1. Overview and Description:
Radiography is performed by transmitting ionizing electromagnetic radiation through bony structures and soft tissue, producing an image based on the absorption of X-ray photons. It is the most commonly used diagnostic imaging study. Radiography refers to multiple modalities: mammography and DEXA are examples of low energy projectional radiography, fluoroscopy and angiography are special applications used for real time imaging, and CT uses computed reconstruction to generate a cross sectional image. This article will focus on plain radiography, known colloquially as X-ray imaging.
Plain radiographs use a heterogeneous beam of X-rays projected toward a detector, creating an image based on the density and composition of the intervening objects. X-ray photons are the main source of ionizing electromagnetic radiation used in medical radiography, and are generated by bombarding an anode with high energy electrons emitted from a hot cathode. Detection methods include radiosensitive amplifying screens, image intensifiers, and digital detectors that reconstruct the image.1
Tissue density is reflected by the capacity to absorb X-rays, the following are listed in order of increasing radio-opacity:
- Air (trachea, lungs, intestine, paranasal sinuses).
- Soft tissues (heart, kidney, muscles).
- Calcium rich tissue (skeleton).
- Enamel of the teeth.
- Dense foreign bodies (metallic fillings), and radio-opaque contrast media (barium).
While there are few contraindications, X-rays produce ionizing radiation as they deposit enough energy to eject an electron from an atom, potentially altering tissue at the molecular level. Ionizing radiation is carcinogenic, and cumulative exposure may increase the risk of cancer and therefore should be used judiciously in young children and pregnant women. Risk factors for tissue damage include radiation dose, younger age, female gender, and imaging radiosensitive regions.1
Radiation at high doses can be harmful to tissues, and is typically measured in milli-Sieverts (mSv). An X-ray of the spine is equivalent to 1.5 mSv, or 6 months of natural background radiation, whereas an extremity X-ray is 0.001 mSV, or 3 hours. For reference, people living in Colorado receive an extra 1.5 mSv per year than sea level, and a coast-to-coast flight exposes travelers to roughly 0.03 mSv. It would take roughly 38 chest X-rays to equal the amount of normal background radiation one receives over the course of a year.2
2. Relevance to Clinical Practice:
Specific features of clinical application:
X-ray imaging is a relatively low cost, widely available, and highly utilized modality for the evaluation of various pathological states. It can assist the physiatrist in the diagnosis and evaluation of numerous conditions. Consideration should be given to cost in those without health insurance.
Common applications include, but are not limited to:
- Diagnosis of fractures or joint dislocation
- Demonstration of proper alignment and stabilization of bony fragments following fracture treatment
- Guidance for orthopedic surgery, such as spine repair, spine fusion, joint replacement, and fracture reduction
- Assessment for trauma, including skeletal injury or sequelae such as pneumothorax or aortic dissection
- Evaluation of osteomyelitis
- Diagnosis and evolution of pneumonia, atelectasis, pleural effusion, asthma, COPD, chronic bronchitis, bronchiolitis, and other pulmonary pathology.
- Evaluation of clinical cardiomegaly or heart failure
- Evaluation of arthritis, abnormal bone growth, and bony changes seen in metabolic conditions
- Evaluation of suspected bowel obstruction or perforation
- Diagnosis and evaluation of scoliosis
- Detection of bone cancer
- Evaluation of non-accidental injury, plagiocephaly, or craniosynostosis in children
- Evaluation of growth plates and skeletal maturity
- Location of foreign objects in soft tissues
- Diagnosis of retropharyngeal abscess
Specific diagnostic criteria that justify the use of radiography:
Plain radiography is best utilized in the context of a patient-specific clinical history and physical examination, in relation to the chief complaint.
- Quality, character, aggravating/alleviating factors
- Neurological concerns
- Associated symptoms
Radiographic examinations are most effective when performed in conjunction with a standard physical examination of the affected region, consisting of:
- Range of motion
- Auscultation (if indicated)
- Neurological examination
- Special tests
There are few contraindications to plain radiography, though caution should be taken in young children and pregnant women, and providers need to weigh the risks and benefits of imaging. Cumulative radiation dosage should be monitored in the case of frequent imaging.
The patient’s ability to tolerate the exam should always be considered prior to ordering.
Radiography can improve patient outcome by offering precise diagnostic and treatment localizations, often without significant delays or high costs seen with other imaging modalities.
One advantage of plain radiography is that it can be conducted in the inpatient or outpatient setting, with portable application for patients who cannot undergo standing exams.
Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills
While readily available, radiography should be used judiciously, as an extension of a thorough history and physical examination with an adequate pre-test probability.
3. Cutting edge/emerging and unique concepts and practice
Cutting edge concepts and practice
Radiography is a well established modality, and most of the innovation in Radiology surrounds MRI, CT scan, PET, fluoroscopy and ultrasound. However recently practitioners have been using breast tomosynthesis in lieu of mammography, where 10 X-rays are taken with 1/10th of the radiation dose per sequence, and the images are taken at different angles so the diagnostician can “scroll” through the tissue. This is thought to increase the sensitivity for detecting masses.3
In addition, tomosynthesis has been used in the detection of bone erosions in patients with established rheumatoid arthritis. One study found that tomosynthesis had a higher sensitivity in detecting bone erosions, increased by 14% when compared to plain radiography, with an almost equivalent radiation burden.4 Tomosynthesis may have other uses in detecting subtle bony abnormalities, though more investigation is required to further delineate specific applications.
4. Gaps in knowledge/evidence base
X-rays are limited in the evaluation of soft tissue, and sensitivity is decreased in cases of chronic osteomyelitis and lung masses. Often CT, MR, or nuclear medicine studies are needed to confirm the diagnosis. In general, plain radiography is an extremely well-established modality, and is the most commonly used diagnostic imaging in medical practice.
National Research Council. Health Risks From Exposure to Low Levels of Ionizing Radiation. The National Academies Press. https://www.nap.edu/read/11340/chapter/1
International Commision on Radiologic Protection. http://www.icrp.org/publication.asp?id=ICRP%20Publication%20103
American College of Radiology. ACR statement on breast tomosynthesis. https://www.acr.org/About-Us/Media-Center/Position-Statements/Position-Statements-Folder/20141124-ACR-Statement-on-Breast-Tomosynthesis
Simoni PA, Gerard LA, Kaiser MJ et al. Use of Tomosynthesis for Detection of Bone Erosions of the Foot in Patients With Established Rheumatoid Arthritis: Comparison With Radiography and CT. American Journal of Roentgenology. http://www.ajronline.org/doi/abs/10.2214/AJR.14.14120
Original Version of the Topic
Peter Torberntsson, MD
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Dustin Anderson, MD
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