Environment

The imaging room’s environment is modified to reduce a child’s anxiety. Smaller equipment can be hidden or concealed with covers and images. Large equipment such as CT scanners can be decorated to give a sense of adventure (Fig. 24-1), and allow study acquisition without sedation. Other distraction techniques include lamps placed in the line of vision of the patient and displaying entertaining images on the ceiling (Fig. 24-2), or the release of piquant aromas in the imaging room (e.g., coconut). Movie goggles allow the child to watch a favorite movie while undergoing magnetic resonance imaging (MRI) or a nuclear medicine scan.

Figure 24-1 PET/CT suite known as “Camp Cozy.”

Figure 24-2 Child-friendly light display that shines on the walls and ceiling of the ultrasound examination room.

Positioning

The technologist usually allows parents to be present in the examining rooms and even to assist with some studies. This decreases the repeat rate and so decreases the radiation dose to the child. When a child lies supine, he or she may feel vulnerable. Comfort positions can give children a sense of control and help them feel more relaxed, that is, sitting on a chair or in a parent’s lap, hand-holding with a parent, or hugging. The child is encouraged to participate in producing the best possible examination by being permitted to make individual choices (e.g., placement of a toy or blanket, the position of a parent, the flavor of oral contrast material, or the selection of a bandage).

Language

The radiology team should always remember to use simple language for child-friendly explanations. For children of any age, the wrong choice of words can have a negative impact and potentially long-lasting effects. Avoid saying “dye/contrast”; say instead, “a drink/sticky water that helps the doctor see the inside of your belly clearer in your pictures.” Also, describe the imaging room environment in ways that can be related to the child’s home, for example, the noise of a CT scanner can be described to be like that of a “washing machine,” or a urinary catheter can be described as a “tiny straw that takes out pee-pee and puts in the x-ray water.” Young children have little sense of time; the radiology team should always prepare them to know when they will be done with their examination. For example, if a child is undergoing a voiding cystourethrogram (VCUG), avoid saying, “this will only take 15 minutes”; instead, say “you’ll be all finished and get up after you potty on the table for us.”

Advantages of Radiography in Pediatric Imaging

The advantages of radiography in pediatric imaging include the following:

Disadvantages

The disadvantages of radiography in pediatric imaging include the following:

Physics

X-rays are a form of short electromagnetic radiation produced by energy conversion when fast-moving electrons from the cathode filament of the x-ray tube interact with the tungsten anode (target) (Fig. 24-6). The amplitude of the tube current (expressed as milliamperes, or mA) depends on the emission rate of electrons from the cathode, which is determined by the cathode temperature. The speed of the electrons as they are propelled from the cathode to the anode is determined by the x-ray tube potential (kilovoltage peak, or kVp). When an x-ray beam is directed toward the examined part of the body, an image is formed. The resultant image is a recording of internal body structures in which the black areas represent the least dense body structures that have allowed the x-rays to pass through (i.e., lungs) and the more dense structures (i.e., bone), which have absorbed the x-rays, appear white (e-Fig. 24-2).

Figure 24-6 X-ray production.

e-Figure 24-2 An x-ray image. Shown is an anteroposterior chest radiograph of an infant, demonstrating the attenuation of the various body structures. The normal lungs are air-filled and therefore black. The heart (H) and liver (L) have absorbed some radiation and are slightly gray. The bones are dense, and are a lighter shade of gray to white. Note the sail sign of the normal thymus (T) and the rightward deviation of the distal trachea (arrow) by the normal left-sided aortic arch.

Computed radiography (CR) has replaced conventional film-based radiography. The acquired image is displayed instantly on the high-resolution monitor of the PACS. e-Table 24-3 lists common indications for plain radiography.

e-Table 24-3 Common Indications for Plain Radiography

Lateral Soft Tissues of the Neck

The retropharyngeal soft tissues extend from the adenoids, which are visible by 3 to 6 months of age, to the origin of the esophagus at the level of C4 to C5. A useful ratio is the width of the retropharyngeal soft tissue to that of the C2 vertebral body. The ratio varies in inspiration from almost 1.0 before 1 year of age to 0.5 by 6 years of age. The soft tissue width should not exceed 50% of the accompanying vertebral body to C4 (Fig. 24-7). Expiratory tracheal buckling can create buckling of the trachea anteriorly, causing an apparent increase in retropharyngeal soft tissues and creating a “pseudo-retropharyngeal abscess” (Fig. 24-8). Pseudo-retropharyngeal abscess can be differentiated from a true abscess when the appropriate inspiratory film demonstrates supraglottic airway and hypopharyngeal distention with air (Fig. 24-9). Appropriate patient positioning is critical. The examination of the lateral view of the soft tissues of the neck must be performed in slight extension and during inspiration (Fig. 24-10). The most common cause of a pseudo-retropharyngeal abscess is a film taken during expiration or swallowing, or with an improperly positioned child.

Figure 24-7 A, Lateral radiograph of a normal airway. The cornua of the hyoid (arrowhead) point to the epiglottis. a, adenoids; t, tonsil. B, Diagrammatic representation of the normal anatomy of the upper airway.

(B, From Blickman JG, Parker BR, Barnes PD: Pediatric radiology: The requisites, ed 3, Philadelphia, 2009, Mosby Elsevier.)

Figure 24-8 Normal tracheal buckling. Chest radiographs of a 4-month-old infant demonstrate tracheal buckling, a normal occurrence when the film is exposed during flexion and/or expiration. A, In the frontal projection, normal tracheal buckling occurs rightward, away from the aortic arch. B, Anterior buckling is evident on the lateral projection. This normal anterior tracheal displacement frequently causes confusion because it simulates a retropharyngeal mass. Note that the airway should be visible on all normal chest films.

Figure 24-9 Effect of phase of respiration on the prevertebral soft tissue space. Arrow in A demonstrates the prevertebral soft tissue widening on expiration that disappears on inspiration (B).

(From Blickman JG, Parker BR, Barnes PD: Pediatric radiology: The requisites, ed 3, Philadelphia, 2009, Mosby Elsevier.)

Figure 24-10 False-positive identification of a retropharyngeal mass. A, An examination with poor head extension suggests a retropharyngeal mass. B, A repeat examination with better head extension and pressure applied to the anterior neck with a lead-gloved finger; the retropharyngeal soft tissues are normal. Intervention with a gloved finger is seldom necessary if the film is repeated in full extension and inspiration.

(From Hilton SvW, Edwards DK III: Practical pediatric radiology, ed 3, Philadelphia, 2006, Saunders Elsevier.)

The lateral view of the neck is optimal for evaluating the supraglottic airway (see Fig. 24-7). The lower border of the nasopharynx is the hard palate, soft palate, and uvula. The oropharynx (below the hard and soft palate) leads to the air spaces at the base of the tongue, which are the valleculae. Immediately behind the valleculae is the epiglottis. The hyoid bone is inferior and anterior to the valleculae. The oropharynx also merges posteriorly with the nasopharynx to form the hypopharynx. The tonsils are seen in the lateral walls of the hypopharynx. Anteriorly, the hypopharynx leads to the larynx and becomes the esophagus. The pyriform sinuses are the most lateral and inferior margins and provide a landmark for the level of the vocal cords.

The lateral film is important in the assessment of (1) the encroachment of adenoidal tissue on the nasopharyngeal airway; (2) retropharyngeal swelling/abscess (air in the retropharyngeal space); (3) the degree of hypopharyngeal airway distention as a measure for airway encroachment (croup); and (4) identification of a radiopaque foreign body. Calcification in respiratory cartilage, although very rare in children, is pathologic; it is seen in chondrodysplasia punctata and relapsing polychondritis. The hyoid bone may be ossified at birth.

Anteroposterior Film of the Neck

The frontal radiograph is best for evaluation of tracheal position. Normally, the trachea is slightly deviated to the right by the aortic arch (deviation to the left is always abnormal). A normal thymus will not affect the trachea. Expiration causes buckling of the trachea to the right (see Fig. 24-8). Note that the airway is a dynamic system and changes in caliber and position so that an isolated, single film may be quite misleading. Nonetheless, an abnormal configuration of the airway should be pursued in light of the clinical history.

Interpretation of the Chest Film: 1. The Radiologist’s Circle

A systematic approach to the radiographic evaluation is crucial for anyone dealing with children. Comparison with previous imaging studies is mandatory and is facilitated by the use of a PACS. A chest film is always examined for information about the heart and lungs, but radiologists look first at the nonpulmonary areas, that is, the abdomen, bones, soft tissues, and airway, to be sure that they do not miss any abnormality. Only then should one progress to the mediastinum. A good habit to develop is to imagine a circle on the film so as to dispense with all the noncardiopulmonary areas. Begin at the corners, where the patient information is. Check the name, date, and especially the left and right markers. An easy way to complete the circle is to progress from the name tag to the markers to the ABCS of the film: A, abdomen; B, bones; C, chest (airway, mediastinum, lungs, and diaphragm); and S, soft tissues. Carefully observe the easily missed areas: under the diaphragm, through the heart, paraspinal lines, lung apices, shoulders, and soft tissues of the neck.

On every chest film, read the abdominal portion as you would read an abdominal film. Evaluate the abdomen (regardless of how little of it can be seen) on every chest film, and note whether the stomach bubble is on the left and the liver on the right. Is it an erect film? If so, examine it specifically for calcifications, gallstones, or pancreatic calcification.

Determine the presence of bowel distention, air–fluid levels, and free intraperitoneal air. The heart and liver are transparent organs; one can see opacities or bronchial markings projecting over their shadows. Then look at bones and soft tissues; one can often see portions of the arms, shoulders, ribs, sternum, and mandible, as well as cervical, thoracic, and lumbar vertebrae. Be alert for fractures (Fig. 24-11), congenital abnormalities (e.g., absent clavicles), bone destruction, or other signs of disease. Examine the soft tissues of the neck, thorax, and abdomen to detect any swelling, foreign body, calcifications, and so on. The soft tissues may reveal multiple artifacts, such as hair braids, buttons, bandages, electrocardiogram (ECG) electrodes, or redundant skin folds. Soft tissue swelling or subcutaneous calcifications can be clues to systemic disease.

Figure 24-11 Supine chest radiograph of a 3-day-old newborn with surfactant deficiency. A radiologist interpreting this chest film systematically, that is, by examining the ABCS (A, abdomen; B, bones; C, chest [airway, mediastinum, lungs, and diaphragm]; and S, soft tissues), shouldn’t miss the fracture involving the right humerus at the edge of the image. Note that the patient is rotated to the left with the heart appearing prominent, likely due to rotation.

Interpretation of the Chest Film: 2. Technical Factors

Mediastinum

The mediastinum is composed of the thymus, trachea, heart, great vessels, esophagus, lymph nodes, and neural elements. The mediastinum is divided on the lateral radiograph into (1) the anterior portion, including the space in front of the heart and great vessels; (2) the middle portion, that is, the space between the anterior and posterior mediastinal components, including the heart, airway, esophagus, and lymph nodes; and (3) the posterior portion, including everything behind a line connecting the mid-portion aspects of the vertebrae, including the vertebrae, neural elements, and paraspinal lymph tissue. In some classifications the posterior mediastinum begins with the anterior aspect of the vertebral body.

Thymus

The thymus may make interpreting pediatric chest radiographs difficult. It can simulate cardiac enlargement, lobar collapse, pulmonary infiltrates, and mediastinal masses. The thymus constitutes the major portion of the mediastinal silhouette in a normal newborn. It may extend from the lung apex to the diaphragmatic surfaces; be insinuated into the minor fissure on the right, giving a “sail sign” (see e-Fig. 24-2); and may be bilaterally symmetrical or predominantly one-sided (Fig. 24-12). The normal thymus is a “soft” organ situated in the anterior mediastinum and never “pushes” on the airway or any other intrathoracic structure. The thymus appears smaller as the child becomes older, but the thymus weighs most in adolescents. It is prominent in some children until 4 to 5 years of age, and may persist beyond 5 years, confounding interpretation. Thymic remnants can remain in adults and will be gradually replaced by fat. In an unwell child the thymus can decrease in size and is often not seen. The contour of the thymus is “wavy” because it insinuates itself between the anterior ribs (Fig. 24-13; and see Fig. 24-12).

Figure 24-12 Coronal MRI of the chest (short tau inversion recovery [STIR] sequence) demonstrates a left-sided normal thymus in a 7-month-old infant. An anterior cut shows the “wavy thymus sign” (arrows) as the thymus insinuates itself between the anterior ribs (r).

Figure 24-13 Chest radiograph of a 1-day-old newborn shows the wavy thymus contour.

Effect of Age on the Normal Appearance of the Heart

The shape of the heart on plain radiographs changes with the patient’s age. The heart in younger individuals appears more globular in shape, making analysis of specific chamber abnormality difficult. The newborn right heart chambers are larger than the left, and before closure of the patent ductus arteriosus, right-sided cardiac output is greater than left-sided output. This makes identification of the aortic arch difficult or impossible. The right atrial contour in the frontal view and the right ventricular contour in the lateral view will appear abnormally enlarged in these patients. Furthermore, the transverse diameter of the heart is increased, thus increasing the normal cardiothoracic ratio. The thymic shadow regresses by the end of the first year of life, and the heart appears to rotate and descend into the chest. The typical “normal” appearance of the heart does not begin to become apparent until 6 to 8 years of life. However, through adolescence, the apparent size of the main pulmonary artery segment remains increased. Through the teens and early twenties, the size of the main pulmonary artery and base of heart continue to decrease, and the size of the aortic arch increases in caliber, so that by the mid-twenties, the appearance of a “normal” heart may be characterized (Fig. 24-14).

Figure 24-14 A, Posteroanterior radiograph of a 30-year-old woman is shown. The lateral border of the left-sided aortic arch (Ao) and proximal descending aorta (short arrows) are clearly seen. The main (MP) and proximal left (L) pulmonary artery are seen cephalad to the left bronchus (long arrow). The left atrial appendage section (small arrowhead) is inferior to the crossing of the left bronchus and cephalad to the left ventricular contour (curved arrows) of the left heart border. The superior vena cava is not seen on this examination. However, the ascending aorta (small open arrow) is seen barely over the hilar right pulmonary artery (R). The right atrial contour (large arrowheads) extends just to the right of the spine. B, Spin-echo MRI obtained from a different 30-year-old woman is shown. The left heart border–forming structures are the aortic arch (Ao), which is to the left of the trachea (T), the distal main pulmonary artery (PA), left atrial appendage (aa), and anterolateral portion of the left ventricle (LV). The transverse right pulmonary artery (RP) passes over the left atrium (LA). Notice that the Ao and PA are equal in caliber. The mitral valve (small arrows) and coronary sinus (large arrow) are shown.

(From Boxt LM: Plain-film examination of the normal heart, Semin Roentgenol 34:169-180, 1999.)