X-ray CT devices measure the attenuation of an X-ray beam
when it penetrates a substance. The beam intensity is reduced
according to the attenuation coefficient and the mass density of
the material [2]. This attenuation can be attributed to several
physical processes, whose predominance depends on the energy
used in the CT devices and therefore on the X-ray acceleration
voltage. Compton scattering is predominant in conventional CTs,
in which case the attenuation is proportional to the density matter.
However, at lower energies, the photoelectric effect governs the
attenuation process, depending mainly on the atomic number
[3]. Whereas most cryoprotectants are alcohols, composed of carbon, hydrogen, and oxygen, the higher atomic number of the
sulfur atom in dimethyl sulfoxide (Me 2 SO) makes the X-ray attenuation proportional to the concentration for this particular CPA.
This makes Me 2 SO more suitable for CT imaging of CPA permeation processes in tissues compared to other CPAs.
X-ray CT has already been used to map crystalline and amorphous phases in frozen samples [4] with applications to cryosurgery
and cryopreservation, although a higher acceleration voltage was
used (420 kV).
We have applied this CT imaging technique to assess cryopreservation procedures of several tissues. We visualized the formation
of ice crystals (up to 2 μL) inside vitrified kidneys [5]. We have also
used X-ray computed tomography for ovarian tissue cryopreservation: we analyzed and optimized freezing procedures for bovine [6]
and human ovarian tissue [7]. We developed a different procedure
for ovarian tissue cryopreservation based on a slow vitrification
procedure [8], consisting of a gradual increase of the vitrification
solution concentration while decreasing the temperature. Finally,
we have characterized the cooling process for a Me 2 SO solution in
order to minimize the formation of fractures by studying the
influence of some parameters: cooling rates, type of vials and insulating containers, degasification, and orientation of the container
[9, 10].
To summarize, this patented X-ray imaging technique [11] is
an excellent tool to monitor any cryopreservation procedure and to
obtain 3D images of tissues and organs with a spatial resolution of
up to 50 μm.
2 Materials
2.1 CT Imaging
1. A NanoCT device (Bioscan NanoCT
® , USA; currently Mediso,
Hungary), with an acceleration voltage range of 45–75 kV (see
Note 1).
2. A cylindrical carbon fiber CT bed with dimensions according to
the CT device.
318
Ariadna Corral et al.
when it penetrates a substance. The beam intensity is reduced
according to the attenuation coefficient and the mass density of
the material [2]. This attenuation can be attributed to several
physical processes, whose predominance depends on the energy
used in the CT devices and therefore on the X-ray acceleration
voltage. Compton scattering is predominant in conventional CTs,
in which case the attenuation is proportional to the density matter.
However, at lower energies, the photoelectric effect governs the
attenuation process, depending mainly on the atomic number
[3]. Whereas most cryoprotectants are alcohols, composed of carbon, hydrogen, and oxygen, the higher atomic number of the
sulfur atom in dimethyl sulfoxide (Me 2 SO) makes the X-ray attenuation proportional to the concentration for this particular CPA.
This makes Me 2 SO more suitable for CT imaging of CPA permeation processes in tissues compared to other CPAs.
X-ray CT has already been used to map crystalline and amorphous phases in frozen samples [4] with applications to cryosurgery
and cryopreservation, although a higher acceleration voltage was
used (420 kV).
We have applied this CT imaging technique to assess cryopreservation procedures of several tissues. We visualized the formation
of ice crystals (up to 2 μL) inside vitrified kidneys [5]. We have also
used X-ray computed tomography for ovarian tissue cryopreservation: we analyzed and optimized freezing procedures for bovine [6]
and human ovarian tissue [7]. We developed a different procedure
for ovarian tissue cryopreservation based on a slow vitrification
procedure [8], consisting of a gradual increase of the vitrification
solution concentration while decreasing the temperature. Finally,
we have characterized the cooling process for a Me 2 SO solution in
order to minimize the formation of fractures by studying the
influence of some parameters: cooling rates, type of vials and insulating containers, degasification, and orientation of the container
[9, 10].
To summarize, this patented X-ray imaging technique [11] is
an excellent tool to monitor any cryopreservation procedure and to
obtain 3D images of tissues and organs with a spatial resolution of
up to 50 μm.
2 Materials
2.1 CT Imaging
1. A NanoCT device (Bioscan NanoCT
® , USA; currently Mediso,
Hungary), with an acceleration voltage range of 45–75 kV (see
Note 1).
2. A cylindrical carbon fiber CT bed with dimensions according to
the CT device.
318
Ariadna Corral et al.