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

�����

� ��������

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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)