Transcript Slide 1
Current Topics in Medical Physics Research Xiaoming Zheng, PhD. School of Dentistry and Health Science Chengdu, China, 2009 Current Research Interests • • • • • • Image reconstruction algorithms Scatter and resolution corrections Image quality assessment Clinical image analysis Computer aided diagnosis Radiation detectors Filtered Back-Projection Butterworth Filter and Cutoff Frequency Iterative Reconstruction Rescaled Block Iterative Reconstruction Algorithm fn k 1 k c rn fn k f n 1 a r a r H mn m c rn d m S 'm H mn Hf m m S k r H mn m S r ; a r max c rn H mn m Attenuation Compensation Scatter Compensation C1 C 3 S ' .5W 2 W1 W 3 Resolution Compensation Images Reconstructions • Iterative Reconstruction: Rescaled Block Iterative Algorithm including attenuation, scatter, and distance resolution compensation. Parameters tested: iteration 1,3,5,7,10 and post Gaussian filter FWHM 0,1,2,3,4 pixels • Filtered Back-Projection: Parameters tested: Butterworth filter cut-off frequencies: 0.10, 0.15, 0.20, 0.25 and 0.30 pixel-1 Reconstructed images FBP Iterative Human and Numerical Observer Image Quality Studies • Human observer study using receiver operating characteristics • Numerical observer employing an ideal observer model. Receiver Operating Characteristics Numerical Observers Types of Channels Numerical Observer Results: RBI Human Observer Results Scatter and Cross-talk Correction in Dual Radionuclide Imaging The Neural Network Before Correction After Correction Image Registration Statistical Parametric Mapping Radiation Dose Optimization in CT • Biological effect of ionizing radiation • Cancer rate vs radiation dose • Radiation dose reduction: image quality vs radiation dose • Technical parameters: kVp, mAs, etc. CT Scan Parameters and Dose Index Scanner kVp mAs CTDIv (mGy) Brain 130 195 32.2 GE 120 220 46.0 Siemens 120 485 69.8 Toshiba Abdomen 120 150 9.60 GE 120 180 14.5 Siemens 120 220 16.9 Toshiba CT Dose Index and image quality scores summary CT machine Brain CTDIV (mGy) Image quality rank score Abdomen CTDIV (mGy) Image quality rank score Machine Image quality score average Single slice 32.2 2.85 9.60 2.56 2.71 16 slice 46.0 3.36 14.5 3.28 3.32 64 slice 69.8 4.43 16.9 4.26 4.35 Single Slice CT Images 16 Slice CT Images 64 Slice CT Images Computer Assisted Diagnosis • Provide second opinion to radiologists. • FDA approved systems include breast and lung cancer detections. • Image processing • Image data base • Artificial intelligence. PET/SPECT Simulation Using GEANT Radiation Detectors • Room temperature Semiconductor Detectors: Materials and mechanisms • Magnetic resonance coils designs. Scintillator-based gamma camera Detector head (GE Medical Systems) CZT / NaI comparison ELGEMS CZT pixilated small field imager Anger camera (NaI) Test image Thyroid phantom Semiconductor - CZT g X CdZnTe: Gamma rays create electron/hole pairs. The gamma energy level is proportional to the electrical current. CdZnTe (CZT) E e- h+ The GaAs detectors The detection system detector Detctor characteristics Si or GaAs pixel: 170 x 170 m2 64 x 64 pixels area 1.18 cm2 Photon Counting Chip ( PCC) CERN EP Microelectronics Group MEDIPIX Collaboration: CERN, Universita’ ed INFN Pisa, Napoli e Cagliari Universita’ di Glasgow e Friburgo charcteristics: SACMOS 1 mm technology pixel: 170 x 170 m2 64 x 64 channels area 1.7 cm2 threshold adjust 3-bit 15-bit counter Hybrid Modalities – PET/CT Hybrid Imaging Systems New Imaging Systems • New detector technology. • Optical imaging: visible, ultraviolet, inferred. • Molecular imaging: PET, fMRI, Optical • Hybrid imaging systems. • T Herts imaging. Optical Imaging Teraherts Imaging Thickness of tissue probed 30 m 100m 1mm 1cm 10cm l 400 nm 800 nm Confocal/ multi-photon microscopy Optical coherence tomography Diffuse optical tomography 1600 nm 10 m 100 m Thermography THz imaging Magnetoencephalography Medical Physics Topics? • Treatment of depression: Transcranial magnetic stimulation. • Killing of cancer cells: Electric field on biological molecules.