Atsushi Momose 1 , Tohoru Takeda 2 , Yuji Itai 2 , Keiichi Hirano 3
2
1 Advanced Research Laboratory, Hitachi, Ltd., Hatoyama, Saitama 350-03, Japan
Institute of Clinical Medicine, University of Tsukuba, Tsukuba, Ibaraki 305, Japan
3 Photon Factory, National Laboratory for High Energy Physics, Tsukuba,
Ibaraki 305, Japan
Abstract.
Human cancerous tissues are observed with phase-contrast
X-ray microtomography using an X-ray interferometer. The high sensitivity of this technique allows us to observe structures inside the nonstained tissues with 17.7 keV synchrotron X-rays.
Tomographic image reconstruction using X-ray phase information enables threedimensional observation of biological soft tissues without the need for staining and without serious exposure to X-rays. We have proposed and developed phasecontrast X-ray tomography [1, 2, 3] using an X-ray interferometer. The cross section of the X-ray phase shift by biological soft tissues is almost a thousand times greater than that of X-ray absorption [4, 5]. Therefore, the image sensitivity was substantial enough to distinguish tumors in a rabbit liver and to see the degree of degeneration of cancerous tissues [6]. In this paper, observation results of human cancerous tissues are presented.
Fig. 1.
An X-ray interferometer monolithically cut out from a crystal block. A sample was rotated in a water-filled cell located in one of the beam paths. A phase shifter placed in the reference beam path was used to apply the fringe scanning method.

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To obtain X-ray phase information, we used the conventional X-ray interferometer invented by Bonse and Hart [7]. Figure 1 shows the interferometer and beam paths. The interferometer was monolithically cut out from a block of silicon crystal. Three parallel slabs are formed, having the same gaps. When a Bragg diffraction condition is satisfied, an X-ray beam is separated into two beams by the slab, which functions like an X-ray half mirror. The diffraction occurs at every slab simultaneously, creating two coherent beam paths. When an object is placed in one of the beam paths, X-ray wavefronts bend because of the phase shift caused by the object. Consequently, a corresponding interference pattern can be observed at the position of the image sensor shown in Fig. 1.
To achieve tomographic image reconstruction using X-ray phase information, the spatial distributions of the phase shift, or phase-mapping images, must be measured from many projection directions. By rotating a sample, the projection direction can be changed. To measure phase-mapping images, we adopted the fringe scanning method [8]. By rotating the phase shifter shown in Fig. 1, the phase difference between the two beam paths is tuned. Interference fringes move depending on the given phase difference. The distance of the fringe displacement is definitively related to the phase shift caused by the object. Therefore, by analyzing the fringe movement, a phase-mapping image can be obtained. When
M interference patterns are registered by changing the phase difference by 2 π / M , a phase-mapping image is obtained by extracting the argument of
X 1
I k k =0 exp( − 2 πik/M ) , (1) where I k is the interference pattern obtained when the phase difference is 2 πk/M
Phase-contrast tomograms can be reconstructed using a standard algorithm, and can then display the internal distribution of the refractive index, which is
.
approximately equivalent to the density distribution.
Experiments were carried out at the Photon Factory of Japan’s National
Laboratory for High Energy Physics. Hard X-rays (17.7 keV) from a vertical wiggler were used. Samples were fixed in formalin and cut in a cylindrical shape with a diameter of about 5 mm. Because the samples were wet, they were placed individually in water-filled cells for observation . Another function of the cell was to reduce the refraction of X-rays at the sample surface. Otherwise, if the samples were in air, finer interference fringes would cause errors in image processing [1].
We adopted a 10-step fringe scan to obtain a phase-mapping image from every projection direction. The sample was rotated at a 0.9
◦
200 phase-mapping images were acquired over 180 ◦ angular step. Thus, rotation. Because we used an X-ray image sensor (X-ray sensing pickup tube [9]), a series of tomograms were obtained using one scan. The pixel size of the tomograms was 12 2 µ m
The thickness of each tomogram was also 12 µ m.
2 .

Phase-Contrast X-Ray Microtomography II - 209
A B
Fig. 2.
Phase-contrast tomograms of human liver tissues. (a), Hepatocellular carcinoma in liver cirrhosis. (b), Metastasis of colon cancer to liver. Image size 5 x 5 mm.
Figure 2 shows phase-contrast tomograms of human liver tissues. Figure 2(a) is a tomogram of hepatocellular carcinoma (lower) in liver cirrhosis. The tumor was clearly differentiated. Figure 2(b) is a metastasis of colon cancer to a liver.
The entire view area is occupied by a tumor in this case. The bright contrasting area corresponds to degenerated tissue. Because the image contrast indicates the density distribution, one can see that the density of the degenerated tissue is larger than nondegenerated cancerous tissue. This is consistent with observations done with an optical microscope which show that a high concentration of red blood cells are found in the degenerated tissue, because the density of red blood cells is relatively high.
Figure 3 shows phase-contrast tomograms of human breast tissues. Figures
3(a) to 3(c) show tomograms of breast cancer from different patients. Comparing these with a tomogram of normal tissue (Fig. 3(d)), one can see there is a tendency for cancerous tissue to give a darker contrast. Degenerated tissues with brighter contrast are also detected. Figures 3(e) and (f) are tomograms of fibrous adenoma (benign tissue). We were interested in whether cancer and benign tumor are distinguishable with the phase-contrast technique. Although a clear conclusion cannot be made with only these two images, the potential is suggested.
We applied phase-contrast microtomography to the observation of nonstained human tissues. The structure of the cancerous tissues was well revealed. The difference between cancerous and normal tissues was also depicted. In the observation of breast tissues, the difference between the tomograms of cancerous tissue and a benign tumor was apparent.

II - 210 A. Momose et al.
A B
C D
E F
Fig. 3.
Phase-contrast tomograms of human breast tissues. (a) to (c), Breast cancer from different patients. (d), Normal breast tissue, (e) and (f), Fibrous adenoma from different patients. Image size 5 x 5 mm.

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Thus, phase-contrast microtomography is a powerful tool for observing the inside structure of biological soft tissue. It is also expected that this technique will be useful in the research field of materials science, especially for organic materials, and in medical applications provided that a larger interferometer is developed to obtain a wider view area.
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