Development of a high-resolution YSO gamma camera system that employs 0.8-mm pixels

Objective

YSO (Ce-doped Y₂SiO₅) is a promising scintillator for a single-photon imaging system since it has relatively high light output and does not contain any natural radioactivity. Since YSO is not hygroscopic, it may be possible to fabricate a block with small pixels for a high-resolution system. For this purpose, we developed a high-resolution gamma camera system that employs smaller than 1-mm YSO pixels.

Methods

The gamma camera’s detector used 0.8 × 0.8 × 7-mm YSO pixels. All the surfaces of these YSO pixels were mechanically polished, combined with a 0.1-mm-thick BaSO₄ reflector to form a 48 × 48 matrix, and optically coupled to a high quantum efficiency, 2-inch square position sensitive photomultiplier tube (Hamamatsu Photonics H10966 A-100). The YSO block was 43.2 × 43.2 mm. The YSO gamma camera was encased in a 5-mm-thick tungsten container, and a parallel collimator was mounted on its front. The parallel hole collimator was made of a 3-layer (each layer was 5-mm thick) tungsten plate, and each plate had 48 × 48, 0.6-mm holes that were positioned by one-to-one coupling with the YSO pixels.

Results

Even with the 0.8-mm YSO pixels, we clearly resolved most of the pixels in a 2-dimensional histogram with a peak-to-valley ratio of 2.9 for the 122-keV gamma photons. The energy resolution was 20.4 % FWHM. The spatial resolutions with a parallel hole collimator 2 mm from the collimator surface were 0.7- and 1.3-mm FWHM for the 122- and ~35-keV gamma photons, respectively. We successfully obtained phantoms and small animal images with our YSO gamma camera system.

Conclusion

Our high-resolution system has a potential to be useful for molecular imaging research.     

Disruption of the anterior commissure in Olig2 deficient mice

In the present study, we examined neural circuit formation in the forebrain of the Olig2 knockout (Olig2-KO) mouse model and found disruption of the anterior commissure at the late foetal stage. Axon bundles of the anterior commissure encountered the wall of the third ventricle and ceased axonal extension. L1-CAM immunohistochemistry showed that Olig2-KO mice lose decussation formation in the basal forebrain. DiI tracing revealed that the thin bundles of the anterior commissure axons crossed the midline but ceased further extension into the deep part of the contralateral side. Furthermore, some fractions of DiI-labelled axons were oriented dorsolaterally, which was not observed in the control mouse forebrain. The rostral part of the third ventricle was much wider in the Olig2-KO mice than in wild-type mice, which likely resulted in the delay of midline fusion and subsequent delay and malformation of the anterior commissure. We analysed gene expression alterations in the Olig2-KO mice using a public database and found multiple genes, which are related to axon guidance and epithelial-mesenchymal transition, showing subtle expression changes. These results suggest that Olig2 is essential for anterior commissure formation, likely by regulating multiple biological processes.     

By inhibiting Src,verapamil and dasatinib overcome multidrug resistance via increased expression of Bim and decreased expressions of MDR1 and survivin in human multidrug-resistant myeloma cells

The calcium channel blocker verapamil inhibits the transport function of multidrug resistance protein 1 (MDR1). Although verapamil acts to reverse MDR in cancer cells, the underlying mechanism remains unclear. In the present study, we investigated the mechanism of reversing MDR by verapamil in anti-cancer drug-resistant multiple myeloma (MM) cell lines. We found that verapamil suppresses MDR1 and survivin expressions and increases Bim expression via suppression of Src activation. Furthermore, dasatinib reversed the drug-resistance of the drug-resistant cell lines. These findings suggest that Src inhibitors are potentially useful as an anti-MDR agent for the treatment of malignant tumor cells.     

Expression and regulation of tumor suppressor gene maspin in human bladder cancer

Maspin is a member of serine protease inhibitor family with tumor suppressing activity for breast and prostate cancers, acting at the level of tumor invasion and metastasis. However, there have been no published data regarding the role of maspin in human bladder cancer. We evaluated maspin expression in 65 series of bladder cancer samples (22 transurethral resection (TUR) and 43 radical cystectomy) and studied the regulatory mechanism of maspin gene activation in bladder cancer cells. Maspin expression was immunohistochemically detected in four (18.2%) patients with TUR and 22 (51.2%) patients with radical cystectomy whereas no expression was observed in normal transitional cells located at tumor-free area in bladder. The maspin expression was significantly correlated with the development of muscle invasive bladder cancer (P=0.00008). Using a luciferase reporter system, maspin promoter activity was induced in the maspin-positive bladder cancer cell lines as well as maspin-negative RT4 cells. Furthermore, treatment with the DNA methyltransferase inhibitor, 5-aza-2' deoxycytidine, and histone deacetylase inhibitor, trichostatin A, led to re-expression of maspin in RT4 cells. Our results indicate that maspin may contribute to bladder cancer development and that DNA methylation and histone deacetylation may be important for regulating maspin gene activation in bladder cancer cells.     

Skin fragility in obese diabetic mice: possible involvement of elevated oxidative stress and upregulation of matrix metalloproteinases

The purpose of this study was to test the hypothesis that obese diabetic mice exhibit marked skin fragility, which is caused by increased oxidative stress and increased matrix metalloproteinase (MMP) gene expression in the subcutaneous adipose tissue. Scanning electron microscopy of skin samples from Tsumura-Suzuki obese diabetic (TSOD) mice revealed thinner collagen bundles, and decreased density and convolution of the collagen fibres. Furthermore, skin tensile strength measurements confirmed that the dorsal skin of TSOD mice was more fragile to tensile force than that of non-obese mice. The mRNA expressions of heme oxygenase 1 (Hmox1), a marker of oxidative stress, Mmp2 and Mmp14 were increased in the adipose tissue of TSOD mice. Antioxidant experiments were subsequently performed to determine whether the changes in collagen fibres and skin fragility were caused by oxidative stress. Strikingly, oral administration of the antioxidant dl-α-tocopherol acetate (vitamin E) decreased Hmox1, Mmp2 and Mmp14 mRNA expressions, and improved the skin tensile strength and structure of collagen fibres in TSOD mice. These findings suggest that the skin fragility in TSOD mice is associated with dermal collagen damage and weakened tensile strength, and that oxidative stress and MMP overexpression in the subcutaneous adipose tissue may, at least in part, affect dermal fragility via a paracrine pathway. These observations may contribute to novel clinical interventions, such as dietary supplementation with antioxidants or application of skin cream containing antioxidants, which may overcome skin fragility in obese patients with diabetes.     

Utility of spinal MRI in children with anorectal malformation

Background  The association between spinal cord anomalies and imperforate anus is well recognized. Until now, the incidence of tethered cord has been assumed to be higher in patients with high-type imperforate anus. However, recent reports suggest that tethered cord is as common in patients with a low lesion as in those with a high lesion. Objective  To review the incidence of spinal cord anomalies in those with a low lesion and those with a high (including intermediate) anorectal malformation (ARM), and to determine the best diagnostic imaging strategy. Materials and methods  A group of 50 consecutive patients with postoperative ARM and in whom spinal MRI had been performed were identified retrospectively. We reviewed and compared the following factors between those with a high lesion and those with a low lesion: (1) clinical symptoms, (2) spinal cord anomalies, and (3) vertebral anomalies. Results  The incidence of spinal cord anomalies was no different between those with a high lesion and those with a low lesion, and spinal cord anomalies were present regardless of the presence of vertebral anomalies or symptoms. Conclusion  Owing to the high incidence of spinal cord anomalies in patients with imperforate anus, MRI is the best imaging tool for detecting such anomalies regardless of the level of the lesion.