Study of Attenuation Correction Using a Cardiac Dynamic Phantom: Synchronized Time-Phase-Gated Attenuation Correction Method.

In cardiac nuclear medicine examinations, absorption in the body is the main factor in the degradation of the image quality. The Chang and external source methods were used to correct for absorption in the body. However, fundamental studies on attenuation correction for electrocardiogram (ECG)-synchronized CT imaging have not been performed. Therefore, we developed and improved an ECG-synchronized cardiac dynamic phantom and investigated the synchronized time-phase-gated attenuation correction (STPGAC) method using ECG-synchronized SPECT and CT images of the same time phase. Methods: As a basic study, SPECT was performed using synchronized time-phase-gated (STPG) SPECT and non-phase-gated (NPG) SPECT. The attenuation-corrected images were, first, CT images with the same time phase as the ECG waveform of the gated SPECT acquisition (with CT images with the ECG waveform of the CT acquisition as the reference); second, CT images with asynchronous ECG; third, CT images of the 75% region; and fourth, CT images of the 40% region. Results: In the analysis of cardiac function in the phantom experiment, left ventricle ejection fraction (heart rate, 11.5%-13.4%; myocardial wall, 49.8%-55.7%) in the CT images was compared with that in the STPGAC method (heart rate, 11.5%-13.3%; myocardial wall, 49.6%-55.5%), which was closer in value to that of the STPGAC method. In the phantom polar map segment analyses, none of the images showed variability (F (10,10) < 0.5, P = 0.05). All images were correlated (r = 0.824-1.00). Conclusion: In this study, we investigated the STPGAC method using a SPECT/CT system. The STPGAC method showed similar values of cardiac function analysis to the CT images, suggesting that the STPGAC method accurately reconstructed the distribution of blood flow in the myocardial region. However, the target area for attenuation correction of the heart region was smaller than that of the whole body, and changing the gated SPECT conditions and attenuation-corrected images did not affect myocardial blood flow analysis.

[Live birth distribution by time and place from 1981 to 1998 in Japan].

OBJECTIVES: To investigate the diurnal rhythm of live births labored spontaneously, and the effects of obstetric intervention on birth time distributions. METHODS: The data of live births tabulated by time (one-hour intervals), date and birthplace throughout Japan between 1981 and 1998 were obtained with permission from the former Ministry of Health and Welfare. Together with an investigation of hourly birth numbers by place in each year, an annual transition of hourly birth rates in medical institutions and the diurnal rhythm of birth numbers in maternity homes and at home were analyzed using regression analysis. RESULTS: In every calendar year studied the hourly live birth numbers at hospitals showed a single-peak distribution pattern with maximum values at 13:00-15:00. The annual transition of hourly birth rates showed a 10% (birth numbers base) decrease in the 11:00-13:00 period in 1998 as compared with that in 1981, while there was a corresponding increase of 8% in the 13:00-15:00 period. Hourly birth numbers at clinics showed a double-peak distribution pattern with maximum values during the 11:00-12:00 and 14:00-15:00 periods in early 1980, while a single-peak distribution with a maximum value during the 13:00-15:00 period appeared in 1989 and has remained thereafter. Hourly birth rates (birth numbers base) increased by over 6% in the 13:00-15:00 and 17:00-20:00 periods over the past 18 years, while they decreased by 10% in the 9:00-13:00 period. The results at maternity homes were clearly different from those at hospitals and clinics. The live birth numbers totaled for the 18 years showed a double-phase distribution with a maximum value in the 6:00-7:00 period and a minimum value in the 19:00-20:00 period. The best-fit regression model for the obtained data was a sine curve with a maximum value at 6:00 (coefficient of determination 0.97). Hourly distributions of live births at home also fitted best to a since curve with the maximum value again at 6:00 (coefficient of determination 0.95). CONCLUSIONS: The results suggested that the timing of spontaneous live births follows a circadian rhythm and that obstetric intervention affects time distributions of live births by shifting over 10% of births during the night and early morning to a working day service time (9:00-17:00).

Nationwide description of live Japanese births by day of the week, hour, and location.

To characterize temporal variations of live births in Japan, we analyzed data on the 1,203,147 births of 1998. In hospitals, with 20+ beds, the daily average of live births was significantly lower at weekends and national holidays (mean=1,433, SD = 100) than on weekdays (mean = 1,957, SD = 126). Hourly distributions of live births showed a single sharp peak at 1:00-2:59 pm on weekdays with a small peak at an earlier hour on Saturdays, Sundays and national holidays. The results in clinics, with no bed or less than 20 beds, were similar to those in hospitals except on Saturdays. The difference in the daily average of live births between Saturdays and weekdays was smaller in clinics than that found in hospitals, and hourly distributions on Saturdays resembled those of weekdays but not Sundays or national holidays. Maternity homes showed no differences in the mean number of daily live births over the days of the week including national holidays, and no clear peak of percentage distributions of hourly live births on each day of the week. The present study suggests that the weekly and hourly variations observed in hospitals and clinics are not due to a biological rhythm of labor, but to obstetric intervention in the timing of delivery, either through induction of labor or elective cesarean section.