Biomedical subjects

Hideaki Haneishi

Publications and source records attributed to Hideaki Haneishi.

4 recordsLinked to original sources

PubMed2006

Nonlinear motion correction of respiratory-gated lung SPECT images.

We propose a method for correcting the motion of the lungs between different phase images obtained by respiratory-gated single photon emission computed tomography (SPECT). This method is applied to SPECT images that show a preserved activity distribution in the lungs such as 99m-Tc macro aggregated albumin (99m-Tc-MAA) perfusion images and 99m-Tc-Technegas ventilation images. In the proposed method, an objective function, which consists of both the degree of similarity between a reference image and a deformed image, and the smoothness of deformation is defined and optimized using a simulated annealing algorithm. For the degree of similarity term in the objective function, an expansion ratio, defined as the ratio of change in local volume due to deformation, is introduced to preserve the total activity during the motion correction process. This method was applied to data simulated from computer phantoms, data acquired from a physical phantom, and 17 sets of clinical data. In all cases, the motion correction between inspiration and expiration phase images was successfully achieved.

Algorithms↗

PubMed2005

Transaxial system models for jPET-D4 image reconstruction.

A high-performance brain PET scanner, jPET-D4, which provides four-layer depth-of-interaction (DOI) information, is being developed to achieve not only high spatial resolution, but also high scanner sensitivity. One technical issue to be dealt with is the data dimensions which increase in proportion to the square of the number of DOI layers. It is, therefore, difficult to apply algebraic or statistical image reconstruction methods directly to DOI-PET, though they improve image quality through accurate system modelling. The process that requires the most computational time and storage space is the calculation of the huge number of system matrix elements. The DOI compression (DOIC) method, which we have previously proposed, reduces data dimensions by a factor of 1/5. In this paper, we propose a transaxial imaging system model optimized for jPET-D4 with the DOIC method. The proposed model assumes that detector response functions (DRFs) are uniform along line-of-responses (LORs). Then each element of the system matrix is calculated as the summed intersection lengths between a pixel and sub-LORs weighted by a value from the DRF look-up-table. 2D numerical simulation results showed that the proposed model cut the calculation time by a factor of several hundred while keeping image quality, compared with the accurate system model. A 3D image reconstruction with the on-the-fly calculation of the system matrix is within the practical limitations by incorporating the proposed model and the DOIC method with one-pass accelerated iterative methods.

Brain↗

PubMed2003

[Computer simulation of DOI-PET detector (1) -analysis of DOI discrimination accuracy in a detector block-].

A detector proposed by Murayama et al. for detection of depth-of-interaction (DOI) in PET consists of three-dimensionally arranged crystal elements with proper optical reflectors and is coupled to an array of photomultiplier tubes. This detector has a great advantage in easiness and cost in fabrication. We implemented a simulator of this detector that allows us to find appropriate values of parameters such as optical properties of crystal or detector unit geometry before making detectors. The simulator is based on the Monte Carlo method that traces the migration of optical photons generated by interaction of a gamma ray with crystal. First, the simulator performance was validated by comparing with the experimental data obtained with some prototype detectors. Then, on some parameters including refractive index of inter-crystal material, reflectance of optical reflector and detector geometry, appropriate values were investigated for accurate discrimination of crystal element of interaction.

Computer Simulation↗

PubMed2001

[Algebraic 2D PET image reconstruction using depth-of-interaction information]

Recently a high-performance PET scanner, which measures depth-of-interaction (DOI) information, is being developed for molecular imaging. DOI measurement of multi-layered thin crystals can improve spatial resolution and scanner sensitivity simultaneously. In this paper, we apply an algebraic image reconstruction method to 2-dimensional (2D) DOI-PET scanners using accurate system modeling, in order to evaluate the effects of using DOI information on PET image quality. Algebraic image reconstruction methods have been successfully used to improve PET image quality, compared with the conventional filtered backprojection method. The proposed method is applied to simulated data for a small 2D DOI-PET scanner. The results show that accurate system modeling improves spatial resolution without noise emphasis, and that DOI information improves uniformity of spatial resolution.

Journal Article↗