A clinical appreciation of medical imaging is important and beneficial to the role it plays in patient care. As the technology behind the various types of diagnostic imaging equipment continues to advance, the more informed the health care professional needs to be at ordering the correct diagnostic examination. Following a thorough evaluation by a qualified health care professional, patients are frequently required to have a basic x-ray examination. Many of these individuals, however, will require the use of an advanced imaging modality such as ultrasound (US), computed tomography (CT), and/or magnetic resonance imaging (MRI) to increase the accuracy in diagnosing the specific nature of the problem. Selecting the correct imaging modality to assist with the diagnostic work-up of the patient is essential to the timely care of the patient.
The purpose of this chapter will be to provide a basic understanding of the five major imaging modalities used to assist in the diagnostic assessment of the patient: x-ray, dual-energy x-ray absorptiometry (DXA), ultrasound, computed tomography, and magnetic resonance imaging. It will also review pertinent terminology, common imaging applications, and important safety precautions.
Using an x-ray tube to produce x-rays and a sheet of x-ray film or image receptor placed in a specially designed cassette to capture the energy of the x-ray beam image is the most commonly used method of taking a radiograph. Since its beginning in the late 1800s, diagnostic radiography, also known as x-ray, has seen several technological advancements in the design of the x-ray tube, x-ray film, and cassette. Advancements made in image receptor technology have evolved from glass plates, which were used initially, to polyester base material, to digital imaging, which is used currently. Film emulsions have experienced considerable change since they were first introduced. Historically, the x-ray image was produced by the direct exposure of the x-ray beam to the x-ray film. Today, the x-ray image is produced when the x-ray beam interacts with special phosphor crystals within intensifying screens located inside the film cassette. When x-rays interact with the phosphor crystals, a light of a specific wavelength is produced and exposes the x-ray film. This method reduces the amount of radiation necessary to create an x-ray image.
The latest technology incorporates the use of computer technology in what may be referred to as computed radiography or digital radiography. Digital radiography introduces a moving away from the traditional film-screen (hardcopy) method of taking an x-ray examination to producing a digital (softcopy) image that is presented on a high-quality monitor. Digital images, once recorded, can be manipulated similar to CT images. The density and contrast scale of the images can be adjusted to demonstrate the anatomy such as bone or soft tissue. The images can also be magnified to better visualize small structures. Another advantage of digitally formatted images is that they can be ...