Thursday, Oct. 23
M06: MIC Poster I
10:30-12:30, Hall 4&5 (Poster)
M06-7: Simulation
Study on Sensitivity and Count Rate Characteristics of gOpenPETh Geometries
E. Yoshida, T. Yamaya,
K. Shibuya, F. Nishikido, N. Inadama, H. Murayama
Molecular Imaging
Center, National Institute of Radiological Sciences, Chiba-shi,
Japan
The OpenPET geometry,
which consists of two axially separated detector rings, has been proposed to
image the 360-degree open gap. The open gap is less stressful for patients and
suitable for simultaneous PET/CT and in-beam PET. It has been shown that
OpenPET geometry can maintain high spatial resolution using a
depth-of-interaction (DOI) detector. However, when the PET scanner is used for
an extended axial field-of-view (FOV), several characteristics of oblique
lines-of-response (LORs), such as decreased sensitivity due to smaller
acceptance angle and increased scatter fraction (SF) and attenuation, should be
carefully discussed. It is expected that these characteristics are dependent on
the gap size and the target object size. In this work, we study sensitivity and
count rate characteristics for OpenPET geometry using GATE simulation. We
simulate two OpenPET geometries. (The dual scanner has 15-cm open gap and 45-cm
axial FOV. The quad scanner has 30-cm open gap and 90-cm axial FOV.) When the
gap is extended, the axial FOV is extended at the cost of the decreased
sensitivity of the skirts of the main peak. Maximum sensitivity of the dual
scanner with the open gap is almost the same as the scanner without the open
gap. In the quad scanner, however, maximum sensitivity decreases by 25 % due to
the decreased acceptance angles. Noise equivalent count rate (NECR) curves
depend on not only the maximum sensitivity but also the target object size,
because the extended gap results in the broadened sensitivity profile. For the
long 100-cm cylinder phantom, the loss of the peak NECR is slight for both
scanners. For the 20-cm cylinder phantom, however, NECR of the quad scanner
maintain approximately half of NECR without the open gap.
M06-83: Development of
a prototype system of a small bore DOI-PET scanner
F. Nishikido1, E. Yoshida1,
T. Yamaya1, N. Inadama1, K. Shibuya1,
T. Tsuda2, H. Tonami2, K. Kitamura2,
H. Murayama1
1National Institute of
Radiological Sciences, Chiba, Japan
2Shimadzu Corporation, Kyoto, Japan
Small animal positron
emission tomography (PET) scanners and positron emission mammography (PEM)
scanner require not only high spatial resolution but also high scanner
sensitivity. One of methods to achieve high scanner sensitivity is to arrange
gamma ray detectors closer to objects. However it increases the gamma rays
entering to the detector obliquely. Therefore, spatial resolution of
reconstructed images is degraded. Depth-of-interaction (DOI) detectors are
required for small bore scanners. We are developing a small bore PET scanner to
achieve high sensitivity as well as high spatial resolution by the use of
four-layer DOI information of the detector. We constructed the prototype
scanner of the four-layer DOI detectors. The prototype system consists of the
six DOI detectors arranged hexagonally. The distance between the opposed DOI
detectors is 9.2 cm and a field-of-view (FOV) is 8.8 cm. The DOI detectors
consist of a 32 (transaxial) ~ 32 (axial) ~ 4 (depth) array
of LGSO crystals and a 256ch flat panel position sensitive position sensitive
photomultiplier tube. The size of each crystal element is 1.46 mm ~ 1.46 mm ~
4.5 mm. In the presentation, the experimental data, especially the evaluation
of the spatial resolution and sensitivity of the scanner, are presented.
M06-187: Four-Layer
DOI-PET Detector with a Silicon Photomultiplier Array
F. Nishikido1, N. Inadama1,
K. Shibuya1, E. Yoshida1, T. Yamaya1,
I. Oda2, K. Kitamura2, H. Murayama1
1National Institute of
Radiological Sciences, Chiba, Japan
2Shimadzu Corporation, Kyoto, Japan
Silicon
photomultipliers are promising photo detectors for use in PET detectors due to
their high internal gain, low power consumption and insensitivity to magnetic
fields. We are developing a PET detector which consists of a scintillation
crystal array and a silicon photomultiplier array. To achieve the uniform
spatial resolution, depth-of-interaction (DOI) detectors are required to reduce
the parallax error. We are studying the four-layer DOI PET detector with a
silicon photomultiplier array. The four-layer DOI detector consists of a 6 ~ 6
~ 4 LYSO crystal array and the SPMArray (SPMArray 3035G16, SensL, Ireland)
which is an array of sixteen silicon photomultiplier detectors (each 3mm ~
3mm). The size of each crystal element is 1.46 mm ~ 1.46 mm ~ 4.5 mm. The DOI
encoding method we applied was a previously presented method which can identify
crystals of four layers with only one photo detector and crystal array using an
arrangement with the reflector inserted between crystals. We measured the
performance of the four-layer DOI PET detector. Additionally, the related
characteristics of the SPMArray when used in the
four-layer DOI PET detector were measured. We found that the crystal
identification capability was similar to that of the detector which consisted
of the same crystal array and the position sensitive photomultiplier tube we
typically used. Sufficient energy resolution for use as a PET detector was
obtained. We will present more detailed results of the experiment.
M06-201: A DOI PET
Detector With Scintillation Crystals Cut in Triangular
Prism
N. Inadama1, H. Murayama1,
T. Yamaya1, F. Nishikido1, K. Shibuya1,
E. Yoshida1, T. Tsuda2, A. Ohmura3,1, Y. Yazaki4,1, H. Osada4,1
1Molecular Imaging
Center, National Institute of Radiological Sciences, Chiba, Japan
2Shimadzu, Kyoto, Japan
3Waseda University, Tokyo, Japan
4Graduate School of Science and Technology, Chiba University, Chiba,
Japan
We propose a new depth
of interaction (DOI) detector which is made of scintillation crystals cut in
triangular prism.
Preliminary study was carried out with Lu.2xGd.2(1-x)SiO.5
(LGSO) crystals cut in three-square of 3.0 mm and 10.0 mm long. They are
arranged in 3-layer DOI array and coupled to a position sensitive
photomultiplier tube (PS-PMT). By removing some reflector from the crystal
array to control scintillation light spread, we could obtain the 2-dimensional
position histogram in which responses of the crystals in all layers are
discriminated with only Anger-type calculation of the PS-PMT signals.
M06-203: Crystal
identification performance of the jPET detector depending on refractive index
of optical cement between scintillators
A. Ohmura1,2, F. Nishikido2,
N. Inadama2, Y. Yazaki3,2, H. Osada3,2,
K. Shibuya2, T. Yamaya2, E. Yoshida2,
S. Torii1, H. Murayama2
1Waseda University,
Shinjuku-ku, Tokyo, Japan
2National Institute of Radiological Sciences, Chiba-shi, Chiba, Japan
3Chiba University, Chiba-shi, Chiba, Japan
Previously we
developed the four-layer DOI detector which consists of four layers of
scintillation crystal array and a position sensitive photomultiplier tube
(PS-PMT). To control the behavior of scintillation light in the DOI crystal
array, some reflectors between crystals are removed so that all crystal
responses in the four layers are expressed in one two-dimensional (2D) position
histogram by implementing Anger-type calculation of the PS-PMT signals.
Since the method utilizes spread of scintillation lights through the space
between crystals with no reflector, positioning performance in the 2D position
histogram depends on the crystal dimensions, the crystal surface finish, and
refractive index of the material in the space. That indicates the degradation
of positioning performance as the result of changing crystal condition can be
improved by using the optical cement of appropriate refractive index. In this
work, we studied positioning characteristics by using an optical cement of
variable refractive index. The results reveal that 2D position histogram
changes as refractive index of an optical cement between crystals changes.
Friday, Oct. 24
M10: MIC Poster II
10:30-12:30, Hall 4&5 (Poster)
M10-2: A Multiplex
"OpenPET" Geometry to Extend Axial FOV Without
Increasing the Number of Detectors
T. Yamaya, E. Yoshida,
N. Inadama, F. Nishikido, K. Shibuya, H. Murayama
Molecular Imaging
Center, National Institute of Radiological Sciences, Chiba, Japan
At the last MIC
conference, we proposed an "OpenPET" geometry, which consists of two
axially separated detector rings of axial length W. A long and continuous
field-of-view (FOV) including a 360-degree open gap G between two detector
rings can be imaged though iterative image reconstruction. In addition to
providing stress-less PET scanning and simultaneous PET/CT, the OpenPET is
expected to lead to realization of in-beam PET. The OpenPET also extends the
axial FOV with a limited number of detectors. The range of G to obtain the
axially continuous FOV is represented as ΏW
(0<Ώ<=1). The extension gain, which is defined as [extended axial FOV
size] / [original axial FOV size], is limited to (2+Ώ)/2. In order to increase
the gap and the axial FOV, therefore, we have to extend W itself. However the
extension of W results in cost enhancement of the scanner. In this paper, we
propose a new "multiplex OpenPET" geometry, which can extend axial
FOV without increasing the number of detectors. In the first step, two detector
rings of axial length W are separated by the gap ΏW,
and we have a pseudo scanner, unit[1], of axial length W[1] =(2+Ώ)W. In the
second step, two unit[1]s can be separated by the gap ΏW[1], and we have unit[2] of axial FOV W[2]=(2+Ώ)2W.
After repeating these steps N times, we finally have unit[N],
which has a long axial FOV of W[N]=(2+Ώ)NW. Here the extension gain
is represented as {(2+Ώ)/2})N.
Theoretically it can be increased to an unlimited extent, although there is no
gain in sensitivity. Simulation results show that fine reconstructed images are
obtained by the multiplex OpenPET geometry. In addition to the extended gap,
the proposed geometry is expected to help realize an affordable entire body PET
scanner that enables whole body dynamic imaging.
N69: Scintillators and Scintillation Detectors V
13:30-15:30, Conference 6
N69-3: Scintillation
Properties of a (C6H5(CH2)2NH3)2PbBr4 Crystal
C. W. E. Van Eijk1,
J. T. M. De Haas1, P. A. Rodnyi2,
I. V. Khodyuk2, K. Shibuya3,
F. Nishikido3, M. Koshimizu4
1Faculty of Applied
Sciences, Delft University of Technology, Delft, The Netherlands
2Physics - Mechanics Faculty, St. Petersburg State Technical
University, St. Petersburg, Russia
3Molecular Imaging Center, National Institute of Radiological
Sciences, Chiba, Japan
4Department of Applied Chemistry, Tohoku University, Sendai, Japan
Luminescence and
scintillation properties have been studied of a crystal of the low-dimensional
perovskite-type organic-inorganic hybrid compound bis-(phenethylammonium) tetrabromoplumbate(II) (C6H5(CH2)2NH3)2PbBr4. Excitation, emission,
pulse-height and decay-time spectra were recorded. The light yield is 10,000
photons per MeV of absorbed gamma-ray energy, measured at 662 keV. The main
decay time under pulsed x-ray excitation is 9.4 ns.