Financial disclosure statement. Fluoroscopic Equipment Design: What s s Different with Flat Panel? Concept of flat panel imager

Transcription

1 Fluoroscopic Equipment Design: What s s Different with Flat Panel? John Rowlands Financial disclosure statement Research supported by Anrad Corp Anrad Corp is a manufacturers of selenium based flat panel imagers Sunnybrook Heath Sciences Centre University of Toronto Concept of flat panel imager Flat Panel Array Design 1000 rows x 1000 columns

2 TOSHIBA TOSHIBA System Architecture Automatic Exposure Control in fluoroscopy X-ray tube Acquisition Workstation Detector X-Ray Generator Control Low Voltage Power Supply A B Real Time Image Processor Fiber Optic Links Image Processing Chain CRT operation and characteristic curve of monitor - Need for gamma correction Flat Panel Detector Real Time Data Correction Real Time Image Processing Correction of: Temporal Offset and spatial filter Gain Image Resizing Pixel defect Gamma correction Horizontal noise X-ray and Acquisition Control Acquisition Workstation and X-ray generator

3 Offset and gain corrections Enlarged bad region Dark field offset correction Bright field gain corrections As acquired image Gain and Offset corrected with Bright field and Dark Field images respectively Bad lines and points replaced by interpolation

4 Distortion in an Pincushion distortion Gamma and sharpness corrected image S-distortion Complete imaging system Quantum accounting diagram for video system

5 Flat panel detector types Quantum accounting diagram for flat panel system Indirect conversion (CsI) Direct conversion (a-se) Intrinsic sources of blurring in x-ray imaging systems Phosphor blurring sources

6 Photoconductor blurring sources Components of MTF in an output screen MTF electron lens CsI input screen spatial frequency (lp/mm) Components of MTF in an and flat panel MTF of and flat panel MTF output screen electron lens CsI input screen spatial frequency (lp/mm) Flat panel MTF (a) CsI flat panel Nyquist 1.6 lp/mm spatial frequency (lp/mm) MTF (b) CsI flat panel Nyquist 3.2 lp/mm zoom spatial frequency (lp/mm) Normal mode Zoomed mode

7 Principle of photolithography Thin film transistor or TFT TFT+Photodiode Pixel Design Array Design Rules Distance between neighboring features 127 µm Width of control lines Thickness of different layers (Courtesy of Dr. R. Weisfield, dpix

8 1 Fill Factor vs Pixel Size Readout of a flat panel detector Photodiode Fill Factor 0 Conservative Design Rules Aggressive Design Rules " Diode on Top " Design Pixel Size (microns) -5 V Data Lines Switch Line 3-5 V Data Lines Switch Line 3-5 V Switch Line 2-5 V Switch Line 2-5 V Switch Line VV Switch Line 1 External Electronics External Electronics

9 -5 V Data Lines Switch Line 3 Data Lines V Switch Line V V Switch Line VV Switch Line VV Switch Line VV Switch Line 1 External Electronics External Electronics Data Lines VV Switch Line 3 Artifacts arising from inadequate corrections -5 V Switch Line 2-5 V Switch Line 1 Regions of different intensity Blurring Line correlated noise External Electronics

10 Image Courtesy of Dr. U Neitzel,, Philips Image Courtesy of Dr. U Neitzel,, Philips DQE of and flat panel Cardiac cine CsI flat panel (a) (b) CsI flat panel DQE DQE zoom spatial frequency (lp/mm) input dose (ngy) As a function of spatial frequency As a function of dose to detector CsI /video CsI flat panel

11 Advantages of flat panel imagers Future developments High dynamic range Corrections for monitor non linearity Compact form factor Suitability for advanced applications Not yet quantum noise limited at low exposures Amplifier per pixel High conversion efficiency photoconductor Avalanche gain System on glass