http://ivylabprev.kaist.ac.kr/image/demo/top_logo.gif

 

http://ivylabprev.kaist.ac.kr/image/demo/project_title.gif

 

 

http://ivylabprev.kaist.ac.kr/image/demo/project_profile.gif

 

 

http://ivylabprev.kaist.ac.kr/image/demo/profile_title.gif

Generation of Conspicuity-improved Synthetic Image from Digital Breast Tomosynthesis

http://ivylabprev.kaist.ac.kr/image/demo/profile_period.gif

2014 . 02 ~ current

 

 

 

http://ivylabprev.kaist.ac.kr/image/demo/project_overview.gif

 

 

1.   Introduction

 

l  Digital breast tomosynthesis (DBT) is a new 3-D imaging modality that utilizes a limited-angle tomography technology to provide quasi 3-D structural information of the breast.

l  DBT has been found to be superior to the full-field digital mammography (FFDM) in detecting and diagnosing cancerous lesions of breast.

l  Currently, as approved by the U.S. Food and Drug Administrator (FDA), DBT has been used in combination with FFDM.

l  Recent studies  have shown that this combined procedure significantly increases the reader performance in screening practice. However, in combined procedure, the interpretation time of radiologist is increased and the radiation dose to breast being imaged is increased at about twice compared to the that of FFDM alone.

l  To overcome the above drawbacks of combined procedure, recent studies have focused on synthesizing 2-D images from 3-D DBT volume to eliminate the need to acquire a separable FFDM with its accompanying doubled dose rate.

l  If 2-D synthetic image is successfully generated from 3-D DBT volume, we can dramatically reduce the radiation dose rate and shooting time in screening.

l  For this purpose, in this paper, we propose a novel 2-D synthetic image generation method which improves the conspicuity of lesions.

l  The conspicuity of lesions is important in screening because it is related to the radiologists performance.

l  To generate the conspicuity-improved 2-D synthetic image, we utilizes the observation that the boundary of the masses and microcalcifications as well as edge of the vasculature (e.g. venous structures) have large intensity differences with surrounding tissues.

 

 

2.  Proposed Synthetic Image Generation Method

 

In order to generate conspicuity-improved 2-D synthetic image, we select the voxels that have large intensity differences with surrounding tissues. The selection is performed on the proposed conspicuity volume that shows conspicuity of voxels. The details are described in the following subsections.

 

A. Generation of Conspicuity Volume

We generate the conspicuity volume that represents the degree of importance in terms of the conspicuity. We utilize the gradient value of DBT volume. A 3-D gradient magnitude volume  is obtained as follows:

,

(1)

where  denotes the input DBT volume and  is the scaling parameter to assign the weight in depth directional intensity changes.  is set to 2 in the experiment.

The conspicuity volume  is obtained by taking local average of the 3-D gradient magnitude volume as

,

(2)

where symbol  represents the 3-D convolution operation and  denotes the 3-D Gaussian kernel. The parameters of , , and  are set to 3mm in experiment. The local average with the convolution is performed to increase the correlation among neighboring voxels.

 

Figure 1. Selecting the z-index of voxel for a given (x, y) coordinate using values in conspicuity volume.

 

 

B. New Synthetic Image Generation

To generate the conspicuity-improved synthetic images, a voxel is selected in the conspicuity volume, which has maximum value of conspicuity at given location (please see Fig. 1). The z-index of voxel for generating synthetic image can be determined by

,

(3)

The maximum conspicuity index map  is estimated as

,

(4)

where the function denotes the 3-by-3 median filter operation to remove the pepper noise in the maximum conspicuity index map. Finally, each pixel value in the 2-D synthetic image  is determined by selecting the voxel value of the 3-D DBT volume  as follows:

.

(5)

 

 

3. Experiment

 

A. Quality Measurement

1) Global Sharpness

To measure the conspicuity of overall anatomical structures including vasculature, the global sharpness of synthesized images was calculated using the Tenegrad measurement. The Tenegrad measurement is known as the optimal method for evaluating the sharpness of the image. It can be calculated by

,

(6)

where I denotes the synthesized image of MN size,. The global sharpness is increased as details (e.g., vasculatures) are more visible in the image.

 

2) Sharpness of Mass Boundary

To measure the conspicuity of masses in terms of discernibleness from the distinct boundary, the sharpness of mass boundary in synthesized images is defined as follows:

,

(7)

where denotes the margin region obtained by constructing a band of pixels along the boundary of mass.

 

3) Contrast

For the purpose of measuring the conspicuity induced from the intensity difference with surrounding tissues, we measure the contrast of mass lesions. The contrast of mass lesions is given by

,

(8)

where  denotes the mean pixel value in mass lesions and  is the mean of the background pixels in the neighborhood of the object. The contrast is increased when the conspicuity of mass is improved e.g., the intensity difference between mass lesion and background is increased.

 

4) Contrast to Noise Ratio (CNR)

The CNR of microcalcifications in synthesized images was calculated to measure the conspicuity of microcalcifications [2]. The CNR value is defined as

,

(9)

where  denotes the mean pixel value of the selected microcalcifications and  is the standard deviation of the background pixels in the neighborhood of the object. The CNR is increased when the conspicuity of microcalcification is improved, e.g., intensity difference between microcalcifications and background is increased.

 

 

B. Experimental Results

 

l  As shown in the results of the Table I, the image quality of the proposed method outperforms MIP and average projection for all four types of quality indices.

l  As shown in Fig. 2, mass lesions are the best visible in the synthetic image generated by the proposed method. Fig. 3 shows that microcalcification clusters are clearly visible in the proposed synthetic image.

 

 

Table 1. Comparion of Measured Performances of Three Image Synthesizing Methods.

 

Measurement

Synthesizing method

Performance

p-value

Global sharpness

Proposed method

0.01480.0005

 

 

MIP

0.00820.0002

< 0.0001

 

Average projection

0.00240.0001

< 0.0001

 

Sharpness of mass boundary

Proposed method

0.05090.0030

 

 

MIP

0.02270.0015

< 0.0001

 

Average projection

0.00980.0007

< 0.0001

 

Contrast

Proposed method

0.22130.0093

 

 

MIP

0.14210.0065

< 0.0001

 

Average projection

0.17910.0082

0.0012

 

CNR

Proposed method

0.60530.0440

 

 

MIP

0.53430.0396

0.2456

 

Average projection

0.19090.0245

0.0001

 

 

 

 

(a)

(b)

(c)

Figure 2. Synthesized 2-D craniocaudal images demonstrate an irregular and hypoechoic mass with speculated margins in a left breast of woman. Images are generated by (a) the proposed method, (b) the MIP, and (c) the average projection.

 

 

(a)

(b)

(c)

Figure 3. Synthesized 2-D mediolateral oblique images demonstrate clustered distribution of fine linear branching calcifications in a right breast of woman. Images are generated by (a) proposed method, (b) the MIP, and (c) the average projection.

 

4. Conclusion

l  A novel conspicuity-enhanced synthetic image generated from 3-D DBT.

l  Comparative experiments with other synthetic images demonstrated that the lesions were most conspicuous in the proposed synthetic image.

 

 

http://ivylabprev.kaist.ac.kr/image/demo/project_researcher.gif

 

Contact Person: Prof. Yong Man Ro (ymro@kaist.ac.kr)

 

 

http://ivylabprev.kaist.ac.kr/image/demo/project_publication.gif

1.     Seong Tae Kim, Dae Hoe Kim, and Yong Man Ro, Generation of Conspicuity-improved Synthetic Image from Digital Breast Tomosynthesis, International Conference on Digital Signal Processing, 2014.