Universal 120-kV Dual-Source Ultra-High Pitch Protocol on the Photon-Counting CT System for Pediatric Abdomen of All Sizes: A Phantom Investigation Comparing With Energy-Integrating CT

OBJECTIVES

The purpose of this study is to determine if a universal 120-kV ultra-high pitch and virtual monoenergetic images (VMIs) protocol on the photon-counting computed tomography (PCCT) system can provide sufficient image quality for pediatric abdominal imaging, regardless of size, compared with protocols using a size-dependent kV and dual-source flash mode on the energy-integrating CT (EICT) system.

MATERIALS AND METHODS

One solid water insert and 3 iodine (2, 5, 10 mg I/mL) inserts were attached or inserted into phantoms of variable sizes, simulating the abdomens of a newborn, 5-year-old, 10-year-old, and adult-sized pediatric patients. Each phantom setting was scanned on an EICT using clinical size-specific kV dual-source protocols with a pitch of 3.0. The scans were performed with fixed scanning parameters, and the CTDI vol values of full dose were 0.30, 0.71, 1.05, and 7.40 mGy for newborn to adult size, respectively. In addition, half dose scans were acquired on EICT. Each phantom was then scanned on a PCCT (Siemens Alpha) using a universal 120-kV protocol with the same full dose and half dose as determined above on the EICT scanner. All other parameters matched to EICT settings. Virtual monoenergetic images were generated from PCCT scans between 40 and 80 keV with a 5-keV interval. Image quality metrics were compared between PCCT VMIs and EICT, including image noise (measured as standard deviation of solid water), contrast-to-noise ratio (CNR) (measured at iodine inserts with solid water as background), and noise power spectrum (measured in uniform phantom regions).

RESULTS

Noise at a PCCT VMI of 70 keV (7.0 ± 0.6 HU for newborn, 14.7 ± 1.6 HU for adult) is comparable ( P > 0.05, t test) or significantly lower ( P < 0.05, t test) compared with EICT (7.8 ± 0.8 HU for newborn, 15.3 ± 1.5 HU for adult). Iodine CNR from PCCT VMI at 50 keV (50.8 ± 8.4 for newborn, 27.3 ± 2.8 for adult) is comparable ( P > 0.05, t test) or significantly higher ( P < 0.05, t test) to the corresponding EICT measurements (57.5 ± 6.7 for newborn, 13.8 ± 1.7 for adult). The noise power spectrum curve shape of PCCT VMI is similar to EICT, despite PCCT VMI exhibiting higher noise at low keV levels.

CONCLUSIONS

The universal PCCT 120 kV with ultra-high pitch and postprocessed VMIs demonstrated equivalent or improved performance in noise (70 keV) and iodine CNR (50 keV) for pediatric abdominal CT, compared with size-specific kV images on the EICT.

2DeteCT - A large 2D expandable, trainable, experimental Computed Tomography dataset for machine learning

Recent research in computational imaging largely focuses on developing machine learning (ML) techniques for image reconstruction, which requires large-scale training datasets consisting of measurement data and ground-truth images. However, suitable experimental datasets for X-ray Computed Tomography (CT) are scarce, and methods are often developed and evaluated only on simulated data. We fill this gap by providing the community with a versatile, open 2D fan-beam CT dataset suitable for developing ML techniques for a range of image reconstruction tasks. To acquire it, we designed a sophisticated, semi-automatic scan procedure that utilizes a highly-flexible laboratory X-ray CT setup. A diverse mix of samples with high natural variability in shape and density was scanned slice-by-slice (5,000 slices in total) with high angular and spatial resolution and three different beam characteristics: A high-fidelity, a low-dose and a beam-hardening-inflicted mode. In addition, 750 out-of-distribution slices were scanned with sample and beam variations to accommodate robustness and segmentation tasks. We provide raw projection data, reference reconstructions and segmentations based on an open-source data processing pipeline.

Assessment of organ and effective doses received by adult patients undergoing computed tomography in three hospitals in Brazzaville, Congo Republic

The present study aimed to evaluate adult patient data collected from three hospitals in Brazzaville, Congo Republic, for the purpose of estimating organ and effective doses for each included examination type. A total of 1277 adult patients (aged 16-97 years) who underwent head, chest, abdominopelvic (AP), chest-abdomen-pelvis (CAP), and lumbar spine computed tomography scans were considered. The organ and effective doses were estimated using a Monte Carlo-based method. The effective doses were also determined using k-factors. In general, the organ and effective doses estimated in this study were higher than those reported in the literature. The k-factor method underestimated the effective dose by up to 65.9%. This study demonstrates that urgent steps should be taken to reduce doses administered to patients to optimal levels. Such optimal levels may be achieved by adopting local diagnostic reference levels, together with the implementation of dose reduction strategies.

The Role of a DirectDensity® CT Reconstruction in A Radiotherapy Workflow: A Phantom Study

The DirectDensity® CT reconstruction algorithm provides a reconstruction approach independent of the tube voltage, directly reconstructing the CT projection data into CT numbers related to the electron densities of the materials. This work examines the efficacy of DirectDensity® in the treatment planning process with both tissues and metallic materials. CT scans of a Cheese phantom were acquired at 80, 100, 120 and 140 kVp and reconstructed with different algorithms. Calibration curves were built for each kVp and reconstruction technique. To evaluate the flexibility of the DirectDensity® in dose calculations, a prostate cancer treatment plan was simulated on phantom images with and without metal inserts. Moreover, the robustness of the algorithm was tested by simulating a possible error in the selection of the calibration curve. As expected, the calibration curves related to DirectDensity® showed a tube voltage dependence only for densities above 1.82 g/cm3. The maximum percentage differences in dose distributions comparations never exceeded the 3% of tolerance and the 3D gamma analysis always returned indices greater than 90%. The results suggest that the DD reconstruction algorithm can be employed in most clinical cases and allows for a personalized radiotherapy cancer treatment workflow, maintaining its robustness and simplicity.

Variation in tube voltage for pediatric neck 64VCT: Effect on radiation dose and image quality

Exposure to ionizing radiation can cause cancer, especially in children. In computed tomography (CT), a trade-off exists between the radiation dose and image quality. Few studies have investigated the effect of dose reduction on image quality in pediatric neck CT. We aimed to assess the effect of peak kilovoltage on the radiation dose and image quality in pediatric neck multidetector-row CT. Measurements were made using three phantoms representative of children aged 1, 5, and 10 years, with tube voltages of 80, 100, and 120 kilovoltage peak (kVp); tube current of 10, 40, 80, 120, 150, 200, and 250 mA; and exposure time = 0.5 s (pitch, 0.984:1). Radiation dose estimates were derived from the dose-length product with a 64-multidetector-row CT scanner. Images obtained from the control protocol (120 kVp) were compared with the 80- and 100-kVp protocols. The effective dose (ED) was determined for each protocol and compared with the 120-kVp protocol. Quantitative analysis entailed noise measurements by recording the standard deviation of attenuation for a circular 1-cm² region of interest placed on homogeneous soft tissue structures in the phantom. The mean noise of the various kVp protocols was compared using the unpaired Student t-test. Reduction of ED was 37.58% and 68.58% for neck CT with 100 kVp and 80 kVp, respectively. The image noise level increased with the decrease in peak kilovoltage. Noise values were higher at 80 kVp at all neck levels, but did not increase at 100 kVp, compared to 120 kVp in the three phantoms. The measured noise difference was the greatest at 80 kVp (absolute increases<2.5 HU). The subjective image quality did not differ among the protocols. Thus, reducing voltage from 120 to 80 kVp for neck CT may achieve ED reduction of 68.58%, without compromising image quality.

Low dose cone beam CT for paediatric image-guided radiotherapy: Image quality and practical recommendations

PURPOSE

Cone beam CT (CBCT) is used in paediatric image-guided radiotherapy (IGRT) for patient setup and internal anatomy assessment. Adult CBCT protocols lead to excessive doses in children, increasing the risk of radiation-induced malignancies. Reducing imaging dose increases quantum noise, degrading image quality. Patient CBCTs also include 'anatomical noise' (e.g. motion artefacts), further degrading quality. We determine noise contributions in paediatric CBCT, recommending practical imaging protocols and thresholds above which increasing dose yields no improvement in image quality.

METHODS AND MATERIALS

Sixty CBCTs including the thorax or abdomen/pelvis from 7 paediatric patients (aged 6-13 years) were acquired at a range of doses and used to simulate lower dose scans, totalling 192 scans (0.5-12.8 mGy). Noise measured in corresponding regions of each patient and a 10-year-old phantom were compared, modelling total (including anatomical) noise, and quantum noise contributions as a function of dose. Contrast-to-noise ratio (CNR) was measured between fat/muscle. Soft tissue registration was performed on the kidneys, comparing accuracy to the highest dose scans.

RESULTS

Quantum noise contributed <20% to total noise in all cases, suggesting anatomical noise is the largest determinant of image quality in the abdominal/pelvic region. CNR exceeded 3 in over 90% of cases ≥ 1 mGy, and 57% of cases at 0.5 mGy. Soft tissue registration was accurate for doses > 1 mGy.

CONCLUSION

Anatomical noise dominates quantum noise in paediatric CBCT. Appropriate soft tissue contrast and registration accuracy can be achieved for doses as low as 1 mGy. Increasing dose above 1 mGy holds no benefit in improving image quality or registration accuracy due to the presence of anatomical noise.

A review on chest CT scanning parameters implemented in COVID-19 patients: bringing low-dose CT protocols into play

Background

This study aims to review chest computed tomography (CT) scanning parameters which are utilized to evaluate patients for COVID-19-induced pneumonia. Also, some of radiation dose reduction techniques in CT would be mentioned, because using these techniques or low-dose protocol can decrease the radiation burden on the population.

Main body

Chest CT scan can play a key diagnostic role in COVID-19 patients. Additionally, it can be useful to monitor imaging changes during treatment. However, CT scan overuse during the COVID-19 pandemic raises concerns about radiation-induced adverse effects, both in patients and healthcare workers.

Conclusion

By evaluating the CT scanning parameters used in several studies, one can find the necessity for optimizing these parameters. It has been found that chest CT scan taken using low-dose CT protocol is a reliable diagnostic tool to detect COVID-19 pneumonia in daily practice. Moreover, the low-dose chest CT protocol results in a remarkable reduction (up to 89%) in the radiation dose compared to the standard-dose protocol, not lowering diagnostic accuracy of COVID-19-induced pneumonia in CT images. Therefore, its employment in the era of the COVID-19 pandemic is highly recommended.

Clinical Implementation of Dual-Energy CT for Gastrointestinal Imaging

Dual-energy CT (DECT) overcomes several limitations of conventional single-energy CT (SECT) for the evaluation of gastrointestinal diseases. This article provides an overview of practical aspects of the DECT technology and acquisition protocols, reviews existing clinical applications, discusses current challenges, and describes future directions, with a focus on gastrointestinal imaging. A head-to-head comparison of technical specifications among DECT scanner implementations is provided. Energy- and material-specific DECT image reconstructions enable retrospective (i.e., after examination acquisition) image quality adjustments that are not possible using SECT. Such adjustments may, for example, correct insufficient contrast bolus or metal artifacts, thereby potentially avoiding patient recalls. A combination of low-energy monochromatic images, iodine maps, and virtual unenhanced images can be included in protocols to improve lesion detection and disease characterization. Relevant literature is reviewed regarding use of DECT for evaluation of the liver, gallbladder, pancreas, and bowel. Challenges involving cost, workflow, body habitus, and variability in DECT measurements are considered. Artificial intelligence and machine-learning image reconstruction algorithms, PACS integration, photon-counting hardware, and novel contrast agents are expected to expand the multienergy capability of DECT and further augment its value.

Evaluation of Ultra-low-dose Paediatric Cone-beam Computed Tomography for Image-guided Radiotherapy

AIMS

In image-guided radiotherapy, daily cone-beam computed tomography (CBCT) is rarely applied to children due to concerns over imaging dose. Simulating low-dose CBCT can aid clinical protocol design by allowing visualisation of new scan protocols in patients without delivering additional dose. This work simulated ultra-low-dose CBCT and evaluated its use for paediatric image-guided radiotherapy by assessment of image registration accuracy and visual image quality.

MATERIALS AND METHODS

Ultra-low-dose CBCT was simulated by adding the appropriate amount of noise to projection images prior to reconstruction. This simulation was validated in phantoms before application to paediatric patient data. Scans from 20 patients acquired at our current clinical protocol (0.8 mGy) were simulated for a range of ultra-low doses (0.5, 0.4, 0.2 and 0.125 mGy) creating 100 scans in total. Automatic registration accuracy was assessed in all 100 scans. Inter-observer registration variation was next assessed for a subset of 40 scans (five scans at each simulated dose and 20 scans at the current clinical protocol). This subset was assessed for visual image quality by Likert scale grading of registration performance and visibility of target coverage, organs at risk, soft-tissue structures and bony anatomy.

RESULTS

Simulated and acquired phantom scans were in excellent agreement. For patient scans, bony atomy registration discrepancies for ultra-low-dose scans fell within 2 mm (translation) and 1° (rotation) compared with the current clinical protocol, with excellent inter-observer agreement. Soft-tissue registration showed large discrepancies. Bone visualisation and registration performance reached over 75% acceptability (rated 'well' or 'very well') down to the lowest doses. Soft-tissue visualisation did not reach this threshold for any dose.

CONCLUSION

Ultra-low-dose CBCT was accurately simulated and evaluated in patient data. Patient scans simulated down to 0.125 mGy were appropriate for bony anatomy set-up. The large dose reduction could allow for more frequent (e.g. daily) image guidance and, hence, more accurate set-up for paediatric radiotherapy.

Best practice for the nuclear medicine technologist in CT-based attenuation correction and calcium score for nuclear cardiology

The use of hybrid systems is increasingly growing in Europe and this is progressively important for the final result of diagnostic tests. As an integral part of the hybrid imaging system, computed tomography (CT) plays a crucial role in myocardial perfusion imaging diagnostics. Throughout Europe, a variety of equipment is available and also different university curricula of the nuclear medicine technologist are observed. Hence, the Technologist Committee of the European Association of Nuclear Medicine proposes to identify, through a bibliographic review, the recommendations for best practice in computed tomography applied to attenuation correction and calcium score in myocardial perfusion imaging, which courses in the set of knowledge, skills, and competencies for nuclear medicine technologists. This document aims at providing recommendations for CT acquisition protocols and CT image optimization in nuclear cardiology.

Quantitative evaluation of the effect of changes in effective energy on the image quality in X-ray computed tomography

The X-ray effective energy differs for each computed tomography (CT) scanner even at the same tube voltage because of differences in the bow-tie filter and additional filter. Even when scanning with the same tube voltage and dose setting, these differences in effective energy result in different image noise levels. Although this qualitative change is known, the related quantitative changes have not been clarified. In this study, using two CT scanners with the same geometric specifications and detector configurations, we quantitatively assessed the reduction in image noise accompanying the increase in effective energy. We also clarified the fluctuations in CT number. For both CT scanners, the effective energy, the standard deviation (SD) of the noise image when using two water phantoms with diameters of 240 mm and 320 mm, and CT numbers of the sensitometry module were measured. Further, the dose required to obtain the same image noise level in each CT scanner was calculated. The effective energy difference was 5.5 keV to 10.7 keV, and the difference tended to be larger when the scan field of view was larger. The SD differences were 24% and 14% for the 320-mm and 240-mm phantoms, respectively. For converting to the dose required to obtain the same SD, the dose can be reduced by 42% and 24% for the 320-mm and 240-mm phantoms, respectively. The CT number difference of both CT scanners was small. Therefore, higher effective energy contributes to the reduction of image noise.

Using a Somatosensory Controller to Assess Body Size for Size-Specific Dose Estimates in Computed Tomography

Computed tomography (CT) has been widely used in the healthcare environment. Presently, the radiation dose in CT is determined using the size-specific dose estimate (SSDE). Accurate assessment of individual's body size is essential for dose estimation. In this study, we integrated a somatosensory controller with a CT scanner to measure patient's anterior-posterior diameter (APD) and lateral diameter (LATD) and calculate the corresponding effective diameter (ED). A total of 108 individuals with an average age of 38.6 years were enrolled in this study. Microsoft Kinect was used to acquire the depth image of subjects. A grayscale-to-surface height conversion curve was created using acrylic sheets for APD estimation. The APD, LATD, and ED were measured and compared with the results obtained using F ruler and CT images. The mean absolute differences for APD, LATD, and ED between Kinect and F ruler measurements were 5.2%, 1.3%, and 2.5%, respectively, while those between Kinect and CT measurements were 8.8%, 2.6%, and 5.0%, respectively. Kinect can replace CT or F ruler for real-time body size measurements. The use of the somatosensory controller has the advantages of simple, low cost, no radiation, and automatic calculation. It can accurately estimate patient's APD, LATD, and ED for SSDE.

Relationship between the radiation doses at nonenhanced CT studies using different tube voltages and automatic tube current modulation during anthropomorphic phantoms of young children

To compare the radiation dose and image noise of nonenhanced CT scans performed at 80, 100, and 120 kVp with tube current modulation (TCM) we used anthropomorphic phantoms of newborn, 1‐year‐old, and 5‐year‐old children. The noise index was set at 12. The image noise in the center of the phantoms at the level of the chest and abdomen was measured within a circumscribed region of interest. We measured the doses in individual tissues or organs with radio‐photoluminescence glass dosimeters for each phantom. Various tissues or organs were assigned and the radiation dose was calculated based on the international commission on radiological protection definition. With TCM the respective radiation dose at tube voltages of 80, 100, and 120 was 29.71, 31.60, and 33.79 mGy for the newborn, 32.00, 36.79, and 39.48 mGy for the 1‐year‐old, and 32.78, 38.11, and 40.85 mGy for the 5‐year‐old phantom. There were no significant differences in the radiation dose among the tube voltages and phantoms (P > 0.05). Our comparison of the radiation dose using anthropomorphic phantoms of young children showed that the radiation dose of nonenhanced CT performed at different tube voltages with TCM was not significantly different.

Radiation dose reduction based on CNR index with low-tube voltage scan for pediatric CT scan: experimental study using anthropomorphic phantoms

Background

To figure out the relationship between image noise and contrast noise ratio (CNR) at different tube voltages, using anthropomorphic new-born and 1-year-old phantoms, and to discuss the feasibility of radiation dose reduction, based on the obtained CNR index from image noise. We performed helical scans of the anthropomorphic new-born and 1-year-old phantoms. The CT numbers of the simulated aorta and image noise of the simulated mediastinum were measured; then CNR was calculated on 80, 100, and 120-kVp images reconstructed with filtered back projection (FBP) and iterative reconstruction (IR). We also measured the center and surface dose in the case of CNR of 14 using radio-photoluminescence glass dosimeters.

Results

The CT number of the simulated aorta was increased with decreasing tube voltage from 120 to 80 kVp (362.5–535.1 HU for the new-born, 358.9–532.6 HU for the 1-year-old). At CNR of 14, the center dose was 0.4, 0.6 and 0.9 mGy at FBP and 0.5, 0.6 and 0.9 mGy at IR and with the new-born phantom acquired at 80, 100 and 120 kVp, respectively. The center dose for FBP image was reduced by 56% at 80 kVp, 34% at 100 kVp for the new-born and 36% at 80 kVp, 22% at 100 kVp for the 1-year-old compared with that at 120 kVp. We obtained a relationship between image noise and CNR at different tube voltages using the anthropomorphic new-born and 1-year-old phantoms.

Conclusion

The use of index of CNR with low-tube voltage may achieve further radiation dose reduction in pediatric CT examination.

Pediatric Exposures to Ionizing Radiation: Carcinogenic Considerations

Children are at a greater risk than adults of developing cancer after being exposed to ionizing radiation. Because of their developing bodies and long life expectancy post-exposure, children require specific attention in the aftermath of nuclear accidents and when radiation is used for diagnosis or treatment purposes. In this review, we discuss the carcinogenic potential of pediatric exposures to ionizing radiation from accidental, diagnostic, and therapeutic modalities. Particular emphasis is given to leukemia and thyroid cancers as consequences of accidental exposures. We further discuss the evidence of cancers that arise as a result of radiotherapy and conclude the review with a summary on the available literature on the links between computer tomography (CT) and carcinogenesis. Appropriate actions taken to mitigate or minimize the negative health effects of pediatric exposures to ionizing radiation and future considerations are discussed.

Small Bowel Imaging: an Update

Bowel imaging had experienced relevant technical advances during the last decade. The developments in the field of cross-sectional imaging had a particular impact on the assessment of Crohn's disease. The purpose of this manuscript is to provide a review of the main progress of cross-sectional imaging in the assessment of Crohn's disease and other small bowel diseases with relevance in clinical practice and in research. Also, we outline the technical advances, trends, and potential contributions of new technological cross-sectional imaging improvements that may have potential impact and contribution in the near future.

Statistical model based iterative reconstruction in clinical CT systems. Part III. Task-based kV/mAs optimization for radiation dose reduction

PURPOSE

For a given imaging task and patient size, the optimal selection of x-ray tube potential (kV) and tube current-rotation time product (mAs) is pivotal in achieving the maximal radiation dose reduction while maintaining the needed diagnostic performance. Although contrast-to-noise (CNR)-based strategies can be used to optimize kV/mAs for computed tomography (CT) imaging systems employing the linear filtered backprojection (FBP) reconstruction method, a more general framework needs to be developed for systems using the nonlinear statistical model-based iterative reconstruction (MBIR) method. The purpose of this paper is to present such a unified framework for the optimization of kV/mAs selection for both FBP- and MBIR-based CT systems.

METHODS

The optimal selection of kV and mAs was formulated as a constrained optimization problem to minimize the objective function, Dose(kV,mAs), under the constraint that the achievable detectability index d'(kV,mAs) is not lower than the prescribed value of d'R for a given imaging task. Since it is difficult to analytically model the dependence of d' on kV and mAs for the highly nonlinear MBIR method, this constrained optimization problem is solved with comprehensive measurements of Dose(kV,mAs) and d'(kV,mAs) at a variety of kV-mAs combinations, after which the overlay of the dose contours and d' contours is used to graphically determine the optimal kV-mAs combination to achieve the lowest dose while maintaining the needed detectability for the given imaging task. As an example, d' for a 17 mm hypoattenuating liver lesion detection task was experimentally measured with an anthropomorphic abdominal phantom at four tube potentials (80, 100, 120, and 140 kV) and fifteen mA levels (25 and 50-700) with a sampling interval of 50 mA at a fixed rotation time of 0.5 s, which corresponded to a dose (CTDIvol) range of [0.6, 70] mGy. Using the proposed method, the optimal kV and mA that minimized dose for the prescribed detectability level of d'R=16 were determined. As another example, the optimal kV and mA for an 8 mm hyperattenuating liver lesion detection task were also measured using the developed framework. Both an in vivo animal and human subject study were used as demonstrations of how the developed framework can be applied to the clinical work flow.

RESULTS

For the first task, the optimal kV and mAs were measured to be 100 and 500, respectively, for FBP, which corresponded to a dose level of 24 mGy. In comparison, the optimal kV and mAs for MBIR were 80 and 150, respectively, which corresponded to a dose level of 4 mGy. The topographies of the iso-d' map and the iso-CNR map were the same for FBP; thus, the use of d'- and CNR-based optimization methods generated the same results for FBP. However, the topographies of the iso-d' and iso-CNR map were significantly different in MBIR; the CNR-based method overestimated the performance of MBIR, predicting an overly aggressive dose reduction factor. For the second task, the developed framework generated the following optimization results: for FBP, kV = 140, mA = 350, dose = 37.5 mGy; for MBIR, kV = 120, mA = 250, dose = 18.8 mGy. Again, the CNR-based method overestimated the performance of MBIR. Results of the preliminary in vivo studies were consistent with those of the phantom experiments.

CONCLUSIONS

A unified and task-driven kV/mAs optimization framework has been developed in this work. The framework is applicable to both linear and nonlinear CT systems such as those using the MBIR method. As expected, the developed framework can be reduced to the conventional CNR-based kV/mAs optimization frameworks if the system is linear. For MBIR-based nonlinear CT systems, however, the developed task-based kV/mAs optimization framework is needed to achieve the maximal dose reduction while maintaining the desired diagnostic performance.

Practical dose reduction tips for abdominal interventional procedures using CT-guidance

Reducing the radiation dose should be an endeavor not only for diagnostic CT exams but also for interventional procedures using CT-guidance. Given that interventional procedures vary in scope and complexity, there is greater variability in radiation doses delivered during CT procedures. The goal in an interventional procedure is simply to advance the interventional instruments into the target lesions, and as such diagnostic level doses are not required and only narrow scan range scans need to be acquired. Adherence to the principles outlined in this article will allow such procedures to be performed with reduced radiation doses.

The impact of pediatric-specific dose modulation curves on radiation dose and image quality in head computed tomography

BACKGROUND

The volume of CT examinations has increased with resultant increases in collective dose values over the last decade.

OBJECTIVE

To analyze the impact of the tube current and voltage modulation for dose values and image quality of pediatric head CT examinations.

MATERIALS AND METHODS

Head CT examinations were performed on anthropomorphic phantoms and four pediatric age categories before and after the introduction of dedicated pediatric curves for tube voltage and current modulation. Local diagnostic reference levels were calculated. Visual grading characteristic image quality evaluation was performed by four pediatric neuroradiologists and image noise comparisons were performed.

RESULTS

Pediatric-specific modulation curves demonstrated a 49% decrease in mean radiation dose for phantom examinations. The local diagnostic reference levels (CTDIvol) for clinical examinations decreased by 52%, 41%, 46% and 40% for newborn, 5-, 10- and 15-year-old patients, respectively. Visual grading characteristic image quality was maintained for the majority of age categorizations (area under the curve = 0.5) and image noise measurements did not change (P = 0.693).

CONCLUSION

Pediatric-specific dose modulation curves resulted in an overall mean dose reduction of 45% with no significant differences in subjective or objective image quality findings.

Concomitant Imaging Dose and Cancer Risk in Image Guided Thoracic Radiation Therapy

PURPOSE

Kilovoltage cone beam computed tomography (CT) (kVCBCT) imaging guidance improves the accuracy of radiation therapy but imposes an extra radiation dose to cancer patients. This study aimed to investigate concomitant imaging dose and associated cancer risk in image guided thoracic radiation therapy.

METHODS AND MATERIALS

The planning CT images and structure sets of 72 patients were converted to CT phantoms whose chest circumferences (Cchest) were calculated retrospectively. A low-dose thorax protocol on a Varian kVCBCT scanner was simulated by a validated Monte Carlo code. Computed doses to organs and cardiac substructures (for 5 selected patients of various dimensions) were regressed as empirical functions of Cchest, and associated cancer risk was calculated using the published models. The exposures to nonthoracic organs in children were also investigated.

RESULTS

The structural mean doses decreased monotonically with increasing Cchest. For all 72 patients, the median doses to the heart, spinal cord, breasts, lungs, and involved chest were 1.68, 1.33, 1.64, 1.62, and 1.58 cGy/scan, respectively. Nonthoracic organs in children received 0.6 to 2.8 cGy/scan if they were directly irradiated. The mean doses to the descending aorta (1.43 ± 0.68 cGy), left atrium (1.55 ± 0.75 cGy), left ventricle (1.68 ± 0.81 cGy), and right ventricle (1.85 ± 0.84 cGy) were significantly different (P<.05) from the heart mean dose (1.73 ± 0.82 cGy). The blade shielding alleviated the exposure to nonthoracic organs in children by an order of magnitude.

CONCLUSIONS

As functions of patient size, a series of models for personalized estimation of kVCBCT doses to thoracic organs and cardiac substructures have been proposed. Pediatric patients received much higher doses than did the adults, and some nonthoracic organs could be irradiated unexpectedly by the default scanning protocol. Increased cancer risks and disease adverse events in the thorax were strongly related to higher imaging doses and smaller chest dimensions.

Pediatric Computed Tomography Dose Optimization Strategies: A Literature Review

INTRODUCTION

Computed tomography (CT) dose optimization is an important issue in radiography because CT is the largest contributor to medical radiation dose and its use is increasing. However, CT dose optimization for pediatric patients could be more challenging than their adult counterparts. The purpose of this literature review was to identify and discuss the current pediatric CT dose saving techniques. Optimized pediatric protocols were also proposed.

METHODS

A comprehensive literature search was conducted using the Medline, ProQuest Health and Medical Complete, PubMed, ScienceDirect, Scopus, Springer Link, and Web of Science databases and the keywords CT, pediatric, optimization, protocol, and radiation dose to identify articles focusing on pediatric CT dose optimization strategies published between 2004 and 2014.

RESULTS AND SUMMARY

Seventy-seven articles were identified in the literature search. Strategies for optimizing a range of scan parameters and technical considerations including tube voltage and current, iterative reconstruction, diagnostic reference levels, bowtie filters, scout view, pitch, scan collimation and time, overscanning, and overbeaming for pediatric patients with different ages and body sizes and compositions were discussed. An example of optimized pediatric protocols specific to age and body size for the 64-slice CT scanners was devised. It is expected that this example could provide medical radiation technologists, radiologists, and medical physicists with ideas to optimize their pediatric protocols.

Combined Use of Automatic Tube Voltage Selection and Current Modulation with Iterative Reconstruction for CT Evaluation of Small Hypervascular Hepatocellular Carcinomas: Effect on Lesion Conspicuity and Image Quality

Objective

To assess the lesion conspicuity and image quality in CT evaluation of small (≤ 3 cm) hepatocellular carcinomas (HCCs) using automatic tube voltage selection (ATVS) and automatic tube current modulation (ATCM) with or without iterative reconstruction.

Materials and Methods

One hundred and five patients with 123 HCC lesions were included. Fifty-seven patients were scanned using both ATVS and ATCM and images were reconstructed using either filtered back-projection (FBP) (group A1) or sinogram-affirmed iterative reconstruction (SAFIRE) (group A2). Forty-eight patients were imaged using only ATCM, with a fixed tube potential of 120 kVp and FBP reconstruction (group B). Quantitative parameters (image noise in Hounsfield unit and contrast-to-noise ratio of the aorta, the liver, and the hepatic tumors) and qualitative visual parameters (image noise, overall image quality, and lesion conspicuity as graded on a 5-point scale) were compared among the groups.

Results

Group A2 scanned with the automatically chosen 80 kVp and 100 kVp tube voltages ranked the best in lesion conspicuity and subjective and objective image quality (p values ranging from < 0.001 to 0.004) among the three groups, except for overall image quality between group A2 and group B (p = 0.022). Group A1 showed higher image noise (p = 0.005) but similar lesion conspicuity and overall image quality as compared with group B. The radiation dose in group A was 19% lower than that in group B (p = 0.022).

Conclusion

CT scanning with combined use of ATVS and ATCM and image reconstruction with SAFIRE algorithm provides higher lesion conspicuity and better image quality for evaluating small hepatic HCCs with radiation dose reduction.

Paediatric CT optimisation utilising Catphan® 600 and age-specific anthropomorphic phantoms

The purpose of the study is to perform phantom-based optimisation of paediatric computed tomography (CT) protocols and quantify the impact upon radiation dose and image noise levels. The study involved three Portuguese paediatric centres. Currently employed scanning protocols for head and chest examinations and combinations of exposure parameters were applied to a Catphan(®)600 phantom to review the CT dose impact. Contrast-noise ratio (CNR) was quantified using Radia Diagnostic(®) tool. Imaging parameters, returning similar CNRs (<1) and dose savings were applied to three paediatric anthropomorphic phantoms. OsiriX software based on standard deviation pixel values facilitated image noise analysis. Currently employed protocols and age categorisation varied between centres. Manipulation of exposure parameters facilitated mean dose reductions of 33 and 28 % for paediatric head and chest CT examinations, respectively. The majority of the optimised CT examinations resulted in image noise similar to currently employed protocols. Dose reductions of up to 33 % were achieved with image quality maintained.

Development of pediatric CT protocols for specific scanners: why bother?

When determining a strategy for pediatric CT scanning, clinical staff can either elect to adjust routine adult-protocol parameter settings on a case-by-case basis or rely on pre-set pediatric protocol parameters. The advantages of the latter approach are the topic of this manuscript. This paper outlines specific options to consider, including the need for regular protocol review.

Perspectives on radiation dose in abdominal imaging

Reported instances of patients' overexposure to imaging-related radiation have spurred the radiology and medical physics communities to identify and develop methods for decreasing the amount of radiation used to achieve diagnostic-quality images. These initiatives include examining and optimizing conventional CT scanning parameters, introducing innovative scan protocols, and incorporating novel dose reduction technologies. The greatest challenge to effective dose reduction in the abdomen and pelvis remains patient size. Here, we review the state of the art in abdominopelvic CT in both adult and pediatric patients and describe some of our own efforts in dose reduction for these types of examinations.

Can a revised paediatric radiation dose reduction CT protocol be applied and still maintain anatomical delineation, diagnostic confidence and overall imaging quality?

OBJECTIVE

To compare multidetector CT (MDCT) radiation doses between default settings and a revised dose reduction protocol and to determine whether the diagnostic confidence can be maintained with imaging quality made under the revised protocol in paediatric head, chest and abdominal CT studies.

METHODS

The study retrospectively reviewed head, chest, abdominal and thoracoabdominal MDCT studies, comparing 231 CT studies taken before (Phase 1) and 195 CT studies taken after (Phase 2) the implemented revised protocol. Image quality was assessed using a five-point grading scale based on anatomical criteria, diagnostic confidence and overall quality. Image noise and dose-length product (DLP) were collected and compared.

RESULTS

The relative dose reductions between Phase 1 and Phase 2 were statistically significant in 35%, 51% and 54% (p < 0.001) of head, chest and abdominal CT studies, respectively. There were no statistically significant differences in overall image quality score comparisons in the head (p = 0.3), chest (p = 0.7), abdominal (p = 0.7) and contiguous thoracic (p = 0.1) and abdominal (p = 0.2) CT studies, with the exception of anatomical quality in definition of bronchial walls and delineation of intrahepatic portal branches in thoracoabdominal CTs, and diagnostic confidence in mass lesion in head CTs, liver lesion (>1 cm), splanchnic venous thrombosis, pancreatitis in abdominal CTs, and emphysema and aortic dissection in thoracoabdominal CTs.

CONCLUSION

Paediatric CT radiation doses can be significantly reduced from manufacturer's default protocol while still maintaining anatomical delineation, diagnostic confidence and overall imaging quality.

ADVANCES IN KNOWLEDGE

Revised paediatric CT protocol can provide a half DLP reduction while preserving overall imaging quality.

Radiation dose optimization for CT-guided interventional procedures in the abdomen and pelvis

Radiation dose to patients can be high for some CT-guided interventional procedures in the abdomen and pelvis, especially tumor ablations. Strategies for radiation dose reduction include choosing an alternative guidance modality that does not use radiation whenever feasible, restricting the cranio-caudal length of interventional scans to the interventional target, and refinement of technical skills in order to minimize the number of scans acquired for interventional guidance. Dose optimization for these procedures is best achieved by lowering the tube current relative to the prior diagnostic scan, choosing dose efficient scanning modes, and using intermittent-mode, narrowly collimated CT fluoroscopy for interventional guidance.

CT angiography in potential living kidney donors: 80 kVp versus 120 kVp

OBJECTIVE

The purpose of this article is to retrospectively investigate the diagnostic accuracy, image quality, and radiation dose of renal artery CT angiography (CTA), at 80 kVp compared with 120 kVp, in adult kidney donors.

MATERIALS AND METHODS

CTA examinations of 258 consecutive potential kidney donors were retrospectively evaluated; 189 patients were scanned using 64-MDCT scanners (higher maximal tube current), and 69 patients were scanned using 16-MDCT scanners (lower maximal tube current). On the basis of the tube potential and scanners, the study population was divided into four groups. Qualitative and quantitative analysis include vascular attenuation measurements, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Volume CT dose index (CTDIvol) was recorded, and size-specific dose estimate was also estimated.

RESULTS

Using 80 kVp for the 16-MDCT scanner, there was a 64.9% reduction in size-specific dose estimate (66.1% reduction in CTDIvol), increased noise, and tube current saturation in all cases. Axial image quality was significantly lower compared with that obtained at 120 kVp (p = 0.02), but image quality and visibility of renal artery branch order were comparable. Using 80 kVp for the 64-MDCT scanner, there was a 40.5% reduction in size-specific dose estimate (43.6% reduction in CTDIvol) and increased SNR and CNR (p < 0.001). No significant differences in 3D image quality and branch order visibility were observed. Tube current saturation was reached in 31% of cases. One hundred fifty-one patients (86 imaged at 80 kVp and 65 imaged at 120 kVp) underwent donor nephrectomy; CTA diagnostic accuracy was 100%.

CONCLUSION

Renal artery CTA using 80 kVp combined with limiting the tube current results in a significant reduction in radiation dose and improved SNR and CNR, without deterioration of image quality.

Reducing Radiation Dose in Emergency CT Scans While Maintaining Equal Image Quality: Just a Promise or Reality for Severely Injured Patients?

Objective. This study aims to assess the impact of adaptive statistical iterative reconstruction (ASIR) on CT imaging quality, diagnostic interpretability, and radiation dose reduction for a proven CT acquisition protocol for total body trauma. Methods. 18 patients with multiple trauma (ISS ≥ 16) were examined either with a routine protocol (n = 6), 30% (n = 6), or 40% (n = 6) of iterative reconstruction (IR) modification in the raw data domain of the routine protocol (140 kV, collimation: 40, noise index: 15). Study groups were matched by scan range and maximal abdominal diameter. Image noise was quantitatively measured. Image contrast, image noise, and overall interpretability were evaluated by two experienced and blinded readers. The amount of radiation dose reductions was evaluated. Results. No statistically significant differences between routine and IR protocols regarding image noise, contrast, and interpretability were present. Mean effective dose for the routine protocol was 25.3 ± 2.9 mSv, 19.7 ± 5.8 mSv for the IR 30, and 17.5 ± 4.2 mSv for the IR 40 protocol, that is, 22.1% effective dose reduction for IR 30 (P = 0.093) and 30.8% effective dose reduction for IR 40 (P = 0.0203). Conclusions. IR does not reduce study interpretability in total body trauma protocols while providing a significant reduction in effective radiation dose.

Survey of clinical doses from computed tomography examinations in the Canadian province of Manitoba

The purpose of this study was to document CT doses for common CT examinations performed throughout the province of Manitoba. Survey forms were sent out to all provincial CT sites. Thirteen out of sixteen (81 %) sites participated. The authors assessed scans of the brain, routine abdomen-pelvis, routine chest, sinuses, lumbar spine, low-dose lung nodule studies, CT pulmonary angiograms, CT KUBs, CT colonographies and combination chest-abdomen-pelvis exams. Sites recorded scanner model, protocol techniques and patient and dose data for 100 consecutive patients who were scanned with any of the aforementioned examinations. Mean effective doses and standard deviations for the province and for individual scanners were computed. The Kruskal-Wallis test was used to compare the variability of effective doses amongst scanners. The t test was used to compare doses and their provincial ranges between newer and older scanners and scanners that used dose saving tools and those that did not. Abdomen-pelvis, chest and brain scans accounted for over 70 % of scans. Their mean effective doses were 18.0 ± 6.7, 13.2 ± 6.4 and 3.0 ± 1.0 mSv, respectively. Variations in doses amongst scanners were statistically significant. Most examinations were performed at 120 kVp, and no lower kVp was used. Dose variations due to scanner age and use of dose saving tools were not statistically significant. Clinical CT doses in Manitoba are broadly similar to but higher than those reported in other Canadian provinces. Results suggest that further dose reduction can be achieved by modifying scanning techniques, such as using lower kVp. Wide variation in doses amongst different scanners suggests that standardisation of scanning protocols can reduce patient dose. New technological advances, such as dose-reduction software algorithms, can be adopted to reduce patient dose.

Effect of tube voltage on CT noise levels in different phantom sizes

OBJECTIVE

The purpose of this study was to determine the effect of lowering tube voltage on dose and noise in cylindric water phantoms to optimize quality and decrease the radiation dose for body CT.

MATERIALS AND METHODS

We performed CT on cylindric water phantoms with diameters of 10, 20, 25, and 30 cm, simulating the abdomen of an infant, child, adolescent, and adult. We used tube voltages of 120, 100, and 80 kVp. The CT dose index (32-cm reference) ranged from 1 to 10 mGy in 10- and 20-cm phantoms and from 2 to 20 mGy in the 25- and 30-cm phantoms. The noise was measured at the center and periphery of the scans. Central and peripheral doses were measured in 16- and 32-cm CT dose index phantoms, and the ratio of central to peripheral doses was calculated.

RESULTS

At the same noise levels, there was no significant increase in dose in 10-cm cylindric water phantoms when tube voltage was decreased to either 80 or 100 kVp. In 20-, 25-, and 30-cm phantoms, there was a 1-6% increase in dose when tube voltage was decreased to 100 kVp. Central-to-peripheral noise ratios increased 7-37% with increased phantom size. The measured peripheral dose increased as much as 5%.

CONCLUSION

Our findings support the practice of lowering tube voltage to 80 kVp for imaging of infants and to 100 kVp for imaging of older children. The increase in peripheral dose with decreased tube voltage is minimal and is unlikely to cause substantial change in the effective dose.

Reducing radiation dose in body CT: a primer on dose metrics and key CT technical parameters

OBJECTIVE

The purpose of this article is to describe how to interpret radiation dosi-metric data available on a body CT dose report and to explain the effects of key operator-chosen CT parameters on patient radiation dose.

CONCLUSION

To apply dose reduction strategies in body CT, radiologists must understand the information contained in the CT dose report and know the effects of key CT technical parameters on patient radiation exposure.

CT enterography at 80 kVp with adaptive statistical iterative reconstruction versus at 120 kVp with standard reconstruction: image quality, diagnostic adequacy, and dose reduction

OBJECTIVE

The objective of our study was to evaluate the image quality and diagnostic adequacy of the following two CT enterography protocols in patients weighing less than 160 lb (72 kg): 80-kVp imaging with the adaptive statistical iterative reconstruction (ASIR) in comparison with 120-kVp imaging with the filtered back projection reconstruction.

MATERIALS AND METHODS

We retrospectively reviewed 133 CT enterography examinations of 127 patients weighing less than 160 lb, 64 80-kVp examinations, and 69 120-kVp examinations. Image quality for evaluation of the bowel wall, mesenteric vessels, and hepatic parenchyma and the overall image quality were graded on a scale of 1-5 (1 = poor, 2 = acceptable, 3 = good, 4 = very good, 5 = excellent). Diagnostic accuracy for the detection of inflammatory bowel disease was evaluated. The volume CT dose index (CTDI(vol)) was recorded and effective dose was calculated from scanner-generated dose-length product.

RESULTS

There was a statistically significant decrease in the mean image quality scores for 80-kVp examinations compared with 120-kVp examinations for evaluation of the bowel wall (3.19 vs 3.70, respectively) and liver (3.12 vs 3.81) and for overall image quality (3.23 vs 3.68), but there was no significant decrease in score for evaluation of the mesenteric vessels (3.63 vs 3.67). None of the 80-kVp examinations was graded as poor, and all were considered to be of acceptable quality. Both techniques had comparable diagnostic accuracy for the detection of inflammatory bowel disease. Interobserver agreement was fair to moderate for qualitative image grading and was substantial for the detection of features of inflammatory bowel disease. The mean CTDI(vol) and effective dose for the 80-kVp examinations were 6.15 mGy and 4.60 mSv, respectively, and for the 120-kVp examinations, 20.79 mGy and 15.81 mSv.

CONCLUSION

In patients weighing less than 160 lb, CT enterography examinations at 80 kVp with 30% ASIR produce diagnostically acceptable image quality with an average CTDI(vol) of 6.15 mGy and an average effective dose of 4.60 mSv.

Impact of iterative reconstruction on image quality and radiation dose in multidetector CT of large body size adults

OBJECTIVE

To compare image quality and radiation dose using Adaptive Statistical Iterative Reconstruction (ASiR) and Filtered Back Projection (FBP) in patients weighing ≥ 91 kg.

METHODS

In this Institution Review Board-approved retrospective study, single-phase contrast-enhanced abdominopelvic CT examinations of 100 adults weighing ≥ 91 kg (mean body weight: 107.6 ± 17.4 kg range: 91-181.9 kg) with (1) ASiR and (2) FBP were reviewed by two readers in a blinded fashion for subjective measures of image quality (using a subjective standardized numerical scale and objective noise) and for radiation exposure. Imaging parameters and radiation dose results of the two techniques were compared within weight and BMI sub-categories.

RESULTS

All examinations were found to be of adequate quality. Both subjective (mean = 1.4 ± 0.5 vs. 1.6 ± 0.6, P < 0.05) and objective noise (13.0 ± 3.2 vs.19.5 ± 5.7, P < 0.0001) were lower with ASiR. Average radiation dose reduction of 31.5 % was achieved using ASiR (mean CTDIvol. ASiR: 13.5 ± 7.3 mGy; FBP: 19.7 ± 9.0 mGy, P < 0.0001). Other measures of image quality were comparable between the two techniques. Trends for all parameters were similar in patients across weight and BMI sub-categories.

CONCLUSION

In obese individuals, abdominal CT images reconstructed using ASiR provide diagnostic images with reduced image noise at lower radiation dose.

KEY POINTS

• CT images in obese adults are noisy, even with high radiation dose. • Newer iterative reconstruction techniques have theoretical advantages in obese patients. • Adaptive statistical iterative reconstruction should reduce image noise and radiation dose. • This has been proven in abdominopelvic CT images of obese patients.

CT radiation dose optimization and estimation: an update for radiologists

In keeping with the increasing utilization of CT examinations, the greater concern about radiation hazards from examinations has been addressed. In this regard, CT radiation dose optimization has been given a great deal of attention by radiologists, referring physicians, technologists, and physicists. Dose-saving strategies are continuously evolving in terms of imaging techniques as well as dose management. Consequently, regular updates of this issue are necessary especially for radiologists who play a pivotal role in this activity. This review article will provide an update on how we can optimize CT dose in order to maximize the benefit-to-risk ratio of this clinically useful diagnostic imaging method.

Quality initiatives: CT radiation dose reduction: how to implement change without sacrificing diagnostic quality

The risks and benefits of using computed tomography (CT) as opposed to another imaging modality to accomplish a particular clinical goal should be weighed carefully. To accurately assess radiation risks and keep radiation doses as low as reasonably achievable, radiologists must be knowledgeable about the doses delivered during various types of CT studies performed at their institutions. The authors of this article propose a process improvement approach that includes the estimation of effective radiation dose levels, formulation of dose reduction goals, modification of acquisition protocols, assessment of effects on image quality, and implementation of changes necessary to ensure quality. A first step toward developing informed radiation dose reduction goals is to become familiar with the radiation dose values and radiation-associated health risks reported in the literature. Next, to determine the baseline dose values for a CT study at a particular institution, dose data can be collected from the CT scanners, interpreted, tabulated, and graphed. CT protocols can be modified to reduce overall effective dose by using techniques such as automated exposure control and iterative reconstruction, as well as by decreasing the number of scanning phases, increasing the section thickness, and adjusting the peak voltage (kVp setting), tube current-time product (milliampere-seconds), and pitch. Last, PDSA (plan, do, study, act) cycles can be established to detect and minimize negative effects of dose reduction methods on image quality.

Image Gently: progress and challenges in CT education and advocacy

Significant progress has been made in radiation protection for children during the last 10 years. This includes increased awareness of the need for radiation protection for pediatric patients with international partnerships through the Alliance for Radiation Safety in Pediatric Imaging. This paper identifies five areas of significant progress in radiation safety for children: the growth of the Alliance; the development of an adult radiation protection campaign Image Wisely™; increased collaboration with government agencies, societies and the vendor community; the development of national guidelines in pediatric nuclear medicine, and the development of a size-based patient dose correction factor by the American Association of Physicists in Medicine, Task Group 204. However, many challenges remain. These include the need for continued education and change of practice at adult-focused hospitals where many pediatric CT exams are performed; the need for increased emphasis on appropriateness of pediatric imaging and outcomes research to validate the performance of CT studies, and the advancement of the work of the first pediatric national dose registry to determine the "state of the practice" with the final goal of establishing ranges of optimal CT technique for specific scan indications when imaging children with CT.