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Topics in Medical Physics
Xiaoming Zheng, PhD.School of Dentistry and Health
SciencesDecember 2009, Chengdu.
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Medical Physics at CSU
• Major medical imaging modalities• Physics in nuclear medicine• Magnetic resonance imaging• Physics in computed tomography• Ultrasound physics• Health physics.
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Major Imaging Modalities
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Typical CT Images
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Positron Emission Tomography
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On Site Cyclotron
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Whole Body PET Images
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Magnetic Resonance Imaging
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MRI Radio Frequency Coils
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MRI Pulse Sequence
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MRI Tissue Contrast Images
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Ultrasound Imaging
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Ultrasound Image
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Medical Physics Research Topics
• Image reconstruction algorithms
• Scatter and resolution corrections
• Image quality assessment
• Clinical image analysis
• Computer aided diagnosis
• Radiation Detectors
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Filtered Back-Projection
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Butterworth Filter and Cutoff Frequency
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Iterative Reconstruction
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Rescaled Block Iterative Reconstruction Algorithm
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Attenuation Compensation
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Scatter Compensation
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Resolution Compensation
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PET simulation using GEANT
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Problems in Dual Radionuclide Imaging: Scatter and Cross-talk
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The Neural Network
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Receiver Operating Characteristics
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Numerical Observers
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Image Registration
Compositeusing
intensity-based
registration
Compositeusingpoint-based
registration
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Brain Activation Mapping
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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,
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Computer Assisted Diagnosis
• Provide second opinion to radiologists.
• FDA approved systems include breast and lung cancer detections.
• Image processing
• Image data base
• Artificial intelligence.
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Radiation Detectors
• Room temperature Semiconductor Detectors: Materials and mechanisms
• Magnetic resonance coils designs.
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(GE Medical Systems)
Detector head
Scintillator-based gamma camera
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CZT / NaI comparison
ELGEMS CZT pixilatedsmall field imager
Anger camera (NaI)
Test image Thyroid phantom
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CdZnTe (CZT)Eh
e+
-
X CdZnTe: Gamma rays
create electron/hole pairs. The gamma energy level is proportional to the electrical current.
Semiconductor - CZT
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The GaAs The GaAs detectorsdetectors
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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
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Hybrid Modalities – PET/CT
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Hybrid Imaging Systems
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New Imaging Systems
• New detector technology.
• Optical imaging: visible, ultraviolet, inferred.
• Molecular imaging: PET, fMRI, Optical
• Hybrid imaging systems.
• T Herts imaging.
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Optical Imaging
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Teraherts Imaging
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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
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Magnetoencephalography
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Medical Physics Topics?
• Treatment of depression: Transcranial magnetic stimulation.
• Killing of cancer cells: Electric field on biological molecules.