Airway abnormalities associated with congenital heart disease.

Airway abnormalities are important but sometimes overlooked problems in children with congenital heart disease. It is often difficult to separate symptoms related to cardiac disease from those associated with airway or lung disease. Some of the lesions are incidental while others cause significant symptoms and are important in overall functional outcome. Congenital and acquired as well as intrinsic and extrinsic lesions occur and can overlap. We review and illustrate these lesions here. Imaging plays a crucial role in diagnosing and assessing the severity of airway abnormalities and guiding medical and surgical management decisions.

Magnetic resonance imaging for congenital lung malformations.

Congenital lung malformations are most often identified on prenatal US screening. Fetal MRI is often performed to further evaluate these lesions. Although some of these lesions might cause prenatal or early postnatal symptoms that require urgent management, the majority are asymptomatic at birth and might be subtle or invisible on chest radiographs. Postnatal imaging is frequently deferred until 3-6 months of age, when surgery or long-term conservative management is contemplated. High-quality imaging and interpretation is needed to assist with appropriate decision-making. Contrast-enhanced chest CT, typically with angiographic technique, has been the usual postnatal imaging choice. In this review, the author discusses and illustrates the indications and use of postnatal MR imaging for bronchopulmonary malformations as well as some differential diagnoses and the advantages and disadvantages of MR versus CT.

Congenital central pulmonary artery anomalies: Part 1.

There is a broad spectrum of congenital anomalies of the central pulmonary arteries including abnormalities of development, origin, course and caliber. These anomalies incorporate simple lesions such as isolated pulmonary valve stenosis to very complex anomalies with many associated abnormalities. Part 1 and Part 2 of this review describe the range of anatomical variations that are encountered as well as important aspects of anatomy, physiology and surgical correction. The authors summarize and illustrate well-recognized as well as more complex anomalies to provide a broad and comprehensive understanding of these lesions and their appearances on CT and MR imaging. Part 1 covers anomalous development or origin of the main pulmonary artery.

Congenital central pulmonary artery anomalies: Part 2.

There is a broad spectrum of congenital anomalies of the central pulmonary arteries including abnormalities of development, origin, course and caliber. These anomalies incorporate simple lesions such as isolated pulmonary valve stenosis to very complex anomalies with many associated abnormalities. Part 1 and Part 2 of this review describe the range of anatomical variations that are encountered as well as important aspects of anatomy, physiology and surgical correction. The authors summarize and illustrate both well-recognized and more complex anomalies to provide a broad and comprehensive understanding of these lesions and their appearances on CT and MR imaging. In Part 2 the authors review abnormalities in development, origin and course of the central branch pulmonary arteries as well as abnormal pulmonary artery caliber.

Ultrafast pediatric chest computed tomography: comparison of free-breathing vs. breath-hold imaging with and without anesthesia in young children.

BACKGROUND: General anesthesia (GA) or sedation has been used to obtain good-quality motion-free breath-hold chest CT scans in young children; however pulmonary atelectasis is a common and problematic accompaniment that can confound diagnostic utility. Dual-source multidetector CT permits ultrafast high-pitch sub-second examinations, minimizing motion artifact and potentially eliminating the need for a breath-hold. OBJECTIVE: The purpose of this study was to evaluate the feasibility of free-breathing ultrafast pediatric chest CT without GA and to compare it with breath-hold and non-breath-hold CT with GA. MATERIALS AND METHODS: Young (≤3 years old) pediatric outpatients scheduled for chest CT under GA were recruited into the study and scanned using one of three protocols: GA with intubation, lung recruitment and breath-hold; GA without breath-hold; and free-breathing CT without anesthesia. In all three protocols an ultrafast high-pitch CT technique was used. We evaluated CT images for overall image quality, presence of atelectasis and motion artifacts. RESULTS: We included 101 scans in the study. However the GA non-breath-hold technique was discontinued after 15 scans, when it became clear that atelectasis was a major issue despite diligent attempts to mitigate it. This technique was therefore not included in statistical evaluation (86 remaining patients). Overall image quality was higher (P=0.001) and motion artifacts were fewer (P<.001) for scans using the GA with intubation and recruitment technique compared to scans in the non-GA free-breathing group. However no significant differences were observed regarding the presence of atelectasis between these groups. CONCLUSION: We demonstrated that although overall image quality was best and motion artifact least with a GA-breath-hold intubation and recruitment technique, free-breathing ultrafast pediatric chest CT without anesthesia provides sufficient image quality for diagnostic purposes and can be successfully performed both without and with contrast agent in young infants.

Congenital Variants and Anomalies of the Aortic Arch.

Congenital variants and anomalies of the aortic arch are important to recognize as they may be associated with vascular rings, congenital heart disease, and chromosomal abnormalities, and can have important implications for prognosis and management. The purpose of this article is to review cross-sectional imaging techniques used in the evaluation of the aortic arch, describe the embryology and anatomy of the aortic arch system, discuss aortic arch variants and anomalies, and review other malformations of the aortic arch, including interrupted aortic arch, hypoplastic aortic arch, and aortic coarctation. Aortic arch variants and anomalies will be reviewed in the context of a theoretical double aortic arch system. Arch anomalies can be associated with symptoms, such as dysphagia lusoria in the setting of left aortic arch with aberrant right subclavian artery. Arch variants that form a vascular ring, such as double aortic arch, can result in respiratory distress due to tracheal compression. Certain arch anomalies are strongly associated with congenital heart disease, including right aortic arch with mirror image branching. Other malformations of the aortic arch have important associations, such as type B interrupted aortic arch, which is associated with a locus 22q11.2 microdeletion. Noninvasive imaging at CT angiography and MR angiography allows for comprehensive evaluation of the aortic arch and branch vessels in relation to surrounding structures. Familiarity with the spectrum and imaging appearances of aortic arch variants, anomalies, and malformations is essential for accurate diagnosis and classification and to guide management. Online supplemental material is available for this article. ©RSNA, 2016.

Tumor-induced Osteomalacia in a 3-Year-Old With Unresectable Central Giant Cell Lesions.

Tumor-induced osteomalacia (TIO) is a rare cause of hypophosphatemia involving overproduction of fibroblast growth factor 23. TIO has been described largely in adults with small mesenchymal tumors. We report a case of TIO in a child who presented with knee pain and radiographic findings concerning for rickets, and was found to have maxillomandibular giant cell lesions. The patient was treated with oral phosphorus and calcitriol, surgical debulking, and intralesional corticosteroids, which resulted in tumor regression and normalization of serum fibroblast growth factor 23 and phosphorus. This case illustrates the occurrence of this rare paraneoplastic syndrome in children and adds to our knowledge about clinical manifestations and pathologic findings associated with pediatric TIO.

Analysis of Kidney Ultrasound Dimensions by Body Habitus and Position.

PURPOSE: Renal dimensions are an important assessment of the genitourinary tract used to evaluate critical aspects of renal growth and development. Understanding the effect of patient position is important to use and interpret these parameters. In this prospective study we determined the effect of patient position and general body habitus on renal length and parenchymal area in children undergoing renal ultrasound. MATERIALS AND METHODS: Between October 2010 and January 2011 children underwent renal ultrasound while prone and supine. Bilateral renal length and renal parenchymal area were measured. Pearson and Bland-Altman statistical analyses were used to examine correlations, measurement bias and the degree of agreement between methods. RESULTS: Renal length measurements in both positions were complete for 201 right and 196 left kidneys. Parenchymal area measurements were complete for both kidneys in 177 children. When compared individually, supine and prone measures of renal length and parenchymal area highly correlated on Pearson analysis (greater than 0.96 and greater than 0.89, respectively). When compared by method, Bland-Altman analyses of differences vs means showed greater than 50% variance, representing wide limits of agreement with poor interrelation. Neither persistent systematic bias nor body habitus influenced results. CONCLUSIONS: While Pearson analysis showed high correlation for supine and prone renal measurements, Bland-Altman analysis of renal length and parenchymal area demonstrated wide limits of agreement, not allowing interchangeable use of prone and supine measurements. As such, renal ultrasound should specify standardized positions and benchmarks. These results provide guidance to standardize renal ultrasound measurements when renal size is used as an indicator of kidney health.

Persistent fifth arch anomalies - broadening the spectrum to include a variation of double aortic arch vascular ring.

Fifth arch anomalies are rare and complex and frequently misdiagnosed or mistaken for other entities. We report a double arch vascular ring that is thought to consist of right fourth arch and left fifth arch components, a previously undescribed persistent fifth arch variant. The currently recognized spectrum and classification of fifth arch vascular anomalies are expanded along with illustrative images to justify the proposed changes. Reviewing and expanding the classification of fifth arch anomalies to include a double arch ring variant will promote recognition, correct diagnosis and appropriate management of these anomalies.

Improved quantification and mapping of anomalous pulmonary venous flow with four-dimensional phase-contrast MRI and interactive streamline rendering.

BACKGROUND: Cardiac MRI is routinely performed for quantification of shunt flow in patients with anomalous pulmonary veins, but can be technically-challenging to perform. Four-dimensional phase-contrast (4D-PC) MRI has potential to simplify this exam. We sought to determine whether 4D-PC may be a viable clinical alternative to conventional 2D phase-contrast MR imaging. METHODS: With institutional review board approval and HIPAA-compliance, we retrospectively identified all patients with anomalous pulmonary veins who underwent cardiac MRI at either 1.5 Tesla (T) or 3T with parallel-imaging compressed-sensing (PI-CS) 4D-PC between April, 2011 and October, 2013. A total of 15 exams were included (10 male, 5 female). Algorithms for interactive streamline visualization were developed and integrated into in-house software. Blood flow was measured at the valves, pulmonary arteries and veins, cavae, and any associated shunts. Pulmonary veins were mapped to their receiving atrial chamber with streamlines. The intraobserver, interobserver, internal consistency of flow measurements, and consistency with conventional MRI were then evaluated with Pearson correlation and Bland-Altman analysis. RESULTS: Triplicate measurements of blood flow from 4D-PC were highly consistent, particularly at the aortic and pulmonary valves (cv 2-3%). Flow measurements were reproducible by a second observer (ρ = 0.986-0.999). Direct measurements of shunt volume from anomalous veins and intracardiac shunts matched indirect estimates from the outflow valves (ρ = 0.966). Measurements of shunt fraction using 4D-PC using any approach were more consistent with ventricular volumetric displacements than conventional 2D-PC (ρ = 0.972-0.991 versus 0.929). CONCLUSION: Shunt flow may be reliably quantified with 4D-PC MRI, either indirectly or with detailed delineation of flow from multiple shunts. The 4D-PC may be a more accurate alternative to conventional MRI.

Added Value of Radiologist Consultation for Pediatric Ultrasound: Implementation and Survey Assessment.

OBJECTIVE: The purpose of this study was to determine whether radiologist-parent (guardian) consultation sessions for pediatric ultrasound with immediate disclosure of examination results if desired increases visit satisfaction, decreases anxiety, and increases understanding of the radiologist's role. SUBJECTS AND METHODS: Parents chaperoning any outpatient pediatric ultrasound were eligible and completed surveys before and after ultrasound examinations. Before the second survey, parents met with a pediatric radiologist on a randomized basis but could opt out and request or decline the consultation. Differences in anxiety and understanding of the radiologist's role before and after the examination were compared, and overall visit satisfaction measures were tabulated. RESULTS: Seventy-seven subjects participated, 71 (92%) of whom spoke to a radiologist, mostly on request. In the consultation group, the mean score (1, lowest; 4, highest) for overall experience was 3.8 ± 0.4 (SD), consultation benefit was 3.7 ± 0.6, and radiologist interaction was 3.7 ± 0.6. Demographics were not predictive of satisfaction with statistical significance in a multivariate model. Forty-six of 68 (68%) respondents correctly described the radiologist's role before consultation. The number increased to 60 (88%) after consultation, and the difference was statistically significant (p < 0.001). There was also a statistically significant decrease in mean anxiety score from 2.0 ± 1.0 to 1.5 ± 0.8 after consultation (p < 0.001). Sixty-four of 70 (91%) respondents indicated that they would prefer to speak with a radiologist during every visit. CONCLUSION: Radiologist consultation is well received among parents and associated with decreased anxiety and increased understanding of the radiologist's role. The results of this study support the value of routine radiologist-parent interaction for pediatric ultrasound.

Radiologist compliance with California CT dose reporting requirements: a single-center review of pediatric chest CT.

OBJECTIVE: Effective July 1, 2012, CT dose reporting became mandatory in California. We sought to assess radiologist compliance with this legislation and to determine areas for improvement. MATERIALS AND METHODS: We retrospectively reviewed reports from all chest CT examinations performed at our institution from July 1, 2012, through June 30, 2013, for errors in documentation of volume CT dose index (CTDIvol), dose-length product (DLP), and phantom size. Reports were considered as legally compliant if both CTDIvol and DLP were documented accurately and as institutionally compliant if phantom size was also documented accurately. Additionally, we tracked reports that did not document dose in our standard format (phantom size, CTDIvol for each series, and total DLP). RESULTS: Radiologists omitted CTDIvol, DLP, or both in nine of 664 examinations (1.4%) and inaccurately reported one or both of them in 56 of the remaining 655 examinations (8.5%). Radiologists omitted phantom size in 11 of 664 examinations (1.7%) and inaccurately documented it in 20 of the remaining 653 examinations (3.1%). Of 664 examinations, 599 (90.2%) met legal reporting requirements, and 583 (87.8%) met institutional requirements. In reporting dose, radiologists variably used less decimal precision than available, summed CTDIvol, included only series-level DLP, and specified dose information from the scout topogram or a nonchest series for combination examinations. CONCLUSION: Our institutional processes, which primarily rely on correct human performance, do not ensure accurate dose reporting and are prone to variation in dose reporting format. In view of this finding, we are exploring higher-reliability processes, including better-defined standards and automated dose reporting systems, to improve compliance.

The incidental pulmonary nodule in a child. Part 1: recommendations from the SPR Thoracic Imaging Committee regarding characterization, significance and follow-up.

No guidelines are in place for the follow-up and management of pulmonary nodules that are incidentally detected on CT in the pediatric population. The Fleischner guidelines, which were developed for the older adult population, do not apply to children. This review summarizes the evidence collected by the Society for Pediatric Radiology (SPR) Thoracic Imaging Committee in its attempt to develop pediatric-specific guidelines.Small pulmonary opacities can be characterized as linear or as ground-glass or solid nodules. Linear opacities and ground-glass nodules are extremely unlikely to represent an early primary or metastatic malignancy in a child. In our review, we found a virtual absence of reported cases of a primary pulmonary malignancy presenting as an incidentally detected small lung nodule on CT in a healthy immune-competent child.Because of the lack of definitive information on the clinical significance of small lung nodules that are incidentally detected on CT in children, the management of those that do not have the typical characteristics of an intrapulmonary lymph node should be dictated by the clinical history as to possible exposure to infectious agents, the presence of an occult immunodeficiency, the much higher likelihood that the nodule represents a metastasis than a primary lung tumor, and ultimately the individual preference of the child's caregiver. Nodules appearing in children with a history of immune deficiency, malignancy or congenital pulmonary airway malformation should not be considered incidental, and their workup should be dictated by the natural history of these underlying conditions.

Heterotaxy syndromes and abnormal bowel rotation.

BACKGROUND: Bowel rotation abnormalities in heterotaxy are common. As more children survive cardiac surgery, the management of gastrointestinal abnormalities has become controversial. OBJECTIVE: To evaluate imaging of malrotation in heterotaxy with surgical correlation and provide an algorithm for management. MATERIALS AND METHODS: Imaging reports of heterotaxic children with upper gastrointestinal (UGI) and/or small bowel follow-through (SBFT) were reviewed. Subsequently, fluoroscopic images were re-reviewed in conjunction with CT/MR studies. The original reports and re-reviewed images were compared and correlated with surgical findings. RESULTS: Nineteen of 34 children with heterotaxy underwent UGI, 13/19 also had SBFT. In 15/19 reports, bowel rotation was called abnormal: 11 malrotation, 4 non-rotation, no cases of volvulus. Re-review, including CT (10/19) and MR (2/19), designated 17/19 (90%) as abnormal, 10 malrotation (abnormal bowel arrangement, narrow or uncertain length of mesentery) and 7 non-rotation (small bowel and colon on opposite sides plus low cecum with probable broad mesentery). The most useful CT/MR findings were absence of retroperitoneal duodenum in most abnormal cases and location of bowel, especially cecum. Abnormal orientation of mesenteric vessels suggested malrotation but was not universal. Nine children had elective bowel surgery; non-rotation was found in 4/9 and malrotation was found in 5/9, with discrepancies (non-rotation at surgery, malrotation on imaging) with 4 original interpretations and 1 re-review. CONCLUSION: We recommend routine, early UGI and SBFT studies once other, urgent clinical concerns have been stabilized, with elective laparoscopic surgery in abnormal or equivocal cases. Cross-sectional imaging, usually obtained for other reasons, can contribute diagnostically. Attempting to assess mesenteric width is important in differentiating non-rotation from malrotation and more accurately identifies appropriate surgical candidates.

Perforated appendicitis: an underappreciated mimic of intussusception on ultrasound.

BACKGROUND: We encountered multiple cases in which the US appearance of ruptured appendicitis mimicked intussusception, resulting in diagnostic and therapeutic delay and multiple additional imaging studies. OBJECTIVE: To explore the clinical and imaging discriminatory features between the conditions. MATERIALS AND METHODS: Initial US images in six children (age 16 months to 8 years; 4 boys, 2 girls) were reviewed independently and by consensus by three pediatric radiologists. These findings were compared and correlated with the original reports and subsequent US, fluoroscopic, and CT images and reports. RESULTS: All initial US studies demonstrated a multiple-ring-like appearance (target sign, most apparent on transverse views) with diagnostic consensus supportive of intussusception. In three cases, US findings were somewhat discrepant with clinical concerns. Subsequently, four of the six children had contrast enemas; two were thought to have partial or complete intussusception reduction. Three had a repeat US examination, with recognition of the correct diagnosis. None of the US examinations demonstrated definite intralesional lymph nodes or mesenteric fat, but central echogenicity caused by debris/appendicolith was misinterpreted as fat. All showed perilesional hyperechogenicity that, in retrospect, represented inflamed fat "walling off" of the perforated appendix. There were four CTs, all of which demonstrated a double-ring appearance that correlated with the US target appearance, with inner and outer rings representing the dilated appendix and walled-off appendiceal rupture, respectively. All six children had surgical confirmation of perforated appendicitis. CONCLUSION: Contained perforated appendicitis can produce US findings closely mimicking intussusception. Clinical correlation and careful multiplanar evaluation should allow for sonographic suspicion of perforated appendicitis, which can be confirmed on CT if necessary.

Pediatric CT quality management and improvement program.

Modern CT is a powerful yet increasingly complex technology that continues to rapidly evolve; optimal clinical implementation as well as appropriate quality management and improvement in CT are challenging but attainable. This article outlines the organizational structure on which a CT quality management and improvement program can be built, followed by a discussion of common as well as pediatric-specific challenges. Organizational elements of a CT quality management and improvement program include the formulation of clear objectives; definition of the roles and responsibilities of key personnel; implementation of a technologist training, coaching and feedback program; and use of an efficient and accurate monitoring system. Key personnel and roles include a radiologist as the CT director, a qualified CT medical physicist, as well as technologists with specific responsibilities and adequate time dedicated to operation management, CT protocol management and CT technologist education. Common challenges in managing a clinical CT operation are related to the complexity of newly introduced technology, of training and communication and of performance monitoring. Challenges specific to pediatric patients include the importance of including patient size in protocol and dose considerations, a lower tolerance for error in these patients, and a smaller sample size from which to learn and improve.

Chest CT in children: anesthesia and atelectasis.

BACKGROUND: There has been an increasing tendency for anesthesiologists to be responsible for providing sedation or anesthesia during chest CT imaging in young children. Anesthesia-related atelectasis noted on chest CT imaging has proven to be a common and troublesome problem, affecting image quality and diagnostic sensitivity. OBJECTIVE: To evaluate the safety and effectiveness of a standardized anesthesia, lung recruitment, controlled-ventilation technique developed at our institution to prevent atelectasis for chest CT imaging in young children. MATERIALS AND METHODS: Fifty-six chest CT scans were obtained in 42 children using a research-based intubation, lung recruitment and controlled-ventilation CT scanning protocol. These studies were compared with 70 non-protocolized chest CT scans under anesthesia taken from 18 of the same children, who were tested at different times, without the specific lung recruitment and controlled-ventilation technique. Two radiology readers scored all inspiratory chest CT scans for overall CT quality and atelectasis. Detailed cardiorespiratory parameters were evaluated at baseline, and during recruitment and inspiratory imaging on 21 controlled-ventilation cases and 8 control cases. RESULTS: Significant differences were noted between groups for both quality and atelectasis scores with optimal scoring demonstrated in the controlled-ventilation cases where 70% were rated very good to excellent quality scans compared with only 24% of non-protocol cases. There was no or minimal atelectasis in 48% of the controlled ventilation cases compared to 51% of non-protocol cases with segmental, multisegmental or lobar atelectasis present. No significant difference in cardiorespiratory parameters was found between controlled ventilation and other chest CT cases and no procedure-related adverse events occurred. CONCLUSION: Controlled-ventilation infant CT scanning under general anesthesia, utilizing intubation and recruitment maneuvers followed by chest CT scans, appears to be a safe and effective method to obtain reliable and reproducible high-quality, motion-free chest CT images in children.

Comparison of different methods of calculating CT radiation effective dose in children.

OBJECTIVE: CT radiation dose is a subject of intense interest and concern, especially in children. Effective dose, a summation of whole-body exposure weighted by specific organ sensitivities, is most often used to compute and compare radiation dose; however, there is little standardization, and there are numerous different methods of calculating effective dose. This study compares five such methods in a group of children undergoing routine chest CT and explores their advantages and pitfalls. MATERIALS AND METHODS: Patient data from 120 pediatric chest CT examinations were retrospectively used to calculate effective dose: two scanner dose-length product (DLP) methods using published sets of conversion factors by Shrimpton and Deak, the imaging performance and assessment of CT (ImPact) calculator method, the Alessio online calculator, and the Huda method. RESULTS: The Huda method mean effective dose (4.4 ± 2.2 mSv) and Alessio online calculator (5.2 ± 2.8 mSv) yielded higher mean numbers for effective dose than both DLP calculations (Shrimpton, 3.65 ± 1.8 mSv, and Deak, 3.2 ± 1.5 mSv) as well as the ImPact calculator effective dose (3.4 ± 1.7 mSv). Mean differences ranged from 10.2% ± 10.1% lower to 28% ± 37.3% higher than the Shrimpton method (used as the standard for comparison). Differences were more marked at 120 kVp than at 80 or 100 kVp and varied at different ages. Concordance coefficients relative to the Shrimpton DLP method were Deak DLP, 0.907; Alessio online calculator, 0.735; ImPact calculator, 0.926; and Huda, 0.777. CONCLUSION: Different methods of computing effective dose for pediatric CT produce varying results. The method used must be clearly described to allay confusion about documenting and communicating dose for archiving as well as comparative research purposes.

Congenital Absence of the Pericardium: Pearls and Pitfalls.

Congenital absence of the pericardium is a very uncommon condition that may be focal, unilateral or bilateral but most frequently involves the left sided pericardium. Clinical signs and symptoms are often absent or nonspecific, overlapping with many other more common conditions. Imaging findings are distinctive if the features are sought and recognized.

Effectiveness of a staged US and CT protocol for the diagnosis of pediatric appendicitis: reducing radiation exposure in the age of ALARA.

PURPOSE: To evaluate the effectiveness of a staged ultrasonography (US) and computed tomography (CT) imaging protocol for the accurate diagnosis of suspected appendicitis in children and the opportunity for reducing the number of CT examinations and associated radiation exposure. MATERIALS AND METHODS: This retrospective study was compliant with HIPAA, and a waiver of informed consent was approved by the institutional review board. This study is a review of all imaging studies obtained in children suspected of having appendicitis between 2003 and 2008 at a suburban pediatric emergency department. A multidisciplinary staged US and CT imaging protocol for the diagnosis of appendicitis was implemented in 2003. In the staged protocol, US was performed first in patients suspected of having appendicitis; follow-up CT was recommended when US findings were equivocal. Of 1228 pediatric patients who presented to the emergency department for suspected appendicitis, 631 (287 boys, 344 girls; age range, 2 months to 18 years; median age, 10 years) were compliant with the imaging pathway. The sensitivity, specificity, negative appendectomy rate (number of appendectomies with normal pathologic findings divided by the number of surgeries performed for suspected appendicitis), missed appendicitis rate, and number of CT examinations avoided by using the staged protocol were analyzed. RESULTS: The sensitivity and specificity of the staged protocol were 98.6% and 90.6%, respectively. The negative appendectomy rate was 8.1% (19 of 235 patients), and the missed appendicitis rate was less than 0.5% (one of 631 patients). CT was avoided in 333 of the 631 patients (53%) in whom the protocol was followed and in whom the US findings were definitive. CONCLUSION: A staged US and CT imaging protocol in which US is performed first in children suspected of having acute appendicitis is highly accurate and offers the opportunity to substantially reduce radiation.