#90471: Safe Clinical Use of Fluoroscopy

The x-ray generator provides the power source necessary to accelerate the electrons through the x-ray tube. The duration of x-ray exposure is similar to the shutter speed on a regular camera, and it can be adjusted and optimized for the tissue being examined. For example, exposure may be increased for more mobile organs and slowed for less mobile organs [6]. Exposure times of 3 to 6 msec reduce the blurring effect associated with movement, which is ideal for cardiac studies. Most modern x-ray generators can provide sufficient and precise power with automatically adjusted exposure timing. They are enabled with multiple phase and long versus short widths that are automatically adjusted for ideal exposure. The manual settings on modern x-ray generators (which are operator-selected) are available in film frame rates, such as 60, 30, or 15 frames per second.

The purpose of the x-ray tube is to convert electrical energy provided by the generator into an x-ray beam. Electrons are emitted from a cathode (a heated filament) and are accelerated toward a rapidly rotating disc (the anode). Usually, the anode is made from high atomic target material (e.g., tungsten). When these electrons collide with their target, they undergo conversion to x-radiation. However, approximately 99% of the collisions simply result in the heating of the target. The heat capacity of x-ray tubes is a major limiting factor in their design. Approximately 0.2% to 0.6% of the electrical energy provided to the tube is eventually converted to x-rays. Therefore, in the x-ray tube, a thermal overload interrupt switch becomes a necessity [7].

In addition to the exposure times (controlled by the generator system) and the size of the imaging field (controlled by the x-ray tube), there are two other factors of the x-ray that determine the quality of x-ray for proper image exposures: the electrical current and the level of kilovoltage. Modern radiographic equipment allows for variability of the amperage and voltage to attain optimal quality radiographic images. These modern machines are capable of automatically adjusting exposure times as well as current and voltage in order to produce the most optimal radiographic images [7].

The electrical current is a measure (in milliamperes or mA) of the number of photons generated per unit of time. The greater the electrical current, the greater the number of photons, leading to an improved image resolution. If the photon volume is suboptimal, the resulting image may have a spotty appearance [6]. It is important to recognize that increasing the milliamperage will improve image quality, but the level of milliamperage is limited by the heat capacity of the x-ray tubes. In addition, higher milliamperes significantly increase radiation exposure and scatter to patients and staff members involved in the procedure.

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.

X-Ray Tube Housing

The x-ray tube is capable of producing x-rays, but it does not independently manage, manipulate, or modify the x-rays produced. The x-ray tube housing, a lead-lined structure, is capable of modifying the images. The housing includes the x-ray beam filter, the beam collimator, and the thermal switch. The beam collimator functions to limit the x-ray field size, while the thermal switch senses the degree of overheating of the x-ray tube and acts accordingly.

The x-ray tube housing also serves as a barrier against x-rays. According to FDA regulation, the x-rays escaping the tube housing (termed "leakage x-rays") must result in a radiation exposure rate less than 0.1 roentgen per hour, measured 1 m from the x-ray source, when operated at its maximum voltage energy and maximum continuous tube current [7].

X-Ray Beam Filter

The x-ray tube also contains x-ray beam filters, usually aluminum or copper metal filters, put in place to generate a cleaner and more effective beam. The filter eliminates lower energy rays, which do not contribute to the creation of the diagnostic image.

When the refined, higher energy beams reach the patient, they are attenuated selectively by the tissues. Eventually, the x-rays exit the patient and interact with the image intensifier, initiating the process of image creation.

Collimator

The x-ray beam can never be wider than the image intensifier's diameter, and the purpose of the collimator is to fit the x-ray beam exiting the tube to the image intensifier. It is critical to position the image intensifier such that it intercepts the x-ray beam. Manufacturers place a cone that acts as a collimator at the x-ray tube to fulfill the beam-size criteria, but mishandling can compromise the beam-to-image intensifier alignment.

The image intensifier assembly in a fluoroscopy unit contains an anti-scatter grid to reduce the number of scattered x-rays entering the fluoroscopy unit. It also includes a vacuum tube (consisting of photoabsorptive and electroemissive surfaces, electrostatic focusing electrodes, and an output phosphor), light-focusing lenses, diaphragm, and video signal pickup. In addition, image intensifiers have electronic shielding and a lead-lined enclosure, which serves as the primary x-ray barrier.

The electrostatic focusing lenses are able to compress or expand the stream of electrons coming from the photocathode surface. This results in a reduction or magnification of the resultant image being captured. The output phosphor's purpose is to produce light photons.

Other components of the imaging system include the x-ray control panel, the exposure activation switches (typically a "dead man"-type foot switch), and the image display and recording device.

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].

The typical portable fluoroscope used today is versatile and mobile and occupies less space in confined quarters than fixed units. These units also allow one to store and archive images for scanning, reprinting, or illustrating details, such as where needle placements are located. Electronic images and reports are transmitted digitally in digital imaging and communication in medicine (DICOM) format. Non-image data, such as scanned documents, may be incorporated as well.

As discussed, a fluoroscopic system in which the image receptor and x-ray tube are mounted at the opposite ends of a C-shaped arm allows the x-ray tube and image receptor to be rotated at least 90° relative to the patient with no motion of the x-ray tube relative to the image receptor [7]. Stationary C-arm fluoroscopic units, such as those found in a busy interventional suite, can come equipped with an 18-inch image intensifier, although a 15-inch intensifier is more common [7]. Mobile C-arm units are equipped with wheels and a steering mechanism for transport to the procedure room or operatory.

Cardiac Abnormalities

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.

Metformin Interaction

Patients with type 2 diabetes receiving metformin may have an accumulation of the drug after administering iodinated radioactive contrast material, resulting in biguanide-related lactic acidosis with symptoms of vomiting, diarrhea, and somnolence. Metformin-related lactic acidosis has been reported to be fatal in approximately 50% to 83% of these cases, but it is very rarely reported in patients with normal renal function [11]. Therefore, in patients with normal renal function and no known comorbidities, there is no need to discontinue metformin before iodinated radiographic contrast use or to check creatinine levels following the imaging study. However, in patients with renal insufficiency, metformin should be discontinued the day of the study and withheld for 48 hours. Postprocedure creatinine level should be measured at 48 hours, with metformin resumed when kidney function is normal [12].

Contrast-Induced Nephropathy

Although there are no standard criteria for the diagnosis of contrast-induced nephropathy, diagnosis is usually made if any of the following scenarios occur within 48 hours after the administration of iodinated contrast:

The etiology of contrast-induced nephropathy remains unknown, but it has been reported to be related to tubular obstruction, tubular toxicity, and renal ischemia secondary to vasoconstriction [12].

High doses of iodinated radiopaque contrast materials can impair renal function in certain patients for up to five days. However, serum creatinine levels will usually return to baseline in 10 to 14 days, and contrast-induced nephropathy occurs in less than 5% of patients with normal renal function. Up to 25% of patients with contrast-induced nephropathy will have persistent abnormalities in renal function [13]. The clinical manifestations of contrast-induced nephropathy range from no clinical signs and symptoms to oliguria. It is the third most common cause of acute kidney injury in hospitalized patients [14].

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].

Contrast-induced nephropathy remains a controversial topic, and a review of multiple meta-analyses reveals that there is no absolute creatinine level that necessitates prohibition of the use of the contrast media [12]. The consensus remains that the threshold should be lowered in patients with diabetes. It is important to note that patients with end-stage renal disease on dialysis can receive iodinated contrast media and then get dialysis with no significant adverse effects. Preferably, these patients should receive iso-osmolar or low-osmolar contrast agents [12].

Prevention of contrast-induced nephropathy should be a priority. Hydration prior to contrast administration remains the primary method for prevention of contrast-induced nephropathy [14]. Preprocedural IV hydration with normal saline at 100 mL/hour beginning 12 hours before and continuing for 12 hours after the procedure has been shown to reduce the incidence of contrast-induced nephropathy. The use of sodium bicarbonate has not been shown to definitely reduce the incidence [15,16]. The use of N-acetylcysteine in place of hydration is not recommended. One systematic review and meta-analysis determined that prophylaxis with N-acetylcysteine supplementation was more beneficial in patients with kidney dysfunction and high-contrast medium dose than in those with normal kidney function and low dose of contrast agent [17]. Furosemide has been found to increase the risk of contrast-induced nephropathy [12,14].

Extravasation

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.

Management of extravasation includes stopping the contrast injection immediately, elevating the affected extremity above the level of the heart, and notifying the responsible providers. Manual massage is recommended to promote drainage in cases of large-volume extravasation. If the patient remains symptomatic, a plastic surgery consultation is recommended. Occasionally, the patient may need to be admitted to the hospital for observation.

Adverse Reactions

Modern contrast agents have greatly reduced, but not completely eradicated, the risk of adverse reactions. In order to mitigate the risk of adverse events, radiopaque contrast material should be used in the lowest concentrations and smallest doses possible to allow adequate visualization. Contrast reactions fall into three general groups: anaphylactoid or idiosyncratic, non-anaphylactoid, and mixed. As noted, the risk of adverse reactions is significantly greater with the use of high-osmolar, ionic agents when compared with low-osmolar, non-ionic agents.

Anaphylactoid reactions are the most serious type of reaction. They occur independent of dose and will occasionally lead to fatal outcomes. This type of reaction occurs relatively more frequently in patients with a history of asthma, allergies, previous reactions, or cardiovascular or renal disease, and in patients currently receiving beta blockers.

The symptoms associated with anaphylactoid reactions can range from skin rash, nausea, and pruritus to severe reactions such as hypotension, bronchospasm, laryngeal edema, seizures, and life-threatening arrhythmias. The overall risk for severe reactions from low-osmolar contrast media is 0.03% [9].

It is not possible to reliably predict or prevent anaphylactoid reactions. These reactions usually begin within five minutes of injection and can progress rapidly to life-threatening cardiovascular collapse and death unless swift action is taken [8].

The severity of non-anaphylactoid reactions depends on qualities of the medium, including the concentration of iodine, whether or not the contrast injected is ionic, the level of osmolality, and the volume of contrast injected. In addition, intra-arterial route of administration is more likely to cause a reaction. Epinephrine is the drug of choice for the treatment of anaphylaxis; the usual adult starting dose is 0.01 mg/kg, with a maximum dose of 0.5 mg [8].

Reactions are theorized to be caused by disturbances in homeostasis, specifically alterations in blood circulation. Symptoms typically include warmth, nausea, vomiting, a metallic taste, bradycardia, hypotension, and vasovagal reactions. Pretreatment with a corticosteroid, antihistamine, or both may be considered in patients with previous reactions or with significant risk factors. The most commonly affected systems are the respiratory, gastrointestinal, and nervous systems [9].

Non-anaphylactoid reactions to contrast media can be classified as mild, moderate, or severe. When administering large volumes of IV contrast materials, the incidence of mild reactions is about 5% to 15%. These reactions include flushing, anxiety, nausea and vomiting, pain at the injection site, pruritus, and headaches. In general, mild reactions are self-limiting, requiring no specific treatment. Occasionally, an oral antihistamine may be administered to manage pruritus and anxiety [8]. Moderate adverse reactions occur in 0.5% to 2% of those receiving IV contrast media and include more severe symptoms outlined for mild reactions as well as moderate hypotension and bronchospasm.

Severe, life-threatening non-anaphylactoid reactions occur in less than 0.04% of those receiving IV contrast agents and include convulsions, unconsciousness, laryngeal edema, severe bronchospasm, pulmonary edema, severe cardiac arrhythmias, and cardiovascular collapse. Treatment of these reactions is urgent, necessitating the immediate availability of full resuscitation equipment and trained personnel who routinely respond to these events [8]. Management of severe adverse reactions includes adhering to advanced cardiovascular life support guidelines, including airway management, oxygen administration, mechanical ventilation, external cardiac massage, and electrical cardiac defibrillation.

Recognition of the factors that predispose patients to adverse reactions when receiving contrast materials is the most important step in prevention. As mentioned, the risk is increased in those with previous reaction to contrast agents, asthma, allergies/atopy, and advanced heart disease. Patients with an unstable arrhythmia, recent myocardial infarction, diabetic nephropathy, renal failure from other causes, anxiety, or hematologic or metabolic disorders (e.g., sickle cell anemia, pheochromocytoma) are also at risk [8]. If there is any possibility that contrast agents could be injected into the subarachnoid space, a low-osmolar, non-ionic contrast agent should be used.

There is no known premedication regimen that completely eliminates the risk of severe reactions to contrast agents. The most frequent medications used include corticosteroids (e.g., prednisone) and antihistamines. Some experts recommend the addition of H2-antagonists such as ranitidine [18]. This approach has been shown to be effective in reducing the incidence of subsequent adverse reactions in those with a history of previous reaction to high-osmolar contrast agents. It remains unclear whether prophylactic treatment is necessary prior to the use of a low-osmolar, non-ionic contrast agents.

Gadolinium chelates are IV contrast agents commonly used to enhance vascular structures during diagnostic magnetic resonance imaging (MRI). Gadolinium chelates are capable of attenuating x-rays and have been used successfully in place of iodinated contrast media for angiography and spinal injection procedures under fluoroscopy [8].

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.

Nephrogenic Systemic Fibrosis

The use of gadolinium-based contrast agents has been linked to the subsequent development of nephrogenic systemic fibrosis in patients with pre-existing renal disease, but the risk is low given the small doses being administered [8].

Nephrogenic systemic fibrosis is a fibrosing disease affecting the skin and subcutaneous tissues, heart, lungs, esophagus, and skeletal muscle. The signs and symptoms tend to develop and progress rapidly. Some patients develop contractures and immobility within a few days after exposure to gadolinium-based contrast. In some patients, visceral organ involvement may lead to death. The average onset varies between two days and three months. Overall, about 4% of patients with severe kidney problems will develop nephrogenic systemic fibrosis [19].

In the case of an air-contrast esophagram, the images are obtained in the upright and in slightly left anterior obliquity. An effervescent agent is first administered, followed by a thick barium suspension. The barium coats the mucosal surface, whereas the gas from the effervescent agent distends the lumen. This provides fine mucosal detail and is most useful for the evaluation of small, plaque-like mucosal tumors and mucosal irregularities of esophagitis. If a patient is unable to undergo the air-contrast portion of the thoracic esophagogram, prone full-column imaging may be obtained in two orthogonal planes as an alternative [20].

Air-contrast images of the pharynx are not always necessary, because this region is amenable to endoscopic inspection. However, in some cases, such as with tumors that arise in the hypopharynx, air-contrast images are useful. After the administration of a thick barium suspension, phonation and a modified Valsalva maneuver are used to distend the pharynx [20].

For functional assessment with barium swallow, the American College of Radiology recommends the fluoroscopic portion of the examination should be recorded on high-resolution videofluorographic and/or rapid digital fluorographic imaging. For morphologic assessment, spot images and/or rapid digital fluorographic imaging with double-contrast or single-contrast technique should be used.

(https://www.acr.org/-/media/ACR/Files/Practice-Parameters/Modified-Ba-Swallow.pdf Last Accessed: July 21, 2022)

Level of Evidence: Expert Opinion/Consensus Statement

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 various barium suspensions are intended to mimic different food consistencies and provide a more complete assessment of aspiration risk. If tracheal aspiration or laryngeal penetration is identified with the head in a neutral position, the speech pathologist may direct the patient to perform certain maneuvers in order to protect the airway, including chin tuck, neck turn, and a forced cough after swallowing. The examination can be supplemented with images in the frontal projection to evaluate symmetry of the piriform sinuses.

Functional endoscopic evaluation of swallowing with or without sensory testing has been proposed as an alternative to the modified barium swallow. However, the modified swallow provides a more appropriate physiologic environment, because the endoscope is not present to interfere with motility. Additionally, protective maneuvers cannot be used during an endoscopic swallowing evaluation. Finally, the modified barium swallow evaluates the upper phases of swallowing in greater detail than an endoscopic evaluation. Most clinicians consider endoscopic swallowing evaluation and the modified barium study as complementary but not interchangeable [20].

Occasionally, there may be brief contrast penetration into the larynx, which may or may not clear rapidly. If the laryngeal penetration clears rapidly and without cough, the patient is not considered at risk for tracheal aspiration. However, if there is penetration and pooling of contrast in the valleculae or in the piriform sinuses, the patient is at risk for aspiration, especially if the peristaltic wave does not clear this contrast [20].

Both cineradiography, which produces high-resolution images obtained at a low frame rate, and video capture, which produces low-resolution images obtained at a high frame rate, are useful in performing esophagrams and modified barium studies. Cineradiography offers better mucosal detail, while video capture provides an evaluation of function with less radiation.

Oral Contrast Agents

The barium suspension is the best fluoroscopic contrast agent available, but its use is contraindicated in some patients. Perforation of the pharynx or esophagus is a risk factor for barium extravasation into the soft tissues of the neck or chest. Extravasated barium may incite an extensive inflammatory reaction or may become inspissated over time and fail to resorb [20].

Water-soluble contrast agents, such as those used for IV contrast CT, may be used as an alternative. Unfortunately, water-soluble agents are not as dense as barium agents, so they are less sensitive to small leaks. If no leak is detected after the administration of a water-soluble agent, the examination should be repeated with barium.

Ionic contrast agents have another disadvantage; if they are aspirated into the lungs, they may cause chemical pneumonitis and pulmonary edema. Non-ionic water-soluble agents are presumed to be safer and thus should be used if there is a preprocedural risk of aspiration or if there is a tracheoesophageal fistula present. Oil-based contrast agents for the evaluation of the larynx and pharynx are no longer being used in clinical practice [20].

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.

Contraindications to trans-septal cardiac catheterization include left or right atrial thrombus, atrial myxoma, low platelet counts, current anticoagulation therapy, or hemostatic dysfunction. Patients with an inferior vena cava mass or obstruction are also contraindicated from undergoing endovascular catheterization. Trans-septal left heart catheterization should be considered carefully in patients with distorted cardiac anatomy as a result of congenital heart disease, marked atrial enlargement, or a severely dilated aortic root. Possible serious complications of this procedure include perforation of the coronary sinus, the aortic root, or the posterior free wall of the atrium.

Pericardiocentesis is performed to aid in the diagnosis and management of acute and chronic pericardial effusions; it can be a life-saving procedure in cases of cardiac tamponade. A significant degree of skill is necessary in order to perform this procedure safely and to avoid damage to the pericardium and the heart. Pericardiocentesis is performed from a subxiphoid approach into the pericardial space. In general, an echocardiogram is performed prior to pericardiocentesis to confirm the presence and amount of pericardial fluid. However, in acute situations when tamponade is suspected or known, an echocardiogram may cause unnecessary delay.

Intra-aortic balloon pump counterpulsation, first introduced in 1967, consists of a balloon pump positioned in the descending aorta to improve hemodynamics (i.e., the balance between myocardial oxygen supply and demand). It is used for temporary mechanical support of patients in a variety of clinical settings, including the cardiac catheterization suite, the intensive care unit, and the operating room.

The balloon pump works by inflating during diastole to increase coronary blood flow and deflating at the end of diastole to decrease myocardial oxygen consumption and increase cardiac output. Common indications for intra-aortic balloon pumps include hypotension unresponsive to volume loading or intravenous pressor agents, refractory angina, acute myocardial infarction with or without cardiogenic shock, weaning from cardiopulmonary bypass, bridge to cardiac transplantation, and right ventricle failure. Contraindications include severe peripheral vascular disease, severe aortic incompetence, active bleeding, thrombocytopenia, and acute stroke. Potential complications of intra-aortic balloon pump placement include perforation of the superficial femoral artery, forceful arterial dissection due to advancement of the guidewire, hemorrhage, and thrombus formation [6].

Although IV urography was once the standard in urologic imaging, it has essentially been replaced by CT and MRI. With the ability of new scanners to perform axial, sagittal, and coronal reconstruction of the upper urinary tract system, essentially all of the data and information obtained by traditional IV urography can be realized with CT imaging. In addition, some parenchymal defects, cysts, and tumors can be better delineated with CT than with IV urography.

IV urography may be indicated to assess the renal collecting systems and ureters, including investigation of the level of ureteral obstruction and demonstration of intraoperative opacification of the collecting system during extracorporeal shock wave lithotripsy. It may also be used to demonstrate renal function during emergent evaluation of unstable patients. Finally, it can demonstrate renal and ureteral anatomy after interventions such as transureteroureterostomy and urinary diversion.

When using fluoroscopy for percutaneous nephrostomy, the American College of Radiology recommends tight collimation should be used and radiation dose should be minimized. Radiation dose estimates should also be recorded in the patient's medical record. In accordance with the ALARA principle, a radiation dose reduction package, including pulsed fluoroscopy and last image hold capabilities, is recommended.

(https://www.acr.org/-/media/ACR/Files/Practice-Parameters/Percutaneous-Nephros.pdf Last Accessed: July 21, 2022)

Level of Evidence: Expert Opinion/Consensus Statement

Percutaneous nephrostomy (PCN) provides a less invasive means to drain the renal collecting system in cases where obstruction of the kidney and ureter has resulted in hydronephrosis. Most often used for patients with kidney stones or bladder or pelvic tumor obstructions, PCN may be used to divert urine from the renal collecting system to allow leaks and fistulas to heal. The procedure is often performed after attempts at placing a ureteral stent through retrograde cystoscopy have proven unsuccessful. Providing drainage for that kidney is an urgent necessity, and PCN provides an exact method of accomplishing this task.

The approach is extremely important for PCN, and the procedure is performed under ultrasound or fluoroscopic guidance. In some cases, a small amount of intravenous iodinated contrast is administered at the start of the procedure to opacify the collecting system. The patient is placed in the prone position with both arms above his or her head or one arm up and the other at the noninvolved side. The entry site is prepped and draped and infiltrated with local anesthetic. A small puncture is made with a scalpel, and a posterior lateral approach is made with a needle and directed toward a lower calyx of the kidney. If the tip of the needle has entered a dilated part of the collecting system, urine will flow back from the needle when the stylet is removed. A specimen should be collected and sent to the laboratory for microscopic and bacterial studies. Obviously, infected urine will be cloudy and turbid.

Hemorrhage is the major risk of PCN, but the risk can be reduced substantially with use of a very small needle. Nephrostomies are performed frequently in interventional radiology departments and are a major part of the treatment for patients with malignant obstructions, renal stones, and other kidney problems.

Retrograde pyelograms are performed to visualize the ureters and intrarenal collecting system by the retrograde injection of contrast media. Any contrast media that can be used for excretory urography is also acceptable for retrograde pyelography. It is important that measures are taken to attempt to sterilize the urine before retrograde pyelography, because there is a risk of introducing bacteria into the upper urinary tract or the bloodstream. Although many studies are able to document the presence or absence of dilation of the ureter, retrograde pyelography has the unique ability to document the patency of the ureter distal to the level of obstruction and to help better define the extent of the ureteral abnormality.

Retrograde pyelograms are usually performed with the patient in the dorsal lithotomy position. An abdominal plain radiograph (i.e., scout film) is obtained to ensure that the patient is in the appropriate position to evaluate the entire ureter and intrarenal collecting system. Next, the ureteral orifice is identified via cystoscopy, and contrast may be injected through either a non-obstructing or obstructing catheter.

Non-obstructing catheters include whistle tip, spiral tip, or open-ended catheters. These catheters allow passage of the device into the ureter and up to the collecting system, over a guidewire if necessary. Contrast can then be introduced directly into the upper collecting system and the ureters visualized as the catheter is withdrawn.

Obstructing ureteral catheters include bulb-tip, cone-tip, and wedge-tip catheters. These catheters are inserted into the ureteral orifice and then pulled back to effectively obstruct the ureter. Contrast is then injected to visualize the ureter and intrarenal collecting system. Depending on the indication for the study, it may be useful to dilute the contrast material with sterile fluid. This prevents subtle filling defects in the collecting system or ureter from being obscured. Care should be taken to evacuate air bubbles from the syringe and catheter before injection, as such artifacts could be mistaken for stones or tumors.

Historically, when a retrograde pyelogram consisted of a series of radiographs taken at intervals, it was important to document various stages of filling and emptying of the ureter and collecting systems. Because of peristalsis, viewing the entire ureter is often not possible with a single static exposure or view. With modern equipment, including tables incorporating fluoroscopy, it is possible to evaluate the ureter during peristalsis in real time, thus reducing the need for static-image documentation. Occasionally, still images may be saved for future comparison. In general, however, urologists interpret retrograde pyelograms in real time as they are performed.

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.

Retrograde pyelography may be difficult in cases in which there is diffuse inflammation or neoplastic changes of the bladder, especially when bleeding is present. In these cases, identification of the ureteral orifices may be facilitated by the IV injection of indigotindisulfonate sodium (indigo carmine) or methylene blue. Changes associated with bladder outlet obstruction may result in angulation of the intramural ureters, which may make cannulation with an obstructing catheter difficult. Attempts to cannulate may result in trauma to the ureteral orifice and extravasation of contrast material into the bladder wall. The potential for damage to the intramural ureter should be weighed against the potential information obtained by the retrograde pyelogram.

Loopography is a diagnostic procedure performed in patients who have undergone urinary diversion. Historically, the term loopogram has been associated with ileal conduit diversion, but it may also be used in reference to any bowel segment serving as a urinary conduit. Because an ileal conduit urinary diversion usually has freely refluxing uretero-intestinal anastomoses, the ureters and upper collecting systems may be visualized. In other forms of diversion, the uretero-intestinal anastomoses may be purposely non-refluxing [12].

The patient is positioned supine and an abdominal plain radiograph is obtained before introduction of contrast material. A commonly employed technique is to insert a small-gauge catheter into the stoma of the loop, advancing it just proximal to the abdominal wall fascia. The balloon on such a catheter can then be inflated to 5–10 mL with sterile water. By gently introducing contrast through the catheter, the loop can be distended, usually producing bilateral reflux into the upper tracts. Oblique films should be obtained in order to evaluate the entire length of the loop. Because of the angle at which many loops are constructed, a traditional anteroposterior view will often show a foreshortened loop and could miss a substantial pathology. A drain film should also be obtained, as this may demonstrate whether there is obstruction of the conduit [12].

Indications for a loopogram include evaluation of infection, hematuria, renal insufficiency, or pain after urinary diversion. It can be used for surveillance of upper urinary tract obstruction or urothelial neoplasia, or it may be used to evaluate the integrity of the intestinal segment or reservoir [12].

A retrograde urethrogram is a study performed to evaluate the anterior and posterior urethra, usually in male patients. It may be particularly beneficial in demonstrating the total length of a urethral stricture that cannot be negotiated by cystoscopy and the anatomy of the urethra distal to a stricture that may not be assessable by voiding cystourethrography. This procedure is performed in the radiology department or in the operating room before performing visual internal urethrotomy or formal urethroplasty [12].

A plain film radiograph is obtained before injection of contrast, and the patient is usually positioned slightly obliquely to allow evaluation of the full length of urethra, with the penis placed on slight tension. A small catheter may be inserted into the fossa navicularis with the balloon inflated to 2 mL with sterile water. Contrast is then introduced via a catheter-tipped syringe. Alternatively, a penile clamp may be used to occlude the urethra around the catheter. Indications for a retrograde urethrogram include evaluation of urethral stricture disease (including location and length of a stricture), assessment for foreign bodies, evaluation of penile or urethral penetrating trauma, and evaluation of traumatic gross hematuria [12].

A voiding cystourethrogram is performed to evaluate the anatomy and physiology of the bladder and urethra. The study provides valuable information regarding the posterior urethra in pediatric patients and has long been used to demonstrate vesicoureteral reflux.

Voiding cystourethrogram may be performed with the patient supine or in a semi-upright position using a table capable of bringing the patient into the full upright position. A preliminary plain pelvic radiograph is obtained. In children, a tube (8 French or smaller) is used to fill the bladder to the appropriate volume, as determined by the radiologist's needs and patient comfort. In the adult population, a standard catheter may be placed and the bladder filled to 200–400 mL. The catheter is then removed and a film is obtained. During voiding, anteroposterior and oblique films are obtained. The bladder neck and urethra may be evaluated by fluoroscopy during voiding. Bilateral oblique views may demonstrate low-grade reflux, which is not able to be appreciated on the anteroposterior film. In addition, oblique films will demonstrate bladder or urethral diverticula, which are not always visible in the straight anteroposterior projection. Post-voiding films should also be performed [12].

Indications for a voiding cystourethrogram include evaluation of the urethra, possible reflux, and structural and functional bladder outlet obstruction. There are certain limitations with a voiding cystourethrogram. Using a catheter may be traumatic in children and difficult in some patients with anatomic abnormalities of the urethra or bladder neck. Filling of the bladder may stimulate bladder spasms at low volumes, and some patients may be unable to hold adequate volumes for investigation. Bladder filling in patients with spinal cord injuries higher than T6 may precipitate autonomic dysreflexia [12].

The use of unenhanced CT imaging is now the standard diagnostic tool to evaluate renal colic. It offers the advantage over IV urography of avoiding contrast and enabling diagnosis of other abdominal abnormalities that can cause pain. Multi-dose CT scan can readily diagnose radiolucent stones, which may not be seen on IV urography, as well as small stones, even in the distal ureter. With the exception of some indinavir stones, almost all renal and ureteral stones can be detected on helical CT scan. In the detection of urolithiasis, unenhanced CT has a sensitivity ranging between 96% and 100% and specificity ranging between 92% and 100% [12].

Stones in the distal ureter can be difficult to differentiate from pelvic calcifications. In these cases, the urologist will look for other signs of obstruction indicating the presence of a stone, including ureteral dilation, inflammatory changes in the perinephric fat, hydronephrosis, and a soft tissue rim surrounding the calcification within the ureter. The soft tissue rim around a stone represents irritation and edema in the ureteral wall [12].

The National Cancer Institute has created a grading system for radiation dermatitis (Table 1) [28]. A single-site acute skin dose between 0–2 Gy will usually cause no observable effects. A dose between 2–5 Gy will produce transient erythema within two weeks. There will be some hair loss within 8 weeks, with recovery of hair lost within 52 weeks with no expected long-term effects. With slightly higher doses (5–10 Gy), some erythema and permanent partial hair loss may be observed after 56 weeks. Long term, patients exposed to 5–10 Gy may notice permanent dermal atrophy and/or skin induration.

A radiation dose between 10–15 Gy will cause transient erythema within two weeks. Within eight weeks, one may note erythema, hair loss, and desquamation. After eight weeks, prolonged erythema and permanent desquamation are often noted. Long term (≥40 weeks), telangiectasia, dermal atrophy, and induration may be present.

A radiation dose greater than 15 Gy will almost certainly cause transient erythema. At these high doses, acute ulceration and edema may develop. Up to eight weeks post-injury, erythema, hair loss, and moist desquamation may be present. After 8 weeks and up to 52 weeks, dermal atrophy accompanied by ulceration (due to the failure of moist desquamation to heal) is likely. Finally, dermal necrosis may make the need for a surgical intervention inevitable.

The Joint Commission identifies prolonged fluoroscopy with a peak skin dose greater than 15 Gy to a single field over a period of six months as a sentinel event [29]. However, the American Association of Physicists in Medicine has requested that the definition of this sentinel event be modified, because they challenge the Joint Commission implication that the radiation dose is always unexpected and preventable [30]. In some cases, a life-saving measure may require radiation doses that exceed the 15-Gy threshold. In addition, this level could be attained if a patient has had prior procedures requiring radiation to be delivered to the same area.

Ionization Chamber Dosimeter

The ionizing chamber dosimeter includes a gas-filled cavity with positive and negative electrodes with a voltage applied. Ionization chambers measure the amount of radiation passing through the cavity. The chamber is connected through a cable with an electrometer to make the measurement. Ionization chambers are the reference dosimeters for radiology and can be used for quality assurance and cross-calibration of other dosimeters. The International Atomic Energy Agency recommends two types of ionization chambers for use in radiology: cylindrical or plane-parallel chambers [32].

Diode Dosimeter

The diode dosimeter consists of diodes that are more sensitive and have a smaller size compared to ionization chambers. The irradiation of a semiconductor induces electron-hole pairs, causing the junction to become conductive and produce a current, which in turn increases with the rate of electron-hole pair's production [32]. The diode shows some energy dependence, with a variation in dose response with temperature, dose rate, and angular incidence with the beam [32].

Metal-Oxide Semiconductor Field Effect Transistor Dosimeter

The metal-oxide semiconductor field effect transistor (MOSFET) dosimeter is a miniature silicon transistor with higher sensitivity and energy dependence. The disadvantage of the MOSFET is that it is visible in radiographs [32]. It is recommended to read the MOSFET signal during the first 15 minutes after irradiation.

Diamond Dosimeter

The diamond dosimeter is well-suited for in vivo measurements because of its small size, tissue equivalence, and resistance to radiation damage. These dosimeters have been evaluated and used for proton therapy, stereotactic radiosurgery beams, and megavoltage x-ray fields [32]. However, if a diamond dosimeter is used for low-energy x-ray, correction factors are necessary to estimate dose rate and energy.

Optical Fiber Dosimeter

Optical fiber dosimeters detect the light resulting from the irradiation of a plastic scintillator. The light (scintillation photon) is guided and transmitted from the sensitive element to a photomultiplier tube via a transmission fiber, and then the signal is analyzed by a computer. The use of a photomultiplier tube allows a real-time monitoring of the light output from the dosimeter.

The main disadvantage of the optical fiber dosimeter is the noise signal produced in the light-guide by Cerenkov radiation for higher megaelectron volt and fluorescence for low-energy x-ray beam. Optical fiber dosimeters can be used from 10 mcGy/minute with ophthalmic plaque dosimetry to about 10 Gy/minute for external beam dosimetry. This dosimeter has no significant directional dependence and does not need correction factors for temperature or pressure [32].

Thermoluminescent Dosimeter

Thermoluminescent dosimetry is based on the physical property of certain crystals to emit light when they are heated after having been irradiated. The quantity of light is proportional to the energy deposited during irradiation. The detection system consists of a heating component and a light measurement device. Dosimeters most commonly used in medical applications are based on lithium fluoride doped with magnesium and titanium, because of its tissue equivalence and high sensitivity. These dosimeters can be used to measure doses ranging from 10 mcGy to 10 kGy [32].

Optically Stimulated Luminescence

OSL is based on a similar principle to that of the thermoluminescent dosimeter. Instead of heating, the light from a laser is used to release the trapped energy and generate the luminescence. The most common OSL dosimeter is aluminum oxide coated with carbon. If appropriately instrumented, the OSL can deliver the dose information immediately after the irradiation, in conditions close, but not equal, to real-time measurements [32].

All medical radiation workers are required to participate in a facility-based radiation dosimetry monitoring program. Regulations regarding these programs vary from state to state, but generally, an imaging service that may result in the operator or exposed staff receiving more than 10% of the yearly allowable maximum radiation exposure will necessitate the use of radiation dosimeters [7]. Typically, workers are issued dosimeters to be worn outside the lead apron at neck level. These dosimeters record a dose that approximates that of the exposed head and neck. Some programs also include a second dosimeter to be worn under the lead apron at the waist level to serve as a proxy for the gonadal dose. Worker dosimeters are read at monthly intervals. Doses that exceed permissible levels are followed up by the facility's radiation safety office. Follow-up measures may include recommendations regarding a change in work habits or a change in shielding methods [5].

Thyroid shields and leaded glasses are optional pieces of protective equipment, but in very busy or higher exposure environments, they may be required. The quality and condition of the radiation safety protective wear for the staff, visitors, patients, and family members should be regularly assessed. Records should be kept of the initial x-ray inspection of a new shield by radiation safety staff, assignment of a unique inventory identifier of the shield, yearly visual evaluation by the local user or staff, and any notifications of suspected defective equipment.

Any patient who receives a significant radiation dose during a fluoroscopic procedure should be followed up after the procedure and should receive written radiation follow-up instructions upon discharge. The patient should be instructed to notify the fluoroscope operator or the medical physicist after discharge in case of the development of signs or symptoms of adverse radiation effects. A medical physicist should review the dosimetry of the procedure performed in these cases. In circumstances in which the same anatomic area has been irradiated in the previous 60 days, follow-up should be performed at lower radiation doses.

Standards for patient follow-up have not been established with respect to monitoring for potential fluoroscopy-induced skin injury. Multiple factors contribute to this lack. First, significant skin injury is rare, even in patients who have undergone long fluoroscopically guided procedures. Second, there is no clear evidence that early intervention changes outcomes when injury does occur. Finally, practitioners are reluctant to alarm patients when they have no clear recommendations for management of such an injury. In an ideal postprocedural setting, the patient should know that the procedure was medically necessary and performed in a way that optimizes the risk/benefit ratio, should be told that development of a rash in the region that was imaged could be due to radiation exposure, and should be instructed to call the interventionalist if a rash or irritation occurs. The interventionist's responsibility is to then refer the patient to a dermatologist or plastic surgeon who is aware that radiation injury is a possibility and can incorporate that information into treatment planning. Biopsy of a radiation injury should be avoided because it may not heal well [5].

All institutions accredited by the Joint Commission are required to perform safety inspections of radiologic equipment at least yearly [39]. State and local governments may have more stringent requirements and retain the right to conduct public health inspections and examine x-ray-producing equipment, the records associated with their continued use, and the maintenance provided.

Hospital facilities with large radiology, nuclear medicine, and/or radiation oncology departments are likely to have medical physicists on staff to perform equipment inspection tasks and to ensure that patient images are of the highest possible quality. A preventive maintenance program will also identify any equipment that is failing to perform as intended. This is essential for the safe and accurate diagnostic imaging services of the institution and is a valuable resource to the clinicians and the technologists who image patients [7].

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.

Based on animal studies, malformations after in utero exposure to radiation doses less than 100 mSv are not expected. Central nervous system malformations may appear if a dose threshold of 100 mSv has been exceeded. Fetal doses of 100 mSv or higher, especially if incurred between 8 and 16 weeks' gestation, can be associated with reduction of intelligence and microcephaly. As an example, in victims exposed to in utero radiation during the 1945 atomic bombing of Hiroshima, the risk of intellectual disability has been estimated to be about 0.04% per mSv of exposure, with an estimated loss of 2 to 3 IQ points per mSv [40].

It has been shown that prenatal exposure at high doses of radiation is associated with deterministic effects. In the first two weeks after conception, when the number of cells is small, radiation can terminate the pregnancy or the conceptus can recover completely (an all-or-none effect). During this early period of gestation, the blastocyte or embryo has a decreased sensitivity to teratogenic effects and a greater degree of sensitivity to the lethal effects of irradiation. A reversal of these effects is observed in the organogenesis period, from the 3rd to the 8th week after conception. Because of the high sensitivity to teratogenic effects during this period, the most likely form of damage is malformation of the organs of the fetus. As has been observed in the offspring of the survivors of atomic bomb detonations, there is a risk for microencephaly, about 1 in 100 per centigray (cGy) (1% per rad). From the 8th to 15th week of gestation, there is a potential for intellectual or developmental disability; the risk is about 4 in 1,000 per cGy (0.4% per rad). After the 16th week, the central nervous system becomes less radiosensitive. During the last trimester, major organ malformations and functional anomalies are unlikely.

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.

Stochastic effects should be considered, but the risk for cancer from prenatal radiation exposure at low doses remains a controversial issue. Case-control studies and several studies of twins have shown an increased risk for childhood leukemia after in utero irradiation, but cohort studies have not supported this association [41]. The power of epidemiologic studies is usually not sufficient to demonstrate the existence of these effects in exposed populations.

If the conceptus absorbed dose is 50 mGy (5 rad), the risk for childhood fatal cancer is 0.3%. This value, however, coincides with the natural risk for fatal childhood cancer, which is also about 0.3%. Therefore, fatal childhood cancer risks after pelvic procedures (e.g., barium enema, CT scan) are similar to the natural incidence of fatal cancer before 15 years of age. The risk for carcinogenesis due to radiation exposure is relatively low for conceptus doses less than 100 mGy (10 rad). At doses greater than 100 mGy, both deterministic and stochastic effects of radiation should be considered [41].

Studies have also been carried out to investigate the possible effects on the children of personnel exposed to ionizing radiation occupationally. Some researchers found a borderline increase of chromosomal anomalies other than Down syndrome in the children of female radiographers, but Doyle et al. found no evidence of an association between exposure to low-level ionizing radiation before conception and increased risk for malformations in the offspring of staff members working in the nuclear industry [41,42].

Based on federal law, a pregnant woman can choose to continue to receive occupational radiation exposure at the level allowed for adult workers. However, it is recommended that an occupationally exposed pregnant woman declare pregnancy for the purpose of reducing the risk to the unborn child. After pregnancy is declared, additional precautions should be adopted to protect the fetus and limit the radiation exposure to recommended levels [40].

When an expectant mother is a radiation worker, her occupational radiation is monitored in accordance with radiation protection regulations. There is a difference in the dose limits for the unborn in the United States and those set by the ICRP. The ICRP states that "the working conditions of a pregnant worker, after declaration of pregnancy, should be such as to ensure that the additional dose to the embryo/fetus would not exceed about 1 mSv during the remainder of the pregnancy" [43]. In the United States, federal regulations pertinent to nuclear radiation require licensees to ensure that the dose to an embryo or fetus during the entire pregnancy due to the occupational exposure of a declared pregnant woman does not exceed 5 mGy (500 mrad) during the gestational period [44]. Many state regulations extend these requirements to x-rays, and some place additional restrictions on the dose (equivalent) that a declared pregnant woman may receive during a one-month period (one-tenth of the limit). Although the dose limits for the conceptus of a pregnant staff member differ among radiation protection agencies, most countries and institutions have in place radiation protection programs to address the needs of pregnant personnel. The education and counseling of a woman who formally declares her pregnancy in writing is the most important element of a program designed to protect the conceptus of an occupationally exposed worker.

In the fluoroscopy environment, one method of planning the protection of pregnant personnel (interventionalists in particular) is to measure air kerma rates separately for each projection of a fluoroscopic procedure. This information may aid in establishing an acceptable workload per week and for the entire pregnancy. This method, however, may be impractical in some circumstances, for example, for a general interventionalist who performs a broad range of procedure types and whose workload may not be easy to adjust because of staffing constraints and patient care demands. Another approach to reducing occupational exposure is to gather dosimetry information before pregnancy and use it in planning shielding methods to be used during pregnancy. A worker planning pregnancy can request a radiation dosimeter (if she is not already assigned one by her facility) to wear under the lead apron to acquire data about her radiation dose before pregnancy. She may use the information to adjust her workload, shielding, or work habits.

Modifications in shielding to reduce dose, even in instances in which dose reduction may not be strictly necessary from a regulatory standpoint, could include, in extreme circumstances, increasing the thickness of lead aprons from 0.5 mm to 1.0 mm lead equivalent or using additional boom-mounted, floor-mounted, or patient-mounted protective shielding to reduce scatter. The latter options have the advantage of not adding to the weight carried by pregnant workers. Real-time dose information with an audible radiation monitor could be included in a radiation protection program, in addition to standard dosimetry badges read monthly, to provide immediate feedback as to the effectiveness of radiation protection measures.

There are some data to support the contention that a 1-mGy fetal dose limit is feasible for full-time interventional fluoroscopy physicians. In a study of 30 interventional radiologists, readings from waist-level dosimeters worn under a lead apron for a two-month period ranged from 0.02 mSv to 0.39 mSv (2 mrem to 39 mrem). The projected yearly dose equivalent at the waist under lead for this study group was estimated to be 0.22–4.11 mSv (22–411 mrem) for a 10.6-month work-year. Substantial differences in the average projected yearly dose value related to lead apron thickness were noted, with 0.4 mSv (40 mrem) and 1.3 mSv (130 mrem) noted for persons wearing 1.0-mm and 0.5-mm lead equivalent aprons, respectively. These data suggest that additional radiation protection above the standard 0.5-mm lead equivalent apron may be warranted for some workers in the interventional radiology environment [41].