Topics in Medical Physics
Xiaoming Zheng, PhD.
School of Dentistry and Health
Sciences
December 2009, Chengdu.
Medical Physics at CSU
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Major medical imaging modalities
Physics in nuclear medicine
Magnetic resonance imaging
Physics in computed tomography
Ultrasound physics
Health physics.
Major Imaging Modalities
Typical CT Images
Positron Emission Tomography
On Site Cyclotron
Whole Body PET Images
Magnetic Resonance Imaging
MRI Radio Frequency Coils
MRI Pulse Sequence
MRI Tissue Contrast Images
Ultrasound Imaging
Ultrasound Image
Medical Physics Research Topics
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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
PET simulation using GEANT
Problems in Dual Radionuclide
Imaging: Scatter and Cross-talk
The Neural Network
Receiver Operating Characteristics
Numerical Observers
Image Registration
Composite
using
intensitybased
registration
Composite
using
pointbased
registration
Brain Activation 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,
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.
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
100m 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.