Enhanced quantitative X-ray phase-contrast images
using Foucault differential filters
Jaeho Choi
1,
* and Young-Sung Park
1,2
1
Department of Physics, Dankook University, Cheonan 31116, Korea
2
Division of RI Convergence Research, Korea Institute of Radiological and Medical Sciences, Seoul 01812, Korea
*Corresponding author: choi@dankook.ac.kr
Received January 10, 2017; accepted May 18, 2017; posted online June 14, 2017
Enhanced quantitative X-ray phase-contrast (QXPC) imaging is implemented with a Foucault knife-edge array
filter (FKAF), which is a real differential spatial filter. The intensities of Foucault differential filtering (FDF) are
acquired according to the linear translation of the FKAF along the axes. The FDF using the FKAF scheme for
obtaining the QXPC images is demonstrated by a stereoscopic rendering of the quantitative phase images of the
tail fin of an anchovy containing soft and hard components in specimen. FDF is a noninterferometric quanti-
tative phase-imaging method that depicts quantitative phase images and renders stereoscopic images.
OCIS codes: 110.7440, 180.7460, 100.5070, 070.6110.
doi: 10.3788/COL201715.081103.
Several X-ray phas e visualization methods are being real-
ized for imaging of phase objects, such as biological and
polymeric specimens
[1–3]
. Grating-based phase-contrast
imaging using a source-grating-attached X-ray tube that
provides partially coherent X rays is one of the most suc-
cessful methods in this field
[4]
. The propagation-based
phase-contrast computed tomography has demonstrated
samples containing both weakly and strongly abso rbing
biomedical materials
[5]
. Since the report of direct observa-
tion of thermal air turbulence using the Schlieren method,
modifications of this technique have been used in fluid and
aerodynamic research to depict the deviations of light
beams induced by density gradients using an incoherent
light source
[6]
. This improvement was accompanied by
the development of spatial filters. The knife-edge test
was reported for extraction of quantitative measurement
of a nonsymmetric surface
[7]
. A phase-shift imaging
method based on the multiline filter in the conventional
Schlieren and phase-shift technique has been reported
[8]
.
The Zernike-type phase-imaging method first used a
filtering device evolved from knife-edge filters in visible
light
[9]
. Thereafter, electron phase-contrast imaging was
developed using this scheme
[10,11]
. However, this method
could not be immediately applied to X-ray imaging,
possibly because X-ray beams are intrinsically difficul t
to manipulate into highly coherent focused beams
[12,13]
.
The X-ray Foucault knife-edge filtering method was dem-
onstrated following the development of electron-phase
imaging
[14–16]
. The achievement of quantitative phase im-
aging is one of the main topics in the field of X-ray imag-
ing, especially regarding using a low flux and incoherent
radiations source in the general laboratory environments.
In this study, we report quantitative X-ray phase-contrast
(QXPC) images gene rated using a Foucault differential
filter (FDF) that was realized by the linear scanning of
a Foucault knife-edge array filter (FKAF). The schematic
diagram of the experimental setup is illustrated in Fig.
1.
It adopted the basic features of the Schlieren imaging
apparatus, which uses an incoherent light source. A colli-
mated beam is needed to perform spatial filtering. How-
ever, the spatial filtering in the hard X-ray region is
restricted due to the generally low efficiency of X-ray col-
limation optics. In order to overcome the weakness of hard
X-ray optics and to illuminate the partially collimated
beam on the specimen, a pinhole array (PA) is utilized
as an X-ray collimator. Then, an FKAF is exploited as
f
K
1
K
2
K
3
S
A
PA
FKAF
SC
IO
SP
Z (optical axis)
x
y
g
Fig. 1. (Color online) Schematic diagram of the FDF method. S,
X-ray tube source; A, lead aperture; SC, scintillation crystal; IO,
visible light imaging optics; SP, specimen; f , focal length of PA;
g, distance between the end of the specimen surface and the
FKAF; blue arrow, translation direction of SP. k1, k2, k3, knife
edges; z axis, optical axis.
COL 15(8), 081103(2017) CHINESE OPTICS LETTERS August 10, 2017
1671-7694/2017/081103(4) 081103-1 © 2017 Chinese Optics Letters