging with spectral fat saturation.

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ADC Values

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Table 3

Apparent Diffusion Coefficient (ADC) Values (10 −3 mm 2 /sec) of All Evaluated Lesions (b = benign, m = malignant) in Both MR Diffusion Weighted Sequences

ADC values (10 −3 mm 2 /sec) n Mean ± SD Maximum Minimum 95% CI b m b m b m b m b m DW EPI STIR 15 45 1.92 ± 0.53 0.91 ± 0.24 3.20 1.43 1.10 0.35 1.62–2.22 0.83–0.98 DW EPI fs 15 49 1.76 ± 0.42 0.90 ± 0.18 2.58 1.19 1.21 0.34 1.53–2.00 0.85–0.96

SD, standard deviation; EPI STIR, echo-planar imaging with short time inversion recovery; EPI fs, echo-planar imaging with spectral fat saturation.

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Discussion

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Table 4

Apparent Diffusion Coefficient (ADC) Values (10 −3 mm 2 /sec) of Benign (b) and Malignant Lesions (m) in Three Prior Published Studies

ADC values (10 −3 mm 2 /sec) n Mean ± SD b m b m Rubesova et al. ( ) 22 65 1.51 ± 0.32 0.95 ± 0.22 Kuroki et al. ( ) 5 55 1.48 ± 0.45 1.02 ± 0.23 Woodhams et al. ( ) 24 191 1.67 ± 0.54 1.22 ± 0.31

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Conclusion

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References

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Diffusion Weighted Imaging in Breast MRI

Rationale and Objectives

Materials and Methods

Results

Conclusion

Methods and materials

Patients

MRI

Image Analysis

Statistical Analysis

Results

Lesion Delineation in the DW Images

ADC Values

Discussion

Conclusion

References

Further Reading

Abstracts of Funded National Institutes of Health Grants

Apparent Diffusion Coefficient of Subcutaneous Epidermal Cysts in the Head and Neck

Computer-Assisted Mammography Feedback Program (CAMFP)