CTDIvol Values Research Articles

Spectral Beam Shaping in Unenhanced Chest CT Examinations: A Phantom Study on Dose Reduction and Image Quality

This study aimed to determine the optimal tube potential for unenhanced chest computed tomographies (CTs) with age-related phantoms. Three physical anthropomorphic phantoms (newborn, 5-year-old child, and adult) were scanned on a third-generation dual-source CT using CAREkV in semi-mode and CAREDose4D (ref. KV: 120; ref. mAs 50). Scans were performed with all available tube potentials (70-150 kV and Sn150 kV). The lowest volume computed tomography dose index (CTDIvol) was selected to perform additional Sn100-kV scans with matched and half (Sn100-half) CTDIvol value. Image quality was evaluated on the basis of contrast-to-noise ratio (CNR). For the newborn phantom, 70-110 kV was selected as the optimal range (0.36-0.37 mGy). Using Sn150 kV led to an increase in radiation dose (0.75 mGy) without improving CNR (96.9 vs 101.5). Sn100-half showed a decrease in CNR (73.1 vs 101.5). The lowest CTDIvol for the child phantom was achieved between 100 and 120 kV (0.78-0.80 mGy). Using Sn150 kV increased radiation dose (1.02 mGy) without improvement of CNR (92.4 vs 95.8). At Sn100-half CNR was decreased (61.4 vs 95.8). For adults, 140 and 150 kV revealed the lowest CTDIvol (2.68 and 2.67 mGy). The Sn150 kV scan delivered comparable CNR (54.4 vs 56.6), but a lower CTDIvol (2.08 mGy). At Sn100-half CNR was comparable to the 150 kV scan (58.1 vs 56.6). Unenhanced chest CT performed at 100 kV or 150 kV with tin filtration enables radiation dose reduction for the adult phantom, but not for the pediatric phantoms.

Benchmarking adult CT-dose levels to regional and national references using a dose-tracking software: a multicentre experience

ObjectivesTo benchmark CT-dose data for standard adult CT studies to regional and national reference levels using a dose-tracking system.MethodsData from five CT systems from three hospitals were collected over a 1- to 2.5-year period (2012–2014), using the same type of dose management system. Inclusion criteria were adult patients and standard CT-head, CT-abdomen-pelvis, CT-thorax, CT-lumbar spine, CT-pulmonary embolism, CT-cervical spine and CT-thorax-abdomen studies, with one helical scan. Volumetric CT-dose index (CTDIvol), dose length product (DLP) and scan length from 31,709 scans were analysed statistically.ResultsAfter dose optimisation CTDIvol and DLP values were below the national diagnostic reference levels (DRLs) for all CT studies and for all systems investigated. Mostly no significant differences were found between CTDIvol and DLP levels (p values ≥ 0.01) of CT studies performed on different scanners within the same hospital. Significant dose differences (p values < 0.01) were instead observed among hospitals for comparable CT studies. Dose level range and scan length differences for similar CT studies were revealed.ConclusionsDose-tracking systems help to reduce CT-dose levels below national DRLs. However, dose and protocol data comparison between and within hospitals has the potential to further reduce variability in dose data of standard adult CT studies.Key Points• Retrospective three-centre study on dose levels of standard adult CT procedures.• Dose-tracking systems help hospitals to stay below national dose reference levels.• Dose-tracking systems help to align CT dose levels between scanners within hospitals.• Benchmarking shows CT dose level variability for similar examinations in different hospitals.• Differences in dose level range/scan length for similar CT studies are revealed.

Individual radiation exposure from computed tomography: a survey of paediatric practice in French university hospitals, 2010-2013.

To describe computed tomography (CT) scanning parameters, volume CT dose index (CTDIvol) and dose-length product (DLP) in paediatric practice and compare them to current diagnostic reference levels (DRLs). The survey was conducted in radiology departments of six major university hospitals in France in 2010-2013. Data collection was automatised to extract and standardise information on scanning parameters from DICOM-header files. CTDIvol and DLP were estimated based on Monte Carlo transport simulation and computational reference phantoms. CTDIvol and DLP were derived for 4,300 studies, four age groups and 18 protocols. CTDIvol was lower in younger patients for non-head scans, but did not vary with age for routine head scans. Ratios of 95th to 5th percentile CTDIvol values were 2-4 for most body parts, but 5-7 for abdominal examinations and 4-14 for mediastinum CT with contrast, depending on age. The 75th percentile CTDIvol values were below the national DRLs for chest (all ages) and head and abdominal scans (≥10years). The results suggest the need for a better optimisation of scanning parameters for routine head scans and infrequent protocols with patient age, enhanced standardisation of practices across departments and revision of current DRLs for children. • CTDIvol varied little with age for routine head scans. • CTDIvol was lowest in youngest children for chest or abdominal scans. • Individual and inter-department variability warrant enhanced standardisation of practices. • Recent surveys support the need for revised diagnostic reference levels. • More attention should be given to specific protocols (sinuses, neck, spine, mediastinum).

Effects of different scout images on radiation dose in CT scanning using automatic tube current modulation

Objective To investigate the influence of different scout image on the radiation dose of head and chest spiral scanning in CT using automatic tube current modulation(ATCM). Methods CT scanning was performed on the head-neck and chest phantom with ATCM.Five different scout images through the five various positions that include anteroposterior(AP),posteroanterior(PA),lateral,AP, lateral,PA and lateral.The phantom was scanned three times for each position.Then each scout image was scanned by spiral technique once more. ROI in orbital center and C5 upper edge level were selected for Head and neck phantom, ROI in the apical and tracheal bifurcation level were selected for chest phantom. The contrast to noise ratio (CNR) was measured and recorded. The organ dose of eye lens and mammary glands were measured by thermoluminescent dosimeters (TLD) in every scanning(the average of 3 measurements), The cumulative value of scout image and spiral scanning were calculated.The volume CT dose index (CTDIvol) of each scan was recorded, and the cumulative value of CTDIvol was calculated. Results In the five scout images of the head-neck phantom mode, the maximum value of accumulated radiation dose of eye lens and CTDIvol appear on PA scout image(18.354 and 26.43 mGy respectively),while the minimum value appear on the lateral scout image(11.847 and 18.20 mGy respectively). In the chest phantom mode, the maximum value of the accumulated radiation dose of the mammary gland and CTDIvol emerge from the AP scout image(6.873 and 9.42 mGy respectively), while the minimum value of the mammary accumulated radiation dose appear on lateral scout image(4.592 mGy), the minimum value of CTDIvol appear on AP plus lateral scout images(3.94 mGy).The accumulated radiation dose of eye lens and CTDIvol value in PA scout image mode were 54.9%(6.507/11.847) and 45.2%(8.23/18.20) higher than those of the lateral scout image mode. The accumulated radiation dose of mammary gland and CTDIvol value in AP scout image mode were 42.5%(2.051/4.822) and 136.7% (5.44/3.98) higher than that of PA plus lateral scout images mode. In the head-neck phantom mode, the CNR value of orbital center and C5 upper edge level were 102.55 to 115.89, 161.01 to 204.52 respectively. In the chest phantom mode, the CNR value of the apical and tracheal bifurcation level were 82.74 to 164.00, 83.12 to 121.49 respectively. Conclusion The choice of the scout image had significant effect on the radiation dose and the sensitive organ dose in CT. Key words: Tomography,X-ray computed; Radiation dosage; Scout image

Evaluation of a commercial Model Based Iterative reconstruction algorithm in computed tomography

IntroductionIterative reconstruction algorithms have been introduced in clinical practice to obtain dose reduction without compromising the diagnostic performance. PurposeTo investigate the commercial Model Based IMR algorithm by means of patient dose and image quality, with standard Fourier and alternative metrics. Materials and methodsA Catphan phantom, a commercial density phantom and a cylindrical water filled phantom were scanned both varying CTDIvol and reconstruction thickness. Images were then reconstructed with Filtered Back Projection and both statistical (iDose) and Model Based (IMR) Iterative reconstruction algorithms.Spatial resolution was evaluated with Modulation Transfer Function and Target Transfer Function. Noise reduction was investigated with Standard Deviation. Furthermore, its behaviour was analysed with 3D and 2D Noise Power Spectrum. Blur and Low Contrast Detectability were investigated.Patient dose indexes were collected and analysed. ResultsAll results, related to image quality, have been compared to FBP standard reconstructions.Model Based IMR significantly improves Modulation Transfer Function with an increase between 12% and 64%. Target Transfer Function curves confirm this trend for high density objects, while Blur presents a sharpness reduction for low density details.Model Based IMR underlines a noise reduction between 44% and 66% and a variation in noise power spectrum behaviour. Low Contrast Detectability curves underline an averaged improvement of 35–45%; these results are compatible with an achievable reduction of 50% of CTDIvol.A dose reduction between 25% and 35% is confirmed by median values of CTDIvol. ConclusionIMR produces an improvement in image quality and dose reduction.

Do we need 3D tube current modulation information for accurate organ dosimetry in chest CT? Protocols dose comparisons.

To compare the lung and breast dose associated with three chest protocols: standard, organ-based tube current modulation (OBTCM) and fast-speed scanning; and to estimate the error associated with organ dose when modelling the longitudinal (z-) TCM versus the 3D-TCM in Monte Carlo simulations (MC) for these three protocols. Five adult and three paediatric cadavers with different BMI were scanned. The CTDIvol of the OBTCM and the fast-speed protocols were matched to the patient-specific CTDIvol of the standard protocol. Lung and breast doses were estimated using MC with both z- and 3D-TCM simulated and compared between protocols. The fast-speed scanning protocol delivered the highest doses. A slight reduction for breast dose (up to 5.1%) was observed for two of the three female cadavers with the OBTCM in comparison to the standard. For both adult and paediatric, the implementation of the z-TCM data only for organ dose estimation resulted in 10.0% accuracy for the standard and fast-speed protocols, while relative dose differences were up to 15.3% for the OBTCM protocol. At identical CTDIvol values, the standard protocol delivered the lowest overall doses. Only for the OBTCM protocol is the 3D-TCM needed if an accurate (<10.0%) organ dosimetry is desired. • The z-TCM information is sufficient for accurate dosimetry for standard protocols. • The z-TCM information is sufficient for accurate dosimetry for fast-speed scanning protocols. • For organ-based TCM schemes, the 3D-TCM information is necessary for accurate dosimetry. • At identical CTDI vol , the fast-speed scanning protocol delivered the highest doses. • Lung dose was higher in XCare than standard protocol at identical CTDI vol .

A “quality-control-based correction method” for displayed dose indices on CT scanner consoles in patient dose surveys

PurposeA new quality-control-based (QC-based) method is introduced to obtain correction factors to be applied to displayed patient dose indices (CTDIVol and DLP) on CT scanner consoles to verify improvement of dose surveys for diagnostic reference levels (DRLs) determination. MethodAn available data-base of QC documents and reports of 57 CT scanners in Tehran, Iran was used to estimate CTDIVol, DLP and relevant correction factors for three CT examination types including head, chest and abdomen/pelvis. The correction factor is the ratio of QC-based estimated dose to displayed dose. A dose survey was performed by applying on-site “data collection method” and correction factors obtained in order to select CT scanners in three modes for determination of CT DRLs by inclusion of: (a) all CT scanners before displayed dose indices were corrected (57), (b) only CT scanners calibrated by QC experts (41) and (c) all CT scanners after displayed dose indices were corrected (57). ResultsFor the 41 CT scanners, correction factors of three examination types obtained in this study are within the acceptance tolerance of IAEA HHS-19. The correction factors range from 0.45 to 1.7 (average of 3 examinations) which is due to the change in the calibrated value of CTDIVol over extended time. The DRL differences in three modes are within ±1.0% for CTDIVol and ±12.4% for DLP. ConclusionsThe “QC-based correction method” applied to mode (c) has improved the DRLs obtained by other two modes. This method is a strong alternative to “direct dose measurement” with simplicity and cost effectiveness.

Follow-Up Study on Fetal CT Radiation Dose in Japan: Validating the Decrease in Radiation Dose.

In 2011, we collected data on fetal CT radiation dose to determine the diagnostic reference level (DRL); however, continuous evaluation of the DRL is necessary. The hypothesis of this study is that the fetal CT radiation dose has decreased, and we predict a widespread use of iterative reconstruction (IR). We also predict that the national decrease in exposure is because of the DRL reported as a result of the previous national study. Various testing protocols from each site were summarized as part of the study results. The minimum, one-fourth (25th percentile), median, three-fourths (75th percentile), and maximum values were obtained for volume CT dose index (CTDIvol), dose-length product (DLP), and scan length of 120 fetal CT examinations. The trends for IR usage and tube voltage were also investigated. Compared to the results of the 2011 study (n = 119), the minimum, 25th percentile, median, and 75th percentile values for CTDIvol and DLP have decreased for the tabulated results in 2015 (n = 120). The 75th percentile value for CTDIvol was 4.9 mGy, which is 43% of the previous value. IR was used in 70% of the sites. The radiation dose was significantly lower among groups that used IR. Four years passed between our initial survey on DRL and the present follow-up survey, and it appears that the previous report sufficiently fulfilled its objective and role in contributing to the decrease in DRL observed in this follow-up study.

Radiation dose associated with common computed tomography examination

ObjectiveTo survey computed tomography (CT) radiation dose associated with non-contrast spiral Multislice CT examination in our institute. MethodsDetailed parameters for 362 consecutive examinations, including the patient weight, height, volume CT dose index (CTDIvol), scan length, and dose length product (DLP) were recorded from the dose report. Effectivedose(E) was estimated for each patient. The differences between E doses were statistically analyzed using SSPS. ResultsPatients body mass index (BMI) was 13.4 to 51.42 (average BMI 29.5kg/m). Patients dose data (1 scan phase for each patient) from dose information: the median value of DLP was 586.45mGycm (83.30–1179.70mGycm), median value of CTDIvol was 12.07 (2.20–23.9mGy), median value of mAs used was 186.50 (34–334mAs). Effective dose range was (1.1–16.5mSv) according to international commission of radiological protection (ICRP) 103 and according to ICRP60 the range was (1.3–18.93mSv). Median value of frequent CT examinations for the same patient was 2 (min 1 scan/year & max 11 scan/year). CT dose variation was highly significant (p value <0.01) depending on high variation on mAs with (r=0.98). CT dose was moderate depending on BMI (r=0.55). ConclusionThere was statistically highly significant variation in effective radiation doses associated with non-contrast CT scan of abdomen and pelvis. The reason for this variation must be avoided.

Attenuation-based kV pair selection in dual source dual energy computed tomography angiography of the chest: impact on radiation dose and image quality

The purpose of this study was to evaluate the impact of attenuation-based kilovoltage (kV) pair selection in dual source dual energy (DSDE)-pulmonary embolism (PE) protocol examinations on radiation dose savings and image quality. A prospective study was carried out on 118 patients with suspected PE. In patients in whom attenuation-based kV pair selection selected the 80/140Sn kV pair, the pre-scan 100/140Sn CTDIvol (computed tomography dose index volume) values were compared with the pre-scan 80/140Sn CTDIvol values. Subjective and objective image quality parameters were assessed. Attenuation-based kV pair selection switched to the 80/140Sn kV pair ("switched" cohort) in 63 out of 118 patients (53%). The mean 100/140Sn pre-scan CTDIvol was 8.8mGy, while the mean 80/140Sn pre-scan CTDIvol was 7.5mGy. The average estimated dose reduction for the "switched" cohort was 1.3mGy (95% CI 1.2, 1.4; p < 0.001), representing a 15% reduction in dose. After adjusting for patient weight, mean attenuation was significantly higher in the "switched" vs. "non-switched" cohorts in all five pulmonary arteries and in all lobes on iodine maps. This study demonstrates that attenuation-based kV pair selection in DSDE examination is feasible and can offer radiation dose reduction without compromising image quality. • Attenuation-based kV pair selection in dual energy examination is feasible. • It can offer radiation dose reduction to approximately 50% of patients. • Approximate 15% reduction in radiation dose was achieved using this technique. • The image quality is not compromised by use of attenuation-based kV pair selection.

Estimating cancer induction risk from abdominopelvic scanning with 6- and 16-slice computed tomography

Purpose: The biological effects of ionizing radiation (BEIR VII) report estimates that the risk of getting cancer from radiation is increased by about a third from current regulation risk levels. The propose of this study was to estimate cancer induction risk from abdominopelvic computed tomography (CT) scanning of adult patients using 6- and 16-slice CT scanners.Materials and methods: A cross-sectional study on 200 patients with abdominopelvic CT scan in 6- and 16-slice scanners was conducted. The dose-length product (DLP) and volume CT Dose Index (CTDIvol) values from the scanners as well as the effective dose values from the ImPACT CT patient dosimetry calculator with the biological effects of ionizing radiation (BEIR VII) method were used to estimate the cancer induction risk.Results: The mean (and standard deviation) values of CTDIvol and DLP were 6.9 (±1.07) mGy and 306.44 (± 60.57) mGy.cm for 6-slice, and 5.19 (±0.91) mGy and 219.7 (±49.31) mGy.cm for 16-slice scanner, respectively. The range of effective dose in the 6-slice scanner was 2.61–8.15 mSv and, in the 16-slice scanner, it was 1.47–4.72 mSv. The mean and standard deviation values of total cancer induction risk in abdominopelvic examinations were 0.136 ± 0.059% for men and 0.135 ± 0.063% for women in the 6-slice CT scanner. The values were 0.126 ± 0.051% for men and 0.127 ± 0.056% for women in the 16-slice scanner.Conclusions: The cancer induction risk of abdominopelvic scanning was noticeable. Therefore, radiation dose should be minimized by optimizing the protocols and applying appropriate methods.

Optimization of Dose Parameters to Patients Undergoing CT Scan Using Four Different CT Scanners with International Guidelines

Although the use of CT in medical diagnosis delivers radiation doses to patients that are higher than those from other radiological procedures, lack of proper optimized protocols could be an additional source of increased dose in developing countries. The aims of this study is to determine the variations of doses to patients undergoing CT scan using four different CT scanners with different CT scanning protocols for the purposes of optimizations and to compare with other available international standard and guidelines. The method involve the use of patients scanning protocol and image data to estimate patient body regional doses with four common CT examinations. These were obtained from four CT units/hospitals in Ghana. A large variation of mean body regional doses among different CT scanners were observed for similar CT examinations. These variations largely originated from different CT scanning protocols used, with different CT scanner type. The measured CTDIVOL with GE Lightspeed VCT 64 scanner for head, hest, abdomen and pelvis were 7.7mGy, 12.5 mGy, 14.4 mGy, and 12.9 mGy, respectively. Similarly, Philip 16 scanner recorded 6.6mGy, 13.1mGy, 14.8mGy, and 14.5mGy respectively. Furthermore, Siemen Emotion 16 scanner recorded 5.9mGy, 14.2mGy, 16.8mGy and 12.0mGy respectively. While, Toshiba Aquilion one scanner had CTDIVOL value which varies as 7.2mGy, 13.4mGy, 15.2mGy and 13.5mGy respectively. In conclusion the values were mostly lower than the values of CTDI and DLP as reported in literature for EC, IAEA, ICRP, ACR and AAPM Guidelines.

Iterative Reconstruction as a Method for Optimisation of Computed Tomography Procedures

SummaryBackgroundComputed tomography (CT) is still commonly regarded as a method that causes a high radiation exposure. For that reason, producers intensively try to find new solutions for dose reduction while maintaining a high diagnostic value of images. One of the recent strategies focuses on CT image reconstruction. Iterative reconstruction (IR) is an alternative for filtered back projection (FBP) that is commonly used today.The aim of the article is to demonstrate and compare the effects of two IR algorithms on dose value and image details.Material/MethodsInvestigations were performed on two 128 multi-detector (MDCT) CT scanners: – iCT (Philips Healthcare with iDose4); – Definitions AS+ (Siemens Medical Solutions with SAFIRE system).The measurements involved: – image quality indicators for the CATPHAN 600 phantom; – dosimetric indicators of exposure (DLP i CTDIvol).ResultsThe signal-to-noise ratios (SNR) in the images reconstructed with IR and FBP were analysed, and the SNR(IR)/SNR(FBP) ratios were calculated and correlated with CTDIvol values. The effects of IR and FBP algorithms on low-contrast resolution were also compared in relation to CTDIvol values. The smallest diameter of supra-slice objects in the Catphan phantom were taken into consideration.Both iterative algorithms definitely improved the visibility of low-contrast objects in comparison to a standard algorithm (FBP) with similar exposure parameters.These algorithms allow an 80% reduction of the CTDIvol value while maintaining an acceptable visibility of low-contrast objects. However, the results obtained with each of the studied iterative algorithms differ.

A Study to Determine Whether the Volume-Weighted Computed Tomography Dose Index Gives Reasonable Estimates of Organ Doses for Thai Patients Undergoing Abdomen and Pelvis Computed Tomography Examinations.

Introduction:Values for the CTDIvol, which is displayed on scanner consoles, give doses relative to a phantom much larger than most Thai patients, and the CTDIvol does not take account of differences in patient size, which affect organ doses.Objective:The purpose of this study was to evaluate relationships for size specific dose estimate (SSDE) and volume weighted computed tomography (CT) dose index (CTDIvol) with patient size for CT scanners operating under automatic tube current modulation (ATCM).Methods:Retrospective data from 244 patients who had undergone abdomen and pelvis examination on GE and Siemens CT scanners were included in this study. The combination of anteroposterior (AP) and lateral dimensions at the level of the first lumbar vertebra (L1) was used to represent patient size. Image noise within the liver was measured, and values of the absorbed dose for organs covered by the primary beam such as the liver, stomach and kidney were calculated using methods described in the literature. Values of CTDIvol were recorded and SSDE calculated according to the American Association of Physics in Medicine (AAPM) Report No.204. Linear regression models were used to evaluate the relationship between SSDE, CTDIvol, image noise and patient size.Results:SSDE is 20%-50% larger than the CTDIvol, with values for larger patients being more representative. Both the CTDIvol and image noise decreased with patient size for Siemens scanners, but the decline in SSDE was less significant. For the GE scanner, the CTDIvol was a factor of 3-4 lower in small patients compared to larger ones, while the SSDE only decreased by a factor of two. Noise actually decreased slightly with patient size.Conclusion:Values of SSDE were similar to the doses calculated for the liver, stomach and kidney, which are covered by the primary beam, confirming that it provides a good estimate of organ-absorbed dose.

Comparison of Measured Values of CTDI and DPL with Standard Reference values of Different CT Scanners for dose Management

The study is based on estimate of CTDI and DLP values for patients' dose optimization procedures. Technical parameters were obtained for three groups of randomly selected patients undergoing abdominal CT examinations of 320 patients of age 20-80 years. The measured values were obtained on image data and the standard reference values of various machines were obtained from service manual as part of QC/QA and the recommended values from ICRP publication 103. The mean CTDI and DLP parameters were; 6.33mGy and 936.25mGy respectively. Furthermore, the mean recorded values of CTDIVOL values were well within ICRP recommendation when the protocol was completed in one scan. On the other hand, in the case of multiscan the total CTDIVol was higher than the ICRP recommendations. While the mean DLP values were higher than the recommended value of 780 mGy-cm by ICRP publication 103. Finally, approximately 37% of the total varied CTDI and DLP values were higher than the recommended dose by ICRP publication 103.

小児腹部CT 検査における自動露出制御の一手法―年齢および腹部サイズを考慮した標準偏差(SD)値および管電流値の設定法―

We aimed to apply the pediatric abdominal CT protocol of Donnelly et al. in the United States to the pediatric abdominal CT-AEC. Examining CT images of 100 children, we found that the sectional area of the hepatic portal region (y) was strongly correlated with the body weight (x) as follows: y=7.14x + 84.39 (correlation coefficient=0.9574). We scanned an elliptical cone phantom that simulates the human body using a pediatric abdominal CT scanning method of Donnelly et al. in, and measured SD values. We further scanned the same phantom under the settings for adult CT-AEC scan and obtained the relationship between the sectional areas (y) and the SD values. Using these results, we obtained the following preset noise factors for CT-AEC at each body weight range: 6.90 at 4.5-8.9 kg, 8.40 at 9.0-17.9 kg, 8.68 at 18.0-26.9 kg, 9.89 at 27.0-35.9 kg, 12.22 at 36.0-45.0 kg, 13.52 at 45.1-70.0 kg, 15.29 at more than 70 kg. From the relation between age, weight and the distance of liver and tuber ischiadicum of 500 children, we obtained the CTDIvol values and DLP values under the scanning protocol of Donnelly et al. Almost all of DRL from these values turned out to be smaller than the DRL data of IAEA and various countries. Thus, by setting the maximum current values of CT-AEC to be the Donnelly et al.'s age-wise current values, and using our weight-wise noise factors, we think we can perform pediatric abdominal CT-AEC scans that are consistent with the same radiation safety and the image quality as those proposed by Donnelly et al.

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.

43. Evaluation of abdominal CT protocols using a mathematical model observer

Introduction In the last decade, technological breakthroughs in CT allow an improvement of optimization process. With the introduction of iterative algorithms, an adjustment of clinical protocols has been achieved. Classical metrics were become insufficient to assess image quality of clinical protocols. An objective method, based on a clinical task has to be used. The goal of this study is to evaluate abdominal protocols on two newest CT, using a mathematical model observer. We can also underline the impact of a fully model-based iterative reconstruction algorithm when dealing with low-contrast detectability tasks. Method An anthropomorphic abdominal phantom (equivalent o 24 cm) with 8 and 5 mm low contrast targets (20 HU) was scanned on two CT systems: Revolution CT and CT750 HD, GE Healthcare. Peripheral rings (2.5 and 5 cm in thickness) were added to simulate different patient sizes. The phantom was scanned 15 times using a routine abdominal protocol with a slice thickness of 2.5 mm (0.625 mm for VEO® (MBIR algorithm); avoiding any MPR processing). On both units, the noise index was adjusted with the phantom’s size (i.e. 20, 26 and 32 HU). Images were reconstructed using FBP, ASIR50% and VEO® for CT750HD and ASIR-V at 0% and 50% for Revolution CT. To assess low-contrast detectability, a Channelized Hotelling Observer (CHO; 10 DDOG channels) was used. The area under the curve (AUC) index was chosen as figure of merit (FOM). Results Scanning the phantom on the CT750 HD, no significant difference appeared between FBP and ASIR50%. For the largest phantom size, a significant increase of 6% in low contrast detectability was recorded on 5mm targets using VEO (with a longitudinal spatial resolution four times higher) compared to ASIR50%. Concerning the Revolution CT no difference in detectability was noted between ASIR-V at 0% and 50%. Comparing the two CT systems the displayed CTDIvol values for the Revolution CT were systematically lower than for the CT750HD (reaching 40% for the thickest phantom). Low contrast detectability performances were comparable between ASIR-V50% and VEO®. Conclusion Dealing with CT750HD, despite a significantly longer reconstruction time, the use of VEO® on large patients is of particular interest since it yields to high image quality performances. Lower CTDIvol values are required with the Revolution CT than CT750HD to produce comparable low contrast detectability levels.

Patient Size-Specific Analysis of Dose Indexes From CT Lung Cancer Screening.

The U.S. Centers for Medicare & Medicaid Services (CMS) recently approved the use of low-dose CT for lung cancer screening and described volumetric CT dose index (CTDIvol) requirements. These were based on the National Lung Screening Trial, which used only fixed-tube-current techniques. The aim of this study was to evaluate dose index data from a lung cancer screening program using automatic exposure control (AEC) techniques to ensure compliance with requirements and to correlate dose index values with patient size. CTDIvol, dose-length product (DLP), and body mass index (BMI) data were collected for 563 lung cancer screening examinations performed with AEC between January 1, 2014, through August 31, 2015. CTDIvol and DLP were analyzed according to the patient's BMI classification. Results were compared with the CMS requirement that the CTDIvol for a standard-sized patient (height, 170 cm; weight, 70 kg) be 3.0 mGy or less, with adjustments for patients of different sizes. For a subset of patients, the average water-equivalent diameter and size-specific dose estimate were estimated. The average CTDIvol for a standard-sized patient was 1.8 mGy, which meets CMS requirements. CTDIvol values were lower for smaller patients and higher for larger patients. Overall, the mean CTDIvol and DLP were 2.1 mGy and 74 mGy⋅cm, respectively. The size-specific dose estimate for the average water-equivalent diameter (27.5 cm) of the patient subset was 2.6 mGy. The screening protocols using AEC resulted in CTDIvol values that were compliant with CMS requirements. CTDIvol values greater than 3.0 mGy were only observed for overweight or obese patients.

ESTIMATION OF CARDIAC CT ANGIOGRAPHY RADIATION DOSE TOWARD THE ESTABLISHMENT OF NATIONAL DIAGNOSTIC REFERENCE LEVEL FOR CCTA IN IRAN.

In recent years, with the introduction of 64-slice CT and dual-source CT technology, coronary CT angiography (CCTA) has emerged as a useful diagnostic imaging modality as a non-invasive assessment of coronary heart disease.CT produces a larger radiation dose than other imaging tests and cardiac CT involves higher radiation dose with the advances in the spatial and temporal resolution. The aims of this study are patient dose assessment and establishment of national diagnostic reference level for CCTA in Iran.A questionnaire was sent to CCTA centers. Data for patient and CT protocols were obtained. The volumetric CT dose index (CTDIvol), dose length product (DLP) and total DLP were considered in the 32 cm standard body phantom. Calculation of estimated effective dose (ED) was obtained by multiplying the DLP by a conversion factor [k=0.014 mSv (mGy·cm)-1]. Mean value of CTDIvol and DLP for CCTA was 50 mGy and 825 mGy·cm. The third quartile (75th) of the distribution of mean CTDIvol (66.54 mGy) and DLP (1073 mGy·cm) values was expressed as the diagnostic reference level (DRL) for CCTA in Iran. The median of ED was 10.26 mSv and interquartile range of ED was 7.08-15.03 mSv. A large variety in CTDIvol and DLP among CT scanner and different sites due to variability in CT parameter is noted. It seems that training could help to reduce patient's dose.