gated mage 
Tat spatial resolution allowing high resolution microtomography are today obtained on instruments 
3 bulky mye located in synchrotron radiation facilities. The origin of the x-rays is here completely different. 
die Synchrotron radiation is produced by ultra-relativistic electrons in a storage ring when they are 
accelerated by a magnetic field. The x-rays are emitted in a narrow cone tangent to the trajectory of 
the electron (tangent to the ring). Such a source can be found for instance at ESRF in Grenoble. The 
x-ray beam produced is very interesting for microtomography because of the following original 
features (2) : 
0 singe page * Very high intensity of the x-ray beam inside the cone. 
al features lg i » Parallel beam. This simplifies the reconstruction of the images but shifts the resolution 
OY combining te dependance into the detector’s performance. 
ent Orientation of A monochromatic beam can be used: this suppresses for example the cupping effect and allows 
mall enough it for quantitative reconstructions. 
2) each point Avalaibility of high energy photons (beyond 100 keV) which allow to penetrate heavy (high Z) 
are based on the materials. 
Small size of the electron beam cross section (<100 um) at third generation synchrotrons such 
as ESRF. This leads to a very small angular dimension of the source as seen from a point in the 
specimen, hence to a sizeable lateral coherence of the x-rays which is important for phase 
contrast imaging (see next section). 
he object fixed, The ID19 beam line team has combined these specific properties with the availability of a suitable 
directly a two- CCD-based detector exhibiting at the same time a large dynamic range (13 bits), a low noise and a 
into visible light short transfer time (down to 60 ms for 1024x1024 pixels). This unique combination allows a 
limes and rows of resolution of the order of 1 um to be obtained routinely today. The experimental setup used on ID19 
that the axis of is shown in figure 2. 
must be aligned 
count in applying 
value is mainly 
rap as it will be detes ur 
5 limit resolution 
as with a size of 
source 
®—— 
tom can be used x 
stance assembled sam .e 
ce figure 1), the 
space between the 
‚icro-focus which 
i le sores SL Figure 1 : Cone beam setup for medium resolution microtomography at CNDRI. The source is a 
on te ged standard microfocus x-ray tube and the detector includes x-ray visible light conversion and a cooled 
aporairy SP & CCD camera. 
his may introduck 
fv de abs0rDH09 Phase contrast 
The refractive index for x-rays is slightly different from unity and a x-ray beam is modulated in its 
optical phase after passing through a sample or through different constituents inside the sample. A 
. difference in phase can be induced between two parallel rays passing on each side of an interface 
ro because o between two constituents of the studied material. This phase difference induces a contrast which is 
4m noise ratio an 
Lk ote 
pl. 
21