量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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The long patient port of a PET scanner tends to put stress on patients, especially
patients with claustrophobia. It also prevents doctors and technicians from
taking care of patients during scanning. In this paper, we proposed an 'open
PET' geometry, which consists of two axially separated detector rings. A long
and continuous field-of-view (FOV) including a 360 opened gap between two
detector rings can be imaged enabling a fully 3D image reconstruction of all
the possible lines-of-response. The open PET will become practical if iterative
image reconstruction methods are applied even though image reconstruction
of the open PET is analytically an incomplete problem. First we implemented
a 'masked' 3D ordered subset expectation maximization (OS-EM) in which
the system matrix was obtained from a long 'gapless' scanner by applying a
mask to detectors corresponding to the open space. Next, in order to evaluate
imaging performance of the proposed open PET geometry, we simulated a dual
HR+ scanner (ring diameter of D = 827 mm, axial length ofW = 154 mm * 2)
separated by a variable gap. The gapW was the maximum limit to have axially
continuous FOV of 3W though the maximum diameter of FOV at the central
slice was limited to D/2. Artifacts, observed on both sides of the open space
when the gap exceeded W, were effectively reduced by inserting detectors
partially into unnecessary open spaces. We also tested the open PET geometry
using experimental data obtained by the jPET-D4. The jPET-D4 is a prototype
brain scanner, which has 5 rings of 24 detector blocks. We simulated the open
jPET-D4 with a gap of 66 mm by eliminating 1 block-ring from experimental
data. Although some artifacts were seen at both ends of the opened gap, very
similar images were obtained with and without the gap. The proposed open
PET geometry is expected to lead to realization of in-beam PET, which is a
method for an in situ monitoring of charged particle therapy, by letting the
beams pass through the gap. The proposed open PET geometry will also allow
simultaneous PET/CT measurements of the same PET FOV as the CT FOV, in
contrast to the conventional PET/CT where each FOV is separated by several
tens of centimeters.
A proposal of an open PET geometry.
