Hybrid Photon Counting X-ray Detectors for Preclinical CT and Spectral Imaging (#3101)
E. Braig2, C. Broennimann1, M. Duda2, S. Ehn2, S. Gkoumas1, A. Guiller1, M. Habl1, J. Herzen2, M. Kachelrieß4, J. Maier4, K. Mechlem2, D. Muenzel2, P. Noël2, 3, F. Pfeiffer2, M. Rissi1, E. J. Rummeny2, S. Sawall4, T. Sellerer2, P. Zambon1
1 Dectris Ltd., Baden-Daettwil, Aargau, Switzerland
Hybrid photon counting X-ray detectors bump-bonded to CdTe sensors are attractive candidates for medical imaging applications. They exhibit advantages such as absence of readout noise, high dynamic range and excellent point spread function proven through the well-established PILATUS technology. This study aims to compare the performance of hybrid photon counting technology to a commercial CT system using the same acquisition protocols and dose, and moreover to exploit the latest prototype single-shot multi-threshold capabilities for material decomposition spectral imaging. The PILATUS3 X 300K-W detector with a pixel size of 0.172 mm and one energy threshold was tested on a table-top CT setup at the German Cancer Research Center. Since the PILATUS3 detector was not designed primarily for imaging purposes, pre-reconstruction correction algorithms were applied to minimize artefacts. Using clinical acquisition protocols, it was compared to a commercial clinical CT system and it exhibited superior image quality at the same resolution and dose levels. The second part of this study focuses on a novel prototype detector with multi-threshold spectral capabilities designed for medical imaging research. Based on the latest IBEX technology, with a pixel size of 0.150 mm and four simultaneous energy thresholds, the prototype was used for material decomposition at the Technical University of Munich. The powerful combination of spectral hybrid photon counting detection and material decomposition is showcased in an example of coronary angiography of a pig’s heart injected with iodine contrast agent. Current digital subtraction angiography techniques require two consecutive acquisitions. With spectral hybrid photon counting angiography it is possible to provide similar contrast quality in a single-shot, thus eliminating the possibility of motion artefacts commonly appearing in the clinics.
Keywords: CT, spectral imaging, material decomposition, CdTe, hybrid photon counting, multi-threshold detector
Analysis of the effects of silica coating gold nanoparticles with respect to dose enhancement, photon counting multispectral x-ray imaging (x-CSI) and photoacoustic spectral imaging (PASI). (#2583)
O. L. P. P. Scienti1, 2, A. Shah1, 2, J. Bamber1, 2, D. Darambara1, 2
1 Institute of Cancer Research, Radiotherapy and Imaging, London, United Kingdom of Great Britain and Northern Ireland
Gold nanoparticles (AuNPs) have been suggested as suitable agents for a range of medical applications, ranging from receptor based imaging to targeted drug delivery. Of particular interest to our group is the use of AuNPs to deliver a dose enhancing effect (DEE) to target volumes within a tumour during radiotherapy treatment. Quantitative imaging of AuNP concentration and distribution is necessary for the safe realisation of this procedure however, as targeted uptake will need to be confirmed so that DEE can be factored into the radiotherapy plan. Two imaging modalities being developed for such tasks are photoacoustic spectral imaging (PASI) and photon counting multispectral x-ray imaging (x-CSI).
Silica coated AuNPs have been shown to help preserve the spectral properties that are essential to producing a quantitative image of AuNP distributions using PASI, however the effect of such a coating on both the DEE delivered and the clarity of an x-CSI image have not been demonstrated. This work sets out first to confirm that the spectral protection is necessary in our applications and then to determine the effects of silica coating on DEE and x-CSI based images.
The x-CSI work was performed in silico using our custom simulation environment: a combination of Monte Carlo and Finite Element modelling techniques. The current suite is in its 5th generation and has been recently upgraded to include more signal generation and post-processing processes: details of these upgrades will be discussed. This system was used to select the best geometry for an x-CSI system for this application using energy resolution and detection efficiency as metrics. The best system was then simulated with tissue like phantoms containing AuNP inclusions to determine the effect on image quality of silica coating the AuNPs.
A comparison of the DEE in silica coated and PEG-ylated (standard preparation) AuNPs is being studied in vitro using cells derived from a prostate cancer cell line.
Keywords: gold nanoparticles, photon counting
Novel photon-counting low-dose computed tomography using a multi-pixel photon counter (#2588)
H. Morita1, J. Kataoka1, M. Arimoto1, K. Fujieda1, T. Maruhashi1, H. Nitta2
1 Waseda University, Research Institute for Science and Engineering, Shinjuku, Tokyo, Japan
X-ray computed tomography (CT) is widely used in diagnostic imaging. Owing to a strong radiation exposure associated with this method, numerous proposals have been made for reducing the radiation dose. In addition, conventional CT does not provide information on the energy associated with each Xray photon because intensity is rather high. Here, we propose a novel, low-dose photon-counting CT system based on a multipixel photon counter (MPPC) and a high-speed scintillator. To demonstrate high signal-to-noise ratio utilizing the internal gain and the fast time response of the MPPC, we compared CT images acquired under the same conditions among a photodiode (PD), an avalanche photodiode and a MPPC. In particular, the images’ contrast-to-noise ratio (CNR) acquired using the MPPC improved more than 10-fold compared with the images acquired in conventional CT using a PD. We also performed energy-resolved imaging by adopting 4 energy thresholds. As the application, we confirmed a substantial improvement of the imaging contrast, an alleviation of beam hardening artifacts and iodine K-edge imaging. We conclude that the proposed MPPC-based detector is likely to be a promising device for use in future CT scanners.
Keywords: photon counting, MPPC, APD, low-dose
Deep residual learning in CT physics: scatter correction for spectral CT (#1958)
S. Xu1, P. Prinsen2, J. Wiegert2, R. Manjeshwar1
1 Philips healthcare, global advanced technology, highland heights, Ohio, United States of America
Recently, spectral CT has been drawing a lot of attention in a variety of clinical applications primarily due to its capability of providing quantitative information about material properties. The quantitative integrity of the reconstructed data depends on the accuracy of the data corrections applied to the measurements. Scatter correction is a particularly sensitive correction in spectral CT as it depends on system effects as well as the object being imaged and any residual scatter is amplified during the non-linear material decomposition. An accurate way of removing scatter is subtracting the scatter estimated by Monte Carlo simulation. However, to get sufficiently good scatter estimates, extremely large numbers of photons is required, which may lead to unexpectedly high computational costs. Other approaches model scatter as a convolution operation using kernels derived using empirical methods. These techniques have been found to be insufficient in spectral CT due to their inability to sufficiently capture object dependence. In this work, we develop a deep residual learning framework to address both issues of computation simplicity and object dependency. A deep convolution neural network is trained to determine the scatter distribution from the projection content in training sets. In test cases of a digital anthropomorphic phantom and real water phantom, we demonstrate that with much lower computing costs, the proposed network provides sufficiently accurate scatter estimation.
Keywords: deep residual learning, spectral CT, scatter correction, material decomposition, monochromatic images
Algorithm-enabled single-kVp-switch scan configuration for fast dual-energy CT (#1016)
B. Chen1, Z. Zhang1, E. Y. Sidky1, X. Pan1, 2
1 The University of Chicago, Department of Radiology, Chicago, Illinois, United States of America
In this work, we investigate a technique for achieving fast, low-dose dual-energy CT imaging with single-kVp-switch scan configuration. Most current implementations of dual-energy CT require additional system hardware, as compared to a conventional CT scanner. In addition, the slow-kVp-switch technique, where two full-rotation scans are acquired and one kVp switch is invoked following the completion of the first rotation, is easy to implement, however, at a cost of doubling the imaging dose and scanning time. We propose to use single-kVp-switch scan configuration, in which a kVp switch is invoked after the X-ray tube rotates for a short-scan or half-rotation range, before continuing the rotation with another short-scan or half-rotation range, thus reducing the radiation exposure to and scanning time for the patient. The technique is enabled by a one-step algorithm developed for image reconstruction from dual-energy data. It is based on a non-linear data model capturing the polychromatic integral of the X-ray interaction and does not require the ray-consistency condition, enabling flexible scan configuration design. Dual-energy data of a physical phantom were collected with two full-rotation scans (i.e., full scan) at 80 and 135 kVp, from which single-kVp-switch data of either short-scan (i.e., short scan) or half-rotation (i.e., half scan) range are extracted. All full-, short-, and half-scan data, as described above, were reconstructed using the one-step algorithm to basis images, while the full-scan data were also processed with data-domain decomposed followed by analytical-based FBP-like reconstruction. Basis images and monochromatic energy images results suggest that short- and half-scan data can achieve comparable visualization for the monochromatic energy images as the full-scan data using the one-step algorithm, while the images from the one-step algorithm for the full-data are similar to those from the data-domain decomposition method.
Keywords: single-kVp-switch, dual-energy CT, one-step reconstruction algorithm
Simultaneous Dose Reduction and Scatter Correction for 4D Cone-Beam Computed Tomography (#2708)
C. Zhao1, Y. Zhong2, J. Wang2, M. Jin1
1 University of Texas at Arlington, Physics, Arlington, Texas, United States of America
Four dimensional (4D) X-ray cone-beam computed tomography (CBCT) can lead to a precise radiation therapy through accurate tumor motion modeling. However, the repeated use of 4D CBCT in a fractional treatment session raises the concern of radiation dose. In addition, the scatter contamination results in shading artifacts and low contrast in reconstructed images if not corrected. In this work, we propose a novel method to use a moving blocker (MB) to achieve the dose reduction and scatter correction simultaneously for 4D CBCT, termed “MB-4D”. The lead blocker is placed between the X-ray source and the patient and moving back and forth in a certain direction during the CBCT data collection. Not only is part of radiation blocked, but also the scatter signal can be estimated from the blocked region for scatter correction (SC). The spatial total variation (TV) minimization and motion correlations are used to improve 4D reconstruction with incomplete data and to derive the motion fields. As an initial test of this novel method, we used a simulation study using the 4D non-uniform rational B-spline cardiac-torso (NCAT) phantom. Our results show that with 1/3 dose reduction the proposed MB-4D method can achieve much better image quality than 3D reconstruction with SC (“MB-3D”) and 4D reconstruction without SC (“4D”), measured by structural similarity (SSIM) index, root mean square error (RMSE) of CT numbers, and time attenuation coefficient (TAC) curves.
Keywords: 4D CBCT, Moving blocker, Scatter correction, Dose reduction, Spatiotemporal 4D reconstruction