ATOM Phantom Research Articles

Development of a novel automated algorithm for patient dosimetry in computed tomography: a step towards the facilitation of size-specific dose estimates and organs dosimetry estimations in a busy clinical workflow

Abstract Accurate dosimetry in computed tomography (CT) is essential for patient safety and effective radiation management. This study presents the development of an automated algorithm designed to enhance patient dosimetry by facilitating size-specific dose estimates (SSDE) and organ dose estimations. Utilizing a Python-based script, the proposed method integrates advanced image preprocessing, contour detection, and mathematical calculations to quantify key metrics from CT images. This automated approach addresses the limitations of manual measurement techniques. A retrospective analysis was conducted on CT axial images from examinations acquired with an 80-detector scanner. The algorithm processes DICOM images, converts pixel values to Hounsfield Units, applies Gaussian smoothing, windowing, and thresholding, followed by morphological operations to refine segmentation. It measures the water equivalent diameter (Dw) and estimates both region SSDE and organ doses, incorporating tissue attenuation. Validation was performed using an adult anthropomorphic ATOM phantom, with organ doses measured by optically stimulated luminescence dosimeters. The results demonstrated the algorithm's potential in estimating SSDE and organ doses. Validation of the automated method revealed strong correlations for Dw and SSDE between the proposed method and manual measurements of five expert reviewers ranging from 0.86 to 0.99 for determination coefficient. Comparative analysis of organ doses showed close agreement between results from experimental setup against the proposed algorithm. The automated algorithm estimated brain dose with a mean of 21.8 mGy, while measurements from the ATOM phantom and CT Expo indicated 19.74 mGy and 23.05 mGy, respectively. For lung doses, the automated algorithm estimated 12.5 mGy compared to 11.0 mGy from the ATOM phantom and 13.1 mGy from CT Expo. Liver doses were measured at 12.7 mGy by the automated method, versus 12.1 mGy from the ATOM phantom and 11.1 mGy from CT Expo. This study shows the potential of automated image analysis techniques in enhancing dosimetry accuracy in CT examinations.

Digital phantom versus patient-specific radiation dosimetry in adult routine thorax CT examinations.

The aim of this study was to compare the organ doses assessed through a digital phantom-based and a patient specific-based dosimetric tool in adult routine thorax computed tomography (CT) examinations with reference to physical dose measurements performed in anthropomorphic phantoms. Two Monte Carlo based dose calculation tools were used to assess organ doses in routine adult thorax CT examinations. These were a digital phantom-based dosimetry tool (NCICT, National Cancer Institute, USA) and a patient-specific individualized dosimetry tool (ImpactMC, CT Imaging GmbH, Germany). Digital phantoms and patients were classified in four groups according to their water equivalent diameter (Dw). Normalized to volume computed tomography dose index (CTDIvol), organ dose was assessed for lungs, esophagus, heart, breast, active bone marrow, and skin. Organ doses were compared to measurements performed using thermoluminescent detectors (TLDs) in two physical anthropomorphic phantoms that simulate the average adult individual as a male (Alderson Research Labs, USA) and as a female (ATOM Phantoms, USA). The average percent difference of NCICT to TLD and ImpactMC to TLD dose measurements across all organs in both sexes was 13% and 6%, respectively. The average±1 standard deviation in dose values across all organs with NCICT, ImpactMC, and TLDs was±0.06 (mGy/mGy),±0.19 (mGy/mGy), and±0.13 (mGy/mGy), respectively. Organ doses decreased with increasing Dw in both NCICT and ImpactMC. Organ doses estimated with ImpactMC were in closer agreement to TLDs compared to NCICT. This may be attributed to the inherent property of ImpactMC methodology to generate phantoms that resemble the realistic anatomy of the examined patient as opposed to NCICT methodology that incorporates an anatomical discrepancy between phantoms and patients.

Effectiveness of low tube voltage scan in the exposure dose for lenses during paediatric thoracic CT examination: anthropomorphic phantoms study.

To determine whether using lower-tube voltage reduces the scattered dose for the lens during paediatric thoracic computed tomography (CT). Two paediatric anthropomorphic phantoms (ATOM Phantom, CIRS, Norfolk, Virginia, USA) representing a newborn and 5-year-old were placed on the gantry of CT scanner, and optically stimulated luminescence dosemeters were placed on the left and right lenses, in front of the left and right thyroid glands, in front of the left and right mammary glands, and in front of and behind the mammary gland level and we measured scattered dose of the optically stimulated luminescence dosemeter was compared for each phantom between 80 and 120kVp. Significant differences were observed in the scatter doses for the lens between 80 and 120kVp (p<0.01). Compared with the 120kVp scan, the scatter doses for the lens were ~15-40% lower in newborn and 5-year-olds using the 80kVp scan during paediatric CT.

Would lead shielding the eye lenses during a head CT be beneficial?

The lens of the eye is one of the radiosensitive organs. Patients receiving computed tomography (CT) scanning of the head, as well as patients undergoing repeated CT scanning of the head, are at risk for this consequence. The goal of this study was to see if a lead equivalent might reduce radiation reaching the eye’s lens during regular cranial CT. The goal was accomplished by determining the ideal shielding thickness for patient applications by first evaluating the image quality using phantom measurements taken with and without lead shielding. LiF-thermoluminescent dosimeters were used to quantify the entrance surface doses (ESDs) to the eye lenses of the ATOM phantom without, with one, two, and three layers of lead shielding. The use of customized lead shields up to 0.1 mm thick might be used, according to ACR CT Phantom studies, without having a noticeable impact on the image quality for the central and posterior areas. In these experiments, 0.1 mm thick lead shielding reduces ESDs to the eye’s lens by 31%. Eye shields significantly reduced image quality in the anterior region, but just slightly in the centre and posterior regions. Given the foregoing, using modified lead shields could drastically lower dose to the lens without severely affecting image quality.

Low dose pediatric chest computed tomography on a photon counting detector system – initial clinical experience

BackgroundWith the clinical release of a photon counting detector-based computed tomography (CT) system, the potential benefits of this new technology need to be evaluated clinically. Literature concerning this new generation of detector is sparse, especially in the field of pediatric radiology. Therefore, this study outlines our initial experience with ultra-low dose chest CT imaging on the new photon counting CT system.Materials and methodsA pediatric phantom (1-year old, CIRS ATOM phantom, model 704 [CIRS-computerized imaging reference system, Norfolk, VA]) was scanned at different dose levels and different image quality levels to define a protocol for clinical examinations. Next, 20 consecutive pediatric non-contrast ultra-low dose chest CT examinations were evaluated for radiation dose and diagnostic image quality using a 4-point Likert-scale—1 = excellent, 4 = bad image quality—by two radiologists in a consensus reading. This retrospective analysis was approved by the local research ethics committee.ResultsChest CT examinations performed at ultra-low radiation dose (effective dose 0.19 ± 0.07 mSv; size-specific dose estimate 0.45 ± 0.14 mGy) in pediatric patients ages (2.6 ± 1.8 years) show good to excellent image quality for lung structures (1.4 ± 0.4) and moderate image quality for soft tissue structures (2.8 ± 0.2).ConclusionPediatric ultra-low dose chest CT examinations are feasible with the new generation photon counting detector-based CT system. The benefits of this technology must be evaluated for pediatric patients from the outset.

Metal artifact reduction and tumor detection using photon-counting multi-energy computed tomography.

Metal artifacts are considered a major challenge in computed tomography (CT) as these adversely affect the diagnosis and treatment of patients. Several approaches have been developed to address this problem. The present study explored the clinical potential of a novel photon-counting detector (PCD) CT system in reducing metal artifacts in head CT scans. In particular, we studied the recovery of an oral tumor region located under metal artifacts after correction. Three energy thresholds were used to group data into three bins (bin 1: low-energy, bin 2: middle-energy, and bin 3: high-energy) in the prototype PCD CT system. Three types of physical phantoms were scanned on the prototype PCD CT system. First, we assessed the accuracy of iodine quantification using iodine phantoms at varying concentrations. Second, we evaluated the performance of material decomposition (MD) and virtual monochromatic images (VMIs) using a multi-energy CT phantom. Third, we designed an ATOM phantom with metal insertions to verify the effect of the proposed metal artifact reduction. In particular, we placed an insertion-mimicking an iodine-enhanced oral tumor in the beam path of metallic objects. Normalized metal artifact reduction (NMAR) was performed for each energy bin image, followed by an image-based MD and VMI reconstruction. Image quality was analyzed quantitatively by contrast-to-noise ratio (CNR) measurements. The results of iodine quantification showed a good match between the true and measured iodine concentrations. Furthermore, as expected, the contrast between iodine and the surrounding material was higher in bin 1 image than in bin 3 image. On the other hand, the bin 3 image of the ATOM phantom showed fewer metal artifacts than the bin 1 image because of the higher photon energy. The result of quantitative assessment demonstrated that the 40-keV VMI (CNR: 20.6 ± 1.2) with NMAR and MD remarkably increased the contrast of the iodine-enhanced region compared with that of the conventional images (CNR: 10.4 ± 0.5) having 30 to 140 keV energy levels. The PCD-based multi-energy CT imaging has immense potential to maximize the contrast of the target tissue and reduce metal artifacts simultaneously. We believe that it would open the door to novel applications for the diagnosis and treatment of several diseases.

A study on the reduction of radiation dose using carbon fiber-reinforced plastic during X-ray examination of children and infants

The purpose of this study was to investigate the suitability of an assistive device for radiological examination. A Carbon Fiber-Reinforced Plastic (CFRP) with relatively high transmission factor was used to reduce unnecessary radiation exposure for patients and examiners and maintain a stable examination posture and reduce falling of the infant. An average of 10 entrance surface doses (ESDs) were used for the ATOM Phantom T-spine (T6) and the Rando Phantom Thyroid (T), Inguinal Area (I), and Eye Ball (E) for patients and examiners during each infant chest X-ray examination. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were also measured and analyzed via paired sample T-test and Pearson's correlation analysis using SPSS statistics version 21.0 (Chicago, IL, U.S.A.) to quantitatively evaluate changes in image quality before and after using the ancillary device. During infant chest X-ray examination, EST results were as follow: ESDT6 of infants, 233.70 ± 5.74 μGy; ESTs for the examination assistant: ESDT151.40 ± 4.01 μGy; ESDI, 143.20 ± 3.22 μGy; and ESDE, 146.20 ± 3.19 μGy. When the SNR and CNR values of chest X-ray images involving infants were compared using Pearson's correlation analysis, significant (p < 0.001) differences were found between values obtained before and after applying the ancillary device. The radiological examination assist device can stabilize the infant's posture during examination. Thus, it can reduce unnecessary exposure of patients and examination assistants to radiation, ultimately improving the safety of infant X-ray examinations.

Calculating Individual Lifetime Effective Risk from Initial Mean Glandular Dose Arising from the First Screening Mammogram

ObjectivesThe objective of the study was to use the initial mean glandular dose (MGD) arising from the first screening mammogram to estimate the individual total screening lifetime effective risk. MethodsOrgan doses from full-field digital mammography (FFDM) screening exposures (craniocaudal and mediolateral oblique for each breast) were measured using a simulated approach, with average breast thickness and adult ATOM phantoms, on 16 FFDM machines. Doses were measured using thermoluminescent dosimeters accommodated inside the ATOM phantom; examined breast MGD was calculated. Total effective risk during a client's lifetime was calculated for 150 screening scenarios of different screening commencement ages and frequencies. For each scenario, a set of conversion factors were obtained to convert MGD values into total effective risk. ResultsFor the 16 FFDM machines, MGD contributes approximately 98% of total effective risk. This contribution is approximately constant for different screening regimes of different screening commencement ages. MGD contribution remains constant, but the risk reduced because the radiosensitivity of all body tissues, including breast tissue, reduces with age. Three sets of conversion factors were obtained for three screening frequencies (annual, biennial, triennial). Three relationship graphs between screening commencement age and total effective risk, as percentages of MGD, were created. ConclusionsGraphical representation of total risk could be an easy way to illustrate the total effective risk during a client's lifetime. Screening frequency, commencement age, and MGD are good predictors for total effective risk, generating more understandable data for clients than MGD.

HU deviation in lung and bone tissues: Characterization and a corrective strategy.

In the era of precision medicine, quantitative applications of x-ray Computed Tomography (CT) are on the rise. These require accurate measurement of the CT number, also known as the Hounsfield Unit. In this study, we evaluated the effect of patient attenuation-induced beam hardening of the x-ray spectrum on the accuracy of the HU values and a strategy to correct for the resulting deviations in the measured HU values. A CIRS electron density phantom was scanned on a Siemens Biograph mCT Flow CT scanner and a GE Discovery 710 CT scanner using standard techniques that are employed in the clinic to assess the HU deviation caused by beam hardening in different tissue types. In addition, an anthropomorphic ATOM adult male upper torso phantom was scanned on the GE Discovery 710 scanner. Various amounts of Superflab bolus material were wrapped around the phantoms to simulate different patient sizes. The mean HU values that were measured in the phantoms were evaluated as a function of the water-equivalent area (Aw ), a parameter that is described in the report of AAPM Task Group 220. A strategy by which to correct the HU values was developed and tested. The variation in the HU values in the anthropomorphic ATOM phantom under different simulated body sizes, both before and after correction, were compared, with a focus on the lung and bone tissues. Significant HU deviations that depended on the simulated patient size were observed. A positive correlation between HU and Aw was observed for tissue types that have an HU of less than zero, while a negative correlation was observed for tissue types with HU values that are greater than zero. The magnitude of the difference increases as the underlying attenuation property deviates further away from that of water. In the electron density phantom study, the maximum observed HU differences between the measured and reference values in the cortical bone and lung materials were 426 and 94 HU, respectively. In the anthropomorphic phantom study, the HU difference was as much as -136.7 ± 8.2 HU (or -7.6% ± 0.5% of the attenuation coefficient, AC) in the spine region, and up to 37.6 ± 1.6 HU (or 17.3% ± 0.8% of AC) in the lung region between scenarios that simulated normal and obese patients. Our HU correction method reduced the HU deviations to 8.5 ± 9.1 HU (or 0.5% ± 0.5%) for bone and to -6.4 ± 1.7 HU (or -3.0% ± 0.8%) for lung. The HU differences in the soft tissue materials before and after the correction were insignificant. Visual improvement of the tissue contrast was also achieved in the data of the simulated obese patient. The effect of a patient's size on the HU values of lung and bone tissues can be significant. The accuracy of those HU values was substantially improved by the correction method that was developed for and employed in this study.

Effective lifetime radiation risk for a number of national mammography screening programmes

Background and purposeThe performance of mammography screening programmes is focussed mainly on breast cancer detection rates. However, when the benefits and risks of mammography are considered, the risk of radiation-induced cancer is calculated for only the examined breast using Mean Glandular Dose (MGD). The risk from radiation during mammography is often described as low or minimal. This study aims to evaluate the effective lifetime risk from full field digital mammography (FFDM) for a number of national screening programmes. Material and MethodsUsing an ATOM phantom, radiation doses to multiple organs were measured during standard screening mammography. Sixteen FFDM machines were used and the effective lifetime risk was calculated across the female lifespan for each machine. Once the risks were calculated using the phantom, the total effective lifetime risk across 48 national screening programmes was then calculated; this assumed that all these programmes use FFDM for screening. ResultsLarge differences exist in effective lifetime risk, varying from 42.21 [39.12–45.30] cases/106 (mean [95% CI]) in the Maltese screening programme to 1099.67 [1019.25–1180.09] cases/106 for high breast cancer risk women in the United States of America. These differences are mainly attributed to the commencement age of screening mammography and the time interval between successive screens. ConclusionsEffective risk should be considered as an additional parameter for the assessment of screening mammography programme performance, especially for those programmes which recommend an early onset and more frequent screening mammography.

Optimal dose reduction algorithm using an attenuation-based tube current modulation method for cone-beam CT imaging.

To reduce the radiation dose given to patients, a tube current modulation (TCM) method has been widely used in diagnostic CT systems. However, the TCM method has not yet been applied to a kV-CBCT system on a LINAC machine. The purpose of this study is to investigate if a TCM method would be desirable in a kV-CBCT system for image-guided radiation therapy (IGRT) or not. We have developed an attenuation–based TCM method using prior knowledge from planning CT images of patients. The TCM method can provide optimized dose reductions without degrading image quality for kV-CBCT imaging. Here, we investigate whether or not our suggested TCM method is desirable to use in kV-CBCT systems to confirm and revise the exact position of a patient for IGRT. Patients go through diagnostic CT scans for RT planning; therefore, using information from prior CT images can enable estimations of the total X-ray attenuation through a patient’s body in a CBCT setting for radiation treatment. Having this planning CT image allows to use the proposed TCM method in RT. The proposed TCM method provides a minimal amount of current for each projection, as well as total current, required to reconstruct the current modulated CBCT image with an image quality similar to that of CBCT. After applying a calculated TCM current for each projection, projection images were acquired and the current modulated CBCT image was reconstructed using a FDK algorithm. To validate the proposed approach, we used a numerical XCAT phantom and a real ATOM phantom and evaluated the performance of the proposed method via visual and quantitative image quality metrics. The organ dose due to imaging radiation was calculated in both cases and compared using the GATE simulation toolkit. As shown in the quantitative evaluation, normalized noise and SSIM values of the TCM were similar to those of conventional CBCT images. In addition, the proposed TCM method yielded comparable image quality to that of conventional CBCT images for both simulations and experimental studies as organ doses were decreased. We have successfully demonstrated the feasibility and dosimetric merit of a prototypical TCM method for kV-CBCT via simulations and experimental study. The results indicate that the proposed TCM method and overall framework can be a viable option for CBCT imaging that utilizes an optimal dose reduction without degrading image quality. Thus, this method reduces the probability for side effects due to radiation exposure.

Mathematical modelling of radiation-induced cancer risk from breast screening by mammography

ObjectivesEstablish a method to determine and convey lifetime radiation risk from FFDM screening. MethodsRadiation risk from screening mammography was quantified using effective risk (number of radiation-induced cancer cases/million). For effective risk calculations, organ doses and examined breast MGD were used. Screening mammography was simulated by exposing a breast phantom for cranio-caudal and medio-lateral oblique for each breast using 16 FFDM machines. An ATOM phantom loaded with TLD dosimeters was positioned in contact with the breast phantom to simulate the client’s body. Effective risk data were analysed using SPSS software to establish a regression model to predict the effective risk of any screening programme. Graphs were generated to extrapolate the effective risk of all screening programmes for a range of commencement ages and time intervals between screens. ResultsThe most important parameters controlling clients’ total effective risk within breast screening are the screening commencement age and number of screens (correlation coefficients were −0.865 and 0.714, respectively). Since the tissue radio-sensitivity reduces with age, the end age of screening does not result in noteworthy effect on total effective risk. ConclusionsThe regression model can be used to predict the total effective risk for clients within breast screening but it cannot be used for exact assessment of total effective risk. Graphical representation of risk could be an easy way to represent risk in a fashion which might be helpful to clients and clinicians.

Optimization of head radiographic examination protocols in pediatric patients

Introduction Head radiography comprises a common examination protocol in clinical routine. Diagnostic decisions are associated with the detected injuries. Consequently, image quality of the x-ray examinations is essential for the early diagnosis and appropriate treatment, especially for the sensitive population of children. Therefore each examination protocol should be appropriately optimized to achieve images of high diagnostic quality and minimum radiation burden to patients. Purpose To optimize the radiographic technique for head examination protocols in pediatric patients. Methods and materials Three anthropomorphic phantoms (ATOM Phantoms, CIRS, Norfolk, VA) representing the average individual as neonate, 5-year-old, and 10-year-old child were employed. The phantoms were subjected to head radiographs using a state of the art digital radiographic system (AGFA GAEVART, DX-D600) for various tube voltages (50–125 kVp) and current settings (0.2–50 mAs). For each exposure, image quality objective parameters, including contrast to noise ratio values (CNR) were estimated to determine figure of merit (FOM) in the optimization process. The technique associated with the higher CNR value for the same FOM was considered as the optimized method. Results Dose reduction of up to 88% was recorded for the same CNR value when decreasing tube voltage. CNR was found to be improved decreasing tube voltage for all ages of pediatric phantoms. However, due to larger exposure time, motion artifacts may be conspicuous. Conclusion A reliable optimization methodology for head radiographs in pediatric patients was presented. The method described may be also applied in other anatomical regions.

A method for calculating effective lifetime risk of radiation-induced cancer from screening mammography

PurposeTo propose a method for evaluating the effective lifetime risk of radiation-induced cancer from screening mammography and to present initial data for the UK National Breast Screening Programme. Material and methodsThe imaging was undertaken using a Hologic Selenia full field digital mammographic unit. The proposed method utilises an ATOM phantom containing thermoluminescent dosimeters and a perspex-polyethylene breast phantom to measure organ doses during a standard four view screening mammogram. Effective dose was calculated and effective risk was modelled for a range of client ages. The total lifetime effective risk was then calculated for the UK national screening programme. Calculation of effective risk includes the radiation dose to examined and contralateral breasts in addition to other body organs; this is an advantage over the mean glandular dose. ResultsThe contralateral breast, thyroid, thymus, brain, lung, salivary glands, and bone marrow all receive more than 1 μGy radiation dose during screening mammography. A major difference exists for total effective lifetime risk of radiation-induced cancer between clients with average and high breast cancer risk. Differences are attributed to the commencement age of screening and time interval between screens. ConclusionThis study proposes a method to evaluate effective lifetime risk of radiation-induced cancer from screening mammography in order to compare different mammography screening programmes.

Radiation dose calculations for CT scans with tube current modulation using the approach to equilibrium function.

The approach to equilibrium function has been used previously to calculate the radiation dose to a shift-invariant medium undergoing CT scans with constant tube current [Li, Zhang, and Liu, Med. Phys. 39, 5347-5352 (2012)]. The authors have adapted this method to CT scans with tube current modulation (TCM). For a scan with variable tube current, the scan range was divided into multiple subscan ranges, each with a nearly constant tube current. Then the dose calculation algorithm presented previously was applied. For a clinical CT scan series that presented tube current per slice, the authors adopted an efficient approach that computed the longitudinal dose distribution for one scan length equal to the slice thickness, which center was at z = 0. The cumulative dose at a specific point was a summation of the contributions from all slices and the overscan. The dose calculations performed for a total of four constant and variable tube current distributions agreed with the published results of Dixon and Boone [Med. Phys. 40, 111920 (14pp.) (2013)]. For an abdomen/pelvis scan of an anthropomorphic phantom (model ATOM 701-B, CIRS, Inc., VA) on a GE Lightspeed Pro 16 scanner with 120 kV, N × T = 20 mm, pitch = 1.375, z axis current modulation (auto mA), and angular current modulation (smart mA), dose measurements were performed using two lines of optically stimulated luminescence dosimeters, one of which was placed near the phantom center and the other on the surface. Dose calculations were performed on the central and peripheral axes of a cylinder containing water, whose cross-sectional mass was about equal to that of the ATOM phantom in its abdominal region, and the results agreed with the measurements within 28.4%. The described method provides an effective approach that takes into account subject size, scan length, and constant or variable tube current to evaluate CT dose to a shift-invariant medium. For a clinical CT scan, dose calculations may be performed with a water-containing cylinder whose cross-sectional mass is equal to that of the subject. This method has the potential to substantially improve evaluations of patient dose from clinical CT scans, compared to CTDIvol, size-specific dose estimate (SSDE), or the dose evaluated for a TCM scan with a constant tube current equal to the average tube current of the TCM scan.

소아 전산화단층촬영에서 Volume Mode의 유용성 연구

본 연구는 ATOM Phantom을 이용하여 선량, 화질을 비교 분석 하여 Volume mode의 유용성 밝혀 소아 CT 검사에 적극적으로 사용하기 위함이다. Helical mode Noise와 Volume mode의 Noise, HU, SNR은 p>0.05 이므로 통계적으로 유이한 차이가 없음을 알 수 있었다. 각 부위별 선량값은 모두 p>0.05 이므로 통계적 유이한 차이가 없었으나 DLP값이 Helical mode보다 Volume mode가 더 낮게 측정되었다. 유효선량 역시 Volume mode가 Helical mode 보다 낮음을 알 수 있었다. 정성적 분석에서는 Mode에 따른 조건 별로 각각 Helical: 2.6, 3.3, 4.36 Volume: 2.8, 3.64, 4.44, Mode별 Follow up 영상평가 결과로는 Helical mode가 3.8 Volume mode가 3.83점으로 큰 차이가 없는 것으로 나타났다. 5세 이하의 소아 CT검사에 있어서 640-MDCT Volume scan이 Helical mode와 비교해 낮은 선량으로 영상의 질이 큰 차이가 없기에 소아 CT 검사에는 유용 하다고 생각된다. The purpose of this study is to analyze dose comparison and image quality evaluation according to Volume and Helical mode using ATOM Phantom. It is to actively use the Volume mode in pediatric CT examinations. There was no significant difference with Helical and Volume in the value of Noise, HU, SNR(p>0.05). All dose values was no statistical difference(p>0.05). In the value of DLP and effective dose by part, Volume mode was measured lower than Helical mode. For qualitative analysis, by scan parameter helical mode showed respectively 2.6, 3.3, 4.36 and Volume mode indicated 2.8, 3.64, 4.44 point. Image evaluation for the follow-up, Helical mode and Volume mode were respectively 3.8 and 3.83. In fact, There was no significant difference. In CT scans in children under 5 years, because 640-MDCT Volume scan dose compared with Helical mode is lower and there is no significant difference with two modes in the image quality, 640-MDCT Volume scan is thought to be useful for pediatric CT scans.

MO‐E‐17A‐03: Monte Carlo CT Dose Calculation: A Comparison Between Experiment and Simulation Using ARCHER‐CT

Purpose:To compare the CT doses derived from the experiments and GPU‐based Monte Carlo (MC) simulations, using a human cadaver and ATOM phantom.Methods:The cadaver of an 88‐year old male and the ATOM phantom were scanned by a GE LightSpeed Pro 16 MDCT. For the cadaver study, the Thimble chambers (Model 10×5−0.6CT and 10×6−0.6CT) were used to measure the absorbed dose in different deep and superficial organs. Whole‐body scans were first performed to construct a complete image database for MC simulations. Abdomen/pelvis helical scans were then conducted using 120/100 kVps, 300 mAs and a pitch factor of 1.375:1. For the ATOM phantom study, the OSL dosimeters were used and helical scans were performed using 120 kVp and x, y, z tube current modulation (TCM). For the MC simulations, sufficient particles were run in both cases such that the statistical errors of the results by ARCHER‐CT were limited to 1%.Results:For the human cadaver scan, the doses to the stomach, liver, colon, left kidney, pancreas and urinary bladder were compared. The difference between experiments and simulations was within 19% for the 120 kVp and 25% for the 100 kVp. For the ATOM phantom scan, the doses to the lung, thyroid, esophagus, heart, stomach, liver, spleen, kidneys and thymus were compared. The difference was 39.2% for the esophagus, and within 16% for all other organs.Conclusion:In this study the experimental and simulated CT doses were compared. Their difference is primarily attributed to the systematic errors of the MC simulations, including the accuracy of the bowtie filter modeling, and the algorithm to generate voxelized phantom from DICOM images. The experimental error is considered small and may arise from the dosimeters.R01 grant (R01EB015478) from National Institute of Biomedical Imaging and Bioengineering

A method to acquire CT organ dose map using OSL dosimeters and ATOM anthropomorphic phantoms

To present the design and procedure of an experimental method for acquiring densely sampled organ dose map for CT applications, based on optically stimulated luminescence (OSL) dosimeters "nanoDots" and standard ATOM anthropomorphic phantoms; and to provide the results of applying the method--a dose data set with good statistics for the comparison with Monte Carlo simulation result in the future. A standard ATOM phantom has densely located holes (in 3×3 cm or 1.5×1.5 cm grids), which are too small (5 mm in diameter) to host many types of dosimeters, including the nanoDots. The authors modified the conventional way in which nanoDots are used, by removing the OSL disks from the holders before inserting them inside a standard ATOM phantom for dose measurements. The authors solved three technical difficulties introduced by this modification: (1) energy dependent dose calibration for raw OSL readings; (2) influence of the brief background exposure of OSL disks to dimmed room light; (3) correct pairing between the dose readings and measurement locations. The authors acquired 100 dose measurements at various positions in the phantom, which was scanned using a clinical chest protocol with both angular and z-axis tube current modulations. Dose calibration was performed according to the beam qualities inside the phantom as determined from an established Monte Carlo model of the scanner. The influence of the brief exposure to dimmed room light was evaluated and deemed negligible. Pairing between the OSL readings and measurement locations was ensured by the experimental design. The organ doses measured for a routine adult chest scan protocol ranged from 9.4 to 18.8 mGy, depending on the composition, location, and surrounding anatomy of the organs. The dose distribution across different slices of the phantom strongly depended on the z-axis mA modulation. In the same slice, doses to the soft tissues other than the spinal cord demonstrated relatively small variations, with the maximum COV around 11.4%. This might be attributed to the angular mA modulation, the placement of the dosimeters, the chest cavity of the scanned region, and the size of the phantom. Doses to the spinal cord were consistently lower than those to other soft tissues. The method is suited for acquiring densely sampled organ dose maps, and can be used for studying dose distributions relevant to subject size, organ location, and clinical CT protocols.

SU‐E‐I‐14: Image Quality and Patient Dose Dependence on CT Scan Parameters for ATCM (CareDose4D)

Purpose: To develop pediatric CT protocols by characterizing effects of CT parameters on pediatric CT dose using automatic tube‐current modulation (ATCM). Methods: Sections of varying AP thicknesses (∼80, 117, 149, 214mm) from the adult, 10‐year‐old, 5‐year‐old, and 1‐year‐old ATOM phantoms (CIRS, Norfolk, VA) were placed contiguously. They were scanned on a 16‐channel CT (Emotion 16, Siemens) using ATCM (CareDose4D) to characterize the relationships between image quality and patient‐dose under different scan conditions: scan‐kVp, adult/pediatric patient selection, and patient size. Effective‐mAs/slice was extracted from the DICOM header of each CT image to calculate the DLP/slice. Noise was estimated as the standard deviation in ROIs. Two figures of merit (FOM) were defined: FOM1 as (noisê2/DLP)̂^−1; FOM2 as the (CNR̂2/DLP). Each FOM was calculated for each image of each series acquired. Results: for scan acquired as pediatric patients, the effective‐mAs/slice was lower than the reference‐mAs value for patient AP thicknesses below 120 mm but greater above AP thicknesses of 149mm. These differences increased with patient thickness and at lower kVp. For scans acquired as adult patients, the effective‐mAs/slice was always lower than the reference‐mAs. Under ATCM, the percent difference between the FOM1 for 110 and 80kVp relative to 130kVp ranged from [7,−12]% and [13,−58]% for pediatric, and [3, −16]% and [5,−92]% for adult patients. Under ATCM, the percent difference between the FOM2 for 110 (80)kVp and 130kVp for increasing thickness ranged from 54 to 36 (130 to 78)% for pediatric‐entered patients, and 51 to 32 (125 to 43)% for adult entered patients. Conclusion: CT dose with ATCM decreased for adult‐patient and increased for pediatric‐patient selection. The AP thickness at which ATCM will use effective‐mAs/slice &gt; reference‐mAs value for pediatric‐patients selection is 120–149mm. Adult ‐ patient selection maintains effective‐mAs/slice &lt; reference‐mAs value.

SU-GG-I-04: Effect of CT Scan Parameters on Adult and Pediatric CT Dose When Using Automatic Tube Current Modulation

Purpose: To develop pediatric CT protocols by characterizing effects of CT parameters on adult and pediatric CT dose using automatic tube‐current modulation (ATCM). Method and Materials: Adult and 10‐year‐old (10yo) ATOM (CIRS) phantoms were scanned on a 16‐channel CT system (Emotion 16, Siemens) using ATCM (CareDose4D) to characterize the relationships between CT scan parameters and patient dose. The scan parameters investigated include scan‐kVp, reference‐mAs, scout‐kVp, patient‐size selection (adult/pediatric), and rotation‐time. Effective‐mAs delivered by ATCM was extracted from the DICOM header of each CTimage.Results: Effective‐mAs delivered by ATCM varied with patient‐size selection, relative to reference‐mAs, it decreased for adult but increased for pediatric. Using ATCM the average effective‐mAs for 80, 100, 130 scan‐kVp changed by 81%&124%, 61%&110%, 55%&103% relative to reference‐mAs for the adult&10yo phantoms. However, when the 10yo was selected as adult, the average effective‐mAs decreased to 34%, 29%, and 26% of reference‐mAs. When selected as adult, dose decreased for all anatomical regions but when selected as pediatric, dose increase was observed for abdomen and pelvis (120–155%). ATCM effective‐mAs per slice scaled linearly (1±0.06) with input reference‐mAs. However, the minimum mA limited the modulation of effective‐mAs at low reference‐mAs. For both phantoms, 80 kVp scouts reduced the effective‐mAs by 5–7% on average (up to 20% for thorax) compared to 130 kVp scouts. For identical reference‐mAs, ATCM increased effective‐mAs for lower scan‐kVp; however, patient dose also decreased for lower scan‐kVp. For the adult&10yo phantoms, average dose at 80 and 110 scan‐kVp was 42%&39% and 72%&72% of that at 130 scan‐kVp, respectively. Conclusion: Patient dose with ATCM decreased for adult and increased for pediatric patients. The scout‐kVp affects ATCM schema with lower effective‐mAs for lower scout‐kVp. ATCM effective‐mAs is linear with input reference‐mAs. Net patient dose is reduced despite increased effective‐mAs at lower scan‐kVp using ATCM.