Imaging
Sabah Servaes, MD, FAAP
Overview of Modalities
Imaging permits screening, diagnosis, and identification of complications of infections and other disorders of the respiratory system.
•Chest radiography is the most commonly ordered imaging modality. It is quick, easy to perform, relatively inexpensive, and involves a small amount of radiation. It is widely available and portable and can be performed at the patient’s bedside.
•Ultrasonography (US) requires a moderate amount of time, depending on the examination and experience level of the sonographer. The cost is low to moderate, and the examination involves no ionizing radiation. It is widely available (although specialized pediatric sonographers are not as widely available) and can be performed portably, as well.
•Computed tomography (CT) is widely available and provides excellent spatial resolution with a quick examination time at a moderate cost. Radiation can be decreased by use of pediatric dose parameters (CT performed at a center with American College of Radiology CT accreditation is ideal). Sedation may be needed in uncooperative children, especially those 1–3 years of age. CT is excellent for characterization of lung parenchyma and osseous structures.
•Magnetic resonance (MR) imaging provides the best soft-tissue resolution with no ionizing radiation, but the examination is lengthy, may require sedation, is costly, and is less widely available than other modalities. It has limited value in the assessment of lung parenchyma.
•Positron emission tomography (PET)/CT and PET/MR imaging are typically used for oncologic applications but are also used occasionally for infectious or inflammatory entities. The examinations are lengthy, frequently require sedation (especially in children under 6 years of age), are costly, and are not widely available.
•Fluoroscopy is a dynamic examination involving low to moderate levels of ionizing radiation. It is performed in a fluoroscopy suite to image real-time changes in the airways, diaphragm, and thoracic cavity. It may be used in conjunction with a speech pathologist for swallow function studies or in conjunction with an upper gastrointestinal examination performed by a radiologist (both studies are reliant on patient compliance).
•Chest imaging is most commonly performed with chest radiography (Figure 6-1).
•Technical factors to remember include the following.
—The frontal projection is obtained with a posteroanterior radiation beam.
—In patients who are unable to stand or follow instructions (eg, in an intensive care unit or, if very young, typically <5 years old), the frontal (anteroposterior [AP]) projection is obtained, which makes anterior thoracic structures, such as the heart, appear larger.
•Common findings include the following.
—Atelectasis: focal opacity due to loss of lung volume that may appear and resolve rapidly (Figure 6-2).
—Pneumonia (Figure 6-3)
▪Focal consolidation is seen without volume loss.
▪Follow-up radiography is rarely necessary.
▪Radiographic findings of pneumonia can persist for days or weeks, despite clinical improvement.
—Pleural effusion (Figure 6-4) manifests as fluid between the lung and the chest wall. Radiographically, it blunts the diaphragm margin and may be seen tracking along the chest wall. Noncomplicated effusion is free flowing and more easily observed with the patient in a lateral obtained in lieu of US, which can demonstrate the effusion without position (decubitus views). However, decubitus radiographs are rarely additional radiation exposure.
—Bronchiectasis
▪Dilated bronchi typically indicate chronic airway disease
▪Commonly seen in cystic fibrosis, primary ciliary dyskinesia, or immunodeficiency or after severe infection
—Acute chest syndrome
▪Diffuse, acute, patchy lung opacity in children with sickle cell disease
▪Associated with hypoxemia and respiratory distress
▪May initially be a subtle opacity on chest radiographs
▪May progress rapidly to complete unilateral or bilateral opacification of the lungs
▪Imaging does not allow infection to be distinguished from acute chest syndrome
—Hyperinflation
▪Flattened hemidiaphragms, typically bilaterally
▪Often seen with asthma, viral illness in infants, or other obstructive lung disorders
—Pneumothorax
▪Manifests as air within the pleural space, between the chest wall and the lung.
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