Jens Peter Schlomka

Computed tomography in color: NanoK-enhanced spectral CT molecular imaging.

New multidetector cardiac computed tomography (MDCT) can image the heart within the span of a few beats, and as such, it is the favored noninvasive approach to assess coronary anatomy rapidly. However, MDCT has proven to be more useful for excluding coronary disease than for making positive diagnoses. The inability to detect unstable cardiac disease arises from the confounding attenuating effects of calcium deposits within atherosclerotic plaques, which obscure lumen anatomy, and from the insensitivity of CT X-rays to image low attenuating intraluminal thrombus adhered to a disrupted plaque cap, the absolute condition of ruptured plaque and unstable disease.[1–6] It is now well understood that the sensitive detection and quantification of small intravascular thrombus in coronary arteries with molecular imaging techniques could provide a direct metric to diagnose and risk stratify patients presenting with chest pain.[7,8]

Focal cystic high-attenuation lesions: Characterization in renal phantom by using photon-counting spectral CT - Improved differentiation of lesion composition

PURPOSE To evaluate the capability of spectral computed tomography (CT) to improve the characterization of cystic high-attenuation lesions in a renal phantom and to test the hypothesis that spectral CT will improve the differentiation of cystic renal lesions with high protein content and those that have undergone hemorrhage or malignant contrast-enhancing transformation. MATERIALS AND METHODS A renal phantom that contained cystic lesions grouped in nonenhancing cyst and hemorrhage series and an iodine-enhancing series was developed. Spectral CT is based on new detector designs that may possess energy-sensitive photon-counting abilities, thereby facilitating the assessment of quantitative information about the elemental and molecular composition of tissue or contrast materials. Imaging of the renal phantom was performed with a prototype scanner at 20 mAs and 70 keV, allowing characterization of x-ray photons at 25-34, 34-39, 39-44, 44-49, 49-55, and more than 55 keV. Region of interest analysis was used to determine lesion attenuation values at various x-ray energies. Statistical analysis was performed to assess attenuation patterns and identify distinct levels of attenuation on the basis of curve regression analysis with analysis of variance tables. RESULTS Spectral CT depicted linear clusters for the cyst (P < .001, R(2) > 0.940) and hemorrhage (P < .001, R(2) > 0.962) series without spectral overlap. A distinct linear attenuation profile without spectral overlap was also detected for the iodine-enhancing series (P < .001, R(2) > 0.964), with attenuation values attained in the 34-39-keV energy bin statistically identified as outliers (mean slope variation, >37%), corresponding with iodine k-edge effects at 33.2 keV. CONCLUSION Spectral CT has the potential to enable distinct characterization of hyperattenuating fluids in a renal phantom by helping identify proteinaceous and hemorrhagic lesions through assessment of their distinct levels of attenuation as well as by revealing iodine-containing lesions through analysis of their specific k-edge discontinuities.

A reconstruction algorithm for coherent scatter computed tomography based on filtered back‐projection

Coherent scatter computed tomography (CSCT) is a reconstructive x-ray imaging technique that yields the spatially resolved coherent-scatter form factor of the investigated object. Reconstruction from coherently scattered x-rays is commonly done using algebraic reconstruction techniques (ART). In this paper, we propose an alternative approach based on filtered back-projection. For the first time, a three-dimensional (3D) filtered back-projection technique using curved 3D back-projection lines is applied to two-dimensional coherent scatter projection data. The proposed algorithm is tested with simulated projection data as well as with projection data acquired with a demonstrator setup similar to a multi-line CT scanner geometry. While yielding comparable image quality as ART reconstruction, the modified 3D filtered back-projection algorithm is about two orders of magnitude faster. In contrast to iterative reconstruction schemes, it has the advantage that subfield-of-view reconstruction becomes feasible. This allows a selective reconstruction of the coherent-scatter form factor for a region of interest. The proposed modified 3D filtered back-projection algorithm is a powerful reconstruction technique to be implemented in a CSCT scanning system. This method gives coherent scatter CT the potential of becoming a competitive modality for medical imaging or nondestructive testing.

MO‐D‐210A‐03: Energy‐Sensitive, Photon‐Counting Computed Tomography: Opportunities and Technological Challenges

Recent advances in the development of direct‐conversion, energy‐sensitive x‐ray detectors stimulate research in the domain of pre‐clinical and clinical photon‐counting x‐ray computed tomography(CT). The ability to quantify the energy of individual X‐ray photons allows for novel approaches to improve the soft tissue differentiation, material decomposition and labeling techniques, the suppression of beam‐hardening artifacts as well as the potential reduction of radiation dose. Moreover, spectral data acquisition enables the selective and quantitative imaging of certain contrast media on top of the conventional anatomy, by tuning an energy threshold in the detector system to the K‐edge discontinuity of the contrast generating element in the agent. The present lecture will provide an overview of both, the opportunities and the technological challenges arising in the context of clinical, energy‐resolved, photon‐counting CT. Some examples of potential future applications will be given together with the most challenging technical difficulties encountered in the use of photon counting detectors in CT. The problem of counting photons at the high flux conditions of clinical CT will be discussed as well as the degradation of energy resolution by effects like pulse‐pileup or charge sharing. All authors are employees of Philips Research. Learning Objectives: 1. To understand the physical basics of photon counting detectors and the implications on their use in x‐ray computed tomography 2. To learn about a possible future application of energy‐sensitive CT in connection with the identification and quantification of contrast‐agents by means of the K‐edge discontinuity in the attenuation. 3. To obtain an overview of the technological challenges to be overcome in order to realize photon‐counting CT in clinical practice.