Novel CMOS Analog Signal Processing Technique for Solid-State X-Ray Sensors in Medical Imaging Systems
Ability to peer into human body is an essential diagnostic tool in medicine. Out of the four major imaging modalities that include ultra-sound, magnetic resonance imaging (MRI), and positron emission tomography (PET), nuclear medicine is gaining more widespread attention. Nuclear medicine involves measurement of radiation from inside human body using in vivo pharmaceutical tracer. X-ray computed tomography (CT) and single photon emission computer tomography (SPECT) are three-dimensional (3D) extensions of planar nuclear imaging techniques. These 3D images provide a view of physiological processes that determined relative concentration of the pharmaceutical tracer. At present, most nuclear medicine imaging devices use a scintillator-photomultiplier combination to detect X or gamma rays. The scintillator absorbs a photon and re-emits the energy as a visible light. The photocathode of the photomultiplier tube (PMT) absorbs the visible photons from the scintillator and emits a burst of electrons. The electrons are accelerated, their number multiplied by the photomultiplier gain, and subsequently processed by external electronics. Due to multi-step detection process that involves visible light, PMT devices suffer from poor imaging resolution finding limited application in practice. Recently, these shortcomings of PMT detectors were addressed by fabrication of solidstate detectors that operate at room temperature and convert X-ray photons directly to electrical signals1. In these detectors, the charge carriers that are generated by a photoelectric interaction are quickly swept out of the detector by the applied electric field. An array of pixel electrodes senses the motion of these generated carriers and generates a pulse in the attached readout circuit. Ability to use solid-state detectors has enabled great improvements in spatial resolution of SPECT. As a result, SPECT cameras with solid-state detectors are starting to be used in cardiology and cancer detection, two critical fields of medicine that affect human health the most. Further improvements in medical imagining can be expected with improvements in detector design and fabrication. In addition, research effort on suitable highly integrated analog front-end electronics that provide signal processing function is becoming equally important. This paper presents a novel contribution in this area by proposing a technique for analog signal processing of the X-ray sensor generated signal. The proposed approach can be regarded as an application specific analog-signal-based computer system.
Record created on 2011-03-31, modified on 2016-08-09