Download Update Course in Diagnostic Diagnostic Radiology Radiology

RSNA 2010, Chicago, Nov. 28 - Dec
Dec.. 2, 2010
Update Course in
Diagnostic Radiology Physics
Physics::
CT and MR Imaging
Directors::
Directors
Willi A. Kalender, Ph.D. (CT)
Ed Jackson, Ph.D. (MR)
Categorical Course in Diagnostic Radiology Physics:
Physics: CT and MR
RSNA 2010, Chicago, Nov. 28, 2010, RC 132A
CT Image Generation:
From MultiMulti-Slice to ConeCone-Beam CT
A. Advances in CT Technology
Willi A. Kalender, Ph.D.
Institute of Medical Physics
University of Erlangen
http://www.imp.uni--erlangen.de
http://www.imp.uni
AuntMinnie
http://www.auntminnie.com
On Nov. 16, 2009 AuntMinnie wrote:
It‘s not for nothing that CT is able to
maintain its star status at the RSNA show
year after year. Extraordinary flexibility in
head-to-toe
head
to toe imaging applications,
combined with rapid technological
advancement, make CT the modality to
beat once again in 2009.
This year’s Chicago meeting will highlight
several powerful technical innovations
….
Seite 1
1
CT Development:
from fan beam to
cone beam
z
RSNA
1998
1×5 mm 4×1 mm
0.75 s
0.5 s
1995
1998
RSNA
2001
RSNA
2004
RSNA
2008
16×0.75 mm 64×0.6 mm 320×0.5 mm
0.42 s
0.33 s
0.3 s
2001
2004
2009
RSNA
20??
2048×0.4 mm
0.2 s
20??
Advances in CT Technology
• State of the art in clinical CT
• CT Technology
• Flat detector CT
Spiral CT: Scanning Principle
Start of
spiral scan
Path of continuously
rotating x-ray tube
and detector
RSNA 1989
Direction of
continuous
patient transport
0
z, mm
0
t, s
Kalender WA et al. Radiology 1989; 173(P):414 and 1990; 176:181-183
Seite 2
2
State of the Art in Multi
Multi--slice Spiral CT
RSNA 2009
Rotation time per 360°
0.27 - 0.35 s
Slice width
0.5 - 0.6 mm
simultaneously scanned slices
64 (- 320)
z-coverage per rotation
40 - 160 mm
Scan times „whole body“
2 - 20 s
Scan range
>1000 mm
Isotropic spatial resolution
0.4 - 0.6 mm
Effective dose
<1 - 10 mSv
Typical values for high-performance scanners
Spiral CT Angiography in 2004
• 64-slice scanner
• 3 s total scan time
• 0.5 mm isotropic spatial resolution
• 2.4 mSv effective dose
Advances in CT Technology
• State of the art in CT
• Technology
- X-ray sources
- X-ray detectors
- Scanner design
- Dual source CT
- Dual energy CT
- Dose management
• Flat detector CT
Seite 3
3
X-ray Sources for CT
• Limited x-ray power was a severe
problem in the 1980s and 1990s.
• Peak power values of up to 120 kW
are available today.
• Shorter and shorter rotation times
demand higher power values.
• Reduced weight and size of tubes
would be very welcome.
Rotating Anode XX-ray Tubes
The principle of x-ray tube developments for CT
over the years:
Increase the anode‘s mass
to allow for higher heat capacity
”Rotating Vacuum Vessel“ XX-ray Tube Technology
with zz-flying focal spot ((zFFS
zFFS))
Rotating vacuum vessel
Oil for HV insulation
and cooling
Emitter
Straton tube
Motor
Deflection coils
Housing
Ball bearings
Electron beam
X-rays
Schardt et al. Medical Physics 2004; 31:2699-2706
Seite 4
4
A high-power
X-ray tube
Double z-Sampling Technology
z-Flying Focal Spot
Electromagnetic Control
of the Electron Beam
Rotating
Anode
z
0,6 mm
0,6 mm
32 detector rows
(64 slices scanned)
Sampling distance: 0.3 mm
Kalender WA. Computed Tomography. 2nd ed. Wiley, New York 2005
Impact of the zFFS on z-Resolution
MTFs in the z-direction
x
1.2
without zFFS
0.4 mm
1
0.4 mm
with zFFS
z
M TFz
0.8
0.6
04
0.4
0.5mm
0.2
0.5 mm
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
lp/mm
0.6 mm
0.6 mm
without zFFS
with zFFS
Kyriakou … Kalender. Eur Radiol 2006; 16:1206-1215
Seite 5
5
Impact of the zFFS on windmill artifacts
without zFFS
with zFFS
ASSR reconstruction, p=1.2
X-ray Detectors for CT
• Detectors remain to be the most critical
and most costly component of CT scanners.
• Single- and dual row detectors
were used for nearly three decades.
decades
• Multi-row or array detector technology,
introduced in 1998, dominates today.
• 64-slice scanners may offer the optimum
solution for clinical CT.
Multi--row Detectors for Multi
Multi
Multi--slice Spiral CT
D
# rows
M
Smin
# slices mm
z-extent
Mm
GE
64
64
0.625
40.0
Philips
128
256*
0.625*
80.0
Siemens
64
128*
0.6*
38.4
Toshiba
320
Example
320 of a 64-row
0.5 detector
160.0
T. spiral
64 (of 320) 64
(55 modules with 16 channels)
0.5
32.0
*overlapping slices at
0.3 mm increments
Seite 6
6
Standard 6464-slice Multi
Multi--Row CT detector
grid
anti-scatter
protect gaps
64 x16 module
scintillator
reflector
optical coupling
photodiode
amplifiers
and
digitizers
55 × 16 channels, 64 rows
Problems associated with wider detectors
(higher number of rows, greater zz-coverage)
•
Potential image quality problems
•
Higher scattered radiation intensities
•
X-ray tube heel effect
•
Reduced potential for dose optimisation
•
Dose increase in step-and-shoot mode
•
Cost
•
….
Î There are many reasons against
a continuation of the “slice race“
Advantages of wider detectors
(higher number of rows, greater zz-coverage)
•
Dynamic scanning, in case all the anatomy
of interest is covered in a single rotation,
e.g. for brain perfusion measurements.
However,
•
modern 64-slice scanners offer shuttle modes
which allow fast and repeated measurements
with the scan range freely adapted to needs
even for wider ranges.
Seite 7
7
Advances in CT Technology
• State of the art in CT
• Technology
- X-ray sources
- Detectors
- Scanner design
- Dual source CT
- Dual energy CT
- Dose management
• Flat detector CT
Demands on faster scanners
• Mechanic design
has to withstand very fast rotation.
Centrifugal forces acting on the x-ray tube
Î 30 g
for
trot
d
= 300 ms
= 65 cm
rotation time per 360°
distance to center of rotation
“Air--borne“ CT Gantry
“Air
offering
very high rotation speed
with no wear on
components
Schleifring
Seite 8
8
Demands on faster scanners
• Mechanic design
has to withstand very fast rotation.
Centrifugal forces acting on the x-ray tube
Î 30 g
for
trot
d
= 300 ms
= 65 cm
rotation time per 360°
distance to center of rotation
• X-ray power
has to increase with higher speed
Î by 1/trot
for
trot
< 300 ms
P > 100 kW are required
A DualDual-Source CT (DSCT) System
Dual Source CT (DSCT) *
• System set-up
– 2 Straton tubes and 2 x 128-slice
acquisition with double z-sampling
– 280 ms gantry rotation
– 50 and 33 cm field of view
• X-ray power
– Acquisition with up to 2 x 100 kW
• Cardiac CT
– 75 ms temporal resolution (trot/4)
• Dual Energy CT
– Simultaneous acquisition with 80 kV / 140 KV
with 0.5 mm tin filter added for the 140 kV beam
* SOMATOM Definition Flash, Siemens Healthcare, Forchheim, Germany
Seite 9
9
Temporal Resolution
Phase-correlated reconstructions
for heart rates of 40 – 120 bpm
60 bpm
80 bpm
100 bpm
120 bpm
DSCT
SSC
CT
Sphere at rest 40 bpm
Ertel … Kalender. Radiology 2008; 248:1013-1017
Dual Source Cardiac CT
DIASTOLE
SYSTOLE
Achenbach et al., Eur J Radiol 2006; 57(3):331-335
How about a cardiac exam
in about a quarter of a second?
Scan range
Collimation
Rotation time
Pitch
12 cm
38.4 mm
280 ms
3.4
Î
Table speed
Scan time
46.6 cm/s
0.26 s
= 1.59 km/h !!
Seite 10
10
High--pitch dual
High
dual--source CT
0.26 s
Flash Cardiac
Scan direction
75 ms
per
slice
Scan only for one
heart phase and
only during one
heart beat
and at minimum
radiation dose !!!
Cardiac DSCT
with high pitch
100 kV
320 mAs
59 bpm
triphasic CM injection
60 ml Ultravist 370
+ 50 ml saline bolus
Effective dose
0.98 mSv
Courtesy of S. Achenbach, University of Erlangen
Flash performance: High speed
Spiral CT angiography
scan range
pitch
rot. time
Î
scan time
dose
700 mm
2.8
280 ms
1.8 s
1.4 mSv
Seite 11
11
Spatial resolution
Pitch factor: 3.0
Pitch factor: 1.0
0.4 mm
0.4 mm
Ertel D, … Kalender WA. Eur Radiol 2009
Thoracic CT with Flash
Chest Pain – Pulmonary Embolism
100 kV
370 mAs
51 bpm
triphasic CM injection
60 ml Ultravist 370
+ 50 ml saline bolus
Scan time
0.7 s
Courtesy of M. Lell, University of Erlangen
Dual Energy CT Applications
approved by the FDA 2007
1.
2.
3.
4
4.
5.
6.
7.
8.
9.
10.
Direct subtraction of bone
Differentiation between plaque and contrast agent
Virtual unenhanced abdominal organ imaging
Kidney stone characterization
Visualization of cartillage, tendons, ligaments
Evaluation of lung perfusion defects
Heart perfusion blood volume
Uric acid crystal visualization
Lung vessel emblisation
Brain hemorrhage differentiation
Seite 12
12
Dual Energy CT: 1. Direct Bone Removal
Courtesy of C. Becker, Munich, Germany
Dual Energy CT: 2. Differentiation between
hard plaques and contrast
Courtesy of F.Civaia, Centre Cardiothoracique de Monaco
Dual Energy CT: 2. Differentiation of
hard plaques and contrast
Plaque
Plaque ON
OFF
Courtesy of M. Lell, Erlangen, Germany
Seite 13
13
Dual Energy CT: 7. Cardiac Perfusion
I di
Iodine
concentration
in the
myocardium
depicting
perfusion
deficit
vs. Angiography and SPECT
Courtesy of J. Schoepf, Charleston, SC, USA (Circulation, 2008)
Technical Implementations of DECT
• 1970s ff.: Separate scans
obtain 2 successive scans at high and low voltage,
possibly with different filtration
• 1980s: Rapid kV-switching
obtain data at high and low voltage values
in a single scan with fixed filtration
• 1990s ff.: Novel detectors
photon-counting energy-discriminating detectors &
sandwich detectors
• 2000s: Dual Source CT
obtain data simultaneously in a single scan
with mA values and filtration adapted separately
DECT will be covered in RC 432 on Tue at 04:30 p.m.
Dose Management in Modern CT
(RC 732 on Thu at 16:30 a.m.)
Tube current modulation (TCM) and
automated exposure control (AEC)
(AEC),,
introduced in the late 1990ies
and generally available since a few years
years,,
are the essential building blocks.
blocks.
The principle simply is
is::
Adapt the tube current and thereby the x-ray intensity
to the attenuation given for any projection
as a function of rotation angle and z-position
Seite 14
14
In--plane TCM (α
In
(α-TCM)
Attenuation (central ray)
3603
43
0°
0
projection angle α
360°
360
Tube current (for central ROI)
max
Attenuation for the central ray:
in a.p. direction:
43
in lateral direction: 3603
min
0°
projection angle α
360°
Tube Current Modulation (TCM) and
Automatic Exposure Control (AEC)
Standard CT
re
el. image noise
re
el. tube current
re
el. image noise
re
el. tube current
TCM & AEC
α-TCM
z-TCM
z
C 40/W 500
z
C 40/W 500
Principle of operation
Detectors with smaller z-extent yield better performance!
Kalender WA. Computed Tomography. 2nd ed. Wiley, New York 2005
Advances in CT Technology
• State of the art in CT
• Technology
• Flat detector CT
- C-arm-based CT
- Facio-mandibular skull CT
- Breast CT
- Micro-CT
-…
3D Angio
(since <2000)
Seite 15
15
CT Imaging using rotating C-arm Systems
Image Intensifiers
Flat-Panel Detectors
CT Imaging using rotating C-arm Systems
3D Angio
(since <2000)
after intraarterial injection
with image intensifiers
Dyna CT
(since >2000)
after intravenous injection
with flat panel detectors
Interventional Radiology: Vertebroplasty
Images:
Courtesy of Arnd Dörfler,
Erlangen
Seite 16
16
Interventionl Radiology: Vertebroplasty
Images:
Courtesy of Arnd Dörfler,
Erlangen
FD-CT is still inferior to clinical CT
with respect to image quality
and dose utilisation,
but itt offers
o e s excellent
e ce e t co
conditions
dto s
for interventional procedures
and for intraoperative imaging!
Hepatocellular
Carcinoma;
Embolization
Embolisation of a hepatocellular carcinoma
Images: Courtesy of PD R. Loose, Nuremberg
3D Patient Dose Distributions
calculated by Monte Carlo methods
methods**
Kyriakou Y, Dörfler A, Kalender WA. AJNR 2008
* Deak, van Straten, Shrimpton, Zankl, Kalender. Eur Radiol 2008; 18:759-772
Seite 17
17
Robot--driven C-arm Systems
Robot
Prototype in operation
since June 2006
Product installation
in November 2007
Large Volume Coverage with
Robot--driven C
Robot
C--arm CT
30×
30
×40 cm² detector
Conventional mechanics: < 25 cm diameter, <20 cm height
Courtesy of M. Reiser Munich, Germany
… and Fluoroscopy
UFE: 3D vascular anatomy
Courtesy of M. Reiser Munich, Germany
Seite 18
18
C-arm system rotating at 100
100°°/s
to make perfusion measurements
C-arm system rotating at 100
100°°/s
to make perfusion measurements
0~2 s
4~6 s
8~10 s
12~14 s
16~18 s
20~22 s
24~26 s t
High--Resolution CT of the Breast
High
Micro--CT scan of surgical specimens
Micro
DCIS specimen
embedded in paraffine
HiRes Micro-CT
40 µm resolution
Kalender WA. Eur Radiol 2009; 19(S4):849-852
Seite 19
19
Breast CT scanner concept
Transition from
single-circle
singleto
flat detector
spiral
CT detector
Pre-clinical testing expected for the end of 2011
Kalender WA. Eur Radiol 2009; 19(S4):849-852
Thank you for your attention!
attention!
[email protected]
[email protected]
-erlangen.de
Seite 20
20