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X-rays or plain radiographs rely on an external beam of X-radiation to pass through tissue and be detected and transformed into four fundamental shades of gray reflective of four different tissues: air (black), fat (dark gray), soft tissue (light gray), and bone (white) (Mettler 2005). Air allows the greatest transmission of X-rays to the detector and thus appears black; likewise, bone provides the greatest hindrance and appears white (Fig. 6.1). Detectors may include simple plain photographic film or digital plates that display the results on a computer screen.

Plain radiographs provide the greatest contrast at the extreme shades, white (bone) and black (air). They are therefore of great use in providing detail on the relative positions, densities, and shapes of bones and joints (Bogduk 2003) as may occur in fractures, dislocations, osteomyelitis, osteoporosis, and lytic lesions from cancer. Also, because they demonstrate the contrast between air (black) and other tissues well, X-rays have been a mainstay in chest radiographs.

When tissues themselves are not inherently "contrasty," radioopaque contrast agents may be given orally, rectally, or intravenously to contrast "enhance" hollow visci and vessels. When using intravenous contrast agents, there is a risk of a contrast reaction. Reactions are

N. Vadivelu et al. (eds.), Essentials of Pain Management,

DOI 10.1007/978-0-387-87579-8_6, © Springer Science+Business Media, LLC 2011

Soft Tissue

Prosthetic Joint (Opaque-White)

Soft Tissue

Prosthetic Joint (Opaque-White)

Figure 6.1 X-rays or plain radiographs rely on an external beam of X-radiation to pass through tissue and be detected and transformed into four fundamental shades of gray reflective of four different tissues: air (black), fat (dark gray), soft tissue (light gray), and bone (white) [1]. Air allows the greatest transmission of X-rays to the detector and thus appears black. Likewise, bone provides the greatest hindrance and appears white.

Figure 6.1 X-rays or plain radiographs rely on an external beam of X-radiation to pass through tissue and be detected and transformed into four fundamental shades of gray reflective of four different tissues: air (black), fat (dark gray), soft tissue (light gray), and bone (white) [1]. Air allows the greatest transmission of X-rays to the detector and thus appears black. Likewise, bone provides the greatest hindrance and appears white.

most common with iodinated contrast agents and may be classified as idiosyncratic (dose-independent) and non-idiosyncratic. Idiosyncratic reactions are true anaphylactic reactions occurring 20 min after injection and may include the following symptoms: urticaria, pruritus, nausea, vomiting dizziness progressing to bronchospasm, palpitations, bradycardia, hypertension, headache, further progressing to severe bronchospasm, pulmonary edema, hypotension, severe arrhythmias, seizures, and death (Siddiqi 2008).

Non-idiosyncratic reactions may include sensations of warmth, metallic taste, bradycardia, vasovagal reactions, and other autonomic reactions. The similarity to idiosyncratic reaction makes distinction difficult. Of great concern is contrast-induced nephropathy which may occur 1-3 days following injection, peaking at 3-7 days and "is manifested by elevation of the serum creatinine by a level greater than 0.5 mg/dL or more than 50% of the baseline level (Siddiqi 2008)." Although its incidence is low at 2-7%, its effect can be sustained in those who succumb.

Radiographs are two-dimensional and a single view provides little information as to the depth of an object. Dense objects can easily be on a patient or in a patient. A lateral view, in addition to a frontal view, may be required to elucidate greater information and increase the "dimensional" view.

Table 6.1 Conditions for which plain radiograph may be used as initial test.

Plain radiograph may be sufficient

Plain radiograph initially, then bone scan if needed

□ Metastases

□ Prosthetic joint, infection, or joint loosening

Plain radiograph initially, then triple-phase bone scan if needed

□ Reflex sympathetic dystrophy

□ Osteomyelitis

Plain radiograph initially, then MRI if needed

□ Joint pain, monoarticular

□ Osteomyelitis

Plain radiograph initially, then CT if needed

□ Facial fracture

Adapted from Mettler (2005).

Although more sophisticated imaging techniques or magnetic resonance imaging (MRI) may provide a are sometimes sufficient for many situations. Table radiographs are indicated as an initial diagnostic test.

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