2012:15thsession of esmp

Lecture presented in Archamps (Salève Building) by :

2012 :15th SESSION of ESMP

Elly CASTELLANO (London)

European School of Medical Physics - Archamps

Quality control in x-ray imaging and CT

Elly Castellano

2European School of Medical Physics - Archamps

Objectives• the quality assurance programme

• the quality control cycle

• physics testing of the imaging chain

• is QC worth it?


Quality assurance programme• defined as (EU 1997)

All those planned and systematic actions necessary to provide adequate

confidence that a structure, system, component or procedure will perform

satisfactorily in compliance with agreed standards.

• comprises

– quality management

• quality manual

• audit

• training

– quality control

• scheduling and coordinating tests

• making measurements

• analysing and reporting results


The quality control cycle• required under BSS in EU

– IRR 99 in UK

Clinical use

Radiation safety checks Acceptance testing Commissioning

Routine QCService

Equipment fault

X-ray tubes,

detectors,

software?


Radiation safety tests• required under BSS

– room shielding

– warning signs and lights

– engineering controls

• deadman operation

• AEC termination

• x-ray tube housing leakage

• x-ray tube filtration

• how do we do it?

– IPEM report 79

– BIR report Radiation shielding for diagnostic x-rays

– IPEM report 32


Acceptance testing

• manufacturer’s specifications


– manufacturer’s protocol

– IPEM report 32


Commissioning

• opportunity to learn

• pre-requisite for optimisation


– no guidance


Routine Testing

• Guidance in

– IPEM 91

• Simple, frequent tests

• Complex, annual tests

• How do we do it?

– IPEM report 32

• parts I-VII

– IPEM report 89

– IAEA technical reports

• mammography, CT in development


Physics testing of the imaging

chain

• component tests

– x-ray production

– x-ray detection

– image processing

– image display

• system tests

– doses to phantoms

– image quality


X-ray productiontest R&F mammo CT test equipment

kV and exposure

time calibration� � � kVp meter

tube output � � � ionisation chamber or solid state

dosimeter

HVL � � � ionisation chamber or solid state

dosimeter, Al filters

focal spot size � � � pinhole, star test object

x-ray field/light

field and beam

alignment

� � alignment test tool

tube leakage � � � ionisation chamber, film cassettes or CR

plates

dose indicator

calibration� � � ionisation chamber, film cassettes or CR

plates, phantoms


X-ray production: kVp calibration

to CRO

detectors

X-ray

beam

filter pack

• two or more solid state detectors

• filters placed over detectors

• modality specific

0

20

40

60

80

100

120

-0.02 0 0.02 0.04 0.06 0.08 0.1 0.12

Time (Second)

kV

p

50

60

70

80

90

100

110

0.005 0.006 0.007 0.008 0.009 0.01

Time (Second)

kV

p

Frequency ~ 5kHz


X-ray production: tube output

www.radcal.com

• AK-calibrated dosimeters

• small volume < 10 cm3

• modality specific

• free-in-air measurements

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

4.00 4.20 4.40 4.60 4.80 5.00

ln kV)

ln Y

(d)

0 mm Cu

0.1 mm Cu

0.2 mm Cu

0.3 mm Cu


X-ray production: multi-meters• solid state dosimeters

• combined modalities

– e.g. R/F, mammo

• simultaneous parameters

– tube output

– kVp

– HVL

– exposure time

• automatic input to spreadsheet

Unfors Xi

RTI Piranha


X-ray detection: radiography and

fluoroscopytest FS

Rad

CR

Rad

DR

Rad

fluoro-

scopy

fluoro-

graphy

FS CR DR

test equipment

AEC

performance� � � � � phantoms, densitometer

detector dose

under AEC� � � � � ionisation chamber or SS

dosimeter, attenuator

detector

matching� � attenuator, densitometer

detector

response� � � � (DR) ionisation chamber or SS


detector

resolution� � � � *high contrast grating

detector

artifacts� � � � � attenuator, mesh

beam spillover � film or CR cassettes


X-ray detection: detector dose

under AEC• contact measurement

• AK calibrated ionisation

chambers

– medium volume < 100 cm2

– detect backscatter

• AK calibrated dosimeters

– must not occlude AEC sensor


X-ray detection: mammography

and CTtest mammo

FS

mammo

CR

mammo

DR

CT test equipment

AEC

performance� � � � phantoms, densitometer

detector dose

under AEC

detector

matching� �

detector

response� � ionisation chamber or SS


detector

resolution� � � *high contrast grating

detector artifacts � � � attenuator, mesh

beam spillover � � � film or CR cassettes


Image processing

test FS

Rad

CR

Rad

DR

Rad

fluoro mammo CT test equipment

dark room

lightproofing� � (FS) � (FS)

processor tests –

developer temp

replenish rate

pH

� � (FS) � (FS) *

CR reader tests –

calibration

laser function

erasure cycle

efficiency

� � (CR) � (CR) dosimeter, test

objects

processing

algorithms�


Image display

test F/S

Rad

CR

Rad

DR

Rad

fluoro mammo CT test

equipment

film tests –

sensitometry,

resolution

� � � � sensitometer,

densitometer,

test patterns

light box tests –

luminance� (film) lightmeter

monitor tests

(acquisition) –

luminance response

resolution

� lightmeter, test

patterns

monitor tests

(reporting) –

luminance response

resolution

� � � � � lightmeter, test

patterns


System tests

test F/S

Rad

CR

Rad

DR

Rad

fluoro mammo CT test equipment

dose to

phantoms� � � ionisation chamber,

phantoms

image

uniformity� � � � � � phantoms

contrast detail

performance� � � � � phantoms, test objects

system

response� phantoms, test objects

system

resolution� � phantoms, test objects


System tests: dose to phantoms

• phantoms

– modality-specific

– Perspex slabs, cylinders

• AK calibrated ionisation

chambers

– modality specific

– detect backscatter

• typical exposure geometry


System tests: image quality

• test objects

– modality-specific

– used with/in phantoms

• image quality parameters

– uniformity

– contrast detail performance

– system resolution

fluoroscopy

Leeds TOR 18FG

Leeds TO 10


System tests: image quality in

mammography

Leeds TOR MAM Leeds TOR MAX


System tests: image quality in CT

Catphan

GE


Is QC worth it?

• acceptance

– CT scanner table in wrong place

– filtration too low

– mammo collimator in wrong place


Is QC worth it?• routine testing

– fault in stator rotation

– incorrect Cu filter in fluoroscopy unit

– drift in CT scanner calibration

-10

-8

-6

-4

-2

0

2

4

6

8

10

10/12/2002 28/06/2003 14/01/2004 01/08/2004 17/02/2005

QA date

CT

nu

mb

er

ca

l

0.5 mm row 1

0.5 mm row 2-10

-8

-6

-4

-2

0

2

4

6

8

10

10/12/2002 28/06/2003 14/01/2004 01/08/2004 17/02/2005

QA date

CT

nu

mb

er

un

ifo

rmit

y0.5 mm row 1

0.5 mm row 2


Summary• QA and QC introduced

• overview of physics testing of the imaging chain

provided

• merits of QC testing discussed


Acknowledgements

• Claire Skinner

2012:15thsession of esmp

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