Reference mAs Research Articles

The impact of tube current and iterative reconstruction algorithm on dose and image quality of infant CT head examination

Computed Tomography (CT) scan examination has been recognized for its potential in contributing high radiation doses, which raised a public concern towards pediatric exposure, especially infants. Thus, the optimization is vital through well-balanced levels of radiation and image quality. Hence, this study aimed to investigate optimized CT acquisition parameter on radiosensitive organs of infant CT head examination and its influence on the image quality. This study utilized a 1-year-old anthropomorphic phantom and thermoluminescence dosimeter (TLD) for organ dose assessment. The examination was performed by using 128 multi-slice CT (Ingenuity Core, Philips, Netherlands) and varying the tube current and iterative reconstruction algorithm (iDose4) levels. During the process, the reference mAs (ref. mAs) were altered while maintaining the tube potential at 100 kVp. Five protocols were established and denoted by P1, P2, P3, P4, and P5. As per measurement, 3 calibrated TLD chips were implanted into the phantom on slab numbers 2, 4, and 7 that represented brain, lens, and thyroid, respectively. Image quality was evaluated by utilizing the objective assessment in terms of signal to noise ratio (SNR) and contrast to noise ratio (CNR) and subjective image quality using the Visual Grading Analysis (VGA) technique in terms of sharpness, noise, and artefact were assessed from each protocol. Notably, the dose was decreased up to 30% along with the reduction of tube current and the improvement of SNR and CNR values for parameters that enable the iterative reconstruction algorithm. Hence, optimization of CT acquisition parameter should be evaluated and monitored accordingly.

OPTIMIZATION OF LUNG CT PROTOCOL FOR THE DIAGNOSTIC EVALUATION OF COVID-19 LUNG DISEASE.

This study intends to evaluate the different lung CT scan protocols used for the diagnostic evaluation of COVID-19-induced lung disease in Iranian imaging centers in terms of radiation dose and image quality. After data collecting, subjective image quality, radiation dose and objective image quality such as noise, SNR and CNR were assessed.Statistically significant differences in effective dose and image quality were evident among different lung CT protocols. Lowest and highest effective dose was1.31 ± 0.53 mSv related to a protocol with activated AEC (reference mAs = 20) and 6.15 ± 0.57 mSv related to a protocol with Fixed mAs (mAs = 100), respectively.A protocol with enabled tube current modulation with 70 mAs as a reference mAs, and protocol with 20 mAs and enabled AEC had the best and lowest image quality, respectively. To optimize the scan parameters, AEC must be used, and a range of tube currents (between 20 and 50 mAs) can produce acceptable images in terms of diagnostic quality and radiation dose for the diagnosis of COVID-19-induced lung disease.

Estimation of CARE Dose 4D quality reference mAs conversion factors for child to adult reference patient in child protocols on Siemens Symbia SPECT-CT systems.

CARE Dose 4D modulates mAs through several mechanisms according to patient size and shape, whilst maintaining user-defined reference image quality on Siemens Symbia single-photon emission computed tomography (SPECT)-computed tomography (CT) systems. A 20 kg child reference was used in child protocols prior to software version VB10 and a 75 kg adult thereafter. Quality reference mAs conversion factors are estimated for delivering equivalent mAs to children between two comparable SPECT-CT systems using adult and child references for topogram-based patient-size-related dose level adaptations. A child phantom was scanned using child protocols on a Siemens Symbia T16 (child reference) and a Siemens Symbia Intevo Bold (adult reference). On each system, scans of the thorax, abdomen and pelvis were acquired with arms up and down, at 80 and 110 kVp. Quality reference mAs settings of 10-50 were used on the Symbia T16 and 40-200 on the Symbia Intevo Bold. These data were used to propose quality reference mAs (adult/child reference) conversion factors according to scan range, arm position and tube voltage. Quality reference mAs for child protocols using the adult reference should multiply the child quality reference mAs by the following factors, to give comparable delivered mAs: arms up 80 kV: 3.8 (thorax), 3.8 (abdomen), 4.3 (pelvis); arms up at 110 kV: 3.8 (thorax), 4.1 (abdomen), 4.6 (pelvis); arms down at 80 kV: 4.0 (thorax), 3.7 (abdomen), 3.9 (pelvis); arms down at 110 kV: 4.3 (thorax), 4.0 (abdomen), 4.2 (pelvis). Conversion factors for child to adult dose modulation references are proposed, allowing comparable delivered mAs to a child.Video abstract: http://links.lww.com/NMC/A178.

Dual-source computed tomography of the lung with spectral shaping and advanced iterative reconstruction: potential for maximum radiation dose reduction

BackgroundRadiation dose at CT should be as low as possible without compromising diagnostic quality.ObjectiveTo assess the potential for maximum dose reduction of pediatric lung dual-source CT with spectral shaping and advanced iterative reconstruction (ADMIRE).Materials and methodsWe retrospectively analyzed dual-source CT acquisitions in a full-dose group (FD: 100 kV, 64 reference mAs) and in three groups with spectral shaping and differing reference mAs values (Sn: 100 kV, 96/64/32 reference mAs), each group consisting of 16 patients (age mean 11.5 years, standard deviation 4.8 years, median 12.8 years, range 1.3–18 years). Advanced iterative reconstruction of images was performed with different strengths (FD: ADMIRE Level 2; Sn: ADMIRE Levels 2, 3 and 4). We analyzed dose parameters and measured noise. Diagnostic confidence and detectability of lung lesions as well as anatomical structures were assessed using a Likert scale (from 1 [unacceptable] to 4 [fully acceptable]).ResultsCompared to full dose, effective dose was reduced to 16.7% in the Sn 96 group, 11.1% in Sn64, and 5.5% in Sn32 (P<0.001). Noise values of Sn64ADM4 did not statistically differ from those in FDADM2 (45.7 vs. 38.9 Hounsfield units [HU]; P=0.132), whereas noise was significantly higher in Sn32ADM4 compared to Sn64ADM4 (61.5 HU; P<0.001). A Likert score >3 was reached in Sn64ADM4 regarding diagnostic confidence (3.2) and detectability of lung lesions (3.3). For detectability of most anatomical structures, no significant differences were found between FDAM2 and Sn64ADM4 (P≥0.05).ConclusionIn pediatric lung dual-source CT, spectral shaping together with ADMIRE 4 enable radiation dose reduction to about 10% of a full-dose protocol while maintaining an acceptable diagnostic quality.

Investigation of the characteristics of Automatic Exposure Control (AEC) of a Computed Tomography (CT) scanner by utilising cylindrical and anthropomorphic phantoms

One method to optimise the use of x-rays in CT and hence a reduction in patient dose is the application of automatic exposure control (AEC). This study measured the effective mAs, image noise and volume CT dose index (CTDIvol) as the result of changing the AEC index on a Siemens Somatom Definition 64 slices dual source CT scanner. The scans were performed on four phantoms of different geometries, namely the 16 and 32 cm cylindrical CTDI phantoms and two anthropomorphic phantoms, RANDO (20 cm effective diameter) and ATOM (19.8 cm effective diameter). Results showed that the effective mAs increased with increasing tube potential (kVp) and Quality Reference mAs (QRM), therefore increasing CTDIvol while reducing image noise. Meanwhile, no changes of radiation dose and image noise were observed when the pitch was increased. However, for the largest phantom (32 cm effective diameter), a constant effective mAs was found between 120 and 140 kVp. The same trend was also found with increasing QRM from 300 mAs to 400 mAs suggesting a certain limitation of the AEC has been reached. In conclusion, this study showed that AEC is affected by kVp and QRM but not by pitch selection. Further work is required to quantify the characteristics of the AEC system in relation to the mentioned parameters for better optimisation.

A multi-reader invitro study using porcine kidneys to determine the impact of integrated circuit detectors and iterative reconstruction on the detection accuracy, size measurement, and radiation dose for small (

Background Detection of small renal calculi has benefitted from recent advances in computed tomography (CT) scanner design. Information regarding observer performance when using state-of-the-art CT scanners for this application is needed. Purpose To assess observer performance and the impact of radiation dose for detection and size measurement of <4 mm renal stones using CT with integrated circuit detectors and iterative reconstruction. Material and Methods Twenty-nine <4 mm calcium oxalate stones were randomly placed in 20 porcine kidneys in an anthropomorphic phantom. Four radiologists used a workstation to record each calculus detection and size. JAFROC Figure of Merit (FOM), sensitivity, false positive detections, and calculus size were calculated. Results Mean calculus size was 2.2 ± 0.7 mm. The CTDIvol values corresponding to the automatic exposure control settings of 160, 80, 40, 25, and 10 Quality Reference mAs (QRM) were 15.2, 7.9, 4.2, 2.7, and 1.3 mGy, respectively. JAFROC FOM was ≥ 0.97 at ≥ 80 QRM, ≥ 0.89 at ≥ 25 QRM, and was inferior to routine dose (160 QRM) at 10 QRM (0.72, P < 0.05). Per-calculus sensitivity remained ≥ 85% for every reader at ≥ 25 QRM. Mean total false positive detections per reader were ≤ 3 at ≥ 80 QRM, but increased substantially for two readers ( ≥ 12) at ≤ 40 QRM. Measured calculus size significantly decreased at ≤ 25 QRM ( P ≤ 0.01). Conclusion Using low dose renal CT with iterative reconstruction and ≥ 25 QRM results in high sensitivity, but false positive detections increase for some readers at very low dose levels (≤ 40 QRM). At very low doses with iterative reconstruction, measured calculus size will artifactually decrease.

Synergistic Radiation Dose Reduction by Combining Automatic Tube Voltage Selection and Iterative Reconstruction.

The aim of the study was to evaluate radiation dose and image quality in computed tomographic pulmonary angiography (CTPA) scans performed with automatic tube voltage selection (ATVS, CarekV) before and after implementation of iterative reconstruction (IR, Safire). This IRB-approved study was conducted with waiver of informed consent. The cohort included 100 consecutive "standard protocol" CTPAs performed using ATVS and 100 consecutive "combined protocol" CTPAs performed using ATVS with a 33% reduction in reference mAs and IR. CTDIvol and main pulmonary artery enhancement, noise, and signal-to-noise ratio were recorded, along with blinded grading of subjective image quality. Dose and image quality were compared between cohorts with univariate analyses and linear regression models. The 33% reduction in reference mAs with the combined protocol allowed ATVS to select reduced kVp more often than with the standard protocol, with a reduction in 120 and 100 kVp scans (26% to 0% and 61% to 51%, respectively) and an increase in 80 kVp scans (13% to 49%). The combined protocol yielded a CTDIvol reduction of 43% (P<0.0001) and increases in main pulmonary artery enhancement (57 HU, P=0.005) and noise (P=0.019) with unchanged signal-to-noise ratio (P=0.17). With the combined protocol, subjective image quality was unchanged for evaluation of vascular structures but was decreased for evaluation of soft tissues and lung parenchyma. The combination of ATVS and IR resulted in a 43% dose reduction, greater than the 33% reduction that would be achieved by reducing the reference mAs alone. This was accomplished with preserved vascular image quality.

TH‐EF‐BRA‐06: A Novel Method of ACR Dose Index Registry Report Interpretation: Population Dose Reduction for Thoracic CT Angiography

Purpose:To identify a method of ACR Dose Index Registry (DIR) report analysis and interpretation that focuses dose reduction efforts on exams that most affect our patient population.Methods:In place of a direct interpretation of the DIR report, a proposed additional metric — the Total Exposure Variance (TEV) — was calculated for each of the most frequently performed institutional exams. TEV was defined as the product of exam frequency (N) and the difference between institutional and national median dose (CTDIvol or SSDE). TEV indicated total excess institution population dose beyond the equivalent national benchmark. TEV analysis focused investigation of two exams from the 2012 DIR report: 1) CT pulmonary angiography (CTPA), which had SSDE between the median and third quartile; and, 2) CT thoracic angiography (CTTA), optimized for the aorta, which had SSDE in the top quartile.Results:CT scan parameter changes were implemented lowering the quality reference mAs by 20% and limiting the automatic kV selection range to 100–120. DIR data from July–December 2012 were compared to same time period for 2013. CTPA showed a decrease of median CTDIvol and SSDE of 14% and 16%, respectively, representing a realized decrease in TEV of 1776 mGy‐persons. Data for CTTA showed a decrease of median CTDIvol and SSDE of 38% and 44%, respectively, representing a realized decrease in TEV of 1050 mGy‐persons. In both cases, the incremental and population dose metrics moved down toward national benchmarks.Conclusion:TEV analysis used DIR data to shift the paradigm toward reducing population dose instead of frequency‐independent interpretation of the report. The TEV metric highlighted exams that would have otherwise been overlooked with direct DIR report interpretation. Recent modifications to the DIR report contents may avail additional approaches to dose reduction.

Effect of reference mAs in CARE kV technique on image quality and radiation dose in unenhanced chest CT

Objective To evaluate the effect of reference mAs on radiation dose and image quality characteristics of chest CT scanned with CARE kV technique compared with CARE Dose4D. Methods According to the date of examination,158 consecutive patients were selected in our department and randomly divided into 5 groups: CARE Dose4D group (30 cases, group 1); using CARE kV technology, reference mAs were 110 (32 cases), 90 (31 cases), 70 (33 cases), 50 (32 cases), which were recorded asthe group from 2 to 5, respectively. Volume CT dose index (CTDIvol), dose length product (DLP) and the effective dose (ED) were analyzed. CT value and objective image noise were measured in the lungparenchyma and descending aorta.Two radiologists assessed the images for subjective noise, artefacts and diagnostic acceptability.The radiation dose, CT value and objective noise were compared with the analysis of variance, and the difference between two groups was compared with SNK test; the rank sum tests (Kruskal-Wallis) were used in subjective image quality score, and difference between two groups was compared with K-W test. Results The CTDIvol, DLP, ED values in five groups were(7.7±1.7),(7.7±2.0), (5.5±1.4), (4.2±1.5), (2.8±1.2)mGy, (290.7±67.4) , (290.1±85.2) , (194.2±52.1) , (150.7±63.8) , (96.5±38.9) mGy·cm, (4.1±0.9) , (4.1±1.2) , (2.7±0.7) , (2.1±0.9) , (1.3±0.5) mSv, respectively.There were significant difference among the 5 groups(F=59.305, 57.76, 57.76, P 0.05). The objective noise of 5 groups in pulmonary parenchyma and the descending aorta were (48.7±9.1) , (49.2±10.0) , (55.5±11.2) , (56.5±8.3) , (63.7±13.2) HU; (9.2±1.6) , (9.5 ± 2.1) , (10.7 ± 2.6) , (11.6 ± 2.7) , (13.6 ± 2.6) HU respectively, and the difference was significant(F= 10.774, 17.157, P 0.05). Conclusion Comparedwith CARE Dose4D, the use of CARE kV technique of suitable reference mAs for unenhanced chest CT can reduce radiation dose significantly with diagnostically acceptable image quality. Key words: Tomography, X-ray computed; Radiation dosage

Relationships between patient size, dose and image noise under automatic tube current modulation systems

Automatic tube current modulation (ATCM) systems are now used for the majority of CT scans. The principles of ATCM operation are different in CT scanners from different manufacturers. Toshiba and GE scanners base the current modulation on a target noise setting, while Philips and Siemens scanners use reference image and reference mAs concepts respectively. Knowledge of the relationships between patient size, dose and image noise are important for CT patient dose optimisation. In this study, the CT patient doses were surveyed for 14 CT scanners from four different CT scanner manufacturers. The patient cross sectional area, the tube current modulation and the image noise from the CT images were analysed using in-house software. The Toshiba and GE scanner results showed that noise levels are relatively constant but tube currents are dependent on patient size. As a result of this there is a wide range in tube current values across different patient sizes, and doses for large patients are significantly higher in these scanners. In contrast, in the Philips and Siemens scanners, tube currents are less dependent on patient size, the range in tube current is narrower, and the doses for larger patients are not as high. Image noise is more dependent on the patient size.

Iterative reconstruction of pulmonary MDCT angiography: Effects on image quality, effective dose and estimated organ dose to the breast

To compare the image characteristics, effective dose and estimated organ dose to the female breast in pulmonary MDCT angiography (MDCTA), reconstructed with either standard filtered back projection (FBP), or iterative reconstruction in image space (IRIS). Pulmonary MDCTA performed in 116 females (age 18 - 77 years; body mass index 15 - 48) was reconstructed with FBP (n=52) or IRIS (n=64). Scans were acquired on a 128-row MDCT system using automatic tube current modulation, 100 kV tube voltage, and a quality reference mAs value of 120 (FBP) and 80 (IRIS). Dose was calculated from CT dose index (CTDIvol) and dose length product (DLP) values utilising ImPACT software. Image noise was measured within the pulmonary artery. Qualitative visual assessment of the scans was performed (1=negligible noise, 5=noise obscuring diagnostic information). The average CTDIvol yielded 4.33 mGy for FBP and 3.54 mGy for IRIS, respectively (18.2% decrease). The average effective scan dose was 2.73±0.57 mSv (FBP) and 2.29±0.68 mSv (IRIS), respectively (16.1% decrease). The estimated average organ dose to the breast decreased from 5.1±1.1 mGy (FBP) to 4.2±1.2 mGy (IRIS, 17.6% decrease). No non-diagnostic scans (score 5) were encountered in either group. Significant improvement in image noise levels (P<0.01) and subjective image quality (P<0.02) were noted in IRIS group. Pulmonary MDCTA utilizing a 100 kV technique, automatic tube current modulation, and iterative image reconstruction offers robust results in routine conditions among an unselected female population, with breast doses being comparable to two-view digital mammography. Moreover, iterative reconstruction offers improvements in both image noise and visual perception of the scans, thus suggesting a potential for further dose reduction.

The effects of bismuth breast shields in conjunction with automatic tube current modulation in CT imaging

There are mechanisms within CT scanners and shielding that can be used to lower dose to patients. The objective of our study was to evaluate the dose changes and image quality with and without a breast shield for multidetector CT of the chest with angular tube current modulation. An anthropomorphic 5-year-old phantom was scanned with and without bismuth breast shielding and with and without angular tube current modulation. Image quality was assessed by measuring signal-to-noise ratio and contrast-to-noise ratio as well as measuring qualitatively. ANOVA single-factor p-value analysis of paired datasets was used for the statistical analysis. The breast shielding and angular tube current modulation resulted in a dose reduction to 85% for the breast and 90% overall. Although no qualitative differences were noted with and without the breast shielding used with angular tube current modulation, there were statistically significant differences in the contrast-to-noise ratio and CT numbers. When used with angular tube current modulation, breast shields influence the contrast-to-noise ratio and CT numbers, and therefore should not be used for chest CT. Greater dose reduction can be obtained by reducing the reference mAs (or reference noise index).

Whole spine CT for evaluation of scoliosis in children: Feasibility of sub-milliSievert scanning protocol

Optimization of CT radiation dose is important for children due to their higher risk of radiation-induced adverse effects. Anatomical structures with high inherent contrast, such as bones can be imaged at very low radiation doses by optimizing scan parameters. To assess feasibility of sub-milliSievert whole spine CT scanning protocol for evaluation of scoliosis in children. With approval of the ethical board, we performed whole spine CT for evaluation of scoliosis in 22 children (age range, 3-18 years; mean age, 13 years; 13 girls, 9 boys) on a 128-slice dual source multidetector-row CT scanner. Lowest possible quality reference mAs value (image quality factor for xy-z automatic exposure control or xyz-AEC, CARE Dose 4D) was selected on a per patient basis. Remaining parameters were held constant at 3.0:1 pitch, 128 × 0.6 mm detector collimation, 115.2 mm table feed per gantry rotation, 100 kVp, and 1 and 3 mm reconstructed sections. Average mAs, projected estimated dose savings with AEC, computed tomography dose index volume (CTDI vol), and dose length product (DLP) were recorded. Artifacts were graded on a four-point scale (1, no artifacts; 4, severe artifacts). Ability to identify vertebral and pedicular contours, and measure pedicular width and degree of vertebral rotation was graded on a three-point scale (1, unacceptable; 3, excellent). All CT examinations were deemed as reliable for identifying vertebral and pedicular contours as well as for measuring pedicular width (5.9 ± 1.6 mm) and degree of vertebral rotation (28.7 ± 23.4°). Mean objective image noise and signal to noise ratio (SNR) were 57.5 ± 21.5 and 4.7 ± 2.3, respectively. With a mean quality reference mAs of 13, the scanner employed an average actual effective mAs of 10 ± 3.8 (range, 6-18 mAs) with an estimated radiation dose saving of 43.5 ± 16.3% with xyz-AEC compared with fixed mAs. The mean CTDI, DLP, and estimated effective doses were 0.4 ± 0.1 mGy (0.2-0.7 mGy), 21 ± 10 mGy.cm (8-41 mGy.cm), and 0.3 ± 0.1 mSv (0.12-0.64 mSv), respectively. Radiation dose for whole spine CT for evaluation of scoliosis in children can be minimized to less than one-third of a milliSievert while maintaining diagnostic image quality.

Performance of Iterative Reconstruction and Automated Tube Voltage Selection on the Image Quality and Radiation Dose in Abdominal CT Scans

To study the impact of sinogram-affirmed iterative reconstruction (SAFIRE) and concurrent application of automated tube voltage selection (ATVS) on image quality (IQ) and radiation dose. A phantom was scanned using various computed tomography (CT) parameters (kV, 80-120; mAs, 50-200). Abdomen contrast-enhanced CT (CECTs) in 170 adults were performed using dose-modified protocols: in 145 patients (group I), ATVS was applied (mAs, 111-649); in 25 (group II), the kV was fixed at 120 (reference mAs, 150). In 95 patients, standard-dose (SD) scan was available. Two readers evaluated the IQ of filtered back projection (FBP) and SAFIRE (levels 1, 3, and 5) images. In phantom, nonlinear drop in noise with increasing strengths of IR (levels S1-S5) was noted. The dose-modified IR scan was rated diagnostic in all 170 patients, with IQ score comparable to that of SD-FBP (P = 0.3). Lower kV (100/80) was prescribed by ATVS in 70% examinations in group I. In comparison with SD-FBP, the mean dose in CT dose index in group I (IR, 3.2 mGy; SD-FBP, 13.02 mGy; P < 0.0001) and in group II (IR, 4.8 mGy; SD-FBP, 11.8 mGy; P < 0.001) was 75.4% and 59.3% lower. Use of SAFIRE and ATVS provides diagnostic quality images at 59.3% to 75.4% reduced dose compared with SD-FBP scan.

Sinogram-Affirmed Iterative Reconstruction of Low-Dose Chest CT: Effect on Image Quality and Radiation Dose

OBJECTIVE. The purpose of this study is to compare sinogram-affirmed iterative reconstruction (SAFIRE) and filtered back projection (FBP) reconstruction of chest CT acquired with 65% radiation dose reduction. MATERIALS AND METHODS. In this prospective study involving 24 patients (11 women and 13 men; mean [± SD] age, 66 ± 10 years), two scan series were acquired using 100 and 40 Quality Reference mAs over a 10-cm scan length in the chest with a 128-MDCT scanner. The 40 Quality Reference mAs CT projection data were reconstructed with FBP and four settings of SAFIRE (S1, S2, S3, and S4). Six image datasets (FBP with 100 and 40 Quality Reference mAs, and S1, S2, S3, S4 with 40 Quality Reference mAs) were displayed on a DICOM-compliant 55-inch 2-megapixel monitor for blinded evaluation by two thoracic radiologists for number and location of lesions, lesion size, lesion margins, visibility of small structures and fissures, and diagnostic confidence. Objective noise and CT values were measured in thoracic aorta for each image series, and the noise power spectrum was assessed. Data were analyzed with analysis of variance and Wilcoxon signed rank tests. RESULTS. All 186 lesions were seen on 40 Quality Reference mAs SAFIRE images. Diagnostic confidence on SAFIRE images was higher than that for FBP images. Except for the minor blotchy appearance on SAFIRE settings S3 and S4, no significant artifacts were noted. Objective noise with 40 Quality Reference mAs S1 images (21.1 ± 6.1 SD of HU) was significantly lower than that for 40 Quality Reference mAs FBP images (28.5 ± 8.1 SD of HU) (p < 0.001). Noise power spectra were identical for SAFIRE and FBP with progressive noise reduction with higher iteration SAFIRE settings. CONCLUSION. Iterative reconstruction (SAFIRE) allows reducing the radiation exposure by approximately 65% without losing diagnostic information in chest CT.

Assessment of paediatric CT dose indicators for the purpose of optimisation

To establish local diagnostic reference levels (LDRLs) at the Royal Children's Hospital (RCH) Melbourne, Parkville, Australia, for typical paediatric CT examinations and compare these with international diagnostic reference levels (DRLs) to benchmark local practice. In addition, the aim was to develop a method of analysing local scan parameters to enable identification of areas for optimisation. A retrospective audit of patient records for paediatric CT brain, chest and abdomen/pelvis examinations was undertaken. Demographic information, examination parameters and dose indicators--volumetric CT dose index (CTDI(vol)) and dose-length product (DLP)--were collected for 220 patients. LDRLs were derived from mean survey values and the effective dose was estimated from DLP values. The normalised CTDI(vol) values, mAs values and scan length were analysed to better identify parameters that could be optimised. The LDRLs across all age categories were 18-45 mGy (CTDI(vol)) and 250-700 mGy cm (DLP) for brain examinations; 3-23 mGy (CTDI(vol)) and 100-800 mGy cm (DLP) for chest examinations; and 4-15 mGy (CTDI(vol)) and 150-750 mGy cm (DLP) for abdomen/pelvis examinations. Effective dose estimates were 1.0-1.6 mSv, 1.8-13.0 mSv and 2.5-10.0 mSv for brain, chest and abdomen/pelvis examinations, respectively. The RCH mean CTDI(vol) and DLP values are similar to or lower than international DRLs. Use of low-kilovoltage protocols for body imaging in younger patients reduced the dose considerably. There exists potential for optimisation in reducing body scan lengths and justifying the selection of reference mAs values. The assessment method used here proved useful for identifying specific parameters for optimisation. Advances in knowledge Assessment of individual CT parameters in addition to comparison with DRLs enables identification of specific areas for CT optimisation.

SU-GG-I-40: The Effects of Patient Size on Organ Doses in Adaptive Tube Current Modulated CT

Purpose: To quantify the effect of patient size on organ doses in tube‐current modulated CT. Adaptive tube‐current modulation technologies adjust tube output in response to patient attenuation based on user inputted image quality settings. As such, organ doses can vary widely depending on patient size for the same scanner techniques. This project aims to quantify these changes in dose for a variety of exams. Method and Materials: An adipose tissue‐equivalent add‐on was developed for an existing anthropomorphic adult phantom, allowing for average organ doses to be measured in both a 50th and 90th percentile by weight patient. The doses were measured using a fiber‐optic dosimetry system during routine clinical CT exams of the chest, abdomen and pelvis. Exams were performed using the same quality reference mAs for both phantoms on a Siemens 16 slice scanner and the resulting organ doses were catalogued for comparison. Results: Overall, organ doses were seen to increase in the larger phantom for similar exam techniques. These differences were greater in areas where the additional adipose tissue was thicker, resulting in increased tube output in order to maintain image quality. The average organ dose increase seen in the chest, abdominal, and pelvic exams was found to be 10.5%, 22.2%, and 37.34% respectively, with individual organ dose increases as high as 78%. Additionally, due to increased patient medium and scatter, noise in images from the larger phantom exams was found to be 10–15% higher as compared to the smaller patient. Conclusion: Individual organ doses were seen to increase up to 78% in a larger patient for the same exam techniques as a result of adaptive tube‐current modulation. These increases were coupled with reduced image quality due to scatter. The effects of patient size on doses in tube‐current modulated CT exams should be noted when setting patient protocols.

Evaluation of automated attenuation-based tube current adaptation for coronary calcium scoring in MDCT in a cohort of 262 patients

The aim of our study was to evaluate attenuation-based tube current adaptation in coronary calcium scoring using ECG-gated multi-detector-row CT (MDCT). A total of 262 patients underwent non-enhanced cardiac MDCT. Group 1 was scanned using a standard protocol with 120 kV and 150 mAs(eff). Groups 2-4 were scanned using an attenuation-based dose-adaptation template (CARE Dose) with different effective reference mAs settings (150, 180, 210 mAs(eff)). Body-mass index (BMI) and CT-dose index values were calculated for each patient. Image noise and subjective image quality were assessed. Regression analysis was performed, and the variation coefficient of image noise was determined. Compared to the standard scan protocol a dose reduction of 31.1% for group 2 and 20.1% for group 3 was observed. Measurement variation of image noise was smaller for the attenuation-based dose adaptation protocols (group 2-4) (16.2-17.1%) compared to the standard scan protocol (32.3%). Regression analysis of groups 2-4 showed better correlation with improved dose usage based on BMI (all P <or= 0.001). Median image quality was "excellent" in groups 2-4 and "good" in group 1. Automated attenuation-based tube current adaptation in coronary calcium scoring is technically feasible, can decrease patient dose, and reduces variation in image noise as a sign of improved dose usage.