[Gate-users] Problem wih CT-Scans using different energies

Mon Nov 7 18:27:53 CET 2011

Dear Zhaowei,

thank you for your response to my question. But I still have the same
problem. Below you can see two projections of a ct-scan. The one on the left
was taken with 140kV and the one on the right with 80kV. For both
projections I used either the same number of primaries with the command
'application/setNumberOfPrimariesPerRun ' or 'xraygun/setActivity bequerel'
with the same acquisition time. As you can see the contrast within the left
projection is lower than the contrast within the right projection!

dual energy scan.jpg

On your remark concerning the detector materials: I definitely do get
different results if I use different materials. More precisely I count more
photons if I use Gadoliniumoxysulfid instead of Silicon. But the effect
stays the same.

Here are excerpts of my other scripts I have adjusted. Maybe one can see a
mistake there:

#############

# DIGITIZER #

#############

/gate/digitizer/Singles/insert adder

/gate/digitizer/Singles/insert readout

/gate/digitizer/Singles/readout/setDepth 2

/gate/digitizer/Singles/insert thresholder

/gate/digitizer/Singles/thresholder/setThreshold 10 keV

/gate/digitizer/Singles/insert upholder

/gate/digitizer/Singles/upholder/setUphold 140 keV

/gate/digitizer/convertor/verbose 0

/gate/digitizer/verbose 0

############

# CT Image #

############

/gate/output/imageCT/verbose 0

/gate/output/imageCT/enable

/gate/output/imageCT/setFileName benchmarkCT_100x100_5s_80kV_50x50x30_011

/gate/random/setEngineName MersenneTwister

/gate/output/imageCT/setStartSeed 567489

############

# SOURCE  #

############

gate/source/addSource xraygun

/gate/source/verbose 0

/gate/source/xraygun/setActivity 350000. becquerel

/gate/source/xraygun/gps/verbose 0

/gate/source/xraygun/gps/particle gamma

/gate/source/xraygun/gps/energytype Arb

/gate/source/xraygun/gps/histname arb

/gate/source/xraygun/gps/emin 10.00 keV

/gate/source/xraygun/gps/emax 80.00 keV

/gate/source/xraygun/gps/histpoint                0.01     5

/gate/source/xraygun/gps/histpoint                0.079   1165

/gate/source/xraygun/gps/arbint Lin

/gate/source/xraygun/gps/type Plane

/gate/source/xraygun/gps/shape Rectangle

/gate/source/xraygun/gps/halfx 0.025 mm

/gate/source/xraygun/gps/halfy 0.025 mm

/gate/source/xraygun/gps/mintheta 0  deg

/gate/source/xraygun/gps/maxtheta  6.8 deg

/gate/source/xraygun/gps/centre 0. 0. -15.0 cm

/gate/source/xraygun/gps/angtype iso

/gate/source/list

Von: Zhihuaigu [mailto:zhihuaigu at yahoo.com.cn] 
Gesendet: Samstag, 29. Oktober 2011 08:48
An: duschl at hicat.de
Cc: gate-users at lists.opengatecollaboration.org
Betreff: Re : Problem wih CT-Scans using different energies 

Dear Andreas,

It seems your program run well. The Physics.mac is no problem.   how many
number of primaries have you set? Are you sure you set the two process the
same number? Besides, the CT scanner.mac only count the number of photons it
received, so you will get the same results no mater what materials you have
used.

Regards,

zhaowei

IHEP, CAS

----------------------------------------------------------------------

Message: 1
Date: Wed, 26 Oct 2011 12:05:37 +0200
From: "Andreas Duschl" <duschl at hicat.de>
To: <gate-users at lists.opengatecollaboration.org>
Subject: [Gate-users] Problem wih CT-Scans using different energies
Message-ID: <000001cc93c6$cf152960$6d3f7c20$@de>
Content-Type: text/plain;    charset="iso-8859-1"

Dear Gate-Users

I'm trying to make a CT-Scan using Gate v6.0 . Basically I have extended the
CT-Scanner Example (classic) in order to make two scans of the same phantom
with two different energies (80kV and 140kV).  Therefore I calculated the
filtered spectra with the open source matlab tool Spektr which I then
included into the script source.mac . I also have set the energy window of
the digitizer from 10kV to 140kV. The strange thing is that in the low
energy projection the value of the SNR is greater than in the corresponding
high energy projection. Normally it should be the other way round. What I
already tried to do is using different detector materials such as ceasium
iodide and glass as back compartment. But all with the same effect. Maybe
I'm using the wrong physical effects due to the energy switch:

Bremsstrahlung

LowEnergyRayleighScattering

PhotoElectric

ElectronIonistation

Compton

Since I'm not a pysicist this is hard for me  to decide.

I really need to rely on the results. But how can I if even the effect with
the SNR is not correct. Does anyone have an idea what I'm doing wrong or
does anyone have already created a working set of scripts which covers
CT-Scans using different energies which he/she is nice enough to share?

Any help is appreciated. Thanks in advance.

Andreas

___________________________________

Andreas Duschl - Diplommathematiker (FH)

hiCAT GmbH

Brunnenallee 6

53177 Bonn

Germany

Tel  +49(0)228-854697-36

Fax +49(0)228-854697-99

<mailto:duschl at hicat.de> mailto:duschl at hicat.de

<http://www.hicat.de/> http://www.hicat.de <http://www.hicat.de/> 

___________________________________

hiCAT GmbH, Brunnenallee 6, 53177 Bonn
Gesch?ftsf?hrer: Dr. Joachim Hey, Jochen Kusch
Sitz der Gesellschaft: Bonn, Amtsgericht Bonn HRB 13452
Steuernummer:206/5924/0560

UST.-ID: DE240640137

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