++
Ultrasonography is the imaging technique of choice for confirmation of pyloric stenosis, testicular torsion, ectopic pregnancy, ovarian torsion, intussusception, and appendicitis.
Computed tomography (CT) is an extremely valuable imaging tool, but the risk of ionizing radiation exposure should be considered when ordering this test in young children.
Magnetic resonance imaging (MRI) in the emergency department (ED) is usually reserved for emergent conditions such as cord compression and stroke.
++
The practice of emergency medicine brings patients with a variety of complaints to our doorstep. In deciphering the many signs and symptoms, imaging is an important tool to reach a diagnosis. This chapter discusses the various considerations for optimal visualization and patient safety when using diagnostic radiography and computed tomography (CT). Magnetic resonance imaging (MRI) is discussed in a separate chapter. Point-of-care ultrasound (POCUS) is discussed in a separate chapter, but this differs from formal ultrasound studies performed by technicians and radiologists. Ultrasonography is the best means to confirm pyloric stenosis, testicular torsion, ectopic pregnancy, ovarian torsion, intussusception, appendicitis, and many other clinical entities; however, it does not identify all cases. Thus, a high clinical suspicion for a condition in which surgical intervention is highly time-dependent should not be ignored when not confirmed by ultrasonography, which can be very operator and interpreter dependent.
+++
DIAGNOSTIC RADIOGRAPHY
++
Plain radiography accounts for approximately 75% of all imaging studies.1 The image obtained from plain radiography is acquired with the aid of x-rays, which is a collection of electromagnetic energy called a photon. Electromagnetic energy travels at the speed of light at different frequencies, where the higher the frequency, the more energy it possesses. For example, the low frequency of a light photon has 1 eV of energy, compared with the high frequency of an x-ray photon that has 30,000 eV of energy.2 The large amount of energy that x-rays contain allows them to ionize atoms that they encounter, hence labeling x-ray as a form of ionizing radiation.
++
Approximately 1% of x-rays navigate all the way through the patient to the film (Fig. 15-1).2 The remainder of the radiographs are either absorbed or scattered. Absorption of a radiograph results in a white appearance on the film because the x-rays do not penetrate through the given object onto the film. Objects that have a high atomic number (e.g., bone) are more likely to absorb the x-ray and appear white on the image. Approximately one-third of x-rays reaching the film are primary x-rays, which travel directly through the patient in a straight line.2 The other x-rays are the result of scattering, which occurs when x-rays encounters an atom and bounces off in another direction. The scattered x-rays that reach the film appear as a gray color, which decreases the quality of the image. To remove the scattered x-rays, an antiscatter grid is often used, which consists of thin lead ...