Effect Of The Mesh Paddle On The Quality Of Ultrasound Image In A Dual-modality Breast Imaging System

Background and objectiveThe detection and diagnosis of breast cancer in the initial stage is the primary goal of breast imaging. It has been demonstrated that at the time of detection the smaller the lesion is, the better the prognosis is. At present, mammography is the screening method of choice in the evaluation of the breast, and also is the gold standard for detecting breast cancer. Breast ultrasonography is a second line diagnostic tool, which is useful in depicting small, node-negative breast cancers not seen on mammography. The combined use of mammography and ultrasound led to statistically significant improvement in detection of malignant lesions compared with the single use of mammography. However, the ultrasound imaging is performed in a different geometry than the mammograms, which make it difficult to correlate lesions between the two modalities. At least 10% of the time, there is a discrepancy between the lesions detected with the two modalities. A system combining ultrasound and X-ray makes it easy to correlate lesions between the two modalities in the same imaging geometry.However, the materials of the conventional compression paddles limited success of the system. Therefore, a better compression paddle is needed for both mammographic and sonographic requirements. In this study, the mesh paddle was used as a substitute for conventional paddle. The effect of the mesh paddle and conventional TPX paddle was compared on the quality of ultrasound image and the ease of coupling for the ultrasound scan in a dual-modality breast imaging system.Materials and methodsCompression paddlePreliminary study revealed that the TPX paddle with the thickness of 2.5 mm (Fig. la) was acoustically competitive and common for use with dual-modality system. The mesh paddle assessed in the study is weaved by fishing line with diameter of about 0.18 mm, which is similar to a fine mesh tennis racquet with 6 mm pores. Estimation of the mesh paddle on the ultrasoundBetween April and July 2010, a total of 41 consecutive female patients involving 43 breast solid masses (9 malignant,34 benign solid) had breast ultrasonography through different paddles and lack of a compression paddle.All the ultrasound images were obtained using a Philips iU22 ultrasound system. At the beginning of the procedure, a radiologist conducted a direct-contact ultrasound scan across the lesion of the breast to determine the appropriate imaging view, and then marked the position of the transducer on the breast to make sure the images obtained through the mesh and TPX paddle in the same section.Contrast and contrast-to-noise ratio (CNR) between breast tissue and lesion signal levels were calculated for each of the 43 lesions scanned in this study. Signal strength measurements were also made for each of the 43 lesions.The acquired color Doppler images were analyzed to quantify the perimeter and internal blood supply of the lesions by measuring the number of color pixels in the ROI. Evaluating the mesh paddle in the dual-modality systemThe tests were carried out in the combined system using a Philips iU22 ultrasound scanner and a commercial full field digital mammography (FFDM) system (Siemens Mammomat Novation(DR), Siemens AG Medical Solutions, Erlangen, Germany) unit. In the dual-modality system, ten breasts of five volunteers randomly selected from the above-mentioned 41 patients were imaged with ultrasound in the cranial-caudal (CC) view through the mesh and TPX paddle respectively. The coupling time and image quality were analyzed through different paddles to compare the effect of the mesh and TPX paddle on the quality of ultrasound image and the ease of coupling for the ultrasound scan in the dual-modality imaging system.Two radiologists blindly ranked the images of corresponding through the mesh paddle and TPX paddle scans on a scale of 1 to 5, with a score of "1" being "the image quality of through mesh paddle scan was much poorer than its corresponding through TPX paddle scan", a score of "3" being "equivalent image quality" and "5" being "the image quality of through mesh paddle scan was much better than its corresponding through TPX paddle scan".Data Collection and AnalysisTo assess the differences through the mesh paddle, TPX paddle and lack of a compression paddle, data were analyzed in a SPSS database version 10.0 (SPSS Inc, Chicago, IL). The contrast, CNR and signal strength obtained by grey scale ultrasound and the number of color pixels obtained by color Doppler imaging were compared with a paired 2-tailed Student's t test, with aP<0.05 considered to be significant.Results1. Compared with lack of a paddle, the contrast and CNR through the mesh paddle degraded slightly (P>0.05). There were significant differences in contrast, CNR between lack of a paddle and TPX paddle (P<0.01), and between the mesh paddle and TPX paddle (P <0.01). Compared with lack of a compression paddle, the signal strength through the mesh paddle and TPX paddle degraded, and the TPX paddle exhibited more signal losses than the mesh paddle (P<0.001).2. For 22 masses displaying flow signals in direct-contact scans, the display ratios of flow signals through the mesh and TPX paddle were separately 100%and 40.91%. Compared with lack of a paddle, the number of color pixels for mesh paddle decreased slightly (P >0.05), whereas the number of color pixels for TPX paddle decreased apparently (P 0.001).3. The coupling time with the mesh paddle was 14.09±1.04s, and that with the TPX paddle was 40.30±0.81s (P<0.001). Compared with the TPX paddle, the coupling time through the mesh paddle was shorted by 65.04%. 4. The mean rating of the ten breasts images quality was 4.2 on a scale of 1 to 5. The reader study showed that the quality of the images obtained through the mesh paddle was better than that through TPX paddle.ConclusionsThe mesh paddle can efficiently reduce the acoustic attenuation, ease the coupling between the breast and the ultrasound transducer and improve the quality of the ultrasound. It may provide a better choice for the compression paddle to solve the difficulties in the dual-modality system.