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Fluoroscopy: Patient Radiation Exposure Issues¹

¹ From The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, 601 N Caroline St, Baltimore, MD 21287. From the AAPM/RSNA Physics Tutorial at the 1999 RSNA scientific assembly. Received February 16, 2001; revision requested March 29 and received April 19; accepted April 23. Address correspondence to the author (e-mail: mmahesh@jhmi.edu).

	Abstract

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

 
Fluoroscopic procedures (particularly prolonged interventional procedures) may involve high patient radiation doses. The radiation dose depends on the type of examination, the patient size, the equipment, the technique, and many other factors. The performance of the fluoroscopy system with respect to radiation dose is best characterized by the receptor entrance exposure and skin entrance exposure rates, which should be assessed at regular intervals. Management of patient exposure involves not only measurement of these rates but also clinical monitoring of patient doses. Direct monitoring of patient skin doses during procedures is highly desirable, but current methods still have serious limitations. Skin doses may be reduced by using intermittent exposures, grid removal, last image hold, dose spreading, beam filtration, pulsed fluoroscopy, and other dose reduction techniques. Proper training of fluoroscopic operators, understanding the factors that influence radiation dose, and use of various dose reduction techniques may allow effective management of patient dose.

Index Terms: Dosimetry • Education • Fluoroscopy • Physics • Radiations, exposure to patients and personnel • Radiations, injurious effects • Radiations, measurement

	Introduction

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

 
Since the early 20th century, fluoroscopy has been integral to the practice of diagnostic radiology. For the most part, fluoroscopic procedures were primarily diagnostic and involved relatively small risks to patients and personnel. However, over the past 10–15 years, fluoroscopic procedure mixes have included an increasing fraction that are primarily therapeutic. Because these procedures are often technically difficult, they can involve total exposure times exceeding an hour or more. The number of prolonged fluoroscopic procedures performed in the United States has increased dramatically over the past 10 years. This phenomenon is partially driven by the preference of managed care to use methods that are less invasive and less costly than surgery. For example, an estimated 300,000 coronary angioplasty procedures were performed in the United States in 1994 (1). It is likely that the current number of procedures has increased by a factor of two or more. A wide range of other fluoroscopically guided procedures, such as neuroembolization, placement of transjugular intrahepatic portosystemic shunts, and pain management, have also shown considerable growth. The nature of these prolonged fluoroscopic procedures has led to an increase in reports of high skin doses causing significant tissue injury.

In response to the problem, the Center for Devices and Radiological Health of the Food and Drug Administration (FDA) issued an advisory in 1994 (2) warning health care facilities of the potential for radiation-induced burns to patients from prolonged fluoroscopic procedures. According to the advisory, a number of interventional procedures (Table 1) have the potential to cause skin injury even when the fluoroscopic time is 1 hour or less at normal dose rates. An insidious aspect of the problem is that onset of injury is delayed and the extent of damage may not be evident until weeks after the procedure. Approximately 50 injuries were reported to the FDA in 1994 alone (1), and since then the FDA has documented many more cases of radiation-induced burns (3). A number of case histories of injuries to both patients (4–7) and physicians (8) have subsequently appeared in the literature; some of the radiation-induced wounds have required skin grafts, resulting in permanent disfigurement. The actual extent of the problem is essentially unknown, since there are currently neither requirements for reporting nor a central repository for this information.

	Biologic Effects of Radiation

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

 
Biologic effects of radiation can be broadly grouped as stochastic or nonstochastic effects. A stochastic effect is one in which the probability of the effect, rather than its severity, increases with dose. Radiation-induced cancer and genetic effects are stochastic. For example, the probability of radiation-induced leukemia is substantially greater after exposure to 1 Gy (100 rad) than after exposure to 1 cGy (1 rad), but there will be no difference in the severity of the disease if it occurs. Stochastic effects are believed to lack a threshold dose because injury to few cells or even a single cell could theoretically result in production of the effect.

On the other hand, there are other effects for which the probability of causing certain types of harm will be zero at small radiation doses. Above some threshold level, damage will become apparent, with severity increasing as dose rises above the threshold. Such effects are called nonstochastic or deterministic effects. Cataracts, erythema, epilation, and even death are examples of the deterministic effects that can result from high radiation exposures.

Except in the early days of radiology, when precautions were few, the emphasis in radiation safety has been on stochastic effects. The recent popularity of prolonged interventional procedures has added concern about deterministic effects. Since, at diagnostic x-ray energies (eg, those for fluoroscopy, radiography, computed tomography, and angiography), doses are highest at the beam entrance point, the most commonly observed harm has been skin tissue damage and hair loss. Table 2 summarizes some of the skin reactions and their dose thresholds (9).

Although other factors are important, the performance of a fluoroscopy system with respect to radiation dose is best characterized by the receptor entrance exposure rates and skin entrance exposure rates. In addition, exposure rates are dependent on the patient thickness and operational factors; hence, it is becoming increasingly apparent that some sort of dynamic patient dose monitoring is desirable during extended fluoroscopic procedures.

	Receptor Entrance Exposure Rates

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

 
The receptor entrance exposure rate is arguably the most important dose performance parameter. Receptor entrance exposure measures the effective "speed" of the imaging system, that is, the amount of radiation used in image formation. The receptor entrance exposure is critical because skin dose is dependent on and increases with increasing receptor entrance exposure and because the level of image noise, and thus the perceptibility of low-contrast detail, is also dependent on it. Despite the critical importance of this parameter, there are no regulations limiting receptor entrance exposure rates, although x-ray system manufacturers generally set receptor entrance exposure values to comparable levels for similar imaging modes (10).

Receptor entrance exposure is normally specified as the entrance exposure at the surface of the image receptor (with the grid removed) required to produce a single image for a given x-ray spectrum. In the measurement geometry, the ionization chamber is placed 20–30 cm from the image intensifier surface (with a fixed source-to–image intensifier distance of 100 cm) to reduce the backscatter contribution (11) (Fig 1). The exposure rates are corrected to the entrance surface of the image intensifier by using the inverse square law. Receptor entrance exposure rates are measured with the grid removed (12); however, it is often impractical to remove the grid from some systems, in which case the manufacturer-specified grid transmission factor can be used to correct for the presence of the grid (11).

View larger version (21K): [in this window] [in a new window] [Download PPT slide]   Figure 1.   Setup for measuring receptor entrance exposure rates. Constant beam attenuators (aluminum or copper) are placed on the table top or the surface of the collimator (11,12). Measurements are performed by placing the ionization chamber 20 cm from the surface of the image receptor with the grid removed.

	Skin Entrance Exposure Rates

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

The maximum skin entrance exposure value is important, but to obtain a realistic estimate of the level that a patient would receive, a measurement of the average skin entrance exposure is required. Skin entrance exposure values can vary widely with x-ray tube voltage (kilovolt peak) and patient thickness, presence or absence of a grid, source-to-image distance, and so on. As shown in Table 5, an hour of exposure with typical skin entrance exposure rates during normal fluoroscopy and high-dose fluoroscopy can yield a patient entrance exposure of 0.6–3 Gy and 6–12 Gy, respectively. When these values are compared with threshold levels associated with skin injuries (Table 2), it is clear that the potential exists for skin injuries during prolonged fluoroscopic procedures.

	Patient Dose Monitoring Methods

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

 
Average skin entrance exposure measurements can provide an estimate of the skin entrance exposure to a typical patient, and one can use receptor entrance exposure measurements to scale doses from the different imaging modes. For example, one can multiply recorded fluoroscopy time with typical skin entrance exposure values to obtain a rough estimate of skin dose. The estimate can be improved to some extent by recording the average kilovolt peak and tube current (milliamperage) for the patient and appropriate scaling of the skin entrance exposure. This technique has been commonly reported in research surveys (15–18) but in practice is subject to considerable error. Even if parameters are correctly recorded, variations in patient size, imaging modes, and other factors make these estimates less reliable. This method provides a rough estimation of patient dose for very simple procedures but can be misleading if multiple views are involved, as is the case in any standard fluoroscopic examination. In such cases, this method can produce either an underestimate or overestimate of the patient skin dose. Real interventional procedures are often complex and may involve dynamic changes in field size, geometry, position, kilovolt peak, imaging mode, and so on; moreover, few patients are really "average" in size. In reality, the clinician has no idea of skin dose and cannot tell when doses are reaching harmful levels.

There are currently a number of methods available by which one can estimate or measure patient skin dose; they may be classified as direct or indirect methods. Direct methods involve measurement of skin dose during the procedure by using one of several types of small dosimeters taped to the patient’s skin. Indirect methods involve calculation of skin dose from measurements in the beam or from operational factors that affect dose.

Direct Methods
The direct method of skin dose estimation involves use of small detectors placed on the patient’s skin at the beam entrance location. Several types of detectors have been used, including thermoluminescent dosimeters (TLDs), photographic films (16–19), and, more recently, diodes or metal-oxide semiconductor field-effect transistor (MOSFET) detectors. Use of a TLD is potentially the most accurate way of determining actual skin dose, but results can be very inaccurate because it is often impossible to know exactly where on the skin the peak dose will occur in a given procedure. Use of an array of dosimeters can reduce uncertainty, but this strategy is not always practical. With single dosimeters, considerable care is required to correctly place the dosimeter and to ensure that it is not moved from the field during the procedure. The method requires that the entrance field be known a priori, and, since the x-ray source is usually located beneath the patient table, it requires the patient to lie directly on the detector during the procedure.

Photographic films have several advantages such as low cost, an easy-to-locate high-dose region, and dose measurement by using densitometers. However, there are only a few films available in large sizes that have the sensitivity to measure several ranges of doses. MOSFET detectors have the advantage of providing a dynamic reading of the skin dose as it accumulates during the procedure, but some physicians find them to be objectionable due to the visibility of the detector elements and connecting leads in the image field. Although TLDs are essentially invisible, they are read out after the procedure and cannot provide a dynamic display of dose during the procedure.

Indirect Methods
The most convenient and widely used method for indirect monitoring is the dose-area product (DAP) meter. The DAP meter uses a transmission type air-ionization chamber mounted on the face of the x-ray tube collimator, which integrates exposure over the entire image field. The DAP measurement is a function of the x-ray field size and the x-ray exposure at the collimator; thus, the measurement is expressed as either the dose-area product or the air-kerma-area product (20–24). The measured DAP is independent of distance from the focal spot. The distance factor cancels because the exposure rate varies inversely and the x-ray field area varies inversely as the square of the distance from the focal spot to the point of measurement. A given DAP reading can result from a high dose over a small field or a low dose over a large field. The stochastic risk can be roughly assumed to be equivalent under these two conditions; thus, DAP meters have been used to estimate total stochastic risk for latent effects (14,15). Unfortunately, a high dose over a small field is not equivalent to a low dose over a large field in terms of skin damage; hence, the DAP reading requires some interpretation.

Skin entrance dose can be computed from DAP readings only at a specific dose rate and field size. For example, if a 1-minute fluoroscopic procedure produces a DAP reading of 2,000 µGy · cm², this result could be obtained with a 20 x 20-cm field at 5 µGy/min or a 10 x 10-cm field at 20 µGy/min, a factor of four difference in skin dose. When magnification mode is selected, the input field size is reduced, which results in decreased brightness. The automatic brightness stabilizers on many systems then respond by increasing the x-ray dose to maintain constant image brightness. This process can produce a static DAP reading (Fig 2), even though the skin dose rate scales by a factor of two or more. In situations where dose rate and field size are changing dynamically, accurate estimation of skin dose from DAP readings may be problematic.

View larger version (22K): [in this window] [in a new window] [Download PPT slide]   Figure 2.   Computed dose rate for a constant DAP reading as a function of field diameter.

There is at least one system available that will dynamically record and display an estimate of total skin entrance exposure. This product is based on the fact that skin dose can be predicted from operational factors. This device, currently marketed under the name PEMNET (Clinical Microsystems, Arlington, Va), measures peak kilovoltage, tube current (milliamperage), and exposure time signals from the x-ray generator to dynamically compute and display an estimate of the skin entrance dose based on calibration of radiation output as a function of these parameters (25,26). Some versions have the capability to compensate for attenuation by the table and adjust for oblique angles (26) while providing skin entrance exposure at known distances. However, these systems share a limitation with DAP meters in that dose estimates do not take into account overlapping beams from several sources. The source-to–skin entrance distance is a major uncertainty in the estimate, but some versions incorporate a proximity detector to measure this parameter during the procedure. The complexity of installation required for calibration has hindered widespread use of the system, although it has considerable potential.

Recent reviews by Geise and O’Dea (16) and Strauss (10) have examined the features of currently available skin dosimetry methods and have concluded that currently there is no perfect dose monitoring system for complex interventional procedures.

	Patient Doses for Typical Fluoroscopic Procedures

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

 
Patient doses depend on a number of factors such as machine factors; age, size, and body composition of the patient; and user setup, such as collimation, source-to-skin distance, and so on. The dose rate to the patient is greatest at the skin where the x-ray beam enters the patient. The typical fluoroscopic entrance exposure rate for a medium-sized adult is approximately 30 mGy/min (3 rad/min) (since 10 mGy = 1 rad) but is typically higher in image-recording modes. A number of studies have reported patient doses during diagnostic and interventional procedures (17–24,27–29). Table 6 lists entrance skin doses for a number of diagnostic procedures, in which the fluoroscopic time typically ranges from 3 to 15 minutes (18,20,21) with entrance skin dose ranging from 44 to 340 mGy (4.4–34 rad). Doses for the more complex interventional procedures are listed in Table 7. Diagnostic procedures performed under fluoroscopic control have significantly shorter fluoroscopic times and lower entrance skin doses compared with those of interventional procedures. Mean fluoroscopic times for interventional procedures are significantly longer (17,20,21).

	Dose Reduction Techniques

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

Intermittent Fluoroscopy
Most radiologists are trained to control the fluoroscope intermittently, that is, keeping the x rays on only a few seconds at a time, long enough to view the current catheter position. Judicious use of the method can reduce total fluoroscopic times considerably. This simple technique is particularly effective when combined with last image hold features.

Removal of Grid
The presence of grids in x-ray systems primarily increases the contrast and hence the image quality; however, they increase the dose to the patient and staff by a factor of two or more. Studies have shown that, especially in pediatric cases, removal of the grid has resulted in dose reduction of up to one-third to one-half with little or no degradations in contrast and image quality (30,31). Grids should be used with discretion when fluoroscopic examinations are performed on children, and the systems for such examinations should have the capability for easy removal and reintroduction of the grid.

Last Image Hold and Electronic Collimation
A useful feature on many modern fluoroscopy systems is last image hold, whereby the last image is digitally "frozen" on the monitor after x-ray exposure is terminated. Last image hold is a dose-saving feature (32), since it allows physicians to contemplate the last image and plan the next move without additional radiation exposure in an interventional procedure. In addition, some modern systems have electronic collimation, which overlays a collimator blade on the last image hold so that one can adjust field dimensions without exposing the patient.

Dose Spreading
In most interventional fluoroscopic procedures, the bulk of the fluoroscopic time is spent at a particular anatomic region during the procedure. For example, in radio-frequency ablation procedures, the fluoroscope is used to guide the catheter from the femoral artery to the heart but thereafter remains over the heart region. Some reduction of maximum skin dose can be achieved by periodically rotating the fluoroscope about a center within the anatomy of interest. This method tends to spread the maximum dose over a broader area of the patient’s skin so that no single region receives the entire dose (Fig 3).

View larger version (29K): [in this window] [in a new window] [Download PPT slide]   Figure 3.   Effect of dose spreading by varying the beam incidence angle. The maximum dose thus tends to be spread over a broader area of the patient’s skin.

Substantial reductions in skin dose are also achieved by inserting appropriate metal filters (aluminum, copper, or other materials) into the beam at the collimator. Filtration reduces skin dose by preferentially removing lower-energy photons, which would not penetrate the patient to contribute to the image. Nicholson et al (33) have shown that the addition of 0.1–0.3 mm of copper reduced the skin dose by 30%–50%. In general, if optional filters have been designed into the fluoroscopy system (eg, Carefilters [Siemens Medical Systems, Iselin, NJ] and Spectrabeam [Philips Medical Systems, Shelton, Conn]), they should be used for all lengthy or repeated examinations provided the image quality is diagnostically acceptable.

Image Magnification
The ability to create magnified images can be clinically very useful but in almost all cases results in a higher patient dose. There are two basic ways to magnify the image in fluoroscopy: geometric and electronic. Geometric magnification takes advantage of the diverging x-ray beam to project a smaller region in the patient to a larger area on the image intensifier. When source-to–image receptor distance is fixed, both image magnification and skin dose increase as the patient is moved closer to the x-ray source (Fig 4). Many interventional system fluoroscopes do not fix the source-to–image receptor distance, and the positions of the tube and the receptor can both be changed independently. Thus, moving the source closer to the patient or the receptor further away can magnify the image. Also, there is increased penumbra (focal spot blur) with higher magnification, and unless a very small focal spot is used (eg, 0.3 mm), the spatial resolution is degraded. It is generally best to minimize geometric magnification in prolonged procedures by keeping the image receptor close to the patient and the source away.

View larger version (34K): [in this window] [in a new window] [Download PPT slide]   Figure 4.   Effect of geometric magnification on entrance skin dose. With fixed source-to-image receptor distance, both magnification and skin entrance exposure (SEE) increase as the patient is moved closer to the x-ray source.

View larger version (21K): [in this window] [in a new window] [Download PPT slide]   Figure 5.   Effect of electronic magnification on entrance skin dose. The radiation dose increases by the square of the ratio of the image intensifier diameters. arb = arbitrary, Mag = magnification.

Pulsed Fluoroscopy
Some modern fluoroscopes have the capability of pulsed fluoroscopy, whereby the x-ray beam is emitted as a series of short pulses rather than continuously. At reduced frame rates, pulsed fluoroscopy can provide substantial dose savings. Images may be acquired at 15 frames per second rather than the usual 30 frames per second. Each image is displayed multiple times in sequence to provide a 30 frames per second display. Pulsed fluoroscopy can also be performed at even lower frame rates (eg, 7.5 or 3 frames per second) at the expense of a "choppy" display when imaging rapidly moving regions like the heart.

Because simply reducing the number of pulses would result in an increase in image noise, manufacturers may increase the milliamperage setting to achieve a similar visual appearance. For example, one would expect a 50% dose reduction when going from 30 to 15 frames per second, but, because of increased milliamperage, the actual dose savings are 25%–28% (Fig 6). With equivalent perceptibility levels, Aufrichtig et al (34) showed average dose savings of 22%, 38%, and 49% at 15, 10, and 7.5 frames per second, respectively. When operating at lower frame rates and higher magnification (decreased field of view), some systems open the television camera aperture instead of increasing the exposure to maintain similar image brightness. Pulsed fluoroscopy has a great advantage as long as the radiation exposure is lower at lower frame rates. If the tube current is set too high to achieve better-quality images, the entire advantage of pulsed operation is defeated and there may be no actual dose savings.

View larger version (25K): [in this window] [in a new window] [Download PPT slide]   Figure 6.   Effect of pulsed fluoroscopy on entrance skin dose. For example, by switching from continuous fluoroscopy (Cont Fluoro) mode to 15 pulses per second, dose savings of nearly 22% are achieved (34).

	Training of Fluoroscopic Operators

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

To date, there are no uniform national standards regarding who may operate fluoroscopy systems or what minimum training they should have (3,36). All resident physicians undergo a credentialing process that involves verification and assessment of their qualifications to ensure that they are appropriately trained to perform clinical procedures with technical proficiency and henceforth grant clinical privileges (3,36). However, none of the credentialing processes mandate that resident physicians, especially those who work with radiation, learn about radiation management in fluoroscopic procedures (36). Except for radiologists and nuclear medicine specialists, most physicians receive minimal to no training in the safe use of ionizing radiation during their residency program. In addition, except for a few boards such as the American Board of Radiology, American Board of Nuclear Medicine, and Royal College of Physicians and Surgeons of Canada (diagnostic radiology), no other medical specialty board includes radiation in the curriculum (36). However, there have been positive developments, as seen in the position statements taken by some prominent organizations such as the American College of Cardiology (37) and American Heart Association (38), strongly advocating education of fluoroscopy users. For example, the American College of Cardiology consensus document, "Radiation Safety in the Practice of Cardiology" (37), clearly stresses the importance of radiation safety and education for everyone using fluoroscopy.

Some state regulations include mandatory education and training in the safe use of x rays. Even if this is not required by law, it is to the advantage of a facility to establish minimum requirements for the safe use of fluoroscopic equipment for all physicians performing fluoroscopy, particularly those performing prolonged interventional procedures. Any training or credentialing process should include education on radiation safety issues, proper use of fluoroscopic equipment, and control settings (35). In addition, biologic effects of radiation with emphasis on deterministic effects should be discussed along with detailed discussions on dose-reducing techniques. The training or credentialing process can be achieved by means of World Wide Web–based short courses, workshops, or tutorials with tests (39,40); by adding study materials to respective board curricula; or by developing institution-based courses. There are a number of sources, such as medical physics textbooks, AAPM reports (35), and medical literature in radiographic physics series, that can help a facility establish a program to train or credential their physicians using fluoroscopy to obtain minimal competency in terms of the safe use of radiation. Enlisting a qualified medical physicist to assist in training fluoroscopy users, as recommended in the FDA advisory (2), can be of great advantage to the facility.

	Conclusions

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

 
With the increased proliferation of fluoroscopy in modern medicine, it is important to effectively manage radiation exposure by properly setting the fluoroscopy system. A number of factors influence patient radiation dose during fluoroscopic procedures. By understanding the factors that affect patient doses, clinicians can help keep doses as low as possible without compromising image quality or the efficacy of interventional procedures. Direct monitoring of patient skin doses during procedures is highly desirable, but current methods still have serious limitations. Effective management of radiation exposures by proper use of equipment, adequate training of fluoroscopic operators, and frequent quality control can contribute to an overall reduction in patient and personnel exposures.

	Acknowledgments

 
Acknowledgments: The author thanks Thomas J. Beck, ScD, for useful discussions during the preparation of the manuscript and the presentation at the 1999 RSNA/AAPM Physics Tutorial for Residents.

	Footnotes

 
Abbreviations: DAP = dose-area product, FDA = Food and Drug Administration

	References

Top Abstract Introduction Biologic Effects of Radiation Receptor Entrance Exposure Rates Skin Entrance Exposure Rates Patient Dose Monitoring Methods Patient Doses for Typical... Dose Reduction Techniques Training of Fluoroscopic... Conclusions References

 

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