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Thứ Hai, 13 tháng 2, 2017

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 Limitations  of  ABVS  Technique [extracted from  3D Automated  Breast Volume Sonography,  A  Practical  Guide,  Veronika Gazhonova  © Springer International Publishing Switzerland   2017] 

ABVS  technology  has  some  limitations. Automated breast ultrasound is limited in women with macromastia and pronounced ptosis. Isobe et al. pointed out some difficulties in the scanning of large breasts and the retroareolar area despite the large scanning surface. Furthermore, they presume that even with optimal scanning technique, the peripheral areas of the breast parenchyma are not fully covered by ABVS.
Therefore, some areas of the breast, such as deep lateral areas, do not have proper visualization and complete coverage using ABVS. The scanning field of 17 cm does not allow the inclusion of the entire volume of the breast in a single scan for patients with a bracup size (F) or more (Fig.  5.1 ). This reduces the diagnostic value of ABVS when compared with conventional two-dimensional ultrasound. In our view this arises only with coronal scans, in which the outer portions of the gland are not so compressed and could not be evaluated so thoroughly, but we used some special projections in which a patient lies on her side for scanning the lateral portion of the gland or shifting the breast laterally for scanning medial portions of the gland. Similarly we use the technique of shifting the breast down for scanning the upper part and upward for scanning the inferior part. If a mass is detected in the lower or inner quadrants on the mammogram, it is possible to supplement the study by scanning from the mediolateral view or separately capture the lower quadrants. These scanning principles will result in better visualization of the tissues of the subsequent zones. Therefore, we recommend in such cases to follow the principle of sequential study of all zones of interest with maximum capture of all areas and obtaining additional views of quadrants not included in the initial view.
   There is no experience in examining the axillary region with ABVS, although it is of special importance in breast cancer diagnosis. Today, sentinel node biopsy is the standard therapy for women at the preoperative stage with a negative nodal status, which requires ultrasound of the axilla. Furthermore, lymph node alterations may be the first sign in mammographically and/or sonographically occult breast cancer or other malignant diseases. Therefore, additional conventional ultrasound of the axilla would be necessary after a suspicious ABVS scan. This drawback of ABVS is noted by all researchers, and this limits the possibility of using this method for screening. To avoid such false-negative cases, the patient should initially be examined with conventional 2D ultrasound followed by an ABVS study with additional scanning of the breast’s axillary process, which may reveal multifocal tumor growth in the patient.
   Additionally, shadowing artifacts occur in the retroareolar region despite the special algorithm (adaptive nipple shadow reduction tool) used for reduction of nipple shadowing and to a certain extent in the remaining breast volume. Therefore, a certain proportion of breast parenchyma may be lost in the volume data. This may reduce the diagnostic potential in comparison to handheld  ultrasound. As previously mentioned, a special technique for acquiring volumetric data was suggested. Maximum lateralization of the nipple is used to avoid these artifacts and reduces no-show zones (Fig. 5.3 ).
   During an automatic scan, movement or conversation artifacts arise in some cases, which adversely affect the perception of 3D data (Figs.5.4  and 5.5). The lack of contact of the scanning membrane with the skin of the gland can cause some artifacts in the so-called “dumb” zone, such as in scar deformity of the breast after lumpectomy or sectoral resection, in severe retraction of the nipple and breast deformation in infiltrating breast cancer, in breast implants, in expanders, and sometimes in cases of severe pain in mastitis (Fig. 5.6). In these cases, you should conduct an examination using the standard 2D technique.  The ABVS technique, despite its high sensitivity, has low specificity with a high number of false-positive findings. A large number of time- consuming second-look ultrasound examinations have to be taken into account. The lack of standardized interpretation criteria and technical artifacts in the volume data set lead to low specificity of 52.8 %. In all studies the proportion of cases to controls was not the representative of the whole population. Therefore, the results concerning the sensitivity, specificity, and rate of second-look ultrasounds cannot be applied to the general population and hence must be carefully interpreted. This problem may be solved through second readings by an independent examiner. To reduce the number of false-positive findings, we recommend using the full range of diagnostic ultrasound possibilities included in the US device in one study. Some studies include only ABVS in the examination protocol without HHUS data. And with that the ability to immediately further  explore a questionable lesion by modifying factors such as the compression, the orientation of the probe, and the machine’s setting while acquiring the image in real-time Doppler imaging or sonoelastography is lost. 
 As we have already mentioned, 2D ultrasound is the first step with additional options for analysis of the blood supply to the tumor and its density assessment, and ABVS is the second step to detect microcalcifications and “retraction” phenomenon. This, in turn, somewhat increases the length of the study of the breasts but also increases the specificity of the ultrasound examination. In terms of the future broad clinical application of the ABVS technique for the diagnosis of breast cancer, the relatively small number of false-negative cases, evidenced by numerous studies, is encouraging.
 Despite the well-known advantages, ABVS is a time-consuming technique, just like conventional two-dimensional ultrasound. This technique requires the training of not only medical but also nursing staff to reduce the technical load of the procedures on the physician. A number of works on ABVS pointed out that 3D ABVS takes less time than conventional 2D ultrasound . But no full answers were found concerning examination and interpretation time. While exploring these techniques, the time for acquisition and for analysis was significantly  reduced when we gained experience, but still the time of the study was not less than 30 min. Clinical experience shows that more time is consumed by analysis and comparison with X-ray mammogram data. We observed a direct correlation of increased study time with a larger breast size, changes on the X-ray mammogram, and suspected malignancy. If multiple lesions are present in the breast, the time of the study was prolonged.
 With the 3D US technique, questions of storage of digital information arise. The mean volume of a single study is an average of about 2 GB. Unlike digital breast tomosynthesis, one has to maintain tomographic information of six standard views, and this requires a more optimal technical solution. In this regard it is not clear at the moment how the digital archives of ABVS tomograms, mammograms, and digital breast tomosynthesis will be matched. In addition, the widespread use of this technique is still limited by the small number of ultrasonic devices with the function of automatic volume scanning.
 All the above mentioned factors mean that at the moment ABVS must be regarded as an experimental approach. ABVS is far from being accepted in medical practice, and its application still lacks solid data from comprehensive studies.

 In order to move this technique forward, there is a definite need for further research, prospective studies recruiting larger patient’s cohorts, and a multicenter design with multi-observer analysis.

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