A new energy-resolved photon-counting mammography (ERPCM) device with a cadmium telluride (CdTe) series detector (JOB Corporation, Japan) is currently being developed. The CdTe series detector can detect higher-energy photons with high sensitivity, enabling the use of high-energy X-rays for imaging. Our previous research, in which we compared ERPCM using high-energy X-rays (tube voltage 50 kV) with general mammography using low-energy X-rays (tube voltage about 30 kV), reported that ERPCM had a higher CNR (contrast-to-noise ratio) than general mammography. The purpose of this study was to examine the magnitude of the CNR using a simulation and ERPCM; especially we would like to examine the CNR when the tube voltage of higher than 50 kV was adopted. In the comparison of the CNRs, It was necessary to pay attention to equalizing the average glandular dose (AGD). Using the simulation and ERPCM, we compared the CNR between images taken at 50 kV and 75 kV under a constant AGD. The simulation phantom was composed of 50% mammary gland and 50% adipose tissue, and contained tumor regions. The thickness of the simulation phantom was varied. We put an acrylic plate (1 mm thickness) on an RMI-156 phantom. Furthermore, we placed the thicker acrylic plate (10, 20, 30, 40 mm) on the 156 phantom and 1 mm-thick acrylic plate to simulate thicker breast. Based on the results from the simulation, in the phantom thickness of 80 mm, the CNR of image taken by 75kV got extremely closer to that taken by 50kV. The advantage of the image taken at 75 kV for the thicker breast was also confirmed in ERPCM.
We have been developing a new mammography device with a cadmium-telluride series energy-resolved photon-counting X-ray detector. Using a photon-counting technique, we examined the sensitivity of the system for differentiating the composition of breast tissue and detecting breast tumors. To differentiate breast tissues, we prepared surgically resected specimens fixed in formalin, consisting of adipose, mammary-gland, and tumor tissues. In order to obtain the values of certain effective atomic numbers, we prepared phantoms with 0%, 50% and 100% simulated mammary-gland tissue. In our imaging system, the X-ray spectrum penetrating the object was measured using three energy bins, and the products of linear attenuation coefficients and thicknesses for the three bins were calculated. These linear attenuation coefficients were properly corrected for beam hardening and normalized, to ignore the thickness. These calculations were applied for each pixel, and the gravity point per ROI (region of interest) was plotted on scatterplots to examine their distribution. Adiposetissue values were similar to known values; however, mammary-gland values were distant from expected values. In most specimens, the tumor points were focused; however, in some specimens, it was difficult to distinguish between tumor and mammary-gland tissues given their close linear attenuation coefficients. Mammary-gland tissues may have been influenced by formalin, given its tubular structure.
In this study, we propose a new image display method to obtain high contrast-to-noise ratio (CNR) using energy resolved photon-counting mammography (ERPCM) with a cadmium telluride (CdTe) series detector manufactured by JOB CORPOLATION. The CdTe series detector can detect high-energy photons with high sensitivity, enabling users to image with high-energy X-rays. Using this detector, it is possible to reduce the dose given to a patient while increasing the CNR. First, the spectrum was divided into three bins and their corresponding linear attenuation coefficients were calculated from input and output photon numbers. Further, absorption vector length (AVL) and average absorption length (AAL) were calculated from the linear attenuation coefficients and from thicknesses of objects after beam-hardening correction. We further compared the CNR between ERPCM and general mammography images under the constant average glandular dose (AGD). We imaged an acrylic plate (1 mm thick) on RMI-156 phantom, determined regions of interest (ROIs) on an acrylic plate and background, and calculated the CNR. Our ERPCM generated two types of images: an AVL image and an AAL image. AMULET Innovality manufactured by FUJIFILM generated an integrated image. MicroDose SI manufactured by Philips generated a count image and removed electrical noise by the photon-counting technique. The four images, in order of decreasing CNR, were the AAL image, AVL image, MicroDose image, and AMULET image. The proposed method using ERPCM generated an image with higher CNR than images using general mammography under the constant AGD.
In this study, we proposed a method for detecting microcalcifications and tumor tissue using a cadmium telluride (CdTe) series linear
detector. The CdTe series detector was used as an energy resolved photon-counting (hereafter referred to as the photon-counting)
mammography detector. The CdTe series linear detector and two types of phantom were designed using a MATLAB simulation. Each
phantom consisted of mammary gland and adipose tissue. One phantom contained microcalcifications and the other contained tumor
tissue. We varied the size of these structures and the mammary gland composition. We divided the spectrum of an x-ray, which is
transmitted to each phantom, into three energy bins and calculated the corresponding linear attenuation coefficients from the numbers
of input and output photons. Subsequently, the absorption vector length that expresses the amount of absorption was calculated. When
the material composition was different between objects, for example mammary gland and microcalcifications, the absorption vector
length was also different. We compared each absorption vector length and tried to detect the microcalcifications and tumor tissue.
However, as the size of microcalcifications and tumor tissue decreased and/or the mammary gland content rate increased, there was
difficulty in distinguishing them. The microcalcifications and tumor tissue despite the reduction in size or increase in mammary gland
content rate can be distinguished by increasing the x-ray dosage. Therefore, it is necessary to find a condition under which a low
exposure dose is optimally balanced with high detection sensitivity. It is a new method to indicate the image using photon counting
technology.
Energy resolved photon-counting mammography is a new technology, which counts the number of photons that passes through an object, and presents it as a pixel value in an image of the object. Silicon semiconductor detectors are currently used in commercial mammography. However, the disadvantage of silicon is the low absorption efficiency for high X-ray energies. A cadmium telluride (CdTe) series detector has a high absorption efficiency over a wide energy range. In this study, we proposed a method to estimate the composition of the mammary gland using a CdTe series detector as a photon-counting detector. The fact that the detection rate of breast cancer in mammography is affected by mammary gland composition is now widely accepted. Assessment of composition of the mammary gland has important implications. An important advantage of our proposed technique is its ability to discriminate photons using three energy bins. We designed the CdTe series detector system using the MATLAB simulation software. The phantom contains nine regions with the ratio of glandular tissue and adipose varying in increments of 10%. The attenuation coefficient for each bin’s energy was calculated from the number of input and output photons possessed by each. The evaluation results obtained by plotting the attenuation coefficient μ in a three-dimensional (3D) scatter plot show that the plots had a regular composition order congruent with that of the mammary gland. Consequently, we believe that our proposed method can be used to estimate the composition of the mammary gland.
We propose a new mammography system using a cadmium telluride (CdTe) series photon-counting detector, having high absorption efficiency over a wide energy range. In a previous study, we showed that the use of high X-ray energy in digital mammography is useful from the viewpoint of exposure dose and image quality. In addition, the CdTe series detector can acquire X-ray spectrum information following transmission through a subject. This study focused on the tissue composition identified using spectral information obtained by a new photon-counting detector. Normal breast tissue consists entirely of adipose and glandular tissues. However, it is very difficult to find tumor tissue in the region of glandular tissue via a conventional mammogram, especially in dense breast because the attenuation coefficients of glandular tissue and tumor tissue are very close. As a fundamental examination, we considered a simulation phantom and showed the difference between normal breast tissue and tumor tissue of various thicknesses in a three-dimensional (3D) scatter plot. We were able to discriminate between both types of tissues. In addition, there was a tendency for the distribution to depend on the thickness of the tumor tissue. Thinner tumor tissues were shown to be closer in appearance to normal breast tissue. This study also demonstrated that the difference between these tissues could be made obvious by using a CdTe series detector. We believe that this differentiation is important, and therefore, expect this technology to be applied to new tumor detection systems in the future.
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