The operation of the bowtie filter in x-ray CT is correct if the object being scanned is properly centered in the scanner's field-of-view. Otherwise, the dose delivered to the patient and image noise will deviate from optimal setting. We investigate the effect of miscentering on image noise and surface dose on three commercial CT scanners. Six cylindrical phantoms with different size and material were scanned on each scanner. The phantoms were positioned at 0, 2, 4 and 6 cm below the isocenter of the scanner's field-of-view. Regression models of surface dose and noise were produced as a function of miscentering magnitude and phantom's size. 480 patients were assessed using the calculated regression models to estimate the influence of patient miscentering on image noise and patient surface dose in seven imaging centers. For the 64-slice CT scanner, the maximum increase of surface dose using the CTDI-32 phantom was 13.5%, 33.3% and 51.1% for miscenterings of 2, 4 and 6 cm, respectively. The analysis of patients' scout scans showed miscentering of 2.2 cm in average below the isocenter. An average increase of 23% and 7% was observed for patient dose and image noise, respectively. The maximum variation in patient miscentering derived from the comparison of imaging centers using the same scanner was 1.6 cm. Patient miscentering may substantially

This review identifies the important roles of F-AuNPs in current cancer studies that are being undertaken worldwide. The findings of this review confirm that F-AuNP is a new theranostic agent, which has a great potential for simultaneous cancer therapy and diagnosis.

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Objective: Recently introduced energy-sensitive X-ray CT makes it feasible to discriminate different nanoparticulate contrast materials. The purpose of this work is to present a K-edge ratio method for differentiating multiple simultaneous contrast agents using spectral CT. Methods: The ratio of two images relevant to energy bins straddling the K-edge of the materials is calculated using an analytic CT simulator. In the resulting parametric map, the selected contrast agent regions can be identified using a thresholding algorithm. The K-edge ratio algorithm is applied to spectral images of simulated phantoms to identify and differentiate up to four simultaneous and targeted CT contrast agents. Results: We show that different combinations of simultaneous CT contrast agents can be identified by the proposed K-edge ratio method when energy-sensitive CT is used. In the K-edge parametric maps, the pixel values for biological tissues and contrast agents reach a maximum of 0.95, whereas for the selected contrast agents, the pixel values are larger than 1.10. The number of contrast agents that can be discriminated is limited owing to photon starvation. For reliable material discrimination, minimum photon counts corresponding to 140 kVp, 100 mAs and 5-mm slice thickness must be used. Conclusion: The proposed K-edge ratio method is a straightforward and fast method for identification and discrimination of multiple simultaneous CT contrast agents. Advances in knowledge: A new spectral CT-based algorithm is proposed which provides a new concept of molecular CT imaging by non-iteratively identifying multiple contrast agents when they are simultaneously targeting different organs.Despite remarkable advances in diagnostic and therapeutic procedures during the past two decades, annual reports still indicate that cancer remains a challenging disease all over the world. To reduce the morbidity and mortality caused by cancer and many other diseases, endeavours spanning technological innovations in imaging systems to the development of nanoparticulate (NP) materials aim at improving clinical diagnosis and therapy planning. Numerous high-atomic-number agents have been investigated for X-ray imaging applications, such as bismuth [1] [11]. Moreover, NP CT contrast agents proved to be promising in the context of molecular imaging owing to their higher diagnostic efficacy than current contrast agents [12][13][14]. Targetability and high circulation time in vivo make it possible to use multiple contrast agents simultaneously and integrate multiple phases of diagnostic imaging in a single scan. This may decrease CT radiation dose, drug dose and diagnosis time, with higher sensitivity and specificity [12].Although the use of multiple high-atomic-number contrast agents may improve the efficiency of clinical diagnosis, it would require differentiation of the contrast agents used simultaneously. However, owing to the wide range of atomic numbers and concentrations in the body, conventional CT that uses an integrating detection system is unlike...