Breast Cancer

, Volume 15, Issue 3, pp 200–204

Current improvements in breast ultrasound, with a special focus on elastography

Authors

    • Graduate School of Human SciencesUniversity of Tsukuba
  • Ei Ueno
    • Graduate School of Human SciencesUniversity of Tsukuba
Special Feature New trends in breast diagnostic imaging

DOI: 10.1007/s12282-008-0052-1

Cite this article as:
Tohno, E. & Ueno, E. Breast Cancer (2008) 15: 200. doi:10.1007/s12282-008-0052-1

Abstract

Current improvements in the area of breast ultrasound are described. Digital beam formers contributed to improving both contrast and special resolution of B-mode images and enabled other techniques. Four-dimensinal images and CAD are still in progress. Elastography may reduce false-positives and unnecessary interventional procedures, especially in nonsymptomatic patients.

Keywords

UltrasoundBreastElastography

Introduction

Breast ultrasound is one of the basic modalities for diagnosing diseases of the breast. In this paper, we discuss recently introduced technologies effective for lesion characterization and describe elastography results obtained in our institute.

B-mode images

B-mode images are fundamental to the analysis of lesion morphology. Of course, it is important to realize that only the ultrasonic characteristics of the lesions can be observed. The introduction of digital beam forming has improved the quality of B-mode images. In digital beam formers, analog/digital conversion is done at the level of the received signals in each element. This has led to advancements in many other techniques, such as digital focusing as well as harmonic imaging, flow imaging, and elastography.

In matrix array transducers, the elements are arranged in a multiple array rather than a single one, and this has resulted in improved resolution in an elevational direction.

Initially, harmonic imaging was not applied to superficial organs such as the breast because secondary harmonic waves are generated as the fundamental waves are transmitted. However, the introduction of harmonic imaging has reduced artifacts and improved image contrast. Compound images are formed by the combination of ultrasound beams of different angles. This technique has also contributed to the improvement of contrast, particularly by reducing speckle noise, and to the visualization of lesion outlines (Fig. 1).
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Fig. 1

Conventional image (a) and compound image, so-called sono CT® (b)

To improve resolution, the width of transducers tends to decrease. An extended field-of-view (Fig. 2) has developed to compensate this and helps in the assessment of large masses or non-mass-forming lesions, thereby enabling the comparison of lesions with other parts of the breast, which is important for diagnosis.
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Fig. 2

Extended field-of-view helps to understand that there is a non-mass forming abnormality in the medial side of the breast

Flow imaging

Malignant lesions tend to be accompanied by neovascularity, and information about vascular flows in the lesion helps differentiate breast cancers from benign lesions. Because the sensitivity for flow signals has increased, it is possible to detect not only the flow signals of malignant lesions, but also those of benign lesions. To differentiate between these lesions, morphological or quantitative analysis is required [1]. The use of intravenous contrast enhances information regarding vascularity, but the use of new contrast agents that remain in the circulation for longer is not yet permitted for breast lesions by Japanese health insurance.

Four-dimensional probe

Four-dimensional images are obtained by moving (or shaking) the transducer very fast and reconstructing 3-D images almost in real time. This technique can be used to analyze lesion morphology from different planes (Fig. 3) and to guide needles during intervention. The coronal section is very helpful for understanding the desmoplastic reaction caused by breast cancer. The inversion method can be used to better visualize breast cancers that are observed only as vague hypoechoic areas and to visualize intraductal components around the main tumors.
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Fig. 3

Three-dimensional images reconstructed by a 4-D transducer

CAD (computer-aided diagnosis or detection)

Ultrasound examination is commonly performed in real time, and the diagnosis depends on the examiner. To aid diagnosis, CAD is now conducted via the analysis of substantial data [2]. A trial for studying the effectiveness of ultrasound in breast screening is currently underway. If ultrasound is used for screening, whole-breast automatic scanning with CAD may be useful when there is a shortage of staff and for the prevention of erroneous oversight.

Elastography

Most breast cancer lesions are palpable because they are harder than the surrounding breast tissues or benign lesions. The detection of breast cancer in the early stage implies its identification before the lesions are palpable. Many benign lesions are nonpalpable, and the detection of nonpalpable cancers, therefore, often leads to the detection of benign lesions, some of which are morphologically similar to small breast cancers. Even if they are not palpable, breast cancers maintain their characteristic of elasticity, and this provides useful information in addition to the morphological information obtained from B-mode images. We first reported the usefulness of elastography in breast diseases [3]. Ultrasound elastography does not directly demonstrate physical elasticity, but demonstrates the relative degree of tissue strain when subtle compression is applied. To express the degree of ultrasound elasticity, we proposed the elastography score and the FLR (fat lesion ratio). The elasticity score is shown in Fig. 4. In our first study, the elasticity scores of benign and malignant diseases overlapped. However, we believe that if the lesion is as soft as the surrounding breast tissue (i.e., score 1), there is a high probability that it is benign. Therefore, in this study, we analyzed lesions that had the score 1.
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Fig. 4

Elastography scores (cases shown are all cancers)

Materials and methods

Between April 2005 and March 2006, 1,533 breast ultrasounds were performed in Tsukuba University Hospital. Elastography was subsequently applied in routine ultrasound examinations mainly for lesions that were suspected to be malignant or difficult to diagnose. Elastography images were obtained using a digital ultrasound scanner (EUB-8500; Hitachi Medical, Tokyo, Japan). The elastography scores were judged at the time of examination and noted in the ultrasound reports. We analyzed the data retrospectively, but the elastography scores were determined prospectively. When the same lesions were examined twice or more in the indicated period, the elastography scores obtained in the first examination were used. When multiple masses were observed close to each other, especially in the same quadrant, the largest lesions were selected because one-to-one correspondence with histological results is otherwise difficult. Finally, the objects of this study were 517 lesions in 417 cases.

If the lesions were judged as having score 1, they were not subjected to either additional interventional diagnosis (fine-needle aspiration cytology and/or core biopsy) or follow-up ultrasound examination. So the number of the cases with score 1 that were subjected to interventional diagnosis or follow-up ultrasound after more than 6 months is relatively small and counted to be 70 lesions.

Results

Of the 517 lesions, 146 (29%) were judged as having score 1; 133 (26%), score 2; 60 (12%), score 3; 84 (16%), score 4; and 59 (12%), score 5 (Fig. 4). Further, 122 lesions were proven to be malignant, and the positive predictive values of scores 1–5 were 3, 6, 23, 58, and 80%, respectively. If the score 1 lesions were limited to those that were subjected to either interventional diagnosis (by fine-needle aspiration cytology and/or core biopsy) or follow-up ultrasound examination, the negative predictive value decreased from 97 to 93% (Fig. 5).
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Fig. 5

Breast cancer was suspected from the B-mode image (a), but the lesion was score 1 (b). Core-needle biopsy proved the lesion was not a cancer

The analysis of the score 1 lesions that were subsequently proven to be cancerous is shown in Table 1. In all cases, the lesions were not palpable (Table 2).
Table 1

Distribution of each score

 

No. of lesions (%)

No. of malignant lesions (%)

Score 1

146 (29)

5 (3)

Score 2

133 (26)

8 (6)

Score 3

60 (12)

14 (23)

Score 4

84 (16)

49 (58)

Score 5

59 (12)

45 (80)

Total

512 (100)

121

Table 2

Summary of the breast cancer cases with score 1

Case no.

Ultrasound size of the lesion (mm)

Pathological diagnosis

Additional information

1

9.3

DCIS

Opposite breast cancer postoperative state

2

3.1

IDC

Bloody nipple discharge

3

4.9

IDC (predominant intraductal component)

Multiple masses in the same segment

4

6.4

IDC

 

5

11.3

DCIS

Bloody nipple discharge

IDC invasive ductal carcinoma

Discussion

Ultrasound equipment that can also be used to conduct real-time elastography is now commercially available, and the manner in which to exploit elasticity data is under discussion. In the previous report, we reported that when a cutoff point between scores 3 and 4 was used, elastography had 86.5% sensitivity, 89.8% specificity, and 88.3% accuracy [3]. Zhi et al. [4] recently reported even better results: ultrasound elastography was found to be the most specific (95.7%) and had the lowest false-positive rate (4.3%). Elastography scores certainly provide additional information to that provided by B-mode images. In this paper, we analyzed cases in which the elastography score was 1. We focused on score 1 lesions for the following reasons. Ultrasound detects many nonpalpable lesions, and it is less specific when used for breast screening. Elastography may be helpful to obtain additional information based on which we can decide whether we should request the women to return for additional examination. Moreover, in clinical situations, elastography may be useful for determining whether to apply interventional methods or conduct follow-up. In addition, although it is sometimes difficult to differentiate between scores 2 and 3 (because their difference is distribution of blue area), it is easy to judge a lesion as having score 1 because no blue area is observed. In our first report, there were no score 1 lesions, but at that time, the scores were judged by only two persons with experience in elastography. The results provided in this paper were obtained by several examiners who used elastography daily. Our results showed that the elastography score is less helpful in cases of bloody nipple discharge and ductal carcinoma in situ (DCIS) and that very few invasive ductal carcinomas have a score of 1.

Conclusions

Recent improvements in breast ultrasound equipment technology have been overviewed. Breast ultrasound is still being developed further, and this will lead to better diagnosis.

Copyright information

© The Japanese Breast Cancer Society 2008