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Radiology is the field of medicine that uses imaging techniques such as X-rays to diagnose, characterize, or monitor disease. Medical doctors who specialize in radiology are called radiologists.
Radiology can provide evidence of an injury, infection, or disease that cannot be seen without an invasive procedure. It can help establish how severe, extensive, or advanced a condition is and help predict the likely outcome (prognosis). It can provide evidence of a response (or the lack of a response) to treatment and help guide medical procedures like cardiac catheterization.
This article describes the history of radiology and what it takes to become a radiologist. It also looks at the different radiological procedures and how they are used in medicine.
Over the past century, radiology has provided methods for diagnosing a wide array of diseases, as well as a number of alternatives for treating medical conditions that are often less invasive than surgery. While we take for granted the multiple imaging modalities now available, some are only relatively recent additions to medicine.
In 1895, Wilhelm Conrad Röntgen was the first to discover a new type of radiation which he called X-rays. Via this technique, Röntgen was the first to "visualize" the inside of the body (outside of surgery) by taking an X-ray of his wife's hand including her wedding ring. For this he went on to win the Nobel Prize in Physics in 1901.
The first ultrasound allowing healthcare providers to visualize a fetus in utero was performed in 1958. Imaging techniques that are now routine were developed more recently. The first computed tomography (CT) machine was used commercially in 1971 followed by the first magnetic resonance imaging (MRI) in 1979. The first positron emission tomography (PET/CT) scan was performed in 1998.
Interventional radiology in particular, is a very recent addition to medicine. The first balloon-expandable stent (to treat coronary artery disease) was performed in 1895 and was followed by a multitude of other techniques over the last few decades.
The typical radiology team is made up of a radiologist and radiation technologists.
A radiologist is a physician who specializes in the field of radiology. After receiving a bachelor's degree, the radiology candidate attends medical school for four years (receiving either an MD or DO) followed by a one-year internship in medicine, surgery, or both.
This is followed by four years of residency in radiology. After residency, some radiologists will pursue an additional one- to two-year fellowship in a specific area of radiology (such as pediatric radiology, nuclear medicine, or interventional neuroradiology).
Radiation technologists are critical members of the radiology team and are trained to assist the radiologist and manage instruments used to produce images. These technicians usually have an associate degree or bachelor's degree.
There are several different methods of obtaining images to help screen for, diagnose, or monitor medical conditions. These include:
X-rays or plain radiographs are often done to look at bones, the chest, or the abdomen. With X-rays, denser structures, such as bones, appear white (opaque) whereas air filled areas (such as the lungs) appear black. Most structures of the body are in shades of gray between these two.
X-rays may be used alone to diagnose conditions such as fractures, some pneumonias, or a bowel obstruction. But oftentimes additional imaging studies are needed.
The area of the body being investigated can place limitations on the efficacy of X-rays. In regions where several structures overlap (for example, the collar bone, heart, and lung on the left side of the chest), an abnormality is less likely to be visible than on an X-ray of the forearm.
Specialized X-ray techniques may be used to screen for particular conditions. For example, digital mammography is an X-ray technique that uses low-dose radiation to detect breast cancer, and panoramic X-rays are used to detect dental disease.
Computed axial tomography (CAT scans or CT scans) composite multiple X-ray images by computer to produce a cross-sectional image of internal structures. CT provides more detail than an X-ray, and can better define areas where tissues overlap. CT scans can detect smaller abnormalities than can be found with a conventional X-ray.
The use of contrast dyes for CT scan can further improve visualization in some areas, such as the digestive tract. In some situations, CT procedures such as CT angiography may provide information that would otherwise require a more invasive procedure.
Magnetic resonance imaging uses strong magnetic fields and radio waves to produce images of the inside of the body. While CT is often a better method for evaluating bones and blood vessels, MRI is frequently a better test for evaluating soft tissue, such as the brain, spinal cord, nerves, muscles, tendons, and breast tissue.
With brain, spinal cord, and peripheral nerve disorders, MRI has allowed healthcare providers to diagnose conditions that could only be assumed clinically in the past. For example, practitioners can now diagnose multiple sclerosis with an MRI, a diagnosis that was limited to an assessment of symptoms alone before MRI was available (and could only be confirmed on an autopsy).
For breast cancer screening, MRI is more accurate than mammography, but the higher price makes it impractical for people who do not have underlying risk factors for breast cancer. One form of MRI, called functional MRI, can even give an estimate of brain activity.
An advantage of MRI is that it does not use ionizing radiation, which has been linked to an increased risk of cancer, especially in children. Limitations include the cost and that it may not be used in people who have metal in their body.
Ultrasound uses sound waves (acoustic energy) to produce moving images of a part of the body. Best known as a method for examining a fetus during pregnancy, ultrasound is particularly helpful with some medical conditions.
Ultrasound does not involve radiation and is therefore safe in pregnancy.
Fluoroscopy uses X-rays in real time to create moving images of the body. In some settings, these real-time images are particularly important. Fluoroscopy may be used to see how liquid moves through the digestive tract or to monitor progress during the insertion of a pacemaker.
Due to continuous monitoring, the radiation exposure with fluoroscopy is significantly higher than that of conventional X-rays.
Nuclear medicine imaging includes techniques that use radioactive material ("radioactive tracers") that are then detected by a camera in order to produce images of the inside of the body. While most imaging methods are considered structural, that is, they describe structures on the inside of the body, these scans are used to evaluate how regions of the body function.
In some cases, the radioactive substance may also be used to treat cancer (such as the use of radioactive iodine to treat thyroid cancer).
Examples of nuclear medicine scans include:
There are now a multitude of interventional radiology procedures available. In many cases, these "minimally invasive" procedures can replace more invasive measures (such as surgery) that were used in the past.
In turn, these techniques may have fewer complications, involve smaller incisions, cause less discomfort, and help people recuperate more rapidly than had been possible in the past. They are often less expensive. Some of the conditions that may be treated in this way are listed below.
Blood vessels that are blocked in the heart , legs, and lungs may be treated with interventional procedures.
Alternatively, interventional radiology may be used to block a vessel. For example, vein embolization may be done for varicose veins, whereas artery embolization (uterine artery embolization) may be done to treat fibroids.
Aneurysms are sections of an artery than are dilated and weak and hence, are subject to rupture or bleed. Via interventional radiology, a radiologist may place a stent graft in the region of an aneurysm thus essentially relining the blood vessel.
As an alternative to surgery, interventional radiology may be used to control bleeding (hemorrhage) in conditions ranging from gastrointestinal bleeding, to postpartum bleeding, to trauma. Bleeding may be controlled by blocking a blood vessel (as noted above), placing a stent, using a balloon to apply pressure, and more.
When a person is seriously ill, or will be receiving caustic medications such as chemotherapy, rapid access to larger blood vessels for infusion is needed. (Peripheral veins, such as a vein in the hand or forearm, are often insufficient.) Examples of central lines include ports and PICC lines.
The placement of feeding tubes (gastrostomy, jejunostomy) are a relatively common interventional radiology procedure. These are frequently used when a person is unable to eat food for any reason.
A number of different types of biopsy procedures may be performed by a radiologist, and are often guided by ultrasound or CT. Examples include needle biopsies and stereotactic biopsies.
In addition to radiation therapy (discussed below), a number of interventional radiology procedures may be used to treat either a primary tumor or metastases (cancer that has spread).
Tumors may be addressed by ablative treatment (treatments that destroy tumors) such as radio frequency ablation or microwave ablation, or instead by tumor embolization (blocking a blood vessel that feeds a tumor so that the tumor dies).
Alternatively, either chemotherapy or radiation can be directly delivered to an area of tumor or metastasis (chemoembolization/radioembolization).
Procedures known as vertebroplasty or kyphoplasty can be used to treat collapsed vertebrae. In these procedures, a cement type substance is injected by the radiologist to effectively repair a fracture.
When blockages occur in different regions of the body, an interventional radiologist may apply a stent. This may be done to open up a blocked esophagus, blocked bile ducts, a blockage of the ureter draining from the kidney, or a blockage in the bowel.
When fluid collects in a region of the body, an interventional radiologist may insert a drain to remove fluid or pus. This might be done to drain recurrent pleural effusions (fluid buildup in the area around the lungs), in the brain (shunting), and much more.
Radiologists now use a wide array of procedures to treat chronic back pain.
There are a number of ways in which radiation therapy or proton therapy may be given, and the particular use often depends on the goal of treatment. It's thought that roughly 50% of people with cancer will undergo some form of radiation therapy.
In external beam radiotherapy, radiation is applied from outside of the body on a table resembling a CT machine. It may be used:
Brachytherapy is similar to external beam therapy except that the radiation is delivered internally, often through beads that are inserted into an area during surgery or after.
Stereotactic body radiotherapy (SBRT) or Cyberknife refers to a procedure in which a high dose of radiation is directed to a localized area of tissue. Unlike traditional radiation therapy, SBRT allows a curative dose of radiation to be delivered to the tumor cells while minimizing damage to nearby healthy tissue.
SBRT is sometimes used to treat small tumors as an alternative to surgery, especially in people who would not be expected to tolerate surgery as well. It is also often used to treat areas of metastases, such as brain metastases due to a lung cancer or breast cancer.
Proton beam therapy is similar to conventional radiation therapy but uses high energy protons instead of photons or X-rays to damage tumors. It was first used in 1990, and offers similar effectiveness to radiation therapy.
Due to the way the radiation is delivered, it may be less likely to damage nearby healthy tissue. For this reason, proton beam therapy can sometimes be used in an area that was previously treated with radiation (and thus, cannot be treated again with conventional radiation).
Since X-rays and CT scans are forms of ionizing radiation (they knock electrons off of atoms and can cause DNA damage) they may increase the risk of cancer.
This is of greater concern with procedures such as CT or fluoroscopy than with plain X-rays, and more worrisome in children than in adults. With radiology procedures, it's important to weigh the risks and benefits of imaging and to consider possible alternatives when available.
The different interventional procedures can also carry risks, and it's important to discuss these with your healthcare provider.
From early stories of complications related to X-rays (before the dangers were known) to more recent studies looking at cancer risk, the thought of receiving ionizing radiation can be fearsome. Most of the time the benefits of having a procedure outweigh any risks, but it's worthwhile talking to your healthcare provider. In some cases, a procedure such as an ultrasound or MRI may provide similar results without the radiation.
The American College of Radiology provides some excellent patient and family resources through which you can learn more. If you are interested, you an even check out the appropriateness criteria for different scans and procedures.
With children, it's also a good idea to ask if CT machines have been calibrated for children. While this is becoming standard in most big medical centers, it may be useful in a community setting.
Some people think of radiology as a field that's primarily limited to X-rays and CT scans, but the scope is much broader. Once primarily a method to diagnosis injuries and medical conditions, interventional radiology now provides alternatives to a number of previously more invasive procedures.
Another major change has taken place in patient care, and radiologists (who once had minimal contact with patients) are frequently an active and integral part of a multidisciplinary care team.
As with other areas of medicine, however, being your own advocate is critical, and taking time to understand the benefits and limitations of any diagnostic or therapeutic imaging techniques you undergo is essential in getting the quality of health care you deserve.
Correction - February 22, 2024: This article was updated to correct the year listed that Wilhelm Conrad Röntgen discovered X-rays.
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By Lynne Eldridge, MD
Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."
