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

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Attenuation Compensation

Scatter Compensation

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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

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

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.

                              

(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.