Automatic Tube Current Modulation Technique Research Articles

Evaluation of Changes in Dose Estimation on Abdomen CT Scan with Automatic Tube Current Modulation Using In-House Phantom

This study evaluates the effect of the Automatic Tube Current Modulation (ATCM) technique on pitch and effective diameter variation in estimating dose values and noise levels for abdominal examination on Philips Ingenuity CT scan machine using in-house Phantoms. The in-house phantoms are oval in shape with three effective diameter sizes, namely 23.2 cm, 28.3 cm, and 33.3 cm to represent abdominal region. The three size Phantoms were scanned using an Ingenuity 128 Philips CT scan with the abdominal protocol exposure parameters of 120 kVp tube voltage, Dose Right Index (DRI) variations of 10,11,12,13, and 14, and pitch variations of 0.6; 0.8; 1.0; 1.2; and 1.49. The changes in mAs, CTDIvol, and noise to the Philips reference value were then verified (i.e. an addition of one DRI value increases mAs by 12 %). For evaluation, a metric to express the change in DRI is defined as ΔDRI. The study demonstrates that noise level is influenced by object size; size information of the object could be useful to predict the change of tube current and pitch due to ATCM with respect to selected DRI. The DRI value is proportional to the tube current, thus selecting the DRI at a certain pitch will directly determine tube current. The ΔDRI in general, according to Philips specifications, is verified to be approximately 10 % to 13 %, except for DRI 10 to 11 which is relatively high on average 15 % to 17 %. Increasing DRI increases the CTDIvol. The CTDI/mAs constantly ranges of 0.06 to 0.07. The value could serve as a characteristic parameter for quality assurance. The ATCM specifications of the Ingenuity 128 CT Scanner is according to Philips regulations.

Patient dose reduction for a localizer radiograph with an additional tin filter in chest-abdomen-pelvis, spine, and head computed tomography examinations.

This study aimed to evaluate the dose reduction potential of adding a tin filter to localizer radiographs (LR) on computed tomography (CT) examinations in both phantom and clinical studies. LRs were performed using combinations of 120 kVp and 20mA (120/20), 100 kVp with a tin filter, and 50mA or 20mA (Sn100/50, Sn100/20). For the phantom experiment, entrance surface doses (ESD) of the LRs were evaluated for each protocol using an anthropomorphic phantom. This retrospective clinical study included 700 patients (300 for chest-pelvis, 200 for spine, and 200 for head CTs). The volume CT dose indices (CTDIvols) of the main CT scans were recorded and placed into one of three groups based on body mass index (BMI): underweight, normal-weight, and overweight, to evaluate the effect of LR acquisition conditions on the performance of the automatic tube current modulation technique of subsequent CT scans. The ESDs of all LRs with the Sn100/50 protocol were 0.03mGy, a decrease of more than 80% compared to those of the 120/20 protocol. Moreover, the Sn100/20 protocol reduced ESD to 0.02mGy. In chest-pelvis CT, there were no significant differences in the CTDIvol between with and without a tin filter for each BMI group. However, the lateral LRs with the tin filter on the spine CT slightly reduced the CTDIvol in normal-weight and overweight patients. Although there is room to optimize the acquisition conditions for larger patients, an additional tin filter for LR is a useful means to efficiently reduce ESDs.

Effect on Radiation Dose and Image Quality of the Computed Tomography Tube Current Modulation

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.

Relation between age and CT radiation doses: Dose trends in 705 pediatric head CT

PurposeTo 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. MethodsWe 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. ResultsMost 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 < 0.001). ConclusionsRadiation 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.

Effects of the Use of Automatic Tube Current Modulation on Patient Dose and Image Quality in Computed Tomography

Objectives: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.Methods: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.Results: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.Conclusion:These results showed that the ATCM technique reduces patient dose significantly while maintaining a certain level of image quality.

58. Dosimetric changes with Computed Tomography Automatic Tube Current Modulation techniques

Purpose The objective of the study is the verification of dose changes for a Computed Tomography (CT) Automatic Tube Current Modulation (ATCM) technique. In particular, the work aims to verify that (1) previsions of the CT scanner console (in terms of CTDIvol and DLP) are reflected in the dose distribution within the patient and (2) the experimental results coincide with the predictions of the noise theory on which the technique is based. For this purpose, an anthropomorphic Alderon RANDO (AR) phantom and Gafchromic® XR-QA2 films were used. Methods Radiochromic films were cut to shape the AR phantom in two anatomical regions (shoulders and mid-chest). Since the ATCM algorithm used is based on the Noise Index (NI) parameter, three thorax exam protocols were chosen: reference (NI = 13), lower (NI = 10) and higher (NI = 16) noise. All other acquisition parameters during the three scans were maintained unchanged. CTDIvol and DLP values reported by the CT console were recorded after each exam to compare theoretical and experimental measurements. After dose calibration of the films, dose maps were normalized to the reference map (NI = 13) to obtain percentage variations. Experimental results were compared to the relative variations obtained from CT console and quantum noise theory. Results The results showed that the information reported by the CT console in terms of CTDIvol and DLP variation are in agreement, on average, with experimental measurements. The dose distribution, however, is not uniform and CT console dose reports are purely indicative. Variations, in fact, are calculated by considering a uniform water phantom that does not represent the actual composition of the patient, as shown in Fig. 1. The values reported by the CT console are also in agreement with the prediction by the quantum noise theory. Conclusions The study allowed to verify the dose information reported by the CT scanner console for an ATCM technique. The CTDIvol and DLP values represent, on average, the experimentally measured variation in the AR phantom. Although this evaluation represents an estimate, this method can be a starting point for further studies.

ABDOMEN-PELVIS COMPUTED TOMOGRAPHY PROTOCOL OPTIMIZATION: AN IMAGE QUALITY AND DOSE ASSESSMENT.

Computed tomography (CT) has a high level of sensitivity and specificity for the diagnosis and follow-up of pathologies of the abdomen-pelvis region. Some features, such as automatic tube current modulation (ATCM), permits the acquisition of quality images with low radiation doses. This study evaluated the image quality and radiation dose of abdomen-pelvis CT protocols with ATCM technique. Were performed five CT protocols using 16-slice and 64-slice scanners, an anthropomorphic phantom for dosimetric measurements, an analytical phantom and retrospective examinations for image quality analysis. Were found significant reduction in effective dose. The highest absorbed doses were found in the stomach and spleen (56.1 and 47.2 mGy, respectively). Objective parameters as noise, low contrast and spatial resolution did not significantly differ between the protocols (p > 0.05). All protocols received the range of 'Optimum/Acceptable' in patient's image quality analysis. This methodology can be reproduced in any clinical routine to optimize CT protocols.

Craniocervical computed tomography angiography with adaptive iterative dose reduction 3D algorithm and automatic tube current modulation in patients with different body mass indexes.

The aim of this study was to investigate the feasibility of head and neck computed tomography angiography (CTA) using the 80-kV tube voltage and the adaptive iterative dose reduction (AIDR) 3D algorithm in patients with different body mass indexes (BMIs).From November 2016 to January 2017, 128 consecutive patients scheduled for head and neck CTA examinations were randomized into the 100-kV group (n = 60) and the 80-kV group (n = 68). Both groups used the automatic tube current modulation technique and the AIDR 3D algorithm. The patients were further grouped as slender (BMI < 22 kg/m2), normal weight (22 kg/m2≤BMI < 25 kg/m2), and overweight (BMI ≥25 kg/m2). The image quality and the radiation dose of each subgroup were analyzed.The images of the head and neck vessels and the brain tissue obtained with 100 kV were all of diagnostic quality. Slender and normal weight patients imaged with 80 kV also produced images of diagnostic quality. However, 80 kV in the overweight patients failed to produce images of diagnostic quality. The radiation dose in the patients imaged with 80 kV was significantly decreased in comparison with those imaged with 100 kV. The effective dose was 0.36 ± 0.06 and 0.41 ± 0.05 mSv in the slender and normal weight patients imaged with 80 kV.Head and neck CTA scanning with 80 kV, automatic tube current modulation, and AIDR 3D algorithm can produce high quality images with reduced radiation dose in slender or normal weight patients.

Improved image quality of low-dose CT combining with iterative model reconstruction algorithm for response assessment in patients after treatment of malignant tumor.

To evaluate the image quality and radiation dose of low-dose (LD) computed tomography (LD-CT) combining with iterative model reconstruction (IMR) algorithm for response assessment in patients after treatment of malignant tumor compared with routine-dose CT (RD-CT). Forty-seven patients [mean age 57.8±10.9 years, 30 males, body mass index (BMI) 22.09±2.35 kg/m2] after treatment of malignant tumor underwent contrast-enhanced chest and abdomen CT twice for response assessment with an interval of 6 months according to clinical routine. The first CT scans were performed with RD protocol at 120 kVp and images were reconstructed with filtered back projection (FBP) algorithm; while the second scans were performed with LD protocol at 100 kVp and images were reconstructed with FBP and IMR algorithm respectively. All scans were performed using an automatic tube current modulation technique with 150 mAs as reference. Objective image quality including CT attenuation, image noise, and contrast to noise ratio (CNR), and subjective image quality including artifacts, noise, visualization of small structures and confidence of targeted lesions, as well as lesion detection were assessed and compared. Effective radiation dose of LD-CT scans was reduced 54.8% compared to RD-CT scans (26.89±3.35 vs. 12.14±2.09 mSv). Higher CT attenuation was found in both LD-IMR and LD-FBP images compared to RD-FBP images. Better subjective image quality and CNR as well as lower objective noise were found in LD-IMR images (all, P<0.05). Two small lesions with the diameter less than 1 cm were missed in LD-FBP images, which were able to be observed in LD-IMR images. IMR is able to help more than half of reduction of radiation dose without compromising the quality of diagnostic information in patients after treatment of malignant tumors to chest and abdomen CT for response assessment.

Effect of arm position, presence of medical devices, and off-centering during acquisition of scout image on automatic tube voltage selection and current modulation in pediatric chest CT.

PurposeTo evaluate the patients’ morphologic factors affecting radiation dose in pediatric chest CT.Materials and methodsFrom November 2013 to May 2015, 315 pediatric chest CT scans were obtained using a CT scanner, and classified into 5 groups according to the patients’ age. For each age group, the chest CT scans were divided into two subgroups. A cut-off value used was the 75th percentile of size-specific dose estimates (SSDE), age-specific diagnostic reference level (DRL): less than the 75th percentile of SSDE (Group A, n = 238) and greater than the 75th percentile of SSDE (Group B, n = 77). All CT scans were performed with the same protocol using automatic tube voltage selection and current modulation techniques. The morphologic factors of the patients including body mass index (BMI), arm angles, presence of medical devices in the scan field, and degree of off-centering within the CT gantry were compared between groups A and B.ResultsGroup B showed narrower arm angles on scout and coronal reformatted images, higher frequency of the presence of devices and higher BMI than group A (P < 0.001, P < 0.001; P = 0.018, and P < 0.001, respectively). In multivariate analysis, narrower arm angles, the presence of devices on the scout images and higher BMI were independently associated with higher SSDE (P = 0.001, P = 0.037, and P < 0.001, respectively).ConclusionsDuring acquisition of the scout images, arms-down position and the presence of medical devices were associated with a high radiation dose above age-specific DRLs in pediatric chest CT, regardless of repositioning before the actual scanning. In addition, off-centering had no clinical impact on radiation dose in the routine practice.

Dosimetric changes with computed tomography automatic tube-current modulation techniques.

The study is aimed at a verification of dose changes for a computed tomography automatic tube-current modulation (ATCM) technique. For this purpose, anthropomorphic phantom and Gafchromic® XR-QA2 films were used. Radiochromic films were cut according to the shape of two thorax regions. The ATCM algorithm is based on noise index (NI) and three exam protocols with different NI were chosen, of which one was a reference. Results were compared with dose values displayed by the console and with Poisson statistics. The information obtained with radiochromic films has been normalized with respect to the NI reference value to compare dose percentage variations. Results showed that, on average, the information reported by the CT console and calculated values coincide with measurements. The study allowed verification of the dose information reported by the CT console for an ATCM technique. Although this evaluation represents an estimate, the method can be a starting point for further studies.

Study on the optimized scanning conditions of cerebral CT angiography based on the angiographic CT head phantom

Objective To study the impacts of different tube voltage and different noise index(NI) guided automatic tube current modulation on the image quality and radiation dose in cerebrovascular imaging and determine the optimal scanning condition. Methods PH3 angiographic CT head phantom was used for head CTA examination. Scanning protocols: all the scanning objectives were divided into three groups according to the different tube voltages of 80, 100 and 120 kV. Each group applied certain tube current (300, 400 mA) and automatic tube current modulation technique with NI from 3 to 10 to perform head CTA. There were 30 scanning proposals with different parameter combinations of tube voltage and tube current. The radiation dose [CT dose index volume (CTDIvol), dose length product (DLP) and effective dose (ED)], objective indicators of images(CT value of the blood vessels and its noise, CT value of brain tissue and its noise, signal-to-noise ratio, contrast-to-noise ratio) and the subjective scores of the five cerebrovascular segments were recorded. Differences of CT value of the blood vessels and its noise, CT value of brain tissue and its noise, signal-to-noise ratio and contrast-to-noise ratio between different tube voltages and tube currents were analyzed by One-Way ANOVA. Results When the tube voltage was certain, the CTDIvol, DLP and ED were all dropped while NI was increased from 3 to 10. Compared with group(120 kV, 300 mA), CTDIvol of group with 100 kV, 300 mA decreased 35.32% (12.22/34.59) , CTDIvol of group(100 kV, NI=6) decreased 46.72% (16.16/34.59) . Compared with group(100 kV, 300 mA), CTDIvol of group (100 kV, NI=6) decreased 17.61% (3.94/22.37) . When the tube voltage was certain and the tube current and NI were not certain, there is no statistical difference (P>0.05) between CT values of blood vessel and brain, while blood vessel noise, noise of brain, SNR and CNR showed statistical difference (P<0.05). When tube current and NI were certain while tube voltage was varied, all objective indicators discussed above all exhibited statistical difference (P<0.05). SNR and CNR of group(100 kV, NI=6) were higher than group(120 kV, 300 mA) with 6.31% (2.69/42.66) and 7.18% (2.64/36.78) , respectively. The tube voltage, NI and tube current had no effect on the subjective scores of first and second grade vessel but greater impact on the fourth and fifth grade vessel. Conclusion In the head CTA scanning, combined the use of NI 6 guided automatic adjustment tube current and low tube voltage (100 kV) technique not only can get better image quality but also significantly decreased the radiation dose. Key words: Tomography, X-ray computed; Radiation dosage; Comparative study

Effect of topogram-tube angle combination on CT radiation dose reduction

This study assessed the ability of various types of topograms, when used with an automatic tube current modulation (ATCM) technique, to reduce radiation dose from computed tomography (CT) scans. Three types of topograms were used with the ATCM technique: (i) anteroposterior (AP) topograms alone, (ii) AP topograms followed by lateral topograms, and (iii) lateral topograms followed by AP topograms. Various regions (chest, abdomen and whole-body) of a humanoid phantom were scanned at several tube voltages (80, 100 and 120 kVp) with the selected topograms. Although the CT dose depended on the order of topograms, the CT dose with respect to patient positioning depended on the number of topograms performed. The magnitude of the difference in CT dose between number and order of topograms was greater for the scans of the abdomen than the chest. These results suggest that, for the Siemens SOMATOM Definition AS CT scanner, choosing the right combination of CT scan conditions with the ATCM technique can minimize radiation dose to a patient.

Dose optimization in computed tomography comparing automatic tube current modulation and fixed tube current techniques

Introduction High radiation doses received, especially in young patients, have a great importance with the known risk cancer development. Computed Tomography examinations correspond to 70% of all radiation doses in diagnostic imaging modalities. With advances in CT scanners, some features such as automatic tube current modulation (ATCM) permits acquiring high quality images with low radiation doses. However, without an optimization process, the protocols used in CT routine induce low-quality images that compromise the reliable medical diagnosis or induce radiation doses questioning the ALARA principle. Purpose The purpose of this study was to evaluate the radiation dose of fixed mA techniques and tube current modulation techniques in CT the abdomen-pelvis protocol. Material and methods We fixed three current protocols (300 mA, 250 mA and 200 mA) and one ATCM protocol (SD 10.0) performed in a 16-slice Toshiba CT scanner with “SureExposure3D” ATCM system. Protocols were applied in an anthropomorphic phantom (Alderson-Rando Phantom) for a dosimetric evaluation and to determine organ absorbed doses. The effective doses, E , were also calculated according to ICRP 103. Results The ATCM technique SD 10.0 has the lowest amount of absorbed dose. The larger E was found in the protocol with 300 mA. The difference to the SD protocol 10.0, which showed lower E , was of 79.49%. Conclusion ATCM protocols can be an excellent alternative to dose reduction in CT scans, since it does not impair the diagnostic image quality. Disclosure The authors declare that there is no conflict of interests.

Dose and Image Quality in Low-dose CT for Urinary Stone Disease: Added Value of Automatic Tube Current Modulation and Iterative Reconstruction Techniques.

The aim of this study was to compare dose and image quality (IQ) of a baseline low-dose computed tomography (CT) (fix mAs) vs. an ultra-low-dose CT (automatic tube current modulation, ATCM) in patients with suspected urinary stone disease and to assess the added value of iterative reconstruction. CT examination was performed on 193 patients (103 baseline low-dose, 90 ultra-low-dose). Filtered back projection (FBP) was used for both protocols, and Sinogram Affirmed Iterative Reconstruction (SAFIRE) was used for the ultra-low-dose protocol only. Dose and ureter stones information were collected for both protocols. Subjective IQ was assessed by two radiologists scoring noise, visibility of the ureter and overall IQ. Objective IQ (contrast-to-noise ratio, CNR) was assessed for the ultra-low-dose protocol only (FBP and SAFIRE). The ultra-low-dose protocol (ATCM) showed a 22% decrease in mean effective dose (p<0.001) and improved visibility of the pelvic ureter (p=0.02). CNR was higher for SAFIRE (p<0.0001). SAFIRE improves the objective IQ, but not the subjective IQ for the chosen clinical task.

Diagnostic value of CT and MRI in myxoid soft tissue tumours

Objective To study the CT and MRI characteristics of myxoid soft tissue tumours. Methods Fifty-three myxoid soft tissue tumours pathologically confirmed were retrospectively studied. MR and CT scan were performed before operation. Noncontrast T1 and T2 weighted images, fat-suppressed T2 weighted images were obtained before contrast-enhanced scan with fat-suppressed T1 weighted sequence was underwent. Plain and contrast-enhanced CT was performed with tube potential of 120 kV, matrix 512×512, and automatic tube current modulation technique. Results There were 18 myxoid liposarcoma, 3 ganglioneuroma, 8 myxofibrosarcoma, 2 extraskeletal myxoid chondrosarcoma, 10 intramuscular myxoma, and 2 juxta-articular myxoma. Microscopic examination showed myxoid soft tissue tumours which were consisted of abundant myxoid stroma with tumour cells and blood vessels associated with fibrous bands. Low density in CT images, hypointensity in T1 weighted images, significantly hyperintense in T2 weighted images were their common manifestations in the area of abundance of extracellular myxiod matrix. Plain CT images demonstrated equidensite, T1 weighted images isointensity, and fat-suppressed T1 weighted images significant enhancement relatively in the areas of increased number of tumor cells. Hemorrhage, necrosis and capsule of the lesion were revealed in high grade malignant tumors. The septa can be identified in most of myxoid tumours of soft tissue. Conclusion CT and MRI can definitely show the image characteristics of myxiod soft tissue tumours, which can help make a qualitative diagnosis before operation. Key words: Soft tissue neoplasms; Tomography, X-ray computed; Magnetic resonance imaging

Effect of an arm traction device on image quality and radiation exposure during neck computed tomography

ObjectiveTo retrospectively determine the effect of an arm traction device on image quality and radiation exposure during a neck computed tomography (CT) scan. Materials and methodsStandard neck CT examinations with an automatic tube current modulation technique were compared for two groups (intervention group: patients with an arm traction device, n=45; control group: no particular positioning optimization, n=45). Image quality was the primary outcome and was assessed using image noise and the streak artifact. The secondary outcome was radiation exposure, which was measured by the volume CT dose index (CTDIvol) and dose-length product. Potential confounders, including the effective diameter of the neck and scan length, were also assessed. ResultsImage noise and the streak artifact at the lower neck and the supraclavicular fossa were significantly improved in the intervention group compared with the control group (p<0.001). There was a significant decrease in the CTDIvol in the intervention group versus the control group (p=0.042). DLP showed a tendency toward a decrease in the intervention group that was non-significant (p=0.106). The effective diameter and scan length showed no statistical difference between the two groups. ConclusionAn arm traction device improves the image quality in the lower neck and the supraclavicular fossa during a neck CT. Application of this device also reduces the tendency for radiation exposure.

Influence of the adaptive iterative dose reduction 3D algorithm on the detectability of low-contrast lesions and radiation dose repeatability in abdominal computed tomography: a phantom study.

The purpose of the study is to evaluate the influence of the adaptive iterative dose reduction (AIDR 3D) algorithm on the detectability of low-contrast focal liver lesions (FLLs) and the radiation dose repeatability of automatic tube current modulation (ATCM) in abdominal CT scans using anthropomorphic phantoms. Three different sizes of anthropomorphic phantoms, each with 4 low-contrast FLLs, were scanned on a 320-channel CT scanner using the ATCM technique and AIDR 3D, at different radiation doses: full-dose, half-dose, and quarter-dose. Scans were repeated three times and reconstructed with filtered back projection (FBP) and AIDR 3D. Radiation dose repeatability was assessed using the intraclass correlation coefficient (ICC). Image noise, quality, and lesion conspicuity were assessed by four reviewers and the number of invisible FLLs was compared among different radiation doses and reconstruction methods. ICCs of radiation dose among the three CT scans were excellent in all phantoms (0.99). Image noise, quality, and lesion conspicuity in the half-dose group were comparable with full-dose FBP after applying AIDR 3D in all phantoms. In small phantoms, the half-dose group reconstructed with AIDR 3D showed similar sensitivity in visualizing low-contrast FLLs compared to full-dose FBP (P = 0.77-0.84). In medium and large phantoms, AIDR 3D reduced the number of missing low-contrast FLLs [3.1% (9/288), 11.5% (33/288), respectively], compared to FBP [10.4% (30/288), 21.9% (63/288), respectively] in the full-dose group. By applying AIDR 3D, half-dose CT scans may be achievable in small-sized patients without hampering diagnostic performance, while it may improve diagnostic performance in medium- and large-sized patients without increasing the radiation dose.

Application of automatic tube current modulation on image quality and radiation dose at abdominal CT

Objective To investigate the effect of automatic tube current modulation (ATCM) on image quality and radiation dose for abdominal CT. Methods An abdomen-equivalent tissue model in the present study was developed,by referring to the CTP515 auxiliary performance testing model made by the internationally recognized Phantom Laboratory,in conjunction with the real data from 68 Chinese male subjects with BMI between 18 to 24 kg/cm2 (subjects with fatty liver,cirrhosis,intraperitoneal huge tumor,ascites or pleural effusion or who were under 18 years old were excluded).Catphan600 performance served as observation object,and simulating adult abdominal CT low and high contrast characteristics to research.Control groups were scanned with CT protocol at fixed 120 k V,450 m A and experimental group were scanned with the same tube voltage and variable current range from 10 to 450 m A (NI value:4 to 20),respectively.CT value was measured by homogeneous area in the center of Catphan600 to verify the phantom for X-ray attenuation of equivalence.CT dose index (CTDIvol),size-specific dose estimates (SSDE),dose length product (DLP),image noise (SD) and contrast to noise ratio (CNR) were recorded and measured.Fifteen mm diameter low-contrast detectability in CTP515 and high-contrast detectability in CTP528 at Catphan600 were evaluated independently by 3 doctors working in abdominal diagnosis for more than five years from three hospitals in a five-point scale.The correlation between NI value and objective,subjective evaluating indicator of image quality and radiation dose were analyzed,and SD,CNR and LCD,HCD scores in different NI group and those in control group were compared with parameter and non-parametric rank sum test.The differences of SD,CNR and CTDIvol scores between NI group and control group were compared with t test.Kruskal-Wallis test was used for intra-group comparison of LCD and HCD scores,Mann-Whiteney U Test for inter-group and Kappa analysis for consistency check of the subjective evaluation result of the 3 radiologists. Results No significant difference was found between the CT value of ROIin catphan 600 central area[ (50.8±1.0) HU] scanned under various NI and that of the normal liver tissue[ (52.8±9.1) HU]obtained from 68 Chinese male subjects (t=0.31,P>0.05),with a deviation degree of 4.9%.This phantom was equivalent to adult abdomen for X-ray attenuation.One unit increase in NI was associated with 1.23 mGy,2.03 mGy,13.20 mGy·cm,0.20 mSv decrease in CTDlvol,SSDE,DLP and ED respectively.NI and objective,subjective evaluating indicator of image quality and radiation dose was highly linear correlated (r=0.871 to 0.982,P 0.05).No significant differences were found in LCD scores between NI group 4 to 10 and the control group (Z=-1.637 to 0.000,P>0.05).And the HCD scores between NI group 4 to 13 and the control group (Z=-1.423 to 0.000,P>0.05) were not significantly different either.The consistency check result ofKappaanalysis of the 3 doctors' LCD,HCD evaluation was 0.743 and 0.795. Conclusion Application of the ATCM technique in abdomen CT can reduce the radiation dose while ensuring the image quality. Key words: Tomography,X-ray computed; Radiation dosage; Abdomen; Phantom

Automatic tube current modulation for volume scan in a 320-detector row CT scanner

The x-y plane combined with z-axis automatic tube current modulation (ATCM) technique is one of the most comprehensive approaches to CT dose reduction because the radiation dose is adjusted according to patient attenuation in three dimensions. The 320-detector row CT scanner has the widest scan range (16 cm) within one axial rotation and equips with volume scan ATCM (VS-ATCM) mode. Special attention is needed while utilizing VS-ATCM mode in CT acquisitions especially scanning different anatomical regions, such as neck and shoulder in a single volume. However, the mechanism of VS-ATCM of the 320-detector row CT scanner remains unclear. This study aims to evaluate the performance of VS-ATCM mode in a 320-detector row CT scanner. A phantom set consists of three simple-shaped phantoms was scanned with the VS-ATCM mode. A solid-state detector was inserted into the central position of the phantom set to measure the real-time dose profiles at seven positions within five scan volumes. The effective tube-current time product of each slice was recorded. The standard deviation of the CT numbers measured at each image slice was used as a noise measurement. The performance of helical scan ATCM (HS-ATCM) mode was in comparison of VS-ATCM mode. The results indicated that VS-ATCM mode can provide a less dose CT scanning to a patient but resulted in a higher image noise in comparison with those of HS-ATCM mode. In clinical practice, radiologists or radiological technologists should pay more attention on the volume position when using VS-ATCM mode for patient imaging. Our experience can be a reference to others for implementation of clinical practices.