Diagnostic Value of ARFI (Acoustic Radiation Force Impulse) in Differentiating Benign From Malignant Breast Lesions

Rationale and Objectives

The aim of this study was to correlate acoustic radiation force impulse (ARFI) imaging velocities with the pathology results and to evaluate the ability of ARFI in distinguishing benign from malignant breast lesions.

Materials and Methods

B-mode ultrasonography (US) and ARFI were performed in patients with previously diagnosed and selected breast lesions for biopsy. Shear wave velocity (SWV) was measured inside lesions and in the surrounding parenchyma ( m/s ). SWV measurements as well as lesion-to-parenchyma ratio (LPR) were compared between benign and malignant lesions, and receiver operating characteristic (ROC) curves were plotted. Two blinded readers independently classified the lesions as benign or malignant in two separate reading sessions, one using B-mode US alone and the other using a combined set of B-mode US and ARFI.

Results

Eighty-one patients with a total of 92 breast lesions were included (57 benign and 35 malignant nodules). SWV inside lesions were significantly higher for malignant neoplasms compared to benign (medians of 9.1 m/s vs 3.5 m/s; P < 0.001). LPR was also significantly higher for malignant lesions (3.0 vs 1.4; P < 0.001). Parenchyma SWV had no differences between groups ( P = 0.071). ROC curves showed a significant discriminative power for lesion SWV (area under the curve [AUC] = 0.980; P < 0.001) and LPR (AUC = 0.954; P < 0.001). For lesion measures, a cutoff of 6.593 m/s was obtained, with sensitivity and specificity of 88.6% and 96.5%, respectively.

Conclusions

ARFI provides quantitative elasticity measurements, adding valuable complementary information to B-mode ultrasound, that can potentially help in breast lesion characterization and assisting the decision for biopsy recommendations.

Introduction

Ultrasonography (US) is a useful technique that has been increasingly used as an important diagnostic tool complement to mammography in differentiating benign from malignant breast tumors . Although US depicts more cancers than mammography alone, it has a considerable number of false-positives, which also leads to a higher number of benign mass biopsies .

In the last decades, US technology has experienced several advances, including real-time elastography, which evaluates tissue stiffness, detecting its displacement after slight manual compression . Information is converted into color-scale images and is superimposed to B-mode images. Knowing that malignant tumors tend to be stiffer and that benign masses are usually softer , real-time elastography is used as a complementary technique in addition to B-mode sonography, increasing its specificity (83.1% vs 76.9% for B-mode US alone) . However, this technique has some limitations. The first, and perhaps the most important, is the fact that it is operator dependent and has a higher interobserver variability, because it requires compression with the probe, preventing lateral or angulated movements, to obtain good quality images . Besides variability caused by technical limitations, there is also a certain degree of subjectivity in image interpretation . Another limitation is that real-time elastography only provides qualitative information, although ratios between the lesion and surrounding breast parenchyma can be calculated .

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Materials and Methods

Patients and Lesions

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B-Mode Ultrasound and ARFI Acquisition

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Readers and Reading Procedures

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Statistical Analysis

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Results

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Table 1

Histopathologic Diagnosis and Dimensions of Breast Lesions

Malignant Lesions Tumor histology Histologic grade 1 15 2 13 3 7Total35 Tumor type Ductal 31 Lobular 3 Metaplastic 1Total35 Benign Lesions Tumor type Fibroadenoma 34 Intraductal papilloma 4 Complex cyst 7 Hamartoma 4 Tubular adenoma 1 Radial scar 1 Granuloma 2 Other ANDI \* 4Total57 Lesion dimensions (mm) ≥ 5 and < 10 21 ≥ 10 and < 15 28 ≥ 15 and < 20 18 ≥ 20 and < 25 13 ≥ 25 11Total91

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ARFI Quantification

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Table 2

ARFI Measurements for Benign and Malignant Lesions

Measurement Benign Malignant_P_ Value_n_ = 57n = 35 Inside lesion

(m/s) Mean ± SD 3.8 ± 1.41 8.7 ± 1.49 <0.001 \* Median (IQR) 3.5(2.1) 9.1(1.7) Parenchyma

(m/s) Mean ± SD 2.6 ± 0.65 2.8 ± 0.57 0.160 † Median (IQR) 2.4(0.95) 2.8(0.84) LPR Mean ± SD 1.5 ± 0.52 3.3 ± 1.20 <0.001 \* Median (IQR) 1.4(0.59) 3.0(1.37)

ARFI, acoustic radiation force impulse; IQR, interquartile range; LPR, lesion-to-parenchyma ratio; SD, standard deviation.

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Table 3

AUC, Cutoff, Sensitivity, and Specificity for ARFI Measurements

Measurement AUC (SE)P Value Cutoff Sensitivity (%) Specificity (%) Inside lesion 0.980 (0.011) <0.001 6.593 m/s 88.6 96.5 Parenchyma 0.597 (0.060) 0.118 2.527 m/s 71.4 54.4 LPR 0.954 (0.020) <0.001 2.181 88.6 93.0

ARFI, acoustic radiation force impulse; AUC, area under the curve; LPR, lesion-to-parenchyma ratio; SE, standard error.

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Comparison between Readers

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Table 4

BI-RADS Classification by Reader

BI-RADS 3 BI-RADS 4 BI-RADS 5 Reader A (B-mode US) 28 55 9 Reader A (B-mode US + ARFI) 32 51 9 Reader B (B-mode US) 23 60 9 Reader B (B-mode US + ARFI) 40 43 9

ARFI, acoustic radiation force impulse; BI-RADS, Breast Imaging - Reporting and Data System; US, ultrasonography.

Table 5

Sensitivity and Specificity for Each Reader

B-mode US (%) B-mode US + ARFI (%) Reader A Sensitivity 100 100 Specificity 49.1 59.6 Reader B Sensitivity 100 100 Specificity 40.4 70.2

ARFI, acoustic radiation force impulse; US, ultrasonography.

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Discussion

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Conclusion

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Acknowledgments

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References

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Diagnostic Value of ARFI (Acoustic Radiation Force Impulse) in Differentiating Benign From Malignant Breast Lesions

Rationale and Objectives

Materials and Methods

Results

Conclusions

Introduction

Materials and Methods

Patients and Lesions

B-Mode Ultrasound and ARFI Acquisition

Readers and Reading Procedures

Statistical Analysis

Results

ARFI Quantification

Comparison between Readers

Discussion

Conclusion

Acknowledgments

References

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