Rationale and Objectives
Breast 3.0 T magnetic resonance diffusion-weighted imaging (MR-DWI) of benign and malignant lesions were obtained to measure and calculate the signal-to-noise ratio (SNR), signal intensity ratio (SIR), and contrast-to-noise ratio (CNR) of lesions at different b-values. The variation patterns of SNR and SIR were analyzed with different b-values and the images of DWI were compared at four different b-values with higher image quality. The effect of SIR on the differential diagnostic efficiency of benign and malignant lesions was compared using receiver operating characteristic curves to provide a reference for selecting the optimal b-value.
Materials and Methods
A total of 96 qualified patients with 112 lesions and 14 patients with their contralateral 14 normal breasts were included in this study. The single-shot echo planar imaging sequence was used to perform the DWI and a total of 13 b-values were used: 0, 50, 100, 200, 400, 600, 800, 1000, 1200, 1500, 1800, 2000, and 2500 s/mm 2 . On DWI, the suitable regions of interest were selected. The SNRs of normal breasts (SNR normal ), SNR lesions , SIR, and CNR of benign and malignant lesions were measured on DWI with different b-values and calculated. The variation patterns of SNR, SIR, and CNR values on DWI for normal breasts, benign lesions, and malignant lesions with different b-values were analyzed by using Pearson correlation analysis. The SNR and SIR of benign and malignant lesions with the same b-values were compared using t-tests. The diagnostic efficiencies of SIR with different b-values for benign and malignant lesions were evaluated using receiver operating characteristic curves.
Results
Breast DWI had higher CNR for b-values ranging from 600 to 1200 s/mm 2 . It had the best CNR at b = 1000 s/mm 2 for the benign lesions and at b = 1200 s/mm 2 for the malignant lesions. The signal intensity and SNR values of normal breasts decreased with increasing b-values, with a negative correlation ( r = −0.945, P < 0.01). The mean SNR values of benign and malignant lesions were negatively correlated ( r = −0.982 and −0.947, respectively, and P < 0.01), gradually decreasing with increasing b-values. The mean SIR value of benign lesions gradually decreased with increasing b-values, a negative correlation ( r = −0.991, P < 0.01). The mean SIR values of malignant lesions gradually increased with increasing b-values between 0 and 1200 s/mm 2 , and gradually decreased with increasing b-values ≥ 1500 s/mm 2 . For b-values of 600, 800, 1000, and 1200 s/mm 2 , the sensitivity and specificity of SIR in identifying benign and malignant lesions gradually increased with increasing b-values, peaking at 1200 s/mm 2 .
Conclusions
Breast DWI had higher image quality for b-values ranging from 600 to 1200 s/mm 2 , and was best for b-values ranging from 1000 to 1200 s/mm 2 . The SIR had the highest diagnostic efficiency in differentiating benign and malignant lesions for a b-value of 1200 s/mm 2 .
Introduction
Diffusion-weighted imaging (DWI) in magnetic resonance imaging (MRI) plays an important role in the diagnosis and differential diagnosis of breast lesions as well as in the evaluation of therapeutic efficacy in breast cancer . DWI can provide information at the tissue, cellular, and molecular levels, which is often used for diagnosis and prognosis evaluation in breast cancer . Therefore, the selection of DWI parameters for application and studies of its association with diagnostic efficacy have gained increasing attention . B-value is one of the most important parameters of DWI. B-value selection is closely related to the image quality of DWI and its ability to identify lesions. Currently, there are no widely accepted selection criteria for the optimal b-value for breast DWI at 3.0 T MR scanner . Therefore, the study of b-value optimization is of important clinical interest.
This study used multiple b-values to obtain DWI of normal breasts to measure and calculate the signal-to-noise ratio (SNR) for normal mammary glands. Diffusion-weighted images of benign and malignant lesions were obtained to measure and calculate the SNR, signal intensity ratio (SIR), and contrast-to-noise ratio (CNR) of lesions at different b-values to analyze the variations of SNR, SIR, and SIR. Furthermore, we compared diffusion-weighted images at four different b-values with higher image quality. The effect of SIR on the differential diagnostic efficiency of benign and malignant lesions was compared using receiver operating characteristic curves to provide a reference for obtaining the best quality of DWI.
Materials and Methods
Patient Data
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MRI Equipment and Measurement Parameters
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Image Quality Grading and Evaluation Criteria
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CNR=Slesions−Stissueσ2lesions+σ2tissue√ C
N
R
=
S
lesions
−
S
tissue
σ
2
lesions
+
σ
2
tissue
where S lesions is the measured signal intensity of lesions, S tissue is the signal intensity of normal tissue surrounding the lesions of the same level, and σ 2 lesions and σ 2 tissue are the standard deviation of intensity lesions and normal tissue .
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Statistical Methods
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Results
Grouping of Breast Diseases and Evaluation of Image Quality
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TABLE 1
Comparison of Image Quality Gradings for 3.0 T DWI Performed with Different b-Values
b-Values (s/mm 2 ) 0–400 (Average) 600 800 1000 1200 1500 1800 2000 2500 Grade A 98 94 90 89 84 72 69 58 45 Grade B 14 18 22 23 28 38 41 50 62 Grade C 0 0 0 0 0 2 2 4 5
DWI, diffusion-weighted imaging.
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Variation Patterns of SNR and SIR Values on Diffusion-weighted Images
Variation Patterns of Mean SNR Values of the Normal Mammary Glands
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Variation Patterns of Mean SNR Values of Benign and Malignant Lesions
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Variation Patterns of Mean SIR Values of Benign and Malignant Lesions
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Comparison of SNR and SIR Values of Benign and Malignant Lesions with Different b-Values (600, 800, 1000, and 1200) and Evaluation of Diagnostic Efficiency
Comparison of SNR and SIR Values of Diffusion-weighted Images of Benign and Malignant Lesions
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TABLE 2
Comparison of SNR Values of Benign and Malignant Lesions ( t Test)
b-Values (s/mm 2 ) 600 800 1000 1200 Benign (mean ± SD) 132.73 ± 3.41 105.50 ± 1.29 84.29 ± 1.76 72.28 ± 4.18 Malignant (mean ± SD) 135.23 ± 2.09 108.60 ± 1.59 86.90 ± 1.64 77.07 ± 1.80t value −4.81 −16.08 −7.71 −7.99P value <0.01 <0.01 <0.01 <0.01
SD, standard deviation; SNR, signal-to-noise ratio.
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TABLE 3
Comparison of SIR Values of Benign and Malignant Lesions ( t Test)
b-Values (s/mm 2 ) 600 800 1000 1200 Benign (mean ± SD) 2.18 ± 0.15 2.13 ± 0.20 2.08 ± 0.14 1.96 ± 0.15 Malignant (mean ± SD) 2.56 ± 0.14 2.60 ± 0.14 2.65 ± 0.13 2.68 ± 0.13t value −155.05 −185.75 −206.01 −221.91P value <0.01 <0.01 <0.01 <0.01
SD, standard deviation; SIR, signal intensity ratio.
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Evaluation of Differential Diagnostic Values Using SIR for Benign and Malignant Lesions
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TABLE 4
Evaluation of Diagnostic Efficiency of SIR Values with Four Different b-Values
b-Values (s/mm 2 ) AUC Cutoff of SIR 95% CI Sensitivity (%) Specificity (%) 600 0.700 2.19 0.575–0.826 67.9 71.4 800 0.745 2.14 0.653–0.837 79.3 66.7 1000 0.772 2.09 0.682–0.862 83.3 75.0 1200 0.805 1.97 0.719–0.891 85.2 82.4
AUC, area under the curve; CI, confidence interval; SIR, signal intensity ratio.
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Discussion
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