Yasunori Yoshizawa

Effect of collimator choice on quantitative assessment of cardiac iodine 123 MIBG uptake

BackgroundQuantitative accuracy in iodine 123 studies may be impaired by septal penetration. We evaluated the effect of collimator choice on estimation of the heart-tomediastinum (H/M) ratio in cardiac I-123 metaiodobenzylguanidine (MIBG) imaging.Methods and ResultsA low-energy high-resolution (LEHR) collimator, special LEHR (SLEHR) collimator, and medium-energy (ME) collimator were used. In experiments in which a phantom of simple geometry was used, the use of the LEHR collimator provided the lowest contrast accuracy, suggesting the effect of septal penetration. Thoracic phantom studies demonstrated contamination of heart and mediastinum counts by lung and liver activities, which was greatest with the LEHR collimator and least with the ME collimator. In 8 patients anterior chest views were acquired successively with the three collimators after I-123 MIBG injection. H/M ratios were significantly higher with the SLEHR collimator than with the LEHR collimator and were still higher with the ME collimator. The difference in H/M ratios between the LEHR and ME collimators showed a high positive correlation with the lung-to-mediastinum ratio.ConclusionsCollimator choice substantially influences estimation of the H/M ratios in cardiac I-123 MIBG imaging. The use of an ME collimator provides high quantitative accuracy and may enhance reliability in the evaluation of cardiac sympathetic nerve function.

Lateral–Medial Dissociation in Orbitofrontal Cortex–Hypothalamus Connectivity

The orbitofrontal cortex (OFC) is involved in cognitive functions, and is also closely related to autonomic functions. The OFC is densely connected with the hypothalamus, a heterogeneous structure controlling autonomic functions that can be divided into two major parts: the lateral and the medial. Resting-state functional connectivity has allowed us to parcellate the cerebral cortex into putative functional areas based on the changes in the spatial pattern of connectivity in the cerebral cortex when a seed point is moved from one voxel to another. In the present high spatial-resolution fMRI study, we investigate the connectivity-based organization of the OFC with reference to the hypothalamus. The OFC was parcellated using resting-state functional connectivity in an individual subject approach, and then the functional connectivity was examined between the parcellated areas in the OFC and the lateral/medial hypothalamus. We found a functional double dissociation in the OFC: the lateral OFC (the lateral orbital gyrus) was more likely connected with the lateral hypothalamus, whereas the medial OFC (the medial orbital and rectal gyri) was more likely connected with the medial hypothalamus. These results demonstrate the fundamental heterogeneity of the OFC, and suggest a potential neural basis of the OFC–hypothalamic functional interaction.

Relatedness-dependent rapid development of brain activity in anterior temporal cortex during pair-association retrieval

Functional MRI studies have revealed that the brain activity in the anterior temporal cortex during memory retrieval increases over months after memory encoding. Behavioral evidence has demonstrated that long-term memory can sometimes be consolidated more rapidly in one or two days. In the present functional MRI study, we manipulated the relatedness between paired faces to be retrieved in a pair-association task. The brain activity in the anterior temporal cortex during retrieval of paired associates increased rapidly in one day, as shown in previous studies. We found that the speed of the brain activity development was dependent on the level of semantic relatedness of paired faces. The results suggest that the semantic relatedness enhances the speed of formation of memory representation in the anterior temporal cortex.