introduction to fluoroscopy renée (dickinson) butler, ms, dabr medical physicist university of...

INTRODUCTION TO FLUOROSCOPY

Renée (Dickinson) Butler, MS, DABRMedical Physicist

University of Washington Medical CenterDepartment of Radiology

Diagnostic Physics Section

[email protected]

General Fluoroscopy:Modes of Operation & System Components

© UW and Renée Butler, MS, DABR

PARAMETER G.I. FLUOROSCOPY RADIOGRAPHY

kVp’s 60 - 120 50 - 130

mA values0 - 5 (continuous)

200 - 8000 - 100 (pulsed)

X-ray Tube Focal Spot Size 0.3 - 0.6 mm 1.0 - 1.2 mm

Exposure Duration 0.5 - 15 min (IR: 45+ min) 0.01 - 0.3 seconds

Image Receptor Input Radiation Dose per image 0.01 - 0.15 mGy / image 4 - 10 mGy/image

Patient skin Dose Rates 10 - 60 mGy / min 0.2 - 10 mGy / image

Source-to- Skin Distance (SSD) 30 - 50 cm 60 - 145 cm

Source-to-Image Receptor Distance (SID) 80 - 120 cm 100 or 182 cm

Typical Spatial Resolution1 - 2.0 LP/mm (Image Int.)

3 - 10 LP/mm2.5 - 3.0 LP/mm(Flat Panel)

Image Quantum Mottle High Low

Staff Exposure to Scattered Radiation Yes No

PARAMETER G.I. FLUOROSCOPY RADIOGRAPHY

kVp’s 60 - 120 50 - 130

mA values0 - 5 (continuous)

200 - 8000 - 100 (pulsed)

X-ray Tube Focal Spot Size 0.3 - 0.6 mm 1.0 - 1.2 mm

Exposure Duration 0.5 - 15 min (IR: 45+ min) 0.01 - 0.3 seconds

Image Receptor Input Radiation Dose per image 0.01 - 0.15 mGy / image 4 - 10 mGy/image

Patient skin Dose Rates 10 - 60 mGy / min 0.2 - 10 mGy / image

Source-to- Skin Distance (SSD) 30 - 50 cm 60 - 145 cm

Source-to-Image Receptor Distance (SID) 80 - 120 cm 100 or 182 cm

Typical Spatial Resolution1 - 2.0 LP/mm (Image Int.)

3 - 10 LP/mm2.5 - 3.0 LP/mm(Flat Panel)

Image Quantum Mottle High Low

Staff Exposure to Scattered Radiation Yes No

Fluoroscopy vs Projection Radiography

c.f. AAPM/RSNA Web Module: Fluoroscopy systems. Section IV. Table1. © UW and Renée Butler, MS, DABR

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]


• For heavy patient sizes: dose rate is roughly 8-10 R per min

[70 to 87.3 mGy/min]


FluoroscopyModes of Operation


8.76 mGy per R

14.7 R per min = 128.8 mGy per min



FluoroscopyModes of Operation


• 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.


Web ModulesClinical 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.

c.f. AAPM/RSNA Web Module: Fluoroscopy systems. Section III.A-E.


Web ModulesClinical Applications

Fluoroscopy System ComponentsImage Intensifier (II) vs Flat-Panel Detectors (FPD)

Flat-panel detector

c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 232. © UW and Renée Butler, MS, DABR

• 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

Fluoroscopy System ComponentsFlat-Panel Detectors (FPD)

Patient & Personnel Safety in Fluoroscopy


Identify the technique factors and appropriate system features to use to optimize image quality while minimizing patient dose.

1. FPD (or II) close to patient2. Grid in3. Collimate!4. Increase SSD (source-to-skin distance) to

decrease ESD (entrance skin dose)Note: geometry limitations with shorter personnel

AAPM/RSNA Resident Physics Curriculum: Module 13: Fluoroscopy & Interventional Imaging Clinical Application


Describe the geometric factors that affect operator dose during an IR procedure.

1. Lead apron2. Thyroid shield3. Protective eyewear4. Radiation badge5. Adjust dose settings when possible (pulse) to

reduce scatter6. Distance, when possible7. Shielding, when possible



Describe the geometric factors that affect operator dose during an IR procedure – scatter geometry for the frontal and lateral tubes in a NIR suite.

c.f. ZH Anastasian et.al. Radiation Exposure of the Anesthesiologist in the Neurointerventional Suite. Anesthesiology 2011; 114: 512-20.

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!



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: 512-20.


Describe the geometric factors that affect operator dose during an IR procedure – scatter geometry for the frontal and lateral tubes in a NIR suite.

Radiation Protection and Fluoroscopy/IRBadging – 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 = 0.35 - 0.50 mm: absorbs 95 - 99% of scatter

(but heavier, so is it feasible to wear??)• Use a lead thyroid shield at all times


Radiation Protection and Fluoroscopy/IRProtective 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


Radiation Protection and Fluoroscopy/IRLeaded 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.

c.f. LK Wagner & BR Archer. Minimizing Risks from Fluoroscopic X Rays: Bioeffects, Instrumentation, and Examination. 2004: 4th Edition.

Fluoroscopy – the Ten Commandments5. Proximity of II or FPD to Patient – improves image quality and

decreases radiation dose


SID = 110 cm, varied SOD

Fluoroscopy – the Ten Commandments• Inverse Square Law – reduce the dose through the use of distance if

and when you can.

9 ft24 ft21 ft2

2 ft

4 ft

6 ft

Exposure Rate at 4 ft = (90 mR/hr)(2ft/4ft) = 22.5 mR/hr2

Exposure Rate at 6 ft = (90 mR/hr)(2ft/6ft) = 10 mR/hr2

1 ft

1 ft

2 ft

2 ft

3 ft

3 ft

2

2

112 D

DEE ÷÷

ø

öççè

æ=

Given: Exposure rate at 2 ft is 90 mR/hr


Fluoroscopy – the Ten Commandments• 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


Skin Injury Case Reports & Radiation Dose


Skin Injuries – Case Reports

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).


Skin Injuries – Case Reports

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 2010. Vol 254:2


Fluoroscopy RegulationsFDA Advisory issued in September 1994 for all sites that use fluoroscopy for invasive procedures.

WAC 246-225-020• 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 © UW and Renée Butler, MS, DABR

Image Quality (Dose) in Fluoroscopy


Review QuestionsA 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


• Small FS – general fluoroscopy (minimize blurring)• Large FS – digital spots only (tube loading)

• In general, the spatial resolution of the I.I. alone is 3.5-6.0 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.


Web ModulesClinical Applications – Spatial Resolution

• 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 10 10 10 10 10 10 10

10 10 10 10 10 10 10 10

10 10 10 10 10 10 10 10

10 10 10 10 10 10 10 10

10 10 10 10 10 10 10 10

10 10 10 10 10 10 10 10

10 10 10 10 10 10 10 10

10 10 10 10 10 10 10 10

160 160

160 160

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

σ = sqrt(10) = 3.2SNR = N/σ = sqrt(N) = 3.2

σ = sqrt(160) = 12.6SNR = 12.6


Web ModulesClinical Applications – Spatial Resolution (and noise)

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)

0.01-0.15 mGy per image (fluoro)4-10 mGy per image (radiography)


Web ModulesClinical Applications – Radiation Dose

• Spatial resolution • System detector limitations – FOV, matrix, DELs, video capabilities,

binning• e.g.: FPD detector element sizes

• GI studies @ 2.5-3 lp per mm• Using mag, the resolution improves to @ 3.5-6 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


FluoroscopyFactors 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


FluoroscopyFactors Affecting 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


FluoroscopyFactors affecting Radiation Dose (and Image Quality)

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



c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 247.

• 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

Goal is to keep the # photons constant → maintains SNR

c.f. AAPM/RSNA Web Module: Fluoroscopy systems. Section X.A-7. © UW and Renée Butler, MS, DABR


• 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

• Geometry• Decreased SID → ↓ dose• Image receptor close to patient

• FOV selection • ABC or ADRC• kVp and filtration• Pulse vs continuous fluoro

c.f. AAPM/RSNA Web Module: Fluoroscopy systems. Section IX.B.



Review QuestionsAn 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.


Review QuestionsWhich 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.


Questions?


introduction to fluoroscopy renée (dickinson) butler, ms, dabr medical physicist university of...

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