Nuclear medicine diagnostic imaging systems with gamma radiation
Nuclear medicine imaging technologies include single photon emission tomography (SPECT) and positron emission tomography (PET). SPECT and PET allow physicians to quantify the spatio-temporal distribution of radio-labeled tracers (e.g. with 99mTc-sestamibi or 18F-FDG) in the patient body. SPECT and PET systems use gamma cameras and detector modules to acquire images from tracers around the patient. Conventional detector front-ends use scintillators (e.g., NaI, LYSO, BGO) and photomultiplier tubes. Specialized systems and new development prototypes use other detectors, for example, solid-state photon detectors (SiPM, MPPC, APD) or direct semiconductors (e.g., CZT). IDEAS has designed integrated circuits for SPECT and PET systems that are based on solid state photon detectors or CZT. The circuits are designed to measure the amount of the electrical charge and the point of interaction in the detector crystal. Thereby, one can acquire the photon energy spectrum and the images of tracer distribution in the body. The pixelated detectors combined with multi-channel integrated circuit readout improve image quality, reduce acquisition time or lower the cost of the hardware. IDEAS integrated circuits drive miniaturization, to improve overall system performance and reduce system cost. IDEAS integrated circuits process the signals from thousands of detector pixels, increase system performance and reduce the detector size and bill of materials. Multi-channel integrated circuit readout is the key to compact and high-performance SPECT and PET systems.
Product sheet of the CZT module with IDE4184 readout
- Pettersen et al., ASIC for SPECT, IEEE NSS, 2004.
- CIEMAT VATA211p with CZT
- CIEMAT APD readout
- Ishii et al. “First achievement of less than 1-mm FWHM resolution in practical semiconductor animal PET scanner”, Nucl. Instr. Meth. A576 (2007) 435-440
Radiology diagnostic imaging systems with x-rays
X-ray computed tomography (CT) is a medical imaging technique that allows physicians to look inside a patients body without cutting the tissue. The detector front-end acquires x-ray transmission images around the body. The detectors are pixelated and every pixel integrates the electrical current that is proportional to the transmitted flux. In conventional detector front-ends the current is integrated in current integrating amplifiers. IDEAS has designed integrated circuits with current integrating amplifiers. However, current integration is not ideal, because the detector leakage current contributes noise and each x-ray photon contributes a charge proportional to its energy. Better image quality and reduced dose can be achieved with Energy Resolved X-ray Photon Counting for CT (EXPC). IDEAS has designed integrated circuit for EXPC and has built demonstrator systems for energy resolved x-ray photon counting. EXPC incrementally counts the x-ray photons interacting in each pixel of the sensor. XPC with only one energy threshold eliminates contributions from detector leakage current during the time between consecutive interactions and therefore reduces the noise in the image. EXPC with multiple energy thresholds counts in one or more well defined energy bins. Post acquisition multiplication by appropriate weighting factors improves contrast-to-noise ratio in the image and can reduce the integrated dose. In addition energy resolved XPC could exploit the energy dependence of the photo absorption and Compton scatter in different chemical elements. Energy resolved XPC is made possible by new radiation sensors such as cadmium telluride (CdTe), which provide relatively short charge collection (50 ns) and good energy resolution, combined with application specific integrated circuits suitable for multi-pixel readout and fast counting. Energy resolved x-ray photon counting improves the image contrast and can lower the radiation dose. EXPC allows one to distinguish different types of materials or bio-markers. IDEAS has designed integrated circuits for EXPC and has built demonstrator systems for EXPC.
- CA3 ASIC in Mikkelsen et al. “An ASIC for multi-energy x-ray counting”, IEEE Nucl. Sci. Symp. Conf. Rec. Dresden 2008.
- CA3 ASIC in Wang et al. “Material separation in x-ray CT with energy resolved photon-counting detectors”, Med. Phys. 38 (3), 2011
- CA3 ASIC in Schlomka et al. “Experimental feasibility of multi-energy photon-counting K-edge imaging in pre-clinical computed tomography”, Phys. Med. Biol. 53, 4031-4047, 2008.
Radiotherapy and radiation dosimetry
Radiotherapy treats cancers using x-rays or charged particle beams. The beams are directed towards the tumor and destroy the cells in the area that is being treated. The cancer cells cannot repair themselves after radiotherapy, but normal cells usually can. Clinicians are very concerned about the dose delivered to the target region. Clinicians use dosimetry equipment for quality assurance (QA). The equipment is normally used before the treatment. However, it is better to verify the actual radiation dose delivered to the patient during the procedure. IDEAS has designed integrated circuits that are used for radiation dosimetry quality assurance in radiotherapy before treatment. The circuits could also be applied for dosimetry during the procedure (in-vivo).VASCM3 type ASIC, IC with 128 current integrating amplifiers.The main reason for using integrated circuits in medical applications are: Increase diagnostic certainty, Reduce the session time, increase the up-time and patient through-put.IDEAS is has created low-power integrated circuits that can be applied in medical diagnostic imaging and dosimetry.