Chapter 9

### Imaging Techniques: Introduction

Imaging provides significant contribution in evaluation, diagnosis, and follow-ups of pediatric gastrointestinal (GI) problems. Children truly are not merely small adults, and the many unique imaging features of pediatric problems should be recognized. The imaging techniques used to evaluate the pediatric patients with GI symptoms are significantly different from those applied to adults. Radiologists and clinicians should work in concert to select the most appropriate modality, as well as optimal timing of the examination to maximize the benefits and minimize the risks and costs. When imaging modalities requiring radiation are selected, the “as low as reasonably achievable” (ALARA) principle should always be observed to minimize the radiation exposure.1

The technique of using X-rays to evaluate disease is over a century old, having been demonstrated first by Professor Wilhelm Conrad Roentgen in 1895, using a cathode ray tube and photographic emulsion. Despite its antiquity, radiography continues to be used as the first-line imaging technique to evaluate various abdominal conditions, providing important clues directing subsequent workups. Modern X-ray equipment is vastly different from those used during the first decades of development, and uses sensitive digital imaging techniques to minimize exposure to ionizing radiation.

The X-ray machine can be positioned above a supine patient (vertical beam), or can be directed horizontally. Radiographs using a horizontal beam technique are essential to detect a small amount of free air (pneumoperitoneum). This can be most easily accomplished in many patients by obtaining erect frontal films. Patient who cannot stand up may have either decubitus frontal or supine cross-table lateral views. Free air can be detected at the highest part of the peritoneal cavity, under the diaphragm on an erect frontal projection, along the non-dependent flank on a decubitus frontal projection (Figure 9–1), or along the anterior abdominal wall on cross-table lateral projection. Larger amounts of free air can even be diagnosed on routine supine frontal views (using a vertical beam) by outlining intestinal walls sandwiched between the intraluminal and extraluminal air (“double wall” or Rigler sign). Other structures that can be seen in this situation include the falciform ligament of the liver and occasionally the umbilical arterial ligaments. In the neonate, a large amount of free air can dissect into the scrotal cavity on one or both sides through an incompletely closed processus vaginalis.2,3

###### FIGURE 9–1

Ileal perforation. A left-side down decubitus frontal view shows free air along the right flank.

The radiological hallmark of necrotizing enterocolitis is multiple air bubbles in the intestinal wall (pneumatosis intestinalis) (Figure 9–2). It can be seen as bubbly lucency along the intestine or curvilinear/ring-like lucency.4 The intramural gas eventually finds the way to the portal veins via the mesenteric veins (Figure 9–3). ...

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