Chika Honda

Advantages of magnification in digital phase-contrast mammography using a practical X-ray tube

Phase-contrast imaging with a practical cone-beam X-ray tube has been realized for clinical use in digital mammography using computed radiography (CR). To perform phase-contrast imaging, the X-ray detector must be distanced from an object so that the phase-contrast image achieves magnification; in a mammography unit dedicated to phase-contrast imaging, the magnification ratio is 1.75. When using an X-ray tube with a 0.1-mm focal spot, it appears that the penumbra in magnification blurs both projected images and the phase contrast, which generates an edge effect. However, where the sampling pitch of the CR plate is 43.75 microm, the blur stretches the width of the phase contrast so that unit pixels in the detector can capture it. Note that the width of an ideal phase contrast using an X-ray point source results in a phase contrast too narrow for detection with CR. In addition to phase contrast improving image quality, a re-scaling effect increases image sharpness in magnification. Further, image noise induced by magnification can be reduced during printing to photothermographic dry film by demagnifying the digital output image to the original image size. After demagnification by 1/1.75 from 43.75 microm in image acquisition, a 25-microm pixel size of the output image is obtained so that the spatial resolution matches that of conventional screen-film mammography. In this paper, such technical advantages of magnification in digital phase-contrast mammography are reviewed, and the image quality of phase-contrast images is discussed in light of diagnostic requirements in detecting breast cancer.

A Comparison between Film-Screen Mammography and Full-Field Digital Mammography Utilizing Phase Contrast Technology in Breast Cancer Screening Programs

A digital phase contrast mammography (PCM) system was introduced into a hospitals screening programs with the expectation of improved clinical image quality. A total of 3835 examinations with the PCM system and 4338 examinations with a film-screen (FS) system were performed. The screening performance measures of the two systems were compared. Both in recall rates and in cancer detection rates, the performances of PCM and FS exhibited no statistically significant difference. For microcalcifications and masses, recall rates were lower with PCM than with FS despite the fact that more findings were reported with PCM. It would appear that PCMs superior depiction of abnormalities helped radiologists improve the accuracy of categorization. PCM is considered a beneficial imaging modality in breast cancer screening programs.

Phase contrast digital mammography using molybdenum x-ray: clinical implications in detectability improvement

We have applied phase imaging on digital mammography to investigate adequate contrast of printed images for digital phase contrast mammography using a practical molybdenum X-ray tube. Phase contrast mammography procedures were performed with defined air gap (e.g., 0.6 m) configuration using customized mammography equipment and a computed radiography (CR) system. Magnified (x2) phase contrast images acquired with 0.0875mm per pixel were mapped onto the laser imager resolution at 0.04375mm per pixel for printing life-size object on wet processing silver halide recording film. For contact mammography of screen-film system, we used MinR2000 system as a baseline method. ACR 156 phantom printed images with contrasts of 2.8, 3.7, 4.9, 5.7 and 6.7 were evaluated by five radiologists. The ACR scores for the life-size image based on the 2 times magnified phase contrast image acquired by the computed radiography were higher than the scores of MinR2000 image, when the contrast of printed images for both methods was 3.7. The ACR scores were lower in the low contrast images (i.e., 2.8) than its higher contrast counterparts (i.e., >= 3.7) for all techniques used. The detectability improvement should be due to higher spatial resolution and lower noise in the phase contrast images.

Preliminary Evaluation of a Phase Contrast Imaging with Digital Mammography

X-ray beams irradiated from an x-ray tube with a point source or a sufficiently small focal spot produce edge-enhanced images in the boundary of an object due to the effect of phase shift of x-rays. This technique is called phase contrast imaging. A digital phase contrast imaging system based on a photostimulable phosphor plate (imaging plate) designed for mammography has been developed for clinical use recently and now commercially available. In this study, the digital phase contrast images of an acrylic plate and plant seeds were acquired without any increase of incident dose to detector when compared to conventional contact digital imaging. Improvement of image edge sharpness was evaluated in terms of spatial edge response and spectral analysis of the images. In addition, the improvement of the sharpness of the image was also evaluated in clinical mammograms. Our results indicated that higher image sharpness in the boundary of the object was observed. The power spectrum of the digital phase contrast image was found to be higher than that of the digital contact image at wide spatial frequency region. In conclusion, the commercially available phase contrast imaging system can provide breast images with details that are not available in conventional mammograms. The digital phase contrast imaging would be useful to detect diseases, especially microcalcifications, in mammograms without any increase of exposure dose.

Image qualities of phase-contrast mammography

A digital full-filed mammography system using phase-contrast technique has been developed. The system consists of a dedicated mammography unit, a computed radiography unit with a sampling rate of 43.75 microns, and a photothermographic printer with a printing rate of 25 microns for photothermographic film with the maximum optical density of 4.0. The sharpness of the output image is improved with an edge effect due to phase contrast and magnification. The image noise is reduced by an air-gap method with no bucky. In this paper, the image qualities of the phase-contrast mammography are described for full-filed mammography and spot-compression at 1.5x magnification.

Image quality in digital phase contrast imaging using a tungsten anode x-ray tube with small focal-spot size

Phase contrast x-ray imaging has been studied intensively using x-rays from synchrotron radiation and micro-focus x- ray rubes. However, these studies have revealed the difficulty of this techniques application to practical medical imaging. We have created a phase contrast imaging technique using practical x-ray tubes with small focal spot sizes. In a previous study, we identified the radiographic conditions for phase contrast magnification mammography with screen-film systems, where the edge effect due to phase contrast outweighs the geometrical unsharpness introduced by the 0.1mm-focal spot of a molybdenum-anode x-ray tube. In the present study, phase contrast images of a hand and a chest phantoms were obtained using computed radiography and a geometrical magnification of two using a tungsten-anode x- ray tube with a 0.1mm-focal spot. The digital images were printed so that objects were reproduced at their original size. Compared to conventional digital contact images obtained at the same x-ray dose, the life-sized digital phase contrast x-ray images displayed improved sharpness and resolution, and reduced grain. We describe the empirical results of digital phase contrast imaging, and discuss these performance improvements through simulation including x-ray scatter.

Subtle Abnormalities in Highly Dense Breasts Detected by Use of a Digital Phase Contrast Mammography System: A Report of Three Invasive Cancer Cases in the Early Stage

Detection of invasive breast cancers in the early stage is of great significance in reducing mortality. Phase contrast mammography (PCM) is a promising approach to improving the conspicuity of subtle lesions camouflaged by dense glandular tissue by virtue of the edge effect obtained through the phase contrast technique. The specific images of PCM in three cases of invasive, early-stage breast cancers with corresponding pathological images of cancer are reported in this paper. The cases demonstrate that the microlobulated contours of lesions with surrounding fine fibrous structures are well depicted in PCM images. Our findings are consistent with studies evaluating physical image quality in which PCM effectively improved the depiction of fibrous structures. It is expected that the number of abnormalities observed in dense breasts, including subtle findings without microcalcifications, would increase in PCM mammograms.

Full-field Digital Phase-contrast Mammography

Publisher Summary This chapter briefly discusses the present physical properties and clinical experience of the full-field digital phase-contrast mammography (PCM) system, in which the phase-contrast technique is utilized. In order to perform phase-contrast imaging in mammography, a new mammography unit is designed, in which the distance between a focal spot and an object, R1, is first determined to be 0.65 m. This distance is equivalent to that between the focal spot and the object for conventional contact mammography, so that there is no change in the incident angles of X-rays to the object from the conventional contact mammography. The structure of the breast in a projected image on the detector is kept consistent from that of the conventional contact mammography. An X-ray detector should be placed away from an object to obtain phase contrast. The construction of a mammography unit mechanically permits the longest distance from the X-ray source and the detector to be less than 1.2 m. The full-field digital PCM system is aimed at achieving a clinical performance that is equal to or better than that with conventional screen-film (S/F) mammography. Thus, a 25 μm pixel is designed in output for mammographic images because the spatial resolution of S/F mammography is 20 cycles/mm, which is equivalent to a 25 μm pixel in digital mammography. The magnifiers are used for reading mammograms, suggesting that more than twice the spatial resolution is required in mammography. In this system, the acquired image in × l.75 magnification is reduced in size to the original object for an output hardcopy image.