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Imaging Techniques: Introduction
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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
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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.
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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
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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). When ...