Age-specific Dose Catalog for Diagnostic Fluoroscopy and Fluoroscopically Guided Interventional Procedures from a Pediatric Hospital.

Background Fluoroscopy is an imaging modality associated with a wide range of dose levels, characterized using a variety of dose metrics, including effective dose. However, for clinical procedures, effective dose is a seldom-used and unregulated metric in the United States, and thus, it is not extensively studied in radiology despite potentially large clinical implications for patients, especially children and infants. Purpose To formulate and report a dose catalog across all diagnostic and interventional radiology (IR) fluoroscopy examination or procedure types at a specialized tertiary care pediatric hospital. Materials and Methods In this retrospective study, dose metrics taken from radiation dose structured reports of fluoroscopy between October 2014 and March 2023 were analyzed. The reports included fluoroscopy across 18 diagnostic examination types and 24 IR procedure types. The National Cancer Institute dosimetry system for Radiography and Fluoroscopy Monte Carlo software was used to estimate age-specific effective dose from dose-area product (DAP). The DAP-to-effective dose conversion factors were estimated per IR procedure type and diagnostic fluoroscopy examination type based on age. Results A total of 11 536 individual diagnostic fluoroscopy examinations (18 types) and 8017 individual IR procedures (24 types) were analyzed. Median effective dose values per diagnostic fluoroscopy examination type ranged from 0.0010 to 0.44 mSv (mean, 0.0808 mSv ± 0.0998 [SD]). Calculated DAP-to-effective dose conversion factors ranged from 0.04 to 2.48 mSv/Gy · cm2 (mean, 0.758 mSv/Gy · cm2 ± 0.614) across all diagnostic fluoroscopy examination types. Median effective dose values per IR procedure type ranged from 0.0007 to 3.90 mSv (mean, 0.6757 mSv ± 0.8989). Calculated DAP-to-effective dose conversion factors ranged from 0.001 to 0.87 mSv/Gy · cm2 (mean, 0.210 mSv/Gy · cm2 ± 0.235) across all IR procedure types. Conclusion A pediatric fluoroscopy dose catalog was created, including age-specific effective dose, using a repeatable robust method based on accurate clinical data. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Borrego and Balter in this issue.

Peri-surgical imaging of intersex and gender diverse youths.

This publication provides an overview of current imaging indications and practices for patients undergoing gender-affirming surgery, with an emphasis on the importance of tailored, patient-specific care. Gender-affirming surgeries are performed with personalized approaches at various stages of life for those with intersex traits or differences in sex development (I/DSD) and transgender and gender diverse (TGD) individuals. For I/DSD patients, ultrasound, genitography, or MRI occurs during infancy and puberty to evaluate genital and gonadal anatomy. Facial harmonization involves bony and soft tissue modifications, guided by maxillofacial computerized tomography (CT) with three-dimensional reconstruction. Ultrasound is the main modality in assessing hormone-related and post-surgical changes in the chest. Imaging for genital reconstruction uses cross-sectional images and fluoroscopy to assess neoanatomy and complications.

Imaging of Vesicoureteral Reflux: AJR Expert Panel Narrative Review.

Vesicoureteral reflux (VUR) is a common congenital anomaly of the urinary tract that can present with collecting system dilation or as a febrile infection. VUR can lead to permanent renal sequela requiring surgery but can also spontaneously resolve without complication. Therefore, it is important to recognize those patient populations who warrant imaging for screening, confirmation, or ongoing surveillance for VUR, while avoiding overdiagnosis. In the appropriate patient populations, an accurate diagnosis of VUR allows early treatment and prevention of pyelonephritis and scarring. Various imaging modalities are available to diagnose and grade VUR, including voiding cystourethrogram (VCUG), radionucleotide cystography (RNC), and contrast-enhanced voiding urosonography (ceVUS). The objective of this article is to summarize the current understanding of VUR diagnosis and management and to discuss these imaging modalities' strengths and pitfalls. Considerations include indications for VUR imaging, patient preparation, conduct of the examination, issues related to radiologic reporting, and cost-effectiveness. An emphasis is placed on ceVUS, which is the most recently introduced of the three imaging modalities and is receiving growing support among pediatric radiologists.

Quantitative renal magnetic resonance imaging: magnetic resonance urography.

The goal of functional renal imaging is to identify and quantitate irreversible renal damage and nephron loss, as well as potentially reversible hemodynamic changes. MR urography has evolved into a comprehensive evaluation of the urinary tract that combines anatomical imaging with functional evaluation in a single test without ionizing radiation. Quantitative functional MR imaging is based on dynamic contrast-enhanced MR acquisitions that provide progressive, visible enhancement of the renal parenchyma and urinary tract. The signal changes related to perfusion, concentration and excretion of the contrast agent can be evaluated using both quantitative and qualitative measures. Functional evaluation with MR has continued to improve as a result of significant technical advances allowing for faster image acquisition as well as the development of new tracer kinetic models of renal function. The most common indications for MR urography in children are the evaluation of congenital anomalies of the kidney and urinary tract including hydronephrosis and renal malformations, and the identification of ectopic ureters in children with incontinence. In this paper, we review the underlying acquisition schemes and techniques used to generate quantitative functional parameters including the differential renal function (DRF), asymmetry index, mean transit time (MTT), signal intensity versus time curves as well as the calculation of individual kidney glomerular filtration rate (GFR). Visual inspection and semi-quantitative assessment using the renal transit time (RTT) and calyceal transit times (CTT) are fundamental to accurate diagnosis and are used as a basis for the interpretation of the quantitative data. The importance of visual assessment of the images cannot be overstated when analyzing the quantitative measures of renal function.

The radiologist's role in assessing differences of sex development.

When infants are identified with a difference of sex development (DSD), a thoughtful approach to imaging is essential to appropriate clinical management. This review provides a comprehensive guide for radiologists who are tasked with performing this critical assignment. We review the embryologic basis of DSDs, with attention to the imaging findings that can indicate specific diagnoses. We also discuss techniques for optimal imaging, including strategies for identifying the gonads by US, tactics for performing genitograms with fluoroscopy and contrast-enhanced US, and the appropriate utilization of MRI. Finally, we review the clinical data and imaging findings that characterize some of the most common DSDs, including congenital adrenal hyperplasia, complete androgen insensitivity syndrome and gonadal dysgenesis.

2021 update on the urinary tract dilation (UTD) classification system: clarifications, review of the literature, and practical suggestions.

In 2014, a multidisciplinary consensus on the classification of pre- and postnatal urinary tract dilation (UTD classification) was developed. Its goal was to provide a standardized system for evaluating and reporting urinary tract dilation both in the prenatal and postnatal periods. In this review, we summarize insights learned from the implementation of the UTD classification system since its inception, providing clarifications on common points of confusion. In addition, we review current literature in the clinical validation of the UTD classification system to provide credence for its use in managing fetuses and children with urinary tract dilation.

Normative values for ureteral diameter in children.

BACKGROUND: Assessment of the ureter is a fundamental part of the radiologic evaluation of the urinary tract. Abnormal ureteral dilation warrants further investigation to assess the etiology, which includes obstruction and/or reflux. Despite this fundamental need, there are no established normative values in children based on imaging. OBJECTIVE: To provide normative values for ureteral diameter in pediatric patients with age-related ranges. MATERIALS AND METHODS: We retrospectively reviewed all magnetic resonance (MR) urography studies and chose only normal ureters for assessment. The images were analyzed on commercially available software to assess maximum internal diameter. Manual measurements were done in cases where the images were below the resolution for automated assessment. Maximum intraluminal ureteral diameters were measured in upper, mid and lower thirds and the average of the three maximum ureteral diameters was used to obtain the average widest internal ureteral diameter. Multivariable linear regression was performed to test the association between the calculated diameter and gender. Differences in sizes between the left and right ureter were assessed using paired Wilcoxon signed rank test. RESULTS: One hundred twenty-one MR urography studies were selected, which included 160 ureter units. The diameter increases progressively with age, ranging from 3.2 mm during infancy to 5.0 mm in patients older than 16 years of age. After 9 years of age, the average widest internal ureteral diameter is slightly larger in males compared to females (odds ratio [OR]=1.91, 95% confidence interval [CI] [1.63, 2.25], P<0.0001). The right ureter was slightly larger than the left (3.9 mm vs. 3.7 mm, P=0.004) among 39 patients in whom both right and left ureter units were included. The average mid ureteral diameter is widest, followed by the distal third then proximal third. CONCLUSION: We present the normative values for the average widest internal ureteral diameter based on laterality and different segments. In the pediatric population, 3.8 mm should be considered the average widest internal ureteral diameter.

Retrospective Distortion and Motion Correction for Free-Breathing DW-MRI of the Kidneys Using Dual-Echo EPI and Slice-to-Volume Registration.

BACKGROUND: Diffusion-weighted MRI (DW-MRI) of the kidneys is a technique that provides information about the microstructure of renal tissue without requiring exogenous contrasts such as gadolinium, and it can be used for diagnosis in cases of renal disease and assessing response-to-therapy. However, physiological motion and large geometric distortions due to main B0 field inhomogeneities degrade the image quality, reduce the accuracy of quantitative imaging markers, and impede their subsequent clinical applicability. PURPOSE: To retrospectively correct for geometric distortion for free-breathing DW-MRI of the kidneys at 3T, in the presence of a nonstatic distortion field due to breathing and bulk motion. STUDY TYPE: Prospective. SUBJECTS: Ten healthy volunteers (ages 29-38, four females). FIELD STRENGTH/SEQUENCE: 3T; DW-MR dual-echo echo-planar imaging (EPI) sequence (10 b-values and 17 directions) and a T2 volume. ASSESSMENT: The distortion correction was evaluated subjectively (Likert scale 0-5) and numerically with cross-correlation between the DW images at b = 0 s/mm2 and a T2 volume. The intravoxel incoherent motion (IVIM) and diffusion tensor (DTI) model-fitting performance was evaluated using the root-mean-squared error (nRMSE) and the coefficient of variation (CV%) of their parameters. STATISTICAL TESTS: Statistical comparisons were done using Wilcoxon tests. RESULTS: The proposed method improved the Likert scores by 1.1 ± 0.8 (P < 0.05), the cross-correlation with the T2 reference image by 0.13 ± 0.05 (P < 0.05), and reduced the nRMSE by 0.13 ± 0.03 (P < 0.05) and 0.23 ± 0.06 (P < 0.05) for IVIM and DTI, respectively. The CV% of the IVIM parameters (slow and fast diffusion, and diffusion fraction for IVIM and mean diffusivity, and fractional anisotropy for DTI) was reduced by 2.26 ± 3.98% (P = 6.971 × 10-2 ), 11.24 ± 26.26% (P = 6.971 × 10-2 ), 4.12 ± 12.91% (P = 0.101), 3.22 ± 0.55% (P < 0.05), and 2.42 ± 1.15% (P < 0.05). DATA CONCLUSION: The results indicate that the proposed Di + MoCo method can effectively correct for time-varying geometric distortions and for misalignments due to breathing motion. Consequently, the image quality and precision of the DW-MRI model parameters improved. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 1.

Contrast-enhanced genitosonography and colosonography: emerging alternatives to fluoroscopy.

Imaging plays a crucial role in evaluating newborns and infants with cloacal and urogenital malformations. Contrast-enhanced genitosonography (ceGS) and contrast-enhanced colosonography (ceCS) are sensitive and radiation-free alternatives to fluoroscopic genitography and colography for diagnosis and surgical planning. These imaging techniques are performed by instilling a US contrast agent into specific body cavities to define the genitourinary and colorectal anatomy. This review article presents the experience with ceGS and ceCS applications in children, focusing on the background, examination technique, and interpretation of imaging findings, as well as strengths and weaknesses compared to conventional techniques.

Contrast-enhanced voiding urosonography part 2: urethral imaging.

Ultrasound (US) has been increasingly used as an important imaging tool to assess the urethra in children. The earliest reports of pediatric urethral sonography involved imaging the urethra in a non-voiding state, during physiological voiding of urine, and after instillation of saline. The introduction of US contrast agents has continued to improve visualization of urethral anatomy. Contrast-enhanced US of the urethra can be performed during the voiding phase of a standard contrast-enhanced voiding urosonography (ceVUS) exam or with retrograde instillation of a contrast agent, depending on the exam indication. Both techniques are well tolerated by children and provide accurate information about urethral pathology and periurethral soft tissues. This article reviews the technical aspects and imaging findings of urethral pathologies in children using contrast-enhanced US, both by the voiding and retrograde instillation techniques.

Contrast-enhanced voiding urosonography, part 1: vesicoureteral reflux evaluation.

Contrast-enhanced voiding urosonography (ceVUS) is a well-established, sensitive and safe ultrasound (US) modality for detecting and grading vesicoureteral reflux (VUR) and urethral imaging in children. Nearly three decades of remarkable advances in US technology and US contrast agents have refined ceVUS's diagnostic potential. The recent approval of Lumason/SonoVue in the United States, Europe and China for pediatric intravesical applications marked the beginning of a new era for this type of contrast US imaging. Consequently, the use of ceVUS in children has expanded to multiple places around the globe. In the first part of this review article, we describe the current experience in the use of ceVUS for VUR evaluation, with an emphasis on historical background, examination technique, image interpretation and diagnostic accuracy. In the second part, we will present the role of ceVUS for urethral imaging in children.

Improving Automatic Renal Segmentation in Clinically Normal and Abnormal Paediatric DCE-MRI via Contrast Maximisation and Convolutional Networks for Computing Markers of Kidney Function.

There is a growing demand for fast, accurate computation of clinical markers to improve renal function and anatomy assessment with a single study. However, conventional techniques have limitations leading to overestimations of kidney function or failure to provide sufficient spatial resolution to target the disease location. In contrast, the computer-aided analysis of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) could generate significant markers, including the glomerular filtration rate (GFR) and time-intensity curves of the cortex and medulla for determining obstruction in the urinary tract. This paper presents a dual-stage fully modular framework for automatic renal compartment segmentation in 4D DCE-MRI volumes. (1) Memory-efficient 3D deep learning is integrated to localise each kidney by harnessing residual convolutional neural networks for improved convergence; segmentation is performed by efficiently learning spatial-temporal information coupled with boundary-preserving fully convolutional dense nets. (2) Renal contextual information is enhanced via non-linear transformation to segment the cortex and medulla. The proposed framework is evaluated on a paediatric dataset containing 60 4D DCE-MRI volumes exhibiting varying conditions affecting kidney function. Our technique outperforms a state-of-the-art approach based on a GrabCut and support vector machine classifier in mean dice similarity (DSC) by 3.8% and demonstrates higher statistical stability with lower standard deviation by 12.4% and 15.7% for cortex and medulla segmentation, respectively.

Bulk motion-compensated DCE-MRI for functional imaging of kidneys in newborns.

BACKGROUND: Evaluation of kidney function in newborns with hydronephrosis is important for clinical decisions. Dynamic contrast-enhanced (DCE) MRI can provide the necessary anatomical and functional information. Golden angle dynamic radial acquisition and compressed sensing reconstruction provides sufficient spatiotemporal resolution to achieve accurate parameter estimation for functional imaging of kidneys. However, bulk motion during imaging (rigid or nonrigid movement of the subject resulting in signal dropout) remains an unresolved challenge. PURPOSE: To evaluate a motion-compensated (MoCo) DCE-MRI technique for robust evaluation of kidney function in newborns. Our method includes: 1) motion detection, 2) motion-robust image reconstruction, 3) joint realignment of the volumes, and 4) tracer-kinetic (TK) model fitting to evaluate kidney function parameters. STUDY TYPE: Retrospective. SUBJECTS: Eleven newborn patients (ages <6 months, 6 female). FIELD STRENGTH/SEQUENCE: 3T; dynamic "stack-of-stars" 3D fast low-angle shot (FLASH) sequence using a multichannel body-matrix coil. ASSESSMENT: We evaluated the proposed technique in terms of the signal-to-noise ratio (SNR) of the reconstructed images, the presence of discontinuities in the contrast agent concentration time curves due to motion with a total variation (TV) metric and the goodness of fit of the TK model, and the standard variation of its parameters. STATISTICAL TESTS: We used a paired t-test to compare the MoCo and no-MoCo results. RESULTS: The proposed MoCo method successfully detected motion and improved the SNR by 3.3 (P = 0.012) and decreased TV by 0.374 (P = 0.017) across all subjects. Moreover, it decreased nRMSE of the TK model fit for the subjects with less than five isolated bulk motion events in 6 minutes (mean 1.53, P = 0.043), but not for the subjects with more frequent events or no motion (P = 0.745 and P = 0.683). DATA CONCLUSION: Our results indicate that the proposed MoCo technique improves the image quality and accuracy of the TK model fit for subjects who present isolated bulk motion events. LEVEL OF EVIDENCE: 3 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2020;52:207-216.

Prospective pediatric study comparing glomerular filtration rate estimates based on motion-robust dynamic contrast-enhanced magnetic resonance imaging and serum creatinine (eGFR) to 99mTc DTPA.

BACKGROUND: Current methods to estimate glomerular filtration rate (GFR) have shortcomings. Estimates based on serum creatinine are known to be inaccurate in the chronically ill and during acute changes in renal function. Gold standard methods such as inulin and 99mTc diethylenetriamine pentaacetic acid (DTPA) require blood or urine sampling and thus can be difficult to perform in children. Motion-robust radial volumetric interpolated breath-hold examination (VIBE) dynamic contrast-enhanced MRI represents a novel tool for estimating GFR that has not been validated in children. OBJECTIVE: The purpose of our study was to determine the feasibility and accuracy of GFR measured by motion-robust radial VIBE dynamic contrast-enhanced MRI compared to estimates by serum creatinine (eGFR) and 99mTc DTPA in children. MATERIALS AND METHODS: We enrolled children, 0-18 years of age, who were undergoing both a contrast-enhanced MRI and nuclear medicine 99mTc DTPA glomerular filtration rate (NM-GFR) within 2 weeks of each other. Enrolled children consented to an additional 6-min dynamic contrast-enhanced MRI scan using the motion-robust high spatiotemporal resolution prototype dynamic radial VIBE sequence (Siemens, Erlangen, Germany) at 3 tesla (T). The images were reconstructed offline with high temporal resolution (~3 s/volume) using compressed sensing image reconstruction including regularization in temporal dimension to improve image quality and reduce streaking artifacts. Images were then automatically post-processed using in-house-developed software. Post-processing steps included automatic segmentation of kidney parenchyma and aorta using convolutional neural network techniques and tracer kinetic model fitting using the Sourbron two-compartment model to calculate the MR-based GFR (MR-GFR). The NM-GFR was compared to MR-GFR and estimated GFR based on serum creatinine (eGFR) using Pearson correlation coefficient and Bland-Altman analysis. RESULTS: Twenty-one children (7 female, 14 male) were enrolled between February 2017 and May 2018. Data from six of these children were not further analyzed because of deviations from the MRI protocol. Fifteen patients were analyzed (5 female, 10 male; average age 5.9 years); the method was technically feasible in all children. The results showed that the MR-GFR correlated with NM-GFR with a Pearson correlation coefficient (r-value) of 0.98. Bland-Altman analysis (i.e. difference of MR-GFR and NM-GFR versus mean of NM-GFR and MR-GFR) showed a mean difference of -0.32 and reproducibility coefficient of 18 with 95% confidence interval, and the coefficient of variation of 6.7% with values between -19 (-1.96 standard deviation) and 18 (+1.96 standard deviation). In contrast, serum creatinine compared with NM-GFR yielded an r-value of 0.73. Bland-Altman analysis (i.e. difference of eGFR and NM-GFR versus mean of NM-GFR and eGFR) showed a mean difference of 2.9 and reproducibility coefficient of 70 with 95% confidence interval, and the coefficient of variation of 25% with values between -67 (-1.96 standard deviation) and 73 (+1.96 standard deviation). CONCLUSION: MR-GFR is a technically feasible and reliable method of measuring GFR when compared to the reference standard, NM-GFR by serum 99mTc DTPA, and MR-GFR is more reliable than estimates based on serum creatinine.

Correction to: Prospective pediatric study comparing glomerular filtration rate estimates based on motion-robust dynamic contrast-enhanced magnetic resonance imaging and serum creatinine (eGFR) to 99mTc DTPA.

The originally published version of this article contained a typographical error. In the text under the subheading "Dynamic contrast-enhanced MRI method, post-processing, and MR-GFR calculation" and in Table 1 the intravenous injection rate of gadobutrol was incorrectly listed as 0.2 mL/s.

Interobserver and Intra-Observer Reliability of the Urinary Tract Dilation Classification System in Neonates: A Multicenter Study.

PURPOSE: The Urinary Tract Dilation classification system was designed to be more objective and reproducible than currently available grading systems. We evaluated the reliability and consistency of the system in newborns. MATERIALS AND METHODS: Of 1,046 infants 0 to 90 days old undergoing ultrasound for hydronephrosis 243 were randomly selected for study inclusion. Seven readers (4 radiologists and 3 urologists) at 4 institutions classified complete, de-identified ultrasound studies on a Web based platform. Interobserver and intra-observer agreement was evaluated using the Fleiss kappa statistic. RESULTS: Interobserver agreement for Urinary Tract Dilation risk score was moderate among the 7 readers (kappa = 0.421, 95% CI 0.404-0.438). Interobserver agreement using the Society for Fetal Urology scale was worse than with the Urinary Tract Dilation classification (kappa = 0.344, 95% CI 0.330-0.359). All 7 readers assigned the same Urinary Tract Dilation score in 19.3% of cases (47 of 243). In 38.7% of cases (94 of 243) at least 3 readers assigned a Urinary Tract Dilation score different from that assigned by the other readers. In 7% of cases (17 of 243) at least 3 readers assigned a score of P0/P1, while at least 3 readers scored the same cases as P2/P3. At least 3 different Urinary Tract Dilation risk scores were assigned to the same patient in 30.45% of patients (74 of 243). Among individual Urinary Tract Dilation elements calyceal dilatation and bladder status had the highest disagreement. Five readers regraded 80 cases and agreed with their previous Urinary Tract Dilation risk score in 63.8% to 75.0% of cases (kappa 0.458 to 0.729). CONCLUSIONS: Interobserver agreement using the Urinary Tract Dilation grading system is fair to moderate, with variable agreement on individual elements of the system. Agreement was higher for the Urinary Tract Dilation system compared to the Society for Fetal Urology scale.

Contrast-Enhanced Colosonography for the Evaluation of Children With an Imperforate Anus.

This case series describes a novel method for showing the preoperative anatomy of children with anorectal malformations using ultrasound contrast, which we have termed "contrast-enhanced colosonography (ceCS)." Six patients with anorectal malformations without a perineal fistula were studied both by fluoroscopic distal colostography and ceCS, and their results were confirmed surgically. Contrast-enhanced CS precisely showed the complex anatomic relationships in all cases. Compared to traditional fluoroscopic studies, ceCS has the benefit of no associated ionizing radiation and thus is safer for children.

Review of paraneoplastic syndromes in children.

Paraneoplastic syndromes are defined as clinical syndromes that are not related to direct tumor invasion or compression but are secondary to tumor secretion of functional peptides/hormones or related to immune cross-reactivity with normal host tissue. Paraneoplastic syndromes have a wide range of presentations and can present before the primary malignancy or tumor recurrence is diagnosed. They can mimic non-neoplastic processes, making detection, diagnosis and treatment difficult. However, they can also provide clues to the presence of an underlying malignancy. In this paper, we reviewed a range of paraneoplastic syndromes that can occur in children including: (1) neurologic (opsoclonus-myoclonus, limbic, anti-N-methyl-d-aspartate [NMDA] and anti-Ma2 encephalitis and myasthenia gravis); (2) endocrine (neuroendocrine tumors, hypercalcemia, SIADH [syndrome of inappropriate antidiuretic hormone secretion], osteomalacia/rickets and ROHHAD [rapid onset of obesity, hypoventilation, hypothalamic dysfunction and autonomic dysregulation]); and (3) dermatologic/rheumatologic syndromes (hypertrophic osteoarthropathy and paraneoplastic pemphigus). Familiarity with these syndromes can aid in early diagnosis, treatment and imaging optimization.

Common genitourinary catheters: a systematic approach for the radiologist.

Catheters are commonly used to treat and diagnose urinary tract abnormalities in the pediatric population. This pictorial essay reviews commonly placed genitourinary catheters imaged by radiography, fluoroscopy, computed tomography (CT) and ultrasonography (US). The purpose of the catheter, how the catheter is placed, and the imaging findings associated with appropriately positioned catheters as well as misplaced and displaced catheters are described. It is important for radiologists to recognize common genitourinary catheters, and be familiar with their normal and abnormal positions as displacement is often first recognized by diagnostic imaging.