Imaging decisions (Berlin, Germany)最新文献

Quantitative neuroimaging techniques have become emerging technologies within clinical practice. In this paper, we survey a few clinical applications where quantification methods have received increasing attention, namely in the area of brain atrophy, lesion load computation and quantification of diffusion processes. We focus on the reliability and reproducibility of such methods and will use the example of quantitative diffusion tensor imaging to discuss methodological details. There, we show possible avenues for evaluating correctness and reliability. On the one hand, we show results from our novel hardware phantom experiments, where axonal fibres are emulated by synthetic industry fibres. On the other hand, we present a new framework for constructing software phantoms which can be used to evaluate, for example, the impact of partial volume effects in case of axonal loss as to be found in multiple sclerosis. Advantages and disadvantages as well as pitfalls of quantification and evaluation techniques are illustrated throughout the paper.

The amount of coronary calcium is generally used as an indicator for risk stratification of patients with (suspected) coronary artery disease. Orginally, electron beam tomography (EBT) was used to image the amount of coronary calcium and quantification was performed by the Agatston score. Risk stratification has been validated on large patients populations using the EBT scanner in combination with this scoring method. While EBT scanners become more and more obsolete nowadays, these scanners are being replaced by multi-detector computer tomography (MDCT) systems and dedicated cardio scanners like dual source computer tomography (DSCT). However, in order to used the calcium score obtained from a patient scan on these systems, it must be demonstrated to be accurate, clinically relevant and reproducible. In this study we compared the infiuence of cardiac motion on the calcium score for a 64-slice MDCT scanner and for an EBT and a DSCT systems. A moving cardiac phantom was used and the measured Agatston scores were compared on these three systems as a function of heart rate, calcification density and slice thickness. The results show that DSCT is approximately 50% less susceptible to cardiac motion than 64-slice MDCT and that the susceptibility is further reduced by using a smaller slice thickness. At a slice thickness of 3.0 mm DSCT and 64-slice MDCT show similar results, however, at a slice thickness of 0.6 mm DSCT gives the best approximation of the calcium score on EBT in comparison to 64-slice MDCT.

Image quality of a computed tomography image is dependent on temporal and spatial resolution. In this article both factors are addressed in relation to image quality. The effect of temporal resolution on image quality is assessed by comparing image quality scores of dual-source computed tomography (DSCT) to single-source 64-slice multi-detector computed tomography. The effect of calcifications on image quality is discussed also.

In this short historical overview the development of the visualization of the coronary arteries and the visualization of coronary artery calcification is described. The development of non-invasive visualization techniques is also described.

Calcium scoring is a promising tool for acquiring insight in the amount of coronary calcium present in the coronary arteries. Using electron beam tomography in the past, and multi-detector computed tomography (MDCT) nowadays, calcium scoring can be performed within minutes. However, MDCT offers a large scale of possibilities in data acquisition and reconstruction. In this article, a short overview is given on the influence of different parameters on the outcome of calcium scoring in terms of absolute score and variability. In a short study, the influence of two highly influencing parameters is investigated in more detail. The study shows that at higher heart rates the calcium score of high-density calcifications are increased. The opposite behaviour is observed for low-density calcifications. In addition, calcium scores are increased with the use of smaller slice thicknesses. Smaller thicknesses also influence the variability of calcium scoring, for thinner slices the variability is reduced. When assessing the outcome of a calcium score one has to take in to account what parameters were used during the CT scan for calcium scoring.

Voxel-based iso-tumor-control probability (TCP) maps and iso-Complication maps are proposed as a plan-review tool especially for functional image-guided intensity-modulated radiotherapy (IMRT) strategies such as selective boosting (dose painting) and conformal avoidance IMRT. The maps employ voxel-based phenomenological biological dose–response models for target volumes and normal organs. Two IMRT strategies for prostate cancer, namely conventional uniform IMRT delivering an equivalent uniform dose (EUD) = 84 Gy to the entire planning target volume (PTV) and selective boosting delivering an EUD = 82 Gy to the entire PTV, are investigated, to illustrate the advantages of this approach over iso-dose maps. Conventional uniform IMRT did yield a more uniform isodose map to the entire PTV while selective boosting did result in a non-uniform isodose map. However, when employing voxel-based iso-TCP maps selective boosting exhibited a more uniform TCP map compared to what could be achieved using conventional uniform IMRT, which showed TCP cold spots in high-risk tumor subvolumes despite delivering a higher EUD to the entire PTV. Voxel-based iso-Complication maps are presented for rectum and bladder, and their utilization for selective avoidance IMRT strategies are discussed. We believe as the need for functional image-guided treatment planning grows, voxel-based iso-TCP and iso-Complication maps will become an important tool to assess the integrity of such treatment plans.

Technological advances have made it possible for tumoricidal doses of radiation to be delivered to primary and metastatic liver cancers. Computed tomography, magnetic resonance imaging, ultrasound and positron emission tomography are used to help with tumor definition at the time of radiation planning. Specialized imaging techniques are also used for characterization of tumor motion due to breathing at the time of radiation planning. Image-guided radiation therapy (IGRT), referring to the use of frequent imaging in the treatment position during a course of radiotherapy to localize the tumor prior to or during each treatment, improves accuracy and precision of radiation delivery. IGRT improves the concordance between the delivered doses to the tumor and normal tissues and the planned doses, which should improve our understanding of dose–outcome analyses. IGRT also reduces the volume of normal tissue that needs to be irradiated, and facilitates dose escalation to the tumor, potentially improving tumor control probability and reducing the risk of toxicity. Image registration is required to bring imaging data sets together at the time of radiation planning and also for image guidance at treatment. This study provides an overview of multimodality imaging and IGRT used in liver cancer conformal radiation therapy.

Recent developments in 3D X-ray imaging have made available new tools for imaging patients in the treatment room. Several researchers in the radiation oncology community are recognizing that these imaging tools not only help to achieve better patient positioning, but also provide a wealth of information relative to the various changes that occur during the course of treatment. This article discusses some of the changes that are observed and what can be done to assess their importance. Two types of changes that can be observed with in-room 3D imaging are considered: positioning changes and anatomical changes. Examples of such changes are given for head and neck and prostate patients. The different magnitudes of these changes are discussed first. Because the biological effect of radiation on anatomical structures is determined by dose, the importance of these changes is then considered through their dosimetric consequences. Early findings show that not all anatomical structures receive the dose that was intended during treatment planning. Because the convolution of positioning and anatomical changes is difficult to predict, the consequences of these changes is better evaluated on a case-by-case basis as a first step towards adaptive radiation therapy.

Several issues related to functional imaging in treatment planning and response assessment in head and neck cancer exist. In the pre-radiotherapy setting, integrated positron emission tomography (PET)-computed tomography (CT) provides more accurate delineation of disease extent in head and neck cancer than does PET or CT alone, while fluorodeoxyglucose (FDG)-PET shows promise in detecting distant metastases and/or primary tumour after a negative work-up. Incorporating FDG-PET data during the radiotherapy planning stage may significantly alter the gross tumour volume as well as identify primary tumour sites. Given sufficient time following radiation therapy (RT), FDG-PET is valuable in identifying residual tumours where CT and/or magnetic resonance imaging are unable to. While FDG-PET and PET-CT show great potential, challenges exist in successfully integrating the data into radiotherapy planning. No integrated system is used throughout the planning and treatment delivery process, leading to difficulty in reconciling imaged data with accurate radiotherapy delivery. This is particularly true when attempting to accurately delineate the tumour boundary. Although the several discussed methods yield good results, target volume definition remains elusive and uncertain. By identifying targets using mathematical thresholding techniques some of this uncertainty is removed.