Dose reduction in paediatric MDCT: general principles

Cumulative effective doses from radiologic procedures for pediatric oncology patients

OBJECTIVE

Our aim was to estimate the cumulative effective doses (CEDs) from radiologic procedures for a cohort of pediatric oncology patients.

METHODS

A retrospective cohort study of the imaging histories of 150 pediatric oncology patients (30 each in 5 subgroups, that is, leukemia, lymphomas, brain tumors, neuroblastomas, and assorted solid tumors) for 5 years after diagnosis was performed. All procedures involving ionizing radiation were recorded, including radiography, computed tomography (CT), nuclear medicine (NM) studies, fluoroscopy, and interventional procedures. CED estimates were calculated.

RESULTS

Individual CED estimates ranged from <1 mSv to 642 mSv, with a median of 61 mSv. CT and NM were the greatest contributors; CT constituted 30% of procedures but 52% of the total CED, and NM constituted 20% and 46%, respectively. There was considerable variability between tumor subgroups. CED estimates were highest in the neuroblastoma (median: 213 mSv [range: 36-489 mSv]) and lymphoma (median: 191 mSv [range: 10-642 mSv]) groups and lowest in the leukemia group (median: 5 mSv [range: 0.2-57 mSv]).

CONCLUSIONS

CEDs from diagnostic and interventional imaging for pediatric oncology patients vary considerably according to diagnoses, individual clinical courses, and imaging modalities used. Increased awareness may promote strategies to reduce the radiation burden to this population.

Patient size measured on CT images as a function of age at a tertiary care children's hospital

OBJECTIVE

The purpose of our study was to measure patient size on CT images as a function of age at a large tertiary care children's hospital to develop current patient size data for modeling optimal x-ray exposure factors in children.

MATERIALS AND METHODS

Anteroposterior and transverse dimensions of the head, thorax, abdomen, and pelvis were measured on CT examinations of pediatric patients less than 21 years old performed between June and November 2007. Patients with diseases that could affect measurements were excluded. From 1,009 patients, 336 examinations of each of four body regions were selected; 2,688 measurements were made and separated into 21 groups. Statistical model building and prediction equations were established for each region and 95% prediction intervals were used for analyses.

RESULTS

Rapid growth of the head occurred from birth to approximately 2 years followed by a gradual plateau until 21 years. The thoracic, abdominal, and pelvic regions showed a linear relationship between age and size. Fitted equations showed transverse trunk measurements increased more rapidly than anteroposterior measurements. The anteroposterior trunk size growth rate was relatively region independent; transverse pelvic dimensions grew more rapidly than thoracic or abdominal regions. There was a broad overlap of predicted patient size ranges as a function of age within each region. Excellent interobserver agreement was measured by Pearson's correlation coefficient (r) (all p < 0.0001).

CONCLUSION

Fitted average patient sizes are age dependent; however, predicted individual patient size does not correlate well with age. Our study suggests that pediatric patient body size should be determined for individual patients before performing diagnostic imaging procedures that entail radiation risks.

Multidetector CT in children: current concepts and dose reduction strategies

The recent technical development of multidetector CT (MDCT) has contributed to a substantial increase in its diagnostic applications and accuracy in children. A major drawback of MDCT is the use of ionising radiation with the risk of inducing secondary cancer. Therefore, justification and optimisation of paediatric MDCT is of great importance in order to minimise these risks ("as low as reasonably achievable" principle). This review will focus on all technical and non-technical aspects relevant for paediatric MDCT optimisation and includes guidelines for radiation dose level-based CT protocols.

Motion artifact on high-resolution CT images of pediatric patients: comparison of volumetric and axial CT methods

OBJECTIVE

The purpose of this study was to address the controversy whether the quality of volumetric high-resolution CT (HRCT) images is as good as that of axial nonvolumetric HRCT images by assessing the degree of motion artifact on images acquired with the two methods at MDCT of pediatric patients with known or suspected lung disease.

MATERIALS AND METHODS

A search of the hospital information system was conducted to identify the cases of pediatric patients with clinically suspected or known interstitial lung disease who underwent 16-MDCT of the chest with both volumetric and axial HRCT acquisitions (both 1.25-mm slice thickness) from March 2005 to July 2008. Two pediatric radiologists reviewed the images for the presence of motion artifacts at three anatomic levels (upper, middle, and lower lung zones). Motion artifacts were given numerical grades representing no artifact to severe artifact, and the paired Student's t test was used to compare the scores for the two acquisition methods. A total motion score for each acquisition was calculated by summing the scores for each of the three lung zones, and the scores for the two imaging methods were compared. Correlation between degree of motion artifact and age was evaluated. Effective radiation doses were estimated for volumetric and axial CT acquisitions.

RESULTS

The study population consisted of 54 children (28 boys, 26 girls; mean age, 11.7 +/- 3.8 years; range, 5-18 years; eight inpatients, 46 outpatients) who underwent a total of 54 MDCT chest studies with volumetric and axial HRCT acquisitions. Motion artifact scores were higher for axial than for volumetric HRCT images of the upper (1.2 vs 1.0), middle (1.6 vs 1.2), and lower (2.2 vs 1.5) lung zones (p < 0.05 at each level). The total motion score of the axial HRCT images (mean, 5; range, 1-9) was higher than that of the volumetric HRCT images (mean, 3.6; range, 1-8) (p < 0.05). Younger age correlated with higher motion artifact score on axial HRCT images (r = -0.36, p < 0.01), whereas no correlation was found between age and motion artifact score on volumetric HRCT images (r = -0.12, p = 0.38). The effective radiation doses were 0.57 mSv for axial HRCT acquisition and 7.6 mSv for volumetric acquisition. The addition of axial acquisition increased the total radiation dose of the MDCT examination 7.1%.

CONCLUSION

At CT of pediatric patients, reconstructed HRCT images from volumetric MDCT acquisition have significantly less motion artifact than images obtained with traditional axial acquisition.

Pediatric renovascular hypertension in Thailand: CT angiographic findings

BACKGROUND

Renovascular disease is an uncommon but important cause of hypertension in children. When unrecognized and untreated, renovascular hypertension in children can have serious complications.

OBJECTIVE

To review the causes of renovascular hypertension and computed tomography angiographic (CTA) findings in children and adolescents.

MATERIALS AND METHODS

Twenty-eight CTAs from January 2004 to March 2008 of 23 children and adolescents with hypertension were reviewed for the causes and CTA findings.

RESULTS

Nine of the 23 children (39%) had abnormal renal arteries with or without abnormal abdominal aortas. Four of these children had Takayasu arteritis, one had moyamoya disease, and one had median arcuate ligament syndrome. One with chronic pyelonephritis had severe stenosis of the proximal right renal artery. The other two children had renal artery stenosis with a nonspecific cause. One child with a normal abdominal aorta and renal arteries had a right suprarenal mass. On pathological examination a ganglioneuroma was found.

CONCLUSION

CTA can help in diagnosis of renovascular hypertension in children and adolescents. Although CTA is not a screening modality, it is appropriate in some situations.

Radiation dose reduction in computed tomography: techniques and future perspective

Despite universal consensus that computed tomography (CT) overwhelmingly benefits patients when used for appropriate indications, concerns have been raised regarding the potential risk of cancer induction from CT due to the exponentially increased use of CT in medicine. Keeping radiation dose as low as reasonably achievable, consistent with the diagnostic task, remains the most important strategy for decreasing this potential risk. This article summarizes the general technical strategies that are commonly used for radiation dose management in CT. Dose-management strategies for pediatric CT, cardiac CT, dual-energy CT, CT perfusion and interventional CT are specifically discussed, and future perspectives on CT dose reduction are presented.

Association between mucoid Pseudomonas infection and bronchiectasis in children with cystic fibrosis

PURPOSE

To correlate the severity of bronchiectasis in children with cystic fibrosis with clinical and microbiologic variables in order to clarify risk factors for the development of irreversible lung disease.

MATERIALS AND METHODS

After institutional review board approval and parental informed consents were obtained, a HIPAA-compliant longitudinal epidemiologic evaluation was performed in patients with cystic fibrosis who were enrolled in the Wisconsin trial of newborn screening from 1985 to 2009. Thin-section chest computed tomography (CT) was used in a prospective cross-sectional design to study patients ranging in age from 6.6 to 17.6 years (mean, 11.5 years). Thin-section CT scores were determined objectively on coded images by multiple raters in a standardized fashion. Microbiologic data were obtained by means of culture of respiratory secretions by using methods for differentiation of Pseudomonas aeruginosa (PA) as either nonmucoid or mucoid.

RESULTS

Eighty-three percent of patients (68 of 82) showed bronchiectasis of varying severity. Of 12 potential risk factors, only respiratory infection with mucoid PA correlated significantly with bronchiectasis (P = .041).

CONCLUSION

The severity of bronchiectasis in children with cystic fibrosis is significantly related to respiratory infection with mucoid PA; attempts to prevent bronchiectasis should include reducing exposure to and early eradication of PA.

Cystic fibrosis: are volumetric ultra-low-dose expiratory CT scans sufficient for monitoring related lung disease?

PURPOSE

To assess whether chest computed tomography (CT) scores from ultra-low-dose end-expiratory scans alone could suffice for assessment of all cystic fibrosis (CF)-related structural lung abnormalities.

MATERIALS AND METHODS

In this institutional review board-approved study, 20 patients with CF aged 6-20 years (eight males, 12 females) underwent low-dose end-inspiratory CT and ultra-low-dose end-expiratory CT. Informed consent was obtained. Scans were randomized and scored by using the Brody-II CT scoring system to assess bronchiectasis, airway wall thickening, mucus plugging, and opacities. Scoring was performed by two observers who were blinded to patient identity and clinical information. Mean scores were used for all analyses. Statistical analysis included assessment of intra- and interobserver variability, calculation of intraclass correlation coefficients (ICCs), and Bland-Altman plots.

RESULTS

Median age was 12.6 years (range, 6.3-20.3 years), median forced expiratory volume in 1 second was 100% (range, 46%-127%) of the predicted value, and median forced vital capacity was 99% (range, 61%-123%) of the predicted value. Very good agreement was observed between end-inspiratory and end-expiratory CT scores for Brody-II total score (ICC = 0.96), bronchiectasis (ICC = 0.98), airway wall thickening (ICC = 0.94), mucus plugging (ICC = 0.96), and opacities (ICC = 0.90). Intra- and interobserver agreement were good to very good (ICC range, 0.70-0.98). Bland-Altman plots showed that differences in scores were independent of score magnitude.

CONCLUSION

In this pilot study, CT scores from end-expiratory and end-inspiratory CT match closely, suggesting that ultra-low-dose end-expiratory CT alone may be sufficient for monitoring CF-related lung disease. This would help reduce radiation dose for a single investigation by up to 75%.

Update on congenital spinal deformities: preoperative evaluation

STUDY DESIGN

Review.

OBJECTIVE

To review and outline the preoperative evaluation and approach in assessing children with congenital vertebral malformation.

SUMMARY OF BACKGROUND DATA

Congenital vertebral malformations encompass a broad spectrum of conditions. A high association of renal, cardiac, and intraspinal anomalies with congenital vertebral malformation has been well documented in the literature. Vertebral malformation with involvement of the thoracic cage may lead to the development of thoracic insufficiency. The natural history, the character, and location of the deformity ultimately influence the propensity for progression and the necessity for treatment. Multiple factors should be considered before treatment with the goal of treatment aimed at providing the best possible care to be able to optimize the child's overall function and potential for growth.

METHODS

Narrative and review of literature.

CONCLUSION

Congenital scoliosis is a multifaceted condition. The presentation of the condition can be quite varied from those presenting with an isolated hemivertebrae to those with severe malformations, complicated by multiple medical conditions. A thorough preoperative evaluation is necessary before the institution of any treatment protocol. The presence of any medical condition must be addressed; the treatment should be tailor-made for each patient putting into consideration the patients' age and the effects of treatment on pulmonary function at maturity.

Tracheobronchomalacia in infants and children: multidetector CT evaluation

Tracheobronchomalacia (TBM) is the most common congenital central airway anomaly, but it frequently goes unrecognized or is misdiagnosed as other respiratory conditions such as asthma. Recent advances in multidetector computed tomography (CT) have enhanced the ability to noninvasively diagnose TBM with the potential to reduce the morbidity and mortality associated with this condition. Precise indications are evolving but may include symptomatic pediatric patients with known risk factors for TBM and patients with otherwise unexplained impaired exercise tolerance; recurrent lower airways infection; and therapy-resistant, irreversible, and/or atypical asthma. With multidetector CT, radiologists can now perform objective and quantitative assessment of TBM with accuracy similar to that of bronchoscopy, the reference standard for diagnosing this condition. Multidetector CT enables a comprehensive evaluation of pediatric patients suspected of having TBM by facilitating accurate diagnosis, determining the extent and degree of disease, identifying predisposing conditions, and providing objective pre- and postoperative assessments. In this article, the authors present a step-by-step primer of multidetector CT imaging for evaluating infants and children with suspected TBM, including clinical indications, patient preparation, multidetector CT techniques and protocols, two- and three-dimensional processing of multidetector CT data, and image interpretation. The major aim of this article is to facilitate the reader's ability to successfully employ multidetector CT imaging protocols for evaluation of TBM in infants and children in daily clinical practice.

In defense of body CT

OBJECTIVE

Rapid technical developments and an expanding list of applications that have supplanted less accurate or more invasive diagnostic tests have led to a dramatic increase in the use of body CT in medical practice since its introduction in 1975. Our purpose here is to discuss medical justification of the small potential risk associated with the ionizing radiation used in CT and to provide perspectives on practice-specific decisions that can maximize overall patient benefit. In addition, we review available dose management and optimization techniques.

CONCLUSION

Dose reduction strategies described in this article must be well understood and properly used, but also require broad-based practice strategies that extend beyond the CT scanner console and default, generic manufacturer settings. In the final analysis, physicians must request the imaging examination that best addresses the specific medical question without allowing worries about radiation to dissuade them or their patients from obtaining needed CT examinations. Ongoing efforts to ensure that CT examinations are both medically justified and optimally performed must continue, and education must be provided to the medical community and general public that put both the potential risks--and benefits--of CT examinations into proper perspective.

Imaging of accidental paediatric head trauma

Head trauma is the most common form of injury sustained in serious childhood trauma and remains one of the top three causes of death despite improved road planning and safety laws. CT remains the first-line investigation for paediatric head trauma, although MRI may be more sensitive at picking up the full extent of injuries and may be useful for prognosis. Follow-up imaging should be tailored to answer the specific clinical question and to look for possible complications.

The imaging of paediatric thoracic trauma

Major chest trauma in a child is associated with significant morbidity and mortality. It is most frequently encountered within the context of multisystem injury following high-energy trauma such as a motor vehicle accident. The anatomic-physiologic make-up of children is such that the pattern of ensuing injuries differs from that in their adult counterparts. Pulmonary contusion, pneumothorax, haemothorax and rib fractures are most commonly encountered. Although clinically more serious and potentially life threatening, tracheobronchial tear, aortic rupture and cardiac injuries are seldom observed. The most appropriate imaging algorithm is one tailored to the individual child and is guided by the nature of the traumatic event as well as clinical parameters. Chest radiography remains the first and most important imaging tool in paediatric chest trauma and should be supplemented with US and CT as indicated. Multidetector CT allows for the accurate diagnosis of most traumatic injuries, but should be only used in selected cases as its routine use in all paediatric patients would result in an unacceptably high radiation exposure to a large number of patients without proven clinical benefit. When CT is used, appropriate modifications should be incorporated so as to minimize the radiation dose to the patient whilst preserving diagnostic integrity.

The relevance of image quality indices for dose optimization in abdominal multi-detector row CT in children: experimental assessment with pediatric phantoms

This study assessed and compared various image quality indices in order to manage the dose of pediatric abdominal MDCT protocols and to provide guidance on dose reduction. PMMA phantoms representing average body diameters at birth, 1 year, 5 years, 10 years and 15 years of age were scanned in a four-channel MDCT with a standard pediatric abdominal CT protocol. Image noise (SD, standard deviation of CT number), noise derivative (ND, derivative of the function of noise with respect to dose) and contrast-to-noise ratio (CNR) were measured. The 'relative' low-contrast detectability (rLCD) was introduced as a new quantity to adjust LCD to the various phantom diameters on the basis of the LCD(1%) assessed in a Catphan phantom and a constant central absorbed dose. The required variations of CTDIvol(16) with respect to phantom size were analyzed in order to maintain each image quality index constant. The use of a fixed SD or CNR level leads to major dose ratios between extreme patient sizes (factor 22.7 to 44 for SD, 31.7 to 51.5 for CNR(2.8%)), whereas fixed ND and rLCD result in acceptable dose ratios ranging between factors of 2.9 and 3.9 between extreme phantom diameters. For a 5-9 mm rLCD1(%), adjusted ND values range between -0.84 and -0.11 HU mGy(-1). Our data provide guidance on dose reduction on the basis of patient dimensions and the required rLCD (e.g., to get a constant 7 mm rLCD(1%) for abdominal diameters of 10, 13, 16, 20 and 25 cm, tube current-time product should be adjusted in order to obtain CTDIvol(16) values of 6.2, 7.2, 8.8, 11.6 and 17.7 mGy, respectively).

Effective dose estimation in whole-body multislice CT in paediatric trauma patients

BACKGROUND

The number of multislice CT (MSCT) scans performed in polytraumatized children has increased rapidly. There is growing concern regarding the radiation dose in MSCT and its long-term consequences, especially in children.

OBJECTIVE

To determine the effective dose to polytraumatized children who undergo whole-body MSCT.

MATERIALS AND METHODS

A total of 51 traumatized children aged 0-16 years underwent a polytrauma protocol CT scan between November 2004 and August 2006 at our institution. The effective dose was calculated retrospectively by a computer program (CT-Expo 1.5, Hannover, Germany).

RESULTS

The mean effective dose was 20.8 mSv (range 8.6-48.9 mSv, SD +/- 7.9 mSv). There was no statistically significant difference in the effective dose between male and female patients.

CONCLUSION

Whole-body MSCT is a superior diagnostic tool in polytraumatized children with 20.8 mSv per patient being a justified mean effective dose. In a potentially life-threatening situation whole-body MSCT provides the clinicians with relevant information to initiate life-saving therapy. Radiologists should use special paediatric protocols that include dose-saving mechanisms to keep the effective dose as low as possible. Further studies are needed to examine and advance dose-saving strategies in MSCT, especially in children.

Strategies for reducing radiation dose in CT

In recent years, the media has focused on the potential danger of radiation exposure from CT, even though the potential benefit of a medically indicated CT far outweighs the potential risks. This attention has reminded the radiology community that doses must be as low as reasonably achievable (ALARA) while maintaining diagnostic image quality. To satisfy the ALARA principle, the dose reduction strategies described in this article must be well understood and properly used. The use of CT must also be justified for the specific diagnostic task.

Virtual Colonoscopy Screening with Ultra Low-Dose CT and Less-Stressful Bowel Preparation: A computer simulation study

Computed tomography colonography (CTC) or CT-based virtual colonoscopy (VC) is an emerging tool for detection of colonic polyps. Compared to the conventional fiber-optic colonoscopy, VC has demonstrated the potential to become a mass screening modality in terms of safety, cost, and patient compliance. However, current CTC delivers excessive X-ray radiation to the patient during data acquisition. The radiation is a major concern for screening application of CTC. In this work, we performed a simulation study to demonstrate a possible ultra low-dose CT technique for VC. The ultra low-dose abdominal CT images were simulated by adding noise to the sinograms of the patient CTC images acquired with normal dose scans at 100 mAs levels. The simulated noisy sinogram or projection data were first processed by a Karhunen-Loève domain penalized weighted least-squares (KL-PWLS) restoration method and then reconstructed by a filtered backprojection algorithm for the ultra low-dose CT images. The patient-specific virtual colon lumen was constructed and navigated by a VC system after electronic colon cleansing of the orally-tagged residue stool and fluid. By the KL-PWLS noise reduction, the colon lumen can successfully be constructed and the colonic polyp can be detected in an ultra low-dose level below 50 mAs. Polyp detection can be found more easily by the KL-PWLS noise reduction compared to the results using the conventional noise filters, such as Hanning filter. These promising results indicate the feasibility of an ultra low-dose CTC pipeline for colon screening with less-stressful bowel preparation by fecal tagging with oral contrast.

Horseshoe lung associated with rare bilateral variant of scimitar syndrome: demonstration by 64-slice MDCT angiography

Scimitar syndrome with bilateral abnormal venous drainage and horseshoe lung is extremely rare. These rare complex anomalies were diagnosed in a 5-year-old boy by 64-slice multidetector CT (MDCT). This technique provides high-quality visualization of vascular, bronchial and parenchymal structures in a single session, such that no further invasive techniques are required. One obvious disadvantage of MDCT is the radiation exposure, especially in paediatric patients. The use of a single phase of contrast material administration reduces radiation exposure. The workstation platforms of MDCT systems allow multiplanar 2-D and 3-D postprocessing. As a result, various complex pathologies, such as that discussed here, can be diagnosed following a single imaging session with a certain precision.

Gastroenteropancreatic neuroendocrine tumors in children and young adults

We review the imaging findings of pediatric gastroenteropancreatic neuroendocrine tumors (GEP-NETs) using contemporary anatomic and molecular imaging techniques. A low index of suspicion can result in significant delays in diagnosis of pediatric GEP-NETs. A multimodality imaging approach, using both anatomic and functional imaging, is essential in the diagnosis, staging, and surveillance of these potentially malignant tumors.

Paediatric CT: the effects of increasing image noise on pulmonary nodule detection

BACKGROUND

A radiation dose of any magnitude can produce a detrimental effect manifesting as an increased risk of cancer. Cancer development may be delayed for many years following radiation exposure. Minimizing radiation dose in children is particularly important. However, reducing the dose can reduce image quality and may, therefore, hinder lesion detection.

OBJECTIVE

We investigated the effects of reducing the image signal-to-noise ratio (SNR) on CT lung nodule detection for a range of nodule sizes.

MATERIALS AND METHODS

A simulated nodule was placed at the periphery of the lung on an axial CT slice using image editing software. Multiple copies of the manipulated image were saved with various levels of superimposed noise. The image creation process was repeated for a range of nodule sizes. For a given nodule size, output images were read independently by four Fellows of The Royal College of Radiologists.

RESULTS

The overall sensitivities in detecting nodules for the SNR ranges 0.8-0.99, 1-1.49, and 1.5-2.35 were 40.5%, 77.3% and 90.3%, respectively, and the specificities were 47.9%, 73.3% and 75%, respectively. The sensitivity for detecting lung nodules increased with nodule size and increasing SNR. There was 100% sensitivity for the detection of nodules of 4-10 mm in diameter at SNRs greater than 1.5.

CONCLUSION

Reducing medical radiation doses in children is of paramount importance. For chest CT examinations this may be counterbalanced by reduced sensitivity and specificity combined with an increased uncertainty of pulmonary nodule detection. This study demonstrates that pulmonary nodules of 4 mm and greater in diameter can be detected with 100% sensitivity provided that the perceived image SNR is greater than 1.5.