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Purpose Size-specific dose estimate (SSDE) is a metric that adjusts CTDIvol to account for patient size. While not intended to be an estimate of organ dose, AAPM Report 204 notes the difference between the patient organ dose and SSDE is expected to be 10-20%. The purpose of this work was therefore to evaluate SSDE against estimates of organ dose obtained using Monte Carlo (MC) simulation techniques applied to routine exams across a wide range of patient sizes. Materials and methods Size-specific dose estimate was evaluated with respect to organ dose based on three routine protocols taken from Siemens scanners: (a) brain parenchyma dose in routine head exams, (b) lung and breast dose in routine chest exams, and (c) liver, kidney, and spleen dose in routine abdomen/pelvis exams. For each exam, voxelized phantom models were created from existing models or derived from clinical patient scans. For routine head exams, 15 patient models were used which consisted of 10 GSF/ICRP voxelized phantom models and five pediatric voxelized patient models created from CT image data. For all exams, the size metric used was water equivalent diameter (Dw ). For the routine chest exams, data from 161 patients were collected with a Dw range of ~16-44 cm. For the routine abdomen/pelvis exams, data from 107 patients were collected with a range of Dw from ~16 to 44 cm. Image data from these patients were segmented to generate voxelized patient models. For routine head exams, fixed tube current (FTC) was used while tube current modulation (TCM) data for body exams were extracted from raw projection data. The voxelized patient models and tube current information were used in detailed MC simulations for organ dose estimation. Organ doses from MC simulation were normalized by CTDIvol and parameterized as a function of Dw . For each patient scan, the SSDE was obtained using Dw and CTDIvol values of each scan, according to AAPM Report 220 for body scans and Report 293 for head scans. For each protocol and each patient, normalized organ doses were compared with SSDE. A one-sided tolerance limit covering 95% (P = 0.95) of the population with 95% confidence (α = 0.05) was used to assess the upper tolerance limit (TU ) between SSDE and normalized organ dose. Results For head exams, the TU between SSDE and brain parenchyma dose was observed to be 12.5%. For routine chest exams, the TU between SSDE and lung and breast dose was observed to be 35.6% and 68.3%, respectively. For routine abdomen/pelvis exams, the TU between SSDE and liver, spleen, and kidney dose was observed to be 30.7%, 33.2%, and 33.0%, respectively. Conclusions The TU of 20% between SSDE and organ dose was found to be insufficient to cover 95% of the sampled population with 95% confidence for all of the organs and protocols investigated, except for brain parenchyma dose. For the routine body exams, excluding the breasts, a wider threshold difference of ~30-36% would be needed. These results are, however, specific to Siemens scanners.

In this study, a new ATCM phantom was developed to test the performance of the automatic tube current modulation (ATCM) of computed tomography (CT) scanners.. Based on the Chinese reference man and Monte Carlo simulations of x-ray attenuation, a more realistic ATCM phantom made of polymethyl methacrylate was developed. The phantom has a length of 20 cm, and it can be used to measure the dose profile along the central axis using 19 real-time MOSFET detectors. The image noise can be calculated slice by slice in the phantom’s center. Test experiments showed that the phantom could initiate tube current modulation under different modulation levels of CT scans, and the actual effects of ATCM could be evaluated with the aid of the dose profile measurements. Using the measured dose profiles and image noise, the preferred dose can easily be identified from a choice of different modulation levels. The new phantom developed in this study can be used to test the ATCM performance of CT scanners, and is useful for further studies of the optimization of CT scan protocols with ATCM.

Objective: To compare radiation dose, radiologists’ satisfaction, and image noise between the standard dose abdominal CT currently performed at our hospital and the new automatic tube current modulation (ATCM) low dose abdominal CT, using various parameters (0%, 10%, 20%, and 30%) of the Adaptive Statistical Iterative Reconstruction (ASiR). Materials and Methods: We prospectively performed the ATCM low dose abdominal CT in 111 participants who had prior standard dose CT for comparison. The ATCM low dose CT images were post processed with 4 parameters (0%, 10%, 20% and 30%) of ASiR on a CT workstation. The volume CT dose index (CTDIvol) of the ATCM low dose and the standard dose CT were compared. Four experienced abdominal radiologists independently assessed the quality of the ATCM low dose CT with the aforementioned ASiR parameters using a 5-point-scale satisfaction score (1 = unacceptable, 2 = poor, 3 = average, 4 = good, and 5 = excellent image quality) by using the prior standard dose CT as a reference of an excellent image quality (5). Each reader selected the preferred ASiR parameter for each participant. The image noise of the liver and the aorta in all 5 techniques (1 prior standard dose and 4 current ATCM low dose techniques) was measured. The correlation between the image quality vs the participants’ body mass index (BMI) and waist circumferences were analyzed. Results: The mean CTDIvol of the ATCM low dose CT was significantly lower than of the standard dose CT (7.29 ± 0.20 vs 11.28 ± 0.23 mGy, p

Purpose We compare the effect of tube current modulation (TCM) and fixed tube current (FTC) on size‐specific dose estimates (SSDE) and image quality in lung cancer screening with low‐dose CT (LDCT) for patients of all sizes. Methods Initially, 107 lung screening examinations were performed using FTC, which satisfied the Centers for Medicare & Medicaid Services' volumetric CT dose index (CTDIvol) limit of 3.0 mGy for standard‐sized patients. Following protocol modification, 287 examinations were performed using TCM. Patient size and examination parameters were collected and water‐equivalent diameter (Dw) and SSDE were determined for each patient. Regression models were used to correlate CTDIvol and SSDE with Dw. Objective and subjective image quality were measured in 20 patients who had consecutive annual screenings with both FTC and TCM. Results CTDIvol was 2.3 mGy for all FTC scans and increased exponentially with Dw (range = 0.96–4.50 mGy, R2 = 0.73) for TCM scans. As patient Dw increased, SSDE decreased for FTC examinations (R2 = 1) and increased for TCM examinations (R2 = 0.54). Image quality measurements were superior with FTC for smaller sized patients and with TCM for larger sized patients (R2 > 0.5, P

Objectives This study aims to evaluate the radiation exposure to patients undergoing an abdominopelvic or a chest and abdominopelvic (trunk) CT examination and to assess compliance to imaging referral guidelines. Methods To this end, 357 standard abdominopelvic and trunk CT scans were collected from 8 Belgian institutions in 2011 and 2015. Effective dose (E) and collective dose were calculated using CT dose descriptors (CTDIvol and DLP), which were obtained from dose reports generated by the CT scanner. Subsequently, these CT requests were compared against the national referral guidelines to assess compliance. Population estimates for dose and compliance were obtained using multilevel linear regression and generalized estimating equation models. Results Between 2011 and 2015, a significant decrease of 28% in CTDIvol and DLP was found for abdominopelvic CT. The corresponding E decreased by 27%, and the collective dose by 23%. For trunk CT, a non-significant decrease of 6% was found in CTDIvol and a significant decrease of 14% in both DLP and E. However, the collective dose of trunk examinations increased by 39%. In 2011, 24% of the abdominopelvic examinations were not compliant with the guidelines, whereas this percentage dropped to 17% in 2015. Non-justified examinations accounted for 8% and 12% of all trunk CT scans in 2011 and 2015, respectively. Conclusion Between 2011 and 2015, there was a decrease in dose for patients undergoing abdominopelvic or trunk CT in Belgium. However, a fraction of the estimated doses are linked to unnecessary CT examinations, which should be avoided.

The novel deep learning image reconstruction (DLIR) is known to change its image quality characteristics according to object contrast and image noise. In clinical practice, computed tomography (CT) image noise is usually controlled by tube current modulation (TCM) to accommodate changes in object size. This study aimed to evaluate the image quality characteristics of DLIR for different object sizes when in-plane noise is controlled by TCM. We used Mercury 4.0 phantoms with different object sizes. Phantom image acquisition was performed on a GE Revolution CT system to investigate the impact of the DLIR algorithm compared to standard reconstructions: filtered back projection (FBP) and hybrid iterative reconstruction (hybrid-IR). For image quality evaluation, the noise power spectrum (NPS), task-based transfer function (TTF), and detectability index (d') were determined. The NPS of DLIR was very similar to that of FBP, and the information in the high-frequency region was maintained. In terms of TTF, DLIR showed higher resolution than hybrid-IR at low- to medium-contrast (Δ50, Δ90HU), but not necessarily higher than FBP. At the simulated contrast and lesion size, DLIR showed higher detectability than hybrid-IR, regardless of the phantom size. In this study, we evaluated a novel DLIR algorithm by reproducing clinical behaviors. The findings indicate that DLIR produces higher image quality than hybrid-IR regardless of the phantom size, although it depends on the reconstruction strength.

Author(s): Layman, Rick R; Hardy, Anthony J; Kim, Hyun J; Chou, Ei Ne; Bostani, Maryam; Cagnon, Chris; Cody, Dianna; McNitt-Gray, Michael | Abstract: PurposeThe purpose of this work was to estimate and compare breast and lung doses of chest CT scans using organ-based tube current modulation (OBTCM) to those from conventional, attenuation-based automatic tube current modulation (ATCM) across a range of patient sizes.MethodsThirty-four patients (17 females, 17 males) who underwent clinically indicated CT chest/abdomen/pelvis (CAP) examinations employing OBTCM were collected from two multi-detector row CT scanners. Patient size metric was assessed as water equivalent diameter (Dw ) taken at the center of the scan volume. Breast and lung tissues were segmented from patient image data to create voxelized models for use in anMonte Carlontransport code. The OBTCM schemes for the chest portion were extracted from the raw projection data. ATCM schemes were estimated using a recently developed method.nBreast and lungndoses for each TCM scenario were estimated for each patient model. CTDIvol -normalized breast (nDbreast ) and lung (nDlung ) dosesnwere subsequently calculated. The differences between OBTCM and ATCM normalized organ dose estimates were tested using linear regression models that included CT scanner and Dw as covariates.ResultsMean dose reduction from OBTCM in nDbreast was significant after adjusting for the scanner models and patient size (Pn=n0.047). When pooled with females and male patient, mean dose reduction from OBTCM in nDlung was observed to be trending after adjusting for the scanner model and patient size (Pn=n0.085).ConclusionsOne specific manufacturer's OBTCM was analyzed. OBTCM was observed to significantly decrease normalized breast relative to a modeled version of that same manufacturer's ATCM scheme. However, significant dose savings were not observed in lung dose over all. Results from this study support the use of OBTCM chest protocols for females only.

Purpose To investigate retrospective classification of adult patients into small, average, and large based on effective diameter (EDia) from localizer image of computed tomography (CT) scans and to develop regional diagnostic reference levels (DRLs) and achievable doses (AD). Method The patients falling within the mean ± standard deviation (SD) of EDia were classified as average; those below this range as small and above as large. The CTDIvol, dose-length-product (DLP) and size-specific dose estimates (SSDE) of all adult patients undergoing CT examinations in 8 CT facilities for 11 months (Dec. 2019 - Oct. 2020) were evaluated. The 75th and 50th percentile values were compared with national and international values. Results Of the total of 69,434 CT examinations, nearly 80% fell within average size. The 75th percentile values of CTDIvol and DLP for small patients for abdomen-pelvic exams were nearly half of average sized patients. Similarly, the 75th percentile values for large patients were nearly double. Similar findings were not found for chest exams. Analysis of image quality and dose factors such as noise, mean axial length, slice thickness, mean number of sequences, use of iterative reconstruction and tube current modulation (TCM) resulted in identification of opportunities for improvement and optimization of different CT facilities. Conclusions DRLs for adult patients were found to vary widely with patient size and thus establishing DRLs only for standard sized patient is not adequate. Simplified and intuitive methods for size classification was shown to provide meaningful information for optimization for patients outside the standard size adult.

Computed tomography (CT) is a digital radiological modality which has been classified as the largest source of medical radiation exposure. In this study, we estimated the effective dose to patients undergoing CT examinations using information obtained from DICOM images, including tube current, patient size and positioning, collimation etc. The custom code was used to calculate the conversion factors between an effective dose and air kerma length product. Their values are 0.0232 mSv/(mGy cm) and 0.0263 mSv/(mGy cm), for male and female patients, respectively. The effective dose for the whole-body CT is estimated to be 8.7 mSv.

On March 11, 2020, the World Health Organization declared the coronavirus disease 2019 (COVID-19) pandemic. The expert organisations recommend more cautious use of thoracic computed tomography (CT), opting for low-dose protocols. We aimed at determining a threshold value of automatic tube current modulation noise index below which there is a chance to miss an onset of ground-glass opacities (GGO) in COVID-19. A team of radiologists and medical physicists performed 25 phantom CT studies using different automatic tube current modulation settings (SUREExposure3D technology). We then conducted a retrospective evaluation of the chest CT images from 22 patients with COVID-19 and calculated the density difference between the GGO and unaffected tissue. Finally, the results were matched to the phantom study results to determine the minimum noise index threshold value. The minimum density difference at the onset of COVID-19 was 252 HU (p < 0.001). This was found to correspond to the SUREExposure 3D noise index of 36. We established the noise index threshold of 36 for the Canon scanner without iterative reconstructions, allowing for a decrease in the dose-length product by 80%. The proposed protocol needs to be validated in a prospective study.

In the present study, the radiation dose and image quality between two techniques, namely; automatic tube current modulation (ATCM) and fixed tube current (FTC), in computed tomography (CT) of multiphasic examination of the liver, were evaluated. For this objective, fifty liver CT patients examined were investigated by arterial, portal, venous, and equilibrium measures following scans of hepatic circulatory phases. All stages, except for tube current, a portal, and a venous phase, have been carried out by the FTC, ATCM and correlated with their dosage and image quality, with similar scanning and reconstruction parameters. In these techniques, the CT unit automatically displays , both the radiation dose measurements and the dose index volume (CTDIvol), simultaneously. Also, for quality insurance, the images obtained were quantitatively evaluated by the contrast noise ratio (CNR). The results showed that the averaged of CTDIvol was 26.07 mGy in FTC, and 13.71 mGy in ATCM. As compared with the FTC technique, CTDIvol was reduced by using the ATCM technique. The average value of CNR were(28.93, 29.98) HU in FTC and ATCM, respectively.

Purpose Organ-based tube current modulation (OB-TCM) techniques, which are provided by three vendors, reduces the radiation dose to the lens of the eyes by decreasing the tube current, when the X-ray tube passes over the anterior surface of critical organs. However, the characteristics of dose modulation of these techniques are different. The purpose of this study was to understand the performance characteristics of OB-TCM technique of each computed tomography (CT) vendor at head CT. Methods We used three CT scanners (SOMATOM Definition Flash; Siemens Healthcare, Revolution CT; GE Healthcare, and Aquilion ONE Genesis Edition; Canon Medical Systems). We measured the radiation dose to the lens surface as evaluation of radiation dose reduction and measured the image noise as index of image quality. We measured the radiation dose rate in the air for analysis of the characteristics of dose modulation in each OB-TCM. Results When applying OB-TCM, the radiation doses for the lens surface were decreased by 28%, 22%, and 25% for Siemens, GE, and Canon CT scanners, respectively, and the image noise level was increased by 5.6%, 8.5%, and 15.1% for Siemens, GE, and Canon CT scanners, respectively. The characteristics of dose modulation in each OB-TCM were also confirmed by measured the radiation dose rate. Conclusion We confirmed that each OB-TCM has different influence on image quality and radiation doses for lens surface, due to the different characteristics of dose modulation for each CT vendor.

Automatic tube current modulation (ATCM) is now available on all computed tomography (CT) scanners, but there is no standard phantom for testing its operation. For this study, a phantom comprising five elliptical sections of varying diameters in the shape of a pagoda has been made to represent the range of sizes for patients in Thailand and the Far East. ATCM performance can be evaluated in terms of how tube current and image noise vary with changes in the sizes of the sections. Additional rods of different materials with similar properties to human tissues have been inserted to allow the measurement of contrast-to-noise ratios (CNRs) for assessment of image quality. The phantom has been used to test and compare the performance of CT ATCM systems for the major four CT scanner vendors. The results showed that the ATCM systems of Toshiba and GE CT scanners maintained image noise and CNR within narrower ranges by varying tube current aggressively along the scan length, and commencing modulation before the high attenuation sections are reached. In contrast, the ATCM systems of Philips and Siemens scanners adjusted the tube current within narrower ranges, allowed larger variations in image noise and CNR, and commenced modulation at the start of sections with higher attenuation. The phantom can be used to confirm functionality of the system for acceptance testing, as well as providing information on the tradeoff between radiation dose and image quality when setting up clinical protocols during commissioning of new CT scanners. The phantom can also be used on a routine basis to check that performance is maintained, and could be used in the future for selecting protocol settings to give required values of CNR or adjusting protocol settings on different CT scanners to provide similar levels of clinical performance.

Purpose To prospectively evaluate contemporary indications, safety and diagnostic impact of cardiac CTA in patients undergoing cardiac CTA examinations for non-coronary clinical indications. Method We analyzed 1097 consecutive patients from the German Cardiac CT Registry who underwent cardiac CTA between 2009 and 2014 due to clinically indicated non-coronary reasons using 64-slice or newer CT systems in twelve tertiary German heart centers in order to evaluate the impact of clinical indications on procedure-associated parameters. All participating centers electronically submitted patient and examination data including detailed indications, clinical symptoms, procedural parameters, complications and diagnostic results in a predefined template. Results The most frequent indication for non-coronary cardiac CTA was the evaluation of pulmonary vein anatomy (65.9 %, 723/1097). In the remaining cases, most frequent indications were planning before TAVI (44.5 %, 69/155), evaluation of valvular disease (31.6 %, 49/155), and evaluation of implants (5.8 %, 9/155). Non-coronary cardiac CTA required a median amount of iodinated contrast agent of 100.0 mL (IQR 95.0–110.0 mL). Prospectively ECG-triggered acquisition was the most frequently used protocol (74.0 %), followed by retrospectively ECG-gated acquisition with and without tube current modulation (19.9 % and 6.0 %, respectively), resulting in a mean estimated effective dose of 5.2 mSv (IQR 2.9−9.5 mSv, average conversion factor k = 0.026). Overall, complication rate was very low (1.5 %). Non-coronary cardiac CTA revealed a new clinical diagnostic aspect in 3.2 % of all patients, and a new main clinical diagnosis in 2.2 %. Conclusions Non-coronary cardiac CTA as a routinely applied diagnostic modality is associated with a very low procedure-related rate of complications and reasonably low radiation exposure using contemporary CT systems.

For the optimisation of radiation dose in computed tomography (CT), dose reduction is attempted while preserving diagnostic performance. To reduce the overall radiation dose related to CT, the dose from scout radiography may be reduced by decreasing the tube voltage and tube current. We evaluated the effects of scout imaging conditions on CT radiation dose. An anthropomorphic chest phantom was imaged on two CT scanners (scanners A and B) from different vendors, manipulating the scout imaging conditions in terms of imaging direction, tube voltage and tube current, and assessed the tube current modulation in subsequent CT and pixel values in scout radiographs. The direction of the scout radiography influenced the shape of the tube current modulation curve and total radiation dose in subsequent CT. When compared with the use of the lateral projection, use of the posteroanterior or anteroposterior projection alone increased the radiation dose substantially on scanner A, but did not change, or mildly decreased, the dose on scanner B. When imaged using the lateral scout on scanner A, reduction in tube voltage and tube current for scout radiography decreased the CT dose in the cranial part of the scan range and, to a lesser degree, the total radiation dose. On the low-voltage, low-current lateral radiograph, the image contrast was impaired and pixel values were underestimated around the lung apex. Without the use of the lateral radiograph, neither the tube voltage nor tube current for scout radiography influenced the CT dose. On scanner B, reduced tube voltage for scout radiography increased the CT dose. In conclusion, reduced tube voltage and tube current may affect scout radiographs, resulting in alteration of the tube current modulation pattern and total radiation dose in subsequent CT. These effects vary depending on the CT scanners and scout direction.

Purpose To evaluate the relationship between patient age and radiation doses associated with routine pediatric head CT performed with automatic tube potential selection and tube current modulation techniques. Methods We obtained patient demographics, scan parameters, and radiation dose descriptors (CT dose index volume -CTDIvol and dose length product -DLP) associated with consecutive routine head CT in 705 children (mean age 6.9 ± 5 years). Children were scanned on one of the three multidetector-row CTs (64–128 slices, Siemens) over 6 months period in a tertiary hospital. All head CT exams were performed in helical scan mode using automatic tube potential selection (Care kV) and automatic tube current modulation (Care Dose 4D) techniques. The information was obtained from a radiation dose monitoring software. Data were analyzed using linear correlation and analysis of variance. Results Most age-wise median CTDIvol (9−27 mGy; 703/705 pediatric head CT, >99 %) from our institution were lower than the European Diagnostic Reference Levels (EDRL, CTDIvol 24−50 mGy) but median DLP (151−586 mGy cm) from 201/705 children (28 %) was higher than the EDRL (DLP 300−650 mGy cm). Unlike the age-stratified EDRL, a combination of automatic tube potential selection and tube current modulation for pediatric head results in a significant linear correlation between radiation doses and patient age (r2 = 0.66, p Conclusions Radiation doses for head CT change linearly with children's age. Despite lower CTDIvol and DLP for most children, longer scan length resulted in higher DLP for some pediatric head CT compared to the corresponding EDRL; this result underscores the need to promote clear guidelines for technologists operating CT.

Computed tomography (CT) is commonly associated with relatively high patient doses. To keep the patient doses from the CT examinations on the acceptable level it is necessary to apply the principle of optimization. An essential part of optimization is the compromise between the patient dose reduction and the maintenance of the image quality that provides accurate diagnostic information. The aim of the study was to determine the relations between the patient doses, CT image quality and the parameters of the tube current modulation program (Auto mA, CareDose and DoseRight) for the CT of the chest. The study was performed on the three most common CT models in Russia: Ingenuity Core 128, Philips; Optima 64, General Electric; Definition AS, Siemens, using the anthropomorphic phantom Lungman (Kyoto Kagaku CO., LTD). To assess the tube current modulation for the range of tube voltage (80–120 kV), the reference mA·s (ref. mAs), Noise Index (NI) and Dose Right Index (DRI) were changed for the CareDose (Siemens), Auto mA (GE) and RightDose (Philips), respectively. Signal-noise ratio (SNR) of a CT image in the mediastinum area was selected to evaluate the image quality. It was estimated, that for the Philips units with DoseRight program the patient dose is directly proportional to DRI; image noise decreases and SNR increasing with DRI. For GE unit with Auto mA program image noise proportional to NI, SNR inversely proportional to NI and patient dose decreases with increasing NI. For Siemens unit with CareDose program the patient dose is directly proportional to ref.mAs; image noise decreases with ref.mAs and SNR increases with ref.mAs The tube current modulations are proprietary for each manufacturer; it is necessary to consider them for the protocol development. The obtained dependences could be useful for optimization of CT protocols.

Rationale and Objectives Implementation of low dose computed tomography (LDCT) lung cancer screening programs has followed the demonstration of reduced lung cancer mortality in the National Lung Screening Trial and subsequent consensus screening recommendations. Here we aim to assess the initial results of a screening program at an academic medical center, to discuss the challenges of implementing such a program, and suggest strategies for reducing patient dose. Materials and Methods Retrospective review of all patients who underwent LDCT lung cancer screening at our institution between March 2015 and July 2016 was performed to assess the lung cancer detection rate, the spectrum of imaging findings (nodule or mass characteristics, degree of emphysema, etc.), and patient radiation dose indices. Results A total of 272 patients were screened during the study period. Approximately 50% (n = 135) were women. The lung cancer detection rate was 2.2% (n = 6). One patient underwent chemoradiation therapy, whereas the remainder underwent uneventful thoracoscopic resection. Approximately, 80% of screened patients met United States Preventative Services Task Force criteria for LDCT screening. The median pack-years of smoking was 42 pack-years. The mean volume CT dose index for the screening CTs was 3.12 mGy. Utilizing tube current modulation and iterative reconstruction, where available, resulted in lower patient doses. Conclusion Initial LDCT lung cancer screening at our institution yielded results similar to those of the National Lung Screening Trial. Thorough prescreening evaluation, joint decision-making, centralized coordination of screening-related care, and patient size conscious scanning protocols are critical elements of a safe and successful lung cancer screening program.

We aimed to develop a software for facilitating absorbed dose per pixel (pixel dose) calculation using a size-specific dose estimate (SSDE). We calculated the pixel dose at nine equal points inserted into the radiophotoluminescence glass dosemeter (RPLD) and compared the pixel dose with the measured doses using RPLD. With this method, the relative errors of average pixel dose was -0.1% for adults and 2.86, 3.36 and 1.17% for those aged 10, 5 and 1 years without tube current modulation, respectively. In contrast, the relative error of SSDE was 17.37% for adults and 20.38, 20.73 and 19.20% for those aged 10, 5 and 1 years, respectively. In other words, the pixel dose was almost equal to the measured doses. Therefore, our software can be useful for determining arbitrary point.

Background Multiple rounds of head computed tomography (CT) scans increase the risk of radiation-induced lens opacification. Purpose To investigate the effects of CT eye shielding and topogram-based tube current modulation (TCM) on the radiation dose received by the lens and the image quality of nasal and periorbital imaging. Material and Methods An anthropomorphic phantom was CT-scanned using either automatic tube current modulation or a fixed tube current. The lens radiation dose was estimated using cropped Gafchromic films irradiated with or without a shield over the orbit. Image quality, assessed using regions of interest drawn on the bilateral extraorbital areas and the nasal bone with a water-based marker, was evaluated using both a signal-to-noise ratio (SNR) and contrast-noise ratio (CNR). Two CT specialists independently assessed image artifacts using a three-point Likert scale. Results The estimated radiation dose received by the lens was significantly lower when barium sulfate or bismuth-antimony shields were used in conjunction with a fixed tube current (22.0% and 35.6% reduction, respectively). Topogram-based TCM mitigated the beam hardening-associated artifacts of bismuth-antimony and barium sulfate shields. This increased the SNR by 21.6% in the extraorbital region and the CNR by 7.2% between the nasal bones and extraorbital regions. The combination of topogram-based TCM and barium sulfate or bismuth-antimony shields reduced lens doses by 12.2% and 27.2%, respectively. Conclusion Image artifacts induced by the bismuth-antimony shield at a fixed tube current for lenticular radioprotection were significantly reduced by topogram-based TCM, which increased the SNR of the anthropomorphic nasal bones and periorbital tissues.

Purpose To investigate lens dose reduction with organ based tube current modulation (TCM) using the Monte Carlo method. Methods To calculate lens dose with organ based TCM, 36 pairs of X-ray sources with bowtie filters were placed around the patient head using a projection angle interval of 10° for one rotation of Computed Tomography (CT). Each projection was simulated respectively. Both voxelized and stylized eye models and Chinese reference male phantoms were used in the simulation, and tube voltages 80, 100, 120 and 140 kVp were used. Results Dose differences between two eye models were less than 20%, but large variations were observed among dose results from different projections of all tube voltages investigated. Dose results from 0° (AP) directions were 60 times greater than those from 180° (PA) directions, which enables organ based TCM reduce lens doses by more than 47%. Conclusions Organ based TCM may be used to reduce lens doses. Stylized eye models are more anatomically realistic compared with voxelized eye models and are more reliable for dose evaluation.

The purpose of this study is to compare dose-length product (DLP)-based calculation of effective dose (EDDose data were obtained from 50 consecutive unenhanced head CT examinations, unenhanced chest CT examinations, and unenhanced and contrast-enhanced abdominopelvic CT examinations performed using 16- and 64-MDCT scanners, as well as from 50 pulmonary CT angiography (CTA) examinations performed using a 64-MDCT scanner and 31 pulmonary CTA examinations performed using a 16-MDCT scanner. The EDEDED

Estimate organ and effective doses from computed tomography scans of pediatric oncologic patients using patient-specific information.With IRB approval patient-specific scan parameters and patient size obtained from DICOM images and vendor-provided dose monitoring application were obtained for a cross-sectional study of 1250 pediatric patients from 0 through 20 y-olds who underwent head, chest, abdomen-pelvis, or chest-abdomen-pelvis CT scans. Patients were categorized by age. Organ doses and effective doses were estimated using VirtualDose™ CT based on patient-specific information, tube current modulation (TCM), and age-specific realistic phantoms. CTDIvol, DLP, and dose results were compared with those reported in the literature.CTDIvol and DLP varied widely as patient size varied. The 75th percentiles of CTDIvol and DLP were no greater than in the literature with the exception of head scans of 16-20 y-olds and of abdomen-pelvis scans of larger patients. Eye lens dose from a head scan was up to 69 mGy. Mean organ doses agreed with other studies at maximal difference of 38% for chest and 41% for abdomen-pelvis scans. Mean effective dose was generally higher for older patients. The highest effective doses were estimated for the 16-20 y-olds as: head 3.3 mSv, chest 4.1 mSv, abdomen-pelvis 10.0 mSv, chest-abdomen-pelvis 14.0 mSv.Patient-specific organ and effective doses have been estimated for pediatric oncologic patients from1 through 20 y-olds. The effect of TCM was successfully accounted for in the estimates. Output parameters varied with patient size. CTDIvol and DLP results are useful for future protocol optimization.

Purpose: The purpose of this study was to preliminarily estimate patient-specific organ doses in chest CT examinations for Chinese adults, and to investigate the effect of patient size on organ doses. Methods: By considering the body-size and body-build effects on the organ doses and taking the mid-chest water equivalent diameter (WED) as a body-size indicator, the chest scan images of 18 Chinese adults were acquired on a multi-detector CT to generate the regional voxel models. For each patient, the lungs, heart, and breasts (glandular breast tissues for both breasts) were segmented, and other organs were semi-automated segmented based on their HU values. The CT scanner and patient models simulated by MCNPX 2.4.0 software (Los Alamos National LaboratoryLos Alamos, USA) were used to calculate lung, breast, and heart doses. CTDIvol values were used to normalize simulated organ doses, and the exponential estimation model between the normalized organ dose and WED was investigated. Results: Among the 18 patients in this study, the simulated doses of lung, heart, and breast were 18.15 ± 2.69 mGy, 18.68 ± 2.87 mGy, and 16.11 ± 3.08 mGy, respectively. Larger patients received higher organ doses than smaller ones due to the higher tube current used. The ratios of lung, heart, and breast doses to the CTDIvol were 1.48 ± 0.22, 1.54 ± 0.20, and 1.41 ± 0.13, respectively. The normalized organ doses of all the three organs decreased with the increase in WED, and the normalized doses decreased more obviously in the lung and the heart than that in the breasts. Conclusions: The output of CT scanner under ATCM is positively related to the attenuation of patients, larger-size patients receive higher organ doses. The organ dose normalized by CTDIvol was negatively correlated with patient size. The organ doses could be estimated by using the indicated CTDIvol combined with the estimated WED.

Purpose CTDIvol-to-fetal-dose coefficients from Monte Carlo simulations are useful for fetal dose evaluations, but the available data is limited to the fetus being completely inside the abdominopelvic scan range. Whereas in a chest examination, the fetus is completely outside the scan range. In an abdominal examination, the fetus after 16 gestational weeks is partly in the scan region, and an earlier fetus is completely outside of it. This work proposes a practical approach to evaluate fetal dose for pregnant patients undergoing body CT examinations, without using Monte Carlo simulation. Methods The proposed method was based on the z-axis dose profile computed for a CT examination, considering CTDIvol, scan range, mA, and maternal WED (water equivalent diameter) at the fetus centroid. Fetal average dose was calculated over the fetus z-axis coverage. For validation, we considered a reference dataset of 24 pregnant patients, each underwent two abdominopelvic examinations (fixed mA, tube current modulation). WED was 30.1 ± 3.3 (25.3–35.6) cm [mean(range)]. Gestational age was Results The fetal dose difference between profile-based evaluations and Monte Carlo simulations was (5.9 ± 3.8)% for 24 fixed-mA examinations, (5.8 ± 4.6)% for 24 tube current modulated examinations, and (8.8 ± 5.9)% for the whole-body models in three scan ranges. Conclusions Profile-based fetal dose calculations can be performed for patients in body CT, considering maternal size, fetus size and location, and whether fetus is completely inside, partly inside, or outside scan ranges.

To compare image quality, radiation, and contrast medium (CM) doses between individualized and conventional scan protocols in combined coronary CT angiography (CCTA) and iliac artery CTA for kidney transplantation patients.148 patients needing assessment for coronary and iliac arteries before kidney transplantation were prospectively enrolled and randomly divided into the conventional and individualized groups. All patients underwent one-stop combined scans on a 256-row CT scanner with automatic tube current modulation, 50 % pre-ASIR-V to control radiation dose. CCTA was performed first using one heartbeat axial scan mode with bolus tracking technique and iliac CTA was performed 3 s after CCTA using a spiral scan. The conventional group (n = 72) used the standard protocol: 100 kVp, 60 mL of 350 mgI/mL CM at 4.5 mL/s flow rate. The individualized group (n = 76) used a body-mass-index (BMI)-dependent protocol: kVp: 80 (BMI 24) and 100 (BMI ≥ 24) and CM: 19 mgI/kg (BMI 18); 21 mgI/kg (18 ≤ BMI 24); and 22 mgI/kg (BMI ≥ 24). Image quality radiation and CM doses of the two groups were compared.There was no significant difference in patient demographic data. Compared with the conventional group, the individualized group reduced contrast flow rate (in mL/s) by 14.4 % (3.85 ± 0.72 vs. 4.5), contrast dose (in mL) by 35.8 % (38.53 ± 7.18 vs. 60) and radiation dose (in mSv) by 34.3 % (4.30 ± 1.73 vs. 6.54 ± 1.45). The individualized group had significantly higher subjective image quality score (P ＜ 0.05), lower noise (17.30 ± 4.97 HU vs. 19.13 ± 4.73 HU, P = 0.02) and higher signal-to-noise ratio (22.09 ± 7.41 vs. 19.55 ± 6.18, P = 0.03) for the three main vessels in CCTA compared with the conventional group. There were no differences in both subjective scores and objective measurements in iliac artery CTA between the two groups.The individualized scanning protocol in the one-stop assessment of coronary and iliac arteries before kidney transplantation significantly reduces both radiation and CM doses while maintaining image quality in iliac artery CTA and providing better coronary artery images in CCTA.

Objectives To compare the effectiveness of two different patient size metrics based on water equivalent diameter (D w), the mid‐scan water equivalent diameter D w_c, and the mean (average) water equivalent diameter in the imaged region, D w_ave, for automatic detection of accidental changes in computed tomography (CT) acquisition protocols. Methods Patient biometric data (height and weight) were available from a previous survey for 80 adult chest examinations, and 119 adult single‐acquisition chest–abdomen–pelvis (CAP) examinations for two 16 slice scanners (GE LightSpeed and Toshiba Aquilion RXL) equipped with automatic tube current modulation (ATCM). D w_c and D w_ave were calculated from the archived CT images. Size‐specific dose estimates (SSDE) were obtained from volume CT dose index (CTDI vol), using the conversion factors for a patient diameter of D w_c. Results CTDI vol and SSDE correlate better with D w_ave than with D w_c. R‐squared values of linear fits to CTDI vol of CAP examinations were 0.81–0.89 for D w_c and 0.93–0.94 for D w_ave (SSDE: 0.69–080 for D w_c, 0.87–0.92 for D w_ave). Percentage differences between D w_c and D w_ave were −4 ± 4% for chest and +5 ± 4% for CAP examinations (in % of D w_ave). However, small D w variations translated as larger variations in CTDI vol for these ATCM systems (e.g., a 24% increase in D w doubled CTDI vol). The dependence of CTDI vol on D w_ave was similar for chest and CAP examinations performed with similar ATCM parameters, while use of D w_c resulted in a clear separation of the same data according to examination type. Maximum D w variation in the imaged region was 5.6 ± 1.6 cm for chest and 6.5 ± 1.4 cm for CAP examinations. Conclusions D w_ave is a better metric than D w_c for binning similar‐sized patients in dose comparison studies, despite the additional computational effort required for its calculation Therefore, when implementing automatic determination of D w for SSDE calculations, automatic calculation of D w_ave should be considered.

To compare the radiation dose and image noise of nonenhanced CT scans performed at 80, 100, and 120 kVp with tube current modulation (TCM) we used anthropomorphic phantoms of newborn, 1‐year‐old, and 5‐year‐old children. The noise index was set at 12. The image noise in the center of the phantoms at the level of the chest and abdomen was measured within a circumscribed region of interest. We measured the doses in individual tissues or organs with radio‐photoluminescence glass dosimeters for each phantom. Various tissues or organs were assigned and the radiation dose was calculated based on the international commission on radiological protection definition. With TCM the respective radiation dose at tube voltages of 80, 100, and 120 was 29.71, 31.60, and 33.79 mGy for the newborn, 32.00, 36.79, and 39.48 mGy for the 1‐year‐old, and 32.78, 38.11, and 40.85 mGy for the 5‐year‐old phantom. There were no significant differences in the radiation dose among the tube voltages and phantoms (P > 0.05). Our comparison of the radiation dose using anthropomorphic phantoms of young children showed that the radiation dose of nonenhanced CT performed at different tube voltages with TCM was not significantly different.

Purpose The volume CT dose index (CTDIvol) and the size-specific dose estimate (SSDE) are widely used for monitoring patient dose from CT examinations. Both metrics may represent the average dose over the central scan plane of the CTDI phantom or the patient under constant tube current (mA), but they are not intended for the tube current modulation (TCM)-enabled CT examinations, in which the peak dose across the scanned range may not be at the scan range center. To overcome the limitation, this paper illustrates an alternative approach, its implementation, and the relationship between longitudinal dose distribution DL(z) in water cylinder and mA lineshape, scan length, as well as phantom diameter. Methods A dose calculation algorithm and the published data by Li et al. [Med. Phys. 40, 031903 (10pp.) (2013); 41, 111910 (5pp.) (2014)] were used to calculate DL(z) for the central and peripheral axes of 10- to 50-cm diameter water phantoms undergoing CT scans of one constant and three variable mA distributions, each of which in three scan lengths of 10, 28.6, and 50 cm. All scans had an identical average tube current over the scan ranges. The results in the scanned ranges were used to assess the DL(z) to mA(z) ratios, and their coefficients of variation (CV = stdev/mean) were used to compare the lineshapes of DL(z) and mA(z) for congruence: identical lineshapes would result in CV = 0, but largely different lineshapes would result in high CV. Results In 30-cm diameter water phantom, the lineshape of DL(z) was largely different from that of mA(z). CV was higher in a variable mA scan than in a constant mA scan. As the scan length of variable mA scan increased, CV mostly decreased, and the lineshape of DL(z) more closely resembled that of mA(z). When two phantom axes were compared, CV was smaller and the lineshape of DL(z) more closely resembled that of mA(z) on the peripheral axis than on the central axis. In forty-one water phantoms included in this study, CV mostly increased with phantom diameter, and approached the limiting levels on the peripheral axes of large phantoms. In constant mA scans, CV ranged from 5.5% to 14.0% on the phantom central axes and from 4.6% to 6.4% on the phantom peripheral axes. Whereas in variable tube current scans, CV ranged from 7.4% to 70.0% on the phantom central axes and from 5.1% to 35.9% on the phantom peripheral axes. Conclusion DL(z)(water) may be advantageous over current CT dose metrics in characterizing the dose dependences on both patient size and mA lineshape from tube current modulated examinations. Evaluating DL(z)(water) with the water equivalent diameter and tube current curve from clinical examinations has a potential to improve CT dose monitoring program. This article is protected by copyright. All rights reserved.

No consistent guidelines exist for the acquisition of a CT scan as part of pediatric PET/CT. Given that children may be more vulnerable to the effects of ionizing radiation, it is necessary to develop methods that provide diagnostic-quality imaging when needed, in the shortest time and with the lowest patient radiation exposure. This article describes the basics of CT dosimetry and PET/CT acquisition in children. We describe the variability in pediatric PET/CT techniques, based on a survey of 19 PET/CT pediatric institutions in North America. The results of the survey demonstrated that, although most institutions used automatic tube current modulation, there remained a large variation of practice, on the order of a factor of 2–3, across sites, pointing to the need for guidelines. We introduce the approach developed at our institution for using a multiseries PET/CT acquisition technique that combines diagnostic-quality CT in the essential portion of the field of view and a low-dose technique to image the remainder of the body. This approach leads to a reduction in radiation dose to the patient while combining the PET and the diagnostic CT into a single acquisition. The standardization of pediatric PET/CT provides an opportunity for a reduction in the radiation dose to these patients while maintaining an appropriate level of diagnostic image quality.

Purpose The vast majority of body CT exams are performed with automatic exposure control (AEC), which adapts the mean tube current to the patient size and modulates the tube current either angularly, longitudinally or both. However, most radiation dose estimation tools are based on fixed tube current scans. Accurate estimates of patient dose from AEC scans require knowledge of the tube current values, which is usually unavailable. The purpose of this work was to develop and validate methods to accurately estimate the tube current values prescribed by one manufacturer's AEC system to enable accurate estimates of patient dose. Methods Methods were developed that took into account available patient attenuation information, user selected image quality reference parameters and x-ray system limits to estimate tube current values for patient scans. Methods consistent with AAPM Report 220 were developed that used patient attenuation data that was: (1) supplied by the manufacturer in the CT localizer radiograph and (2) based on a simulated CT localizer radiograph derived from image data. For comparison, actual tube current values were extracted from the projection data of each patient. Validation of each approach was based on data collected from 40 pediatric and adult patients who received clinically indicated chest (n=20) and abdomen/pelvis (n=20) scans on a 64 slice multidetector row CT (Sensation 64, Siemens Healthcare, Forchheim, Germany). For each patient dataset, the following were collected with Institutional Review Board (IRB) approval: (1) projection data containing actual tube current values at each projection view, (2) CT localizer radiograph (topogram) and (3) reconstructed image data. Tube current values were estimated based on the actual topogram (actual-topo) as well as the simulated topogram based on image data (sim-topo). Each of these was compared to the actual tube current values from the patient scan. In addition, to assess the accuracy of each method in estimating patient organ doses, Monte Carlo simulations were performed by creating voxelized models of each patient, identifying key organs and incorporating tube current values into the simulations to estimate dose to the lungs and breasts (females only) for chest scans and the liver, kidney and spleen for abdomen/pelvis scans. Organ doses from simulations using the actual tube current values were compared to those using each of the estimated tube current values (actual-topo and sim-topo). Results When compared to the actual tube current values, the average error for tube current values estimated from the actual topogram (actual-topo) and simulated topogram (sim-topo) was 3.9% and 5.8% respectively. For Monte Carlo simulations of chest CT exams using the actual tube current values and estimated tube current values (based on the actual-topo and sim-topo methods), the average differences for lung and breast doses ranged from 3.4% to 6.6%. For abdomen/pelvis exams, the average differences for liver, kidney and spleen doses ranged from 4.2% to 5.3%. Conclusions Strong agreement between organ doses estimated using actual and estimated tube current values provides validation of both methods for estimating tube current values based on data provided in the topogram or simulated from image data. This article is protected by copyright. All rights reserved.

Purpose To assess patient doses and relative frequencies of standard CT examinations performed in Germany in 2013/14 as well as the effect of modern CT technology on patient exposure. Methods All known CT facilities in Germany were requested to complete a questionnaire on the frequency of 34 examinations and the respective parameter settings used. Taking into account type-specific properties of each scanner, effective doses were estimated for each reported examination. The mean and the percentiles of the CT dose index, scan length, dose length product, and effective dose were determined for each type of examination. Results According to the data provided for about 11% of all medical CT scanners operated in 2013/14, the effective dose was 4.6/5.9 mSv per scan/examination. The effective dose was significantly reduced by about 15% compared to the CT practice before 2010. Modern CT technology, such as tube current modulation and iterative image reconstruction reduced the effective dose significantly by 6% and 13%, respectively. The mean effective dose applied at scanners produced by different manufacturers differed by 25%, at maximum. Conclusion Patient exposure was reduced substantially in recent years. There is, however, still a considerable potential for further dose reduction by adapting scan protocols to the medical purpose and by a consequent exploitation of modern CT technologies.

The purpose of our study was to determine diagnostic accuracy, image quality, and radiation dose of low-dose single- and dual-energy unenhanced third-generation dual-source head CT for detection of intracranial hemorrhage (ICH).A total of 123 patients with suspected ICH were examined using a dual-source 192-MDCT scanner. Standard-dose 120-kVp single-energy CT (SECT; n = 36) and 80-kVp and 150-kVp dual-energy CT (DECT; n = 30) images were compared with low-dose SECT (n = 32) and DECT (n = 25) images obtained using automated tube current modulation (ATCM). Advanced modeled iterative reconstruction (ADMIRE) was used for all protocols. Detection of ICH was performed by three readers who were blinded to the image acquisition parameters of each image series. Image quality was assessed both quantitatively and qualitatively. Interobserver agreement was calculated using the Fleiss kappa. Radiation dose was measured as dose-length product (DLP).Detection of ICH was excellent (sensitivity, 94.9-100%; specificity, 94.7-100%) in all protocols (p = 1.00) with perfect interobserver agreement (0.83-0.96). Qualitative ratings showed significantly better ratings for both standard-dose protocols regarding gray matter-to-white matter contrast (p ≤ 0.014), whereas highest gray matter-to-white matter contrast-to-noise ratio was observed with low-dose DECT images (p ≥ 0.057). The lowest posterior fossa artifact index was measured for standard-dose DECT, which showed significantly lower values compared with low-dose protocols (p ≤ 0.034). Delineation of ventricular margins and sharpness of subarachnoidal spaces were rated excellent in all protocols (p ≥ 0.096). Low-dose techniques lowered radiation dose by 26% for SECT images (DLP, 575.0 ± 72.3 mGy · cm vs 771.5 ± 146.8 mGy · cm; p0.001) and by 24% in DECT images (DLP, 587.0 ± 103.2 mGy · cm vs 770.6 ± 90.2 mGy · cm; p0.001). No significant difference was observed between the low-dose protocols (p = 1.00).Low-dose unenhanced head SECT and DECT using ATCM and ADMIRE provide excellent diagnostic accuracy for detection of ICH with good quantitative and qualitative image quality in third-generation dual-source CT while allowing significant radiation dose reduction.

The aim of this study was to evaluate the objective and subjective image quality of a novel computed tomography (CT) protocol with reduced radiation dose for body packing with 80 kVp and automated tube current modulation (ATCM) compared to a standard body packing CT protocol. 80 individuals who were examined between March 2012 and July 2015 in suspicion of ingested drug packets were retrospectively included in this study. Thirty-one CT examinations were performed using ATCM and a fixed tube voltage of 80 kVp (group A). Forty-nine CT examinations were performed using a standard protocol with a tube voltage of 120 kVp and a fixed tube current time product of 40 mAs (group B). Subjective and objective image quality and visibility of drug packets were assessed. Radiation exposure of both protocols was compared. Contrast-to-noise ratio (group A: 0.56 ± 0.36; group B: 1.13 ± 0.91) and Signal-to-noise ratio (group A: 3.69 ± 0.98; group B: 7.08 ± 2.67) were significantly lower for group A compared to group B (p

Purpose This study aimed to investigate the breast dose reduction potential of a breast positioning (BP) technique for thoracic CT examinations with organ-based tube current modulation (OTCM). Methods This study included 13 female anthropomorphic computational phantoms (XCAT, age range: 27 - 65 y.o., weight range: 52 - 105.8 kg). Each phantom was modified to simulate three breast sizes in standard supine geometry. The modeled breasts were then morphed to emulate BP that constrained the majority of the breast tissue inside the 120° anterior tube current (mA) reduction zone. The OTCM mA value was modeled using a ray-tracing program, which reduced the mA to 20% in the anterior region with a corresponding increase to the posterior region. The organ doses were estimated by a validated Monte Carlo program for a typical clinical CT system (SOMATOM Definition Flash, Siemens Healthcare). The simulated organ doses and organ doses normalized by CTDIvol were used to compare three CT protocols: attenuation-based tube current modulation (ATCM), OTCM, and OTCM with BP (OTCMBP). Results On average, compared to ATCM, OTCM reduced the breast dose by 19.3 ± 4.5%, whereas OTCMBP reduced breast dose by 38.6 ± 8.1% (an additional 23.8 ± 9.4%). The dose saving of OTCMBP was more significant for larger breasts (on average 33, 38, and 44% reduction for 0.5, 1, and 2 kg breasts, respectively). Compared to ATCM, OTCMBP also reduced thymus and heart dose by 15.1 ± 7.4% and 15.9 ± 6.2%, respectively. Conclusions In thoracic CT examinations, OTCM with a breast positioning technique can markedly reduce unnecessary exposure to the radiosensitive organs in the anterior chest wall, specifically breast tissue. The breast dose reduction is more notable for women with larger breasts. This article is protected by copyright. All rights reserved.

Purpose The aim of this study was to evaluate the impact of automated attenuation-based tube potential selection (ATPS) on image quality and radiation dose exposure parameters at a computed tomography angiography (CTA) lower-extremity runoff. Materials and methods Two hundred forty patients (156 men, 84 women) underwent CTA examinations of the lower-extremity runoff on a second-generation dual-source computed tomography system: 120 patients at a fixed tube potential of 120 kV and a tube current of 180 reference mAs, another 120 patients using automated ATPS. Volume computed tomography dose index (CTDIvol), dose-length-product (DLP), body diameters, noise, signal-to-noise ratio, and subjective image quality were compared. Results In the ATPS group, 80 kV was automatically selected in 102 patients, 100 kV in 15 patients, and 120 kV in 3 patients; 140 kV was not chosen in any of the cases. The median CTDIvol of 4.81 mGy (2.2-10.6 mGy) and DLP of 568 mGy⋅cm (203-1324 mGy⋅cm) in the ATPS group were significantly lower compared with the CTDIvol of 8.1 mGy (4.4-14.4 mGy) and DLP of 1027.5 mGy⋅cm (509-1806 mGy⋅cm) in the fixed 120-kV group (P 0.05). Conclusion Automated ATPS allows for significant dose savings in lower-extremity runoff CTA, whereas image quality remains constant at a high level.

Purpose To investigate the effect of scan projection radiography (SPR) coverage on tube current modulation in pediatric and adult thoracic CT examinations. Methods Sixty pediatric and 60 adult chest CT examinations were retrospectively studied to determine the incidence rate of examinations involving SPRs that did not include the entire image volume (IV) or the entire primarily exposed body volume (PEBV). The routine chest CT acquisition procedure on a modern 64-slice CT system was imitated on five anthropomorphic phantoms of different size. SPRs of varying length were successively acquired. The same IV was prescribed each time and the computed tube current modulation plan was recorded. The SPR boundaries were altered symmetrically by several steps of ±10 mm with respect to the IV boundaries. Results The upper IV boundary was found to be excluded from SPR in 52% of pediatric and 40% adult chest CT examinations. The corresponding values for the lower boundary were 15% and 20%, respectively. The computed tube current modulation was found to be considerably affected when the SPR did not encompass the entire IV. SPR deficit of 3 cm was found to induce up to 46% increase in the computed tube current value to be applied during the first tube rotations over lung apex. Conclusions The tube current modulation mechanism functions properly only if the IV set by the operator is entirely included in the localizing SPR image. Operators should cautiously set the SPR boundaries to avoid partial exclusion of prescribed IV from SPRs and thus achieve optimum tube current modulation.

Purpose We investigated whether a tungsten functional paper (TFP) shield and/or organ-based tube current modulation (TCM) can reduce the dose to the eye lens. Materials and methods All scans were performed using our routine head examination protocol (spiral acquisition, 120 kVp, noise Index 3.5) with an anthropomorphic head phantom. The dose reduction rate was measured by the following methods with a scintillation fiber optic dosimeter: (a) without any dose reduction techniques (Original scan), (b) TFP shield, (c) TCM, and (d) TFP shield plus TCM. Image noise and CT number were obtained and compared between the three groups. In addition, image noise in method (d) was measured with varying distances between the TFP shield and eye lens. Results The reduction rates using TFP shield, TCM, and TFP shield plus TCM compared with those for the Original scan were 17.8 %, 13.6 %, and 27.7 %, respectively. Image noise (mean ± standard deviation) in the anterior region for the Original scan, TFP shield, TCM, and TFP shield plus TCM were 4.1 ± 0.2, 4.6 ± 0.2, 4.4 ± 0.3, and 5.0 ± 0.2, while the CT numbers were 19.3 ± 0.8, 23.8 ± 0.8, 19.6 ± 0.8, and 24.1 ± 0.8, respectively. Increasing the distance between the TFP and the eye significantly decreased the CT number when using TFP shield plus TCM (p Conclusion TFP shield plus TCM reduced the dose to the eye lens in head CT while maintaining image quality with an air gap between the TFP and skin surface.

The frequency of abdominal computed tomography examinations is increasing, leading to a significant level of patient dose. This study aims to quantify and evaluate the effects of automatic tube current modulation (ATCM) technique on patient dose and image quality in contrast-enhanced biphasic abdominal examinations.Two different scan protocols, based on constant tube current and ATCM technique, were used on 64 patients who visited our radiology department periodically. For three patient groups with different patient size, results from two protocols were compared with respect to patient dose and image quality. Dosimetric evaluations were based on the Computed Tomography Dose Index, dose length product, and effective dose. For the comparison of image qualities between two protocols, Noise Index (NI) and Contrast to Noise Ratio (CNR) values were determined for each image. Additionally, the quality of each image was evaluated subjectively by an experienced radiologist, and the results were compared between the two protocols.Dose reductions of 31% and 21% were achieved by the ATCM protocol in the arterial and portal phases, respectively. On the other hand, NI exhibited an increase between 9% and 46% for liver, fat and aorta. CNR values were observed to decrease between 5% and 19%. All images were evaluated by a radiologist, and no obstacle limiting a reliable diagnostic evaluation was found in any image obtained by either technique.These results showed that the ATCM technique reduces patient dose significantly while maintaining a certain level of image quality.Abdominal bilgisayarlı tomografi incelemelerinin sıklığı artmakta ve önemli miktarda hasta dozuna yol açmaktadır. Bu çalışma, kontrastlı, çift fazlı abdomen incelemelerinde otomatik tüp akım modülasyon tekniğinin hasta dozu ve görüntü kalitesi üzerine etkilerini ölçmeyi ve değerlendirmeyi amaçlamaktadır.Radyoloji anabilim dalını periyodik olarak ziyaret eden 64 hastaya sabit tüp akımı ve otomatik tüp akımı modülasyonu tekniğine dayanan iki farklı tarama protokolü uygulandı. Farklı hasta boyutlarına sahip üç hasta grubu için, iki protokolden elde edilen sonuçlar hasta dozu ve görüntü kalitesi açısından karşılaştırıldı. Dozimetrik değerlendirmeler, Bilgisayarlı Tomografi Doz İndeksi, doz uzunluk çarpımı ve etkin doza dayandırıldı. İki protokol arasındaki görüntü kalitesinin karşılaştırılması amacıyla her görüntü için Gürültü İndeksi (NI) ve Kontrast Gürültü Oranı (CNR) değerleri belirlendi. Ek olarak, her görüntü deneyimli bir radyolog tarafından öznel olarak değerlendirildi ve sonuçlar iki protokol arasında karşılaştırıldı.Otomatik tüp akım modülasyon protokolü ile arteriyel ve portal fazlarda sırasıyla %31 ve %21 doz düşüşleri sağlandı. Öte yandan, NI karaciğer, yağ ve aort için %9 ile %46 arasında bir artış gösterdi. CNR değerlerinin ise %5 ile %19 arasında azaldığı gözlendi. Tüm görüntüler bir radyolog tarafından değerlendirildi ve herhangi bir teknikle elde edilen görüntülerde güvenilir bir tanısal değerlendirmeyi sınırlayan bir engel bulunmadı.Bu sonuçlar, otomatik tüp akım modülasyon tekniğinin, belirli bir görüntü kalitesi seviyesini korurken hastanın dozunu önemli ölçüde azalttığını göstermiştir.

PurposeThe purpose of this work was to estimate scanner-independent CTDIvol -to-fetal-dose coefficients for tube current-modulated (TCM) and fixed tube current (FTC) computed tomography (CT) examinations of pregnant patients of various gestational ages undergoing abdominal/pelvic CT examinations.MethodsFor 24 pregnant patients of gestational age from

The introduction of protocol developments and software modifications for cardiac computed tomography (CT) imaging such as automatic tube current modulation, optimized tube potential selection, electrocardiography (ECG) pulsing, and iterative reconstruction algorithms enabled a considerable decrease of ionizing radiation dose of cardiac CT examinations. In parallel, submillimeter spatial resolution and high temporal resolution for motion-free imaging of the small anatomic structures of the heart were achieved. Efforts must be made for choosing the best combination of all available techniques for radiation dose reduction for optimizing and minimizing the radiation exposure to each patient undergoing cardiac CT.

First-generation cardiac CT imaging techniques comprise simultaneous recording of the ECG signal combined with continuous low-pitch spiral scan acquisition with relatively high incident radiation dose. Because of the increasing number of cardiac CT studies and anticipated further growth, the contribution of cardiac CT to the radiation exposure of the population may not be negligible. With growing radiation dose awareness, a variety of different cardiac CT acquisition techniques have been developed over the past 15 years improving the dose efficiency of ECG-synchronized cardiac CT. Recent innovations have demonstrated that radiation dose at cardiac CT can be substantially reduced without detrimental effects on diagnostic image quality including single-heartbeat acquisitions, ECG-based tube current modulation, low tube voltage imaging, and advances in CT raw data reconstruction by means of iterative image reconstruction. New-generation CT scanners allow excellent image quality in the majority of cases and in a wider range of heart rates or rhythms. The aim of this chapter is to provide an overview on the various imaging acquisition techniques used in cardiac CT including the various concepts developed by the main CT vendors.

Background: Coronary computed tomography angiography (CCTA) is now widely used in the diagnosis of coronary artery disease since it is a rapid, minimally invasive test with a diagnostic accuracy comparable to coronary angiography. However, to meet demands for increasing spatial and temporal resolution, higher x-ray radiation doses are required to circumvent the resulting increase in image noise. Exposure to high doses of ionizing radiation with CT imaging is a major health concern due to the potential risk of radiation-associated malignancy. Given its increasing use, a number of dose saving algorithms have been implemented to CCTA to minimize radiation exposure to “as low as reasonably achievable (ALARA)” without compromising diagnostic image quality. Objective: The purpose of this review is to outline the most recent advances and current status of dose saving techniques in CCTA. Methods: PubMed, Medline, EMBASE and Scholar databases were searched to identify feasibility studies, clinical trials, and technology guidelines on the technical advances in CT scanner hardware and reconstruction software. Results: Sub-millisievert (mSv) radiation doses have been reported for CCTA due to a combination of strategies such as prospective electrocardiogram-gating, high-pitch helical acquisition, tube current modulation, tube voltage reduction, heart rate reduction, and the most recent novel adaptive iterative reconstruction algorithms. Conclusion: Advances in radiation dose reduction without loss of image quality justify the use of CCTA as a non-invasive alternative to coronary catheterization in the diagnosis of coronary artery disease.

The study aimed to evaluate the image quality in terms of signal-to-noise ratio (SNR) and dose to the lens of the eye and the other nearby organs from the CT brain scan using an automatic tube current modulation (ATCM) system with or without CT gantry tilt is needed. An anthropomorphic phantom was scanned with different settings including use of different ATCM, fixed tube current time product (mAs) settings and degree angles of gantry tilt. Gafchromic film XR-QA2 was used to measure absorbed dose of the organs. Relative doses and SNR for the various scan settings were compared with the reference setting of the fixed 330 mAs. Average absorbed dose for the lens of the eyes varied from 8.7 to 21.7 mGy. The use of the ATCM system with the gantry tilt resulted in up to 60% decrease in the dose to the lens of the eye. SNR significantly decreased while tilting the gantry using the fixed mAs techniques, compared to that of the reference setting. However, there were no statistical significant differences for SNRs between the reference setting and all ATCM settings. Compared to the reference setting of the fixed effective mAs, using the ATCM system and appropriate tilting, the gantry resulted in a substantial decrease in the dose to the lens of the eye while preserving signal-to-noise ratio. CT brain examination should be carefully controlled to optimize dose for lens of the eye and image quality of the examination.

The purpose of this study was to compare the dose and image noise associated with two methods of radiation dose reduction to the superficial anterior organs: bismuth shielding and a net dose-reducing organ-based tube current modulation TCM technique.Three scanning modes-the reference dose, bismuth-shielded, and organ dose-modulated modes-were evaluated. With the use of an anthropomorphic phantom, surface doses to the eye, thyroid, and female breast were measured using optically stimulated luminescence detectors. A CT dose index (CTDI) phantom was used to compare doses with the overall phantom volume in the different modes.The dose to the anterior surface was reduced by 35%, 42%, and 37% in the head, neck, and chest regions, respectively, when the bismuth-shielded scanning mode was used, whereas surface dose reductions of 20%, 34%, and 38%, respectively, were noted for the organ-based TCM scanning mode. The CTDI-type dose was reduced by 13%, 14%, and 17% in the head, neck, and chest regions, respectively, when the bismuth-shielded mode was used, whereas dose reductions of 9%, 18%, and 20%, respectively, were observed for the organ-based TCM mode. Anterior image noise increased by 0.1, 9.5, and 0.7 HU in the head, neck, and chest regions, respectively, when the bismuth-shielded mode was used. These findings compared with increases in image noise of 0.1, 0.5, and 0.6 HU, respectively, for the organ-based TCM mode.The implementation of organ-based TCM reduces the net tube current per rotation, so no body region receives increased radiation exposure. The use of this method allows the dose to the anterior surface to be reduced to an extent similar to that observed with the use of the bismuth shield, yet it does not produce the image quality degradation associated with bismuth shielding.

To compare different methods available in the literature for estimating radiation dose to the conceptus (Dconceptus) against a patient-specific Monte Carlo (MC) simulation and a commercial software package (CSP). Eight voxel models from abdominopelvic CT exams of pregnant patients were generated. Dconceptus was calculated with an MC framework including patient-specific longitudinal tube current modulation (TCM). For the same patients, dose to the uterus, Duterus, was calculated as an alternative for Dconceptus, with a CSP that uses a standard-size, non-pregnant phantom and a generic TCM curve. The percentage error between Duterus and Dconceptus was studied. Dose to the conceptus and percent error with respect to Dconceptus was also estimated for three methods in the literature. The percentage error ranged from -15.9% to 40.0% when comparing MC to CSP. When comparing the TCM profiles with the generic TCM profile from the CSP, differences were observed due to patient habitus and conceptus position. For the other methods, the percentage error ranged from -30.1% to 13.5% but applicability was limited. Estimating an accurate Dconceptus requires a patient-specific approach that the CSP investigated cannot provide. Available methods in the literature can provide a better estimation if applicable to patient-specific cases. • A patient’s internal anatomy affects the dose to the conceptus. • Conceptus position has an influence on its dose estimation. • Patient anatomy and specific TCM must be considered for accurate conceptus dosimetry. • D uterus to a standard-size phantom should not be used as D conceptus .

Purpose: To develop a method for estimating doses to primarily exposed organs in pediatric CT by taking into account patient size and automatic tube current modulation (ATCM). Methods: A Monte Carlo CT dosimetry software package, which creates patient-specific voxelized phantoms, accurately simulates CT exposures, and generates dose images depicting the energy imparted on the exposed volume, was used. Routine head, thorax, and abdomen/pelvis CT examinations in 92 pediatric patients, ranging from 1-month to 14-yr-old (49 boys and 43 girls), were simulated on a 64-slice CT scanner. Two sets of simulations were performed in each patient using (i) a fixed tube current (FTC) value over the entire examination length and (ii) the ATCM profile extracted from the DICOM header of the reconstructed images. Normalized to CTDIvol organ dose was derived for all primary irradiated radiosensitive organs. Normalized dose data were correlated to patient's water equivalent diameter using log-transformed linear regression analysis. Results: The maximum percent difference in normalized organ dose between FTC and ATCM acquisitions was 10% for eyes in head, 26% for thymus in thorax, and 76% for kidneys in abdomen/pelvis. In most of the organs, the correlation between dose and water equivalent diameter was significantly improved in ATCM compared to FTC acquisitions (P < 0.001). Conclusions: The proposed method employs size specific CTDIvol-normalized organ dose coefficients for ATCM-activated and FTC acquisitions in pediatric CT. These coefficients are substantially different between ATCM and FTC modes of operation and enable a more accurate assessment of patient-specific organ dose in the clinical setting.

The use of cardiac computed tomography (CT) for quantification of ventricular function is limited by relatively high radiation dose.The goal of this study was to describe the radiation exposure and image quality of 70 kVp functional cardiac CT in patients with congenital heart disease (CHD).A retrospective review of 70 kVp ECG gated functional CT scans using tube current modulation was performed in CHD patients at a single institution. Quantitative and qualitative (assessed by myocardial segment, 1-4; 1 = optimal) image quality was determined. Per segment image quality was compared between thin (1.5 mm) and thick (8 mm) reconstructions and by patient age and size. Scan DLP was used to estimate radiation dose.72 scans were performed during the time of review (7/2013-6/2015). Median patient age was 19.5 years (8.0, 27.1) and BMI was 20.1 (16.6, 24.5) kg/m(2). Median functional scan DLP was 78.8 (45.5, 98) and unadjusted and adjusted procedural mSv were 1.10 (0.64, 1.37) and 1.13 (0.90, 1.37). Image quality of 1 was achieved in all myocardial segments in75% of scans. Patients with a weight ≥75 kg were more likely to have a scan achieve optimal image when using thick reconstructions compared to thin (81.3% vs. 43.8%; p = 0.028).Imaging of ventricular function with 70 kVp in CHD patients can be done with low radiation doses and provides diagnostic image quality, particularly for patients75 kg. In larger patients, thicker slice reconstruction improved image quality.

Highlights • Superiority of spiral versus sequential cCT in image quality and organ-specific-radiation dose. • Spiral cCT: lower organ-specific-radiation-dose in eye lense compared to tilted sequential cCT. • State-of-the-art IR spiral cCT techniques has significant advantages over sequential cCT techniques., Objectives To prospectively evaluate image quality and organ-specific-radiation dose of spiral cranial CT (cCT) combined with automated tube current modulation (ATCM) and iterative image reconstruction (IR) in comparison to sequential tilted cCT reconstructed with filtered back projection (FBP) without ATCM. Methods 31 patients with a previous performed tilted non-contrast enhanced sequential cCT aquisition on a 4-slice CT system with only FBP reconstruction and no ATCM were prospectively enrolled in this study for a clinical indicated cCT scan. All spiral cCT examinations were performed on a 3rd generation dual-source CT system using ATCM in z-axis direction. Images were reconstructed using both, FBP and IR (level 1–5). A Monte-Carlo-simulation-based analysis was used to compare organ-specific-radiation dose. Subjective image quality for various anatomic structures was evaluated using a 4-point Likert-scale and objective image quality was evaluated by comparing signal-to-noise ratios (SNR). Results Spiral cCT led to a significantly lower (p

Computed Tomography (CT) examinations in the pediatric patient are sensitive to the impact of ionizing radiation, which gives long-term risk. In addition, the actual radiation dose delivered during CT examinations has not been well-described mainly when using tube current modulation (TCM) technique. To quantified this effect, an algorithm for calculating radiation dose is needed. Therefore, this study aims to calculate and analyze the estimated effective dose of head examinations from 3D CT images, based on the equivalent water diameter (Dw)For the TCM technique. Four pediatric patients in the 0-6-year-old age groups were examinations using Somatom Definition Flash with variation in the number of slices. CTDIvol and Tube current values were obtained from the DICOM header. There are two main parts algorithm for Dw calculation. First, images of CT data were converted to Hounsfield units (HU). Then, Dw values based on the patients contour using the K-mean cluster and morphological gradient algorithm were calculated for every slice. The coefficient factor is obtained by American Association of Physicists in Medicine (AAPM) report 220. The values then multiplied by CTDIvolto acquire values of SSDE. The results showed that the relation between SSDE and tube current was strongly correlated with R2 values of 0.982.