Methods- Thorough description of the current imaging and functional investigation techniques in nuclear medicine and radiology- Detailed portrayal of .
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In the neonate the renal cortex can be isoechoic or even hyperechoic compared with the liver Figure , and the corticomedullary differentiation can be pronounced. By the time a child is several months of age, the renal cortex should be hypoechoic compared with the echogenicity of the liver. The pyramids, particularly in neonates, can be so hypoechoic that they can be mistaken for a dilated collecting system.
There are exceptions to the hypoechogenicity of the renal pyramids, the majority of which relate to disease states that is, medullary nephrocalcinosis or interventions that is, Lasix administration. The most common exception, however, seen in many neonates, may be the transient increase in echogenicity, which has been attributed to precipitation of Tamm Horsfall proteins. Additionally there may be lobulation of the renal outline, especially in neonates.
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This should not be confused with scarring. Normal lobulation tends to be seen in the portion of the cortex between pyramids, whereas focal scarring tends to occur in portions of the cortex directly overlying the pyramid. The renal collecting system can be assessed both qualitatively and quantitatively regarding the degree of dilatation. Measurement of pelvic dilatation can be assessed at the level of the renal hilum—or just beyond it in the case of an extrarenal pelvis.
A full bladder can exaggerate the degree of dilatation. It is therefore useful to assess the pelvic diameter after voiding if the urinary bladder is overdistended. If the ureter is dilated, its diameter can be assessed along its course, although it can be visualized most reliably proximally and distally Figure The midportion of the ureter is often obscured by overlying bowel gas. The thickness of the wall of the ureter or bladder can also be assessed. Thickening of the urothelium anywhere along the urinary tract can be associated with, though is not pathognomonic for, infection or inflammation.
Urolithiasis can be diagnosed as an echogenic focus with distal acoustic shadowing. The degree of obstruction caused by a calculus can also be assessed with sonography. Color Doppler and pulsed Doppler interrogation can be used to assess vascularity of the kidneys. The study can assess the vessels from the main renal arteries and veins through the arcuate vessels in the renal parenchyma. Indications for Doppler evaluation include suspicion of renal arterial or venous thrombosis, arterial stenosis, trauma, infection, acute tubular necrosis, and transplant rejection, although the role of rejection in evaluation remains controversial.
Eric Crotty, Alan S. Plain film radiography continues to be the mainstay of pediatric imaging , and pediatric pulmonologists should be comfortable with evaluating a chest radiograph. Cross-sectional imaging techniques, especially HRCT, are becoming increasingly important as a means of investigating the respiratory tract but should be used only when the clinical information to be gained outweighs the potential risk of radiation and also the risk of any required sedation.
Special techniques such as controlled ventilation or decubitus imaging can be used to optimize the quality of the images obtained in sedated children. Imaging of the airway for intrinsic abnormalities is primarily performed with radiography. Extrinsic airway compression and mediastinal abnormalities can be imaged with CT or MR imaging. The choice of which modality to use should be decided on a case-by-case basis. Nasal and paranasal structures are optimally imaged with CT and MR imaging. Offiah, in Pediatric Bone Second Edition , This technique uses the principles of magnetism instead of ionizing radiation, an advantage in pediatric imaging [28—31].
MRI depends on intrinsic tissue parameters that reflect the chemical characteristics of that tissue. MRI is the phenomenon in which certain atoms can absorb and re-emit radiofrequency waves of a specific energy when in a magnetic field. It is principally the distribution of hydrogen ions protons , abundant in biologic tissues, which contributes to MR images. MR imaging was introduced into clinical practice in the early s. Clinical whole-body scanners operate with a field strength of 1.
Pulses of radiofrequency radiation are applied and the magnitude of the nuclear signal following this pulse is measured as relaxation times. Variations in pulse sequences can alter tissue contrast, which is determined by T 1 and T 2 relaxation times and proton density. A great number of pulse sequences have been developed to potentiate differences in tissue contrast and enhance the conspicuity of pathologic lesions.
In bone and soft-tissue lesions, T 1 - and T 2 -weighted T1W and T2W images are usually acquired, and tissues may have specific signal intensities:. Cortical bone and fibrous tissue: The high contrast sensitivity of MRI makes it the imaging method of choice for defining soft-tissue margins and marrow changes within bones. Vessels that contain flowing blood appear as signal voids on MRI and are easily identified. MR angiography can be performed without the use of intravenous contrast media.
Images can be obtained in multiple planes Fig.
To maximize the signal-to-noise ratio and spatial resolution in MR images, specialized surface transmitter-receiver coils have been designed for scanning specific anatomical sites, such as the extremities. The advent of faster MRI scanning techniques gradient-echo enables the acquisition of three-dimensional data; this has important applications in musculoskeletal disorders.
Turnbull, in Methods in Enzymology , Compared to developmental biology studies in lower organisms, such as Caenorhabditis elegans and zebrafish, the mouse presents significant challenges for direct visualization and analysis of volumetric and dynamic changes in embryos and their developing organ systems. Despite advances in optical microscopy and the availability of mouse reporter lines expressing fluorescent proteins, in vivo optical imaging is generally restricted to tissue explants and exo utero imaging of early-stage embryos that are amenable to whole embryo culture, and imaging studies cover relatively short time windows over which normal development can be maintained.
Ultrasound and magnetic resonance imaging MRI are widely used for human fetal and pediatric imaging , and can be scaled to provide effective microimaging tools for application in mice. A major challenge for imaging methods, including ultrasound and MRI, is the need for high image throughput necessary to match the requirements for efficient phenotypic screening of mutant and transgenic embryos and postnatal mice. In this context, both ultrasound and MRI offer significant advantages in terms of real-time imaging capability ultrasound and the recent development of multiple-mouse imaging systems MRI.
For phenotype screening with either method, the image analysis process is critically important, but is not discussed in detail in this chapter. It is worth noting that MRI data are particularly well-suited to computational 3D analysis approaches, providing the potential to greatly improve phenotyping throughput and detection of more subtle changes than can be evaluated by simple inspection of images.
It is the criterion test for renal scarring. The "top-down" approach has suggested that the DMSA scan be used as the primary test in patients with UTI, in that it selects for patients with renal injury. A small feeding tube 8 French for newborns, 10 French for infants is passed via the urethra into the bladder. Contrast material is then dripped into the bladder under gravity. Serial radiographs of the pelvis and abdomen are then taken. The first film obtained is important for the diagnosis of ureterocele.
Radiographic Evaluation of Pediatric Urinary Tract
It is observed as a round filling defect at this point but may be compressed with further filling. The bladder is then filled until the expected capacity is reached. Tapping on the bladder or gentle massaging it is sometimes necessary to encourage the patient to void. Views of the kidneys and an oblique view of the male urethra are obtained once voiding has started. Parents often ask whether sedation will be used for VCUG. The contrast in the bladder is usually as opaque or as bright as the contrast that refluxes.
Dilution of contrast suggests stasis of urine ie, urine mixing with the refluxed contrast and suggests coexisting obstruction at the ureteral or renal pelvis level. Intrarenal reflux or reflux into compound papillae typically occurs at the poles of the kidney, which is why the poles are more susceptible to infection and scarring. During the first void, the urine in the pressurized obstructed system drains, and, on the subsequent void, contrast may be observed to reflux.
Cyclic VCUG has also been demonstrated to increase the sensitivity of the test. Nuclear VCUG is a good choice for follow-up studies in patients with UTI or in screening for siblings of patients with reflux, in that the radiation exposure is decreased; however, in patients with an abnormal ureteral anatomy eg, duplication that would influence a surgical approach, contrast VCUG is indicated.
When VCUG is performed after valve ablation, the posterior urethral dilation may not resolve completely, but good distention of the anterior urethra should be present, as well as a decrease in the previous size gradient in the urethra caused by the valve. CT is mainly used in children for evaluation of blunt abdominal trauma, as well as the diagnosis and follow-up of renal and ureteral calculi.
The use of noncontrast spiral CT is growing in patients with urolithiasis because of its higher sensitivity at detecting calculi, and this modality is becoming increasingly popular as a second-line study in selected patients with spina bifida whose body habitus prevents good visualization with US.
If the diagnosis of urolithiasis is considered in a child with minimal symptoms, it is reasonable to start with renal US and plain radiography iand then proceed to CT if initial findings are negative and clinical symptoms persist. Pediatric radiologists adjust the CT study so that children are exposed to much lower radiation doses than adults undergoing the same study. The use of US and plain radiography in the follow-up of renal and ureteral calculi should be encouraged, unless the calculi can only be detected via CT.
Each of these methods requires precise synchronization between contrast media delivery and scan acquisition.
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Each should be considered if US and MRI yield indeterminate results, if higher spatial resolution is required, or if a more rapid scan time is desired. CTA can evaluate renal hypertension, vasculitis, vascular malformations, and traumatic injury. CTU is used less often and can be applied in assessing congenital anomalies, obstruction, and traumatic collecting system injury. The use of MRU is increasing in children. Applications of MRU include identification of congenital anomalies, urinary tract obstruction, and hematuria; differentiation of infection from scarring; and posttreatment assessment of the urinary tract.
MRU correlates well with diuretic renal scanning in terms of assessing renal function and may be superior in terms of distinguishing nonobstructive hydronephrosis from obstructive hydronephrosis. Functional MRU for hydronephrosis requires prehydration and a bladder catheter. Furosemide is given 10 minutes before the patient is placed on the table. Because the contrast agent is heavier than urine, the patient should be positioned prone so that contrast collects at the UPJ. The following three sets of data are generated during functional MRU:. Functional data are determined by calculating renal parenchymal volume to determine relative function, and the Patlak number serves as an index for the GFR.
Having the preoperative images, informing the radiologist of the details of the procedure, and having the question to be answered persistent reflux or hydronephrosis are helpful when performing postoperative imaging, so that the study can be appropriately tailored to the situation. Perform RBUS 1 month after surgery to evaluate for silent obstruction. Follow-up US can be performed at 1 year and 5 years after surgery. The follow-up protocol depends on the function of the kidney and the original indication for surgery. Postoperative problems usually present within 18 months, and prolonged follow-up is not useful.
The three variables to be evaluated are as follows:. If the kidney had poor function or if significant intrarenal hydronephrosis was present, leaving a nephrostomy tube should be considered because the renal dilation may always appear significant. Allowing contrast to cross the anastomosis may be the only way to assess patency. If a nephrostomy tube has been placed intraoperatively, low-pressure injection through the tube nephrostography can be performed 2 weeks after surgery, with the patient in the prone position, with the contrast hung at a height of 40 cm. If nephrostography reveals good drainage into the bladder, the nephrostomy tube can be clamped.
If the patient remains asymptomatic, the tube is removed a few days later. Occasionally, the nephrostomy tube is placed too close to the repair and causes edema, obstructing the UPJ. This is remedied by pulling the tube back into the renal pelvis and repeating nephrostography a week later.
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This step ensures that the anastomosis is patent and that adequate drainage has been achieved. Renal US can be performed 6 months after surgery to evaluate the hydronephrosis, and renal scanning is performed one year after surgery to determine the final relative function. Dynamic MRU can be used to assess the results of pyeloplasty by comparing preoperative and postoperative parameters. If the pyeloplasty was performed to correct a decrease in relative renal function, perform RBUS 1 month after surgery and renal scanning 3 months after surgery to ensure that renal function is stable or improved.
IVU can be performed 6 months after surgery to define the anatomy. A follow-up renal scan 1 year after surgery shows the degree of ultimate renal improvement. Some patients present with classic flank pain and nausea and have symmetric function on renal scanning. Perform US 1 month after surgery to check for hydronephrosis, and consider a renal scan 3 months after surgery to check drainage and function. For these patients, the important outcome is that they no longer have symptomatic UPJ obstruction.
If the patient is improving clinically creatinine level decreasing appropriately , perform RBUS 1 month after surgery. Timing of the VCUG is controversial. Some authors prefer performing VCUG shortly after PUV ablation to ensure that no obstruction persists, whereas others advocate waiting 6 months. If persistent urethral obstruction is suspected, perform the studies earlier.
Renal scans are useful to evaluate relative renal function. Perform RBUS 1 month after surgery earlier if the patient presented with sepsis to ensure that adequate decompression has occurred. Subsequent imaging will depend on the presence of residual VUR. Ultrasound grading of hydronephrosis: Does every patient with prenatal hydronephrosis need voiding cystourethrography?. Vesicoureteral reflux and urinary tract infection in children with a history of prenatal hydronephrosis--should voiding cystourethrography be performed in cases of postnatally persistent grade II hydronephrosis?.
Imaging recommendations in paediatric uroradiology: The predictive value of the first postnatal ultrasound in children with antenatal hydronephrosis. Continuous antibiotic prophylaxis in the setting of prenatal hydronephrosis and vesicoureteral reflux. Can Urol Assoc J. Imaging studies and biomarkers to detect clinically meaningful vesicoureteral reflux. Reliability of grading of vesicoureteral reflux and other findings on voiding cystourethrography. The characteristics of primary vesico-ureteric reflux in male and female infants with pre-natal hydronephrosis.
Pediatric ureteropelvic junction obstruction: Long-term followup of primary nonrefluxing megaureter. Prospective trial of operative versus non-operative treatment of severe vesicoureteric reflux: Antimicrobial prophylaxis for children with vesicoureteral reflux. N Engl J Med. Gleeson FV, Gordon I. Imaging in urinary tract infection. Predictive value of specific ultrasound findings when used as a screening test for abnormalities on VCUG. Imaging studies after a first febrile urinary tract infection in young children.
Febrile urinary tract infections in infants: Normal dimercaptosuccinic acid scintigraphy makes voiding cystourethrography unnecessary after urinary tract infection. Incidence of post-pyelonephritic renal scarring: The relationship between early renal status, and the resolution of vesico-ureteric reflux and bladder function at 16 months. Surveillance for Wilms tumour in at-risk children: Advances in uroradiologic imaging in children. Radiol Clin North Am. Ultrasonography in the evaluation of renal scarring using DMSA scan as the gold standard.
Radiation risk to children from computed tomography. MR urography in children. A prospective study comparing ultrasound, nuclear scintigraphy and dynamic contrast enhanced magnetic resonance imaging in the evaluation of hydronephrosis. Ultrafast fetal MRI and prenatal diagnosis. Magnetic resonance and computed tomography in pediatric urology: Sign Up It's Free! If you log out, you will be required to enter your username and password the next time you visit. Share Email Print Feedback Close. Radiographic Evaluation of Pediatric Urinary Tract.
Background This article provides a practical guide to the appropriate imaging of the pediatric urinary tract. Grade IV - Diffuse calyceal dilation; parenchyma thinned to less than half the thickness of the contralateral kidney. Grade I - Ureteral reflux that does not reach the renal collecting system. Grade II - Reflux into the ureter and pelvis with crisp calyceal impressions. Grade III - Mild dilation of the ureter and pelvis with mild caliectasis and blunting of the fornices.
Grade IV - Moderate dilation of the ureter and pelvis with ureteral tortuosity and major blunting of calyces but maintenance of papillary impressions. Grade V - Massive ureteral tortuosity and caliectasis with loss of papillary impressions. Evaluation of possible ectopic ureter or megaureters that are dilated to the level of the bladder. A possible intermittent UPJ obstruction with normal renal scan findings. Time-to-peak TTP , which is the time for maximal concentration of contrast in the parenchyma.
Calyceal transit time CTT , which is the time for contrast to first appear in the calyces. Postoperative Imaging Having the preoperative images, informing the radiologist of the details of the procedure, and having the question to be answered persistent reflux or hydronephrosis are helpful when performing postoperative imaging, so that the study can be appropriately tailored to the situation. What would you like to print? This is a sagittal ultrasound scan of the pelvis of an elderly man. What structures are shown and what procedure has been performed? This IVU, performed in a child, shows several abnormalities.
What unusual findings can be seen and what is the underlying cause of these findings? What abnormality is shown here in the plain abdominal X-ray of a lady who underwent hysterectomy and then developed recurrent bladder infections with left loin pain? This is a bone scintigram in an elderly man with back pain and obstructive lower urinary tract symptoms. What does the scintigram show and what is the most likely cause of the abnormalities? This is the plain abdominal X-ray of a lady who had accidentally introduced a foreign body into her bladder.
What is the foreign body and why had the patient inserted it into her bladder?