Fact or fiction: An analysis of the 10 kVp ‘rule’ in computed radiography

PurposeTo determine whether increasing the tube voltage by 10 kVp whilst reducing the tube current by 50% (10 kVp ‘rule’) produces similar perceptual image quality.Method391 matched pairs of anthropomorphic chest phantom X-ray images were produced on a computed radiography (CR) system. Five experienced clinicians graded the images using a 2 alternative forced choice comparison method. Based on acquisition parameters and dose area product (DAP) readings, effective dose (E) was calculated for all images using dose calculation software.ResultsPerceptual image quality scores prior to and following application of the 10 kVp ‘rule’ were found have no statistical difference (p > 0.1), indicating that the increase in kVp and reduction in mAs had limited impact on the perceptual image quality. In all cases E reduced, with an average 36% (s.d 7%) after the ‘rule’ had been applied (p < 0.001).ConclusionResults demonstrate that application of the 10 kVp ‘rule’ significantly reduces E, with no significant reduction in perceptual image quality. Further research should be conducted for a range of examinations using CR and digital radiography (DR) systems.     

10 kVp rule – An anthropomorphic pelvis phantom imaging study using a CR system: Impact on image quality and effective dose using AEC and manual mode

PurposeThis study aims to investigate the influence of tube potential (kVp) variation in relation to perceptual image quality and effective dose (E) for pelvis using automatic exposure control (AEC) and non-AEC in a Computed Radiography (CR) system.Methods and materialsTo determine the effects of using AEC and non-AEC by applying the 10 kVp rule in two experiments using an anthropomorphic pelvis phantom. Images were acquired using 10 kVp increments (60–120 kVp) for both experiments. The first experiment, based on seven AEC combinations, produced 49 images. The mean mAs from each kVp increment were used as a baseline for the second experiment producing 35 images. A total of 84 images were produced and a panel of 5 experienced observers participated for the image scoring using the two alternative forced choice (2AFC) visual grading software. PCXMC software was used to estimate E.ResultsA decrease in perceptual image quality as the kVp increases was observed both in non-AEC and AEC experiments, however no significant statistical differences (p > 0.05) were found. Image quality scores from all observers at 10 kVp increments for all mAs values using non-AEC mode demonstrates a better score up to 90 kVp. E results show a statistically significant decrease (p = 0.000) on the 75th quartile from 0.37 mSv at 60 kVp to 0.13 mSv at 120 kVp when applying the 10 kVp rule in non-AEC mode.ConclusionUsing the 10 kVp rule, no significant reduction in perceptual image quality is observed when increasing kVp whilst a marked and significant E reduction is observed.     

Effect of high- and low-energy entrance surface dose allocation ratio for two-shot dual-energy subtraction imaging on low-contrast resolution

IntroductionDual-energy subtraction (DES) imaging can obtain chest radiographs with high contrast between nodules and healthy lung tissue, and evaluating of chest radiography and evaluating exposure conditions is crucial to obtain a high-quality diagnostic image. This study aimed to investigate the effect of the dose allocation ratio of entrance surface dose (ESD) between high- and low-energy projection in low-contrast resolution of soft-tissue images for two-shot DES imaging in digital radiography using a contrast-detail phantom (CD phantom).MethodsA custom-made phantom mimicking a human chest that combined a CD phantom, polymethylmethacrylate square plate, and an aluminum plate (1–3 mm) was used. The tube voltage was 120 kVp (high-energy) and 60 kVp (low-energy). The ESD was changed from 0.1 to 0.5 mGy in 0.1 mGy increments. Dose allocation ratio of ESD between 120 kVp and 60 kVp projection was set at 1:1, 1:2, 1:3, and 2:1. Inverse image quality figure (IQF_inv) was calculated from the custom-made phantom images.ResultsWhen the total ESD and aluminum thickness were constant, no significant difference in IQF_inv was observed under most conditions of varied dose allocation ratio. Similarly, when the total ESD and the dose allocation ratio were constant, there was no significant difference in IQF_inv based on the aluminum plate thickness.ConclusionUsing IQF_inv to evaluate the quality of the two-shot DES image suggested that dose allocation ratio did not have a significant effect on low-contrast resolution of soft-tissue images.Implications for practiceThe present results provide useful information for determining exposure conditions for two-shot DES imaging.     

Mammography Diagnostic Reference Levels (DRLs) in Ghana

IntroductionDiagnostic Reference Levels (DRLs) are essential for optimisation in mammography. A local DRL for screen-film mammography has been established in Ghana but none exists for the digital mammography systems. Furthermore, technological advancement is phasing out the use of screen-film mammography and replacing it with digital mammography systems. This study aims to establish the local DRLs used in digital mammography across three institutions in Ghana to guide mammography practice.MethodsAverage glandular dose (AGD), compressed breast thickness (CBT), age of patients, entrance surface exposure (ESE), kVp, and mAs were retrospectively extracted from three digital mammography systems. The 75th and 95th percentile values were obtained for the AGD of each mammography projection and at CBT of 60 ± 5 mm. The correlation between the AGD and CBT, kVp, mAs, and ESE were investigated.ResultsThe 75th percentile for the AGD at CBT of 60 ± 5 mm for Centres 1, 2, 3, and all centres were 2.3, 1.8, 2.1, and 2.0 mGy respectively. The DRLs obtained were comparably higher than international studies except those of the United Kingdom. The AGD showed a strong positive correlation with the CBT, kVp, mAs, and ESE. There was variability in the AGD applied across the three centres for the craniocaudal (CC) and mediolateral oblique (MLO) projections. The mean AGD, mAs, and ESE for all the three centres and per centre recorded were higher than previous studies, but the mean kVp and CBT were lower than previous studies.ConclusionThe higher DRLs estimated in this preliminary study indicates that there is a need for dose optimisation in digital mammography practice in Ghana to improve radiation protection.Implications for practiceThe findings will guide the process of optimisation and limit the variations in the radiation dose during mammography practice.     

Evaluating the use of higher kVp and copper filtration as a dose optimisation tool in digital planar radiography

IntroductionTo identify the potential of beam hardening techniques, specifically the use of higher kilo voltage (kV) and copper (Cu) filtration, to optimise digital planar radiographic projections. The study assessed the suitability of such techniques in radiation dose reductions while maintaining diagnostic image quality for four common radiographic projections: antero-posterior (AP) abdomen, AP-knee, AP-lumbar spine, and lateral lumbar spine.MethodsAnthropomorphic phantom radiographs were obtained at varying kVp (standard kVp, +10 kVp, and +20 kVp) and varying Cu filtration thickness (0 mm, 0.1 mm, and 0.2 mm Cu). The Dose Area Product (DAP), mAs and time (s) were recorded as an indication of the emitted radiation dose. Image quality was assessed objectively via Contrast-Noise-Ratio (CNR) calculations and subjectively via Visual Grading Analysis (VGA) performed by radiographers and radiologists.ResultsOptimised exposure protocols were established for the AP-abdomen (100 kVp with 0.2 mm Cu), AP-knee (85 kVp, and 0.1 mm Cu), AP-lumbar spine (110 kVp and 0.2 mm Cu), and lateral lumbar spine (110 kVp and 0.2 mm Cu). This strategy resulted in respective DAP reductions of 71.98%, 62.50%, 64.51% and 71.85%. While CNR values decreased as beam hardening techniques were applied, VGA demonstrated either a lack of statistical variation or improved image quality between the standard and the optimised exposure protocols.ConclusionsDAP reductions without compromising image quality can be achieved through beam hardening for the AP-abdomen, AP-knee, AP-lumbar spine, and lateral lumbar spine projections.Implications for practiceBeam hardening techniques should be considered as an optimisation strategy in medical imaging departments. Research into the applicability of this strategy for other radiographic projections is recommended.     

Optimisation of the AP abdomen projection for larger patient body thicknesses

IntroductionThis study aims to identify optimal exposure parameters, delivering the lowest radiation dose while maintaining images of diagnostic quality for the antero-posterior (AP) abdomen x-ray projection in large patients with an AP abdominal diameter of >22.3 cm.MethodologyThe study was composed of two phases. In phase 1, an anthropomorphic phantom (20 cm AP abdominal diameter) was repetitively radiographed while adding 3 layers (5 cm thick each) of fat onto the phantom reaching a maximum AP abdominal diameter of 35 cm. For every 5 cm thickness, images were taken at 10 kVp (kilovoltage peak) intervals, starting from 80 kVp as the standard protocol currently in use at the local medical imaging department, to 120 kVp in combination with the use of automatic exposure control (AEC). The dose area product (DAP), milliampere-second (mAs) delivered by the AEC, and measurements to calculate the signal to noise ratio (SNR) and contrast to noise ratio (CNR) were recorded. Phase 2 included image quality evaluation of the resultant images by radiographers and radiologists through absolute visual grading analysis (VGA). The resultant VGA scores were analysed using visual grading characteristics (VGC) curves.ResultsThe optimal kVp setting for AP abdominal diameters at: 20 cm, 25 cm and 30 cm was found to be 110 kVp increased from 80 kVp as the standard protocol (with a 56.5% decrease in DAP and 76.2% in mAs, a 54.2% decrease in DAP and 76.2% decrease in mAs and a 29.2% decrease in DAP and 59.7% decrease in mAs, respectively). The optimal kVp setting for AP abdominal diameter at 35 cm was found to be 120 kVp increased from 80 kvp as the standard protocol (with a 50.7% decrease in DAP and 73.4% decrease in mAs). All this was achieved while maintaining images of diagnostic quality.ConclusionTailoring the exposure parameters for large patients in radiography of the abdomen results in a significant reductions in DAP which correlates to lower patient doses while still maintaining diagnostic image quality.Implications for clinical practiceThis research study and resultant parameters may help guide clinical departments to optimise AP abdomen radiographic exposures for large patients in the clinical setting.     

Can the anode heel effect be used to optimise radiation dose and image quality for AP pelvis radiography?

IntroductionA study was conducted to determine whether the anode heel effect can be used to influence optimisation of radiation dose and image quality (IQ) for AP pelvis radiography.MethodsATOM dosimetry phantom and an anthropomorphic phantom were positioned for AP pelvis. Using a CR system, images were acquired and doses were measured with phantom feet toward anode and then feet toward cathode. Exposure factors (kVp, mAs and SID) were systematically generated using a factorial design. Images were scored visually for quality using relative visual grading together with a 3 point Likert scale. Signal to noise ratio was also calculated as a physical measure of image quality. Dosimetry data were collected for the ovaries and testes.ResultsThe optimum technique for male, which resulted in lower dose and suitable image quality, was with feet positioned toward the anode (0.80 ± 0.03 mGy; SNR of 38 ± 2.9; visual IQ score 3.13 ± 0.35). The optimum technique for female was with feet toward anode (0.23 ± 0.02 mGy; SNR of 34.7 ± 2.6; visual IQ score 3.15 ± 0.26). kVp had the biggest effect on both visual and physical image quality metrics (p < 0.001) for both tube orientations, whereas SID had the lowest effect on both visual and physical image quality metrics compared with mAs and kVp (p < 0.001). The effect of SID on the SNR was not significant (p > 0.05) with feet toward anode.ConclusionPositioning the patient with feet toward the anode, as opposed to the cathode, has no adverse effect on visual image quality assessment but it does have an effect on physical image quality.Implications for practiceThis study would add a new clinical concept in positioning of AP pelvis radiography especially for male positioning.     

Optimum patient orientation for pelvic and hip radiography: A randomised trial

PurposeTo investigate the effect of patient orientation on the radiation dose and image quality (IQ) for digital (DR) and computed radiography (CR) examinations of the pelvis.MethodsA randomised study was conducted using DR and CR X-ray equipment. The standard patient orientation of head towards (HT) the two outer Automatic Exposure Device (AED) chambers was compared with a group of patients with their head away (HA) from the two outer AED chambers. Collection of mAs, source-to-skin distance and kVp data facilitated the calculation of entrance surface dose (ESD) and effective dose (ED) which were compared between groups. Each image was graded independently by three observers. IQ data were analysed for inter-observer variability and statistical differences.ResultsFor DR pelvis examinations switching orientation (HT to HA) reduced the mean ESD and ED by 31% (P < 0.001), respectively. For CR examinations the dose reduction was greater between the two orientations (38%; P = 0.009). Examinations of the hips allowed dose reductions of around 50% when switching between orientations. For DR examinations minor reductions in IQ were seen and favoured the HT orientation (P = 0.03). For CR examinations there were no statistical differences in IQ between orientations.ConclusionSwitching patient orientation relative to the AED chambers can help optimise radiation dose. In order to facilitate this chamber position should be clearly marked on all equipment and patient orientation should be a consideration when tailoring individual examinations. For DR minor changes in IQ are a consequence of changing orientation and should be factored into the decision making.     

The effect of different exposure parameters on radiation dose in digital mammography and digital breast tomosynthesis: A phantom study

IntroductionThere are concerns regarding the increase in radiation dose among women undergoing both digital mammography (DM) and digital breast tomosynthesis (DBT). The aim of this study was to evaluate the effect of different exposure parameters on entrance skin dose (ESD) and average glandular dose (AGD) for DM and DBT using a phantom.MethodsThe ESD and AGD of 30 DM and DBT (cranio-caudal projection) examinations using a tissue equivalent phantom where acquired using a GE Senographe Essential DM unit. Commercial phantoms were used to simulate three different breast thicknesses and compositions. Tube potential, tube load, and target/filter combinations were also varied with ESD and AGD recorded directly from the DM unit. Comparisons were made using the non-parametric Kruskal Wallis, Mann–Whitney, and Wilcoxon signed rank tests.ResultsThe individual ESD values for 4 cm, 5 cm, and 6 cm thick phantoms for DM and DBT at Rh/Rh target/filter combination and 30–32 kV/56 mAs levels were 5.06 and 4.18 mGy; 5.82 and 5.08 mGy; and 7.26 and 11.4 mGy, respectively; while AGDs were 1.57 and 1.30 mGy, 1.33 and 1.39 mGy; and 1.29 and 3.60 mGy, respectively. The Kruskal–Wallis test showed a statistically significant difference in AGD for DM (P = .029) but not for DBT (P = 0.368). The Mann–Whitney and Wilcoxon signed rank tests showed no statistically significant difference for ESD or AGD between both DM and DBT techniques (P = .827 and .513). The percentage differences in ESD for phantom thicknesses of 4 cm, 5 cm, and 6 cm between DBT and DM ranged between −21% and 36%; while for AGD between −21% and 64.2%.ConclusionsThe ESD and AGD for single view projection in DM and DBT showed differences at 4 and 6 cm breast thicknesses and compositions but not at 5 cm thickness with 30–32 kV and a Rh/Rh target/filter combination.Implications for practiceA fibro-fatty breast results in less radiation dose variations in terms of ESD and AGD between DM and DBT techniques.     

X射线胸部摄影曝光剂量与图像质量相关性研究

目的 研究数字化X射线胸部高千伏摄影曝光剂量与图像质量的关系,确定数字化X射线摄影最佳曝光剂量。方法 选择胸部高千伏摄影管电压120 kV,摄影mAs从1 mAs逐档增加至25 mAs,对模拟人体胸部厚度摄影体模与CDRAD 2.0对比度细节体模进行摄影,测量体模表面X射线入射剂量,由5位观察者独立阅读体模影像,比较任意两曝光条件组之间的图像质量因子（IQF）,确定高千伏胸部摄影最佳条件。比较4和10 mAs条件下正常人体胸部摄影图像质量评分。结果 胸部高千伏摄影体模曝光条件从1 mAs增加到25 mAs,体模表面X射线入射剂量从0.067 mGy增加至1.468 mGy。随着X射线入射剂量的增加,影像质量影响因子IQF值不断减小,观察者阅读体模信号的IQF差异有统计学意义（F=31.00,P<0.05）,曝光剂量条件选择在1~4 mAs时所对应的IQF均值差异有统计学意义（F=15.3,P<0.05）,4~10 mAs时所对应的IQF差异无统计学意义,10~25 mAs时所对应的IQF均值差异有统计学意义（F=9.74,P<0.05）。曝光剂量条件选择4和10 mAs所对应的体模表面入射剂量为0.250和0.606 mGy,两种条件下胸部图像质量的综合评分分别为（24.8±1.64）、（25.8±2.05）分,差异无统计学意义。结论 随着数字化X射线摄影剂量的增加所获得图像信息量增加。满足临床诊断的标准人体胸部高千伏数字化X摄影最佳剂量为0.250 mGy左右。     

Increasing source to image distance for AP pelvis imaging – Impact on radiation dose and image quality

AimA quantative primary study to determine whether increasing source to image distance (SID), with and without the use of automatic exposure control (AEC) for antero-posterior (AP) pelvis imaging, reduces dose whilst still producing an image of diagnostic quality.MethodsUsing a computed radiography (CR) system, an anthropomorphic pelvic phantom was positioned for an AP examination using the table bucky. SID was initially set at 110 cm, with tube potential set at a constant 75 kVp, with two outer chambers selected and a fine focal spot of 0.6 mm. SID was then varied from 90 cm to 140 cm with two exposures made at each 5 cm interval, one using the AEC and another with a constant 16 mAs derived from the initial exposure. Effective dose (E) and entrance surface dose (ESD) were calculated for each acquisition. Seven experienced observers blindly graded image quality using a 5-point Likert scale and 2 Alternative Forced Choice software. Signal-to-Noise Ratio (SNR) was calculated for comparison. For each acquisition, femoral head diameter was also measured for magnification indication.ResultsResults demonstrated that when increasing SID from 110 cm to 140 cm, both E and ESD reduced by 3.7% and 17.3% respectively when using AEC and 50.13% and 41.79% respectively, when the constant mAs was used. No significant statistical (T-test) difference (p = 0.967) between image quality was detected when increasing SID, with an intra-observer correlation of 0.77 (95% confidence level). SNR reduced slightly for both AEC (38%) and no AEC (36%) with increasing SID.ConclusionFor CR, increasing SID significantly reduces both E and ESD for AP pelvis imaging without adversely affecting image quality.     

A multi institutional comparison of imaging dose and technique protocols for neonatal chest radiography

IntroductionThe focus on paediatric radiation dose reduction supports reevaluation of paediatric imaging protocols. This is particularly important in the neonates where chest radiographs are frequently requested to assess respiratory illness and line placement. This study aims to assess the impact of neonatal chest radiographic protocols on patient dose in four hospitals in different countries.MethodsExposure parameters, collimation, focus to skin distance (FSD) and radiation dose from 200 neonatal chest radiographs were registered prospectively. Inclusion criteria consisted of both premature and full-term neonates weighing between 1000 and 5000 g. Only data from the examinations meeting diagnostic criteria and approved for the clinical use were included. Radiation dose was assessed using dose area product (DAP).ResultsThe lowest DAP value (4.58 mGy cm²) was recorded in the Norwegian hospital, employing a high kVp, low mAs protocol using a DR system. The Canadian hospital recorded the highest DAP (9.48), using lower kVp and higher mAs with a CR system, including the addition of a lateral projection. The difference in the mean DAP, weight, field of view (FOV) and kVp between the hospitals is statistically significant (p < 0.001).ConclusionUse of non-standardised imaging protocols in neonatal chest radiography results in differences in patient dose across hospitals included in the study. Using higher kVp, lower mAs and reducing the number of lateral projections to clinically relevant indications result in a lower DAP measured in the infant sample studied. Further studies to examine image quality based on exposure factors and added filtration are recommended.Implications for practiceReevaluation of paediatric imaging protocols presents an opportunity to reduce patient dose in a population with increased sensitivity to ionising radiation.     

A study of optimum radiographic conditions on chest examinations with computed radiology (CR) in conjunction with the offset balance of patient dose and image quality]

In a report of a nationwide survey on radiographic conditions of chest radiography in Japan, it was pointed out that the average entrance surface dose (ESD) of the computed radiography (CR) system was higher than that of the film-screen system. It seemed important that an objective index and criteria be established for dose reduction without a loss of image quality that would interfere with diagnostic observation. For this purpose, we investigated the properties of root of mean square (RMS) granularity, since it is a dominant factor in CR image quality and strongly depends on dose. The results indicated that RMS granularity showed little dependence on tube voltage when relative exposure was kept constant and that it decreased with the increment of exposure and approached a finite minimum value in a very high exposure region. For the most frequently used radiographic conditions in Japan (120 kV, 2.5 mmAl, 200 cm SID, 10: 1 grid), the decrement in RMS granularity from 6 to 16 mAs was 0.0276 to 0.0253 (9.1%). This finding suggested that exposure exceeding 6 mAs did not improve image quality, i.e., exposure reduction down to 6 mAs would not cause a significant loss of image quality. It was therefore concluded that RMS granularity was a useful objective index by which to determine the upper limit of exposure. Use of the most frequent conditions with 6 mAs seemed to be recommendable as an initial condition for the technical optimization of CR chest radiography, since ESD under this condition was 0.265 mGy, which was approximately equal to the value of the ESD distribution of a total chest radiogram in Japan.     

Image quality and dose analysis for a PA chest X-ray: Comparison between AEC mode acquisition and manual mode using the 10 kVp ‘rule’

PurposeTo compare the image quality and effective dose applying the 10 kVp rule with manual mode acquisition and AEC mode in PA chest X-ray.Method68 images (with and without lesions) were acquired using an anthropomorphic chest phantom using a Wolverson Arcoma X-ray unit. These images were compared against a reference image using the 2 alternative forced choice (2AFC) method. The effective dose (E) was calculated using PCXMC software using the exposure parameters and the DAP. The exposure index (lgM provided by Agfa systems) was recorded.ResultsExposure time decreases more when applying the 10 kVp rule with manual mode (50%–28%) when compared with automatic mode (36%–23%). Statistical differences for E between several ionization chambers' combinations for AEC mode were found (p = 0.002). E is lower when using only the right AEC ionization chamber. Considering the image quality there are no statistical differences (p = 0.348) between the different ionization chambers' combinations for AEC mode for images with no lesions. Considering lgM values, it was demonstrated that they were higher when the AEC mode was used compared to the manual mode. It was also observed that lgM values obtained with AEC mode increased as kVp value went up. The image quality scores did not demonstrate statistical significant differences (p = 0.343) for the images with lesions comparing manual with AEC mode.ConclusionIn general the E is lower when manual mode is used. By using the right AEC ionising chamber under the lung the E will be the lowest in comparison to other ionising chambers. The use of the 10 kVp rule did not affect the visibility of the lesions or image quality.     

Optimization of chest radiographic imaging parameters: a comparison of image quality and entrance skin dose for digital chest radiography systems

We studied the performance of three computed radiography and three direct radiography systems with regard to the image noise and entrance skin dose based on a chest phantom. Images were obtained with kVp of 100, 110, and 120 and mA settings of 1, 2, 4, 8, and 10. Significant differences of image noise were found in these digital chest radiography systems (P<.0001). Standard deviation was significantly different when the mAs were changed (P<.001), but it was independent of the kVp values (P=.08-.85). Up to 44% of radiation dose could be saved when kVp was reduced from 120 to 100 kVp without compromising image quality.     

Radiation dose reduction and image quality in pediatric abdominal CT with kVp and mAs modulation and an iterative reconstruction technique

ObjectiveThe objective of this study was to compare the radiation dose and image quality of pediatric abdominal computed tomography (CT) using a protocol reconstructed with filtered back projection (FBP) and a protocol with both kVp and mAs modulation and sinogram-affirmed iterative reconstruction (SAFIRE).Materials and methodsWe retrospectively reviewed pediatric abdominal CT examinations performed with both kVp and mAs modulation. These raw data were reconstructed with SAFIRE at different strengths from 2 to 4 (SAFIRE groups 2–4). Another set of age/sex-matched pediatric abdominal CT examinations were also reviewed, which were performed during the same period with only mAs modulation and FBP (control group). The radiation dose and image quality were compared between groups. The image quality was objectively evaluated as the noise measured in the liver, aorta, and spleen at the level of the main portal vein and the image quality was subjectively reviewed by two radiologists for diagnostic acceptability using a four-point scale (0: unacceptable; 1: worse than the control group, but acceptable; 2: comparable with the control group; and 3: better than the control group). An independent t test was used in order to compare the radiation dose. An independent t test with Bonferroni correction and generalized estimating equations were used for the comparison of the objective and subjective image quality, respectively.ResultsTwenty-nine patients (M:F=19:10; mean age, 10.0 years) were enrolled in each group. The SAFIRE group, using the size-specific dose estimates calculation method showed a 64.2% radiation dose reduction (from 8.1 to 2.9 mGy, P< .05), compared with the results of the control group. The objective image noise of the SAFIRE groups 2 and 3 was comparable to that of the control group. The subjective image quality was the best in SAFIRE group 3 [odds ratio (OR) 3.015, P< .001 when comparing to SAFIRE group 0; OR 1.513, P< .001 when comparing to SAFIRE group 2].ConclusionsImage acquisition with both kVp and mAs modulation and iterative reconstruction using SAFIRE with strength 3 can preserve the objective and subjective image quality of pediatric abdominal CT scans with less than half the radiation dose.     

Dosimetry and adequacy of CT-based attenuation correction for pediatric PET: phantom study

PURPOSE: To evaluate the dose from the computed tomographic (CT) portion of positron emission tomography (PET)/CT to determine minimum CT acquisition parameters that provide adequate attenuation correction. MATERIALS AND METHODS: Measurements were made with a PET/CT scanner or a PET scanner, five anthropomorphic phantoms (newborn to medium adult), and an ionization chamber. The CT dose was evaluated for acquisition parameters (10, 20, 40, 80, 160 mA; 80, 100, 120, 140 kVp; 0.5 and 0.8 second per rotation; 1.5:1 pitch). Thermoluminescent dosimetry was used to evaluate the germanium 68/gallium 68 rod sources. A phantom study was performed to evaluate CT image noise and the adequacy of PET attenuation correction as a function of CT acquisition parameters and patient size. RESULTS: The volumetric anthropomorphic CT dose index varied by two orders of magnitude for each phantom over the range of acquisition parameters (0.30 and 21.0 mGy for a 10-year-old with 80 kVp, 10 mAs, and 0.8 second and with 140 kVp, 160 mAs, and 0.8 second, respectively). The volumetric anthropomorphic CT dose index for newborn phantoms was twice that for adult phantoms acquired similarly. The rod source dose was 0.03 mGy (3-minute scan). Although CT noise varied substantially among acquisition parameters, its contribution to PET noise was minimal and yielded only a 2% variation in PET noise. In a pediatric phantom, PET images generated by using CT performed with 80 kVp and 5 mAs for attenuation correction were visually indistinguishable from those generated by using CT performed with 140 kVp and 128 mAs. With very-low-dose CT (80 kVp, 5 mAs) for the adult phantom, undercorrection of the PET data resulted. CONCLUSION: For pediatric patients, adequate attenuation correction can be obtained with very-low-dose CT (80 kVp, 5 mAs, 1.5:1 pitch), and such correction leads to a 100-fold dose reduction relative to diagnostic CT. For adults undergoing CT with 5 mAs and 1.5:1 pitch, the tube voltage needs to be increased to 120 kVp to prevent undercorrection.     

The Image Quality and Radiation Dose of 100-kVp versus 120-kVp ECG-Gated 16-Slice CT Coronary Angiography

Objective

This study was conducted to assess the feasibility of performing 100-kVp electrocardiogram (ECG)-gated coronary CT angiography, as compared to 120-kVp ECG-gated coronary CT angiography.

Materials and Methods

We retrospectively evaluated one hundred eighty five gender- and body mass index-matched 16-slice coronary CT sets of data, which were obtained using either 100 kVp and 620 effective mAs or 120 kVp and 500 effective mAs. The density measurements (image noise, vessel density, signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]) and the estimated radiation dose were calculated. As a preference test, two image readers were independently asked to choose one image from each pair of images. The results of both protocols were compared using the paired t-test or the Wilcoxon signed rank test.

Results

The 100-kVp images showed significantly more noise and a significantly higher vessel density than did the 120-kVp images. There were no significant differences in the SNR and CNR. The estimated reduction of the radiation dose for the 100-kVp protocol was 24%; 7.8 ± 0.4 mSV for 100-kVp and 10.1 ± 1.0 mSV for 120-kVp (p < 0.001). The readers preferred the 100-kVp images for reading (reader 1, p = 0.01; reader 2, p = 0.06), with their preferences being stronger when the subject''s body mass index was less than 25.

Conclusion

Reducing the tube kilovoltage from 120 to 100 kVp allows a significant reduction of the radiation dose without a significant change in the SNR and the CNR.