Introduction to Fluoroscopy

Introduction to Fluoroscopy
Renée (Dickinson) Butler, MS, DABR Medical Physicist University of Washington Medical Center Department of Radiology Diagnostic Physics Section

General Fluoroscopy: Modes of Operation & System Components
© UW and Renée Butler, MS, DABR

Fluoroscopy vs Projection Radiography
PARAMETER G.I. FLUOROSCOPY RADIOGRAPHY kVp’s mA values 0 - 5 (continuous) (pulsed) X-ray Tube Focal Spot Size mm mm Exposure Duration min (IR: 45+ min) seconds Image Receptor Input Radiation Dose per image mGy / image mGy/image Patient skin Dose Rates mGy / min mGy / image Source-to- Skin Distance (SSD) cm cm Source-to-Image Receptor Distance (SID) cm 100 or 182 cm Typical Spatial Resolution LP/mm (Image Int.) LP/mm LP/mm(Flat Panel) Image Quantum Mottle High Low Staff Exposure to Scattered Radiation Yes No PARAMETER G.I. FLUOROSCOPY RADIOGRAPHY kVp’s mA values 0 - 5 (continuous) (pulsed) X-ray Tube Focal Spot Size mm mm Exposure Duration min (IR: 45+ min) seconds Image Receptor Input Radiation Dose per image mGy / image mGy/image Patient skin Dose Rates mGy / min mGy / image Source-to- Skin Distance (SSD) cm cm Source-to-Image Receptor Distance (SID) cm 100 or 182 cm Typical Spatial Resolution LP/mm (Image Int.) LP/mm LP/mm(Flat Panel) Image Quantum Mottle High Low Staff Exposure to Scattered Radiation Yes No © UW and Renée Butler, MS, DABR c.f. AAPM/RSNA Web Module: Fluoroscopy systems. Section IV. Table1.

Fluoroscopy Modes of Operation
Typical entrance exposure rates to the patient: For thin patients/body parts: dose rate is roughly 1-2 R per min [8.7 to 17 mGy per min] for thin body parts Skin injury threshold in normal mode can be reached in approximately 118 to 230 min For average patient sizes: dose rate is roughly 3-5 R per min [26 to 44 mGy/min] Skin injury threshold in normal mode can be reached in approximately 45 to 77 min For heavy patient sizes: dose rate is roughly 8-10 R per min [70 to 87.3 mGy/min] Skin injury threshold in normal mode can be reached in approximately 23 to 29 min © UW and Renée Butler, MS, DABR

Fluoroscopy Modes of Operation
8.76 mGy per R 14.7 R per min = mGy per min 34.6 R per min = mGy per min 63.1 R per min = mGy per min © UW and Renée Butler, MS, DABR

Web Modules Clinical Applications
What type of configuration is preferred for a urology suite? Why? Kidneys & bladder are closer to the image receptor, therefore, reducing focal spot blur. What is the negative of this room set-up? Because the tube is above the patient, the scatter radiation is projected back into the procedure room; whereas for GI fluoroscopy rooms, the entrance point is below the table and lead shield curtains attenuate the scatter radiation. © UW and Renée Butler, MS, DABR

Web Modules Clinical Applications
Application drives system design Type – under table tube (GI), over table tube (urology), remote rooms (sallow studies), C-arm (mobile used in OR) Number of tubes – IR rooms (PA, lateral) and cath/EP labs (LAO, RAO) could have two tubes Filtration – Al or Cu; contrast study? Extras – ultrasound, display set-up, injectors, software, 3D capabilities, etc. © UW and Renée Butler, MS, DABR c.f. AAPM/RSNA Web Module: Fluoroscopy systems. Section III.A-E.

Fluoroscopy System Components Image Intensifier (II) vs Flat-Panel Detectors (FPD)
© UW and Renée Butler, MS, DABR c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 232.

Fluoroscopy System Components Image Intensifier (II) vs Flat-Panel Detectors (FPD)
Image intensifier system components: II – vacuum bottle (housing); input screen (x-ray to e-); electronic lenses; output phosphor (e-s to visible light) Lenses and aperature Optical coupling w/ accessory port Viewing electronic output image – video or more commonly charged-coupled device (CCD) detectors © UW and Renée Butler, MS, DABR c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 232, 239.

Review Questions For the image intensifier shown, match the following: (answers may be used more than once) A. Light photons. B. X-ray photons. C. Microwaves. D. Electrons. E. Infrared photons. I represents II represents III represents IV represents V represents B. A. D. © UW and Renée Butler, MS, DABR

Fluoroscopy System Components Image Intensifier (II)
In vacuum – electrons (e-s) are influence by environment Input screen – converts x-rays to e-s 1 mm aluminum window creates vacuum Support layer Input phosphor – Cesium Iodine (CsI) crystal; Converts x-rays to light Photocathode – Layer of antimony and alkali metal; emits electrons when struck by light; 10-20% conversion efficiency Electronic lenses – 25 kV – 35 kV electric field between input and output (electronic gain) © UW and Renée Butler, MS, DABR c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 233.

Fluoroscopy System Components Image Intensifier (II)
Output phosphor – converts e-s to visible light Zinc cadmium sulfide (ZnCdS) Anode – thin coating of aluminum on the vacuum side of output phosphor Each e- interacts in the phosphor creating ~1000 light photons Some fraction of the output light emitted by ZnCdS phosphor is reflected at the glass window; known as veiling glare, which reduces image contrast © UW and Renée Butler, MS, DABR c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 233.

Fluoroscopy System Components Flat-Panel Detectors (FPD)
Solid-state devices INDIRECT digital detector Thin, carbon fiber – protects CsI phosphor and photodiode array Input phosphor – CsI converts x-rays to light photons Photodiode array An array of detector elements – each element is 200 microns (0.2 mm) Absorbs light and converts energy into free electron charge that is stored in each cell of the array Charge stored is proportional to the incident light, which is proportional to the # incident (absorbed) x-ray c.f. Granfors & Albagli. Scintillator-based flat-panel x-ray imaging detectors. Journal of the Society for Information Display. June 2009. © UW and Renée Butler, MS, DABR

Patient & Personnel Safety in Fluoroscopy

FPD (or II) close to patient Grid in Collimate!
AAPM/RSNA Resident Physics Curriculum: Module 13: Fluoroscopy & Interventional Imaging Clinical Application Identify the technique factors and appropriate system features to use to optimize image quality while minimizing patient dose. FPD (or II) close to patient Grid in Collimate! Increase SSD (source-to-skin distance) to decrease ESD (entrance skin dose) Note: geometry limitations with shorter personnel © UW and Renée Butler, MS, DABR

Adjust dose settings when possible (pulse) to reduce scatter
AAPM/RSNA Resident Physics Curriculum: Module 13: Fluoroscopy & Interventional Imaging Clinical Application Describe the geometric factors that affect operator dose during an IR procedure. Lead apron Thyroid shield Protective eyewear Radiation badge Adjust dose settings when possible (pulse) to reduce scatter Distance, when possible Shielding, when possible © UW and Renée Butler, MS, DABR

General set-up for angio/IR suites:
AAPM/RSNA Resident Physics Curriculum: Module 13: Fluoroscopy & Interventional Imaging Clinical Application Describe the geometric factors that affect operator dose during an IR procedure – scatter geometry for the frontal and lateral tubes in a NIR suite. General set-up for angio/IR suites: Frontal tube: positioned w/ tube below patient Scatter to personnel minimized by lead drapes Lateral tube: positioned so radiologist is on the same side as the FPD or II Scatter is projected from the skin back toward the x-ray tube Higher scatter for personnel on “tube side” of lateral tube. Use moveable shields! c.f. ZH Anastasian et.al. Radiation Exposure of the Anesthesiologist in the Neurointerventional Suite. Anesthesiology 2011; 114: © UW and Renée Butler, MS, DABR

General set-up for angio/IR suites:
AAPM/RSNA Resident Physics Curriculum: Module 13: Fluoroscopy & Interventional Imaging Clinical Application Describe the geometric factors that affect operator dose during an IR procedure – scatter geometry for the frontal and lateral tubes in a NIR suite. General set-up for angio/IR suites: Frontal tube: positioned w/ tube below patient Scatter to personnel minimized by lead drapes Lateral tube: positioned so radiologist is on the same side as the FPD or II Scatter is projected from the skin back toward the x-ray tube Higher scatter for personnl on “tube side” of lateral tube. Use moveable shields! c.f. ZH Anastasian et.al. Radiation Exposure of the Anesthesiologist in the Neurointerventional Suite. Anesthesiology 2011; 114: © UW and Renée Butler, MS, DABR

Radiation Protection and Fluoroscopy/IR
Bushberg Table Nuclear Regulatory Commission (NRC) Regulatory Requirements: Maximum Permissible Dose Equivalent Limitsa Maximum Possible Annual Dose Limit Limits mSv rem Occupational Limits Total effective dose equivalent (ED) 50 5 Total dose equivalent to any individual organ (except lens of eye) 500 Dose equivalent to the lens of the eye 150 15 Dose equivalent to the skin or any extremity Minor (< 18 years old) 10% of adult limit Dose to an embryo/fetusb 5 in 9 months 0.5 in 9 months Non-occupational (Public) Limits Individual members of the public 1.0 per yr 0.1 per yr Unrestricted area 0.02 in any 1 hrc 0.002 in any 1 hrc a These limits are exclusive of natural background and any dose the individual has received for medical purposes; inclusive of internal committed dose equivalent & external effective dose equivalent (i.e., total effective dose equivalent). b Applies only to conceptus of a worker who declares her pregnancy. If the limit exceeds 4.5 mSv (450 mrem) at declaration, conceptus dose for remainder of gestation is not to exceed 0.5 mSv (50 mrem). c This means the dose to an area (irrespective of occupancy) shall not exceed 0.02 mSv (2 mrem) in any 1 hour. This is not a restriction of instantaneous dose rate to 0.02 mSv per hour (2 mrem per hour). © UW and Renée Butler, MS, DABR c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p791.

Badging – OUTSIDE the lead near the neck/collar Generally, no double badging (except pregnant personnel) Monitors total exposure, eye dose, extremity Total annual limit for occupation radiation worker is 50 mSv/year Total eye lens dose limit is 150 mSv (or 20 mSv; new statement on lens dose by ICRP) per year Lead aprons Lead equivalent = 0.25 mm: absorbs > 90% of scatter Lead equivalent = mm: absorbs % of scatter (but heavier, so is it feasible to wear??) Use a lead thyroid shield at all times Badging – where is it worn? What are we measuring and what doses can be modeled from these measurements? Lead – how it is worn? Thyroid shield? What % of incident exposure is absorbed? © UW and Renée Butler, MS, DABR

Protective gloves 0.5 mm lead of greater should be worn if hands are going to be near but outside the primary beam To protect hands during fluoroscopy, it is recommended: Keep hands out of and away from the x-ray field when the beam is on unless physician control of invasive devices is required for patient care during fluoroscopy Work on the exit-beam side of the patient whenever possible Monitor hand dose Badging – where is it worn? What are we measuring and what doses can be modeled from these measurements? Lead – how it is worn? Thyroid shield? What % of incident exposure is absorbed? © UW and Renée Butler, MS, DABR

Leaded glasses: Recommended that all full-time radiology interventionists and anesthesiologists should wear leaded eye protection NEW!! The ICRP recently released a statement stating lower dose thresholds for cataracts were appropriate. The previous ICRP threshold (and current NCRP threshold) of 4 Gy (acute exposure) and 8 Gy (chronic exposure) Reduced to 0.5 Gy for acute and chronic exposures, based on recent studies of patients and occupational workers. Note, even though the USA has yet to adopt this ICRP threshold, it is anticipated change. Because of this lower cataract threshold, the ICRP slashed The occupational dose limit for the lens of the eye to 20 mSv in a year, averaged over a defined period of five years. The cumulative lens dose should not exceed 50 mSv in any single year.

Fluoroscopy – the Ten Commandments
As patient size increases – image quality decreases, patient dose increases, personnel dose increases Exposure time – total fluoro time, but also distributing dose over the skin (can you rotate/move tube to a different position??) X-ray tube position – raise/lower patient away from x-ray tube to decrease ESD; lateral and oblique tube positions general have higher ESDs Use appropriate dose and dose-rate settings Pulsed vs continuous Standard FOV vs mag modes c.f. LK Wagner & BR Archer. Minimizing Risks from Fluoroscopic X Rays: Bioeffects, Instrumentation, and Examination. 2004: 4th Edition. © UW and Renée Butler, MS, DABR

Proximity of II or FPD to Patient – improves image quality and decreases radiation dose c.f. LK Wagner & BR Archer. Minimizing Risks from Fluoroscopic X Rays: Bioeffects, Instrumentation, and Examination. 2004: 4th Edition. SID = 110 cm, varied SOD © UW and Renée Butler, MS, DABR

9 ft 2 4 ft 1 ft 2 ft 6 ft Exposure Rate at 4 ft = (90 mR/hr)(2ft/4ft) = 22.5 mR/hr Exposure Rate at 6 ft = (90 mR/hr)(2ft/6ft) = 10 mR/hr 3 ft 1 D E ÷ ø ö ç è æ = Inverse Square Law – reduce the dose through the use of distance if and when you can. Given: Exposure rate at 2 ft is 90 mR/hr © UW and Renée Butler, MS, DABR

Magnification Electronic mag – generally higher doses when using mag modes (though may not always be Geometric mag – increase distance between patient and II; typically increases dose by the square of the magnification Grid – remove grid for thin patients or if the image contrast is not affected by the scatter Collimation!! Personnel Safety – use time, distance and shielding to your advantage whenever possible; always wear lead aprons, use badges to monitor individual dose © UW and Renée Butler, MS, DABR

Skin Injury Case Reports & Radiation Dose

Skin Injuries – Case Reports
Fig 8b Fig 8d Fig 8c Fig 8e This is a 49-yr old woman with 8-yr history of refractory supraventricular tachycardia. The patient was exposed to about 20 min of fluoroscopy with her elbow about cm from the x-ray source. The circular port of the x-ray system defined the sharply demarcated border of the injury. Fig.8b show sharply demarcated erythema above right elbow at 3 weeks after RF cardiac cath ablation. Fig. 8c shows tissue necrosis 5 months after procedure. Fig. 8d shows injury with humerus visible about 6.5 months after procedure. Fig. 8e shows the surgical flap about 10 months after fluoroscopy procedure. © UW and Renée Butler, MS, DABR

ref: ICRP Publication 85, Case 1 (photographs courtesy of T. Shope). (a) The patient’s back 6–8 weeks after multiple coronary angiography and angioplasty procedures. (b) The injury approximately 16–21 weeks after the procedures. A small, ulcerated area is present. (c) The injury approximately 18–21 months after the procedures. Tissue necrosis is evident. (d) Close-up photograph of the lesion shown in (c). © UW and Renée Butler, MS, DABR

Radiation injury in a 60-year-old woman subsequent to successful neurointerventional procedure for the treatment of acute stroke. Estimated fluoroscopy time was more than 70 minutes; 43 imaging series were performed during course of the procedure. The head was not shaved. Note focal epilation on scalp and skin injury on neck but not on scalp. No dose estimates were available for this case. ref: Balter et al. Radiology. Feb Vol 254:2 © UW and Renée Butler, MS, DABR

© UW and Renée Dickinson, MS

FDA Advisory In the late 1980-early 1990s, the US FDA documented reports of at least 40 cases of radiation-induced burns to patients from fluoroscopically guided procedures. Fluoroscopic radiation is a carcinogen. While the risk of cancer from fluoroscopy is usually very small, it is essential that the radiation be properly controlled to minimize this risk to patients, to operators and to personnel. On September 9th, 1994, the FDA issued an advisory for facilities that use fluoroscopy for invasive procedures. © UW and Renée Butler, MS, DABR

FDA Advisory Recommendations…
Appropriate credentials and training for physicians performing fluoroscopy Operators be trained and understand system operation, and implications of radiation exposure for each mode of operation Physicians be educated in assessing risks and benefits on a case-by-case basis for patients Patients be counseled regarding the symptoms and risks of large radiation exposures Physicians justify and limit use of high dose rate modes of operation © UW and Renée Butler, MS, DABR

Fluoroscopy Regulations
FDA Advisory issued in September 1994 for all sites that use fluoroscopy for invasive procedures. WAC Operators shall be adequately instructed in safe operating procedures and shall be able to demonstrate competence A medical x-ray machine operator shall be licensed, certified or registered by the department as either: a licensed health care practitioner a certified diagnostic or therapeutic RT a registered x-ray technician Nurses or PAs need training if asked to operate x-ray equipment Physician is ultimately responsible for assuring that the x-rays are safely and properly applied and that appropriate radiation protection measures are followed What are the laws in our State? © UW and Renée Butler, MS, DABR

Image Quality (Dose) in Fluoroscopy

Review Questions A 9-in. multi-mode image intensifier (II) is switched to the 6-in. mode. As a result, the image will be ________ , and the automatic brightness control system (ABC) will _________ the exposure to the II and the patient. A. magnified, decrease B. magnified, increase C. minified, increase D. magnified, not change E. minified, decrease © UW and Renée Butler, MS, DABR

Web Modules Clinical Applications – Spatial Resolution
Small FS – general fluoroscopy (minimize blurring) Large FS – digital spots only (tube loading) In general, the spatial resolution of the I.I. alone is LP/mm Smaller structures are minified less (spread over a larger portion of the output phosphor), this enlargement of the displayed image improves the limiting resolution of the imaging system Would you expect the spatial resolution to be better or worse for FPD systems? The typical spatial resolution of most current FPD image receptors is about 2.5 – 3.0 LP/mm for all FOV’s. © UW and Renée Butler, MS, DABR

Web Modules Clinical Applications – Spatial Resolution (and noise)
With regard to a flat panel, what is binning? What is the advantage? What is the disadvantage? Example: 8 x 8 matrix; 10 photons per pixel 4 x 4 matrix; 160 photons per pixel 10 Calculate the noise and SNR of each example? σ = sqrt(10) = 3.2 SNR = N/σ = sqrt(N) = 3.2 160 σ = sqrt(160) = 12.6 SNR = 12.6 Less Quantum Mottle, the patient radiation dose can be significantly reduced while maintaining the same image noise. However, binning does reduce the spatial resolution of the image. Binning is especially useful for a large FOV where there would be too many pixels in the image © UW and Renée Butler, MS, DABR

Web Modules Clinical Applications – Radiation Dose
What percent of dose is a single fluoroscopy image relative to a general radiography image? About 1% (typically 450 to 1800 images per minute of fluoroscopy) mGy per image (fluoro) 4-10 mGy per image (radiography) About 1% (typically 450 to 1800 images per minute of fluoroscopy) mGy per image (fluoro) 4-10 mGy per image (radiography) © UW and Renée Butler, MS, DABR

Fluoroscopy Factors Affecting Image Quality
Spatial resolution System detector limitations – FOV, matrix, DELs, video capabilities, binning e.g.: FPD detector element sizes GI lp per mm Using mag, the resolution improves lp per mm Focal spot size and geometry – keep patient adjacent to detector!! This reduces focal spot blur (remember magnification) Motion, temporal factors affecting image blur; in general, pulsed fluoro reduces motion blur → improve resolution © UW and Renée Butler, MS, DABR

Fluoroscopy Factors Affecting Image Quality
Contrast Scattered x-rays (grid), veiling glare (II only) kVp and filtration – if the average (effective) energy of the x-rays is increased, then contrast decreases Collimation – decreases scatter contribution Radiation dose and noise – increasing the mA, decreases the noise and therefore improved contrast Image processing Smoothing algorithms and frame averaging reduces image noise, which improves contrast Edge enhancement algorithms increase image noise, therefore contrast degrades Contrast media (iodine, barium, or air) enhances contrast of anatomical structures © UW and Renée Butler, MS, DABR

Fluoroscopy Factors affecting Radiation Dose (and Image Quality)
ABC (automatic brightness control, II) or ADRC (automatic dose rate control, FPD) is accomplished by Changing kV or mA or both Opening the aperture to increase the brightness Changing x-ray pulse width Changing x-ray beam filtration or some combination of these factors © UW and Renée Butler, MS, DABR c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 247.

If generator responds by increase kV for thicker (more attenuating) regions, then contrast is compromised but dose is lower For procedures where contrast is critical (e.g. angiography) the generator programmed to increase mA first. Preserves contrast, but at the cost of increased dose to patient © UW and Renée Butler, MS, DABR c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 247.

Goal is to keep the # photons constant → maintains SNR © UW and Renée Butler, MS, DABR c.f. AAPM/RSNA Web Module: Fluoroscopy systems. Section X.A-7.

Geometry Decreased SID → ↓ dose Image receptor close to patient FOV selection ABC or ADRC kVp and filtration Pulse vs continuous fluoro Aperture – smaller aperture blocks more light from output phosphor, and decreases dose rate (the aperture is used to balance an acceptable amount of noise w/ an acceptable level of patient dose rate) Conversion gain – as an II ages, the amount of light produced in the input phosphor decreases and the conversion gain decreases… this results in GREATER RADIATION DOSE because the II is less efficient © UW and Renée Butler, MS, DABR c.f. AAPM/RSNA Web Module: Fluoroscopy systems. Section IX.B.

Review Questions An interventional radiologist performed 5000 fluoroscopically guided procedures last year. His annual occupational exposure was reported as “background.” What is the most likely explanation? A. All procedures were performed remotely from the x-ray control room. B. His badge was worn under a 0.5mm lead apron. C. The radiologist never wore his radiation badge while working. D. The department’s control badges were stored in the interventional control room. E. There was a persistent failure at the radiation badge company. © UW and Renée Butler, MS, DABR

Review Questions Which one of the following scenarios will result in the highest skin dose to the patient? A. B. C. D. Short SSD plus large SID results in higher patient dose. Use of the grid also requires higher patient dose. © UW and Renée Butler, MS, DABR

Introduction to Fluoroscopy

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