Volumetric CT Dose Index Research Articles

Submillisievert chest dual energy computed tomography: a pilot study.

To assess if diagnostic dual energy CT (DECT)of the chest can be achieved at submillisievert (sub-mSv)doses. Our IRB-approved prospective study included 20 patients who were scanned on dual-source multidectorCT(MDCT). All patients gave written informed consent for acquisition of additional image series at reduced radiation dose on a dual-source MDCT (80/140kV) within 10 s after the standard of care acquisition. Dose reduction was achieved by reducing the quality reference milliampere-second, with combined angular exposure control. Four readers, blinded to all clinical data, evaluated the image sets. Image noise, signal-to-noise and contrast-to-noise ratio were assessed. Volumetric CT dose index (CTDIvol), doselength product (DLP), size specific dose estimate, and effective dose were also recorded. The mean age and body mass index of the patients were 71 years ± 9 and24 kgm-2 ± 3, respectively. Although images became noisier, overall image quality and image sharpness on blended images were considered good or excellent in all cases (20/20). All findings made on the reduced dose images presented with good demarcation. The intraobserver and interobserver agreements were κ = 0.83 and 0.73, respectively. Mean CTDIvol, size specific dose estimate, DLP and effective dose for reduced dose DECT were: 1.3 ± 0.2 mGy, 1.8 ± 0.2 mGy, 51 ± 9.9 mGy.cm and 0.7 ± 0.1 mSv, respectively. Routine chest DECT can be performed at sub-mSv doses with good image quality and without loss of relevant diagnostic information. Advances in knowledge: (1) Contrast-enhanced DECT of the chest can be performed at sub-mSv doses, down to mean CTDIvol 1.3 mGy and DLP 51 mGy.cm in patients with body mass index <31 kgm-2. (2) To our knowledge, this is the first time that sub-mSv doses have been successfully applied in a patient study using a dual source DECT scanner.

2. Optimization of CT-scan acquisition parameters and choice of the breathing amplitude margins for non-synchronized freebreathing technique

Introduction Spirometry allows an indirect control of moving targets in breathing hold (BH) or their monitoring in freebreathing (FB). FB technique requires a synchronization between the CT-scan acquisition (4D-CT) and the breathing cycles. This technique is not included in every system. The Slow-CT scan is a possible alternative to optimize the monitoring of moving targets. The purpose of this study is to evaluate the feasibility of non-synchronized FB using Slow-CT scan in terms of image quality, breathing amplitude and respiratory rate. Methods Standard-CT, Slow-CT and 4D-CT acquisitions are made with a Siemens Somatom Scope Power scan, with a voltage of 130 kV and modulated intensity (CARE Dose 4D®). UH, low contrasts, slice thickness and spatial resolution are analyzed on Catphan® 504. The moving target, a lung equivalent cylindrical insert including a 3 cm diameter sphere, is set in motion by Quasar™ Respiratory Motion. The breathing cycles are created by Trace Generator. Reconstruction performances are evaluated for breaths from 10 to 30 breaths per minute (BPM) and an amplitude of 2 cm. The radiation dose is estimated by the volumetric computed tomography dose index (CTDI). The choice of the FB amplitude margins is made from a retrospective analysis of 15 patients treated in BH conditions. The image quality of the 4D-CT Average and Slow-CT sequences is examined on patients. Results Noise is reduced up to 30% in Slow-CT (σ = 3.0 UH) in comparison with 4D-CT Average (σ = 4.9 UH). A systematic error of +0.35 mm of slice thickness reconstruction occurs for 4D-CT Average. The low contrasts score (visual) increases in 4D-CT Average. In 4D-CT Average (>50 s), the amplitude reconstruction is faithful (49.8 mm instead of 50.0 mm in theory) with the 10 BPM/2 cm amplitude couple. In Slow-CT (>60 s), for BPM between 12 and 18, the mean reconstructed amplitude is 47 mm. It is 41 mm for BPM ⩽10 or ⩾30. The amplitude reconstruction is optimized for 15 BPM (49.5 mm). In Standard-CT (6–20 s), it appears distortions in the 3 reconstruction planes and relatives errors up to 60 %. In Slow-CT and 4D-CT, the mean CTDI are respectively 16.4 mGy and 15.2 mGy. The optimized Slow-CT acquisition parameters are 130 kV, collimation of 16x0.6 mm, 2 mm reconstructed slice, pitch of 0.4, rotation time of 1.5 s and a ratio (Acquisition time (s))/BPM⩾4. The retrospective analysis of patients shows a maximum interfraction amplitude difference of 100 mL. The spirometer calibration includes a 60 mL uncertainty (2% of 3 L). A margin of 100 mL is chosen as upper limit (inhalation); the baseline, allowing an automatic stabilization of the system display, is the lower limit (exhalation). On clinical images, Slow-CT shows a motion blur reduction (heart, mediastinum) and a noise reduction in a range of 10–15%. Conclusions The Slow-CT sequence offers an alternative to 4D-CT for incompatible systems. Parameters such as collimation, pitch, rotation time and the ratio (Acquisition time (s))/BPM⩾4 must be adapted. CTDI are similar for Slow-CT and 4D-CT. Margins optimization and further clinical cases are ongoing. A study about dose optimization while obtaining the same amount of signal will be carried out using different level of noise reduction algorithm.

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.

Evaluation of Kidney Stones with Reduced-Radiation Dose CT: Progress from 2011-2012 to 2015-2016-Not There Yet.

Purpose To determine if the use of reduced-dose computed tomography (CT) for evaluation of kidney stones increased in 2015-2016 compared with that in 2011-2012, to determine variability in radiation exposure according to facility for this indication, and to establish a current average radiation dose for CT evaluation for kidney stones by querying a national dose registry. Materials and Methods This cross-sectional study was exempt from institutional review board approval. Data were obtained from the American College of Radiology dose registry for CT examinations submitted from July 2015 to June 2016. Study descriptors consistent with single-phase unenhanced CT for evaluation of kidney stones and associated RadLex® Playbook identifiers (RPIDs) were retrospectively identified. Facilities actively submitting data on kidney stone-specific CT examinations were included. Dose metrics including volumetric CT dose index, dose-length product, and size-specific dose estimate, when available, were reported, and a random effects model was run to account for clustering of CT examinations at facilities. A z-ratio was calculated to test for a significant difference between the proportion of reduced-radiation dose CT examinations (defined as those with a dose-length product of 200 mGy · cm or less) performed in 2015-2016 and the proportion performed in 2011-2012. Results Three hundred four study descriptors for kidney stone CT corresponding to data from 328 facilities that submitted 105 334 kidney stone CT examinations were identified. Reduced-dose CT examinations accounted for 8040 of 105 334 (7.6%) CT examinations, a 5.6% increase from the 1010 of 49 903 (2%) examinations in 2011-2012 (P < .001). Mean overall dose-length product was 689 mGy · cm (95% confidence interval: 667, 712), decreased from the mean of 746 mGy · cm observed in 2011-2012. Median facility dose-length product varied up to sevenfold, from less than 200 mGy · cm to greater than 1600 mGy · cm. Conclusion Use of reduced-radiation dose CT for evaluation of kidney stones has increased since 2011-2012, but remains low; variability of radiation dose according to facility continues to be wide. National mean CT radiation exposure for evaluation of renal colic during 2015-2016 decreased relative to 2011-2012 values, but remained well above what is reasonably achievable. © RSNA, 2017.

Assessment of coronary artery by prospective ECG-triggered 256 multi-slice CT on children with congenital heart disease.

This study aims to investigate the imaging quality and radiation dose of prospective ECG-triggered 256 multi-slice computer tomography (MSCT) in accessing the coronary artery (CA) in children. Coronary arteries of 149 children were evaluated using prospective ECG-triggered 256 MSCT with the same system settings. A four-point scoring system was applied to study the capability of MSCT in detecting CA in these patients. Signal, noise and contrast-to-noise ratios (CNR) were analyzed to investigate the association of image quality with age. Then, volumetric CT dose index (CTDIvol), dose-length product (DLP), and effective dose (ED) were utilized to study the association of radiation dose with age. The detection rate for original, proximal, middle, distal and the 11 segments of CA was 100, 97, 92, 81 and 92%, respectively; and there was no influence on age during the detection (all, P < 0.05). A negative correlation was found between ED and age (r = -0.664, P < 0.001). Significantly larger EDs were found in younger patients (age: <3 years; 1.2 ± 0.5 and 0.6 ± 0.2mSv; P < 0.001), while higher DLPs were found in elder patients, although no correlation was found between ages versus DLP (r = 0.092, P = 0.262). Prospective ECG-triggered 256 MSCT has considerable performance for the evaluation of CA in children. However, great caution is needed for children under the age of three in the selection of this examination. Furthermore, the tube current could be further reduced for the examination of children ≥8 years.

A prospective national survey of coronary CT angiography radiation doses in the United Kingdom

BackgroundLittle real-world radiation dose data exist for the majority of cardiovascular CT. Some data have been published for coronary CT angiography (coronary CTA) specifically, but they invariably arise from high-volume centres with access to the most recent technology. ObjectiveThe aim of this study was to document real-world radiation doses for coronary CTA in the United Kingdom, and to establish their relationship to clinical protocol selection, acquisition heart rate, and scanner technology. MethodsA dose survey questionnaire was distributed to members of the British Society of Cardiovascular Imaging and other UK cardiac CT units. All participating centres collected data for consecutive coronary CTA cases over one month. The survey captured information about the exam conducted, patient demographics, pre-scan details such as beta-blocker administration, acquisition heart rate and scan technique, and post-scan dose indicators – series volumetric CT dose index (CTDIvol), series dose-length product (DLP), and exam DLP. ResultsFifty centres provided data on a total of 1341 coronary CTA exams. Twenty-nine centres (58%) performed at least 20 coronary CTA scans in the collection period. The median BMI, acquisition heart rate and exam DLP were 28 kg/m2, 60 bpm and 209 mGycm respectively. The corresponding effective dose was estimated as 5.9 mSv using a conversion factor of 0.028 mSv/mGycm. There was no statistically significant difference in radiation dose between low and high-volume centres. Median exam DLP increased with the acquisition heart rate due to the selection of wider temporal windows. The highest exam DLPs were obtained on the older scanner technology. ConclusionThis study provides baseline data for benchmarking practice, optimizing radiation dose and improving service quality locally.

Optimizing radiation exposure in screening of body packing: image quality and diagnostic acceptability of an 80 kVp protocol with automated tube current modulation.

The aim of this study was to evaluate the objective and subjective image quality of a novel computed tomography (CT) protocol with reduced radiation dose for body packing with 80 kVp and automated tube current modulation (ATCM) compared to a standard body packing CT protocol. 80 individuals who were examined between March 2012 and July 2015 in suspicion of ingested drug packets were retrospectively included in this study. Thirty-one CT examinations were performed using ATCM and a fixed tube voltage of 80 kVp (group A). Forty-nine CT examinations were performed using a standard protocol with a tube voltage of 120 kVp and a fixed tube current time product of 40 mAs (group B). Subjective and objective image quality and visibility of drug packets were assessed. Radiation exposure of both protocols was compared. Contrast-to-noise ratio (group A: 0.56±0.36; group B: 1.13±0.91) and Signal-to-noise ratio (group A: 3.69±0.98; group B: 7.08±2.67) were significantly lower for group A compared to group B (p<0.001). Subjectively, image quality was decreased for group A compared to group B (2.5±0.8 vs. 1.2±0.4; p<0.001). Attenuation of body packets was higher with the new protocol (group A: 362.2±70.3 Hounsfield Units (HU); group B: 210.6±60.2 HU; p=0.005). Volumetric Computed Tomography Dose Index (CTDIvol) and Dose Length Product (DLP) were significantly lower in group A (CTDIvol 2.2±0.9mGy, DLP 105.7±52.3 mGycm) as compared to group B (CTDIvol 2.7±0.1mGy, DLP 126.0±9.7 mGycm, p=0.002 and p=0.01). The novel 80 kVp CT protocol with ATCM leads to a significant dose reduction compared to a standard CT body packing protocol. The novel protocol led to a diagnostic image quality and cocaine body packets were reliably detected due to the high attenuation.

Development of a chest phantom for testing in Computed Tomography scans

To optimize the process of Computed Tomography (CT) scans, it is important to know the dose distribution in order to vary the acquisition parameters. The aim of this study is to evaluate the variation of CT Dose Index (CTDI) in chest scans, by using two chest phantoms. In this study it was used a cylindrical chest phantom made in polymethylmethacrylate (PMMA) and a second phantom was developed in PMMA with the same volume and an oblong shape, based on the dimensions of an adult human chest. The two phantoms have five openings, one central and four peripheral out of phase 90°, which allow placing a pencil ionizing chamber in five positions. In a CT scanner GE, Discovery model with 64 channels, the central slice of the two phantoms were irradiated successively to obtain air kerma in PMMA measurements using the pencil chamber. From the measurements obtained in these five positions in the phantoms, it was possible to obtain the volumetric CTDI for both chest phantoms. By comparison of the results, it was demonstrated that the oblong phantom, with a similar human chest shape, have received higher doses, mainly in the anterior, posterior and central region. The volumetric CTDI indicates a value 5.1% higher for the oblong phantom.

Measured Head CT/CTA Skin Dose and Intensive Care Unit Patient Cumulative Exposure.

Estimates of cumulative CT/CTA radiation dose based on volumetric CT dose index have raised concern that neurological intensive care unit patient exposures may reach thresholds for deterministic skin injury. Because the accuracy of volumetric CT dose index for this purpose in unknown, we set out to directly measure head CT and CTA peak skin dose, assess the relationship of volumetric CT dose index to measured peak skin dose, and determine whether multiple CT/CTA exposures in typical patients in the neurological intensive care unit produce cumulative doses approaching or exceeding single-dose deterministic thresholds for skin injury. In a prospective study from 2011-2013, nanoDot optical stimulated luminescence dosimeters were used to measure head CT/CTA peak skin dose in 52 patients (28 female, 24 male; mean age, 63 years) divided equally between 2 CT scanners. Volumetric CT dose index and dose-length product were recorded for each examination. Peak skin dose was also measured on an acrylic skull phantom in each scanner. A 2-tailed, unpaired t test was used to compare mean patient skin doses between the 2 scanners. The measured peak skin doses were then used to calculate cumulative peak skin dose in 4 typical patients in intensive care units who received multiple CT/CTA scans. Head CT/CTA peak skin dose agreed between scanners in patients and phantoms: (scanner 1 CT/CTA: patients, 39.2 ± 3.7 mGy and 98.9 ± 5.3 mGy, respectively, versus phantom, 40.0 mGy and 105.4 mGy, respectively; scanner 2 CT/CTA: patients, 42.9 ± 9.4 mGy and 98.8 ± 7.4 mGy, respectively, versus phantom, 37.6 mGy and 95.2 mGy, respectively). Volumetric CT dose index overestimated peak skin dose by a factor of 1.4-1.9 depending on examination and CT scanner. Cumulative doses in 4 patients in the intensive care unit estimated from measured CT/CTA peak skin dose ranged from 1.9-4.5 Gy. Directly measured radiation skin doses from head CT/CTA patient examinations are substantially lower than volumetric CT dose index. Measured peak skin dose confirms that multiple head CT/CTA examinations in representative patients in the neurological intensive care unit may produce cumulative doses exceeding the single-dose deterministic threshold for skin injury.

Radiation dose reduction in parasinus CT by spectral shaping.

Spectral shaping aims to narrow the X-ray spectrum of clinical CT. The aim of this study was to determine the image quality and the extent of radiation dose reduction that can be achieved by tin prefiltration for parasinus CT. All scans were performed with a third generation dual-source CT scanner. A study protocol was designed using 100kV tube voltage with tin prefiltration (200mAs) that provides image noise levels comparable to a low-dose reference protocol using 100kV without spectral shaping (25mAs). One hundred consecutive patients were prospectively enrolled and randomly assigned to the study or control group. All patients signed written informed consent. The study protocol was approved by the local Institutional Review Board and applies to the HIPAA. Subjective and objective image quality (attenuation values, image noise, and contrast-to-noise ratio (CNR)) were assessed. Radiation exposure was assessed as volumetric CT dose index, and effective dose was estimated. Mann-Whitney U test was performed for radiation exposure and for image noise comparison. All scans were of diagnostic image quality. Image noise in air, in the retrobulbar fat, and in the eye globe was comparable between both groups (all p>0.05). CNReye globe/air did not differ significantly between both groups (p=0.7). Radiation exposure (1.7 vs. 2.1mGy, p<0.01) and effective dose (0.055 vs. 0.066mSv, p<0.01) were significantly reduced in the study group. Radiation dose can be further reduced by 17% for low-dose parasinus CT by tin prefiltration maintaining diagnostic image quality.

Assessment of Regional Pediatric Computed Tomography Dose Indices in Tamil Nadu.

The aim of this article is to assess Tamil Nadu pediatric computed tomography (CT) diagnostic reference levels (DRLs) by collecting radiation dose data for the most commonly performed CT examinations. This work was performed for thirty CT scanners installed in various parts of the Tamil Nadu region. The patient cohort was divided into two age groups: <1 year, and 1–5 years. CT dose indices were measured using a 10 cm3 pencil ion chamber with pediatric head and body polymethyl methacrylate phantoms. Dose data such as volumetric CT dose index (CTDIv) and dose length product (DLP) on a minimum of twenty average-sized pediatric patients in each category were recorded to calculate a mean site CTDIv and DLP value. The rounded 75th percentile was used to calculate a pediatric DRL for each hospital, and then region by compiling all results. Data were collected for 3600 pediatric patients. Pediatric CT DRL for two age groups: <1 year (CTDIv and DLP of head [20 mGy, 352 mGy.cm], chest [7 mGy, 120 mGy.cm] and abdomen [12 mGy, 252 mGy.cm]), and 1–5 years (CTDIv and DLP of head [38 mGy, 505 mGy.cm], chest [8 mGy, 132 mGy.cm] and abdomen [14 mGy, 270 mGy.cm]) for select procedures have been calculated. Proposed pediatric DRLs of CTDIv and DLP for head procedure were lower, and for chest and abdomen procedures were higher than European pediatric DRLs for both age groups.

CT brain perfusion: A static phantom study of contrast-to-noise ratio and radiation dose.

Computed tomography perfusion (CTP) is increasingly employed in the diagnosis and management of ischaemic stroke but radiation dose can be significant and optimising contrast-to-noise ratio (CNR) is challenging. This study aimed to quantify and optimise the balance between CNR as a surrogate for image quality and radiation dose. A perspex head phantom with vials of dilute contrast agent was scanned using a Siemens Definition Flash 128-slice scanner. The CTP protocol exposure parameters were adjusted over 70-120kVp and 150-285mAs. Measurements were obtained for the average dose per slice, Hounsfield Units (HU) for iodinated contrast agent, and the image noise for background regions of perspex. The CNR was measured as a function of the volumetric CT dose index (CTDIvol) and kVp. A change from 120 to 80kVp, achieved the same CNR with 60% reduction in dose. Alternatively, for the same dose, the change from 120 to 80kVp improved CNR by +58%. A change from 80 to 70kVp while operating at the same CNR, led to 13% reduction in dose. Alternatively, maintaining the same dose while changing from 80 to 70kVp improved the CNR by +7%. Lower beam energies achieved the same CNR with less dose, or improved CNR at the same dose. A reduction from 80kVp to 70kVp may be clinically useful to optimise CTP acquisitions.

Dose reduction in CT urography and vasculature phantom studies using model-based iterative reconstruction.

To evaluate the feasibility of radiation dose reduction using model‐based iterative reconstruction (MBIR) for evaluating the ureters and vasculature in a phantom, a tissue‐equivalent CT dose phantom was scanned using a 64‐channel CT scanner. Tubes of varying diameters filled with different dilutions of a contrast agent, simulating ureters or vessels, were inserted into the center of the phantom. Each combination was scanned using an existing renal protocol at 140 kVp or 120 kVp, yielding a display volumetric CT dose index (CTDIvol) of 24 mGy. The scans were repeated using reduced scan techniques to achieve lower radiation doses down to 0.8 mGy. The images were reconstructed using filtered back‐projection (FBP) and model‐based iterative reconstruction (MBIR). The noise and contrast‐to‐noise ratio (CNR) was measured for each contrast object. Comparisons between the two reconstruction methods at different dose levels were evaluated using a factorial design. At each CTDIvol the measured image noise was lower using MBIR compared to FBP (p<0.0001). At low doses, the percent change in measured image noise between FBP and MBIR was larger. For the 12 mm object simulating a ureter or large vessel with an HU of 600, the measured CNR using MBIR at a CTDIvol of 1.7 mGy was greater than the CNR of FBP at a CTIDvol of 24 mGy (p<0.0001). For the 5 mm object simulating a medium‐sized vessel with a HU of 250, the measured CNR using MBIR at a CTDIvol of 1.7 mGy was equivalent to that of FBP at a CTDIvol of 24 mGy. For the 2 mm, 100 HU object simulating a small vessel, the measured CNR using MBIR at a CTDIvol of 1.7 mGy was equivalent to that of FBP at a CTDIvol of 24 mGy. Low‐dose (3.6 mGy) CT imaging of vasculature and ureter phantoms using MBIR results in similar noise and CNR compared to FBP at approximately one‐sixth the dose. This suggests that, using MBIR, a one milliSievert exam of the ureters and vasculature may be clinically possible whilst still maintaining adequate image qualityPACS number(s): 87.57.‐s, 87.57.Q‐, 87.57.C‐, 87.57.nf, 87.57.cj, 87.57.cm

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.

CT Pulmonary Angiography Using Automatic Tube Current Modulation Combination with Different Noise Index with Iterative Reconstruction Algorithm in Different Body Mass Index: Image Quality and Radiation Dose

This study aimed to determine the appropriate body mass index (BMI)-dependent noise index (NI) setting in computed tomography pulmonary angiography (CTPA) with automatic tube current modulation with adaptive statistical iterative reconstruction (ASiR). A total of 480 patients who had a CTPA were divided into group A (18.5 kg/m2 ≤ BMI < 25 kg/m2), group B (25 kg/m2 ≤ BMI < 30 kg/m2), and group C (BMI ≥ 30 kg/m2), according to their BMI values; each group had 160 patients. The three groups were further randomly divided into four subgroups: A1, A2, A3, A4; B1, B2, B3, B4; and C1, C2, C3, C4, with corresponding NI values of 26, 36, 40, and 46, respectively. All images were restructured with the ASiR algorithm, and the images with the lowest NI (26 Hounsfield units) in each group were used as reference standard. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) for the pulmonary artery of each group were calculated. Subjective image quality was evaluated using a five-score method by two independent radiologists. The CT dose index of volume and dose-length product were recorded and were converted to effective dose (ED). SNR and CNR in the group A, B, and C subgroups were compared to repeated measures analysis of variance, and the subjective score, Volumetric CT dose index of volume, dose-length product, and ED were compared to one-way analysis of variance. For groups A and B, the SNR, CNR, and subjective scores of the images in their subgroups showed no statistical differences (P >.05). The ED in subgroups A4 and B4 was significantly lower than that in subgroups A1 (by 33.24%) and B1 (by 34.47%) (P <.01). For group C, there was no significant difference in the SNR, CNR, and the subjective image scores between subgroups C3 and C1 (P >.05). The ED in subgroup C3 was significantly lower than the ED in subgroup C1 (by 47.75%) (P <.01) CONCLUSIONS: Patient BMI-dependent NI settings that are higher than the recommended value may be used in CTPA with automatic tube current modulation and ASiR to effectively reduce radiation dose while maintaining diagnostic image quality.

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.

Paediatric multi detector computed tomography radiation doses in a dedicated paediatric hospital in Greece

Introduction Multi detector CT (MDCT) X-ray systems provide high quality paediatric imaging. However, the last years, concern has been expressed on radiation exposure to children. Very few surveys depicting paediatric exposure from MDCT s are available. Purpose To shape the status of radiation dose in children from MDCT practice in a dedicated paediatric hospital in Greece. Materials and methods This was a retrospective study in a 160 bed paediatric hospital equipped with a Philips Brilliance 16 CT scanner installed in 2010. Patient data and acquisition parameters were recorded for CT studies of head, abdomen, chest and spine and were divided in three age groups (1–5 years, 5–10 years, 10–15 years). The dosimetric results were reported in terms of volumetric CT dose index (CTDIvol) (mGy), dose length product (DLP) (mGycm), and total DLP for multiphase studies. The results were compared with adult national DRLs and paediatric European published data. Results Data were collected from 97 MDCT examinations and included 39 head CTs, 12 abdomen CTs, 20 chest CTs and 26 spine CTs. Acquisition parameters used were according to age for head CTs and weight-dependent for the other scans. Spiral or axial scan depended on anatomic area and on the radiologist on duty. Multiphase studies accounted for 10% of patient sample, 80% of these in the abdomen region. For the three age groups, CTDIvol, DLP and total DLP average values were significantly lower than adult national DRLs, although they increased with age, and were in accordance with published paediatric European data. Conclusion Initial data showed that use of protocols tailored to patient’s age or weight results in significant dose reduction. Use of standardized CT protocols should be encouraged.

Reducing Radiation Dose at Chest CT: Comparison Among Model-based Type Iterative Reconstruction, Hybrid Iterative Reconstruction, and Filtered Back Projection

The study aimed to evaluate the performances of two iterative reconstruction (IR) algorithms and of filtered back projection (FBP) when using reduced-dose chest computed tomography (RDCT) compared to standard-of-care CT. An institutional review board approval was obtained. Thirty-six patients with hematologic malignancies referred for a control chest CT of a known lung disease were prospectively enrolled. Patients underwent standard-of-care scan reconstructed with hybrid IR, followed by an RDCT reconstructed with FBP, hybrid IR, and iterative model reconstruction. Objective and subjective quality measurements, lesion detectability, and evolution assessment on RDCT were recorded. For RDCT, the CTDIvol (volumetric computed tomography dose index) was 0.43 mGy⋅cm for all patients, and the median [interquartile range] effective dose was 0.22 mSv [0.22-0.24]; corresponding measurements for standard-of-care scan were 3.4 mGy [3.1-3.9] and 1.8 mSv [1.6-2.0]. Noise significantly decreased from FBP to hybrid IR and from hybrid IR to iterative model reconstruction on RDCT, whereas lesion conspicuity and diagnostic confidence increased. Accurate evolution assessment was obtained in all cases with IR. Emphysema identification was higher with iterative model reconstruction. Although iterative model reconstruction offered better diagnostic confidence and emphysema detection, both IR algorithms allowed an accurate evolution assessment with an effective dose of 0.22 mSv.

Evaluating an Image Gently and Image Wisely Campaign in a Multihospital Health Care System

PurposeThe efficacy of an Image Gently®/Image Wisely® radiology departmental campaign consisting of the optimization of CT protocols to reduce dose while maintaining quality, and an educational effort to alter the ordering patterns of referring physicians at a multihospital academic center, was evaluated. MethodsThe numbers of CT, MR, and ultrasound studies performed at inpatient, outpatient, and emergency facilities in the hospital system before and after the initiation of the departmental campaign (2010) were obtained for a 10-year period (2004-2014) using a radiology information system. For the same time period, dose per scan (volumetric CT dose index) was obtained through the Dose Index Registry®/National Radiology Data Registry for frequently performed studies. Descriptive statistics were used to analyze temporal trends in radiation dose and utilization across differing age groups: <20, 20 to 39, and 40 to 59 years. ResultsThe radiology information system yielded 865,879 imaging examinations and 4,508,030 patients. Although patient and imaging volume grew annually over the study period (by 6.8% and 4.9%, respectively), CT utilization as a percentage of total imaging decreased, compensated for by an increase in ultrasound use. This was most marked in the youngest age group. MR use as a percentage of total imaging was unchanged. The median volumetric CT dose index for each study protocol was reduced or stabilized. ConclusionsThe campaign resulted in a reduction in CT utilization, a reduction in radiation dose per study, and a compensatory rise in ultrasound use. An interactive aggressive educational campaign directed toward referring providers combined with protocol dose reduction efforts can be successful in reducing patient exposure from medical radiation.

SU‐F‐SPS‐03: Direct Measurement of Organ Doses Resulting From Head and Cervical Spine Trauma CT Protocols

Purpose:This retrospective study analyzes the exposure history of emergency department (ED) patients undergoing head and cervical spine trauma computed tomography (CT) studies. This study investigated dose levels received by trauma patients and addressed any potential concerns regarding radiation dose issues.Methods:Under proper IRB approval, a cohort of 300 trauma cases of head and cervical spine trauma CT scans received in the ED was studied. The radiological image viewing software of the hospital was used to view patient images and image data. The following parameters were extracted: the imaging history of patients, the reported dose metrics from the scanner including the volumetric CT Dose Index (CTDIvol) and Dose Length Product (DLP). A postmortem subject was scanned using the same scan techniques utilized in a standard clinical head and cervical spine trauma CT protocol with 120 kVp and 280 mAs. The CTDIvol was recorded for the subject and the organ doses were measured using optically stimulated luminescent (OSL) dosimeters. Typical organ doses to the brain, thyroid, lens, salivary glands, and skin, based on the cadaver studies, were then calculated and reported for the cohort.Results:The CTDIvol reported by the CT scanner was 25.5 mGy for the postmortem subject. The average CTDIvol from the patient cohort was 34.1 mGy. From these metrics, typical average organ doses in mGy were found to be: Brain (44.57), Thyroid (33.40), Lens (82.45), Salivary Glands (61.29), Skin (47.50). The imaging history of the cohort showed that on average trauma patients received 26.1 scans over a lifetime.Conclusion:The average number of scans received on average by trauma ED patients shows that radiation doses in trauma patients may be a concern. Available dose tracking software would be helpful to track doses in trauma ED patients, highlighting the importance of minimizing unnecessary scans and keeping doses ALARA.