View
215
Download
0
Tags:
Embed Size (px)
Citation preview
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
Rescaled Block Iterative Reconstruction Algorithm
f fca
f
a HH
d Snk
nk rn
r
nk
r mnm
mnm S
m m
mr
1 1'
Hf k
c
H
Ha crn
mnm S
mnm
r rnr
; m ax
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
Human and Numerical Observer Image Quality Studies
• Human observer study using receiver operating characteristics
• Numerical observer employing an ideal observer model.
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
Toshiba130 195 32.2
GE 120 220 46.0
Siemens 120 485 69.8
Abdomen
Toshiba120 150 9.60
GE 120 180 14.5
Siemens 120 220 16.9
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
CT Dose Index and image quality scores summary
Computer Assisted Diagnosis
• Provide second opinion to radiologists.
• FDA approved systems include breast and lung cancer detections.
• Image processing
• Image data base
• Artificial intelligence.
Radiation Detectors
• Room temperature Semiconductor Detectors: Materials and mechanisms
• Magnetic resonance coils designs.
CZT / NaI comparison
ELGEMS CZT pixilatedsmall field imager
Anger camera (NaI)
Test image Thyroid phantom
CdZnTe (CZT)Eh
e+
-
X CdZnTe: Gamma rays
create electron/hole pairs. The gamma energy level is proportional to the electrical current.
Semiconductor - CZT
The detection systemThe detection system
Detctor characteristicsSi or GaAspixel: 170 x 170 m2
64 x 64 pixels
area 1.18 cm2
Photon Counting Chip ( PCC)CERN EP Microelectronics Group
MEDI PI X Collaboration:CERN, Universita’ ed I NFN Pisa,
Napoli e CagliariUniversita’ di Glasgow e Friburgo
charcteristics:SACMOS 1 mm technologypixel: 170 x 170 m2
64 x 64 channelsarea 1.7 cm2
threshold adjust 3-bit15-bit counter
detector
New Imaging Systems
• New detector technology.
• Optical imaging: visible, ultraviolet, inferred.
• Molecular imaging: PET, fMRI, Optical
• Hybrid imaging systems.
• T Herts imaging.
Thickness of tissue probed
30 m 100m 1mm 1cm 10cm
400 nm
800 nm
1600 nm
10 m
100 m
Thermography
THz imaging
Confocal/ multi-photon microscopy Diffuse optical
tomographyOptical coherence tomography