Detector designs for nuclear medicine and hybrid ultrasound-gamma probe

다국어 초록 (Multilingual Abstract)

The procurement of molecular level information with the help of radioisotopes for medical diagnosis and treatment is known as Nuclear medicine(NM). Nuclear Medicine(NM) plays crucial
role in the field of medical application, ranges from diagnosis, therapeutic to new drug discovery. The NM systems can be divided into three major categories: NM Imaging systems, NM
non-imaging systems and Hybrid NM imaging/non-imaging systems.The commonly used NM
imaging system are Positron Emission Tomography(PET), Single Photon Emission Tomography(SPECT) and Gamma Camera. In case of non-imaging system gamma probe and positron
probe are widely used for surgical applications. Due to lack of anatomical information availability from NM systems it is beneficial to integrate the NM systems with other type of systems
which can provide anatomical information with high resolution. Such types of integrated systems are known as Hybrid NM systems. The common examples of integrated NM systems are
PET-CT(PET with Computed Tomography), PET-MRI(PET with Magnetic Resonance Imaging),
PET-US(PET with Ultrasound), SPECT-CT and Gamma Camera-CT. These systems are known
to provide both anatomical and molecular level information.
The performance of NM systems depends on number of parameters, such as detector geometry/design, sensitivity, spatial resolution , energy resolution and timing resolution. The detector
design hugely influence the systems performance, complexity and cost. The detector design also
influence the other performance parameters like sensitivity, energy and timing resolution. Therefore optimized detector design is of great importance for better image quality achievement as
well as complexity and cost reduction. The NM procedure for diagnosis and treatment can be
divide into two steps i.e. diagnosis which can be done with the help of NM imaging modules and
surgical operation for treatment which can be carried out with help of probes. In this thesis we
have tried to cover the complete chain of systems required for NM procedure from diagnosis to
surgical operation. We have chose one modality from each category of NM systems (Imaging,
Non-Imaging and Hybrid) and proposed a detector design for performance as well as cost and
complexity improvement. For the imaging modality a detector design is proposed here to extract
the depth of interaction(DoI) information for PET scanner which in turn improve the spatial resolution as well as sensitivity and signal to noise ration (SNR). In non-imaging a detector design for
positron probe is proposed and validated which will reduce the complexity and at the same time
improve the efficiency of the probe. Lastly for hybrid NM system a front-end circuit design for
US-Gamma probe is proposed and preliminary results are provided for the circuit validation. We
have also proposed a detector design for US-gamma probe in this work. The hybrid US-Gamma
probe proposed in this thesis will provide compact, cost-effective and better localization.
The depth of interaction(DoI) information is known to improve the overall performance such
as sensitivity, timing resolution, spatial resolution uniformity and sensitivity of ToF-PET scanners.Here, we proposed a scintillator wavelength discrimination(WLD) based detector for DoI
information extraction for ToF-PET detector. A phoswich detector composed of Ce:GAGG and
Ce:LYSO was designed for the proposed method validation. The DOI information from this
proposed phoswich-type detector can be acquired at the detector level without complex signal
processing by utilizing a single optical filter with customized optical properties. For this, we used
either a short pass filter (SPF) or a long pass filter (LPF) that allows light photons of a specific
wavelength to pass. The two-layered phoswich detector was configured with two scintillators with
different photon-emission spectra. In this study, we used Ce:GAGG (3 mm × 3 mm × 10 mm)
and LYSO:Ce (3 mm × 3 mm × 10 mm) as the top and bottom layer scintillators, respectively.
A digital silicon photo-multiplier (dSiPM) was used as the photo-sensor and for data acquisition.
The phoswich detector was placed in the center of two dSiPM pixels, where one of the dSiPM
pixel was covered with the optical filter, and the light guide was placed on the other pixel. The
detector was tested for energy, timing, and DOI encoding performance.
The intra-operative positron probe, used in the field of nuclear medicine, has been developed to
localize positron (β+) emitted from positron emission tomography (PET) radio-pharmaceuticals
by selectively detecting β+ particles in the presence of background gamma (γ) radiation. In this
research, we propose a new method for real-time discrimination of radiation types in a mixed
radiation field of positron (β+) and gamma(γ) radiation, based on simple electronics and signal
processing. Scintillators often have distinct emission wavelengths, and this method exploits the
scintillator’s emission wavelength, as opposed to conventional pulse shape discrimination (PSD)
approach. In this study, we used a two-layer phoswich detector consisting of europium-dopedcalcium fluoride (CaF2(Eu)) and Ce3+ doped Lu3Al5O12 (Ce:LuAG), with dimensions of 3
mm × 3 mm × 0.5 mm and 3 mm × 3 mm × 10 mm, and emission wavelengths of 380 –
450 nm and 480 – 700 nm respectively. This phoswich detector was placed at the center of two
adjacent optical filters (one short pass and one long pass filter), and each coupled to a silicon
photo-multiplier (SiPM). The optical filters are used for directing a specific scintillator photon
wavelength to its corresponding SiPM for identification of the crystal of interaction.
Lastly we proposed an integrated ultrasound-gamma(US-γ) probe for medical application.
The hybrid US-γ probe can be used for accurate localization of tumor/lymph during surgical
applications. Two different of circuits techniques are proposed for integrated front-end signal
processing of US-γ probe. The first method use the digitally controlled switch to transmit the
US and γ signal through single channel for cos-effective solution. The repetition rate of US is
utilized for channel allocation to each of detector in this method. Secondly we also proposed to
use the frequency multiplexing techniques for signal transmission of both type of system through
a single channel. The preliminary experiments showed a promising results of both techniques.
The integrated detector design for US-γ probe is also proposed. The detector will be designs to
use the backing material of US as collimator for gamma radiation. These proposed circuit and
detector design techniques will ensure the fully integrated US-γ-probe development as well as
cost-effective and portable for medical applications.
Overall the proposed detector designs for NM and circuit design for hybrid US-γ probe has
immensely reduce the complexity without comprising on the system perfomance.

목차 (Table of Contents)

• Abstract
• Acknowledgement
• Contents i
• List of Figures iv
• List of Tables ix
• 1 Introduction 1
• 2 Wavelength Discrimination (WLD) TOF-PET Detector with DOI Information 11
• 2.1 Theoretical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
• 2.2 Material and Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
• 2.2.1 Scintillators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
• 2.2.2 Optical Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
• 2.2.3 Photosensor and data-acquisition system . . . . . . . . . . . . . . . . . . 17
• 2.2.4 Energy and depth of interaction (DOI) measurement . . . . . . . . . . . 17
• 2.2.5 Coincidence resolving time (CRT) measurement setup . . . . . . . . . . 18
• 2.2.6 Depth of interaction localization in phoswich detector . . . . . . . . . . 19
• 2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
• 2.3.1 Energy and FoM measurements . . . . . . . . . . . . . . . . . . . . . . 19
• i2.3.2 Coincidence resolving time (CRT) . . . . . . . . . . . . . . . . . . . . . 23
• 2.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
• 3 Optimization of Wavelength Discrimination (WLD) Method for DOI-TOF-PET Detector 30
• 3.1 Materials and Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
• 3.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
• 3.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
• 3.3.1 Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
• 3.3.2 Depth of interaction (DOI) . . . . . . . . . . . . . . . . . . . . . . . . . 33
• 3.3.3 Coincidence resolving time (CRT) . . . . . . . . . . . . . . . . . . . . . 33
• 3.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
• 4 A New Positron-Gamma Discriminating Phoswich Detector Based on Wavelength
• Discrimination (WLD) 41
• 4.1 Theoretical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
• 4.2 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
• 4.2.1 Scintillators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
• 4.2.2 Optical Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
• 4.2.3 Photo-detectors and Data Acquisition . . . . . . . . . . . . . . . . . . . 48
• 4.3 Results and Detector Performance . . . . . . . . . . . . . . . . . . . . . . . . . 49
• 4.4 Summary and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
• 5 Hybrid Ultrasound-Gamma Probe 53
• 5.1 Background of Ultrasound and Gamma probe . . . . . . . . . . . . . . . . . . . 56
• 5.2 Theoretical Background of Proposed Methods . . . . . . . . . . . . . . . . . . . 58
• 5.3 Materials and Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
• 5.3.1 Gamma and Ultrasound Probe . . . . . . . . . . . . . . . . . . . . . . . 61
• 5.3.2 Data Acquisition System . . . . . . . . . . . . . . . . . . . . . . . . . . 61
• 5.4 Preliminary Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 62
• ii6 Conclusion and Future Work 66
• Bibliography 68