3.8 Positron Emission Tomography (PET)
Using property of positron, PET is used for medical diagnosis for detecting position
of cancer cell on image of human body. Pair annihilation of positron occurs with
external electron such as valence electron, conduction electron and so on, and then
radiates ray of 2.43 pm as two photons in counter directions each other. Mass of
electron and positron is conserved during the pair annihilation and its energy is
511 keV which is rest mass of electron (Fig. 3.23). Water molecules occupy more
than 60 % in total weight of human body and pair annihilation occurs between
positron and electron of water molecule. PET has detectors arranged on circle for γ
ray from the pair annihilation. When two detectors detect ray at the same time,
position of the pair annihilation is identified as middle point of both detectors
(Fig. 3.24). This information is processed by use of computer and reconstituted on
three- dimensional image. For medical diagnosis in PET imaging, nucleus of
positron release should be generated by synchrotron. Half- life of nucleus releasing
positron is order of minutes and synchrotron is located near PET.
11 C,
13 N, 15O and
18 F are used for PET as nucleus species releasing positron, and their half-life time are
20 min, 10 min, 2 min and 110 min, respectively. The process of decay in
11 C is
shown as follows. For PET imaging diagnosis of cancer, glucose analogue,
18 Ffluorodeoxy glucose (FDG) is used because cancer cells are very active for cell
division and require much energy from glucose. And FDG s gathering around cancer
cells are detected by PET and the position is identified in three dimensional image.
However, the resolution is about 5 mm because negative factors such as flying
distance of positron and angular fluctuation.
3.9 Optical trapping
With the progress of biology, a number of techniques have been developed that
allow researchers to measure the force developed by the cell and to manipulate
cellular objects and even molecules. For this purpose, a glass needle has long been
used to measure the forces accompanying the advancement of cells [23] and even
single actomyosin motor forces [24]. Atomic-force microscopy was applied to
measure the force driving the advancement of keratocyte [25]. All these techniques
utilize the precise positioning and optical measurement of the location of needle-like
probes with microscope or split photodiode. The range of the force was roughly from
10 nN down to 10
À2 nN. Another technique is the optical trapping. This technique
emerged from the technique of manipulation of a single atom by strongly focused
laser beams [26, 27]. Later, the possibility was shown to manipulate microscopic
objects with a single laser beam [28]. As schematically shown in Fig. 3.25, the forces
arise when a pair of rays of the incident light beam is refracted and reflected by the
sphere, which has a refractive index higher than the surrounding medium (eg.,
54
3 Methods for Physical Properties of Biomembranes and Cells
Using property of positron, PET is used for medical diagnosis for detecting position
of cancer cell on image of human body. Pair annihilation of positron occurs with
external electron such as valence electron, conduction electron and so on, and then
radiates ray of 2.43 pm as two photons in counter directions each other. Mass of
electron and positron is conserved during the pair annihilation and its energy is
511 keV which is rest mass of electron (Fig. 3.23). Water molecules occupy more
than 60 % in total weight of human body and pair annihilation occurs between
positron and electron of water molecule. PET has detectors arranged on circle for γ
ray from the pair annihilation. When two detectors detect ray at the same time,
position of the pair annihilation is identified as middle point of both detectors
(Fig. 3.24). This information is processed by use of computer and reconstituted on
three- dimensional image. For medical diagnosis in PET imaging, nucleus of
positron release should be generated by synchrotron. Half- life of nucleus releasing
positron is order of minutes and synchrotron is located near PET.
11 C,
13 N, 15O and
18 F are used for PET as nucleus species releasing positron, and their half-life time are
20 min, 10 min, 2 min and 110 min, respectively. The process of decay in
11 C is
shown as follows. For PET imaging diagnosis of cancer, glucose analogue,
18 Ffluorodeoxy glucose (FDG) is used because cancer cells are very active for cell
division and require much energy from glucose. And FDG s gathering around cancer
cells are detected by PET and the position is identified in three dimensional image.
However, the resolution is about 5 mm because negative factors such as flying
distance of positron and angular fluctuation.
3.9 Optical trapping
With the progress of biology, a number of techniques have been developed that
allow researchers to measure the force developed by the cell and to manipulate
cellular objects and even molecules. For this purpose, a glass needle has long been
used to measure the forces accompanying the advancement of cells [23] and even
single actomyosin motor forces [24]. Atomic-force microscopy was applied to
measure the force driving the advancement of keratocyte [25]. All these techniques
utilize the precise positioning and optical measurement of the location of needle-like
probes with microscope or split photodiode. The range of the force was roughly from
10 nN down to 10
À2 nN. Another technique is the optical trapping. This technique
emerged from the technique of manipulation of a single atom by strongly focused
laser beams [26, 27]. Later, the possibility was shown to manipulate microscopic
objects with a single laser beam [28]. As schematically shown in Fig. 3.25, the forces
arise when a pair of rays of the incident light beam is refracted and reflected by the
sphere, which has a refractive index higher than the surrounding medium (eg.,
54
3 Methods for Physical Properties of Biomembranes and Cells