Energy Sensitive Photon Counting Detectors Research Articles

Quantification of water and lipid density with dual-energy mammography: validation in postmortem breasts.

Breast cancer is the most common cancer in women and the second leading cause of cancer death. It is well known that breast density is an important risk factor for breast cancer and also can be used to personalize screening and for assessment of treatment response. Breast density has previously been correlated to volumetric water density. The purpose of this study is to validate the accuracy and precision of dual-energy mammography in measuring water density in postmortem breasts. Twenty pairs of postmortem breasts were imaged using dual-energy mammography with energy-sensitive photon-counting detectors. Chemical analysis was used as the reference standard to assess the accuracy of dual-energy mammography in measuring volumetric water and lipid density. Images from different views and contralateral breasts were used to assess estimate of precision for water and lipid volumetric density measurements. The measured volumetric water and lipid density from dual-energy mammography and chemical analysis were in good agreement, where the standard errors of estimates (SEE) of both were calculated to be 2.1%. Volumetric water and lipid density measurements from different views were also in good agreement, with a SEE of 1.3% and 1.1%, respectively. The results indicate that dual-energy mammography can be used to accurately measure volumetric water and lipid density in breast tissue. Accurate quantification of volumetric water density is expected to enhance its utility as a risk factor for breast cancer and for assessment of response to therapy. • Dual-energy mammography can be used to accurately measure water and lipid volumetric density in breast tissue. • Improved quantification of volumetric water density is expected to enhance its utility for assessment of response to therapy and as a risk factor for breast cancer.

Few-photon computed x-ray imaging

X-rays are a ubiquitous imaging modality in clinical diagnostics and industrial inspections, thanks to their high penetration power. Conventional transmission-based x-ray radiography or computed tomography systems collect approximately 103–104 counts per pixel to ensure sufficient signal to noise ratio. The recent development of energy sensitive photon counting detectors has made x-ray imaging at low photon fluxes possible. In this paper, we report a photon-counting scheme that records the time stamp of individual photons, which follows a negative binomial distribution, and demonstrate the reconstruction based on the few-photon statistics. The x-ray projection and tomography reconstruction from measurements of ∼16 photons per beam show potential for using photon counting detectors for dose-efficient x-ray imaging applications.

Abstract ID: 368 Imaging radiologico a contrasto di fase e a conteggio fotonico

An introduction to novel imaging modalities, which take advantage of energy and phase characteristics of X-ray quanta will be here provided. X-ray detection in medical imaging typically involves an integration of the spectrum of X-rays exiting a patient, weighted by the detector’s energy response. This procedure yields information related to the average energy of the spectrum exiting the patient, which for many clinical applications is sufficient. The spectral imaging methods allow instead the form, or shape, of the X-ray distribution exiting the patient to be measured [1]. In particular, energy-sensitive photon-counting detectors allow for further improvements of the diagnostic information by optimising the signal-to-noise ratio, anatomical background subtraction or quantitative analysis of object constituents [2]. Phase-contrast imaging has had an undeniable impact in the field of X-ray imaging during the last decades, and one of the main advantages lies in the fact that the phase shifting effects are related to characteristic properties of materials that are different from the ones involved in conventional X-ray imaging (i.e. the well-known absorption-contrast imaging) [3]. The mechanism that allows one to produce and to detect images according to this physical phenomenon will be here discussed, together with a review of main phase-contrast imaging techniques. Finally, the potential of both phase-contrast and spectral imaging in diagnostic radiology will be presented by means of specific applications.

Characterization of spectrometric photon-counting X-ray detectors at different pitches

There is growing interest in energy-sensitive photon-counting detectors based on high flux X-ray imaging. Their potential applications include medical imaging, non-destructive testing and security. Innovative detectors of this type will need to count individual photons and sort them into selected energy bins, at several million counts per second and per mm2. Cd(Zn)Te detector grade materials with a thickness of 1.5 to 3 mm and pitches from 800 μm down to 200 μm were assembled onto interposer boards. These devices were tested using in-house-developed full-digital fast readout electronics. The 16-channel demonstrators, with 256 energy bins, were experimentally characterized by determining spectral resolution, count rate, and charge sharing, which becomes challenging at low pitch. Charge sharing correction was found to efficiently correct X-ray spectra up to 40 × 106 incident photons.s−1.mm−2.

Energy-sensitive photon counting detector-based X-ray computed tomography.

Energy-sensitive photon counting detectors (PCDs) have recently been developed for medical X-ray computed tomography (CT) imaging and a handful of prototype PCD-CT systems have been built and evaluated. PCDs detect X-rays by using mechanisms that are completely different from the current CT detectors (i.e., energy integrating detectors or EIDs); PCDs count photons and obtain the information of the object tissues (i.e., the effective atomic numbers and mass densities) to be imaged. Therefore, these PCDs have the potential not only for evolution-to improve the current CT images such as providing dose reduction-but also for a revolution-to enable novel applications with a new concept such as molecular CT imaging. The performance of PCDs, however, is not flawless, and thus, it requires integrated efforts to develop PCD-CT for clinical use. In this article, we review the current status and the prediction for the future of PCDs, PCD-CT systems, and potential clinical applications.

Basis material decomposition in spectral CT using a semi-empirical, polychromatic adaption of the Beer–Lambert model

Following the development of energy-sensitive photon-counting detectors using high-Z sensor materials, application of spectral x-ray imaging methods to clinical practice comes into reach. However, these detectors require extensive calibration efforts in order to perform spectral imaging tasks like basis material decomposition. In this paper, we report a novel approach to basis material decomposition that utilizes a semi-empirical estimator for the number of photons registered in distinct energy bins in the presence of beam-hardening effects which can be termed as a polychromatic Beer–Lambert model. A maximum-likelihood estimator is applied to the model in order to obtain estimates of the underlying sample composition. Using a Monte-Carlo simulation of a typical clinical CT acquisition, the performance of the proposed estimator was evaluated. The estimator is shown to be unbiased and efficient according to the Cramér–Rao lower bound. In particular, the estimator is capable of operating with a minimum number of calibration measurements. Good results were obtained after calibration using less than 10 samples of known composition in a two-material attenuation basis. This opens up the possibility for fast re-calibration in the clinical routine which is considered an advantage of the proposed method over other implementations reported in the literature.

Poster - Thur Eve - 14: The effect of fluence and detector size on image quality in multi-projection compton scatter tomography.

To assess how radiation dose and size of energy sensitive detectors affects image quality in multi-projection Compton scatter tomography. A Compton scatter tomography system was simulated in Maltab. The system consists of a point source generated x-ray fan beam and energy sensitive photon counting detectors, placed along a line with the source outside the periphery of the primary beam. Single scattered photons from a low contrast phantom simulating breast tissues were simulated. Simulation parameters are dose-limited and closely matched to typical breast CT. Poisson distributed noise was added to simulate quantum noise. We have successfully reconstructed electron density images in a clinical fan-beam breast CT system, in the presence of noise. The reconstruction illustrates accurate spatial alignment of the structures of interest in the phantom. The increase in MSE due to noise was ∼11%. The optimal detector size of 2 × 2 mm2 is a trade off between the increased noise, that is present when smaller detector sizes are used, and the blurring of the image that occurs as larger detectors are employed. For breast CT dose of 4-12 mGy, the optimal detector size for a Compton scatter reconstruction using 360 projections and 1000 eV energy resolution was found to be 2 × 2 mm2 . The ability to visualize large low contrast (9%) and small (2 mm diameter) high contrast objects was demonstrated.

WE‐G‐211‐03: Multiple Projection Compton Scatter Tomography

Purpose: To evaluate the use of multiple projections in spectroscopic x‐ray tomography techniques for electron density reconstruction using backprojection over isogonic curves at realistic energy resolutions. Method and Materials: Matlab was used to simulate a clinical breast CT geometry and 55 keV fan‐beam. The system design includes a point source producing an x‐ray fan‐beam, which passes through the object to be imaged, before interacting with the primary detector. The scattered x‐rays, are measured using energy sensitive photon counting detectors aligned with the source and placed outside of the periphery of the primary fan beam. We consider a 2D case where reconstructions are carried out in the fan‐beam plane. We assume no multiple scatter or attenuation of the scattered photons. Image reconstruction was performed using backprojection over isogonic curves passing through the source and detector points. Single projection reconstruction results in an image that varies in resolution and noise throughout the image. The image reconstructed at realistic energy resolutions is not of sufficient quality. For a given energy resolution, images obtained from different projection angles were fused. Results: Results demonstrate the improvement in electron density image quality of a modified Shepp‐Logan phantom as a function of projection number and the energy resolution of the detector. Conclusions: This work has shown that it is possible to improve the image quality in a spectroscopic approach for electron density image reconstruction by combining multiple projections. It appears that it may be feasible to create clinical quality images with current detector technology.

Dual- and multi-energy CT: approach to functional imaging

The energy spectrum of X-ray photons after passage through an absorber contains information about its elemental composition. Thus, tissue characterisation becomes feasible provided that absorption characteristics can be measured or differentiated. Dual-energy CT uses two X-ray spectra enabling material differentiation by analysing material-dependent photo-electric and Compton effects. Elemental concentrations can thereby be determined using three-material decomposition algorithms. In comparison to dual-energy CT used in clinical practice, recently developed energy-sensitive photon-counting detectors sample the material-specific attenuation curves at multiple energy levels and within narrow energy bands; the latter allows the detection of element-specific, k-edge discontinuities of the photo-electric cross section. Multi-energy CT imaging therefore is able to concurrently identify multiple materials with increased accuracy. These specific data on material distribution provide information beyond morphological CT, and approach functional imaging. This article reviews the principles of dual- and multi-energy CT imaging, hardware approaches and clinical applications.

Detectors for the future of X-ray imaging

In recent decades, developments in detectors for X-ray imaging have improved dose efficiency. This has been accomplished with for example, structured scintillators such as columnar CsI, or with direct detectors where the X rays are converted to electric charge carriers in a semiconductor. Scattered radiation remains a major noise source, and fairly inefficient anti-scatter grids are still a gold standard. Hence, any future development should include improved scatter rejection. In recent years, photon-counting detectors have generated significant interest by several companies as well as academic research groups. This method eliminates electronic noise, which is an advantage in low-dose applications. Moreover, energy-sensitive photon-counting detectors allow for further improvements by optimising the signal-to-quantum-noise ratio, anatomical background subtraction or quantitative analysis of object constituents. This paper reviews state-of-the-art photon-counting detectors, scatter control and their application in diagnostic X-ray medical imaging. In particular, spectral imaging with photon-counting detectors, pitfalls such as charge sharing and high rates and various proposals for mitigation are discussed.