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Research paper thumbnail of Construction of 0.15 Tesla Overhauser Enhanced MRI

Advances in Experimental Medicine and Biology, 2017

Overhauser enhanced MRI (OMRI) is one of the free radical imaging technologies and has been used ... more Overhauser enhanced MRI (OMRI) is one of the free radical imaging technologies and has been used in biomedical research such as for partial oxygen measurements in tumor, and redox status in acute oxidative diseases. The external magnetic field of OMRI is frequently in the range of 5-10 mTesla to ensure microwave penetration into small animals, and the S/N ratio is limited. In this study, a 0.15 Tesla OMRI was constructed and tested to improve the S/N ratio for a small sample, or skin measurement. Specification of the main magnet was as follows: 0.15 Tesla permanent magnet; gap size 160 mm; homogenous spherical volume of 80 mm in diameter. The OMRI resonator was designed based on TE 101 cavity mode and machined from a phosphorus deoxidized copper block for electron spin resonance (ESR) excitation and a solenoid transmission/receive resonator for NMR detection. The resonant frequencies and Q values were 6.38 MHz/150 and 4.31-4.41 GHz/120 for NMR and ESR, respectively. The Q values were comparable to those of conventional low field OMRI resonators at 15 mTesla. As expected, the MRI S/N ratio was improved by a factor of 30. Triplet dynamic nuclear polarization spectra were observed for 14 N carboxy-PROXYL, along the excitation microwave sweep. In the current setup, the enhancement factor was ca. 0.5. In conclusion, the results of this preliminary evaluation indicate that the 0.15 Tesla OMRI could be useful for free radical measurement for small samples.

Research paper thumbnail of Direct Evidence for Increased Hydroxyl Radicals Originating From Superoxide in the Failing Myocardium

Circulation Research, 2000

Experimental and clinical studies have suggested an increased production of reactive oxygen speci... more Experimental and clinical studies have suggested an increased production of reactive oxygen species (ROS) in the failing myocardium. The present study aimed to obtain direct evidence for increased ROS and to determine the contribution of superoxide anion (⅐ O 2 Ϫ), H 2 O 2 , and hydroxy radical (⅐ OH) in failing myocardial tissue. Heart failure was produced in adult mongrel dogs by rapid ventricular pacing at 240 bpm for 4 weeks. To assess the production of ROS directly, freeze-clamped myocardial tissue homogenates were reacted with the nitroxide radical, 4-hydroxy-2,2,6,6,tetramethyl-piperidine-N-oxyl, and its spin signals were detected by electron spin resonance spectroscopy. The rate of electron spin resonance signal decay, proportional to ⅐ OH level, was significantly increased in heart failure, which was inhibited by the addition of dimethylthiourea (⅐ OH scavenger) into the reaction mixture. Increased ⅐ OH in the failing heart was abolished to the same extent in the presence of desferrioxamine (iron chelator), catalase (H 2 O 2 scavenger), and 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron; LaMotte) (⅐ O 2 Ϫ scavenger), indicating that ⅐ OH originated from H 2 O 2 and ⅐ O 2 Ϫ. Further, ⅐ O 2 Ϫ produced in normal myocardium in the presence of antimycin A (mitochondrial complex III inhibitor) could reproduce the increase of H 2 O 2 and ⅐ OH seen in the failing tissue. There was a significant positive relation between myocardial ROS level and left ventricular contractile dysfunction. In conclusion, in the failing myocardium, ⅐ OH was produced as a reactive product of ⅐ O 2 Ϫ and H 2 O 2 , which might play an important role in left ventricular failure.

Research paper thumbnail of Construction of 0.15 Tesla Overhauser Enhanced MRI

Advances in Experimental Medicine and Biology, 2017

Overhauser enhanced MRI (OMRI) is one of the free radical imaging technologies and has been used ... more Overhauser enhanced MRI (OMRI) is one of the free radical imaging technologies and has been used in biomedical research such as for partial oxygen measurements in tumor, and redox status in acute oxidative diseases. The external magnetic field of OMRI is frequently in the range of 5-10 mTesla to ensure microwave penetration into small animals, and the S/N ratio is limited. In this study, a 0.15 Tesla OMRI was constructed and tested to improve the S/N ratio for a small sample, or skin measurement. Specification of the main magnet was as follows: 0.15 Tesla permanent magnet; gap size 160 mm; homogenous spherical volume of 80 mm in diameter. The OMRI resonator was designed based on TE 101 cavity mode and machined from a phosphorus deoxidized copper block for electron spin resonance (ESR) excitation and a solenoid transmission/receive resonator for NMR detection. The resonant frequencies and Q values were 6.38 MHz/150 and 4.31-4.41 GHz/120 for NMR and ESR, respectively. The Q values were comparable to those of conventional low field OMRI resonators at 15 mTesla. As expected, the MRI S/N ratio was improved by a factor of 30. Triplet dynamic nuclear polarization spectra were observed for 14 N carboxy-PROXYL, along the excitation microwave sweep. In the current setup, the enhancement factor was ca. 0.5. In conclusion, the results of this preliminary evaluation indicate that the 0.15 Tesla OMRI could be useful for free radical measurement for small samples.

Research paper thumbnail of Direct Evidence for Increased Hydroxyl Radicals Originating From Superoxide in the Failing Myocardium

Circulation Research, 2000

Experimental and clinical studies have suggested an increased production of reactive oxygen speci... more Experimental and clinical studies have suggested an increased production of reactive oxygen species (ROS) in the failing myocardium. The present study aimed to obtain direct evidence for increased ROS and to determine the contribution of superoxide anion (⅐ O 2 Ϫ), H 2 O 2 , and hydroxy radical (⅐ OH) in failing myocardial tissue. Heart failure was produced in adult mongrel dogs by rapid ventricular pacing at 240 bpm for 4 weeks. To assess the production of ROS directly, freeze-clamped myocardial tissue homogenates were reacted with the nitroxide radical, 4-hydroxy-2,2,6,6,tetramethyl-piperidine-N-oxyl, and its spin signals were detected by electron spin resonance spectroscopy. The rate of electron spin resonance signal decay, proportional to ⅐ OH level, was significantly increased in heart failure, which was inhibited by the addition of dimethylthiourea (⅐ OH scavenger) into the reaction mixture. Increased ⅐ OH in the failing heart was abolished to the same extent in the presence of desferrioxamine (iron chelator), catalase (H 2 O 2 scavenger), and 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron; LaMotte) (⅐ O 2 Ϫ scavenger), indicating that ⅐ OH originated from H 2 O 2 and ⅐ O 2 Ϫ. Further, ⅐ O 2 Ϫ produced in normal myocardium in the presence of antimycin A (mitochondrial complex III inhibitor) could reproduce the increase of H 2 O 2 and ⅐ OH seen in the failing tissue. There was a significant positive relation between myocardial ROS level and left ventricular contractile dysfunction. In conclusion, in the failing myocardium, ⅐ OH was produced as a reactive product of ⅐ O 2 Ϫ and H 2 O 2 , which might play an important role in left ventricular failure.