Electronics for High Resolution Breast-Dedicated PET

Institution: Stanford University
Investigator(s): Frances Lau, M.S. -
Award Cycle: 2010 (Cycle 16) Grant #: 16GB-0060 Award: $75,924
Award Type: Dissertation Award
Research Priorities
Detection, Prognosis and Treatment>Imaging, Biomarkers, and Molecular Pathology: improving detection and diagnosis

Initial Award Abstract (2010)

Positron emission tomography (PET) is a non-invasive, molecular imaging technology that has shown promise due to its ability to sense and visualize increased biochemical changes in malignant tissue well before physical changes occur. However, PET has not yet been incorporated into standard practice for breast cancer patient evaluation. Most PET systems are whole body imaging systems and not appropriate for breast imaging due to low sensitivity, inadequate spatial and contrast resolutions necessary to detect small tumors, high cost, and long scan times. As a result, PETís role in breast cancer management is currently limited to only the evaluation and re-staging of recurrent breast cancer and distant metastasis. In order for PETís role in other phases of breast cancer management to increase, the resolution needs to improve. This requires densely-packed sensors and high performance electronics.

The long term goal is to develop a high-resolution (~1mm), portable, breast-dedicated PET camera. A critical part of such a system is the read-out electronics, for which currently there is no satisfactory solution. This project focuses on developing the front-end integrated circuit (IC). An IC is a miniaturized electronic circuit that has been fabricated on the surface of a thin piece of silicon semiconductor material. The proposed electronic readout circuit would enable enhanced PET performance parameters such as spatial, energy, and temporal resolution that are important for visualizing and quantifying molecular signatures of breast cancer as well as allow a highly compact and portable instrument that is critical to clinical utility of a breast-specific PET system.

The IC we will design uses an innovative architecture that enables the analog circuits to be combined with the analog-to-digital converter (ADC) in a single IC, while consuming much less power and having a much smaller electronic footprint than conventional approaches. This architecture also effectively produces a digitized pulse waveform, which is useful in research applications, since various software algorithms can be applied to improve the results. The IC will be programmable so that it can be used by breast imaging system developers at different institutions and with various types of PET detectors. Thus, our methodology involves designing circuit blocks so they can be easily modified and re-used for other applications.

The proposed IC facilitates the development of breast-dedicated PET systems with improved resolution. Potential clinical benefits are: 1) improvement of the prognosis of breast cancer as it can detect lesions earlier (when the lesions are smaller), 2) guiding biopsy by improving the accuracy of sampling malignant tissue, 3) guiding surgical resection of the primary tumor, where visualizing smaller clumps of malignant tissue at the resection margins could possibly help to reduce the rate of recurrence, and 4) early visualization of minuscule focal accumulation of PET tracer, which could help the accuracy of identifying local recurrence after treatment.

Progress Report 1 (2011)

Overview of project:
We are developing electronics that will facilitate the development of high performance Positron Emission Tomography (PET) cameras dedicated to clinical breast imaging. In PET, a small amount of a radioactive chemical that accumulates in cancer cells is introduced into the body. The radiochemical emits energetic particles called photons, which the detectors in PET systems use to form an image. The detectors convert the photons to charge pulses, and then the electronics extract information from the pulses. We are developing integrated circuit electronics that will be the core of the PET electronics and will enable the development of high performance, compact, portable, low cost breast-specific PET systems which can visualize fewer number of breast cancer cells, important for identifying early stage breast cancer.

Status of project aims:
All the analog circuit blocks have been design and simulated, including the comparator and the trans-impedance amplifier. The design of the digital circuit blocks has started but still needs to be completed. We will layout the design in June and July and then aim to send the design out to be fabricated at the end of September. We plan to test and characterize the fabricated integrated circuit electronics performance without and with PET detectors coupled to it from Dec 2011 to Mar 2012 as originally planned.

Barriers and challenges:
It was a challenge to have the trans-impedance amplifier programmable to satisfy the noise and bandwidth requirements of both Silicon Photomultiplier detectors and Avalanche Photodiode detectors, but we eventually found a solution to this. We also designed an additional block, a programmable gain amplifier, to help satisfy the requirements of both Avalanche Photodiode (APD) and Silicon Photomultiplier (SiPM) detectors. We also need additional Digital-to-Analog converter blocks to enable the programmability of the electronics. The design of this is underway and is expected to be completed by the end of July.

Major accomplishments:
The major research milestone achieved was that all the analog circuit blocks have been designed and simulated, including the comparator, the trans-impedance amplifier, and the programmable gain amplifier. Several presentations on this project were given at Stanford to obtain feedback, both to individuals who specialize in breast cancer imaging systems and to individuals who specialize in integrated circuit design. Frances Lau, the PI for this Dissertation Award, gained more exposure to breast cancer research through the CBCRP Symposium and through her continuing work on another project in Prof. Craig Levinís laboratory developing a 1mm3 resolution breast-dedicated PET system. This experience is valuable in ensuring the integrated circuit electronics designed under this CBCRP Dissertation Award will be relevant and useful for breast imaging. Frances also expanded her knowledge of breast cancer, molecular imaging, and electrical engineering thorough seminars and journal clubs.

Plans for next year:
Next year we plan to finish the layout of the design and then send the design out to be fabricated at the end of September. We plan to test and characterize the fabricated integrated circuit electronics performance without and with PET detectors coupled to it from Dec 2011 to Mar 2012 as originally planned, and then document and publish the results.

Analog signal multiplexing for PSAPD-based PET detectors: simulation and experimental validation.
Periodical:Physics in Medicine and Biology
Index Medicus: Phys Med Biol
Authors: Lau FW, Vandenbroucke A, Reynolds PD, Olcott PD, Horowitz MA, Levin CS
Yr: 2010 Vol: 55 Nbr: 23 Abs: Pg:7149-74

Signal Conditioning Technique for Position Sensitive Photodetectors to Manipulate Pixelated Crystal Identification Capabilities
Periodical:IEEE Transactions in Nuclear Science
Index Medicus: IEEE Trans Nucl Sci
Authors: Lau FWY, Vandenbroucke A, Reynolds P, Ho H, Innes D, and Levin CS
Yr: 2012 Vol: 59 Nbr: 5 Abs: Pg:1815-1822