Fluoroscopy can be traced back to 1895, when Wilhelm Röntgen noticed a barium platinocyanide screen fluorescing due to exposure to what he would later define as x-rays. The first fluoroscopes were invented several months after Röntgen's discovery of x-rays. Early fluoroscopes were simple boxes made of cardboard that were open at one end (the narrow end) for the eyes of the observer. The other, wider end was closed with a thin cardboard piece coated on the inside with a layer of fluorescent metal salt. The resultant images obtained from these old "fluoroscopes" were very faint. In an effort to produce enhanced images, Thomas Edison discovered that calcium tungstate screens produced brighter images. Edison is also credited with creating and designing the first commercially available fluoroscope sometime prior to 1900 [2].

Absorbed dose: The energy imparted into a tissue by ionizing radiation at a specific point, as measured in grays (Gy). When assessing the dose or risk of radiation to patients in general, the quantity calculated and documented is usually the mean absorbed dose. The unit of absorbed dose is expressed in joules per kilogram (J/kg) [3]. The absorbed dose in air is referred to as the air kerma.

Biologic variation: Individuals differ significantly in terms of the amount of radiation required to produce a deterministic effect and in the extent of damage caused by the same radiation dose. There are several factors contributing to biologic variation in radiation dose, including the patient's age, underlying disease, and idiopathic etiology. In addition, different skin types and different parts of the body vary in sensitivity to radiation [3].

Threshold dose: The minimum radiation dose at which a specified deterministic effect can occur. It will vary greatly in each individual due to biologic variation. In addition, the threshold dose for different anatomic sites on the same individual will vary. For example, the threshold dose for skin on the eyelid is much different than the radiation threshold dose for the sole of the foot.

The x-ray image generation chain of the standard fluoroscopy unit can be distilled to three major parts: the x-ray generator, the x-ray tube, and the image intensifier.

The kilovoltage refers to the energy spectrum of the x-ray beam, which is a function of the beam's wavelength. The higher the kilovoltage, the shorter the wavelength of radiation and, therefore, the greater the ability of x-rays to penetrate target tissue.

It is important to use increased kilovoltage in certain patients (e.g., those with high body mass) in order to increase penetrance and obtain better images. However, a high kilovolt level will yield a lower resolution because of the increased scatter. This also leads to greater radiation exposure to patients and radiology personnel.

The image display and storage device is the final component of the diagnostic imaging process. The monitors must be of adequate resolution and brightness to clearly display the progress of the procedure. Usually, stored images can be easily projected for review and transfer to other storage devices. However, a finite number of images can be stored. When the storage capacity has been exceeded, the unit usually overwrites the oldest image in storage and then continues on from that point. When operating fluoroscopy units, there is a "last image hold" feature, which allows the last recorded position of the device to be visualized. Therefore, the fluoroscope operators do not need to maintain the x-ray beam "on" at all times to review progress in the procedure [7].

Fluoroscopic images have less sharpness at the periphery due to a falloff in brightness and spatial resolution, a phenomenon called vignetting. Placing the structure of interest in the center of the image will yield maximum image detail. "Pincushion distortion" also occurs toward the periphery of the image because the x-rays emanate from a spherical surface and are detected on a flat surface. This results in an effect much like a fisheye camera lens, with a splaying outward of objects toward the periphery of the image. This can lead to particular difficulties when attempting to advance a needle using a coaxial technique if the needle is toward the periphery of the image. Within the past several years, manufacturers have developed electronic flat-panel detectors to replace conventional image intensifiers. These employ a grid-like detector that eliminates both vignetting and pincushion distortion, providing optimum image quality from the center to the peripheral portions of each image. Flat-plane digital detectors are rapidly replacing traditional image intensifiers, because they are capable of dramatically reducing radiation while improving image quality [8].

As mentioned, one of the major advantages of fluoroscopy is the ability to confirm needle placement in real time. This ability is significantly increased by the use of contrast media. To date, iodine is the only element that has been deemed satisfactory as an intravascular radiographic contrast medium. It is responsible for producing radiopacity; other portions of the medium act as carriers, improving solubility and reducing the toxicity of the medium as a whole. Organic carriers of iodine are likely to remain in widespread use for the foreseeable future [8]. All of the currently used contrast media are based on the 2,4,6-tri-iodinated benzene ring, and these contrast media have a higher viscosity and greater osmolality compared with blood, plasma, and cerebrospinal fluid (CSF).

The most frequently used ionic monomers are diatrizoate (Urografin) and iothalamate (Conray). These monomers are still used for intravenous pyelography. The most common non-ionic monomers in clinical use include iodixanol, iohexol, iopamidol, and ioversol (Optiray). Iohexol and iopamidol are commonly used in interventional pain procedures and are labeled for intrathecal use. The non-ionic monomers are more stable in solution and less toxic than the ionic monomers [8]. These agents provide a balance with the low risk of adverse reaction occurrences and adequate radiopacity for identifying intravascular and intrathecal placement.

Patients with a history of cardiac disease, including prior cardiac arrest or chest pain, have been shown to have an increased incidence and severity of cardiovascular side effects following administration of contrast medium [10]. Pulmonary angiogram and intracardiac coronary artery injections carry the greatest risk for cardiovascular side effects, including arrhythmias, tachycardia, hypotension, and congestive heart failure.

There are several factors that put patients at increased risk for contrast-induced nephropathy, including diabetes, chronic kidney disease, congestive heart failure, concurrent diuretic use, dehydration, older age, low hematocrit level, hypertension, ejection fraction less than 40%, and chronic kidney disease (i.e., creatinine clearance less than 60 mL/min). Of these, diabetes and pre-existing renal disease confer the greatest risk [12,14]. Less common risk factors include nephrotic syndrome, hyperuricemia, end-stage liver disease, renal transplant, renal tumor, multiple myeloma, and the administration of chemotherapy, aminoglycoside, or nonsteroidal anti-inflammatory agents. There are also certain procedure-related factors that increase the risk for contrast-induced nephropathy. These include multiple contrast-enhanced studies performed in a short time, large contrast bolus infusion, increased contrast viscosity, high-osmolar contrast agents, and ionic contrast administration [12].

Extravasation of a large volume of contrast material can occur if there is no monitoring with electrical skin impedance devices. Side effects of extravasation of iodinated radiographic contrast materials are primarily the result of hyperosmolality and include pain, edema, swelling, and cellulitis. These side effects may not be evident immediately, and it may take up to 48 hours for the inflammatory response to reach its peak. Compartment syndrome can occur secondary to mechanical compression as a result of tissue edema and cellulitis.

Gadolinium-based contrast agents have also been successfully used as an alternative contrast in patients with known allergy to iodinated agents. However, the radiopacity of gadolinium is less than that of iodinated contrast agents, resulting in a less conspicuous appearance on fluoroscopic images. The application of digital subtraction techniques has been shown to improve visualization in these cases.

Gadolinium-based contrast agents are less likely to cause adverse reactions compared with iodine-based agents. The frequency of any acute adverse events is approximately 1% to 2% of all injections containing 0.1–0.2 mmol/kg of gadolinium chelate. The majority of adverse events are mild, including coldness, warmth, or pain at the injection site; headache; nausea and vomiting; pruritus; paresthesias; and dizziness. Some reactions resemble an allergic-type reaction, including hives and bronchospasm. Severe anaphylactic reactions are extremely rare, accounting for 0.001% of all adverse reactions to gadolinium; fatal reactions are even more rare. Gadolinium-based agents are not nephrotoxic at approved doses for MRI. However, there is a risk of nephrogenic systemic fibrosis in patients with severe renal dysfunction, and these agents should be used with caution in this group.

Some extracellular MRI agents have been known to interfere with serum chemistry. For example, pseudohypocalcemia has been noted up to 24 hours after MRI with gadolinium-based contrast administration. Other electrolytes may also be affected, including magnesium and iron. In general, all electrolyte measurements are more reliable when performed 24 hours after exposure to gadolinium.

The major drawback of fluoroscopy is exposure to ionizing radiation. It is the responsibility of each operator to use fluoroscopy cautiously to ensure that the benefits outweigh its potential risks. In order to be proficient at making this distinction, clinicians should understand the biologic effects of ionizing radiation. A well-rounded radiation management program is not only concerned with minimizing exposure to the patient but also to the interventional radiology team. It also focuses on providing appropriate meticulous preprocedural and postprocedural patient care [5].

A modified barium swallow evaluates the coordination of the swallow reflex and is most often used to determine the cause and severity of aspiration into the trachea. The speech pathologist, using appropriate radiation safety precautions, administers barium suspensions of varying thickness (e.g., thin liquid, thick liquid, nectar, paste, solid) while the radiologist observes fluoroscopically in the lateral projection. The entire examination is recorded and can be reviewed at a later time.

The two most common indications for an endomyocardial biopsy are to evaluate for cardiac transplant rejection or for cardiotoxicity from anthracycline. Other possible indications include cardiomyopathy and myocarditis.

Major contraindications to endomyocardial biopsy are anticoagulation therapy and anatomic abnormality making it unsafe to place the bioptome. Complications occur more frequently in patients with cardiomyopathy than those with heart transplant and may include arrhythmias and perforation.

Cardiac catheterization is a commonly employed revascularization technique after a myocardial infarction. Other uses of fluoroscopic techniques in the field of interventional cardiology include trans-septal cardiac catheterization to evaluate aortic or mitral stenosis or prosthetic valve dysfunction. Left heart catheterization is indicated for conditions that require a direct measurement of pressure (e.g., pulmonary venous disease, hypertrophic cardiomyopathy) and conditions that necessitate access for mitral balloon catheter valvuloplasty and/or the deployment of atrial septal defect closure devices.

Indications for retrograde pyelogram include the evaluation of congenital ureteral obstruction, evaluation of acquired ureteral obstruction, elucidation of filling defects and deformities of the ureters or intrarenal collecting systems, opacification or distention of the collecting system to facilitate percutaneous access (in conjunction with ureteroscopy or stent placement), evaluation of hematuria, surveillance of transitional cell carcinoma, and evaluation of traumatic or iatrogenic injury to the ureter or collecting system.

Ionizing radiation is further categorized as directly or indirectly ionizing. Electromagnetic radiation (e.g., gamma photons) is indirectly ionizing. This means that the photons give up their energy in various interactions, which produces a charged particle that reacts with a target molecule within biologic tissue. On the other hand, charged particles (e.g., alpha and beta particles) react directly with biologic tissue [24]. In general, indirectly ionizing radiation tends to be more damaging to tissues than directly ionizing radiation.

Ultimately, the concern with radiation exposure (and ionizing radiation in particular) is its potential to induce changes that may increase the risk of cancer. There is also a risk that the changes may cause genetic mutations or possibly birth defects. Examples of ionizing radiation include x-rays, gamma rays, and other rays at the higher ultraviolet (UV) end of the electromagnetic spectrum. Examples of non-ionizing radiation include radio waves and sun (UV-A and UV-B) exposure.

Indirect cellular damage is the result of hydrolysis of water, resulting in production of reactive oxygen species. Two-thirds of radiation-induced DNA damage is attributable to hydroxyl radicals. A reactive oxygen species may combine with protein, resulting in the loss of important enzymatic activity in the cell. Antioxidants that can scavenge free radicals are therefore important in minimizing this type of damage.

It is well-established that radiation-induced DNA damage increases with dose. However, we now know that cells do not passively take insults from radiation sources. Cells have three known techniques for addressing radiation injury: repairing DNA, attacking reactive oxygen species, and eliminating mutated or unstable cells.

The National Council on Radiation Protection and Measurements has published estimates of the maximum permissible doses of annual radiation to various organs and tissues [8]. Exposure below these levels is less likely to cause any significant deleterious effects, but the International Commission on Radiological Protection (ICRP) recommends that individuals should not receive more than 10% of the maximum permissible dose [8]. The annual maximum permissible dose for the thyroid gland, the extremities, and the gonads is 500 mSv (50 rem). The maximum permissible dose for the eye lens is 150 mSv (15 rem). The maximum permissible dose for pregnant women is 5 mSv (0.5 rem) to the fetus [8].

The damaging effects of radiation can be divided into two basic categories: stochastic and deterministic. Deterministic effects are detrimental health effects caused by radiation, the severity of which varies with the dose and level of exposure. When the threshold is crossed, an individual may begin to experience effects with increasing severity as the dose grows. Examples of deterministic effects of radiation exposure include hair loss, cataracts, bone marrow depression, spontaneous miscarriage, congenital defects, and fetal growth restriction [3]. The incidence of deterministic injuries is between 1 in every 10,000 to 100,000 radiologic procedures [27].

Kerma-area product is a good indicator of stochastic risk for the patient, correlates with operator and staff dose, and has been recommended for patient dose monitoring for fluoroscopic procedures [1]. While it is considered a surrogate measure of skin dose, it does not correlate well with skin dose for individual cases of a procedure. As such, this approach does not accurate identify deterministic risk in fluoroscopy [1].

It is important to ensure that interventions with a significant radiation dose are scheduled in the fluoroscopy suite that allows for radiation dose monitoring. The SIR gives a brief review of procedures that are known to have high radiation doses. Examples of these procedures include [38]:

There are several rules when monitoring radiation doses during a procedure. For fluoroscopy units that provide estimates of peak skin dose, the operator should be notified when the peak skin dose reaches 2,000 mGy and then every 500 mGy after that point. For units with air kerma capabilities, the operator should be given initial notification at 3,000 mGy and then every 1,000 mGy after that point. These numbers correspond to an initial peak skin dose of approximately 1,800 mGy and an increment of about 500 mGy.

The major adverse effects of radiation exposure on the fetus include abortion, teratogenicity, developmental or intellectual disability, intrauterine growth restriction, and the induction of cancer. Normal diagnostic procedures seldom involve sufficient dosage to induce malformations, fetal death, or central nervous system defects, but the threshold may be exceeded with complicated interventional procedures.

The threshold dose for deterministic effects is in the range of 100–200 mGy (10–20 rad) for acute exposure to the whole body. The majority of diagnostic extra-abdominal x-ray examinations result in doses to the conceptus of less than 1 mGy (100 mrad). Examinations involving the abdomen or pelvis may deliver higher doses to the fetus or embryo. In cases of accidental irradiation, doses to the conceptus may be greater than 50 mGy (5 rad), especially if the total time of fluoroscopy exceeds seven minutes. However, it is uncommon for diagnostic x-ray examinations to exceed 100 mGy (10 rad). Therefore, deterministic effects are unlikely to be observed after diagnostic x-ray studies.