Radiography is a two-dimensional (2D) static x-ray imaging technique that depicts structures based upon relative densities (e.g., air, fat, water, soft tissue, bone). Radiodense structures (e.g., bone), devices, and foreign bodies are well depicted. Visceral silhouettes and soft tissue lines are depicted with limited detail based upon the adjacent differential densities.

Radiography is the most commonly used modality in neonatal imaging and has historically been and remains one of the first steps in radiologic investigations for most neonatal disease processes. The advantages of radiography are that it is a portable exam, which is easy to perform, process, and interpret in a rapid manner. This makes it a highly effective method to rapidly screen for neonatal pathology and monitor medical and postprocedural treatment responses involving the neck, chest, abdomen-pelvis, and skeletal structures. The evaluation of support device positioning is a further key indication for obtaining radiographs in the neonate. In each of these applications, anatomy outside of the region(s) of interest should always be shielded.

For some clinical presentations, single-anatomical-level radiography is appropriate. For example, a noncyanotic neonate with intermittent tachypnea will initially undergo an anteroposterior (AP) chest radiograph. A neonate with abdominal distention and vomiting but no respiratory distress will initially undergo an AP abdominal-pelvis radiograph. A hemodynamically stable neonate with a suspected osseous congenital anomaly will undergo targeted bone imaging (e.g., forearm for radial array anomaly). For more critical neonates with greater time-sensitive diagnostic needs, multilevel radiography is appropriate. For example, for a neonate in respiratory distress, a combined AP chest and abdominal-pelvis radiograph is performed. This facilitates evaluation of targeted anatomy with categorization of visceral situs, recognition of potential cardiovascular and noncardiovascular congenital disease, and confirmation of appropriate positioning of all support devices placed during initial neonatal resuscitation and evaluation. Subsequent radiographs can then be targeted to a single level of concern, for example, chest or abdomen-pelvis radiograph. Follow-up chest radiographs should extend to at least the upper abdomen to account for variable degrees of inspiration and confirm stability
of support devices. For example, in Figure 6.1, had the upper abdomen not been included in this well-centered chest x-ray, the tip of the doubled back nasogastric tube might have been mistaken for the tip of an umbilical arterial catheter (UAC). The acute clinician would recognize, however, that the UAC if properly placed runs parallel with the left side of the spine on an AP film and would not deviate to the right as shown. When support devices require complete follow-up evaluation, coverage should again extend across multiple anatomical levels to include their entire anticipated locations. At times, lateral projections may be obtained in conjunction with the standard AP radiographs to evaluate anatomy, suspected pathology, and/or confirm positioning of support devices (Figs. 6.2 and 6.3). Diagnostic quality of radiographs
may be degraded by incorrect positioning, motion, overlying devices, and the degree of under- or overexposure (Fig. 6.4B). In addition, low inspiratory volumes may degrade the evaluation of chest radiographs.

Appropriately used radiography exposes the neonate to the least amount of radiation, as compared to other radiation-dependent modalities. The typical dose from an AP chest radiograph is 0.02 mSv, while the dose from a combined AP chest-abdominal-pelvis radiograph is up to 0.12 mSv (2). These values can be applied as a means to understand a neonate’s dose exposure from other radiation modalities and also when assessing a neonate’s cumulative dose. In this manner, dose exposure is expressed as an equivalent number of radiographs (e.g., chest radiographs). While this approach may provide a measure for communicating and understanding a neonate’s exposure and risk for single and cumulative exams, it is not always an accurate means for reporting exposure. As previously discussed, organs may have differential exposure, depending upon coverage, organ radiosensitivity, and shielding.

Ultrasound is a modality that utilizes high-frequency sound waves to generate anatomical images and functional data. B-mode “gray-scale” real-time sonography serves as a primary method to investigate neonatal congenital and acquired pathology across most anatomical regions. This includes assessment of intracranial, intra-abdominal-pelvis, cardiovascular, and musculoskeletal pathologies (Fig. 6.5). Additional use of gray-scale ultrasound includes image guidance for cardiovascular and noncardiovascular interventions (Fig. 6.6). Color and pulse-wave Doppler sonography are supplemental techniques that afford evaluation of cardiovascular physiology. Doppler sonography is also used to evaluate ureteral flow and exclude uterovesicular obstruction. M-mode sonography can be applied along with gray-scale sonography to evaluate diaphragmatic excursion and quantify the degree of
motion. Three-dimensional (3D) ultrasound techniques provide volumetric data and sophisticated morphologic displays, complementary to standard 2D displays.

The key advantage of ultrasound is that it is does not require ionizing radiation to generate images and physiologic data. In addition, it is widely available, is portable, and can be performed rapidly at the bedside in the neonatal ICU. The sonographic window may be degraded by catheters, metallic devices, bone, anatomical deformities, soft tissue edema, body fluid, and normal and abnormal regions of air. Sonography may also be limited by operator skill, emphasizing the importance of continuous quality control and review.

Fluoroscopy is a rapid sequential 2D x-ray imaging technique that affords dynamic real-time imaging. As with static radiography, fluoroscopy depicts structures based upon the relative densities of air, fat, water, soft tissue, and bone. Radiodense structures (e.g., bone), devices, and foreign bodies are well identified, while viscera and soft tissues are depicted with limited structural detail. Oral, intracavity, and direct intravascular iodinated water-soluble contrast are administered to enhance lumens, generate new density interfaces, and increase structural depiction and detail. Multiple specific technical radiation reduction strategies are used simultaneously during fluoroscopy, in conjunction with the previously described core strategies. These include (a) using intermittent, pulsed x-ray beams (as opposed to constant and continuous fluoroscopy) of narrow width and low rates; (b) capturing the majority of the exam with “last image hold” and “fluoroscopic save” options (as opposed to actual radiographic images); (c) using x-ray beam and field-of-view filters; and (d) selecting appropriate larger field of views and greater radiation source to skin distances. (3) In addition, antiscatter grids should be used on a limited basis.

Common neonatal applications of fluoroscopy include evaluations of the gastrointestinal (GI) tract and genitourinary system. Typically, these exams follow an ultrasound of the abdomen, pelvis, or both. Fluoroscopic evaluation of the GI tract requires intraluminal contrast opacification. Once opacified, GI tract shape, luminal integrity, course, caliber, and contour can be assessed. For the upper and mid-GI tract, oral contrast is administered (e.g., barium swallow, esophagram, upper GI series, or small bowel follow-through); the transit of contrast is monitored in an antegrade direction. For the lower GI tract, a contrast enema is administered in retrograde fashion toward the cecum (e.g., barium enema). Performance of the appropriate fluoroscopic GI exam and selection of the correct type and volume of contrast will depend upon the neonate’s clinical presentation and suspected pathology. Neonatal dose exposures from an upper GI series and barium enema may be as low as 0.5 and 0.4 mSv, respectively (2).

The neonatal genitourinary system is evaluated under fluoroscopy, most commonly with voiding cystourethrography (VCUG). For this examination, contrast is instilled into the bladder in a retrograde fashion via a catheter. Images are acquired during bladder filling, maximal distention, and voiding to assess bladder and urethra morphology and exclude ureteral reflux, urethral obstruction, and congenital anomalies involving the bladder, ureters, and urethra (Fig. 6.7). VCUG catheterization should always be performed by a skilled provider using proper, sterile technique. Neonatal dose exposure from a VCUG may be as low as 0.1 mSv (2).

Historically, fluoroscopy has also been used to evaluate diaphragmatic motion, airway morphology, and the cardiovascular system. Fluoroscopy combined with endoscopy has also been used
for diagnostic evaluation of neonatal biliary and pancreatic ducts (e.g., endoscopic retrograde cholangiopancreatography [ERPC]). Fluoroscopy is still an option to evaluate a neonate’s diaphragm and airway. However, ultrasound and MRI are now more common, nonradiation alternatives to evaluate the diaphragm, while both MRI and CT can be used to evaluate the neonatal airway. In most neonatal centers, MR cholangiopancreatography has replaced ERCP, while ultrasound, MRI, magnetic resonance angiography (MRA), and CT angiography (CTA) are now principle noninvasive cardiovascular imaging modalities. Fluoroscopic-based invasive catheter angiography is performed selectively in neonates to investigate congenital heart disease (CHD), congenital vascular disorders (CVD), and acquired cardiovascular pathologies (see Chapter 30, Figs. 30.22, 30.24, and 30.26).

Fluoroscopy remains a primary technique for image-guided cardiovascular and noncardiovascular interventions in the neonate. Fluoroscopic guidance may be combined with ultrasound to improve technical guidance and potentially decrease radiation exposure. Hybrid CT-fluoroscopy and MRI-fluoroscopy technologies are also available and can be applied for neonatal image-guided interventions. Cardiovascular applications include vascular access and interventions for CHD, CVD, and acquired pathologies. Potential noncardiovascular applications include enteric access (e.g., feeding and percutaneous gastrostomy tube placements), percutaneous transhepatic cholangiography and biliary drainage, percutaneous cholecystostomy, and percutaneous nephrostomy. Noncardiovascular applications also include intraoperative guidance in select surgical procedures. Radiation exposure during procedures will depend upon the complexity of the interventional procedure, extent of disease, comorbid risk factors, and the operator’s technique.

CT is a multiprojectional x-ray beam technique that generates 2D cross-sectional images in the z-axis direction across all body systems. With current CT scanners, submillimeter sections can be acquired. These datasets afford multiprojectional 3D anatomical reconstructed displays that enhance interpretation, anatomical understanding, and treatment planning. High spatial resolution and superior tissue characterization, combined with frequent exam availability, rapid scan times, and ease of patient access make CT a desirable modality in select neonatal pathologies. CT scan times in a neonate may range from less than 1 second to 5-8 seconds depending upon the CT scanner technology, range of coverage, and prescribed technique. While motion can degrade CT image quality, more rapid CT acquisitions may afford imaging of the neonate independent of motion and without the need for sedation.

The radiation risks posed by CT are the greatest deterrents to its use in neonates. However, submillisievert exposure is possible when utilizing core and advanced CT-specific radiation reduction strategies (4). CT often follows ultrasound or fluoroscopic diagnostic evaluations. Based upon its advantages, CT imaging is indicated in the neonate for emergent evaluations (e.g., head CT for investigation of intracranial hemorrhage [ICH], ischemia, or trauma); for superior anatomical characterization (e.g., chest CT for congenital lung lesions) (see Chapter 41, Fig. 41.15); and for a neonate who has high sedation or general anesthesia risks. CT is used to define choanal atresia (see Chapter 41, Fig. 41.5A). CT is also indicated when MRI is not available, is contraindicated (e.g., during extracorporeal membrane oxygenation), is nondiagnostic (e.g., ferromagnetic materials—patent ductus arteriosus [PDA] clip), or has a high pretest probability of yielding a nondiagnostic exam. CT may be performed without or with iodinated intravenous contrast, depending upon the exam indications. Intravenous contrast-enhanced CT images may be acquired during the arterial phase, venous phase, or visceral phase, yielding CT arteriography, CT venography, or routine CT scans, respectively. An abdominal-pelvis CT may be performed in a neonate without or with oral water-soluble iodinated contrast.

MRI is an imaging technique that uses high magnetic fields and radio waves to generate 2D and 3D anatomical displays at any targeted plane for an imaged body system. Functional sequences can also be acquired to generate physiologic data. The lack of radiation and iodinated contrast exposure along with the ability to inherently delineate and characterize tissues with high contrast resolution should clearly make MRI an ideal choice for neonatal imaging.

In clinical neonatal practice, however, MRI is used as a secondary modality, typically following ultrasound or CT. In part, this is related to potentially long scan times and limited availability. More importantly, the majority of MRI exams in a neonate require conscious sedation or (less commonly) general anesthesia to control neonatal motion. This places added risks on the neonate. Not only can monitoring be challenging during the exam but the mechanical ventilation, oxygen, and anesthetics can profoundly alter the neonate’s circulatory physiology. Furthermore, anesthetics have been associated with potential neuroapoptotic effects in the brain of young patients (6) (see Chapter 53). In addition to motion, MRI quality may be degraded by metallic (e.g., ferromagnetic) structures and air. Preexam screening is essential to plan for sedation or general anesthesia, discuss the added risks with the family, and identify metallic objects and devices that may degrade image quality (see Chapter 46, Figs. 46.12, 46.14, 46.16, 46.17, 46.18, 46.19 and 46.20).

Nuclear imaging is a technique that uses radioactive material (e.g., radiopharmaceutical) to map out cellular activity in 2D and 3D anatomical displays. The radiopharmaceutical is delivered to target a set of organs and organ system based upon cellular properties. Radiation is emitted from the organs to form an image, directly proportional to the organ uptake and metabolic activity. This affords an ability to evaluate normal and abnormal cellular physiology and indirectly, anatomic morphology. Primary considerations in the neonate include the diagnosis of biliary atresia (e.g., hepatobiliary scan) and the localization of a suspected intrapancreatic insulin producing tumor (e.g., positron emission tomography [PET]-CT exam). While evaluations of the brain, endocrine system, heart, lungs, kidneys (Fig. 40.16D), GI tract, and skeletal system are possible, other applications in the neonate are on a selective basis given the radiation exposure and ability of ultrasound, MRI, and low-dose CT to reliably provide a diagnosis. As an example of the potentially high radiation exposure with nuclear scintigraphy, a hepatobiliary scan in a neonate may result in exposure to 6 to 7 mSv (2). Because of high radiation exposure, nuclear scintigraphy is infrequently used for the neonate.

Clinical care of a neonate in the ICU routinely leads to the placement of several different types of catheters, tubes, and other devices. Core neonatal ICU devices include endotracheal tubes (ETTs), UAC, venous access catheters, enteric access catheters, and intercostal catheters. Following placement of a device and before it is used, confirmation of suitable positioning is an immediate priority. Prompt recognition of an abnormally positioned device is critical for rapid management of a potential iatrogenic injury and prevention of short- and long-term sequelae.

While there are several clinical bedside measures which the clinician can employ to affirm appropriate positioning (e.g., auscultation and carbon dioxide monitoring for ETT placement), radiography serves an essential primary diagnostic role in device management. Device positioning can change during the clinical course of the neonate. Thus, periodic follow-up radiography serves a key secondary role in device management. Beyond these core clinical functions, radiographic assessment of support devices also serves an important ancillary role in the recognition and evaluation of congenital cardiovascular and noncardiovascular disease The abnormal course of several different devices can offer insight into presence of situs inversus, heterotaxy, esophageal atresia, congenital diaphragmatic hernia (CDH), abdominal wall defects, patent foramen ovale, an atrial septal defect, a persistent left superior vena cava (SVC), a persistent left inferior vena cava (IVC), a right aortic arch, and a circumflex descending aorta.

In addition to the general imaging principles previously discussed, there are a few radiographic principles specific for imaging devices. First, to ensure adequate depiction of the devices, kV and mAs radiation parameters may need to be adjusted from the typical neonatal settings. Second, the field of view should completely cover the internal as well as external segments of the device. This may require imaging multiple anatomical regions of the neonate (e.g., chest, abdomen, and pelvis). Third, all external segments should be isolated in a straight course, separate from other devices and aligned at an angle different from the expected internal course. For an AP radiograph, isolating external from internal segments may require manually repositioning the external segment or obliquely positioning the neonate. Fourth, all monitoring leads and other objects not related to the support device should be removed from the field of view. Fifth, when the course and final position of a device are indeterminate based upon a diagnostic-quality AP radiograph, an additional oblique or lateral projection must be obtained (Fig. 6.8A, and B). Alternatively, suboptimal image quality may preclude diagnostic assessment of the device. In this instance, the AP radiograph can be repeated with proper adjustments to correct for potential inappropriate radiation technique, positioning, overlying leads, or a combination thereof.