Radiology is the field of medicine that uses imaging techniques (such as X-rays) to diagnose and treat disease. It may be used diagnostically in order to determine if a medical condition is present or not (such as finding lung cancer), interventionally as a procedure (such as removing a blood clot in an artery), or as a treatment. such as giving radiation therapy to treat cancer. Here's a look at the different uses for diagnostic imaging, conditions that may be treated with radiologic techniques, cautions and warnings about potential adverse effects, and the medical professionals you may encounter when you have a radiological test or procedure.

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.

For example, chest X-rays may sometimes identify a lung cancer, but 20% to 23% of these tumors were missed in people with lung cancer symptoms in one study22 (And thus, CT scans are needed for lung cancer screening). Some fractures (such as stress fractures) may only be seen with an MRI.

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) use a series of X-rays plus a computer to produce a cross-sectional image of the inside of the body. 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 (such as a strong family history, BRCA mutation, or a history of childhood cancer). A newer technique called fast MRI is a rapid, much less expensive test that may be more accurate in detecting early breast cancer in the future.

Other than PET/CT (see below), most imaging techniques are structural but not functional. This means that they reveal the structure of an area of the body but do provide information as to function. One form MRI called functional MRI, can, however, give an estimate of brain activity.

As with CT, contrast is often used to better define regions that are being scanned, with a common agent being gadolinium. Magnetic resonance technology may also be used as an alternative to more invasive procedures at times, such as with magnetic resonance angiography (MRA).

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.3 Limitations include the cost, body mass index (MRI is difficult in very overweight people), 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.

Breast ultrasound can often distinguish breast cysts from masses. Cysts may be aspirated under ultrasound guidance and their disappearance can be reassuring as well (no further evaluation may be needed). Heart ultrasound (echocardiogram) can be used to evaluate the heart valves, heart motion, the pericardium (lining of the heart), and more. This procedure may be done by placing a transducer on the skin overlying the heart, or instead via a transducer that is threaded into the esophagus (transesophageal echocardiogram).

Thyroid ultrasound can be used to evaluate thyroid nodules.

Abdominal ultrasound is often used to look for gallstones as well as other medical conditions.

Pelvic ultrasound is often used to look for ovarian cysts.

Ultrasound does not involve radiation, and is therefore safe in pregnancy. Since it is dependent on finding contrast (such as between a solid mass and a fluid-filled mass), it is less helpful in distinguishing conditions where such a contrast in tissue density is not present.

Fluoroscopy uses X-rays, but in real time, to create moving images of the body. In some settings, these real-time images are particularly important.

For example, fluoroscopy may be used to note the change in flow of contrast in joints associated with different movements, in the digestive tract with an upper gastrointestinal or barium enema study, or to monitor progress during the insertion of a pacemaker.

Due to continuous monitoring (multiple images taken over time), 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 a cancer (such as the use of radioactive iodine to treat thyroid cancer). Examples of nuclear medicine scans include: Positron emission tomography (PET scan): With a PET scan, radioactive glucose (sugar) is injected into a vein, and then a positron emission scanner is used to record the radiation emitted. The radioactive glucose concentrates in areas of the body with a high metabolic rate (i.e., are actively growing). PET scans are commonly used to evaluate for the presence of cancer metastases anywhere in the body. They can be particularly helpful in some situations in which a diagnosis is uncertain. For example, in someone who has had cancer, it may be difficult to determine if an abnormal region in the lungs (or elsewhere) is due to a new and actively growing tumor, or instead is old scar tissue related to previous treatment. Single photon emission computed tomography (SPECT) Bone scan: With a bone scan, a radioactive tracer is injected which is taken up by bones. These scans may identify cancer in the bones, a bone infection (osteomyelitis), fractures (such as stress fractures that may be missed on a plain X-ray), and more. Thyroid scan (radioactive iodine uptake test): In a thyroid scan, radioactive iodine is injected into a vein, and a camera determines the pattern of its uptake in the thyroid gland. It is used most commonly to look for causes of hyperthyroidism. Thallium and Cardiolyte stress tests: During a stress test, a radioactive tracer (thallium-201 or Cardiolyte) is injected. The tracer can help determine how different parts of the heart are functioning, and hence, the presence of coronary artery disease. Arthrogram Sentinel lymph node mapping/biopsy: With cancers such as breast cancer or melanoma, the cancer usually spreads first to specific lymph nodes referred to as the sentinel nodes. Evaluating these nodes for the presence of cancer can help stage the cancer. A tracer is injected directly into a tumor and allowed to follow the lymphatic pathway that would be followed by cancer cells as they spread. These nodes can subsequently be biopsied (by using a camera in order to locate them).

Additional specialized techniques referred to as molecular imaging may also be used. This includes procedures such as CT perfusion, dual-energy CT, and optical imaging. Interventional Radiology Procedures 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. To Detect and Open a Blocked Blood Vessel Blood vessels (either arteries or veins) that are blocked in the heart, legs, and lungs may be treated with interventional procedures. Coronary artery blockages: Narrowing or blockages in the coronary arteries may be treated with angiography , angioplasty, and stent placement. In these procedures, a wire is inserted into the artery and a balloon used to open the narrowing in the artery. As an alternative, a clot busting medication may be injected to open the artery instead. A stent may then be placed to keep the artery open and allow blood to flow to a portion of the heart that would otherwise be damaged. If an artery is blocked acutely in the heart (heart attack) or extremities, clot-blasting medicine may be injected to first open the artery followed by stent placement if needed. Deep venous thrombosis (blood clots in the veins of the legs or pelvis): When detected, clot blasting medication (thrombolytics) may be injected via a catheter placed in a vein with the help of imaging. A balloon or stent placement may then be used. Stents may also be placed in blood vessels that are compressed by a tumor and leading to complications. Pulmonary emboli: When blood clots (deep vein thromboses) occur in the legs or pelvis, they may break off and travel to the lungs (pulmonary emboli). When there is a large clot in the lungs, a radiologist may sometimes insert a catheter into the artery to break up the clot. For people who have recurrent clots in their legs, a radiologist may also insert a filter into the large blood vessel returning blood to the heart (the inferior vena cava). In this case, the filter may prevent pulmonary emboli from occurring.

Alternatively, interventional radiology may be used to block a vessel. 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.4

In external beam radiotherapy, radiation is applied from outside of the body on a table resembling a CT machine. It may be used: Before surgery (neoadjuvant radiation therapy) to reduce the size of a tumor After surgery (adjuvant radiation therapy) to "clean up" any leftover cancer cells and reduce the risk of recurrence As a palliative therapy to reduce pain (such as with bone metastases) or an obstruction due to a tumor Brachytherapy 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 is often used with a "curative" intent, or a hope to cure a cancer rather than simply extend life or reduce symptoms. 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.