7th Annual International Symposium on MDCT San Francisco, June 15-18, 2005

64 from 32: Understanding the Magic64 from 32: Understanding the Magicoror

The Effects of z-Flying Focal Spot (zFFS) The Effects of z-Flying Focal Spot (zFFS) TechnologyTechnology

Willi Kalender, Ph.D.

Institute of Medical PhysicsUniversity of Erlangen

www.imp.uni-erlangen.de

The evaluation of zFFS effects was carried out by Yiannis Kyriakou, Marc Kachelrieß, Michael Knaup, Jens U. Krause and Willi A. Kalender and has been submitted to European Radiology as a Scientific Note

AcknowledgementsAcknowledgements

How about doubling the number of slices

without a change in detector hardware?

The magic lies in The magic lies in the sampling concept!the sampling concept!

„„Rotating Vacuum Vessel“ X-ray Tube Technology Rotating Vacuum Vessel“ X-ray Tube Technology with z-flying focal spot with z-flying focal spot

Housing

Motor

Emitter

Rotating vacuum vessel

Ball bearings

X-rays

Electron beam

Deflection coils

Oil for HV insulation and cooling

Straton tubePhoto:

Courtesyof Siemens

Schardt et al. Medical Physics 2004; 31:2699-2706

A new approach to electron-beam CT

with perfect control of focus position!

A high-powerX-ray tube(Siemens Straton rotating vacuum vessel tube)

A mobile tube?„A hand-held device?“

z

Double z-Sampling Technology

RotatingAnode

Electromagnetic Control of the Electron beam

32 detector rows(64 slices scanned) Sampling distance: 0.3 mm

z-Flying Focal Spot

Kalender WA. Computed Tomography. 2nd ed. Wiley & Sons, New York 2005

The novel z-Flying Focal Spot (zFFS) technology provides

• double sampling as required bythe Nyquist theorem

• measurement of two overlapping slices per detector row,i.e. 64 slices for 32 rows

• no change in dose / image quality relations

Summary and Conclusion (I)Summary and Conclusion (I)

Spatial Resolution Measurements:Spatial Resolution Measurements:Modulation transfer functionModulation transfer function

zFFS increasesspatial resolution

z0.4 mm

0.5 mm

0.6 mm

with zFFSwithout zFFS

0.4 mm

0.5 mm

0.6 mm

xImpact of the zFFS on z-ResolutionImpact of the zFFS on z-Resolution

Scan data reconstructed twice, using one and both focal spot positions, resp.

Kalender WA. Computed Tomography. 2nd ed. Wiley-VCH, New York 2005

Simulated Head PhantomSimulated Head Phantomwithout zFFS with zFFS

pitch=1.4, (C=30 HU, W=300 HU)

32×0.6 mm 232×0.6 mm

without zFFS with zFFS

Windmill ArtifactsWindmill Artifacts

Reconstruction on the VAMP syngo Explorer; p = 1.2

click to start movie

The novel z-Flying Focal Spot (zFFS) technology provides

• measurement of two overlapping slices per detector row,i.e. 64 slices for 32 rows

• no change in dose / image quality relations

• improved spatial resolutionin the z-direction

• Nyquist conformity and therebysuppression of windmill artifacts

Summary and Conclusions (II)Summary and Conclusions (II)

Thank you for your attention!Thank you for your attention!