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Transcript of Trends in X-ray CT Imaging and respective demands on...
iworid 2008, Helsinki, 30iworid 2008, Helsinki, 30--JuneJune--20082008
Trends in X-ray CT Imagingand respective demands on detectors
Willi A. Kalender, Ph.D.Willi A. Kalender, Ph.D.
Institute of Medical PhysicsInstitute of Medical PhysicsUniversity of ErlangenUniversity of Erlangen
http://www.imp.unihttp://www.imp.uni--erlangen.deerlangen.de
X-ray Computed Tomography• State of the art in clincal CT
• Technology for clinical CT
• Flat detector CT
• Discussion and Conclusions
Kalender WA et al. Radiology 1989; 173(P):414 and 1990; 176:181-183
Start ofspiral scan
Path of continuouslyrotating x-ray tubeand detector
Direction of continuouspatient transport 0
0 t, s
z, mm
Spiral CT: Scanning PrincipleSpiral CT: Scanning Principle
1×5 mm0.75 s1995
4×1 mm0.5 s1998
64×0.6 mm0.33 s2004
1024×0.5 mm<0.3 s
>2007?
CT Development: CT Development: from fan beam to cone beamfrom fan beam to cone beam
z
16×0.75 mm0.42 s2001
Rotation time per 360° 0.3 - 0.4 s
Slice width 0.5 - 0.6 mm
simultaneously scanned slices 64 - 320
z-coverage per rotation 40 - 160 mm
Scan times „ whole body“ 10 - 30 s
Scan range >1000 mm
Isotropic spatial resolution 0.4 - 0.6 mm
Effective dose 1 - 20 mSv
State of the Art in MultiState of the Art in Multi --slice Spiral CTslice Spiral CTRSNA 2007RSNA 2007
Typical values for high-performance scanners
���� 28 seconds scan with 0.4 mm isotropic resolution
X-ray Computed Tomography• State of the art in clincal CT
• Technology for clinical CT- X-ray detectors- Dual source CT- Dual energy CT
• Flat detector CT
• Discussion and Conclusions
XX--ray Detectors for CTray Detectors for CT
• Detectors remain to be the most criticaland most costly component of CT scanners.
• Linear detector arrays were used for about three decades.
• Today multi-row or array detector technology dominates.
D, # rows M, # slices
GE LIGHTSPEED CT/i 16 4
Marconi (Picker) Mx8000 8 4
Siemens SOMATOM VZ 8 4
Toshiba Aquilion 34 4
All offer simultaneous acquisition of four slices!
MultiMulti --row Detectors for Multirow Detectors for Multi --slice Spiral CTslice Spiral CTannounced in 1998announced in 1998
’’Adaptive Array DetectorAdaptive Array Detector ’’
4 images per 360° scan
Variable slice collimation by near-focus collimators and electronic switching
5 mm 5 mm2.5 mm2.5 mm 1.5 1.51 1
4 x 2.5mm
4 x 5mm
2 x 0.5mm
4 x 1mm
‘Ultrafast‘ ceramic scintillator (UFC)
’’Matrix Array DetectorMatrix Array Detector ’’
4 images per 360° scan
Variable slice collimation by near-focus collimators and electronic switching
1.25 mm
4 x 3.75mm
4 x 5mm
4 x 1.25mm
4 x 2.5mm
MultiMulti --row Detectors for Multirow Detectors for Multi --slice Spiral CTslice Spiral CT
at RSNA 2007at RSNA 2007
D# rows
M# slices
Smin
mmz-extentmm
GE 64 64 0.625 40.0
Philips 128 256 0.625* 80.0
Siemens 64 128 0.6* 38.4
Toshiba 320 320 0.5 160.0
*overlapping slices at 0.3 mm increments
55 × 16 channels, 64 rows
Number of CT SlicesNumber of CT Slices
0
50
100
150
200
250
300
350
400
450
1986 1990 1994 1998 2002 2006 2010
Year
Num
ber
of D
etec
tor
Row
s
x4 every 3 yearsx4 every 3 years
?
?
Courtesy of G. Glazer, Stanford, 2004
Moore‘s law:
„ Computing power doubles
every 18 months“
What is still needed in clinical CT?What is still needed in clinical CT?
• Higher temporal resolutionfor reliable cardiac imaging
• Higher x-ray power
• Larger z-coverage for perfusion measurements
• New and advanced applications
• More parameters than just Hounsfield units
• ….
““ AirAir--borneborne““ CT GantryCT Gantry
offering offering very high rotation speedvery high rotation speedwith no wear on with no wear on componentscomponents
Schleifring
Demands on faster scannersDemands on faster scanners
• Mechanic designhas to withstand very fast rotation. Centrifugal forces acting on the x-ray tube
���� 30 g for trot = 300 ms rotation time per 360°
d = 65 cm distance to center of rotation
• X-ray powerhas to increase with higher speed
���� by 1/trot
for trot < 300 ms P > 100 kW are required
Dual Source CT System *Dual Source CT System *
• System set-up– 2 Straton tubes and 2 x 64-slice
acquisition with double z-sampling
– 330 ms gantry rotation
– 1.6 tons rotating mass
• X-ray power – Acquisition with up to 2 x 80 kW
• Cardiac CT– 83 ms temporal resolution (trot/4)
– Below 50 ms with multi-segment reconstruction
• Dual Energy CT– Simultaneous acquisition with 80 kV / 140 KV
* SOMATOM Definition, Siemens Medical Solutions, Forchheim, Germany
Dual Energy CT
allows for direct bone removal
Courtesy of C. Becker, Munich, Germany
Dual Energy CT ApplicationsDual Energy CT Applicationsapproved by the FDA 2007approved by the FDA 2007
1.Direct subtraction of bone 2.Differentiation between hard plaque
and contrast agent3.Virtual unenhanced abdominal organ
imaging4.Kidney stone characterization5.Visualization of cartillage, tendons,
and ligaments6.Evaluation of lung perfusion defects
3D Angio(since <2000)
after intraarterial injection
X-ray Computed Tomography• State of the art in clincal CT
• Technology for clinical CT
• Flat detector CT- C-arm CT- Dedicated CT scanners,e.g. for the breast
- Micro-CT
• Discussion and Conclusions
CT Imaging using rotating C-arm Systems
Flat-Panel DetectorsImage Intensifiers
RobotRobot--driven Cdriven C--arm Systems at the IMParm Systems at the IMP
Product installationin November 2007
Prototype in operationsince June 2006
Conventional mechanics: < 25 cm diameter, <20 cm height
Courtesy of M. Reiser Munich, Germany
Large Large Volume Coverage with Volume Coverage with RobotRobot--driven Cdriven C--arm CTarm CT
3030××40 cm40 cm²² detectordetector
UFE: 3D vascular anatomy
Courtesy of M. Reiser Munich, Germany
…… and Fluoroscopyand Fluoroscopy
PrePre--clinical Research with Microclinical Research with Micro--CTCT
�����
� ��������
� ��
In vitro
10 µm res.high dose
In vivo
80 µm res.moderate dose
In vitro
10 µm res.high dose
PrePre--clinical Research with Microclinical Research with Micro--CTCT
X-ray Computed Tomography• State of the art in clincal CT
• Technology for clinical CT
• Flat detector CT
• Summary and Conclusions
Courtesy of University Hospital Munich-Grosshadern, Germany
Visualization of the complete artery tree1889 mm in 42 s with 0.33 mm isotropic resolution
Characteristics of detectors in clinical CT• Exclusively integrating scintillators
typ. 64 × 800 channels
• High speedtyp. 2-5000 readings/s per channel
• High efficiency70-90% for x-ray absorption, <90% for geometry
• Good linearity & high dynamic range16-24 bits,
• Energy resolution only a few experimental setups
• …
Characteristics of flat detectors in medical CT• Exclusively integrating scintillators
typ. 2000 × 3000 pixels
• Low speedtyp. 1 to 30 fps, afterglow and time lag, …
• Limited efficiencyfor x-ray absorption & geometry
• Direct conversion of x-rays to chargenot available yet
• Energy resolution not available yet
• Electronic noise, dark current, limited bit depth etc. are available …
Conclusions / Recommendations• Integrating detectors used in clinical CT today
(arcs of about 100 cm) fulfill most demands.
• Speed is of the highest importance and should not be comprimised.
• Interest in energy-discriminating photon-counting detectors is increasing.
• Flat-detector CT is a new and very promising topic in clinical radiology, primarily for interventional and intraoperative imaging.
• We can expect a number of dedicated CT scanners using flat-detector technology for clinical and pre-clinical research applications.
Specification of a flat detector for CT(a “ personal” request)
• 50 µm pixel pitch
• 20 cm × 30 cm
• 30 frames/s or more
• 16 bits
• Direct convertor
• High efficiency
• Energy discrimination
• …
EU FP7 project:„ Dedicated CT of the Female Breast“
(PI: W. Kalender; No. FP7-213153)
♥♥♥♥Thank you very much for your kind attention!Thank you very much for your kind attention!
Preclinical Imaging with Micro-CT(180 second scan, 80 µm resolution)