The specimens were subsequently loaded in tension with a crosshead displacement speed of 0. Stress and strain were calculated based on the measured machine-recorded forces and displacements. Average results of 10 test specimens are reported for each sample. The electrical resistance was measured in a four-point scheme on stripes cut from the nanolaminates, and the conductivity was calculated from specimen dimensions.
The EMI shielding response of the nanolaminates was investigated in the range 0. Data acquisition was realised by means of a lock-in amplifier coupled with electronics and computer software. A standard setup with four polymethypenetene lenses was used to collimate and focus the beam first impinging onto the sample plane and then received by the detector.
Computer aided motion controller was utilised for accurate target positioning. Since the THz beam waist w 0 at the focus point is approximately 1. Since k 0 w 0 2 is much larger than unity in the investigated frequency range k 0 being the wavevector in free space , we can safely assume that the plane wave approximation holds for all measurements that have been carried out within a few percent relative error The THz beam impinges on the sample surface under normal incidence.
The holder is placed on a kinematic mount for fine adjustment and the sample surface parallelism with respect to the beam wavefront is controlled by a three-points calibration method. Therefore, paraxial error is considered to be very small. In all cases, the reference measurements were performed under the same experimental conditions applied to the samples, namely with the pulsed signal passing through the holed Al holder. The authors declare that the data supporting the findings of this study are available within the article and its supplementary information files.
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Carbon 50 , — In the first dosimetric study data from and gonad shielding was standard, in the second study data from shielding was absent. Together with the discontinuation of the gonad shielding, we continued to optimise our protocols.
In the first place, more guidance for the imaging of larger children 10—15 years was introduced because of large differences in exposure within this group. Secondly, following the European Guidelines [ 35 ], we added an additional copper filter of 0. For the youngest patients 0—1 years the decrease in image quality was considered too large by the paediatric radiologist; for the 10—15 age group, the filter was already used.
The basic filtration of the X-ray beam i. Since most authors had reported the entrance dose as a dose-in-air including backscatter [ 22 , 23 , 25 — 31 ], we followed this convention. We estimated backscatter factors for the conversion of incident air kerma to entrance dose for each age group and radiation quality using data from the NRPB report R [ 36 ].
These factors were 1. Note that these exposure parameters are generally independent of the use of gonad shielding, unless the shield was in front of an active AEC chamber. PCXMC has the option to adjust the size of the phantoms of all ages. The dose estimation in a specific age group of children will be illustrated using the 5—10 age group as an example.
Rather than treating these children as a single group in the dose calculation, we considered 5- to 7. By interpolation between data for child phantoms of different age present in PCXMC, we determined the weight and length of children of 6.
Using the exposure parameters and interpolated patient size and weight for each subgroup, organ doses and effective dose were calculated with PCXMC for the 6. The average dose for the 5—10 age group was then calculated by averaging the results for these two subgroups. Doses for other age groups were estimated in a similar fashion always using two subgroups. The problem of the collimator settings not being stored in the DICOM header necessary as input on field size was addressed by determining the average difference in width and height of the original unshuttered and shuttered images for a limited set of images for which both types of data were retained.
Considerable variations in measured differences existed, but on average 1 cm had to be added in all four directions to compensate for the shuttering. Although this correction for shuttering is necessarily approximate, its application was preferred over leaving it out as this systematically would overestimate the entrance dose. Because we saw no solution to the problem of translating the loss of diagnostic information into a numerical risk that might be compared with the risk of radiation, we limited the quantitative risk analysis to radiation effects only.
Shortcomings of gonad shielding, which manifest themselves inevitably in daily practice, and which have an impact on the patient dose, are: 1 in males, an incomplete coverage of the testes, 2 the need for retakes because vital landmarks are obscured and 3 an increase in dose when an active AEC-chamber is partly shielded by the lead supposed to shield the gonads.
Only point 1 was taken into account, the other two were not, because of missing information. The detriment adjusted hereditary risk of a pelvic radiograph can be calculated using the nominal coefficient of 5. For the computation of the total detriment adjusted risk, the risk coefficient for cancer 5. These calculations further require the effective dose, the testes dose and the dose to the ovaries.
The reduction of hereditary risk achieved by gonad shielding was also expressed as a percentage of the total risk of a radiograph obtained without shielding. In total, AP pelvic radiographs with gonad protection were identified in the period — By keeping very strictly to the criteria for good diagnostic information, our scores for gonad protection left much to be desired Table 1.
In one case a poorly positioned shield covered an osteomyelitic lesion in a boy Fig. Rates of retakes that would be required if all essential landmarks had to be visible are also shown in Table 1.
Summary of gonad shielding during paediatric AP pelvic radiography in the period Conventional pelvic radiograph with testes shielding left. An osteomyelytic lesion is clearly displayed arrow right.
Due to gonad shielding this was missed in the previous examination. So for practical purposes, the fractional testes dose reduction is equal to the fractional coverage.
The study included AP pelvic radiographs acquired without gonad shielding. The imaging technique settings used are shown in Table 2 ; part of these data were necessary in the dose calculations. The basic filtration of the X-ray beam was 3. Table 3 presents the KAP, the incident air kerma, the effective dose for a hermaphrodite , the gonad doses and the contribution of the gonads to the effective dose.
Due to the absence of the Cu filter for the group of children of 0—1 years their dose is higher than that for the 1—5 age group. Note the relative spread in all doses in Table 3 will be a little higher than specified for the KAP due to the additional uncertainty in the X-ray beam area.
The dose data from the — study were only slightly higher and are not shown. Table 4 gives for the different age groups an overview of the total and hereditary detriment-adjusted risks caused by pelvic radiographs. Note the very low absolute magnitude of risks for boys and girls alike. Detriment adjusted risks caused by AP pelvic radiography with and without gonad shielding. The absolute magnitude of the reduction in hereditary risk, even assuming complete uncompromised shielding of the gonads, was very small.
Several factors are responsible for this finding. First of all, technical developments and protocol optimisation have lowered the dose needed for a pelvic radiograph from about 10 mGy in the s to a few tenths of a milligray today. Secondly, the risk coefficient for heritable disease is considerably lower than previously assessed. For about 50 years, radiographers worldwide have been applying gonad shielding in radiography of the pelvis and abdomen.
All available studies, including our own, show that gonad shielding is poor in clinical practice Table 5. Impaired diagnostic information and limited gonad dose reduction are potential consequences. In unfortunate cases there can even be an increase in exposure due to the need for retakes or due to shielding an active AEC chamber, effects that could not be quantitatively included in this study due to the lack of adequate information. The risk reductions we calculated are thus likely to be too optimistic.
The patient doses incurred in our department are relatively low, but not exceptionally, as can be seen in Table 6 , which presents data published in the past 20 years [ 22 — 30 , 33 , 34 ]. We identified more than 40 articles with pertinent data, but only studies giving doses for children of several ages were included.
Note that the dose to a superficially located organ like the testis will be similar to the entrance dose. Mean entrance doses in air, including backscatter, in pelvic radiography according to studies in the past two decades. Children of 15 years weighted only 27 kg. Table 6 also shows considerable spread in doses. Smans et al. The large spread and the many high values reported in the literature indicate that a lot is still to be gained by optimisation. This issue is currently being addressed in many countries by setting DRLs for frequently performed procedures, as recommended by the ICRP [ 32 , 38 ].
Discontinuation of gonad protection should not be considered before optimisation has been performed and dose levels in the low range of Table 6 have been realised.
Installation of a modern digital system is no guarantee for acceptable performance. Patient dose reductions since the fifties were realised by using harder radiation, a larger focus-patient distance, the introduction of faster screens and films, and the discontinuation of fluoroscopy in favour of radiography.
In fluoroscopy the introduction of the image intensifier was a major step. Recently the more sensitive digital detectors and the concomitant development of image processing software helped reduce patient dose.
Despite its limitations, gonad shielding has served its purpose in times when doses were high. Now it appears that its potential advantages are outweighed by the drawbacks. Too many images contain impaired diagnostic information. The high numbers of retakes required, but not actually taken, are symptomatic. Often the radiologist is forced to fill in the gaps with information from previous images. This is not without risk, as illustrated by the incident with the shielded osteomyelytic lesion Fig.
This incident shows that even the peripheral zones of pelvic bones should not be covered. The uncertainties in the derived doses still need to be considered. PCXMC has only a limited number of mathematical phantoms, and the size of the individual patient may not correspond to that of the phantom closest in age. The correction for shuttering to obtain the true X-ray field size introduces an additional uncertainty in the dose estimates. To give an idea of its magnitude, assume that the uncertainty equals the fully applied correction of 1 cm in all directions.
Note that for a given KAP the effect of a change in the beam area on the effective dose is likely to be small, but on the dose to the gonads or any other single organ it will have its full impact. For individual patients the error may be larger, as indicated by the spread in KAP values in Table 3. An important practical aspect for this discussion is the perception of radiation risks. The emphasis over the years on applying gonad shields has nurtured the conviction that major risks have to be countered.
Workers and parents are so used to shielding that not using it is considered a major neglect. Only for the group of large boys of age 10—15 years is the potential reduction in hereditary or total risk 3. Radiographers should learn that the risks associated with the potential loss of diagnostic information outweigh the very small benefit of gonad shielding.
Parents could be helped by showing them the risks of exposures that are commonly accepted as harmless.
For patients or guardians experiencing fear and anxiety about radiation exposure, the use of gonadal or fetal shielding may calm and comfort the patient enough to improve the exam outcome 1. This may be considered when developing shielding policies and procedures. However, blanket statements requiring the use of such shielding are not supported by current evidence Additionally, the AAPM recommends that radiologic technologist educational programs including patient outreach efforts provide information about the limited utility and potential drawbacks of gonadal and fetal shielding.
Rationale for policy: Gonadal and fetal shielding in X-ray imaging has for decades been considered consistent with the ALARA principle and therefore good practice.
Given advances in technology and current evidence of radiation exposure risks, the AAPM has reconsidered the effectiveness of gonadal and fetal shielding. The main concern with radiation exposure to the reproductive organs has been an increased risk of hereditary effects.
In medical x-ray imaging, the main source of radiation dose to internal organs that are outside the imaging field of view is x-rays that scatter inside the body.
However, surface shielding covering these organs has no impact on this scatter. The use of gonadal and fetal shielding can negatively affect the efficacy of the exam. Shielding placed inside the imaging field of view, or shielding that moves into the imaging field of view, can obscure important anatomy or pathology, or introduce artifacts.
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