Purpose: To evaluate the intrinsic characteristics of a new high resolution, large area, small bezel, digital imager developed for a dedicated SPECT-CT system for fully-3D mammotomographic imaging applications.
Methods: A new flat panel digital imager was developed having 127μm pixels (identical to those in the Paxscan 2520) with an active 40×30cm area and 3200×2304 total pixels, which is well suited for pendant breast imaging close to the chest wall. The readout and driver ASIC TAB bonding pads were arranged on only two sides of the imager plate, to eliminate dead edge spacing. A special housing was developed to accommodate this imaging plate providing very narrow 8mm edges (bezels) on two orthogonal sides The TFT array imager was coated with 600μm thick micro-columnar CsI, which provides >90% absorption in the breast CT (60-80kVp) x-ray energy range. It provides better than 70% absorption for RQA5 (70kVp 21mm Al filter) x- ray radiation. The readout ASICs are connected to 14 bit A/D converters, and special readout ASICs with gain switching feature, which provide an additional 4bit virtual (2-3 effective) dynamic range.
Results: The MTF is ∼7.5% at the 3.9 lp/mm Nyquist frequency. The NPS curves continuously decrease with increasing spatial frequencies, characteristic of scintillator based imagers. The excellent DQE (0) measured at RQA5 is ∼75% in the 0.1-1mR dose range and ∼10% at the Nyquist frequency. The imager has excellent linearity over the full dynamic range, and high contrast images are readily acquired.
Conclusions: The new 4030 flat panel imager is a high resolution, state of the art detector, ideal for breast imaging and other applications. This detector is included in the SPECT-CT device in development.
Keywords: Computed tomography; Image sensors; Medical imaging; Modulation transfer functions; Thin film transistors.
© 2012 American Association of Physicists in Medicine.