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Functional computed tomography
using energy resolved
photon counting detectors
Anthony Butler
Overview

Why functional imaging

Recent trends in clinical imaging

Spectral CT and the MARS project

Medical applications


Radiopharmaceutical imaging

Soft tissue imaging
Conclusions
Change in radiology utilisation
1998-2005 => 4.5% /year
2006-2008 => 1.4% /year
Bending the Curve: The Recent Marked Slowdown in Growth
of Noninvasive Diagnostic Imaging
American Journal of Roentgenology, Jan. 2011
Drivers of change
2000-2008 “CT Slice War”

fan beam geometry to cone beam geometry

2000: acquire a single transverse slice per rotation

2012: acquire up to 64-500 slices per rotation
Current State
Anatomical imaging is now really good
Very little benefit in more speed or resolution
Anatomical imaging is now really good
Functional imaging is the future
What is the tissue?
What is its behaviour?
Is the treatment working?
(not just size, shape, location)
What the diagnostician wants to know

Constituents (fat, water, calcium, iron)

Cancer and pathogen labels

Physiological markers

etc
MARS spectral CT project
Goals


To obtain novel information about tissues

Compositional information

Functional information
To have a route to human imaging
The Team
Technical team
University of Canterbury
Clinical team
University of Otago
International Partners
Incl. CERN, Mayo Clinic, etc
The company
MARS Bioimaging Ltd
Single
energy CT
Single- , dual-, and spectral CT
Xray source
B/W
Patient
Grey scale
detector
Hounsfield Units
Single
energy CT
Single- , dual-, and spectral CT
Xray source
B/W
Dual energy
CT
Patient
Grey scale
detector
Xray source
B/W
Xray source
B/W
Two grey
scale detectors
Hounsfield Units
Single
energy CT
Single- , dual-, and spectral CT
Xray source
B/W
MARS
spectral CT
Dual energy
CT
Patient
Grey scale
detector
Xray source
B/W
Xray source
B/W
Two grey
scale detectors
Xray source
Medipix
Color
detectors
Hounsfield Units
Spectral CT is now possible
Medipix All Resolution System
Energy resolution
Spatial resolution
Temporal resolution
Current single-energy CT provides
Spatial resolution
Temporal resolution
Brightness only (grey scale)
X-ray camera

Medipix3 photon processing detector

Quantum / counting detector
(Film, CR, DR, CT are all integrating detectors)

Pixel detector

Each pixel has its
own electronics

Spectral detector

Measure energy of photons
Reconstruction tailored to photon
counting
Photon counting detectors poor in high flux
0.15
Water
x-ray
source
Ca
Fe
Sunflowe
r oil
Iodine
0.1
0.05
0
Medipix
Air
Reconstruction tailored to photon
counting
Photon counting detectors poor in high flux
High x-ray flux beam
0.15
Water
x-ray
source
Ca
Fe
Sunflowe
r oil
Iodine
0.1
Medipix
Air
0.05
High x-ray flux beam
0
Reconstruction tailored to photon
counting
Reconstruct only from central detector elements
0.15
Water
x-ray
source
Ca
Fe
Sunflowe
r oil
Iodine
0.1
0.05
0
Medipix
Air
ROI
Measure individual materials
Iodine: Pulmonary circulation
Barium: Lung
Calcium: normal bone
Pharmaceuticals identified by
spectral information
Iodine: Pulmonary circulation
Barium: Lung
Calcium: normal bone
Functional cartilage imaging
Histology and spectral CT to demonstrate GAG content
•
Low GAG
•
High hexabrix
Cartilage
Bone
- Volume rendering
- Energy gradient by PCA
•
High GAG
•
Low hexabrix
Funded by NZ Arthritis Foundation
Quantification of fat and water
Spectral CT of a mouse
10-35keV
“Fat-like”
“Calcium-like”
Initial work funded by Health Research Council
“Water-like”
Atheroma characterization
Aim to indentify plaque
components
Unstable plaques need
therapy
Next Steps:
Ca versus Fe
Inflammatory markers
Funded by National Heart Foundation
The future: Functional labels
•Complex physiological markers can be
made
•These often have unique spectral response
(contain heavy atoms)
We can measure the spectral response of
nano-particle that target aggregated
platelets.
Next step: Measure them in mice…
Conclusion

Recently radiology improvements have been
speed and spatial resolution

Functional imaging is the future of radiology

Spectral CT is able provide this information
Anthony Butler, M Walsh, P Ronaldson, N Scott, R Zainon,
S Geiseg, T Janmale, N Cook, A Opie, R Amir, R
Doesburg, N de Ruiter,H Yu, J Bennett, G Wang, T
Woodfield, N Cook, P Bones, J Mohr, N Anderson, P
Butler