ABSTRACT
Objective:To explore the value of size-specific dose estimate (SSDE) based on effective diameter and water equivalent diameter ( Dw) in pediatric head CT. Methods:A retrospective analysis of 187 children underwent unenhanced head CT scanning were reviewed and divided into 3 groups according to the age: Group 1 (<1 m), Group 2(≥1 m~6 y), Group 3 (≥6~14 y). All CTDI vol values were recorded. The central axial image in the scanning range was selected. The region of interest (ROI) containing all anatomical structures (including skin) was outlined and the area of ROI ( AROI), head circumference, average CT value (CT ROI) were measured. The Dw, conversion factor fH16 and SSDE were calculated. The CTDI vol, SSDE and the rate of change( Δvalue)were compared among groups. The regression model between CTDI vol and SSDE was established. Results:The Dw values of groups 1-3 were (11.24±0.51), (14.48±1.47), (16.69±0.90)mm, respectively. The CTDI vol values were(15.36±2.78), (18.83±4.60), (23.24±4.13)mGy, respectively. SSDE values were(27.92±4.91), (29.16±6.64), (32.38±5.35)mGy, respectively. The differences among Dw, CTDI vol and SSDE groups were all statistically significant ( F=207.69、38.48、8.15, P<0.001). The values of Dw, CTDI vol and SSDE were gradually increasing while the age was increasing. However, the Δ value gradually was decreasing with increasing age. The linear regression equation of CTDI vol and SSDE was established as SSDE=7.252 + 1.137×CTDI vol. Conclusions:The radiation dose of children′s head CT can be accurately assessed based on Dw combined with head conversion factor fH16 to estimate the body-specific dose SSDE. The radiation dose of children′s head CT was underestimated with the greater degree for smaller age.
ABSTRACT
This paper proposes an architecture of the wireless monitoring system for the real-time monitoring of the orthopedic implants, which monitors the implant duty cycle, detects abnormal asymmetry, high amounts of force, and other conditions of the orthopedic implants. Data for diagnosis are communicated wirelessly by the radio-frequency (RF) signal between the embedded chip and the remote circuit. In different working modes, the system can be powered by the RF signal or stiff lead zirconate-titanate (PZT) ceramics which are able to convert mechanical energy inside the orthopedic implant into electrical energy. The power circuits with a variable ratio switched-capacitor (SC) dc-dc converter have been taped out with 0.35-mum complementary metal-oxide semiconductor (CMOS) technology. The test results show that the SC converter can transfer the input voltage that ranges from 5 V to 14 V from the PZT ceramics into the voltage ranging from 2 V to 2.5 V which will be dealt with by a low drop-out circuit in the future work. The total efficiency of the SC converter is from 28% to 42% at full-time working mode. The analog-to-digital converter (ADC) circuits have been fabricated in a 0.18-mum 1P6M CMOS process. The test results show that the ADC chip consumes only 12.5 muW in working mode and 150 nW in the sleep mode. The circuits, including RF circuits, ADC, and the microcontrol unit, have been implemented in a 0.18-mu m CMOS process. Future work includes some clinical experiments test in the application where PZT elements are used for power generation in total knee-replacement implants.
