Automatic exposure control in CT: the effect of patient size, anatomical region and prescribed modulation strength on tube current and image quality

Accuracy of patient-specific CT organ doses from Monte Carlo simulations: influence of CT-based voxel models

Monte Carlo simulations using patient CT images as input are the gold standard to perform patient-specific dosimetry. However, in standard clinical practice patient's CT images are limited to the reconstructed CT scan range. In this study, organ dose calculations were performed with ImpactMC for chest and cardiac CT using whole-body and anatomy-specific voxel models to estimate the accuracy of CT organ doses based on the latter model. When the 3D patient model is limited to the CT scan range, CT organ doses from Monte Carlo simulations are the most accurate for organs entirely in the field of view. For these organs only the radiation dose related to scatter from the rest of the body is not incorporated. For organs lying partially outside the field of view organ doses are overestimated by not accounting for the non-irradiated tissue mass. This overestimation depends strongly on the amount of the organ volume located outside the field of view. To get a more accurate estimation of the radiation dose to these organs, the ICRP reference organ masses and densities could form a solution. Except for the breast, good agreement in dose was found for most organs. Voxel models generated from clinical CT examinations do not include the overscan in the z-direction. The availability of whole-body voxel models allowed to study this influence as well. As expected, overscan induces slightly higher organ doses.

Multi-institutional Protocol Guidance for Pediatric Photon-counting CT

Performing CT in children comes with unique challenges such as greater degrees of patient motion, smaller and densely packed anatomy, and potential risks of radiation exposure. The technical advancements of photon-counting detector (PCD) CT enable decreased radiation dose and noise, as well as increased spatial and contrast resolution across all ages, compared with conventional energy-integrating detector CT. It is therefore valuable to review the relevant technical aspects and principles specific to protocol development on the new PCD CT platform to realize the potential benefits for this population. The purpose of this article, based on multi-institutional clinical and research experience from pediatric radiologists and medical physicists, is to provide protocol guidance for use of PCD CT in the imaging of pediatric patients.

Pathology-based radiation dose in computed tomography: investigation of the effect of lung lesions on water-equivalent diameter, CTDIVol and SSDE in COVID-19 patients

Lung lesions can increase the CT number and affect the water-equivalent diameter (Dw), Dw-based conversion factor (CFw), and Dw-based size-specific dose estimate (SSDEw). We evaluated the effect of COVID-19 lesions and total severity score (TSS) on radiation dose considering the effect of automatic tube current modulation (ATCM) and fixed tube current (FTC). A total of 186 chest CT scans were categorised into five TSS groups, including healthy, minimal, mild, moderate and severe. The effective diameter (Deff), Dw, CFw, Deff-based conversion factor (CFeff), volume computed tomography dose index (CTDIVol), pathological dose impact factor (PDIF) 1 and SSDEw were calculated. TSS was correlated with Dw (r = 0.29, p-value = 0.001), CTDIVol (ATCM) (r = 0.23, p = 0.001) and PDIF (r = - 0.51, p-value = 0.001). $\overline{{\mathrm{SSDE}}_{\mathrm{w}}}$ (FTC) was significantly different among all groups. $\overline{{\mathrm{SSDE}}_{\mathrm{w}}}$ (ATCM) was greater for moderate (13%) and mild (14%) groups. Increasing TSS increase the Dw and causes a decrease in CFw and $\overline{{\mathrm{SSDE}}_{\mathrm{w}}}$ (FTC), and can increase $\overline{{\mathrm{SSDE}}_{\mathrm{w}}}$ (ATCM) in some Dw ranges.

Assessing the knowledge of CT radiographers regarding how CT parameters affect patient dose and image quality

PURPOSE

The objective of this study was to assess the current knowledge of CT radiographers regarding the optimization of CT parameters and their consequential effects on both patient dose and image quality.

METHOD

A nationwide, cross sectional study was conducted from the 2nd of January 2023 to 1st of March 2023 to evaluate CT radiographers' knowledge in managing CT parameters in Jordan. Recruitment involved convenience sampling where radiographers were invited to participate and complete the questionnaire. Descriptive statistics were used to report the normalized knowledge scores. Student's t-test and ANOVA were used to investigate and compare the outcomes between different subgroups. A forward stepwise linear regression was used to investigate the influence of a number of technologist related factors on the knowledge score.

RESULTS

Three hundred and fifty-seven radiographers participated in the study, with a mean knowledge score of 69.0%. Participants with an academic master's degree had a significantly higher score of 72.1% compared to the ones with a diploma degree, with a score of 66.8% (p = 0.026). No statistically significant difference was found between radiographers that received additional training and the ones that did not. Furthermore, when investigating the effects of academic education, working sector, additional training and years of experience, only education had a statistically significant impact on the knowledge score.

CONCLUSION

The results demonstrate that radiographers have an overall good understanding of CT parameters, with academic education having a significant influence on their performance.

Optimisation of CT protocols in PET-CT across different scanner models using different automatic exposure control methods and iterative reconstruction algorithms

Background

A significant proportion of the radiation dose from a PET-CT examination is dependent on the CT protocol, which should be optimised for clinical purposes. Matching protocols on different scanners within an imaging centre is important for the consistency of image quality and dose. This paper describes our experience translating low-dose CT protocols between scanner models utilising different automatic exposure control (AEC) methods and reconstruction algorithms.

Methods

The scanners investigated were a newly installed Siemens Biograph mCT PET with 64-slice SOMATOM Definition AS CT using sinogram affirmed iterative reconstruction (SAFIRE) and two GE Discovery 710 PET scanners with 128-slice Optima 660 CT using adaptive statistical reconstruction (ASiR). Following exploratory phantom work, 33 adult patients of various sizes were scanned using the Siemens scanner and matched to patients scanned using our established GE protocol to give 33 patient pairs. A comparison of volumetric CT dose index (CTDI_vol) and image noise within these patient pairs informed optimisation, specifically for obese patients. Another matched patient study containing 27 patient pairs was used to confirm protocol matching. Size-specific dose estimates (SSDEs) were calculated for patients in the second cohort. With the acquisition protocol for the Siemens scanner determined, clinicians visually graded the images to identify optimal reconstruction parameters.

Results

In the first matched patient study, the mean percentage difference in CTDI_vol for Siemens compared to GE was − 10.7% (range − 41.7 to 50.1%), and the mean percentage difference in noise measured in the patients’ liver was 7.6% (range − 31.0 to 76.8%). In the second matched patient study, the mean percentage difference in CTDI_vol for Siemens compared to GE was − 20.5% (range − 43.1 to 1.9%), and the mean percentage difference in noise was 19.8% (range − 27.0 to 146.8%). For these patients, the mean SSDEs for patients scanned on the Siemens and GE scanners were 3.27 (range 2.83 to 4.22) mGy and 4.09 (range 2.81 to 4.82) mGy, respectively. The analysis of the visual grading study indicated no preference for any of the SAFIRE strengths.

Conclusions

Given the different implementations of acquisition parameters and reconstruction algorithms between vendors, careful consideration is required to ensure optimisation and standardisation of protocols.

CT diagnostic reference levels based on clinical indications: results of a large-scale European survey

OBJECTIVES

The objective of this study was to investigate the feasibility of defining diagnostic reference levels (DRLs) on a European basis for specific clinical indications (CIs), within the context of the European Clinical DRLs (EUCLID) European Commission project.

METHODS

A prospective, multicenter, industry-independent European study was performed to provide data on 10 CIs (stroke, chronic sinusitis, cervical spine trauma, pulmonary embolism, coronary calcium scoring, coronary angiography, lung cancer, hepatocellular carcinoma, colic/abdominal pain, and appendicitis) via an online survey that included information on patient clinical, technical, and dosimetric parameters. Data from at least 20 patients per CI were requested from each hospital. To establish DRLs, a methodology in line with the International Commission on Radiological Protection (ICRP) Report 135 good practice recommendations was followed.

RESULTS

Data were collected from 19 hospitals in 14 European countries on 4299 adult patients and 10 CIs to determine DRLs. DRLs differ considerably between sites for the same CI. Differences were attributed mainly to technical protocol and variable number of phases/scan lengths. Stroke and hepatocellular carcinoma were the CIs with the highest DRLs. Coronary calcium scoring had the lowest DRL value. Comparison with published literature was limited, as there was scarce information on DRLs based on CI.

CONCLUSIONS

This is the first study reporting on feasibility of establishing CT DRLs based on CI using European data. Resulting values will serve as a baseline for comparison with local radiological practice, national authorities when DRLs are set/updated, or as a guideline for local DRL establishment.

KEY POINTS

• First study reporting on the feasibility of establishing CT diagnostic reference levels based on clinical indication using data collected across Europe. • Only one-fourth of the hospitals had CT machines less than 5 years old. • Large dose variations were observed among hospitals and CT protocols were quite different between hospitals.

Evaluation of anatomical landmark position differences for head computed tomography: A reliability study among technologists

INTRODUCTION

In computed tomography (CT) imaging protocols, lack of practice standards and variability in head positioning may all yield substantial inter-study image variance in the clinical setting which may limit the diagnostic and comparative value of subsequent scans. We aimed to evaluate repeatability of multiplanar reformatting of head CT based on the tuberculum sella (TS) to internal occipital protuberance (IOP) reference line and reduce variance.

METHODS

Reference lines that correspond to the TS-IOP plane on high-resolution CT scans were reviewed by technologists manually to calculate Yaw (z-rotation, rotation along the superoinferior direction), Pitch (x-rotation, rotation along the left-right direction), and Roll (y-rotation, rotation along the anteroposterior direction) angles in this pre-post design intervention study. The Yaw, Pitch, and Roll angles deviating from the reference TS-IOP in the head CT images before and after technologist training were measured with the technologists' actual graphical prescriptions, and their differences were calculated with t-tests. The intra-rater agreement was calculated using the intraclass correlation coefficient (ICC).

RESULTS

Mean pitch, yaw, and roll before technologist training was 6.7° ± 5.4°, 0.9° ± 1.5°, and 1.1° ± 1.2° and after training were 3.2° ± 2.6°, 0.6° ± 1.1°, and 0.6° ± 1.1°, respectively. Technologist training resulted in a significant decrease in pitch (p < 0.001) and roll (p = 0.001) inter-subject variability with respect to the TS-IOP line, however no significant difference for the yaw correction (p = 0.065) was noted. Intra-rater agreement regarding the reproducibility of TS-IOP reformation was excellent (ICC>0.950).

CONCLUSION

TS-IOP reference line corrected for direct roll, yaw, and pitch can be readily achieved by trained technologists.

IMPLICATIONS FOR PRACTICE

Adoption of the TS-IOP reference line should facilitate intra- and intermodality comparisons, leading to more reproducible and readily interpretable CT images.

Technical Note: Evaluating automatic tube current modulation in CT using the standard CTDI dosimetry phantom

PURPOSE

To assess the utility of the standard body CTDI phantom in characterizing the operation scheme of tube current modulation (TCM) systems in CT.

METHODS

The body CDTI phantom was used to characterize two TCM systems: TCM₁ and TCM₂ , implemented in scanners from different vendors. The phantom was aligned at the gantry isocenter in two configurations. In configuration A, the facet planes of the phantom were parallel to the patient table, while in configuration B they were vertical to the patient table and parallel to the patient's long axis. Acquisitions were performed using the routine abdominal examination protocol. mA(z) profiles were recorded from images' DICOM header. The water equivalent diameter (d_w ) and oval ratio (OR) were calculated as a function of z-axis location. Image noise was defined as the standard deviation (SD) of the mean Hounsfield unit value measured in a region of interest at the center of the phantom's image. Regression analysis was performed to modulated mA and SD vs d_w and OR. The spatial concordance between the change in phantom size and change in mA (SC_mA ) was calculated as the percent difference in the slope of mA(z) change between the 1st and 2nd half of the phantom. The corresponding spatial concordance between the change in phantom size and change in image noise (SC_noise ) was calculated.

RESULTS

Modulated mA(z) along the z-axis did not substantially differentiate between configurations A and B. Correlation between ln(mA) and OR was found to be higher compared to correlation between ln(mA) and d_w . SC_mA was 48% for TCM₁ and 33% for TCM₂ . The corresponding SC_noise was 29% for TCM₁ and 16% for TCM₂ .

CONCLUSION

Apart from routine CT dosimetry evaluations, the standard CTDI phantom positioned in configuration A or B may additionally be used by medical physicists to evaluate the performance of TCM operational characteristics.

Evaluation of an organ-based tube current modulation tool in pediatric CT examinations

Objectives

To investigate the effect of an organ-based tube current modulation (OTCM) technique on organ absorbed dose and assess image quality in pediatric CT examinations.

Methods

Four physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old were used. Standard head and thorax acquisitions were performed with automatic tube current modulation (ATCM) and ATCM+OTCM. Dose calculations were performed by means of Monte Carlo simulations. Radiation dose was measured for superficial and centrally located radiosensitive organs. The angular range of the OTCM exposure window was determined for different tube rotation times (t) by means of a solid-state detector. Image noise was measured as the standard deviation of the Hounsfield unit value in regions of interest drawn at selected anatomical sites.

Results

ATCM+OTCM resulted in a reduction of radiation dose to all radiosensitive organs. In head, eye lens dose was reduced by up to 13% in ATCM+OTCM compared with ATCM. In thorax, the corresponding reduction for breast dose was up to 10%. The angular range of the OTCM exposure window decreased with t. For t = 0.4 s, the angular range was limited to 74° in head and 135° for thorax. Image noise was significantly increased in ATCM+OTCM acquisitions across most examined phantoms (p < 0.05).

Conclusions

OTCM reduces radiation dose to exposed radiosensitive organs with the eye lens and breast buds exhibiting the highest dose reduction. The OTCM exposure window is narrowed at short t. An increase in noise is inevitable in images located within the OTCM-activated imaged volume.

Key Points

• In pediatric CT, organ-based tube current modulation reduces radiation dose to all major primarily exposed radiosensitive organs.

• Image noise increases within the organ-based tube current modulation enabled imaged volume.

• The angular range of the organ-based tube current modulation low exposure window is reduced with tube rotation time.

A new brain CT reference line: the lower eyelid to the inner occipital base line closely parallels the Talairach-Tournoux line

Background

There is no standardized brain computed tomography (CT) reference line that can be determined on both scout and reformatted sagittal CT images. Here, a tangential line from the anterior edge of the lower eyelid to the inner table of the occipital base (LEL/O line) appears nearly parallel to the Talairach–Tournoux (T/T) line, which shows a consistent intracranial anatomical relationship among subjects, and acts as a standard reference line for magnetic resonance (MR) imaging.

Purpose

To quantitatively validate the LEL/O line as a new standard brain CT reference line.

Material and Methods

We measured: angle 1 = the LEL/O line on scout images from the LEL/O line on parasagittal CT images (n=93); and angle 2 = the LEL/O line on scout images from the T/T line on high resolution midsagittal MR images (n=97). Angles in a clockwise direction were defined as positive and were expressed as mean±SD with the 95% confidence interval (CI) of the SD. Angle 2 was measured independently by two observers and intraclass correlation coefficients (ICCs) were calculated.

Results

Angle 1 was –0.4°±1.2° (95% CI of SD 1.1°–1.5°); angle 2 was –0.4°±2.0° (95% CI of SD, 1.8°–2.4°). The ICC in the angle 2 measurement was 0.780 (P<0.001), which indicated high inter-observer reliability.

Conclusion

The LEL/O lines on scout and parasagittal CT images show practically the same gradient, and these LEL/O lines are almost parallel to the T/T line. Use of the LEL/O line either for direct scanning or reformation can minimize intra- and inter-subject variations on CT images and mismatch between CT and MR images.

Automatic Tube Current Modulation and Tube Voltage Selection in Pediatric Computed Tomography: A Phantom Study on Radiation Dose and Image Quality

OBJECTIVES

The aim of this study was to investigate the effects of a modern automatic tube current modulation (ATCM) and automatic tube voltage selection (ATVS) system on radiation dose and image quality in pediatric head, and torso computed tomography (CT) examinations for various clinical indications.

MATERIALS AND METHODS

Four physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old child were used. Standard head, thorax, and abdomen/pelvis acquisitions were performed with (1) fixed tube current, (2) ATCM, and (3) ATVS. Acquisitions were performed at various radiation dose levels to generate images at different levels of quality. Reference volume CT dose index (CTDIvol), reference image noise, and reference contrast-to-noise ratios were determined. The potential dose reductions with ATCM and ATVS were assessed.

RESULTS

The percent reduction of CTDIvol with ATCM ranged from 8% to 24% for head, 16% to 39% for thorax, and 25% to 41% for abdomen/pelvis. The percent reduction of CTDIvol with ATVS varied on the clinical indication. In CT angiography, ATVS resulted to the highest dose reduction, which was up to 70% for head, 77% for thorax, and 34% for abdomen/pelvis. In noncontrast examinations, ATVS increased dose by up to 21% for head, whereas reduced dose by up to 34% for thorax and 48% for abdomen/pelvis.

CONCLUSIONS

In pediatric CT, the use of ATCM significantly reduces radiation dose and maintains image noise. The additional use of ATVS reduces further the radiation dose for thorax and abdomen/pelvis, and maintains contrast-to-noise ratio for the specified clinical diagnostic task.

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

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

Contrast-to-Noise Ratio Optimization in Coronary Computed Tomography Angiography: Validation in a Swine Model

RATIONALE AND OBJECTIVES

The accuracy of coronary computed tomography (CT) angiography depends upon the degree of coronary enhancement as compared to the background noise. Unfortunately, coronary contrast-to-noise ratio (CNR) optimization is difficult on a patient-specific basis. Hence, the objective of this study was to validate a new combined diluted test bolus and CT angiography protocol for improved coronary enhancement and CNR.

MATERIALS AND METHODS

The combined diluted test bolus and CT angiography protocol was validated in six swine (28.9 ± 2.7 kg). Specifically, the aortic and coronary enhancement and CNR of a standard CT angiography protocol, and a new combined diluted test bolus and CT angiography protocol were compared to a reference retrospective CT angiography protocol. Comparisons for all data were made using box plots, t tests, regression, Bland-Altman, root-mean-square error and deviation, as well as Lin's concordance correlation.

RESULTS

The combined diluted test bolus and CT angiography protocol was found to improve aortic and coronary enhancement by 26% and 13%, respectively, as compared to the standard CT angiography protocol. More importantly, the combined protocol was found to improve aortic and coronary CNR by 29% and 20%, respectively, as compared to the standard protocol.

CONCLUSION

A new combined diluted test bolus and CT angiography protocol was shown to improve coronary enhancement and CNR as compared to an existing standard CT angiography protocol.

Joint European Society of Paediatric Radiology (ESPR) and International Society for Forensic Radiology and Imaging (ISFRI) guidelines: paediatric postmortem computed tomography imaging protocol

Postmortem CT for investigating childhood deaths is increasingly utilised as a noninvasive adjunct or alternative to standard autopsy; however there are no standardised published imaging protocols. This article describes a standardised imaging protocol that has been developed based on current practices of international postmortem imaging practitioners and experts. This recommendation is expected to be useful for postmortem imaging centres wishing to update their existing practices and for those starting paediatric postmortem CT as a new service.

EFFECT OF PATIENT SIZE, ANATOMICAL LOCATION AND MODULATION STRENGTH ON DOSE DELIVERED AND IMAGE-QUALITY ON CT EXAMINATION

To study the effect of patient size, anatomical location and modulation strength (MS) on image-quality and delivered dose of CT scans acquired with automatic-exposure-control system (AEC). Four anthropomorphic phantoms (three paediatric and one thin adult) were studied, and normal and obese adults were simulated by placing bolus plates around the adult phantom. Thorax and abdomen-pelvis CT were performed using an AEC system equipped with five possible MS. Modulated tube current (mAsmod) was compared to Reference mAs and image-noise was assessed. Effective-mAs were lower than Reference-mAs for all but the obese phantom. However, reversal points were estimated for an effective diameter of 27.8 cm in thorax and 26.9 cm in abdomen-pelvis scans, beyond which the patterns of MS were inversed. mAsmod were dependent on attenuation differences among distinct anatomical location. Finally, dose delivered was associated to the mAsmod and patient's size, with both affecting image-quality.

A CONSORT-compliant prospective randomized controlled trial: radiation dose reducing in computed tomography using an additional lateral scout view combined with automatic tube current modulation: Phantom and patient study

BACKGROUND

Radiation exposure has been a hot point in research field of computed tomography (CT). Recently, automated tube current modulation (ATCM) has emerged as an important technique to reduce radiation exposure. Many studies have shown that the difference in scout view would affect modulation. This prospective randomized controlled study is aimed to investigate the impact of an additional lateral scout view on radiation dose and image quality in CT using ACTM.

METHODS

Combined with ATCM (Care Dose 4D) on multidetector CT, 2 thoracic phantom CT image series were acquired in which planning was conducted with either an anteroposterior (AP) or an AP-lateral scout view. Also, 410 patients underwent thoracic CT examinations using Care Dose 4D modulation and were randomized to either a scan planned with an AP-lateral scout or a single AP scout. Effects of the different scout views on applied effective milliampere seconds (mAs), volume CT dose index (CTDIvol) and dose-length-product (DLP) were analyzed. The quality of patient CT images was also assessed. Data were analyzed using independent t tests and linear correlation analysis.

RESULTS

Compared with AP groups, the mean CTDIvol (phantom, 0.89 ± 0.08 vs 1.36 ± 0.26 mGy, P < .001; in patients, 1.12 [0.96, 1.34] vs 2.16 [1.66, 2.64] mGy, P < .001) and DLP (in phantom, 26 [23.25, 28] vs 40 [34.25, 48] mGy×cm, P < .001; in patients, 41 [33, 41] vs 77 [60.5, 99.5] mGy×cm, P < .001) were significantly reduced by approximately 50% in AP-lateral scout view group. With the AP-lateral topogram, the radiation dose on different off-center positions was essentially equal (CTDIvol: 0.76-0.99 mGy; DLP: 22-28 mGy×cm effective dose: 0.31-0. 39 mSv). For image quality, contrast-to-noise ratio and signal-to-noise ratio values in the AP group were similar to those of AP-lateral scout view group.

CONCLUSION

AP combined with an additional lateral scout view using ACTM can significantly reduce the radiation dose without compromising image quality in chest screening CT.

PAEDIATRIC NECK MULTIDETECTOR COMPUTED TOMOGRAPHY: THE EFFECT OF BISMUTH SHIELDING ON THYROID DOSE AND IMAGE QUALITY

This study investigated the effect of bismuth shielding on thyroid dose and image quality in paediatric neck multidetector computed tomography (MDCT) performed with fixed tube current (FTC) and automatic exposure control (AEC). Four paediatric anthropomorphic phantoms representing the equivalent newborn, 1-, 5- and 10-y-old child were subjected to neck CT using a 16-slice MDCT system. Each scan was performed without and with single- and double-layered bismuth shield placed on the skin surface above the thyroid. Scans were repeated with cotton spacers of 1, 2 and 3 cm thick placed between the skin and shield, to study the effect of skin-to-shielding distance on image noise. Thyroid dose was measured with thermoluminescent dosemeters. The location of the thyroid within the phantom slices was determined by anthropometric data from patients' CT examinations whose body stature closely matched the phantoms. Effective dose (E) was estimated using the dose-length product (DLP) method. Image quality of resulted CT images was assessed through the image noise. Activation of AEC was found to decrease the thyroid dose by 46 % to the 10-y-old phantom subjected to neck CT. When FTC technique is used, single- and double-layered bismuth shielding was found to reduce the thyroid dose to the same phantom by 35 and 47 %, respectively. The corresponding reductions in AEC-activated scans were 60 and 66 %, respectively. Elevation of shields by 1-, 2- and 3-cm cotton spacers decreased the image noise by 69, 87 and 92 %, respectively, for single-layered FTC, without considerably affecting the thyroid dose. AEC was more effective in thyroid dose reduction than in-plane bismuth shields. Application of cotton spacers had no significant impact on thyroid dose, but significantly decreased the image noise.

MONITORING DOSE-LENGTH PRODUCT IN COMPUTED TOMOGRAPHY OF THE CHEST CONSIDERING SEX AND BODY WEIGHT

Dose-length product (DLP) is widely used as an indicator of the radiation dose in computed tomography. The aim of this study was to investigate the significance of sex and body weight in DLP-based monitoring of the radiation dose. Eight hundred computed tomographies of the chest performed using four different scanners were analysed. The DLP was compared with body weight by linear regression in men and women separately. The DLP was positively correlated with body weight, and dependence on sex and weight differed among scanners. Standard DLP values adjusted for sex and weight facilitated interscanner comparison of the radiation dose and its dependence on sex and weight. Adjusting the DLP for sex and weight allowed one to identify examinations with possibly excessive doses independently of weight. Monitoring the DLP in relation to sex and body weight appears to aid detailed comparison of the radiation dose among imaging protocols and scanners and daily observations to find unexpected variance.

Ultra-low-dose chest CT with iterative reconstruction does not alter anatomical image quality

PURPOSE

To evaluate the effect of dose reduction with iterative reconstruction (IR) on image quality of chest CT scan.

MATERIALS AND METHODS

Eighteen human cadavers had chest CT with one reference CT protocol (RP-CT; 120kVp/200mAs) and two protocols with dose reduction: low-dose-CT (LD-CT; 120kVp/40mAs) and ultra-low-dose CT (ULD-CT; 120kVp/10mAs). Data were reconstructed with filter-back-projection (FBP) for RP-CT and with FBP and IR (sinogram affirmed iterative reconstruction [SAFIRE^®]) algorithm for LD-CT and ULD-CT. Volume CT dose index (CTDIvol) were recorded. The signal-to-noise (SNR), contrast-to-noise (CNR) ratios of LD-CT and ULD-CT and quantitative parameters were compared to RP-CT. Two radiologists reviewed the CT examinations assessed independently the quality of anatomical structures and expressed a confidence level using a 2-point scale (50% and 95%).

RESULTS

CTDIvol was 2.69 mGy for LD-CT (-80%; P<0.01) and 0.67 mGy for ULD-CT (-95%; P<0.01) as compared to 13.42 mGy for RP-CT. SNR and CNR were significantly decreased (P<0.01) for LD-CT and ULD-CT, but IR improved these values satisfactorily. No significant differences were observed for quantitative measurements. Radiologists rated excellent/good the RP-CT and LD-CT images, whereas good/fair the ULD-CT images. Confidence level for subjective anatomical analysis was 95% for all protocols.

CONCLUSIONS

Dose reduction with a dose lower than 1 mGy, used in conjunction with IR allows performing chest CT examinations that provide a high quality of anatomical structures.