Medical Imaging

1. Redefining the Rules of clinical CT
Imaging with Spectral Imaging and
Iterative Reconstruction techniques
Johan de Mey PhD. MD Head of Radiology Department
Koenraad Nieboer MD Head of Emergency Radiology
Nico Buls PhD. MSc Medical Imaging and Physical Sciences
Gert Van Gompel PhD. MSc Medical Imaging and Physical Sciences
Toon Van Cauteren MSc Medical Imaging and Physical Sciences

2. Multislice CT and clinical outcome
What makes a good CT?
accuracy
Spatial
Resolution
Temporal Coverage
perfusion
Workflow Dose
Characterization

3. Low Dose CT = quality ?
1980 – 2007: Dose optimalisation
More images
Higher resolution
2008 - …: Dose optimalisation
Less dose??? Functional???
Iterative recon Dual energy

4. Noise suppression
The straightforward way…
increase # photons, increase patient dose (mAs)
10 mAs 60 mAs 120 mAs
CTDIv = 0,8 mGy CTDIv = 5 mGy CTDIv = 10 mGy

5. Effective doses for CT procedures
(review over 20 published articles)

6. Does the age of the patient at time of
exposure affect the patient risk?
Children are 2-10 x more sensitive!
Hall Pediatric Radiology Apr 2002 pg 226

7. Iterative reconstruction
detector
s
θ
source
source
Image acquisition sinogram Goal:
reconstruction

8. Adaptive Statistical Iterative Reconstruction
(0%.....100%) and noise
45
40
35
30
noise
25
20 0.8 mGy
15
10
5 16.8 mGy
0
0 20 40 60 80 100
asir (%)
GE CT750 HD, 100 kVp, p = 0.9, r = 1, t = 2.5 mm, FOV = 230 mm

9. ASIR (60%) and Spatial resolution
FBP
18
17
16
15
14 FBP
13
ASIR
12
11
ASIR 10
9
-6 -4 -2 0 2 4 6

10. Female 45
 Acute dyspnea, suspicion pulmonary
embolism
 Scan Parameters
 Range 26 cm Ni: 30
 120KV ASiR: 40%
 CTDIv 7.44 (mGy)
 E 2.7 (mSv)
0.625 mm
1.25 mm
1.25 mm

11. Body packers: low dose CT / GSI
ECR EPPOS: C-2068 ECR 2011 K. H. Nieboer, N. Buls, J. de Mey, G. Van Gompel; Brussels/BE, The use of iterative
reconstruction in ultra low dose computed tomography for bodypacker screening

12. VeoTM – future in dose reduction
= Model Based Iterative Reconstruction
REAL 3D
SYSTEM
OPTICS
SYSTEM NOISE
STATISTICS

13. FBP ASIR VEO

14. Iterative – impact on image noise
100
90
N 80
FBP
o 70
Relative Noise (SD)
i 60
s 50
e 40 ASIR50
30
20
10
VEO
0
0 50 100 150 200 250 300 350 400 450 500
tube current - relative radiation dose
Tube current

15. Resolution at standard dose
Catphan 504 phantom
CTDIvol = 12.5 mGy
FBP ASIR 50% VEO
Performance at 6 lp/cm and 8 lp/cm

16. Ultra low dose Chest follow-up with VEO
4mAs, 0.06mSv*
FBP ASiR Veo
“Typical CXR effective dose is about 0.06 mSv.”
Source: Health Physics Society.
http://www.hps.org/publicinformation/ate/q2372.html * Determined by internal organ dosimetry on a humanoid phantom

17. Chest CT with Veo – Cystic Fibrosis 26y
CDTIvol = 0.10 mGy
Effective dose = 0.05 mSv*
* Obtained by EUR-16262 EN, using a chest factor of 0.017*DLP
Conversions of CTDI or DLP to effective dose are only rough estimations for children

18. Chest CT with Veo – Cystic Fibrosis 15y
FBP- Images 2010 FBP-images 2011 Veo-images 2011
Low dose Ultra low dose Ultra low dose
DLP = 54,3 mGy.cm DLP = 2.51 mGy.cm
CTDIvol: 1,65 mGy CTDIvol:0,09 mGy
Scan protocol: 4 mAs, 80 kV
Slice thickness: 0.625mm

19. Chest CT with Veo – Cystic Fibrosis 15y
FBP reconstruction 2010 VEO reconstruction 2011
95 % dose reduction

20. Chest CT with Veo – Cystic Fibrosis 15y
Previous Chest X-ray Veo-images: Ray Sum CT

21. PATIENT 1 (2010) PATIENT 2 (2011)
3Y Old, empyema 3 y old, empyema
FBP-images Veo-images
CTDi 2.1 CTDi 1.25
40% dose reduction

22. Pediatric maxilo-facial CT with Veo <9y
Patient 1 Patient 2
FBP-images 2010 Veo-images 2011
DLP = 348.88 mGy.cm DLP = 18.04 mGy.cm

23. VEO: Liver Lesion Detection Study
Standard FBP FBP
10 mA FBP VEO
10 mA VEO
20 mA FBP 20 mA VEO

24. VEO: Liver Lesion Detection Study
 Dose Reduction
Standard dose VEO 10 mA VEO 20 mA
7.22 mSv 0.25 mSv 0.45mSv
-28.9 (-96.5%) -16 (-93.8%)

25. VEO: Liver Lesion Detection Study
 ROC analysis
1
0.9
0.8
0.7
0.6
Sensitivity
0.5
0.4
FBP full dose
VEO 10mA
0.3
VEO 20mA
0.2
0.1
0
0 0.2 0.4 0.6 0.8 1
1-Specificity

26. Iterative reconstruction
impact on Contrast reduction with low kVp
12
10
8
CNRD
6
4 120 kVp
100 kVp
2
80 kVp
0
1 2 3 4 5 6 7 8 9 10
iodine concentration (mgI/ml)
CNRD increases for low beam (kVp) energies

27. Low kVp scanning with ASiRTM and VeoTM
Potential Iodine reduction for equal CNRD compared to 120 kV
75 %
compared to standard
70 %
contrast fraction
65 %
60 % 120 kV ASIR60% 120 kV VEO
55 %
50 %
45 %
40 %
35 %
30 % 80 kV ASIR60 80 kV VEO
6 8 10
mgI/ml
at CTDIvol of 10.7 mGy

28. 120 kV - 320 mgI/ml - 100 % dose
standard
FBP ASIR 60% VEO
Aorta: 251.8(±34.1) Aorta: 249.8(±23.8) Aorta: 250.5(±19.5)
Muscle: 71.0 (±24.3) Muscle: 72.9(±15.7) Muscle: 72.2(±9.3)
80 kV - 170 mgI/ml - 50% dose
equal better
FBP ASIR 60% VEO
Aorta: 245.6(±53.6) Aorta: 245.7(±33.1) Aorta: 243.5(±16.0)
Muscle: 69.2 (±48.8) Muscle: 68.3(±33.0) Muscle: 68.7(±12.8)

29. Conclusion: Modal based Iterative reconstruction:
1. >95% dose reduction CT at plain film dose +/- 0.06 mSv
1. 70% dose reduction No quality loss
1. 50% dose and low KVp No quality loss + 50 % contrast reduction
1. 40% dose reduction Better image, less artifacts
1. Equal dose and low KVp Up to 60% contrast reduction

30. Dual energy…spectral imaging:
Need for at least two datasets on different energy level
Discovery CT750 HD
Dual tube
Fast switching tube
Making two scans
Dual layer detector
Photon counting

31. Dual energy…spectral imaging:
Need for at least two datasets on different energy level
Discovery CT750 HD
Dual tube
FOV max 33 cm
Spectral filter on 140
Making two scans
Time Difference
FOV 50 cm
Dual layer detector
Research Real Time
Photon counting
Future ?

32. Photon energy with Tungsten? What is dual energy?
120 KV scan Mean 61.1 KeV
80 KV scan Mean 49.9 KeV 140 KV scan Mean 66.1 KeV

34. Spectral – material differentiation

35. From 2 datasets to 101 datasets? Is this real?
Phantom data
Qualitative comparison DECT
<-> literature (NIST)
ECR: B-851 Monday 14.00
G. Van Gompel, N.Buls, K. Nieboer, J. de Mey
Accuracy estimation of spectral attenuation curves obtained by dual energy

36. Clinical use?
Cadaver blood vessels
Filled with CM concentration, GSI scan
ROI2: water + CM
ROI3: soft plaque
ROI4: calcified plaque

37. „Relative‟ dose reduction? (No need for non-CE scans)
Contrast reduction? (Higher contrast in image)
Iodine
Water
250
CNRD @ iodineconc 1mgI/ml
200
1 mg I / ml 2
1.8
150 1.6 120
1.4
CT value (HU)
kV
1.2
CNRD
100 1 GSI v2
0.8
0.6
50 0.4
0.2
0
0
40 60 80 100 120 140
30 50 70 90 110 130
Photon energy (keV)
energy (keV)

38. Pleural effusion: Exudate >< transudate?
ECR EPOS: C-1996 Y. De Brucker, N. Buls, G. Van Gompel, F. Vandenbroucke, H. Nieboer, T. De Keukeleire, J.
de Mey; Brussels/BE Characterization of pleural effusion using dual energy CT: feasibility study.

39. Phantom size on quantitative iodine measurement:
dual energy CT >< standard CT.
Obtained CT-values (HU)
120 keV GSI 70 keV
Ø 23 cm 291 9 310 6
Ø 17 cm 325 5 315 8
Ø 17 cm + t 318 9 314 5
range 34 5
VAR 10.9% 1.6%

40. Standard
Phantom size on quantitative iodine measurement:
spectral CT >< standard CT.
Standard Spectral
120 kV DECT at 70 keV

41. Male 77
 Acute dyspnea, suspicion
pulmonary embolism
Axial recon image
Monochromatic 40 – 140 KeV Iodine image Water image

42. Water image Iodine image
Scatterplot

43. S GSI: spectral imaging
Subsegmental pulmonary embolism
Clinical value
• Pulmonary embolism was not
Embolism depicted during 1st reading on
standard images
• MD Iodine shows clearly a hypo
perfusion on the left.
• 2nd reading confirms pulmonary
embolism resulting from a small
thrombus in a small pulmonary
vessel
• GSI allows physicians to
detect pulmonary embolism by
showing subtle lung perfusion
defect

44. Pulmonary Embolism
Clinical value
• Pulmonary embolism was
not depicted during 1st
reading on standard images
• MD Iodine shows clearly a
hypo perfusion in left lung
resulting from a pulmonary
embolism. Hypo perfusion
could not be seen on
standard CT image
Iodine Based Images 70 keV images with lung window
• 2nd reading confirms
pulmonary embolism resulting
from a small thrombus in a
small pulmonary vessel
• GSI allows physicians to
detect pulmonary embolism
by showing subtle lung
perfusion defect
70 keV Monochromatic Images 70 keV Monochromatic Images
Images Courtesy of Dr. Jean Louis Sablayrolles; Centre Cardiologique du Nord

46. Standard 120 kV acquisition
GSI: Artefact reduction Monochromatic with MARs

47. Iliac Stent Bleeding
Clinical value
• Endoleak is better
visualized on low energy
(55 keV) images (green
Arrows)
80 keV MD Water (Iodine)
• MD Iodine suggests Iodine
leak
• GSI allows physicians to
better visualize bleeding
vs. conventional CT
MD Iodine (Water) 55 keV
Images Courtesy of Pr Dacher, CHU de Rouen

48. Metal Artifact Reduction: Spine
• GSI acquisition allows to
create a spectrum of
monochromatic images
where beam hardening is
highly reduced
• In this case the radiologist
could recover information
previously hidden by the
beam hardening
70 keV image 110 keV images
Images Courtesy of Dr. Sablayrolles, CCN, France

49. Conclusion: New dimensions in CT
 Statistical iterative reconstruction: important dose reduction
- Dose reduction up to 50% and same quality
- Scanning at low KVp and contrast reduction
- In some cases alternative for plain film
 Spectral imaging and real iterative rec.: a new dimension in CT
- Ultra low dose at diagnostic quality up to 95% reduction
- Artifact reduction and high quality images
- Characterization and differentiation
- Contrast amount and concentration reduction
Thank you for your attention