Glossary

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Angiography (Angiogram)

A special technique in radiology which uses the combination of fluoroscopy (live “movie” clip of x-ray images) and the injection of blood vessels with contrast to watch real time blood flow.  This study is useful in detecting blood clots, bleeding, aneurysms, and diseases of the blood vessels. Common procedures include coronary angiography in which the blood vessels feeding the heart muscle are imaged.

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Background Radiation

Natural background radiation comes from the Sun (cosmic radiation, 0.3 mSv), the Earth (mostly Radon gas, 2.0 mSv) and from naturally radioactive substances in our body. Natural background radiation exposure accounts for an average of 3.1 mSv/yr with variations depending on where you live.10

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Barium Enema

A specialized study which uses fluoroscopy (live “movie” clip of x-ray images) and a combination of contrast and air inserted into the rectum.  This study allows real time viewing of the colon and rectum as contrast moves through the abdomen.  The study is useful for detecting cancer and other diseases of the colon.

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Brain Scan

A radioactive material is injected into a vein which allows for imaging of the brain’s blood flow. The most common reason for performing this study is to determine the location of seizure origin and for surgical planning. This is different from a CT scan of the brain.

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Brain and Neck CTA/CTP

Specialized exam for evaluation of acute stroke includes a non contrast Brain CT, CT Angiogram of the Brain and Neck, CT Perfusion of the Brain and delayed imaging of the Brain. Often referred to as an Acute Stroke or Brain Attack Protocol. Average radiation dose is 16.4 mSv12

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Bone Scan

A radioactive material is injected into a vein which has the tendency to accumulate in the bones, specifically at areas of bone turnover. The most common reasons for performing this study are looking for cancer, infection, and fractures. This is different from a DEXA scan which is a test for osteoporosis.

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Cardiac CT (Calcium Score)

CT of the heart without IV contrast to evaluate for calcified atherosclerotic plaque. This study does not provide as much information about the coronary arteries as Coronary CTA (with IV contrast). This study is commonly used to risk stratify patients (put them into low or high risk groups). Calcium score is not a substitute for Coronary CTA.

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Cardiac CT (Coronary CTA)

CT of the heart with IV contrast to evaluate for blockages in the coronary arteries that supply the heart muscle. Typically, a Calcium Score is performed with this study (similar scan but without IV contrast) to evaluate for calcified atherosclerotic plaque. Calcium score is not a substitute for Coronary CTA. The way the CTA images are obtained (ex. Retrospective vs Prospective) depends on multiple factors including; heart rate, heart rhythm, scanner technology and operator experience. This variation leads to variations in radiation exposure.

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Cardiac Stress Test

A radioactive material is injected into a vein and accumulates in the heart muscle. Pictures are taken while the patient is at rest and also while exercising to see if blood is flowing to all parts of the heart equally.  Blockage in blood flow can cause chest pain or lead to a heart attack.

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Computed Tomography (CT or CAT Scan)

Images are obtained with patients lying down on a table which moves through a rotating x-ray tube. Multiple sequential images are obtained using x-rays that are reconstructed in slices to provide detail of internal organs.  The tube can look much like a MRI scanner, but MRI’s usually take between 30 minutes to an hour, while CT scans only take a few seconds.

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Contrast

There are many types of contrast agents that are used to enhance various imaging modalities. CT scans can use fluids that are injected into a vein (iodine based) as well as liquid that the patient drinks (barium or iodine based) to help obtain additional information from an imaging study. MRI can also utilize contrast in the vein (gadolinium based). Contrast agents do not change your radiation dose or estimated cancer risk.  Contrast agents have their own risks which are not discussed here.

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Cosmic Radiation

Energetic protons and alpha particles which originate in the galaxies. Most cosmic rays interact with the atmosphere, with fewer than 0.05% reaching sea level. Exposure to cosmic rays increases with increasing altitude. Therefore, if you live in the mountains or travel by airplane, you have a higher exposure to cosmic radiation.

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DEXA Scan

Dual-Energy X-ray Absorptiometry (DEXA) Scan is used to test bone mineral density.  It does not use the injection of radioactive material into a vein, but it is frequently performed in the nuclear medicine department. X-rays are used to determine bone density and to test for osteoporosis.

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Dose Length Product (DLP)

A measure of the total radiation exposure for a CT scan.  This number is calculated after your CT scan and you can ask for it if you want, but the average listed in Table 2 should be fairly close.  It is calculated by multiplying the CTDIvol (the exposure per slice) by the scan length.  Units of DLP are in mGy · cm.

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Fluoroscopy

Enables real-time visualization of moving anatomic structures by passing a continuous x-ray beam through a patient. This technique uses multiple low dose images to create a “movie” of various parts of the body. The total dose is added up from the multiple images taken and can vary greatly based on the length of the procedure.

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Gastric Emptying Study

Small amounts of radioactive material are typically mixed with eggs or oatmeal for the patient to eat, and then images are obtained.  This study is used to determine if delayed gastric emptying is responsible for a patient’s symptoms (e.g., nausea, vomiting).

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Hysterosalpingogram

This test used fluoroscopy (“live x-rays”) during the injection of dye inside the uterus and fallopian tubes during a procedure similar to a gynecological exam. The test is often performed to look for scarring or uterine abnormalities as a cause for infertility.

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Interventional Radiology

A subspecialty of radiology in which radiologists perform minimally invasive procedures using imaging guidance (CT scans, x-rays, ultrasound).  This field includes common procedures such as angioplasty, using a balloon to open a blood vessel, and angiograms, taking pictures of vessels. The field also makes use of imaging guidance to place drains, catheters, or embolization coils.

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Intravenous Pyelogram (IVP, IV Urogram)

A special test in which contrast material is injected into a vein followed by multiple plain film x-rays of the abdomen.  The injected contrast is normally filtered by the kidneys and can be seen there as well as in the ureters and bladder.  This is different from the often misnamed CT IVP, which is a non-contrast CT of the Abdomen and Pelvis.  Also different from a CT Urogram which is a CT of the Abdomen and Pelvis with images taken both before and after the administration of IV contrast.  These three different studies use very different techniques to look for different types of diseases and result in different radiation exposures.

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Linear No Threshold Model

Because there is no scientifically proven link between cancer and low dose radiation exposure from medical imaging, there are many theories which try to estimate the risk. One such model or theory is the Linear No Threshold Model which suggests a linear relationship exists between exposure and increased risk of cancer.  This model assumes that even the smallest amount of radiation results in the smallest fraction of increased risk.  Opposing theories suggest there is a level of radiation below which there is no increased risk of cancer.  Currently, the most widely accepted model is the Linear No Threshold Model to ensure the highest standard of patient safety.  

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Liver Scan, HIDA Scan

A radioactive material is injected into a vein which accumulates in the liver and is excreted into the biliary system. The most common reason for performing this study is to determine if the gallbladder is responsible for a patient’s abdominal pain. Another common indication for this study is after liver transplant or surgical removal of the gallbladder.  This study can be performed to ensure that bile flows correctly from the liver into the small bowel.

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Lung Scan, Ventilation Perfusion, VQ Scan

A radioactive material is injected into a vein which accumulates in the lungs.  Images are obtained to determine if the blood flow to all areas of the lungs is equal (perfusion).  Radioactive material is then inhaled and images are obtained to see if air flow to all areas of the lungs is equal (ventilation).  The comparison of the two sets of images helps determine if there is a blood clot in the lungs that may be causing a patient’s shortness of breath.

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Magnetic Resonance Imaging (MRI)

MRI is a technique that produces multiple sequential images by means of magnetic fields and radiowaves.  The images are obtained with the patient lying down on a table and being placed inside a long tube.  The tube can look much like a CT scanner, but MRI’s usually take between 30 minutes to an hour, while CT scans only take a few seconds.   MRI does not expose patients to ionizing radiation and therefore does not increase your estimated cancer risk.

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Mammography

Plain films (x-rays) are taken of the breasts to help detect early stage breast cancer.  The American Cancer Society currently recommends a yearly screening mammogram in women over age 40.  Studies have proven that screening mammograms help detect cancer sooner and improve outcomes.

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Nuclear Medicine

A subspecialty of radiology that uses radioactive material to treat and diagnose disease.  Small amounts of a radiopharmaceutical (radioactive drug) or radiotracer are injected into a vein, swallowed, or inhaled as a gas.  The radiotracer collects in various areas of the body where it gives off energy in the form of gamma rays.  That energy is then picked up by a camera (gamma camera, PET scanner or probe).

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Parathyroid Scan

A radioactive material is injected into a vein and accumulates in the thyroid and parathyroid glands. The most common reason for performing this study is to localize overactive parathyroid glands which can result in high levels of calcium in the blood.

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PET Scan

Positron Emission Tomography (PET) uses radioactive material attached to glucose (sugar) which is injected into a vein and accumulates in areas of the body that are metabolically active. The most common reason for performing this study is to determine the presence of cancer or the response to treatment. PET scans are commonly combined with CT Scans to aid in anatomic localization which range in dose between 2-18 mSv depending on whether the study is for attenuation or diagnostic purposes.

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Plain Films

A single projection of x-rays that interact with body tissues to provide an image of overlapping shadows for the radiologist to interpret.  These usually involve the patient standing in front of a film cassette (as with a chest x-ray) or placing a hand or foot on top of a film cassette while getting exposed to radiation over a fraction of a second.  Also commonly referred to as an “x-ray”.

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Radiation

Radiation is simply energy moving through space. Radiation can take many forms, including visible light, x-rays, gamma-rays, microwaves, radiowaves, etc. This site specifically addresses high energy or ionizing radiation, which includes x-rays obtained in a medical imaging center. Ionizing radiation has many uses, e.g., sterilization of food and medical equipment, creation of medical images, and even in the treatment of certain types of cancer.

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Radioactive

Certain elements both natural and man-made emit radiation.  The field of Nuclear Medicine uses these special materials to help diagnose patients with certain diseases.  This is different from the use of x-rays which are created by high voltage electricity.

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Radiologic Technologist

Radiologic technologists are the medical personnel who perform diagnostic imaging examinations and administer radiation therapy treatments. Registered technologists must complete at least two years of formal education in an accredited hospital-based program or a two or four year educational program at an academic institution and must pass a national certification examination. While radiologists primarily interpret the images, technologists acquiring the images have a key role in balancing image quality and radiation dose.

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Radiologist

The physician imaging specialist who is responsible for creating and interpreting imaging studies. This is not the person you typically see when you have your x-ray or CT scan (technologist), but the doctor who is specially trained to read the images.  Training to become a Radiologist includes a 4 year undergraduate degree, 4 years of medical school, 5 years of residency (on the job training), and often an additional 1-2 years of fellowship (specialized on the job training).

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Radiologist Assistant (RA)

Radiologist assistants are experienced, registered radiologic technologists who have obtained additional education and certification that qualifies them to serve as radiologist extenders. They work under the supervision of a radiologist to provide patient care in the diagnostic imaging environment. All educational programs are established at the baccalaureate degree or higher and include a radiologist-directed clinical preceptorship. After graduating from an RA program, the individual must additionally pass the RA certification examination offered by the American Registry of Radiologic Technologists (ARRT).

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Radiology

A field of medicine that encompasses the diagnosis and treatment of disease using imaging technology.

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Radionuclide Ventriculogram

A small amount of your red blood cells are removed, labeled with a radioactive isotope and re-injected into a vein. Pictures are then taken to demonstrate how well the heart pumps blood.

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Radon

A naturally occurring radioactive gas which is the biggest contributor of background radiation exposure and is the second leading cause of lung cancer (the first is smoking).

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Renal Scan

A radioactive material is injected into a vein which accumulates in the kidneys and is filtered into the collecting system based on renal function. The most common indications for performing this study are to determine kidney function, presence of obstruction, or renal induced high blood pressure.

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Sieverts (Sv)

A unit of measurement commonly used to describe radiation dose and its effects on the human body.  It is the official International System (SI) unit for dose equivalent reflecting the biological effects of radiation. Often expressed in mSv (millisieverts) which is equal to 0.001 Sieverts.

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Small Bowel Follow Through

A specialized study which uses fluoroscopy (live “movie” clip of x-ray images) and contrast that you drink.  This study allows for real time viewing of the small bowel (small intestine) as the contrast moves through the abdomen.  This study is useful for detecting obstructions and other diseases of the small bowel.

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Tagged White Blood Cell Study

A small amount of white blood cells are removed from the patient, labeled with a radioactive material and re-injected into a vein. The white blood cells travel to the area of infection, carrying the radiotracer with them.  The radiotracer is then picked up by a camera and the site of infection is identified.

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Thyroid Scan

A radioactive material is injected into a vein which accumulates in the thyroid gland. The most common reason for performing this study is to determine the cause of an overactive thyroid. The scan can also be performed to evaluate if a known thyroid nodule is overactive or under active.

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Ultrasound (US)

An imaging technique which uses sound waves to visualize anatomical structures in real time. This is done by converting electrical energy to a brief pulse of high-frequency sound energy that is transmitted into the patient's tissues. The ultrasound transducer then becomes a receiver, detecting echoes of sound energy reflected from tissue. Ultrasound does not expose patients to ionizing radiation and therefore does not increase your estimated cancer risk.

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Upper GI (Barium Swallow)

A specialized study which uses fluoroscopy (live “movie” clip of x-ray images) and contrast that you drink.  This study allows for real time viewing of swallowing function as well as the esophagus, stomach and first part of the small intestine.  This study is used to document gastroesophageal reflux (GERD), ulcers, cancer and associated diseases.  This study can also be useful for detecting problems with swallowing, often with a speech pathologist present (Modified Barium Swallow Study).  

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Urea Breath Test

This test is performed to diagnose the presence of Helicobacter pylori bacterium in the stomach. Patients swallow a capsule containing a radioactive carbon isotope (C-14) which is then measured in the patient’s breath.

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Virtual Colonoscopy CT

CT scan of the abdomen and pelvis that is specifically designed to evaluate the lining of the colon and rectum. Current studies are underway comparing this method of screening for colon cancer with traditional colonoscopy.

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X-rays

X-rays are a type of radiation that are created using large amounts of electricity in a x-ray tube.  X-rays are used in medical imaging much like a camera uses visible light to create an image. X-rays pass through the body and create an image on film based on how many x-rays get absorbed and how many pass through.  The film is commonly referred to as an “x-ray”, but x-rays are actually the type of radiation used to make the image.  Studies that use x-rays include plain films, fluoroscopy and computed tomography (CT scans). 

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Together, dedicated to improving the understanding of radiation risks from medical imaging. Calculate your dose and estimate cancer risk from studies including CT scans, x-rays, nuclear scans and interventional procedures.