• Introduction

– Conventional radiology– Why digital?– Why dual energy?

• Experimental setup• Image acquisition• Image processing and results

Dual energy radiologyDual energy radiology

Introduction: what are X-raysIntroduction: what are X-rays

Energy

10-9

10-6

10-3

1

103

106

eV

• X rays = electromagnetic radiation (=photons) in the range

– 10-11 m < < 10-8 m– 31016 Hz < < 3 1019

Hz– 0.1 keV < E < 100 keV

X-ray generationX-ray generation

• Sorgenti• Radiazione di

sincrotrone• Tubi a raggi X

37GBq1Ci

second/1decay1Bq

=

=ACTIVITY

X-ray tubeX-ray tube

At diagnostic energies more than 99% of e- energy goes into heating; less than 1% is used for X-rays!

Anode heating

K L

Ionization

Characteristic lines

KL

K-shell e- extraction

• Electrons emitted by cathod and accelerated towards the anode (W, Mo)•Then in the anode do:

Breemstrahlung

Continuous spectrumMax. energy eV

X-ray interactionsX-ray interactions

Photoelectirc effect

Compton scattering

e+e _

production

Mass attenuation coefficient (cm2/g)

Silicon

X-ray absorptionX-ray absorption• Intensity of a beam traversing a material attenuation

I(x) = I0 e-x

• Absorption coefficient: (E) = N = (NA)/ A• Radiographs are based on the different absorption

coefficient of different materials

Bones absorb more X rays than soft tissue: appear white on the radiograph (photons darken the film)

Bone:O 43.5%Ca 22.5%C 15.5%P 10.3%Other 8.2%

Soft Tissue:O 70.8%C 14.3%H 10.2%N 3.4%Other 1.3%

Conventional radiography: image receptorsConventional radiography: image receptors• Direct-exposure X-ray film

– emulsion of grains of AgBr ( 1 m) suspended in gelatin– X-rays interact mostly with Ag and Br

• Ag and Br have a larger than the elements in gelatine• A latent image is built up of sensitised BrAg grains• The latent image is then developed (senitised grains converted to silver)

– Problem: very low efficiency 0.65% of incident X-rays are detected

• Screen-film combinations– Phosphor screen to absorb X-ray photons and re-emit part of its

energy in the form of light fluorescent photons– The light photons expose the film (emulsion of AgBr in gelatine)

• The interaction of light photons with the AgBr is a photochemical reaction• The silver distribution forms the latent image

– Problem: compromise between detection efficiency and unsharpness (=loss of edge details)

• The larger the screen thickness, the larger the efficiency, but also the unsharpness

Why digital radiology?Why digital radiology?• Digital radiography has well known advantages over

conventional screen-film systems

– Enhance detecting efficiency w.r.t. screen-film

– Image analysis– Easy data transfer

Why silicon detectors?Why silicon detectors?

Main characteristics of silicon detectors:

• Small band gap (Eg = 1.12 V)

good resolution in the deposited energy

3.6 eV of deposited energy needed to create a pair of charges, vs. 30 eV in a gas detector

•Excellent mechanical properties

•Detector production by means of microelectronic techniques

small dimensions

spatial resolution of the order of 10 m

speed of the order of 10 ns

Eg=1.12 V

• Dual energy techniques

• GOAL: improve image contrast

Based on different energy dependence of

the absorption coefficient of different

materials

Enhance detail visibility (SNR)

Decrease dose to the patient

Decrease contrast media concentration

Introduction: why dual energy ?Introduction: why dual energy ?

Example 1: dual energy Example 1: dual energy mammographymammography

Example 1: dual energy Example 1: dual energy mammographymammography

E 15-20 keV:Signal from cancer tissue deteriorated by the adipose tissue signal

E 30-40 keVCancer tissue not visible, image allows to map glandular and adipose tissues

Example 2: angiographyExample 2: angiography•Angiography = X-ray examination of blood vessels

determine if the vessels are diseased, narrowed or blocked

Injection of a contrast medium (Iodine) which absorbs X-ray differently from surrounding tissues

•Coronary angiographyIodine must be injected into the heart or very close to itA catheter is inserted into the femoral artery and managed up

to the heart→Long fluoroscopy exposure time to guide the catheter→Invasive examination

•Why not to inject iodine in a peripheral vein?Because lower iodine concentration would be obtained,

requiring longer exposures and larger doses to obtain a good image

But, if the image contrast could be enhanced in some way…

Example 2: angiography at the Example 2: angiography at the iodine K-edge (II)iodine K-edge (II)

Iodine injected in patient vessels acts as radio-opaque contrast medium

Dramatic change of iodine absorption coeff. at K-edge energy (33 keV)

Subtraction of 2 images taken with photons of 2 energies (below and above the K-edge)→ in the resulting image only the iodine signal remains and all other materials are canceled

Experimental setupExperimental setup• To implement dual energy imaging we need:

• a dichromatic beam

• a position- and energy-sensitive detector

Quasi-monochromatic beams • ordinary X-ray tube + mosaic

crystals • instead of truly monochromatic

synchrotron radiationAdvantages: cost, dimensions, availability in hospitals

Linear array of silicon microstrips + electonics for single photon counting•Binary readout

•1 or 2 discriminators (and counters) per channel

•Integrated counts for each pixel are readout

• Scanning required to build 2D image

Experimental setup: beamExperimental setup: beam

Bd

chnB

Esin2

..

Bragg Diffraction on Highly Oriented Pyrolitic Grafite Crystal

W anode tube

Double slit collimator

Two spatially separated beams with different energies E-E and E+E obtained in 2 separate beams

• Fully parallel signal processing for all channels• Binary architecture for readout electronics

1 bit information (yes/no) is extracted from each stripThreshold scans needed to extract analog information

• Counts integrated over the measurement period transmitted to DAQ

• Fully parallel signal processing for all channels• Binary architecture for readout electronics

1 bit information (yes/no) is extracted from each stripThreshold scans needed to extract analog information

• Counts integrated over the measurement period transmitted to DAQ

data, control

Silicon strip detector Integrated circuit

100 m

current pulses

X-rays

PC

N. I. I/O cards PCI-DIO-N. I. I/O cards PCI-DIO-96 96

and DAQCard-DIO-24and DAQCard-DIO-24

Experimental setup: Single Photon Experimental setup: Single Photon Counting SystemCounting System

Detecting systemDetecting system

Chip RX64 → counts incident photons on each strip of the detector

4 cm

6.4 mm10 strip = 1 mm

micro-bondings

Silicon microstrip detectoreach strip is an independent detector which gives an electric signal when an X-ray photon crosses it and interacts with a silicon atom

Knowing from which strip the electric signal comes from,the position of the incoming X-ray phonton is reconstructed.

Experimental setup: RX64 chipExperimental setup: RX64 chipCracow U.M.M. design - (28006500 m2) - CMOS 0.8 µm process

(1) (1) 64 front-end channels a) preamplifierb) shaperc) 1 or 2 discriminators

(2)(2) (1 or 2)x64 pseudo-random counters (20-bit)

(3)(3) internal DACs: 8-bit threshold setting and 5-bit for bias settings

(4)(4) internal calibration circuit (square wave 1mV-30 mV)

(5)(5) control logic and I/O circuit (interface to external bus)

Cracow U.M.M. design - (28006500 m2) - CMOS 0.8 µm process

(1) (1) 64 front-end channels a) preamplifierb) shaperc) 1 or 2 discriminators

(2)(2) (1 or 2)x64 pseudo-random counters (20-bit)

(3)(3) internal DACs: 8-bit threshold setting and 5-bit for bias settings

(4)(4) internal calibration circuit (square wave 1mV-30 mV)

(5)(5) control logic and I/O circuit (interface to external bus)

11 22

3344

55

Det

ecto

rD

etec

tor

System calibration setup in AlessandriaSystem calibration setup in Alessandria

Detector in Front config.Fluorescence target

(Cu, Ge, Mo, Nb, Zr, Ag, Sn)

Cu anode X-ray tube

→ X-ray energies = characteristic lines of target material

150

100

50

0

Co

un

ts

500400300200100

Threshold (mV)

Source Am+Rb target Source Am+Mo target Source Am+Ag target Tube+Cu target Tube+Ge target Tube+Mo target Tube+Ag target Tube+Sn target

Cu K

Mo K

Ge K

Rb K

Ag K

Sn K

Ag K

Mo K

Sn K

System Tp

GAINV/el.

ENC Energy resolution

6 x RX64 0.7 s 64 ≈170 el. ≈0.61 keV

6 x RX64DTH 0.8 s 47 ≈ 200 el. ≈0.72 keV

241241Am source with rotary target holder (targets: Cu, Rb, Mo, Ag, Ba)Am source with rotary target holder (targets: Cu, Rb, Mo, Ag, Ba)Cu-anode X-ray tube with fluorescence targets (Cu, Ge, Mo, Ag, Sn)Cu-anode X-ray tube with fluorescence targets (Cu, Ge, Mo, Ag, Sn)

System calibrationSystem calibration

Imaging testImaging test1-dimensional array of strips → 2D image obtained by scanning

Cd-109 source (22.24 keV)

Detector

Collimator (0.5 mm)

Tes

t O

bje

ct

5 mm

Imaging testImaging test1-dimensional array of strips → 2D image obtained by scanning

0 1 0 2 0 3 0 4 0 5 0 6 0

5 0

6 0

7 0

8 0

9 0

1 0 0

1 1 0

1 2 0

1 3 0

1 4 0

1 5 0

1 6 0

1 7 0

1 8 0

1 9 0

2 0 0

2 1 0

C a n a le s

Pas

os

0

3 , 0 0 0

6 , 0 0 0

9 , 0 0 0

1 2 , 0 0

1 5 , 0 0

1 8 , 0 0

2 1 , 0 0

2 4 , 0 0

Sca

nn

ing

• Map the concentration of a particular element in a sample X-ray energies chosen so that the element under study has

the K-edge discontinuity between them Cancel background structures by subtracting 2 images taken

at the 2 energiesFor best background cancellation the 2 energies must be

close to each other Best choice: energies just above and below the K-edge of

the interesting material

• Art painting analysis• Isolate one typical material (ec. Zn, Cd) to date a painting

• Medical imaging with contrast medium Suited for angiography at iodine K-edge

- Cancel background structures to enhance vessel visibility Possible application at the Gadolinium K-edge (50.2 keV) Possible application in mammography (study vascularization

extent)- Hypervascularity characterizes most malignant formations

K-edge subtraction imagingK-edge subtraction imaging

X-ray tube with dual energy output

Phantom

Detector box with 2 collimators

1.1. X-ray tube + mosaic crystal and 2 collimators to provide dual-energy output X-ray tube + mosaic crystal and 2 collimators to provide dual-energy output

- E1= 31.5 keV, E2 =35.5 keV (above and below iodine k-edge)- E1= 31.5 keV, E2 =35.5 keV (above and below iodine k-edge)

2.2. Detector box with two detectors aligned with two collimatorsDetector box with two detectors aligned with two collimators

3.3. Step wedge phantom made of PMMA + Al Step wedge phantom made of PMMA + Al with 4 iodine solution filled with 4 iodine solution filled cavities of 1 or 2 mm diametercavities of 1 or 2 mm diameter

Angiography setupAngiography setup

15

10

5

0

pixe

ls

3002001000pixels

-0.8

-0.6

-0.4

-0.2

0.0

log

con

tegg

i

0 50 100 150 200 250 300 350

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

0,2 Conc(I) = 370 mg/ml Measurement Simulation

ln[c

ou

nt(

E=

35.5

Kev)]

- ln

[co

un

t(E

=31.5

Kev)]

Strip Number

15

10

5

0

pix

els

3002001000pixels

161412108642

Co

nte

gg

i (

x1

03 )

0 50 100 150 200 250 300 350

0,0

0,2

0,4

0,6

0,8

1,0 Conc(I) = 370 mg/ml E = 31.5 KeV

Measurement Simulation

Co

un

ts / M

ax.C

ou

nts

Strip Number

E = 31.5 keVE = 31.5 keV

15

10

5

0

pix

els

3002001000pixels

6

5

4

3

2

1

Co

nte

gg

i (x

103 )

0 50 100 150 200 250 300 350

0,0

0,2

0,4

0,6

0,8

1,0

Strip Number

Measurement Simulation

Conc(I) = 370 mg/ml E = 35.5 KeV

Co

un

ts / M

ax.C

ou

nts

E = 35.5 keV

5.3125.351 lnln NCNC logarithmic subtraction

Phantom structure not

visible in final image

Angiographic test results (I)Angiographic test results (I)

15

10

5

0

pix

els

3002001000pixels

-0.8

-0.6

-0.4

-0.2

0.0

log

co

nte

gg

i

Conc = 370 mg / mlConc = 370 mg / ml

15

10

5

0

pix

els

3002001000pixels

-0.3

-0.2

-0.1

0.0

0.1

0.2

log

co

nte

gg

iConc = 92.5 mg / mlConc = 92.5 mg / ml

15

10

5

0

pix

els

3002001000pixels

-0.15

-0.10

-0.05

0.00

0.05

0.100.15

log

co

nte

gg

i

Conc = 23.1 mg / mlConc = 23.1 mg / ml

100

80

60

40

20

0

SN

R

4003002001000Concentrazione (mg/ml)

cavità 4 teor. cavità 4 cavità 3 teor. cavità 3 cavità 2 teor. cavità 2 cavità 1 teor. cavità 1

Possible decrease of iodine concentration keeping the same rad. dose

Angiographic test results (II)Angiographic test results (II)

nsfluctuatioBckgr

CountsBckgrCountsSig

contrastNoise

contrastSignalSNR

.

..

Results with a second phantomResults with a second phantom

140 140

120 120

100 100

80 80

60 60

40 40

20 20

0 0

300

um p

ixel

300

300

200

200

100

100

0

0

100 um pixel

140 140

120 120

100 100

80 80

60 60

40 40

20 20

0 0

300

um p

ixel

300

300

200

200

100

100

0

0

100 um pixel

140 140

120 120

100 100

80 80

60 60

40 40

20 20

300

um p

ixel

300

300

200

200

100

100

0

0

100 um pixel

Phantom

Digital SubtractionAngiography

Dual Energy Angiography

smaller cavity (=0.4 mm) visible in DEA and not in DSA

Iodine conc. = 95 mg/ml

Application to art painting analysisApplication to art painting analysis Detect the presence of cadmium in a painting

60

50

40

30

20

10

0

3002001000

E = 24.2 keV

60

50

40

30

20

10

0

3002001000

E = 27.5 keV

Cd K-edge = 26.7 keV

Cd red

Cu red

Test object

60

50

40

30

20

10

0

3002001000

logarithmic subtraction

After subtraction:• Cd grains contrast enhanced• Cu wires contrast decreased