X-ray systems for Interventional radiology.pdf

5/26/2018 X-ray systems for Interventional radiology.pdf

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X ray systems for Interventionalradiology

Key topics: Filtration effect, pulsed radiation versus continuous, gridcontrolled effect on the beam, virtual collimation, temporalintegration and road map, DSA, rotational angiography

ANASTAS LICHEV

Imaging Department,University Hospital Sveti Georgi

PLOVDIV

X-Ray Equipment Standards AndRegulations

Requirements for angiography equipment, standards

Standards - different groups regarding the kind of theequipment

Standards are applicable to mechanical, electrical,electronical and other aspects of the equipment

A part of the standards are requirements for electrical,mechanical and radiation safety

Standards are applicable at the time of manufacturingof the equipment and at the time of installing


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Main points concerning radiation protection

If the relevant standards are fulfilled.

If a medical physicist is available.

If radiation protection tools are available.

If patient dose measuring and recordingsystem is available.

If acceptance tests, commissioning andquality assurance program have beenforeseen.

Main points concerning radiation protection

If the X rays system selected isappropriate for the procedures to be

carried out in the catheterizationlaboratory.

If some other relevant informationdescribed in standards, guidelines andregulations have been taken into account.


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Applicable standards

Food and Drug Administration FDA

International electrotechnical commision IEC

American college of radiologists ACR

AAPM reports

Specific pediatric recommendations

Bulgarian standards

()

2004.

No 30 () 31 2005.


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Bulgarian standards

Regulation for radiation protection duringactivities with sources of ionizing radiation(2004)

Regulation No 30 for conditions and forassuring protection of individuals during medical

procedures 31 October 2005

Limitations FDA

Limitations posed by FDA - May 19, 1994

21 CFR Part 1020

Entrance dose limit

normal operation 100mGr/min (10 R/min)

Entrance dose limit

high level dose operation 200mGr/min (20 R/min)

Not applicable in recording image mode


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Measure

Measuring of theentrance dose atthe side of the PMMAphantom objectfacing the tube

Typical dose rate

20-80mGr/min

with 24cm PMMAphantom

Limitations according toBulgarian regulations

Limitations posed by Regulation 30 :

at II with input diameter 25cm :

Entrance dose limit normal operation - 50 mGr/min ( 5R/min)

Entrance dose limit

high level dose operation 100 mGr/min (10R/min)

Measuring of the entrance dose - at the face of the waterphantom object 30x30cm, 20cm thick


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1111


Limitations posed by Regulation 30 :

at II with input diameter 25cm :

II entrance dose limit

normal operation - 0.8 micrGr/s ( R/min)

II entrance dose limit

high level dose operation 1 micrGr/s ( R/min)

Measuring of the entrance doseat the face of the water phantom object 20cm, withoutantiscatter grid


Concerning image recording mode:

II with input diameter 23m :

100-300 mGr/min in 25 frames/s entransedose (skin dose)

0.20 micrGr/frame II entrance dose rate

Measuring of the entrance dose at the face ofthe water phantom object 20cm, withoutantiscatter grid


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IEC standard on Interventional Radiology Radioscopically guided invasive (and interventional)

procedures.

Interventional reference point.

Isokerma maps shall be provided.

The anti-scatter grid should be removable without theuse of tools.

Dosimetric indications: reference air kerma rate,cumulative reference air kerma, cumulative area kerma

product, (shall be accurate to within 50 %).

Supplementary indications: cumulative time ofradioscopy, cumulative number of radiographicirradiations, integrated reference air kerma.

Requirements to maincomponents of the system

System includes : Imaging chain :

X-ray tube, inherent and added filtration, housing

Light Beam Diaphragm (LBD) Collimator High voltage generator and control circuits Image intensifier

Electronics and computers, software tools Dose evaluation tools Mechanical and Patient support

Patient table C-arm and motorization

Fluoro and acquisition protocols used for examinations


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Types

Monoplane systemsMonoplane systems

one Cone C--arm, floor orarm, floor or

ceiling suspensionceiling suspension

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Types

BiBi--plane systemsplane systems

two Ctwo C--arms, floor andarms, floor and

ceiling suspensionceiling suspension


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High voltage generator - 1

Power 100-150kW

High voltage range 40 140kV

Time of exposure 0.001s - 1s

Digital Cine rate 25-50 frames /s with

1-10ms duration and up to 10mAs per frame

Conventional cine used up to 200 frames/s

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Typically HV generator is a high frequencyvoltage converter (high frequency generator)


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Control of the exposures :

at the stage of the generator

HF generators

HV tethrode controlled

at the stage of the tube grid controlledtubes, better radiation bursts


High voltage pulse

Grid controlled tube

At generator


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High voltage pulse

Grid controlled tube

At generator

soft radiation

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High voltage pulse real world

High frequency generator


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High voltage pulse real world

High voltage generator

with HV tethrodes

commutation

High voltage generator andpediatrics - 1

If pediatrics is concerned, the generator should allowimaging on patients from 3 to 140 kg

This places additional demands on the generator The generator should allow mAs of the tube per cine

pulse to be varied from 0.1 mAs (100 mA and 1 msec)up to 6 mAs (e.g., 800 mA and 7 msec) according to

patient size in order to maintain a kVp 65 - 75 kVp.

Cine frame rate should be possible more or at least60fps for small children.


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The generator and tube should support three focalspots.

Patients up to 3 to 4 years old can be imaged with an 0.3 mmfocal spot size

Patients up to 8 to 9 years old can be imaged with cine using an0.6 mm focal spot

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The 0.3 mm focal spot can also be used on smallchildren in combination with removing the anti-scattergrid and using a geometric magnification factor up to 2.

This method may reduce patient dose because

the electronic magnification modes of the image intensifier arenot used less dose rate and

the Bucky factor due to the grid is eliminated


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Collimation in cardiac equipment

Beam quality modulation: extra filtering(Cu, Ta, etc)

Spatial beam modulation: collimation (andvirtual collimation), wedge filters, etc.

Temporal beam modulation: pulsed

fluoroscopy (grid controlled, temporalintegration, etc).

Filtration - 1

Filtration changes the spectrum of the X-ray beam,removing low-energy part of it the X-ray beam hardens

This contributes to reducing

of the patients dose as

penetration power of

the beam increases

However a degradation

in image quaity is possible

due to beam hardening


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Filtration - 2 Several manufacturers are using relatively thick copper

filtration and relatively reduced kVp during fluoroscopyto generate an energy spectrum better matched to theK-edge of iodine contrast media.

This technique requires high fluoroscopic tubecurrents with the benefit of

reducing patient exposure to

radiation while improving

image contrast.

Replaceable filters

High filtration - 1

The introduction ofadditional filtration in theX ray beam (copperfilters) reduces thenumber of low energy

photons and asconsequence, saves skindose for the patients


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High filtration - 2

Reduction of Radiation Exposure with extra filtration

Additional Cu filters can reduce the skin dose by morethan 70%.

Some systems offer variable extra filtration

(0.2 mm - 0.9 mm) that is automatically set according topatient weight and angulation of the C-arm.

Automatic filter insertion try to keep the dose as low aspossible without degrading image quality.

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Filtration - 3

Replaceable filters


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Collimation - 1

Collimation reducesarea of irradiating tothe region of interest.

Scatter radiation alsodecreases withdecrease of the

irradiated area.

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Collimation - 2

Dual-shapecollimators

incorporating bothcircular and ellipticalshutters may be usedto modify the field forcardiac contourcollimation


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Collimation - 3

Dual-shapecollimatorsincorporating bothcircular and ellipticalshutters may be usedto modify the field for

cardiac contourcollimation

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Collimation and filtration

Partially absorbentcontoured filters are

also available tocontrol the brightareas outside of theROI

(border of the heart)


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Collimation:

Partially absorbent contoured filters are also available tocontrol the bright areas outside of the ROI

(border of the heart)

Virtual Collimation

Radiation-free Collimation work with memorizedimage and computer

Manipulation of diaphragms in Last Image Hold.

No fluoroscopy required

No dose to the patient


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Image intensifiers 1

Need for imaging of large fields - for ventriculography,aortography)

Need of imaging of small fields - coronary arteries

Multimode image intensifiers are recommended - with 2 or 3imaging fields (zooms)

Image intensifiers 2

Material for the screen is cesium iodide CsI

Formats available vary with the manufacturers :

9 in/ 6 in/4.5 in (9/6/4.5) 23/16/11 cm

9/6 23/16 cm

9/5 23/13 cm

10/4 25/10 cm


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Image intensifiers 3AAPM-70 (2001) For adult studies, a 9 to 11 inch (23 to 27 cm) size is

preferable

Pediatric cardiac studies use smaller fieldsdue to thesmall size of the pediatric heart 4.5 in (11cm) in mostcases should be enough

An image intensifier with a diameter of more than 9-10in(23-25cm) is not recommended for cardiaccatheterization laboratories because such relatively largesize interferes with the ability to obtain steep sagittalangulation.

New detectors

Flat panels

Dynamic flat panel

Based on CsI as well as II


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Electronics and computers - 1

Last image hold

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Patient dose measurement, display and archive -DAP meters, time of fluoroscopy


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Electronics and computers - 3 Work stations equipped with software tools for

image and data processing

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Work stations equipped with software tools forimage and data processing

(incl. automatic review)


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Connectivity andDICOM compliance

DICOM headerinformation

Philips Integris 5000 cardio(0008,0032) : Acquisition Time : 12:36:27

(0018,0060) : KVP : 83

(0018,1030) : Protocol Name : 12.5 IPS Coronaria

(0018,1110) : Distance Source to Detector : 940

(0018,1150) : Exposure Time : 8

(0018,1151) : X-ray Tube Current : 873

(0018,1162) : Intensifier Size : 169.99998

(0018,1510) : Positioner Primary Angle : -32.099998

(0018,1511) : Positioner Secondary Angle : 0.69999999

(0020,0013) : Image Number : 8

(0028,0008) : Number of Frames : 73

GE ADVANTX LCV-DLX (Card io mode)(0008,0032) : Acquisition Time : 19:24:33

(0008,103E) : Series Description : CORONARIO

(0018,0060) : KVP : 75

(0018,1110) : Distance Source to Detector : 1060.000

(0018,1111) : Distance Source to Patient : 705(0018,1149) : Field of View Dimension(s) 152

(0018,1150) : Exposure Time : 328 (number fr x ms per fr)

(0018,1151) : X-ray Tube Current : 81

(0018,1510) : Positioner Primary Angle : -30 (left is +)

(0018,1511) : Positioner Secondary Angle : 0 (cra is +)

(0019,101B) : 1.2 (this is the focus size)

(0019,101C) : 1 (Dose mode: 0,1, 2 and 3 for A,B,C and D)

(0019,101F) : 4 (This is the real pulse time in ms)

(0020,0013) : Image Number : 2 (this is the series number)

(0028,0008) : Number of Frames : 82

Patient and Equipment Support The ability to obtain very steep sagittal plane

angulation (in excess of 45 ) is desirable.


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Pulsed fluoroscopy Pulsed fluoroscopy can be used as a method of

reducing radiation dose, particularly when thepulse rate is reduced.

However pulsed fluoroscopy does not mean thatdose rate automatically is lowered down incomparison with continuous fluoroscopy

Pulsed fluoroscopy

Dose rate depends of the dose per pulse and thenumber of pulses per second

Pulse width modulation Frequency modulation

One may vary conditions by changing thefrequency and width of the pulses differentmodes (lo, high, pediatric)

Measurement for a time period in the sameconditions


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Roadmap

Overlying of two images. An existing subtractedOverlying of two images. An existing subtracted

image of a blood vessel filled with contrastimage of a blood vessel filled with contrast

medium can be superimposed on a cathetermedium can be superimposed on a catheter

image during fluoroscopy. Very useful in viewingimage during fluoroscopy. Very useful in viewing

blood vesselsblood vessels

Saves time and contrast mediumSaves time and contrast medium

Patient dosePatient dose reductionreduction

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Digital subtraction angiography - DSA

Temporal subtraction refers to a number of computerTemporal subtraction refers to a number of computer--assisted techniques whereby an image obtained at oneassisted techniques whereby an image obtained at onetime is subtracted from an image obtained at a latertime is subtracted from an image obtained at a latertime.time.

If, during the intervening period, contrast material wasIf, during the intervening period, contrast material wasintroduced into the vasculature, the subtracted imageintroduced into the vasculature, the subtracted imagewill contain only the vessels filled with the contrastwill contain only the vessels filled with the contrastmaterialmaterial


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Temporal subtractionTemporal subtraction

Mask mode studyMask mode study

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Temporal subtractionTemporal subtraction

Time intervalTime interval differensedifferense studystudy


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Rotational angiography

A series of images are acquiredA series of images are acquired

during one continuous rotationduring one continuous rotation

of the Cof the C--arm around thearm around the

patient, allowing a largepatient, allowing a large

number of projections to benumber of projections to be

obtained with a single injectionobtained with a single injection

of contrast mediumof contrast medium

Rotational angiography

A series of images are acquired during one continuousA series of images are acquired during one continuous

rotation of the Crotation of the C--arm around the patient, allowing a largearm around the patient, allowing a large

number of projections to be obtained with a singlenumber of projections to be obtained with a single

injection of contrast mediuminjection of contrast medium

Permits rendering images

similar to that from

CT equipment

Patient dose should be

taken into account


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Dose evaluation and limiting tools

The operator should be made aware of the cumulative amount ofexposure time during the procedure.

There have to be mechanical or electronics limitation of the time offluoroscopy

Dose evaluation and limiting tools

In training programs there should be a limit to the amount offluoroscopic time granted to a trainee to complete a specific task,based on a number of considerations such as the progress being madeand the complexity of the procedure.

There should be equipment for

recording of the applied

dose-area product (DAP)

DAP meter


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Auxiliary radiation protection apliances

Protective tools in thesystem - A freelymovable lead glass oracrylic shieldsuspended from theceiling should be

used. Its sterility maybe maintained byusing disposableplastic covers.

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Ergonomy in the room and system geometry


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Each procedure roomshould have adetaileddetermination ofexposure levelsperformed by a

qualified radiationphysicist.

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Operational modes and how they are settled

There is a tendency in the busy laboratory to

assign a low priority to preventive maintenanceand quality assurance inspections.


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Conclusions from the IAEA survey

Patient dose and image quality depend largelyon the settings made at the commissioning ofthe radiological equipment.

For different systems and different operationmodes, entrance air kerma can increase by afactor of 20 (including electronic magnification)

for the same patient thickness.

Conclusions from the IAEA survey

Increasing phantom thickness increasesdose by an additional factor of up to 12.

Differences in radiation doses from theevaluated systems show a potential fordose reduction whilst maintaining imagequality.


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Importance of testing X ray equipment

Characterization of the X- ray system, thatshould be part of the acceptance and statustests, should inform cardiologists about the doserates and dose/frame for the different operationmodes and for the different patient thicknesses.Image quality has to be evaluated also.

Regular constancy checks should verify ifimportant changes could been occurred.

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X-ray systems for Interventional radiology.pdf

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