Conducting the Fluoroscopic Examination & Basic Operational Procedures Based on: Syllabus on Fluoroscopy Radiation Protection, 6th Rev. By: Radiologic Health Branch – Certification Unit PPT created by: Jed Miles, BSRS, RT(R), CRT-CA

Introduction Several facts and information should be kept in mind when operating a fluoroscope Operator radiation dose to scatter radiation is directly proportional to patient radiation dose Image brightness is directly proportional to the radiation dose rate at the input phosphor Technical factors used when conducting a fluoroscopic examination are really a compromises between image quality and patient radiation dose Each selected factor will never be optimal for both image quality or patient radiation dose at the same time

Introduction Technical factors that “directly” influence the radiation dose rate at the panel or tabletop and consequently the dose rate to both the patient an operator Milliamperage (mA) Kilovoltage (kVp) Collimation Filtration Exposure time Target-panel distance These technical factors will be discussed on the next several slides Further detail and examples are discussed in the Syllabus

Milliamperage (mA) Milliamperage as a measure of tube current directly affects the intensity or quantity of x-ray being emitted from the tube As x-ray output is directly proportional to a chosen mA setting, it can be deducted that a reduction from 5 mA to 3 mA will reduce the beam intensity by 40% Conversely, increasing the mA will directly increase the dose rate (beam intensity) to the patient and input phosphor and create brighter image due to increased electron flow within the image intensifier Increased dose to patient also directly increases scatter and subsequently dose to operator Collimation will improve image quality due to limiting scatter, but will not change image brightness because the automatic brightness control (ABC) will adjust the mA to an optimal level

Kilovoltage (kVp) Kilovoltage peak (kVp) is a measure of x-ray tube potential which determines the quality or penetrating ability of the x-ray beam Selection of the proper kVp is critical so that the “effective” kV range will produce maximum differential absorption by the tissue thus enhancing subject contrast An increase in kVp will tend to reduce patient/operator dose due to the ABC reducing the mA. However, subject contrast will be decreased Increasing kVp will slightly increase internal organ dose rate due to increased internal scatter, but it is more than offset by a marked decrease in patient skin dose

Collimation Radiation dose rate at the input phosphor is almost independent of the beam size The image will not become brighter with an increasingly open x-ray field, again due to the ABC However, the total volume of the patient that is exposed will increase and subsequently the exposure to the operator by scatter radiation During fluoroscopy, the field size should be restricted to the smallest size practicable for the given exam Increasing the exposure area also increases patient dose If the exposure area is doubled in size the total patient “integral dose” will also double

Integral Dose Defined as the “Total energy absorbed from the beam by the patient” The integral dose to a mass of tissue is the product of the mass of tissue and the dose which it receives The unit of integral dose is the “gram rad” 1 gm rad = 100 ergs ****Using the mathematical example given in the syllabus, one can easily see that using good collimation will both decrease the patient’s absorbed dose and increase image quality by limiting scatter to the image receptor (in this case the image intensifier)

Filtration The main purpose of a filter is to reduce the number/amount of lower energy photons from reaching the patient These low energy photons would never reach the image intensifier an contribute to image production, but would increase the patient’s absorbed dose Appropriate filtration in terms of aluminum equivalency are: Up to 125 kVp // 2.5 mm Al (equivalency) Over 125 kVp // 3.0 mm Al (equivalency) Appropriate primary beam filtration will also Reduce scatter radiation Improve image quality

Filtration Regulatory Requirements Total filtration of an x-ray beam includes both an inherent and add filtration Inherent filtration includes the glass window of the x-ray tube where the useful beam exits the tube Added filtration includes sheets of metal (usually aluminum) placed in the direct path of the useful x-ray beam

Filtration Regulatory Requirements Regulations require total filtration is permanently placed in the path of the beam at normal operating voltages may not be less than 2.5 mm Al equivalency Normal operating voltages for average adult patient vary between 80-120 kVp, this requirement may be “assumed” to met if the half-value layer is not less than 3.0 mm Al equivalency Regulations state that the intensity of the x-ray beam as measured at the tabletop of a fluoroscope “should not exceed 2.2 rads/min for each mA of operating tube current at 80 kVp”

Half-Value Layer (HVL) The quality or energy of an x-ray beam is “characterized” by the half-value layer (HVL) HVL is defined as the thickness of absorbing material necessary to reduce the x-ray intensity to half its original value This concept is also used in shielding were lead is used as the material of choice Example: In order to reduce 200 millirads/min radiation dose rate to 50 millirads/min, enough attenuating material to create two HVL’s would be used

Exposure Time X-ray beam “on” time obviously exposes a patient to radiation and as such should be kept to a minimum Doubling the exposure time will also double the radiation dose the patient receives Usually the x-ray beam on time does not need to be “on” continuously, but rather a series of short “looks” can be sufficient Example - assuming a beam intensity of 5 rads/min 5 “looks” at 12 seconds each would equal 60 seconds or 1 minute of exposure equaling 5 rads Each 12 sec “look” would equal roughly a 400 millirad dose the patient (500 millirad / 12)

Exposure Tine All fluoroscopy systems have a cumulative timer which must be manually reset after 5 minutes of fluoroscopy x-ray beam “on” time Timer may either Produce an audible signal or Temporarily interrupt the x-ray beam This timer mandate is designed to protect the patient by making sure the fluoroscopist is aware of the x-ray beam “on” time during each procedure Make sure you know and understand how to calculate the mathematical examples given in this section as they will be asked on the exam!!!

Allowable Exposure Rates For routine fluoroscopy, the dose rate measured at the panel or tabletop shall be as low a practicable and may not exceed 5 rads/min This limit does not apply during magnification procedures where decreased field size limits electron flow – Thus the ABS will increase the tube current This limit does not apply when a post intensified image is being recorded However, fluoroscopic equipment manufactured after August 1, 1974 fall into different categories as listed on the next slide

After August 1, 1974 Fluoroscope equipped with automatic exposure rate controls May operate up to but not over 10 rads/min unless recording or using when using the optional “boost” position If a “boost” or high level output control is provided, then the fluoroscope may not operate over 5 rads/min unless the boost is manually activated Remember the boost or high level must be activated manually and produce an audible signal during operation

After August 1, 1974 Fluoroscope equipped without automatic exposure rate controls May operate up to but not over 5 rads/min unless recording or using when using the optional “boost” position If a “boost” or high level output control is provided, then the fluoroscope may not operate over 5 rads/min unless the boost is manually activated

Allowable Exposure Rates Devices which display the operating tube potential (kVp) and tube current (mA) must be located where the operator can see them California law states: “For fluoroscopes with automatic exposure control (automatic brightness control), the operator must monitor the x-ray tube current and potential at least once each week with a designated phantom in the beam during use to ascertain that they are in the normal range for a given set of operating parameters.” California law states: “Logs must be kept of all monitored readings.” These requirements are your weekly “fluoro checks”

Allowable Exposure Rates The previously mentioned California State requirements of dose rate measurement must also be made by a health or medical physicist At least once each year for units equipped with automatic exposure control (ABC) At least once each 3 years for units without automatic exposure control (ABC) Also, the physicist must check any fluoroscope that has received any alteration or replacement of a major component, such as a new x-ray tube, exposure controls, image intensifier tube, or new generator For cineradiography fluorographic equipment, a physicist must check the dose rate every year – due to the increased cumulative dose rates received by the patient

Target-to-Panel Distance (TPD) Target-to-panel distance is only an over the table tube or portable C-arm concern as under-the-table tubes are fixed in position Cross referencing to page 6 of the syllabus states TPD is a concern for both under and over table tubes – bottom line is the tube to skin distance is the real issue Shorter TPD distances results in greater skin doses to the patient and greater image distortion (pincushion and magnification) Assuming the same x-ray beam intensify is used for two exposures, increasing the TPD from 12 to 18 inches will reduce the entrance skin dose by 30%

Target-to-Panel Distance (TPD) California Regulations state: “The target-to-panel or target-to-tabletop distance should not be less than 18 inches and shall not be less than 12 inches The technologist must clearly understand that while the target (tube) distance can be varied when using a c-arm, the image intensifier should be positioned as close as possible to the patient to reduce the entrance skin dose Moving the tube closer will not increase image brightness as the automatic brightness control (ABC) will compensate to maintain a consistent image brightness as all times

Indirect Influence by Technical Factors Technical factors that “indirectly” influence the radiation dose rate at the panel or tabletop and consequently the dose rate to both the patient an operator Lighting in the fluoroscopy room Poor image receptor quality Low absorption tabletop These technical factors will be discussed on the next several slides Further detail and examples are discussed in the Syllabus

Lighting in the Fluoroscopy Room First, a an excerpt regarding human vision The human eyes contains two types of light receptors (human image receptors) in the retina Cones: Function in daylight or photopic levels of brightness Perceive color and are located on the center or the retina and thus visual acuity is best in central visual areas Rods: Function in night or scoptopic level of brightness Perceive only gray scale tones and located on the periphery of the retina and thus dimly lit objects are best observed using peripheral vision Fact: Visual acuity of photopic vision is about 10 times better than scotopic vision

Lighting in the Fluoroscopy Room Normal viewing distance using human binocular vision is about 12-15 inches for a 15-20 inch TV monitor Thus the monitor should be moved closer to the observer to perceive the detail present in the image – it is too close if you can see the raster lines of the monitor… The time required by the eye for recognition of an image is 0.2 seconds If a light burst is shorter than this time – you may not perceive it existed If a strobe light is blinked faster that 0.2 seconds you will perceive it to be a solid light Consequently, if a fluoroscopic image is not bright enough for diagnostic purposes, prolonged observance or staring at it will not improve it…

Lighting in the Fluoroscopy Room Now to the point - provisions must be made to eliminate extraneous light that interferes with the fluoroscopy examination Visual acuity of retinal rods (scotopic vision) is poor compared to that of retinal cones which require daylight (photopic) levels of light in order to function Fact: Photopic (cone) visual acuity is about 10 times greater than scotopic (rod) acuity For this very reason, image intensifier were created – to intensify the image in order to bring brightness levels into the photopic visual range

Lighting in the Fluoroscopy Room When conducting the fluoroscopy examination the room lighting should be dim to enhance visualization of the black and white TV image Excessive room light will decrease visual acuity and cause the image to appear dim This may cause the operator to change the technical factors to increase image brightness – this then is considered an indirect influence effecting patient dose

Poor Image Receptor Quality Inadequate image receptor system (i.e. the image intensifier in this case) If it is old thus having a poor conversion gain Is not finely tuned to produce the best image If these conditions exist, this may cause or require the operator to increase the kVp or mA thus increasing the exposure to the patient and operator This again is considered an indirect effect of technical factors that will increase the dose rate to the patient and operator

Low Absorption Tabletop The Aluminum equivalence of the tabletop may not be more than 1.0 mm This is true for both when a cassette tray is used under-the-tabletop and for the front panel of a vertical cassette holder Carbon fiber tabletops, which are very radiolucent, serve well to reduce patient radiation dose rates Due to less overall exposure being required to properly expose the image receptor be it a film/screen, imaging plate, or image intensifier Again, this is considered to have an indirect influence on the technical factors used to conduct a fluoroscopy examination

Bucky Slot Cover Regulation: When using a stationary fluoroscopy unit (R&F room) with an under-the-table x-ray tube, the cassette tray is moved and parked at the end of the exam table This leaves a two inch wide opening where the bucky tray is, nearly at the height of the gonads when standing at the side of the table This opening must have an automatic covering of at least 0.25 mm lead equivalent material If one looks inside the bucky tray opening when moving the tray to the end of the table, you will see a shield automatically slide into place providing a shield

Three-Phase / High-Frequency Generator There are certain technical advantages of three-phase and high frequency generators as compared to single-phase generators Near constant tube potential High mA available for very short exposure times This is useful for angiographic studies and spot film radiography to eliminate motion Higher effective kVp Due to not having to ramp up the kVp from zero in each phase…the kVp potential is held or kept near the peak value

Basic Operation Procedures Operators of fluoroscopy equipment must reduce unnecessary radiation dose to the patient, themselves and others by observing and following these operational procedures Carefully read and understand Chapter V in the syllabus – questions will be asked regarding these procedures and provisions… This includes both stationary and mobile fluoroscopy equipment

Next up… Gonadal Shielding & Radiation Safety