K. Perisinakis

The effect of z overscanning on patient effective dose from multidetector helical computed tomography examinations

z overscanning in multidetector (MD) helical CT scanning is prerequisite for the interpolation of acquired data required during image reconstruction and refers to the exposure of tissues beyond the boundaries of the volume to be imaged. The aim of the present study was to evaluate the effect of z overscanning on the patient effective dose from helical MD CT examinations. The Monte Carlo N-particle radiation transport code was employed in the current study to simulate CT exposure. The validity of the Monte Carlo simulation was verified by (a) a comparison of calculated and measured standard computed tomography dose index (CTDI) dosimetric data, and (b) a comparison of calculated and measured dose profiles along the z axis. CTDI was measured using a pencil ionization chamber and head and body CT phantoms. Dose profiles along the z axis were obtained using thermoluminescence dosimeters. A commercially available mathematical anthropomorphic phantom was used for the estimation of effective doses from four standard CT examinations, i.e., head and neck, chest, abdomen and pelvis, and trunk studies. Data for both axial and helical modes of operation were obtained. In the helical mode, z overscanning was taken into account. The calculated effective dose from a CT exposure was normalized to CTDIfreeinair. The percentage differences in the normalized effective dose between contiguous axial and helical scans with pitch=1, may reach 13.1%, 35.8%, 29.0%, and 21.5%, for head and neck, chest, abdomen and pelvis, and trunk studies, respectively. Given that the same kilovoltage and tube load per rotation were used in both axial and helical scans, the above differences may be attributed to z overscanning. For helical scans with pitch=1, broader beam collimation is associated with increased z overscanning and consequently higher normalized effective dose value, when other scanning parameters are held constant. For a given beam collimation, the selection of a higher value of reconstructed image slice width increases the normalized effective dose. In conclusion, z overscanning may significantly affect the patient effective dose from CT examinations performed on MD CT scanners. Therefore, an estimation of the patient effective dose from MD helical CT examinations should always take into consideration the effect of z overscanning.

Therapeutic ERCP and pregnancy: is the radiation risk for the conceptus trivial?

BACKGROUNDnSymptomatic choledocholithiasis can be treated during pregnancy. Conceptus doses ranged from 0.1 mGy to 3 mGy in previous studies.nnnOBJECTIVEnThe objectives of the current study were to investigate whether the conceptus dose may exceed the threshold of 10 mGy in the case of a pregnant patient undergoing ERCP, and to provide data for the accurate assessment of a conceptus dose.nnnDESIGNnMonte Carlo methodology and mathematical anthropomorphic phantoms were used to determine normalized conceptus dose data. Phantoms simulated pregnant patients of different body sizes and gestational stages. Monte Carlo simulations were performed to estimate the efficiency of external shielding.nnnSETTINGnUniversity hospital.nnnPATIENTSnTwenty-four consecutive patients.nnnINTERVENTIONSnAll patients underwent therapeutic ERCP. Exposure parameters and dose-area product were recorded during the procedures.nnnMAIN OUTCOME MEASUREMENTSnThe total dose-area product recorded during ERCP procedures ranged between 62 x 10(3) and 491 x 10(3) mGy . cm(2).nnnRESULTSnMonte Carlo normalized conceptus dose data are presented as a function of kV(p), total filtration, gestational stage, and body mass index. The conceptus dose may exceed 10 mGy when the total dose-area product surpasses 130 mGy . cm(2).nnnLIMITATIONSnVariations of conceptus location and size from the average.nnnCONCLUSIONSnConceptus dose from ERCP may occasionally exceed 10 mGy, the dose above which the analytical dose calculation is recommended. The use of external shielding is unnecessary because the associated dose reduction is negligible. The normalized dose data may be used for the accurate estimation of conceptus dose from an ERCP procedure performed on a pregnant patient, regardless of body size, gestational stage, operating parameters, and equipment used.

Imaging Ultrasonometry of the Calcaneus: Optimum T-Score Thresholds for the Identification of Osteoporotic Subjects

The purpose of the present study was to (1) examine the age dependence of T-score results for calcaneal imaging ultrasonometry and dual X-ray absorptiometry of the axial skeleton and (2) determine the optimum T-score thresholds appropriate for broadband ultrasound attenuation (BUA) and speed of sound (SOS) measurements. A total of 453 healthy women aged 20-9 years were included in the study. All study participants underwent bone mineral density (BMD) measurements of the lumbar spine, femoral neck, total hip and calcaneal measurements of the BUA and SOS. An imaging ultrasound device (UBIS, DMS, France) was used for the ultrasound measurements. T-scores were calculated using a subgroup of 71 healthy women aged 20-35 years to estimate the mean value of young normals and SD for BUA, SOS, and BMD. The age-related decline in both BUA and SOS T-scores was slower than that in the equivalent figures obtained by BMD measurements. The optimum T-score thresholds estimated by receiver operating characteristic (ROC) analysis were 1.3 for BUA and 1.5 for SOS. Using the optimum threshold, the sensitivity and specificity for BUA was 68% and 83%, respectively. Corresponding values for SOS were 63% and 79%. Utilizing calculated optimum T score thresholds for BUA and SOS, the agreement among BUA, SOS, and BMD at the femoral neck was improved compared with that found using the T-score of < or = -2.5 criterion. In conclusion, the definition of osteoporosis by a T-score of , or = -2.5 was not applicable to imaging ultrasonometry of the calcaneus. Optimum T-score thresholds were determined for both BUA and SOS suitable to Ubis QUS device.

Effect of Lifetime Occupational Physical Activity on Indices of Bone Mineral Status in Healthy Postmenopausal Women

Abstract. The purpose of this study was to examine the effect of lifetime physical activity of farmers on skeletal status. Seventy-one healthy, postmenopausal women (mean age 52.3 ± 5.9 years, range 42–61 years) who worked professionally on farms were compared with 78 matched controls (mean age 51.8 ± 5.5 years, range 42–61 years). Broadband ultrasound attenuation (BUA) and speed of sound (SOS) at the os calcis were measured using an ultrasound transmission imaging system. Bone mineral density (BMD) of the lumbar spine and femoral neck were measured by dual-energy X-ray absorptiometry (DXA). Differences in BUA, SOS, and BMD between farmers and controls were expressed relative to standard deviation (SD) of the farmers. Farmers had significantly higher density values than controls (difference = 1.3 SD in the spine and 1.5 SD in the femoral neck, P < 0.0001 for both comparisons). Ultrasound values were significantly higher in the farmers compared with the controls in calcaneus (difference = 1.1 SD for BUA and 0.7 SD for SOS, P < 0.0001 for both comparisons). The difference of spine BMD, femoral neck BMD, BUA, and SOS between farmers and controls, as judged by comparison of the slopes of the regression lines, was unchanged with age and years since menopause. These results suggest that lifetime physical activity has a positive effect on bone status of postmenopausal farmers.

EFFECT OF REGION OF INTEREST LOCATION ON ULTRASOUND MEASUREMENTS OF THE CALCANEUS

Abstract. Ultrasound (US) measurements of the calcaneus are usually carried out in a region of interest (ROI) at a fixed site relative to a footplate. Recently, US transmission systems have been developed with imaging capability that enable selection of the position of ROI; the region of measurement is always the area of minimum attenuation in the posterior part of the calcaneus. This study compares measurements of broadband ultrasound attenuation (BUA) and speed of sound (SOS) at the variable ROI of minimum attenuation (ROIv) and at fixed coordinates (ROIf). Ultrasound variables were estimated at ROIv and ROIf in 212 female subjects, including 26 patients with osteoporotic fractures. Among the 186 women without fractures, 63 were classified as having osteoporosis on the basis of their vertebral bone density. Precision of BUA and SOS were better at ROIv than at ROIf. BUA was more highly correlated with bone mineral density (BMD) at the lumbar spine and femoral neck at ROIv than ROIf (r = 0.64 for lumbar spine and 0.68 for femoral neck at ROIv versus 0.50 for lumbar spine and 0.54 for femoral neck at ROIf, P < 0.05 for both comparisons). There were no significant differences between the correlations of SOS with axial BMD at ROIv compared with ROIf. Significant difference was found between the areas under the ROC curve for each ultrasound variable at ROIv and ROIf for both groups of patients, subjects with osteoporosis (area under curve = 0.87 for BUA at ROIv versus 0.82 at ROIf, P < 0.05; area under curve = 0.85 for SOS at ROIv versus 0.81 at ROIf, P < 0.05), and women with fractures (area under curve = 0.93 for BUA at ROIv versus 0.86 at ROIf, P < 0.05; area under curve = 0.91 for SOS at ROIv versus 0.82 at ROIf, P < 0.05). Ultrasound variables measured at ROIv enable improved reproducibility and significantly better differentiation of diseased subjects from healthy individuals as compared with measurements at ROIf.

Embryo/Fetus Radiation Dose and Risk from Dual X-ray Absorptiometry Examinations

Abstract: The aim of the current study was to estimate the embryo/fetus radiation doses and risks associated with spinal and hip dual X-ray absorptiometry (DXA) scans performed on the pregnant mother. The results were compared with the embryo/fetus dose from a thoracolumbar radiograph and pelvic radiograph. Posteroanterior (PA) lumbar spine and proximal femur scans during the first, second and third trimesters were performed on a phantom simulating pregnancy at the three trimesters of gestation. All scans were carried out using a Hologic 1000/W pencil beam DXA unit. Moreover, embryo/fetus doses from a (a) thoracolumbar radiograph and (b) pelvic radiograph were estimated for all periods of gestation using the same phantom. Radiation doses were measured using thermoluminescent dosimeters. The dose reduction achievable by shielding the embryo/fetus with a protective apron during DXA scans was studied for all trimesters of gestation. The embryo/fetus doses during the first trimester were measured to be 1.7 mGy and 2.7 mGy for the PA spine and femur DXA scan, respectively, for an embryo/fetus located 8.5 cm from the anterior maternal surface. The risk of excess fatal cancer was 0.2 per million unborn children irradiated in utero for measurements of the spine and 0.3 per million unborn children for measurements of the femur. The embryo/fetus doses during the second and third trimesters were 2.7 mGy and 4.9 mGy respectively for the scans of the lumbar spine. The risk of childhood fatal cancer was 0.3 per million for the second trimester and 0.5 per million for the third trimester. The embryo/fetus radiation doses during the second and third trimesters were estimated as 1.4 mGy and 1.0 mGy respectively for the examinations of the proximal femur. The risk of childhood fatal cancer was 0.1 per million for both trimesters. The use of the apron resulted in a very small change in the dose absorbed by the embryo/fetus. The embryo/fetus dose associated with both DXA modes investigated in the current study is at least 700 times lower in comparison with embryo/fetus dose from a thoracolumbar or pelvic radiograph in all periods of gestation. In conclusion, the embryo/fetus dose in bone density measurements of spine and femur using pencil beam DXA is lower than the average daily natural background in the United States of 8 mGy. The health provider can decide whether a DXA scanning is beneficial to a pregnant woman, taking into account the potential radiation risks to the embryo/fetus presented in the current study.

Can radial bone mineral density and quantitative ultrasound measurements reduce the number of women who need axial density skeletal assessment

The purpose of this study was to investigate the clinical usefulness of forearm bone mineral density (BMD) and speed of sound (SOS) at the phalanx and radius as pre-selection tests to identify women with low BMD at the axial skeleton. BMD was measured by dual-energy X-ray absorptiometry (DXA) in the forearm, lumbar spine and femoral neck. SOS at the radius and phalanx was measured using a multisite quantitative ultrasound (QUS) device. Measurements were performed on 524 consecutive women referred for the assessment of BMD. Women with a T-score <−1 and T-score ≤−2.5 at either spine or femoral neck were identified, and T-score cut-off values for the forearm DXA and QUS variables were determined. Cut-off values for the forearm BMD estimated to detect normal women and those with T-score <−1 at the axial skeleton identified a total of 82% of subjects with 91% certainty. Cut-off values for the forearm BMD determined to detect women with T-score >−2.5 and those with osteoporosis allowed the identification of 62% of the study population with 90% certainty. Cut-off values for the phalangeal and radial SOS estimated to detect normal women and those with T-score <−1xa0at the axial skeleton identified a total of 49% and 1% of subjects, respectively. Cut-off values estimated for QUS variables to detect women with T-score >−2.5 and those with osteoporosis at the axial skeleton either failed to detect subjects with sufficient certainty (phalangeal SOS) or detected a negligible percentage of patients (radial SOS). In conclusion, forearm BMD may be used as a pre-selection test to identify women with low BMD at the axial skeleton, thus enabling reduction of the number of women who need axial BMD assessment. SOS of the phalanges and radius appears to have less value in the detection of the women with low axial BMD.

CT of the sacroiliac joints. Dosimetry and optimal settings for a high-resolution technique.

Purpose: The aim was to select an optimal technique for low-dose high-resolution CT of the sacroiliac joints (SJ). Material and Methods: Dose measurements were performed on a Rando anthropomorphic phantom using thermoluminescence dosimeters for 4 CT protocols and 2 conventional radiography protocols used for SJ evaluation. Six available reconstruction algorithms were tested on CT protocols using 285–665 mAs and 120 or 130 kVp settings and noncontiguous 1.5-mm-thin sections with 3.5-mm intervals. Settings with optimum performance on phantom tests were also applied in a series of 10 patients with SJ arthropathies. Results: A CT protocol using 120 kVp/175 mA2.9 s/1.5-mm slice thicknessb-mm table increment implied the lower radiation dose among all examination protocols tested and provided high image quality of the SJ. A reconstruction algorithm yielding images of improved spatial resolution with acceptable noise was selected. Conclusion: A high spatial frequency reconstruction algorithm, and 120 kVp and 508 mAs were considered optimal for a low-dose CT examination of the SJ that employed narrow (1.5 mm) slice images with interspacing.

Conceptus radiation dose assessment from fluoroscopically assisted surgical treatment of hip fractures.

Our aims in the present study were to (a) provide normalized dose data for the estimation of the conceptus dose from fluoroscopically assisted surgical treatment of hip fractures carried out during all trimesters of pregnancy and (b) estimate the conceptus radiation dose and risks associated with fluoroscopy during a typical treatment of hip fracture performed on a pregnant woman. Conceptus doses normalized to entrance surface dose (ESD) or dose area product (DAP) were obtained with the help of anthropomorphic phantoms simulating pregnancy in the three trimesters of gestation. ESD and conceptus dose measurements were carried out using thermoluminescent dosimeters. DAP to conceptus dose conversion factors were estimated for the first, second and third trimesters of gestation. Conceptus dose data normalized to ESD were also estimated to investigate whether these conversion factors may be used for procedures carried out in x-ray units not equipped with a DAP meter. Fluoroscopically assisted surgical treatments were performed in 18 women. The projections involved in these procedures are (a) posteroanterior (PA) and (b) lateral crosstable 45 degrees (LC). Radiation doses for a potential conceptus were estimated by using normalized dose data obtained in phantoms. The results consist of tabulated dose data normalized to DAP or ESD for the estimation of a conceptus dose. An important finding of this study was that the total DAP of a procedure, instead of the individual DAP values of each projection, could be used for the accurate estimation of the conceptus dose. Conceptus doses calculated using dose data normalized to ESD are about 23% higher compared to those estimated using data normalized to DAP. This discrepancy may be attributed to the contribution of scattering radiation from PA projection to ESD measurement of LC projection and vice versa. Therefore, dose data normalized to ESD do not provide accurate conceptus dose estimation. Doses normalized to DAP showed a dependence on (a) tube potential and (b) tube filtration. Data are provided to extent the doses normalized to DAP for the standard spectrum to other tube voltages and filtrations. The maximum dose for a potential conceptus was 0.425 mGy for a patient irradiated for 50 seconds during the PA projection and for 40 seconds during the LC projection. Although the total duration of fluoroscopy is usually less than 2 minutes during a typical procedure, screening time as long as 14 minutes has been reported in the literature for treatment of complex fractures. The relationship between conceptus dose and fluoroscopy time found in the current study showed that, in these cases, the radiation dose received by a conceptus may exceed 1 mGy. In conclusion, an accurate estimation of conceptus doses associated with fluoroscopically assisted surgical treatment of hip fractures can be made using the DAP normalized dose data provided in this study. Conceptus doses from a typical procedure is less than 1 mGy during all trimesters.

Determination of dose-area product from panoramic radiography using a pencil ionization chamber: Normalized data for the estimation of patient effective and organ doses

The aims of the present study were (a) to investigate the potential of pencil ionization chamber to be used for the determination of dose-width product (DWP) and dose-area product (DAP) from panoramic radiographic exposures and (b) to provide data normalized to DAP for the determination of patient effective and gonadal dose from panoramic radiography performed in any laboratory. A pencil ionization chamber commonly used to measure CT dose index (CTDI) in CT scanners was employed to determine DWP for various combinations of panoramic exposure settings at the beam exit slit of a Cranex Tome panoramic x-ray unit (Soredex, Helsinki, Finland). DWP values were also measured using an array of thermoluminescence dosimeters. Reproducibility of the DWP measurement was tested. The effect of milliamperage and kilovoltage of panoramic exposures on DWP was investigated. DAP was estimated using the value of DWP measured using the pencil ionization chamber and the beam exit slit length measured using dosimetric film attached on the beam exit slit. A Rando anthropomorphic phantom appropriately loaded with thermoluminescent dosimeters (TLDs) was used to obtain organ dose and effective dose values from panoramic radiography. Reproducibility of DWP determination using the proposed method was better than 1.5%. DWP was found to be linearly related to milliamperage (r>0.999, p<0.001) and to kilovoltage raised in a power ranging from 2.18 to 2.55. DWP measured using the pencil chamber was found to be up to 11% higher than the corresponding values determined using TLD array. The panoramic exposure obtained with settings appropriate for the typical adult patient was found to result in 0.008 mSv patient effective dose, 0.0002 mGy gonadal dose, and 11.3 cGy cm2 DAP. The use of a pencil ionization chamber is proposed for the determination of DWP and DAP from panoramic radiographic exposures. Normalized data over DAP were provided for the determination of patient effective and gonadal dose from panoramic radiography.