Pulse-Width Modulation for Photon Scanning Apparatus
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Solution Overview
Problem
Conventional photon-counting CT scanners face significant calibration challenges due to the non-linear response of detectors caused by pulse pile-up and variations in X-ray spectrum, requiring extensive calibration for multiple material combinations and flux modulation settings, which increases complexity and effort.
Innovation Solution
Implementing a photon scanning apparatus with pulse width modulation that excludes the time periods of flux ramp-up and ramp-down, allowing the detector to operate at a single flux rate and reducing calibration needs by using a predetermined pulse width scheme, where the photon detector starts counting photons with a delay relative to the source's emission and stops before the source ceases emission, thereby minimizing pile-up effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional photon-counting CT scanners use dose modulation with varying X-ray flux, then dose efficiency is improved, but detector calibration complexity increases significantly due to non-linear response and pulse pile-up effects
Solution Approach 1:
The patent applies periodic pulse width modulation to the X-ray tube current, switching it on and off in periodic pulses. This allows the detector to be calibrated at a single flux rate (during the on-period) while still achieving dose modulation through variable pulse widths, thereby resolving the contradiction between dose efficiency and calibration complexity
Solution Approach 2:
The patent changes the temporal parameter of X-ray flux delivery by using pulse width modulation instead of continuous flux. By controlling the duration of flux pulses rather than the flux amplitude, the system maintains dose modulation capability while keeping the detector operating at a constant flux rate during measurement periods, simplifying calibration
2Duration of action of moving object
If the detector counts photons during the entire X-ray emission period, then measurement time is maximized, but pulse pile-up effects increase due to flux ramp-up and ramp-down periods
Solution Approach 1:
The patent extracts and excludes the problematic flux ramp-up and ramp-down periods from the photon counting measurement window. By starting counting after a delay and stopping before the flux ceases, the system removes the portions of the signal that would cause pulse pile-up, maintaining measurement accuracy while preserving most of the useful counting time
Solution Approach 2:
The patent implements preliminary action by delaying the start of photon counting until after the flux has stabilized. This preliminary waiting period allows the flux to reach its steady state before measurements begin, preventing pulse pile-up from occurring during the measurement window
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces calibration effort by allowing the detector to be calibrated for a single flux rate, effectively managing pile-up effects and improving dose modulation efficiency in photon scanning applications.
Implementation Method 1
a photon detector positioned in the propagation direction of the photon beam to detect photons emitted from the photon source
Data Source
AI summary
The present invention relates to a photon scanning apparatus comprising a photon source (2) to emit a photon beam (4), a photon detector (6) to detect photons emitted from the photon source (2). The photon source (2) is adapted to emit the photon beam (4) in accordance with a predetermined pulse width modulation scheme at a predetermined flux rate, wherein the pulse width modulation scheme defines pulse widths of the photon beam (4) for respective positions of the photon source (2) and the photon detector around a central axis (R) and an object to be scanned. The photon detector (6) is adapted to start detecting photons with a delay relative to the photon source starting to emit photons and to finish detecting photons prior to the photon source stopping to emit photons. The photon scanning apparatus thus only has to be calibrated for the predetermined flux rate.