Radiation dose reduction without degrading image quality during computed tomography examinations: Dosimetry and quality control study

Background Currently there is a trend towards reducing radiation dose while maintaining image quality during computer tomography (CT) examination. This results from the concerns about radiation exposure from CT and the potential increase in the incidence of radiation induced carcinogenesis. This study aimed to investigate the lowest radiation dose for maintaining good image quality in adult chest scanning using GE CT equipment. Methods Seventy-two adult patients were examined by Gemstone Spectral CT. They were randomly divided into six groups. We set up a different value of noise index (NI) when evaluating each group every other number from 13.0 to 23.0. The original images were acquired with a slice of 5 mm thickness. For each group, several image series were reconstructed using different levels of adaptive statistical iterative reconstruction (ASIR) (30%, 50%, and 70%). We got a total of 18 image sequences of different combinations of NI and ASIR percentage. On one hand, quantitative indicators, such as CT value and standard deviation (SD), were assessed at the region of interest. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The volume CT dose index (CTDI) and dose length product (DLP) were recorded. On the other hand, two radiologists with ≥5 years of experience blindly reviewed the subjective image quality using the standards we had previously set. Results The different combinations of noise index and ASIR were assessed. There was no significant difference in CT values among the 18 image sequences. The SD value was reduced with the noise index's reduction or ASIR's increase. There was a trend towards gradually lower SNR and CNR with an NI increase. The CTDI and DLP were diminishing as the NI increased. The scores from subjective image quality evaluation were reduced in all groups as the ASIR increased. Conclusions Increasing NI can reduce radiation dose. With the premise of maintaining the same image quality, using a suitable percentage of ASIR can increase the value of NI. To assure image quality, we concluded that when the NI was set at 17.0 and ASIR was 50%, the image quality could be optimal for not only satisfying the requirements of clinical diagnosis, but also achieving the purpose of low-dose scanning.

Estimates of individual patient risk, and epidemiologic studies assessing potential late effects, must use patient size–specific dose estimates—they cannot use only scanner output (volume CT dose index or dose-length product).

For the past several years, increased levels of imaging radiation and cumulative radiation to children has been a significant concern. Although several measures have been taken to reduce radiation dose during computed tomography (CT) scan, the newer dose reduction software adaptive statistical iterative reconstruction (ASIR) has been an effective technique in reducing radiation dose. To our knowledge, no studies are published that assess the effect of ASIR on extremity CT scans in children. To compare radiation dose, image noise, and subjective image quality in pediatric lower extremity CT scans acquired with and without ASIR. The study group consisted of 53 patients imaged on a CT scanner equipped with ASIR software. The control group consisted of 37 patients whose CT images were acquired without ASIR. Image noise, Computed Tomography Dose Index (CTDI) and dose length product (DLP) were measured. Two pediatric radiologists rated the studies in subjective categories: image sharpness, noise, diagnostic acceptability, and artifacts. The CTDI (p value = 0.0184) and DLP (p value <0.0002) were significantly decreased with the use of ASIR compared with non-ASIR studies. However, the subjective ratings for sharpness (p < 0.0001) and diagnostic acceptability of the ASIR images (p < 0.0128) were decreased compared with standard, non-ASIR CT studies. Adaptive statistical iterative reconstruction reduces radiation dose for lower extremity CTs in children, but at the expense of diagnostic imaging quality. Further studies are warranted to determine the specific utility of ASIR for pediatric musculoskeletal CT imaging.

BackgroundIn medical imaging, a computed tomography (CT) scanner is a major source of ionizing radiation. All medical radiation exposures should be justified and optimized to meet the clinical diagnosis. Thus, to avoid unnecessary radiation doses for patients, diagnostic reference levels (DRLs) have been used. The DRLs are used to identify unusually high radiation doses during CT procedures, which are not appropriate for the clinical diagnosis. It has been successfully implemented in Europe, Canada, Australia, the United States, several industrialized countries, and a few underdeveloped countries. The present study aimed to establish DRLs for the head, chest, and abdominopelvic (AP) CT procedures in Addis Ababa, Ethiopia.MethodsA pilot study identified the most frequent CT examinations in the city. At the time of the pilot, eighteen CT scan facilities were identified as having functioning CT scanners. Then, on nine CT facilities (50% of functional CT scanners), a prospective analysis of volume CT dose index (CTDIvol) and dose length product (DLP) was performed. We collected data for 838 adult patients’ head, chest, and AP CT examinations. SPSS version 25 was used to compute the median values of the DLP and CTDIvol dose indicators. The rounded 75th percentile of CTDIvol and DLP median values were used to define the DRLs. The results are compared to DRL data from the local, regional, and international levels.ResultThe proposed DRLs using CTDIvol (mGy) are 53, 13, and 16 for the head, chest, and AP examinations respectively, while the DLP (mGy.cm) for the respective examinations were 1210, 635, and 822 mGy.cm.ConclusionBaseline CT DRLs figures for the most frequently performed in Addis Ababa were provided. The discrepancies in dose between CT facilities and as well as between identical scanners suggests a large potential for dose optimization of examinations. This can be actually achieved through appropriate training of CT technologists and continuous dose audits.

The number of CT (computed tomography) examinations in the diagnosis field has increased, and X-ray exposure to patients has also continued to increase. As the number of CT examinations is increasing in the general population, the number of pediatric CT examinations is rapidly increasing as well. The radiation dose from CT for pediatric patients remains a major concern because the risk related to ionizing radiations is higher in children than in adults. The purpose of this study was to evaluate radiation dose, image noise, and image contrast as a function of tube voltage (kVp) and tube current (mAs) in dierent phantoms, which were intended to simulate abdominal size, and to provide guidance on dose reduction on the basis of patient dimensions, as well as technical parameters. In this study, MDCT (multi-detector computed tomography) was used as an X-ray generator, and PMMA (polymethylmethacrylate) phantoms were used in all experiments. PMMA phantom diameters were 10 cm, 16 cm, and 32 cm corresponding to newborn, age 5, and adult abdominal sizes, respectively. To evaluate radiation dose, the CTDIw (weighted CT dose index) was calculated from the CTDI measured using ion chamber, and to evaluate image quality, image noise and image contrast were measured from a scanned image. Finally, the CNRD (dose-weighted contrast-to-noise ratio) was calculated from the radiation dose, image noise, and image contrast to optimize the technical factors. The radiation dose increased as a function of kVp and mAs and decreased as a function of the phantom diameter. Especially, for increasing tube voltage from 80 to 140 kVp, there were 395.08% and 448.27% increases in radiation dose for 10 cm and 32 cm PMMA phantoms, respectively. The image noise decreased as a function of kVp and mAs and increased as a function of the phantom diameter. And, the image contrast decreased as a function of kVp and phantom diameter and remained fixed as a function of mAs. The values of the CNRD were maximum at 80 kVp for all three phantoms. The results of this study show that it is possible to reduce radiation dose and maintain image quality through the use of lower technical factors (kVp and mAs) for small-sized phantom corresponding to pediatric patients and to provide guidance on radiation dose reduction on the basis of the patient’s dimensions.

Combination of Adaptive Statistical Iterative Reconstruction-V and Lower Tube Voltage During Craniocervical Computed Tomographic Angiography Yields Better Image Quality with a Reduced Radiation Dose

Introduction: The rapid use of computed tomography (CT) scan is of great concern, due to increase in patients’ dose. Optimization of CT protocol is a vital issue in dose reduction. This study aimed to optimize radiation dose in cranial CT and assess modifications in image quality under radiation dose reduction. Material and Methods: A poly(methyl methacrylate) phantom was used for quality control test on CT scanners. Data of 214 scan parameters, dose indicators; volume CT dose index (CTDIvol) and dose-length product (DLP) of patients who underwent cranial CT scans were collected. The data were grouped into three, with respect to the slice numbers of 24, 28, and 32. Tube voltage (kVp) and slice thickness were constant; (110 kVp and 4.8 mm, respectively), at variable tube currents (mAs). A one-sample t-test was used to compare the dose indicator values of the hospital protocol with a recommended protocol. Scan parameters were optimized for radiation dose against image quality. Results: Increased mAs resulted in increased CTDIvol and DLP at constant kVp and slice thickness. Moreover, dose indicators recorded the lowest and highest values at the slice numbers of 24 and 32, respectively. An increase in slice numbers affected dose indicators. Dose indicators recorded significant reduction (p <0.001) in comparison to the recommended protocol. Conclusion: Optimization of CT protocol considers radiation dose and image quality. Radiologists adopted protocols acquired with lower scan parameters and dose indicators lower than the recommended achievable dose limit of 58 mGy.

Automatic radiation dose monitoring for CT of trauma patients with different protocols: feasibility and accuracy

The IAEA — UAE Project on Patient Radiation Protection aimed at evaluating radiation dose levels received by patients during radiological examinations. In this paper, we are presenting the preliminary results of patient doses in Computed Tomography (CT) examinations at 4 UAE hospitals (3 major governmental hospitals and 1 private). Five Multi-slice CT (MSCT) systems (4S, 16S and 64S) were included in this study. All these systems are enrolled in quality control program. CT dose levels were evaluated through either thermoluminescent detectors (TLD-100) or by using Head (16-cm Diameter) and Body (32-cm Diameter) cylindrical CTDI PMMA phantom fitted with a 10 cm pencil ionization chamber. Adult and pediatric patient CT doses were collected from common CT examinations of the Head, Chest and Abdomen & Pelvis. The CT Dose Index (CTDIvol), Dose Length Product (DLP) and Effective Doses (E) were the main CT dosimetry parameters evaluated in this project. The CTDIvol results of all CT systems showed acceptable compliance with those reported by professional organizations. The range of 3rd quartile of adult DLP values for CT Head examinations among the 4 hospitals was 384.106–5031.92 mGy.cm. The adult CT Chest examinations demonstrated the range of the 3rd quartile DLP values between 122.035–1423.06 mGy.cm while the Abdomen & Pelvis examinations showed a range of 258.446–1701.135 mGy.cm. Hospitals DD3, AA13 and ANM14 are within the UAE initial adapted local Dose Reference Levels (DRLs) and are comparable to the European guidelines while hospitals TA1 and TA2 are higher. The CT effective doses of almost all the examination types were within the level mentioned by international organizations such as the ICRP (Report 102, 2007) with the exception of CT examinations performed at TA1 & TA2. Further work is developed to reduce patient radiation doses of the common CT examinations of the Head, Chest and Abdomen & Pelvis. Adult and pediatric patient data collection and analysis of CT doses from other hospitals at the UAE are in progress.

Objective To study the application of the intelligent optimum tube voltage (Care kV) combined with automatic tube current (Care Dose 4D) technique in dual source CT scanning for the abdomen. Methods 180 adult patients underwent whole abdominal CT examination from February 2016 to March 2016 of were selected as the retrospective research objects. On the basis of reference mAs of the image quality the patients were divided into three groups using completely randomized grouping method with 60 patients in each group, such as 250 mAs group, 200 mAs group, and 150 mAs group. The other scanning parameters and image reconstruction parameters were the same. The liver parenchyma CT values and image noise(SD) at the second hepatic portal level were measured. The signal-to-noise ratios (SNR) in the three groups were compared as well as contrast to noise ratio (CNR), noise (SD), the average volume CT dose index (CTDIvol), dose length product (DLP) and effective dose(E). Results The kV and mAs values in the plain scan, arterial phase scan and portal phase scan in the three groups of patients had statistically significant differences(F=35.25, P 0.05). In 250 mAs group and 150 mAs group, the SNR and the noise of plain scan and arterial phase images had no statistically significant difference (F=1.98, P>0.05), and SNR of portal phase images and CNR of three phases had statistically significant difference (F=27.64, P 0.05), and the SNR and CNR of portal phase images had significant difference (F=19.63, P< 0.05). Conclusions For the combined use of Care kV and Care dose 4D, it is feasible to select appropriate reference mAs in reducing radiation dose without sacrificing imaging quality. Key words: Tomography, X-ray computed; Intelligent optimum tube voltage technique(Care kV); Radiation dose

Radiation dose reduction with the adaptive statistical iterative reconstruction (ASIR) technique for chest CT in children: An intra-individual comparison

Objective To study the impact on the radiation dose, organ doses of eye lens and thyroid and image quality with different scanning modes in head and neck CT scan. Methods The simulation phantom of head and neck was scanned by using fixed scanning condition (120 kV and 200 mAs), as well as the combinations of automatic tube current modulation (CARE Dose 4D), automatic tube voltage modulation technique (CARE kV) and partial angle scanning mode (X-CARE) respectively. Six kinds of scanning modes were adopted, including 120 kV+ 200 mAs, 120 kV+ 200 mAs+ X-CARE, CARE Dose 4D+ 120 kV, CARE Dose 4D+ 120 kV+ X-CARE, CARE Dose 4D+ CARE kV, CARE Dose 4D+ CARE kV+ X-CARE. Two thermoluminescece dosimeters(TLDs) were exposed at the skin surface positions of eye lens and thyroid, and the values measured with two TLDs were averaged. The CT dose index volume(CTDIvol) and dose length product (DLP) for every scan were recorded, and the contrast to noise ratio (CNR) in eye lens section and thyroid section were measured. Results The organ doses of lens and thyroid were 19.8 and 26 mGy at 120 kV and 200 mAs, as well as 13.3 and 22.2 mGy at X-CARE mode. Compared with the manual selection of 120 kV, the combination of CARE kV and CARE Dose 4D made the values of CTDIvol drop from 13.1 to 10.1 mGy, the doses of eye lens and thyroid from 16.6 and 20.8 mGy to 23.7 and 19.9 mGy respectively, while the image quality reduced significantly. Compared with CARE Dose 4D+ 120 kV, the organ doses of eye lens and thyroid were reduced from 20.8 and 23.7 mGy to 9.6 and 15.1 mGy for with additional X-CARE, while CTDIvol dropped from 13.1 to 9.3 mGy. When the combination of CARE Dose 4D+ CARE kV+ X-CARE was used, CTDIvol and organ doses were reduced to a minimum, when the CNRs of head and neck were also minimized. Conclusions The scanning mode CARE Dose 4D+ 120 kV+ X-CARE for head and CARE Dose 4D+ CARE kV for neck can effectively reduce the radiation dose while keeping good image quality. When requirements for image quality are not high, CARE Dose 4D+ CARE kV+ X-CARE mode can be selected to reduce the radiation dose significantly. Key words: Dual-source CT; Head and neck; Radiation dose; Eye lens; Thyroid

The objective of this study is to compare radiation doses given to ovarian cancer patients by different computed tomographies (CTs) and to evaluate association between doses and subjective and objective image quality.CT examinations included were performed either on a 16-slice CT, equipped with automatic z-axis tube current modulation, or on a 64-slice CT, equipped with z-axis, xy-axis modulation, and adaptive statistical iterative algorithm (ASIR). Evaluation of dose included the following dose descriptors: volumetric CT dose index (CTDIvol), dose length product (DLP), and effective dose (E). Objective image noise was evaluated in abdominal aorta and liver. Subjective image quality was evaluated by assessment of image noise, spatial resolution and diagnostic acceptability.Mean and median CTDIvol, DLP, and E; correlation between CTDIvol and DLP and patients’ weight; comparison of objective noise for the 2 scanners; association between dose descriptors and subjective image quality.The 64-slice CT delivered to patients 24.5% lower dose (P < 0.0001) than 16-slice CT. There was a significant correlation between all dose descriptors (CTDIvol, DLP, E) and weight (P < 0.0001). Objective noise was comparable for the 2 CT scanners. There was a significant correlation between dose descriptors and image noise for the 64-slice CT, and between dose descriptors and spatial resolution for the 16-slice CT.Current dose reduction systems may reduce radiation dose without significantly affecting image quality and diagnostic acceptability of CT exams.

To evaluate effects of varying tube current and voltage on radiation dose, image noise, and image contrast with different phantom sizes and shapes. Four round lucite phantoms with 8-32-cm diameters were scanned with multi-detector row computed tomography (CT) and 80-120 kVp. Radiation dose was based on CT dose index, image noise, and iodine contrast and measured with constant and variable tube currents that were age appropriate for each tube voltage. Radiation dose and image noise and contrast were compared in round and oval 24-cm phantoms. For various combinations of technical factors and phantom sizes and shapes, percentage differences were calculated for radiation dose and image noise and contrast. Associations between tube voltage and radiation dose, image noise, and image contrast in round and oval phantoms were determined by fitting second-degree polynomials to data. Differences in radiation dose and image noise and contrast, which were attributable to differences in tube voltage, were tested with paired t tests. With 165-mAs tube current, radiation doses with 140- and 80-kVp tube voltages were 103% ([41.9 mGy - 20.6 mGy]/20.6 mGy) and 58% ([10.2 mGy - 4.2 mGy]/10.1 mGy) higher in the 8-cm phantom than in the 32-cm phantom. When tube current was adapted for phantom size, radiation dose at 80 kVp in the 8-cm phantom was reduced by 82% ([10.1 mGy - 1.8 mGy]/10.1 mGy). In the 8-cm phantom, tube voltage was decreased from 120 to 80 kVp and tube current remained at 165 mAs, resulting in a 68% noise increase ([3.1 HU - 1.8 HU]/1.8 HU). With variable tube current, 80-kVp tube voltage in the 8-cm phantom led to a 138% noise increase ([7.3 HU - 3.1 HU]/3.1 HU). With reduced tube voltage, image contrast increased. In the 8-cm phantom, with a constant 165-mAs tube current and a decrease in tube voltage from 120 to 80 kVp, there was a 35% ([333 HU - 217 HU]/333 HU) increase in contrast. No difference was noted in radiation dose or noise between round and oval phantoms (P = .604 and P = .06, respectively), but a small statistically significant difference (1%) in contrast attenuation was demonstrated (P = .025). Reduced tube voltage for pediatric contrast material-enhanced CT reduces radiation dose and maintains image contrast. Image noise increases, but the effect is minimal in smaller phantoms. An additional reduction in tube current further reduces radiation dose.

Introduction: Computed tomography (CT) is a medical imaging modality that produces 3-D cross-sectional images of tissues using several X-ray projections at different angles. Since its introduction in the 1970s, CT usage has been on the increase for both adults and pediatrics. A major challenge of this modality is the high doses of radiation exposure to patients, especially in pediatrics, who are more radiosensitive compared to adults. Hence, the need to ensure that radiation safety standards are adhered to. This will go a long way in reducing the adverse effects of radiation. The aim of this study was to assess the level of compliance to international dose reference levels (DRLs) in terms of effective doses in pediatric CT scans conducted in three Iraqi hospitals. Materials and Methods: CT brain and abdomen/pelvis examinations were conducted for pediatric patients aged between few months and 15 years in three Iraqi hospitals (Al Wasiti, Neuroscience and Al Omara). All scans were performed on a Somatom Sensation® 16 multidetector CT (MDCT) scanner with a Straton® X-ray tube (Siemens, Erlangen, Germany) utilising automatic tube current modulation (CARE Dose4DTM; Siemens, Erlangen, Germany). Volumetric CT dose index (CTDIvol) and dose length product (DLP) were collected for 180 patients (60 in each hospital). Afterwards, their effective doses were estimated from DLP values and compared with international DRLs. Results: Brain CT: The DLP values obtained for Al Wasiti, Neuroscience and Al Omara hospitals were in the range; 789-918.8 mGy.cm, 833-874.6 mGy.cm and 627.6-810 mGy.cm respectively, while their corresponding effective doses were in the range; 1.8-2.09 mSv, 1.9- 2.06 mSv and 1.43-1.83 mSv. Abdomen/Pelvis: The DLP values obtained for Al Wasiti, Neuroscience and Al Omara hospitals were in the range; 392.9-425.8 mGy.cm, 355-395 mGy.cm and 314.8-383.6 mGy.cm respectively, while their corresponding effective doses were in the range; 6.65-7.22 mSv, 6- 6.7 mSv and 5.34-6.51 mSv. Using the International Commission on Radiological Protection (ICRP) publication 103 as basis for assessing compliance level, for brain CT we observe slightly higher values in Al Wasiti and Neuroscience hospitals while Al Omara was similar to the international DRLs. However, for abdomen/pelvis CT examinations, the effective doses in all three hospitals were within the acceptable limits of international DRLs. Conclusion: This study has shown an encouraging level of compliance towards adequate radiation protection management in pediatric CT examinations among the three hospitals. Although, the best compliance level was observed in Al Omara hospital. Regular monitoring should be enforced to ensure that CT doses delivered to pediatric patients are as low as reasonably achievable without compromising diagnostic quality.