1．5TMR乳腺扩散加权成像b值的优化

Optimization of b-value in breast diffusion-weighted 1.5 T MR imaging

目的通过分析水模、正常乳腺腺体、乳腺良性及恶性病变的ADC值及图像信噪比（SNR）随b值的变化规律，探讨1．5TMR乳腺DWI合理的b值取值范围。方法对32例经病理证实的乳腺病变（恶性18例，良性14例）及对侧正常腺体进行乳腺MR检查，采用EPI—DWI序列；b值分别采用0、50、100、200、400、600、800、1000、1200、1400、1600、1800、2000、2200、2400、2600s／mm^2。测量不同b值下水模、正常乳腺腺体、乳腺良性及恶性病变的平均ADC值和图像SNR，采用Pearson相关分析法分析不同b值时的变化规律。结果DWI的SNR均随b值的增加逐渐下降，二者呈负相关（r=-0．802，P〈0．01），乳腺良、恶性病变的ADC值均随着b值的增加而下降（r=-0．923和-0．855，P〈0．01）；当b值取800～1000s／mm^2时，恶性病变与良性病变和正常腺体之间的ADC值差异最大（0．7×10^-3mm^2／s）；当b值〉1400s／mm^2，差异逐渐减小。结论取b值800～1000s／mm^2时，既能取得良好的图像质量，又能有效地鉴别乳腺良、恶性病变，是1．5TMR乳腺DWI最合理的b值取值范围。

Objective To optimize the b-value of breast diffusion-weighted MRI （DW-MRI） at 1.5T by applying a range of b values and comparing the apparent diffusion coefficient （ADC） and signal-to-noise ratio （SNR） on a phantom, disease-fi＇ee breast tissues, and benign and malignant lesions. Methods A phantom and 32 women with pathologically confirmed malignant （ 18 ） and benign （ 14 ） lesions were examined using EPI-DWI with different b values on a 1.5 T MR scanner. The b-value of EPI-DWI was 0, 50, 100, 200, 400, 600, 800, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, and 2600 s/mm^2, respectively. The SNR and ADC values of the phantom, disease-free breast tissues, and benign and malignant lesions were measured. The correlation between the b-value and ADC or SNR of each image was analyzed. Results The SNR of DWI decreased as the b-value increased, showing an inverse correlation （r = -0. 802,P 〈 0. 01 ）. The ADC values of benign and malignant lesion decreased as the b-value increased （r = -0. 923 and -0. 855,P 〈 0.01 ）. The maximum difference in ADC between malignant and benign lesions was observed when the b-value is between 800 and 1000 s/mm^2 and diminished when the b-value was greater than 1400 s/mm^2. Conclusion For good image quality and valid differentiation between malignant and benign lesions, the optimized b-value of DWI at 1.5 T is between 800 s/mm^2 and 1000 s/mm^2.