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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.
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Objective:To investigate the feasibility of size-specific dose estimate of head based on pediatric patients′ age.Methods:A retrospective study was conducted on plain head CT scans of 210 patients in Tianjin Children′s Hospital from January to March in 2022. The volume CT dose index (CTDI vol) values, age and sex of the patients were recorded. The anteroposterior diameter (AP) and lateral diameter(LAT), aera and CT value in the middle slice of the scan region were measured on the workspace. According to the AAPM reports 220 and 293, the water equivalent diameter ( DW) of head, size-specific conversion factors ( fmeasuredH16), and size-specific dose estimate (SSDE measured) were calculated. The effective diameter ( Deff; WHO) was calculated for male and female individuals using the ralationship between the standard head circumference and age of children provided by World Health Organization (WHO). The effective diameter ( Deff; WHO) was converted into a water equivalent diameter ( DW; WHO), using a correlation established from the Deff and DWwhich were measured in 210 image sets of male and female patients. Then the corresponding fWHOH16 and SSDE WHO of head can be calculated. The correlation between DW and DW; WHO, fmeasuredH16 and fWHOH16, the correlation and consistency between SSDE measured and SSDE WHO, and the conversion relationship between age and fWHOH16 were analyzed for male and female patients. Results:A significant correlation were found between the measured DW and DW; WHO(female: r=0.917, P<0.01; male: r=0.873, P<0.01), fmeasuredH16 and fWHOH16(female: r=0.916, P<0.01; male: r=0.883, P<0.01), SSDE measured and SSDE WHO( r=0.991, P<0.01; male: r=0.992, P<0.01). The Bland-Altman test indicated that there was good coherence between SSDE measured and SSDE WHO. Maximal mean root-mean-square errors of SSDE measured and SSDE WHO were 5.61% in female and 5.25% in male. The conversion relationship between fWHOH16 and patient age in different genders was obtained by curve fitting. Conclusion:The SSDE of head in pediatric patients can be estimated simply and accurately by directly using the patient′s age.
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Objective:To investigate the value of the size-specific dose estimate (SSDE) on dose estimations of children's head CT scans.Methods:A retrospective study was conducted on plain head CT scans of 252 patients with the 64-row detector CT device of Discovery 750HD in the Union Hospital, Tongji Medical College, Huazhong University of Science and Technology from January to September in 2019. The volume CT dose index (CTDI vol)values were recorded. The head circumference (HC), area, and CT value were measured using a self-developed computer program, and the water equivalent diameter (WED), size-specific conversion factors ( f293 and f220), and absorbed dose (SSDE 293 and SSDE 220) were calculated according to the AAPM reports 293 and 220.The patients were divided into three groups by the quartering meth odaccording to their HC(<47.8 cm, 47.8-52.7 cm, >52.7 cm)and four groups based on their ages(0-2, 3-6, 7-10 and 11-14 years old). The difference between parameters ( f220 and f293, SSDE 220 and SSDE 293、SSDE 293 and CTDI vol) were compared for different groups, and the correlation of HC with f293 and SSDE 293 was analyzed. Results:There was an overestimation of f220 by 11.11% ( t=252.61, P<0.05) compared with f293. SSDE 220 was overestimated by 10.31% ( t=228.21, P<0.05) compared with SSDE 293, and SSDE 293 was underestimated by 9.60% ( t=-31.34, P<0.05)compared with CTDI vol. For the three HC groups, SSDE 220 was overestimated by 8.54%, 10.37%, and 11.57% ( t=73.73, 438.58, 275.52, P<0.05)compared with SSDE 293, and SSDE 293 was underestimated by 1.30%, 9.79%, and 14.61% ( t=-1.91, -60.95, -47.64, P<0.05)compared with CTDI vol. For the four age groups SSDE 220 was overestimated by 8.45%, 10.00%, 10.57%, and 11.36% ( t=63.58, 232.29, 247.84, 302.95, P< 0.05)compared with SSDE 293, and SSDE 293 was underestimated by 1.49%, 8.27%, 10.63%, and 13.78% ( t=-1.83, -28.27, -37.30, -49.80, P< 0.05)compared with CTDI vol. Furthermore, HC was highly correlated with f293 and SSDE 293 ( r2=0.88 and 0.76, respectively, P< 0.05). Conclusions:The radiation dose in children′s head CT scanning can be more accurately estimated according to the AAPM Report 293, while it can be overestimated by CTDI vol. Meanwhile, the CT radiation dose can be patently overestimated with the AAPM Report 220 compared with Report 293.HC is closely correlated with f293 and SSDE 293 and it can be used to estimatee more accurately for SSDE and the radiation dose received by children during head CT scanning.
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Objective@#To investigate the application value of CTDIvol and size-specific dose estimate(SSDE) in evaluating the radiation dose of adult chest CT.@*Methods@#A retrospective analysis was made on the CTDIvoland SSDE of 128 patients who underwent chest CT scanning in the First Affiliated Hospital of Zhejiang Chinese Medical University from March to April 2017 and all images are adequate for diagnosis. The subjects were divided into three groups according to body mass index (BMI): Group A, 38 cases with 16≤BMI<21.1 kg/m2; Group B, 53 cases with 21.1≤BMI<23.9 kg/m2; Group C, 37 cases with 23.9≤BMI<34.1 kg/m2. The diameters of anterior-posterior (AP) and left-right (LAT) of each patient were measured in the slice of nipple level, and CTDIvol, effective diameter (ED), conversion factor (fsize) and SSDE of each patient were recorded and calculated. Meanwhile, the differences between CTDIvol and SSDE in different BMI groups were compared.@*Results@#SSDE of each group was higher than CTDIvol, and increased by 50.13%, 42.83% and 33.68% in group A, B and C, respectively. There were significant differences in radiation dose between CTDIvol and SSDE in the three groups (t=-48.873, -57.001, -32.651, P<0.05). There were significant differences in ED, fsize, CTDIvol and SSDE among the three groups (F=51.456, 47.749, 113.916, 106.449, P<0.05).@*Conclusions@#SSDE can evaluate the radiation dose absorbed by patients with different body types in chest CT, while CTDIvol underestimated the radiation dose.The lower BMI, the greater the underestimated dose value, the more radiation dose absorbed.
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Objective To investigate the application value of CTDIvol and size-specific dose estimate( SSDE) in evaluating the radiation dose of adult chest CT. Methods A retrospective analysis was made on the CTDIvol and SSDE of 128 patients who underwent chest CT scanning in the First Affiliated Hospital of Zhejiang Chinese Medical University from March to April 2017 and all images are adequate for diagnosis. The subjects were divided into three groups according to body mass index ( BMI):Group A,38 cases with 16≤BMI<21. 1 kg/m2; Group B,53 cases with 21. 1≤BMI<23. 9 kg/m2; Group C,37 cases with 23. 9≤BMI<34. 1 kg/m2. The diameters of anterior-posterior (AP) and left-right (LAT) of each patient were measured in the slice of nipple level, and CTDIvol , effective diameter ( ED) , conversion factor ( fsize ) and SSDE of each patient were recorded and calculated. Meanwhile, the differences between CTDIvol and SSDE in different BMI groups were compared. Results SSDE of each group was higher than CTDIvol , and increased by 50. 13％, 42. 83％ and 33. 68％ in group A, B and C, respectively. There were significant differences in radiation dose between CTDIvol and SSDE in the three groups ( t=-48. 873,-57. 001, -32. 651, P<0. 05) . There were significant differences in ED, fsize , CTDIvol and SSDE among the three groups ( F=51. 456, 47. 749, 113. 916, 106. 449, P<0. 05) . Conclusions SSDE can evaluate the radiation dose absorbed by patients with different body types in chest CT, while CTDIvol underestimated the radiation dose. The lower BMI, the greater the underestimated dose value, the more radiation dose absorbed.
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Objective To investigate the effect of scan table on size-specific dose estimate ( size-specific dose estimate, SSDE) in children's CT scan. Methods CT imaging data and CTDIvol of 44 children ( 15 heads, 13 chests, 16 abdomen-pelvis) who underwent Siemens SOMATOM Definition AS+ 64 row 128-slice CT scan were retrospectively collected. CTDIvol of each patient was recored, WED ( water equivalent diameter) was calculated by two different methods ( with or without table) , donated as WED-T and WED-NT, then the corresponding SSDEWED ( SSDEWED-T and SSDEWED-NT ) was calculated. And the SSDEWED-NT was used as reference to evaluate the difference between WED and SSDEWED obtained by two different methods. Results Including part of table will lead to the overestimate for WED, with mean differences of 0. 10％, 2. 82％ and 2. 54％ for head, chest and abdomen-pelvis, respectively, while SSDEWED will be underestimated by 0. 06％ ( head ) , 2. 70％ ( chest ) and 1. 59％ ( abdomen-pelvis ) . Conclusions Including par of the patient table has a certain effect on SSDEWED for children, more attention should be paid for the application of SSDEWED.
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Objective To explore the validity of the size-specific dose estimate (SSDE) derived from the water-equivalent diameter (Dw)value of the slice located in the middle of the scan range in the head CT examination. Methods A total of 197 patients underwent head CT nonenhanced scan were enrolled in this retrospective study. The Dw, size-dependent conversion factor (f), normalized volume CT dose index (CTDIvol) and SSDE values of all slices were calculated. Two sets of SSDE, SSDEgroand SSDEcenbased on the Dwvalues slice by slice (Dw-gro) and the Dwvalues of the slices in the middle of the scan range (Dw-cen), were obtained across all patients. Pearson correlation analysis and linear regression analysis were performed for Dw-grovs Dw-cen, Spearman correlation analysis and linear regression analysis for SSDEgrovs SSDEcen, SSDE vs Dw, CTDIvolvs Dw. With the reference of SSDEgrovalue, mean absolute relative difference (MARD) of SSDEcen values were calculated to assess its accuracy and the correlated factors of MARD was analyzed with multivariate linear stepwise regression analysis. Results The minimal Dwvalue close to the roof of the skull corresponded to the maximal value of f and SSDE, which was the minimal value of CTDIvol. The significant positive correlation was showed between Dw-grovs Dw-cen, SSDEgrovs SSDEcen, SSDE vs Dw, CTDIvolvs Dw(r=0.947, 0.931, 0.416, 0.626;P＜0.05). The values of Dw,groand Dw-cenwere (16.94±0.69) and (18.50±0.62) cm respectively. The values of SSDEgroand SSDEcenwere [54.10 (52.29, 56.39)] mGy and [53.77 (51.85, 55.25)] mGy respectively. An approximation of SSDEcenvalues with an average of 1.62% of the gross MARD was found to match the reference value. Multivariate linear stepwise regression analysis indicated that MARD had negative correlation with Dw(β=–1.319,P＜0.05), positive correlation with CTDIvol(β=0.202,P＜0.05), and f was not included in the multivariate regression equation. Conclusion SSDEcenbased on the Dwvalue of the slice located at the center of the scan range yields small MARD value and can represent a reliable SSDE estimation in the head CT examination.
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Objective@#To compare and quantify the differences in size-specific dose estimates (SSDE) obtained by effective diameter and water-equivalent diameter from the central slice of the scan range in head CT examination.@*Methods@#A total of 111 consecutive adult patients who underwent head CT examination were enrolled in this study. All of CTDIvol values in the dose report were documented. The dataset was assigned into group A and group B, based on the individual size-dependent conversion factors (f) of effective diameter (deff) and water-equivalent diameter (dw) at the central slice multiplied by normalized volume computed tomography dose index (CTDIvol ) respectively. Body size, f and SSDE were calculated. With SSDEgross served as the reference level, the performance of SSDEdeff and SSDEdw was evaluated.@*Results@#Statistically significant differences were found in body size (t=47.587, P<0.05) and f(z=-9.242, P<0.05) between group A and group B. Statistically significant difference also existed in SSDE (t=-46.687, P<0.05), (56.20±2.66) and (53.49±2.48) mGy for group A and group B respectively. Strongly positive correlation was shown in body size (r=0.873, R2 =0.761) and SSDE (r=0.974, R2 =0.949) between group A and group B(all P<0.05). Positive correlation was also found between SSDEdeff and SSDEgross(r=0.900, R2 =0.809), SSDEdw and SSDEgross (r=0.904, R2 =0.817, all P<0.05). Mean absolute difference was 2.34 and 0.78 mGy, for SSDEdeff vs. SSDEgross and SSDEdw vs. SSDEgross respectively; mean absolute relative difference was 4.38%, 1.40%; root mean square difference was 1.17 mGy (2.17%), 1.06 mGy (1.91%). Interquartile range and full range of SSDEdeff and SSDEdw were 3.22 vs. 2.39 mGy, 13.65 vs. 12.48mGy, respectively. A less degree of variation was observed in SSDEdw than that in SSDEdeff.@*Conclusions@#SSDEdw values based on the water-equivalent diameter at the central slice of the scan range got better agreement with those derived from all slices, which could serve as a simpler and more valid indicator to represent the average value of size-specific dose estimates of the whole scan range in head CT examination.
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Abstract. In order to have a more accurate estimation of the dose delivered for computed tomography (CT) studies, and given that the current dose estimates do not include the size of the patient, a retrospective study was conducted on a sample of 388 patients from the radiology department of a general hospital, to make a better assessment of the dose delivered for CT scans of the chest, abdomen and pelvis in adult and paediatric patients. A comparison was made between the volume computed tomography dose index (CTDIvol) delivered by the scanner and CTDIvol value corrected by the incorporation of the effective patient diameter according to the report 204 of the American Association of Physicists in Medicine (AAPM). It was found that the values of CTDIvol vary in all cases when the patient size parameter is included, with this variation being greater as sizes go to extremes.
Resumen. Con el objetivo de tener una estimación de dosis más exacta entregada por los estudios de tomografía computarizada (TC) y dado que los estimadores de dosis actuales no incluyen el tamaño del paciente en la estimación, se realizó un estudio retrospectivo en una muestra de 388 pacientes de un servicio de radiología de un hospital general, para calcular las dosis entregadas en exámenes de TC de tórax, abdomen y pelvis en pacientes adultos y pediátricos. Se elaboró y realizó una comparación entre el índice de dosis de TC (CTDI VOL) entregado por el equipo y el CTDI VOL corregido mediante la incorporación del parámetro del diámetro efectivo del paciente según el reporte 204 de la Asociación Americana de Físicos Médicos (AAPM). Se pudo comprobar que los valores de CTDI VOL varían en la totalidad de los casos al ingresar el parámetro de tamaño del paciente y que esta variación es mayor a medida que los tamaños se van a los extremos.