Anatomy of Fluoroscopy & CT Fluoroscopy Equipment L04

Anatomy of Fluoroscopy & CT Fluoroscopy Equipment

L04

IAEA Training Course on Radiation Protection for Doctors (non-radiologists, non-cardiologists)

using Fluoroscopy

Educational objectives

• How is fluoroscopy equipment designed?

• What are the different factors that influence the X ray output from a fluoroscopic system?

• What are the new developments in fluoroscopy equipment?

2IAEA Training Course on Radiation Protection for Doctors (non-radiologists, non-cardiologists) using Fluoroscopy

L04. Anatomy of Fluoroscopy & CT Fluoroscopy Equipment

Fluorescent screen with leaded glass

Early (Screen Only) Fluoroscopy



Modern Image Intensifier based fluoroscopy system



Components of C-arm equipment

Camera

Image Intensifier

X-ray TubeFilters

Collimators

Optics

Generator &AutomaticBrightnessControl

Grid



From: R Kruger et al, Spine 2003

Bi-plane C-arm setup



A Modern Bi-Plane C-Arm with Flat Panel Detectors

X ray Tubes

Flat panelImage Receptors



Multi-purpose C-arm Fluoroscopy System

Image Intensifier

X ray tube



Over-couch vs Under-couch X ray Tubes

Image Intensifier

X ray Tube fixed under table

Image Intensifier

X ray Tube fixed over table



Over-couch vs Under-couch X ray Tubes

• Under-Table X ray tube system subject the operator to much less scattered radiation than do over-table X ray tube systems.

• It is therefore preferable to have the X ray tube mounted below the table when purchasing fixed configuration systems.



The Image Intensifier (II)

Its function is to

• Convert X rays into visible light

• Increase the image brightness so it is visible to the camera and recording devices



Automatic Brightness Control (ABC)

• Adjusts X ray intensity to produce image of predefined brightness

• Adjusts kV and mA in various ways to achieve predefined image brightness.

• Normally adjusts kV with associated adjustment in mA



Theory of Operation – ABC

Camera

Iris/Diaphragm

Optics

Image Intensifier

Grid

FilterX ray Tube kV,mAK

AutomaticBrightnessControl

Collimator

Generator

ImageBrightnessFeedback

Table

Monitor

Reference Brightness



Automatic Exposure Control and

Patient Thickness

kV

mA

Filtration

Focal Spot Size

Pulse Width

VerySmall

Small Medium Large VeryLarge

Patient size

Imaging modes

Fluoroscopy versus Acquisition,Magnification, Dose level

Synonyms:MAGZoom Field View (FOV)Image Intensifier field size

Magnification



Smaller Image Intensifier Mode (“MAG”) has better resolution

6” 9”

0.15 mm / pixel vs. 0.23 mm/pixel

… but higher exposure to patient and staff

Magnification



Radiation Output and Mag Modes

• Exposure Rate change = (old FOV)2/(new FOV)2

• Example: go from 40 cm to 30 cm

• 402/302 = 1.77

• So the smaller FOV will need 1.77x more radiation for the same image brightness



IAEA Training Course on Radiation Protection for Doctors (non-radiologists, non-cardiologists) using Fluoroscopy


ABC increases patient dose for increased MAG

Normal, 40 cm FOV, 1 dose unit MAG 1, 33 cm FOV, 1.46 dose units

MAG 2, 23 cm FOV, 3.0 dose units MAG 3, 17 cm FOV, 5.5 dose units19

(+) mode increases dose by 50% compared to normal.(-) mode decreases dose by 50% compared to normal.

13 cm17 cm

23 cm

Low Fluoro,No MAG

High Fluoro,MAG 2

> 10 fold more exposure rate



Can you tell ……….Which image is FLUOROSCOPY, which one is ACQUISITION?

Fluoroscopy vs Image Acquisition



Continuous display of images, normally without recording, except last image hold (LIH)

Discrete or multiple images recorded in sequence. Commonly known as runs or cine runs

Fluoroscopy

Image Acquisition

> 10 fold more exposure rate22



RadiationDose

ImageQuality

Better image quality with higher radiation dose reaching the image receptor.

Tradeoff: higher patient and staff dose!!



ALARAAs Low As Reasonably Achievable

No known safe limit of magnitude of radiation exposure

Patients

Professionalstaff

Physicians



Pulsed Fluoroscopy

Pulsed fluoroscopy



• What is beam filtration?• Absorber placed between source and object

• Will preferentially absorb the lower energy photons

• Patient skin dose reduction

Effect of filtration



LowFiltrationSpectrum


Inte

nsit

y

Photon energy, keV

With increased filter and increased mA

For equal kVpIncreased mean beam energy



kVp

IncreasedMean Energy


• Additional Cu filters can reduce the skin dose by more than 70%.

• Some systems offer variable extra filtration (0.2 mm - 0.9 mm) that is automatically set according to patient weight and angulation of the C-arm.



Dose Area Product (DAP)meter

Other important elements

Collimator



Collimator



Collimation confines the X ray beam to an area of the user’s choice.

Collimator



Why is narrowing the field-of-view beneficial?1. Reduces exposure to patient by reducing volume of

tissue at risk2. Reduces scatter radiation at image receptor to improve

image contrast3. Reduces scatter radiation to in-room personnel4. Reduces potential overlap of fields when beam is

reoriented

Collimator



Dose Rates and Aging Equipment

• Image Intensifier efficiency at converting X rays to light reduces over time. Thus the image becomes dimmer.

• Via the ABC, Image Intensifier input doses rates go up to compensate. (Patient and staff doses also increase.)

• A service engineer can open optical iris of TV camera to compensate, but at some stage no further adjustment available & image intensifier replacement needs to be considered.



C-arm Control Panel

kVp, mA display “Radiation on” warning Tube temperature alarm Image transfer controls Procedure timer

On Off

Manual fluoro

Automatic fluoro

Pulsed fluoro

Fluoro dose modeLow / high

Manual controlsMAG/Zoom/II field size

Image acquisition/



New developments

• Flat panel detectors

• CT fluoroscopy

• Mobile CT in operation theatre



Flat panel detector

Flat panel detector instead of image intensifier

Camera

Image Intensifier

X-ray TubeFilters

Collimators

Optics

Generator &AutomaticBrightnessControl

Grid

For the user, dose level, MAG, filters and other parameters remain more or less the same



Flat panel detector: bi-plane system





CT Fluoroscopy – real-time CT

• Staff enters CT room during acquisition

Needle holder

Biopsy mediastinal mass

39

Core biopsies, precise needle placement, fluid collection aspirations, drainage, local drug injection, RF ablation, lumbar nerve root blocks, vertebroplasty, arthrography, etc

Applications

UsersRadiologist, pneumologist, orthopedic surgeon, anesthetist

Patient skin dose rates typical > 10 times higher than in C-arm fluoroscopy




10 mA paediatrics, 10-40 mA chest, 40-50 mA abdominal

Typical tube current settings in CTF

Staff protectionStandoff needle device to increase distance to primary beam




CT in the operating theatre

• CT based surgical navigation – mobile system

• Staff leaves room during acquisition



CT in the operating theatre

• Also works in 2D conventional fluoroscopy mode

3D mode delivers radiation dose to patients that is comparable to that of a 64 slice CT scanner.

2D mode delivers radiation dose to patients and staff comparable to that of a conventional C-arm system



Thank you



Documents

Anatomy of Fluoroscopy & CT Fluoroscopy Equipment L04