Biomedical subjects

Naoki Hagiwara

Publications and source records attributed to Naoki Hagiwara.

5 recordsLinked to original sources

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↗

PubMed2005

[2D imaging simulations of a small animal PET scanner with DOI measurement: jPET-RD.].

We present a preliminary study on the design of a high sensitivity small animal DOI-PET scanner: jPET-RD (for Rodents with DOI detectors), which will contribute to molecular imaging. The 4-layer DOI block detector for the jPET-RD that consists of scintillation crystals (1.4 mm x 1.4 mm x 4.5 mm) and a flat panel position-sensitive photomultiplier tube (52 mm x 52 mm) was previously proposed. In this paper, we investigate imaging performance of the jPET-RD through numerical simulations. The scanner has a hexagonal geometry with a small diameter and a large axial aperture. Therefore DOI information is expected to improve resolution uniformity in the whole field of view (FOV). We simulate the scanner for various parameters of the number of DOI channels and the crystal length. Simulated data are reconstructed using the maximum likelihood expectation maximization with accurate system modeling. The trade-off results between background noise and spatial resolution show that only shortening the length of crystal does not improve the trade-off at all, and that 4-layer DOI information improves uniformity of spatial resolution in the whole FOV. Excellent performance of the jPET-RD can be expected based on the numerical simulation results.

Animals↗

PubMed2004

Static balance impairment and its change after pallidotomy in Parkinson's disease.

We compared postural sway parameters during a 1-minute quiet stance in 28 patients with idiopathic Parkinson's disease (PD) in off phase with those in 17 age-matched normal subjects and investigated differences in the sway parameters before and after unilateral pallidotomy in 16 PD patients. The PD patients showed larger sway area (SA) and longer total sway path length (SPL) compared with normal subjects. Total SPL after subtraction of tremor effect did not differ from that in normal subjects. The shift of the mean center of foot pressure (CFP) position from the first 30 seconds to the last 30 seconds showed that the CFP tended to move forward in PD patients compared with normal subjects and to move laterally more in PD patients than normal subjects, especially in those with less severity (Unified Parkinson's Disease Rating Scale, motor score < 40). After the operation, there was little change in either SA or lateral movement of CFP, but forward movement of CFP and total SPL tended to be normalized, along with an improvement of major parkinsonian symptoms. From these results, it is concluded that SPL elongation significantly involves tremor effect, forward movement of CFP in PD derives from basal ganglia dysfunction, and SA enlargement and large lateral movement of CFP may be caused partly by compensatory movements or by dysfunction outside the basal ganglia circuitry.

Aged↗

PubMed2003

Hepatocellular carcinoma in a case of adult-onset type II citrullinemia.

A 40-year-old woman was admitted with altered consciousness and hyperammonemia after she had delivered her first baby. DNA analysis of the citrin gene and enzymatic assay of argininosuccinate synthetase in the liver led to a diagnosis of adult-onset type II citrullinemia (CTLN2). She was also found to have hepatocellular carcinoma (HCC) and underwent palliative surgery consisting of partial liver section of the HCC. Delivery may be a trigger for the development of CTLN2, while certain pathologic conditions associated with citrin gene abnormality are likely to induce hepatocellular carcinoma in patients with this disorder.

Adult↗

PubMed2003

[Two patients with different types of vasculitic neuropathy--a comparison between cutaneous polyarteritis nodosa and nonsystemic vasculitic neuropathy].

We describe a patient with cutaneous polyarteritis nodosa (CPN) and a patient with nonsystemic vasculitic neuropathy (NSVN), both presenting mononeuritis multiplex. Patient 1 was a 50 year-old woman. She developed livedo reticularis, palpable purpura, and sensory disturbance of lower extremities. Laboratory examinations showed no abnormal findings except for slight elevation of ESR, CRP, and anti-nuclear antibody. Skin biopsy revealed vasculitis of small to medium sized arterioles in dermis and subcutaneous adipose tissue. Sural nerve biopsy revealed axonal degeneration of myelinated fibers and infiltration of polymorphonuclear cells and mononuclear cells around feeding arteries. From these findings, she was diagnosed as having CPN. She was treated with intravenous injections of methylprednisolone (1,000 mg/day) followed by oral prednisolone (40 mg/day), which had a limited effect. Addition of an immunosuppressive agent (azathioprine 50 mg/day) produced marked improvement in her clinical symptoms. However, azathioprine was discontinued because of liver injury. Then, we added cyclophosphamide which was as effective as azathioprine. Patient 2 was a 57 year-old man. He developed weakness of legs and sensory disturbance of lower extremities and trunk. Laboratory examinations showed no abnormal findings except for slight elevation of CRP and anti-nuclear antibody. Sural nerve biopsy revealed infiltration of inflammatory cells mainly consisting of mononuclear cells around small sized arterioles in the epineurium and severe loss of myelinated fibers. From these findings, he was diagnosed as having NSVN. Treatment with oral prednisolone (60 mg/day) and azathioprine (50 mg/day) improved his clinical symptoms. CPN is differentiated from NSVN by the existence of skin lesions and the type of inflammatory cells involved. However, these two diseases share common clinical features such as mononeuritis multiplex, absence of systemic organ involvement, no specific abnormal laboratory data, effectiveness of immunosuppressive therapy, and relatively good prognosis. We suggest that CPN and NSVN are included in the same category of nonsystemic vasculitis that can involve peripheral nerves and/or skin.

Diagnosis, Differential↗