Topics in Medical Physics

Xiaoming Zheng, PhD.School of Dentistry and Health

SciencesDecember 2009, Chengdu.

Medical Physics at CSU

• 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

• 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

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

Attenuation Compensation

Scatter Compensation

S WCW

CW

' .

5 2

1

1

3

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

Compositeusing

intensity-based

registration

Compositeusingpoint-based

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.

                              

(GE Medical Systems)

Detector head

Scintillator-based gamma camera

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 GaAs The GaAs detectorsdetectors

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

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

400 nm

800 nm

1600 nm

10 m

100 m

Thermography

THz imaging

Confocal/ multi-photon microscopy Diffuse optical

tomographyOptical coherence tomography

Magnetoencephalography

Medical Physics Topics?

• Treatment of depression: Transcranial magnetic stimulation.

• Killing of cancer cells: Electric field on biological molecules.