Possibilities of dose reduction in lateral cephalometric radiographs and its effects on clinical diagnostics

OBJECTIVES: The aim of the present study was to determine (1) the absorbed and the exit radiation doses for cephalometric exposures on a phantom head with various exposure settings and image receivers, and (2) the diagnostic image quality for various modalities assessed on cephalometric radiographs of patients. METHODS: The dose measurements for lateral cephalometric radiographs were performed with a semiconductor detector, and also with thermoluminescent detectors and an Alderson phantom. Both the integral and the effective doses were determined. Two radiographs of each patient (n=119) were taken at two different times, one at a low tube potential setting, 75+/-5 kV, and one with a decreased dose. Film-screen systems with speed class 400 and one storage phosphor plate were used. Five observers assessed the radiographs for the visualization of six cephalometric reference points on a three-point scale with -1, 0 and 1. Twenty-seven image pairs were rescored to determine inter- and intrarater reliability. The statistical analysis was done using analysis of variance and Tukey's HSD (honestly significant difference) post hoc test. RESULTS: Increasing the tube potential setting led to an average dose reduction to 83% (integral dose) or to 87% (effective dose). Instead of taking the radiograph at a low tube potential setting (75 kV), a dose reduction of about 15% was feasible at a high tube potential setting (90 kV). A significant difference in reference point visibility existed between film radiographs at low tube potential settings (mean score 0.984) and at high tube potential settings (90 kV, mean score 0.958). For the storage phosphor plates, there was no significant difference to the film-screen combinations at low tube potential and halved milliampere seconds settings. In the second assessment, there was a high degree of agreement (96.6%) compared with the first assessment (unadjusted for random agreement). CONCLUSIONS: As there is only minimal dose reduction at increased tube potential settings, for a dose reduction, it seems to be more useful to use storage phosphor plates at unchanged tube potential and halved milliampere seconds settings compared with the film-screen combination.     

Computed radiography versus screen-film radiography: detection of pulmonary edema in a rabbit model that simulates neonatal pulmonary infiltrates.

PURPOSE: To determine if computed radiography is equivalent to screen-film radiography in depicting pulmonary edema and to determine if radiation exposure can be reduced with computed radiography while maintaining equivalent diagnostic accuracy for pulmonary edema. MATERIALS AND METHODS: Oleic acid was intravenously injected into three rabbits at each of four doses: 0, 0.02, 0.04, and 0.06 mL/kg. Two hours later, chest computed radiographs and screen-film radiographs were obtained at 60 kVp and 1.1 mAs. Additional computed radiographs were obtained after reducing milliampere seconds or by reducing milliampere seconds and increasing the kilovolt peak, which reduced bone marrow exposure by up to 20%. The presence of pulmonary opacities, "truth," was established by the wet-dry weight ratio and by chest computed tomography (CT). The radiographs were masked and randomized. Four observers rated the images for the presence of parenchymal opacities with a dichotomous score and judged the quality of the radiographs on a scale from 1 (worst) to 6 (best). Cochran Q tests and McNemar tests were used to analyze the differences in paired comparisons. Image quality was evaluated with logistic regression analysis. RESULTS: There was no significant difference between truth and observer ability to detect opacity for either modality or for any exposure (P > .05). There was no significant difference between computed radiography and screen-film radiography for image quality (P > .05). CONCLUSION: Computed radiography is equivalent to screen-film radiography in the detection of pulmonary edema. Radiation exposure reduction of 20% can be achieved without affecting pulmonary edema detection or image quality.     

The effect of beam tube potential variation on gonad dose to patients during chest radiography investigated using high sensitivity LiF:Mg,Cu,P thermoluminescent dosemeters

Optimization of X-ray beam tube potential (kVp) in radiological examinations can minimize patient dose. This research aims to investigate the effect of tube potential variation on gonad doses to patients during posteroanterior (PA) chest radiography examinations. This study was carried out using a Toshiba general purpose X-ray unit and a Rando phantom. Dose measuring equipment included an ion chamber system, a dose-area product (DAP) meter and a thermoluminescent dosemeter (TLD) reader system with high sensitivity TLD pellets of LiF:Mg,Cu,P for low level gonad dose measurement. PA chest exposures of the phantom to produce a constant exit dose were made using a standard low tube potential (range 60-100 kVp) non-grid technique and a high tube potential (range 95-150 kVp) grid technique. Entrance surface doses (ESDs) and DAPs were also included in the measurements. Effective doses (EDs) were computed from ESD and DAP measurements using NRPB-SR262 and Xdose software. Results show that with the low tube potential technique both ovary dose and testes dose increase with increasing tube potential; statistically significant correlations of r = 0.994 (p = 0.0006) and r = 0.998 (p = 0.001), respectively, were found. For both organs, doses increase at a rate of approximately 2% per kVp. With the high tube potential technique there is insignificant correlation between gonad doses and tube potential. When comparing patient doses from typical exposures made at 70 kVp (low tube potential non-grid technique) with doses from exposures made at 120 kVp (high tube potential grid technique), the high tube potential technique delivers significantly higher values for ESD, and ovary, testes and effective doses by factors of 1.7, 5.2, 5.5 and 2.7, respectively.     

The influence of the X-ray spectrum at compact bone-titanium interfaces in digital dental radiography

OBJECTIVES: To determine the optimum X-ray spectrum in digital dental radiography once the dose around an implant and the diagnostic usefulness of the image are taken into account. MATERIALS AND METHODS: A Monte Carlo code (MCNP4B) was employed for computing the dose distribution across the bone-titanium interface. The X-ray spectra used were those met in digital dental radiography; 50-70 kVp, 2 mm Al total filtration, 5 kVp increment. RESULTS: The variation of the ratio of dose with as opposed to without implant against depth reaches maximum values at the bone-implant interface that vary between 2.9 and 3.2. For the same number of photon histories followed, the higher the tube potential setting, the greater the dose both in contact and inside the implant. CONCLUSION: In digital dental radiography, a 60-65 kVp spectrum accompanied by the known 30% reduction in mAs leads to lower dose to the patient for a diagnostically useful image.     

Attitude of the Belgian dentist population towards radiation protection

OBJECTIVES: To perform a survey of private dental offices in Belgium and gain insight in the knowledge and attitude of Belgian dentists towards quality care in radiography and radiation protection. METHODS: A questionnaire was distributed among 700 Belgian dental offices, which were included based on demographic data and the use of intraoral radiographic equipment. RESULTS: The response rate was 71%. Implementation of standards for quality care and radiation protection was suboptimal. In most offices, exposure settings of the intraoral radiation tube were 65 kV/kVp to 70 kV/kVp and 10 mA to 12 mA, with an average exposure time of 0.45 s. No reduction of exposure time was noticed when using faster film types. About one-third of the responders worked with digital image receptors. Aiming devices and rectangular collimation were used in a minority of practices (40% and 6%, respectively). The distance of the dentist to the radiation tube during exposure was on average 2.2 m, although 8% of the dentists assisted in holding the image receptor inside the patient's mouth. One quarter of the dentists were standing behind a wall when taking radiographs. Lead aprons were worn more often by female dentists. Dose estimation revealed that male dentists received a significantly larger effective dose per year than female dentists (8.3 mSv vs 3.2 mSv). CONCLUSIONS: The implementation of standards of quality care for radiography and radiation protection could be improved among Belgian dentists. An elaborate educational programme in dental radiography is a prerequisite. Furthermore, recommendations could help to attain a change in attitude towards the use of ionizing radiation in order to meet European guidelines.     

The reduction in radiation dose for intra-oral radiographs by the use of thin K-edge filters

The aim of this investigation was to reduce the radiation dose to patients undergoing intra-oral dental radiography by using thin K-edge filters in addition to the existing aluminum filter. The subject was a head phantom (a human skull embedded in tissue-equivalent material), which was exposed to X rays over a range of tube voltages (50-90 kVp) for each of the four filter systems. These were 2.7 mm aluminium alone (the existing total filtration) or with added 0.1 mm erbium, 0.1 mm yttrium or 0.05 mm niobium. The radiation dose was measured at four selected sites along the primary beam. These were the entrance skin dose, the exit skin dose and intra-orally both in front and behind the dental film packet. The exposure times and radiation doses required to produce an equivalent density (degree of blackening) on a radiograph of an upper molar tooth were determined. Within the usual diagnostic range of 60-80 kV the use of the thin K-edge filter resulted in a doubling of the exposure time (owing to the additional attenuation of the added filters). However, the skin dose and the total dose imparted to the patient were significantly reduced.     

Coronary artery calcium scoring with multislice computed tomography: in vitro assessment of a low tube voltage protocol

OBJECTIVES: We sought to compare an 80-kVp coronary calcium scoring protocol with the standard protocol of 120 kVp in terms of accuracy and reproducibility and to assess its dose reduction potential. MATERIALS AND METHOD: An anthropomorphic heart phantom with calcium cylinders was scanned with different tube currents at 80 kVp and 120 kVp using a 16-slice multislice CT (MSCT) scanner. An adapted threshold for 80 kVp was calculated. Accuracy and reproducibility for calcium mass, volume, and Agatston score were analyzed using F-tests. The radiation doses needed to produce artifact-free images were determined. RESULTS: Accuracy (measurement errors: mass 120 kVp +4.6%, mass 80 kVp -6.9%, volume 120 kVp +78.8%, volume 80 kVp +58.2%) and reproducibility (F-tests: mass: P = 0.4998, volume: P = 0.9168, Agatston: P = 0.5422) were comparable at both tube voltages. Avoiding the appearance of artificial lesions, a CTDI(w,eff) of 10.7 mGy was needed at 120 kVp versus 4.6 mGy at 80 kVp (dose reduction of 57%). CONCLUSIONS: Using an 80-kVp protocol in coronary calcium scoring, a relevant dose reduction is possible without compromising reproducibility and accuracy.     

Investigation of optimum X-ray beam tube voltage and filtration for chest radiography with a computed radiography system

The purpose of this study was to determine the optimum tube voltage and amount of added copper (Cu) filtration for processed chest radiographs obtained with an Agfa 75.0 Computed Radiography (CR) system. The contrast-to-noise ratio (CNR) was measured in the lung, heart/spine and diaphragm compartments of a validated chest phantom using various tube voltages and amounts of Cu filtration. The CNR was derived as a function of air kerma at the CR plate and with the effective dose. As rib contrast can interfere with detection of nodules in chest radiography, a tissue-to-rib ratio (TRR) was derived to investigate which tube voltages suppress the contrast of rib. Although processing algorithms affect the signal and noise in a way that is hard to predict, we found that, for a given set of processing parameters, the CNR was related to the plate air kerma and effective dose in a logarithmic manner (all R(2) >or=0.97). For imaging of the lung region, a low voltage (60 kVp) produced the highest CNR, whereas a high voltage (125 kVp) produced the highest TRR. In the heart/spine region, 80-125 kVp produced the highest CNR, while in the diaphragm region 60-90 kVp produced the highest CNR. For chest radiography with this CR system, the optimal tube voltage depends upon the region of interest. Of the filters tested, a 0.1 mm Cu thickness was found to provide a statistically significant increase in the CNR in the diaphragm region with tube potentials of 60 kVp and 80 kVp, without affecting the CNR in the other anatomical compartments.     

Radiological characteristics of lead foils in dental film packets: analysis of components and shielding effect.

The radiological characteristics of the lead in five different dental film packets currently on the market in Japan were studied with monochromatic X-rays. Four packets were of a foil type while in the fifth, the lead was incorporated in the vinyl of the film packet. The samples were analysed by polychromatic photon absorptiometry, and the main component found to be lead with tin and/or antimony in smaller amounts. The shielding effect was calculated and, with the exception of the lead vinyl type, all found to exceed the ISO standard 3665. The lead foils attenuated the primary beam by, on average, 77% and 56% at 60 and 90 kVp respectively: in contrast, the reduction with the lead vinyl packet was only 38% and 23%. Using a 7 cm round beam, the lead foils reduced the dose by an average of 15% compared with 30% with a rectangular beam; the average dose reduction with the lead vinyl type was 8% and 15% respectively. These data show that the lead vinyl packet is unsuitable for clinical use and confirm the importance of optimum beam collimation for the reduction of patient risk.     

A comparison of fixed and variable kVp technique protocols for film-screen mammography

Mammographic image quality, contrast and dose for a variable tube potential (kVp) technique protocol for film-screen mammography have been investigated. In this protocol, the tube potential is increased for larger breast thicknesses. Comparisons were made with fixed kVp protocols, in which the tube potential is kept constant and the breast thickness compensated for by prolonging the exposure ("fixed kVp" protocol). All measurements were performed on a mammography unit with a molybdenum target and filter. Image quality was quantified by image contrast, image detail detection and the minimum detectable dimension of low contrast objects. It was demonstrated that for a compressed breast thickness of less than about 40 mm, varying the tube potential had a negligible effect upon dose but a significant effect upon image quality. For a compressed breast thickness greater than about 60 mm, the effect of the tube potential upon image quality was much reduced; however, the effect upon dose was significantly greater. The variable kVp protocol takes advantage of this feature to yield a significantly lower dose for thicker breasts with a small reduction in image quality, often only within experimental uncertainty. For an exposure under automatic exposure control, increasing the tube potential from 26 kVp to 30 kVp for a breast of a reference tissue composition (50% adipose and 50% glandular) with a compressed thickness of 60 mm reduced the mean glandular dose from 6 mGy to 3.9 mGy (-35%), but increased the minimum detectable dimension of a low contrast mass from 0.8 (+/- 0.1) mm to 1.1 (+/- 0.1) mm. Adopting a variable kVp protocol led to a median patient mean glandular dose per film of 2.7 mGy, nearly independent of compressed breast thickness. In our survey, the mean age of women presenting for mammography is younger and the mean compressed breast thickness is less than reported from screening centres. This suggests that there will be a higher proportion of denser, glandular tissue in the breasts incorporated within this survey than for surveys from screening centres. The clinical use of the variable kVp protocol allows the extraction from patient data of separate changes in breast composition which are due to patient age and breast thickness. It is concluded that the reference breast tissue composition is not an accurate representation of the women presenting at this centre.     

Technique factors and image quality as functions of patient weight at abdominal CT

PURPOSE: To investigate how changes in kilovolt peak and milliampere second settings, and patient weight affect transmitted x-ray energy fluence and the image contrast-to-noise ratio (CNR) at abdominal computed tomography (CT). MATERIALS AND METHODS: Cylinders of water were used as patient models, and x-ray spectra, including x-ray tube potentials of 80-140 kVp, were investigated. The mean photon energy and energy fluence transmitted through water cylinders with varying diameters and the image contrast for fat, muscle, bone, and iodine relative to water were determined. The effect of changing the x-ray tube potential on CNR also was investigated. RESULTS: At a constant kVp, increasing patient weight from 10 kg to 120 kg reduced the transmitted energy fluence by two orders of magnitude. Changing the x-ray tube potential from 80 kVp to 140 kVp increased the mean photon energy from approximately 52 keV to approximately 72 keV and thus reduced the image contrast relative to water by 12% for muscle, 21% for fat, 39% for bone, and 50% for iodine (approximate reduction values). Increasing the x-ray tube potential from 80 kVp to 140 kVp increased the CNR by a factor of 2.6 for muscle and by a factor of 1. 4 for iodine. CONCLUSION: With changes in patient weight at abdominal CT, x-ray tube potentials must be varied to maintain a constant detector energy fluence. Increasing the x-ray tube potential generally improves CNR.     

碘化铯/非晶硅数字摄影系统拍摄胸片的适宜管电压:高千伏摄影是否适用于间接DR

目的探索碘化铯/非晶硅数字摄影系统(间接DR)拍摄胸片的适宜管电压。方法(1)分别对60名正常成人拍摄80、100、150 kV正位胸片,由5位放射科医师对比每人的3张图像质量,对多个解剖部位的显示情况和图像总体印象进行评分;(2)分别固定表面入射剂量和出射剂量,对人胸部体模拍摄80、100、120、150 kV正位胸片,对肺内模拟病变进行评分。结果成人胸片和肺内模拟病变的显示均随管电压增高,图像质量降低;80 kV对比度最好,但外观略接近低千伏摄影胸片。结论间接DR拍摄正位胸片的适宜管电压为80~100 kV,高千伏摄影不再适用于DR。     

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.     

Optimisation of radiological protocols for chest imaging using computed radiography and flat-panel X-ray detectors

Purpose

Digital radiography technology has replaced conventional screen-film systems in many hospitals. Despite the different characteristics of new detector materials, frequently, the same radiological protocols previously optimised for screen film are still used with digital equipment without any critical review. This study addressed optimisation of exposure settings for chest examinations with digital systems, considering both image quality and patient dose.

Materials and methods

Images acquired with direct digital radiography equipment and a computed radiography system were analysed with specially developed commercial software with a four-alternative forced-choice method: the most promising protocols were then scored by two senior radiologists.

Results

Digital technology offers a wide dynamic range and the ability to postprocess images, allowing use of lower tube potentials in chest examinations. The computed radiography system showed both better image quality and lower dose at lower energies (85 kVp and 95 kVp) than those currently used (125 kVp). Direct digital radiography equipment confirmed both its superior image quality and lower dose requirements compared with the storage phosphor plate system.

Conclusions

Generally, lowering tube potentials in chest examinations seems to allow better image quality/effective dose ratio when using digital equipment.     

Radiation dose reduction in direct digital panoramic radiography

Objectives

(a) To measure the absorbed radiation doses at 16 anatomical sites of a Rando phantom and (b) to calculate the effective doses including and excluding the salivary gland doses in panoramic radiography using a conventional and a digital panoramic device.

Study design

Thermoluminescent dosimeters (TLD-100) were placed at 16 sites in a Rando phantom, using a conventional, Planmeca Promax and a digital, Planmeca PM2002CC Proline 2000 (Planmeca Oy, 00880 Helsinki, Finland) panoramic device for panoramic radiography. During conventional radiography the selected exposure settings were 66 kVp, 6 mA and 16 s, while during digital radiography two combinations were selected 60 kVp, 4 mA, 18 s and 66 kVp, 8 mA, 18 s with and without image processing function. The dosimeters were annealed in a PTW-TLDO Harshaw oven. TLD energy response was studied using RQN beam narrow series at GAEC's Secondary Standard Calibration Laboratory. The reader used was a Harshaw, 4500. Effective dose was estimated according to ICRP₆₀ report (E_ICRP60). An additional estimation of the effective dose was accomplished including the doses of the salivary glands (E_SAL). A Wilcoxon signed ranks test was used for statistical analysis.

Results

The effective dose, according to ICRP report (E_ICRP60) in conventional panoramic radiography was 17 μSv and E_SAL was 26 μSv. The respective values in digital panoramic radiography were E_ICRP60 = 23 μSv and E_SAL = 38 μSv; while using the lowest possible radiographic settings E_ICRP60 was 8 μSv and E_SAL was 12 μSv.

Conclusions

The effective dose reduction in digital panoramic radiography can be achieved, if the lowest possible radiographic settings are used.     

不同摄影源像距对小儿胸部数字X线技术辐射剂量图像质量的影响

目的不同摄影源像距对小儿胸部数字X线技术(DR)辐射剂量、图像质量的影响。方法选取我院2017至2018年收治的60例行胸部X线(DR)检查的患儿为研究对象开展回顾性分析,首先进行体模预实验曝光,采用同一管电压和不同摄影源像距(SID)(80~150 cm),其中10 cm为1组,记录每次曝光的毫安秒和入射体表剂量(ESD)。选取体模预实验中ESD相对低剂量和剂量适中的2组(90 cm和110 cm)开展临床试验。所有患儿住院期间采用同一X线机对同一患儿进行胸部DR的初查和复查,并分为初查组和复查组,初查组采用SID=110 cm,复查组采用SID=90 cm,由3位影像学专家采用5分法对图像质量进行打分。结果通过影像学专家评判,80~150 cm的DR曝光图像质量无差异,且不同的SID下实施胸部体模DR,得到的毫安秒与辐射剂量不相同,同一体模在相同曝光指数下,随着SID的增大,毫安秒与辐射剂量均逐渐增大;初查组的图像质量评分为(4.9±1.0)分,复查组的图像质量评分为(4.9±1.0),2组的图像质量评分比较差异无统计学意义(P>0.05)。结论患儿DR胸部摄影中不同SID,其体表辐射剂量具有明显差异,SID为90 cm时能够大幅度地降低X线管的输出剂量,减少体表辐射剂量,延长X线管的使用寿命。     

Amorphous silicon,flat-panel,x-ray detector versus storage phosphor-based computed radiography: contrast-detail phantom study at different tube voltages and detector entrance doses

RATIONALE AND OBJECTIVES: Evaluation of the contrast-detail performance of an active-matrix flat-panel x-ray detector in comparison with a storage phosphor system with special regard to the potential of dose reduction. METHODS: A digital x-ray detector based on cesium iodide (CsI) and amorphous silicon (a-Si) technology was compared with a fifth-generation storage phosphor system. A lucite plate with 36 drilled holes of varying diameters and depths was used as contrast-detail phantom. At 45 kVp, 70 kVp, and 113 kVp, images at 8 different detector entrance doses ranging between 0.3 microGy and 40 microGy were obtained. On soft-copy displays, 3 masked observers evaluated the detectability of each aperture in each image according to a 5-point scale. The mean sum scores of corresponding images were compared. RESULTS: For all tube voltages and detector entrance doses, the images obtained with the CsI/a-Si detector resulted in better observer contrast-detail performance as compared with the images of the storage phosphor system. The CsI/a-Si system allowed a calculated dose reduction of 39% at 45 kVp, 68% at 70 kVp, and 81% at 113 kVp as compared with the storage phosphor system, without loss of contrast-detail detectability. CONCLUSIONS: Under the conditions of the chosen experimental design, the CsI/a-Si system provided a superior contrast-detail performance as compared with the storage phosphor system. The potential of dose reduction increased with rising tube voltage.     

Estimation of radiation exposure in low-dose multislice computed tomography of the heart and comparison with a calculation program

The purpose of this study was to evaluate the achievable organ dose savings in low-dose multislice computed tomography (MSCT) of the heart using different tube voltages (80 kVp, 100 kVp, 120 kVp) and compare it with calculated values. A female Alderson-Rando phantom was equipped with thermoluminescent dosimeters (TLDs) in five different positions to assess the mean doses within representative organs (thyroid gland, thymus, oesophagus, pancreas, liver). Radiation exposure was performed on a 16-row MSCT scanner with six different routine scan protocols: a 120-kV and a 100-kV CT angiography (CTA) protocol with the same collimation, two 120-kV Ca-scoring (CS) protocols with different collimations and two 80-kV CS protocols with the same collimation as the 120-kV CS protocols. Each scan protocol was repeated five times. The measured dose values for the organs were compared with the values calculated by a commercially available computer program. Directly irradiated organs, such as the esophagus, received doses of 34.7 mSv (CTA 16×0.75 120 kVp), 21.9 mSv (CTA 16×0.75 100 kVp) and 4.96 mSv (CS score 12×1.5 80 kVp), the thyroid as an organ receiving only scattered radiation collected organ doses of 2.98 mSv (CTA 16×0.75 120 kVp), 1.97 mSv (CTA 16×0.75 100 kVp) and 0.58 mSv (CS score 12×1.5 80 kVp). The measured relative organ dose reductions from standard to low-kV protocols ranged from 30.9% to 55.9% and were statistically significant (P<0.05). The comparison with the calculated organ doses showed that the calculation program can predict the relative dose reduction of cardiac low photon-energy protocols precisely.     

Contrast-detail phantom study for x-ray spectrum optimization regarding chest radiography using a cesium iodide-amorphous silicon flat-panel detector

RATIONALE AND OBJECTIVES: The purpose of this study evaluating a cesium iodide-amorphous silicon-based flat-panel detector was to optimize the x-ray spectrum for chest radiography combining excellent contrast-detail visibility with reduced patient exposure. MATERIALS AND METHODS: A Lucite plate with 36 drilled holes of varying diameter and depth was used as contrast-detail phantom. For 3 scatter body thicknesses (7.5 cm, 12.5 cm, 21.5 cm Lucite) images were obtained at 113 kVp, 117 kVp, and 125 kVp with additional copper filter of 0.2 and 0.3 mm, respectively. For each setting, radiographs acquired with 125 kVp and no copper filter were taken as standard of reference. On soft-copy displays, 3 observers blinded to the exposure technique evaluated the detectability of each aperture in each image according to a 5-point scale. The number of points given to all 36 holes per image was added. The scores of images acquired with filtration were compared with the standard images by means of a multivariate analysis of variance. Radiation burden was approximated by referring to the entrance dose and calculated using Monte Carlo method. RESULTS: All 6 evaluated x-ray spectra resulted in a statistically equivalent contrast-detail performance when compared with the standard of reference. The combination 125 kVp with 0.3 mm copper was most favorable in terms of dose reduction (approximately 33%). CONCLUSION: Within the constraints of the presented contrast-detail phantom study simulating chest radiography, the CsI/a-Si system enables an addition of up to 0.3 mm copper filtration without the need for compensatory reduction of the tube voltage for providing constant image quality. Beam filtration reduces radiation burden by about 33%.     

A pilot study investigating two dose reduction techniques for AP lumbar spine radiography using direct dosimetry and Projection VR

IntroductionThe purpose of this study was to compare radiation dose measurements generated using a virtual radiography simulation with experimental dosimeter measurements for two radiation dose reduction techniques in digital radiography.MethodsEntrance Surface Dose (ESD) measurements were generated for an antero-posterior lumbar spine radiograph experimentally using NanoDOT™, single point dosimeters, for two radiographic systems (systems 1 and 2) and using Projection VR™, a virtual radiography simulation (system 3). Two dose reduction methods were tested, application of the 15% kVp rule, or simplified 10 kVp rule, and the exposure maintenance formula. The 15% or 10 kVp rules use a specified increase in kVp and halving of the mAs to reduce patient ESD. The exposure maintenance formula uses the increase in source-to-object distance to reduce ESD.ResultsIncreasing kVp from 75 to 96 kVp, with the concomitant decrease in mAs, resulted in percent ESD reduction of 59.5% (4.02–1.63 mGy), 60.8% (3.55–1.39 mGy), and 60.3% (6.65–2.64 mGy), for experimental systems 1 and 2, and virtual simulation (system 3), respectively. Increasing the SID (with the appropriate increase in mAs) from 100 to 140 cm reduced ESD by 22.3% 18.8%, and 23.5%, for experimental systems 1 and 2, and virtual simulation (system 3), respectively.ConclusionPercent dose reduction measurements were similar between the experimental and virtual measurement systems investigated. For the dose reduction practices tested, Projection VR™ provides a realistic alternate of percent dose reduction to direct dosimetry.