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Background Sarcopenia, the unintentional loss of skeletal muscle mass, is associated with poor outcomes in adult patient populations. In adults, sarcopenia is often ascertained by cross‐sectional imaging of the psoas muscle area (PMA). Although children with chronic medical illnesses may be at increased risk for muscle loss because of nutritional deficiencies, physical deconditioning, endocrine anomalies, and systemic inflammation, consistent quantitative definitions for sarcopenia in children are lacking. We aimed to generate paediatric reference values for PMA at two intervertebral lumbar levels, L3–4 and L4–5. Methods In this cross‐sectional study, we analysed abdominal computed tomography scans of consecutive children presenting to the emergency department. Participants were children 1–16 years who required abdominal cross‐sectional imaging after paediatric trauma between January 1, 2005 and December 31, 2015 in a large Canadian quaternary care centre. Children with a documented chronic medical illness or an acute spinal trauma at presentation were excluded. Total PMA (tPMA) at levels L3–4 and L4–5 were measured in square millimetres (mm2) as the sum of left and right PMA. Age‐specific and sex‐specific tPMA percentile curves were modelled using quantile regression. Results Computed tomography images from 779 children were included. Values of tPMA at L4–5 were significantly larger than at L3–4 at all ages, but their correlation was high for both girls (r = 0.95) and boys (r = 0.98). Amongst girls, tPMA 50th percentile values ranged from 365 to 2336 mm2 at L3–4 and from 447 to 2704 mm2 for L4–5. Amongst boys, 50th percentile values for tPMA ranged between 394 and 3050 mm2 at L3–4 and from 498 to 3513 mm2 at L4–5. Intraclass correlation coefficients were excellent at L3–4 (0.97, 95% CI 0.94 to 0.981) and L4–5 (0.99, 95% CI 0.986 to 0.995). Weight and tPMA were correlated, stratified by sex for boys (L3–4 r = 0.90; L4–5 r = 0.90) and for girls (L3–4 r = 0.87; L4–5 r = 0.87). An online application was subsequently developed to easily calculate age‐specific and sex‐specific z‐scores and percentiles. Conclusions We provide novel paediatric age‐specific and sex‐specific growth curves for tPMA at intervertebral L3–4 and L4–5 levels for children between the ages of 1‐16 years. Together with an online tool (https://ahrc‐apps.shinyapps.io/sarcopenia/), these tPMA curves should serve as a reference enabling earlier identification and targeted intervention of sarcopenia in children with chronic medical conditions.

Longer examination time, need for anesthesia in smaller children and the inability of most children to hold their breath are major limitations of MRI in pediatric body imaging. Fortunately, with technical advances, many new and upcoming MRI sequences are overcoming these limitations. Advances in data acquisition and k-space sampling methods have enabled sequences with improved temporal and spatial resolution, and minimal artifacts. Sequences to minimize movement artifacts mainly utilize radial k-space filling, and examples include the stack-of-stars method for T1-weighted imaging and the periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER)/BLADE method for T2-weighted imaging. Similarly, the sequences with improved temporal resolution and the ability to obtain multiple phases in a single breath-hold in dynamic imaging mainly use some form of partial k-space filling method. New sequences use a variable combination of data sampling methods like compressed sensing, golden-angle radial k-space filling, parallel imaging and partial k-space filling to achieve free-breathing, faster sequences that could be useful for pediatric abdominal and thoracic imaging. Simultaneous multi-slice method has improved diffusion-weighted imaging (DWI) with reduction in scan time and artifacts. In this review, we provide an overview of data sampling methods like parallel imaging, compressed sensing, radial k-space sampling, partial k-space sampling and simultaneous multi-slice. This is followed by newer available and upcoming sequences for T1-, T2- and DWI based on these other advances. We also discuss the Dixon method and newer approaches to reducing metal artifacts.

Knowledge about sequence properties is essential to plan and acquire a diagnostic MRI examination. The broad four categories of sequences include spin echo (SE), gradient echo (GRE), inversion recovery (IR) and echoplanar imaging (EPI). Varieties of sequences from these four categories are available for clinical application. They have different contrast mechanisms, spatial and contrast resolution and speed of acquisition. Choice of sequence differs in various scenarios in clinical practice such as solid organ imaging, moving target imaging, bone and bone marrow imaging, cartilage imaging and vessel imaging, taking into consideration properties of sequences to answer the clinical question. Broad classification of sequences and differences in their contrast, spatial and contrast resolution, and speed of acquisition are discussed in this review. A few common clinical scenarios of MRI imaging are illustrated, along with reasons for the given sequence choices.

Magnetic resonance imaging is a multipurpose imaging modality that is largely safe, given the lack of ionizing radiation. However there are electromagnetic and biological effects on human tissue when exposed to magnetic environments, and hence there is a risk of adverse events occurring with these exams. It is imperative to understand these risks and develop methods to minimize them and prevent consequent adverse events. Implementing these safety practices in pediatric MR imaging has been somewhat limited because of gaps in information and knowledge among the personnel who are closely involved in the MR environment. The American College of Radiology has provided guidelines on MR safety practices that are helpful in minimizing such adverse events. This article provides an overview of the issues related to MR safety and practical ways to implement them across different health care facilities.

Abstract Purpose: To compare whole-body magnetic resonance imaging (WBMRI) performed at 1.5 and 3 T for technical quality, artifacts, and visibility of selected fixed structures. Patients and Methods: 21 children who had WBMRI at both 1.5 and 3 T scanners within a relatively short interval (3-13 months; average-8.6 months) were included. The images were objectively compared with scores from 4 to 1 for five parameters including severity of artifacts; visibility of liver, vertebral column, and marrow in legs; and overall image quality. Inter-observer agreement was calculated using Kendall's coefficient of Concordance (W) and scores were compared using Signed Rank test. Results: There was substantial inter-observer agreement for all five categories at both field strengths. The difference between averages of mean scores of all five parameters for two field strengths was statistically significant ( P < 0.05), indicating less artifact, better fixed structure visibility, and overall image quality at 1.5 T as compared to 3 T. However, scores at 3 T were also rated within a good range (around 3) indicating its feasibility for WBMRI in children. Conclusion: WBMRI at 1.5 T has significantly better image quality, fixed structure visibility, and fewer artifacts, as compared to WBMRI at 3 T in children. This difference is unlikely to significantly affect detection of pathology on 3 T WBMRI as the image quality score at 3 T was also within good range.

Background Hepatocellular adenomas (HCAs) are rare, benign hepatic tumors in children, with limited imaging data available for pediatric cases. Objective To describe the magnetic resonance imaging (MRI) and clinical features of histologically proven HCAs in children. Materials and methods Single-center retrospective review of pathology-proven HCA from January 2004 to February 2024. Patients with available pre-intervention imaging in our PACS were included. Two independent readers reviewed the imaging studies. The features were summarized using descriptive statistics and inter-reader agreement was assessed using Cohen’s kappa. Results This study included 11 children (6 boys and 5 girls; median age 15 years) with 13 pathologically proven HCAs. Three patients had type 1a glycogen storage disease. Five patients had a single lesion, while six had multiple lesions. The lesions were well-defined with a median average diameter of 3.6 cm. Most were homogenously T1 iso-intense (61.5%) and mildly hyperintense (76.9%) on T2-w fat saturated images. The atoll sign was present in two lesions. Intralesional fat was observed in 69.2% of cases: microscopic in eight lesions and macroscopic in one. Hemorrhage occurred in three (23.07%) lesions and necrosis in one (7.7%). Nine out of 10 (90%) lesions showed arterial phase hyperenhancement, and only 3/10 (30%) lesions retained contrast on hepatobiliary phase. In total, 6/13 (46.1%) lesions showed washout, and all received hepatobiliary agent. One lesion ruptured with the hemoperitoneum. Of the 11, 63.6% of patients underwent percutaneous biopsy and 36.4% underwent surgical resection. Conclusion MR imaging features are nonspecific, but homogenous slight T2 hyperintensity, arterial phase hyperenhancement, and intralesional fat content are common features. Hepatobiliary contrast uptake is variable. Graphical Abstract

BackgroundAngiosarcomas are rare malignant vascular tumors and there is scarcity of data on their imaging features.ObjectiveTo review and illustrate the imaging, clinical, and pathologic features of angiosarcoma in children.Materials and methodsA list of pathologically proven angiosarcoma seen between Nov 1992 and Jan 2023 was obtained from a pathology database and picture archiving and communication system. Those with pre-treatment imaging available on our PACS were included in the study. Imaging studies were reviewed by two readers in consensus.ResultsA total of six children (two males and four females; median age of 8.8 years; range 2.9 years to 15.5 years) had angiosarcoma during the study period. Organ of origin included breast (n = 2), liver (n = 2), spleen (n = 1), and paranasal sinuses (n = 1). The patient with splenic angiosarcoma had Li-Fraumeni syndrome. Five patients had a single lesion while one had multifocal lesions. The tumors were large with a median diameter of 12.9 cm (range 2.7 cm to 24 cm). Most tumors were heterogeneous on T2-weighted imaging with hemorrhage and necrosis and showed heterogeneous enhancement. Three had well-defined borders and three had infiltrative borders. None of the tumors showed calcifications. Two tumors in the liver showed gradual non-centripetal progressive diffuse enhancement on dynamic imaging. One patient had metastases at presentation and four patients subsequently developed metastases on follow-up. Five patients underwent surgical resection and chemotherapy; one patient with a liver lesion underwent arterial embolization followed by liver transplant. Three patients died at the last follow-up.ConclusionThe imaging features of angiosarcomas are nonspecific, but the tumors are large heterogeneously enhancing masses with hemorrhage and necrosis. Hepatic angiosarcomas may show non-centripetal progressive and heterogeneous enhancement on dynamic imaging.

Diffusion-weighted MRI is being increasingly used in pediatric body imaging. Its role is still emerging. It is used for detection of tumors and abscesses, differentiation of benign and malignant tumors, and detection of inflamed bowel segments in inflammatory bowel disease in children. It holds great promise in the assessment of therapy response in body tumors, with apparent diffusion coefficient (ADC) value as a potential biomarker. Significant overlap of ADC values of benign and malignant processes and less reproducibility of ADC measurements are hampering its widespread use in clinical practice. With standardization of the technique, diffusion-weighted imaging (DWI) is likely to be used more frequently in clinical practice. We discuss the principles and technique of DWI, selection of b value, qualitative and quantitative assessment, and current status of DWI in evaluation of disease processes in the pediatric body.

Malignant hepatic tumors in children are rare, comprising 1.3% of all pediatric malignancies. Following hepatoblastoma, hepatocellular carcinoma is the second most common. Other malignant hepatic tumors seen in childhood include those of mesenchymal origin including undifferentiated embryonal sarcoma, angiosarcoma, rhabdomyosarcoma and epithelioid hemangioendothelioma, as well as biliary tumors such as cholangiocarcinoma. Diagnosis can be challenging because of their rarity, and the recognition of distinctive imaging features for certain tumors such as epithelioid hemangioendothelioma and biliary rhabdomyosarcoma can focus the differential diagnosis and expedite the diagnostic process. A complete MRI examination with hepatocyte-specific contrast media and diffusion-weighted imaging helps to focus the differential diagnosis, and, although findings are often nonspecific, in some cases typical features on MRI can be helpful in diagnosis. Histopathological analysis is usually required for definitive diagnosis. Hepatic tumors tend to be aggressive, and full staging is imperative to establish disease extent. Significant proportions are not amenable to upfront surgical resection and often require a multimodality approach including neoadjuvant chemotherapy within a multidisciplinary setting. Facilitating complete surgical resection is usually required for better survival. In this review, we emphasize pathology and imaging features for rare liver tumors that are useful in reaching a prompt diagnosis. We also discuss general clinical findings, prognosis and management of these tumors.