Dynamic contrast-enhanced MRI in clinical oncology: current status and future directions

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is performed after the administration of intravenous contrast medium to noninvasively access tumor vascular characteristics. DCE-MRI techniques utilizing low-molecular-weight contrast media have successfully made the transition from methodological development to preclinical and clinical validation and are now rapidly becoming mainstream clinical tools. DCE-MRI using macromolecular contrast medium (MMCM) can also assay microvascular characteristics of human tumor xenografts. MMCM approval for human use will occur soon. The success of both techniques depends on their ability to demonstrate quantitative differences of contrast medium behavior in a variety of tissues. Evidence is mounting that kinetic parameters correlate with immunohistochemical surrogates of tumor angiogenesis, including microvessel density, and with pathologic tumor grade. DCE-MRI is being applied to monitor the clinical effectiveness of a variety of treatments, including antiangiogenic drugs. Kinetic parameter changes following treatment have correlated with histopathological outcome and patient survival. This article reviews the current clinical status of low-molecular-weight DCE-MRI and reviews the potential of MMCM techniques for evaluating human tumors. Ongoing challenges faced by DCE-MRI as clinical and research tools will be explored.     

Diagnostic breast ultrasound: current status and future directions

This summary of breast ultrasound reviews the current indications for its use, discusses the potential technical and human pitfalls in its performance, and briefly examines possible future applications that currently are works in progress. It also contains an in-depth discussion of the use and interpretation of color Doppler and power Doppler imaging, techniques that do not seem to be understood or used fully in daily practice.     

多肽受体靶向放射治疗:现状与进展

临床前及临床多中心试验结果已证实应用放射性核素标记的生长抑素类似物进行多肽受体靶向放射治疗(PRRT)的有效性,不同治疗手段联合治疗能进一步提高PRRT的临床疗效,177Lu与90Y标记的生长抑素类似物联合治疗可以获得更好的疗效,其受体在前列腺与乳腺癌等常见肿瘤细胞上表达的蛙皮素和神经肽Y类似物正在研究中。联合放射性核素标记的蛙皮素和神经肽Y类似物进行多受体肿瘤靶向治疗对于乳腺癌及其淋巴结转移灶的诊断与PRRT也很有希望。     

Diagnostic breast MR imaging: current status and future directions

Breast MRI has become an integral component in breast imaging. Indications have become clearer and better defined. Guidelines and recommendations are evolving and many are recognized and published. Future applications are exciting and may possibly improve our ability to diagnose breast cancer, improving the patient's treatment options and ultimately patient outcome.     

Radiolabelled peptides for tumour therapy: current status and future directions

On their plasma membranes, cells express receptor proteins with high affinity for regulatory peptides, such as somatostatin. Changes in the density of these receptors during disease, e.g. overexpression in many tumours, provide the basis for new imaging methods. The first peptide analogues successfully applied for visualisation of receptor-positive tumours were radiolabelled somatostatin analogues. The next step was to label these analogues with therapeutic radionuclides for peptide receptor radionuclide therapy (PRRT). Results from preclinical and clinical multicentre studies have already shown an effective therapeutic response when using radiolabelled somatostatin analogues to treat receptor-positive tumours. Infusion of positively charged amino acids reduces kidney uptake, enlarging the therapeutic window. For PRRT of CCK-B receptor-positive tumours, such as medullary thyroid carcinoma, radiolabelled minigastrin analogues are currently being successfully applied. The combination of different therapy modalities holds interest as a means of improving the clinical therapeutic effects of radiolabelled peptides. The combination of different radionuclides, such as (177)Lu- and (90)Y-labelled somatostatin analogues, to reach a wider tumour region of high curability, has been described. A variety of other peptide-based radioligands, such as bombesin and NPY(Y(1)) analogues, receptors for which are expressed on common cancers such as prostate and breast cancer, are currently under development and in different phases of (pre)clinical investigation. Multi-receptor tumour targeting using the combination of bombesin and NPY(Y(1)) analogues is promising for scintigraphy and PRRT of breast carcinomas and their lymph node metastases.     

Imaging in primary penile cancer: current status and future directions

Penile cancer is a rare neoplasm in the developed world. Clinical assessment often results in inaccurate staging and radiological techniques have a key role in staging and postoperative assessment. Magnetic resonance imaging (MRI) depicts penile anatomy in detail and is the most accurate technique for local staging and postoperative follow-up. MRI and ultrasound (US), although helpful for assessment of lymph nodes, are not reliable enough for accurate nodal staging. US-guided fine needle aspiration cytology (FNAC), however, remains a valuable tool to confirm metastases in suspicious inguinal nodes. Lymphoscintigraphy with dynamic sentinel node biopsy (DSNB) is a promising technique used to predict occult lymph node metastases. Novel imaging techniques such as positron emission tomography/computed tomography (PET-CT) and nanoparticle enhanced MRI have high sensitivity and specificity for lymph node metastases but their availability is limited and clinical utility is not fully established. The radiologist needs to be familiar with the normal penile anatomy, imaging appearances of pre- and post-treatment penile cancer, and the advantages and limitations of the available imaging techniques. This review highlights the above points and presents a systematic approach to make the best use of imaging in the management of patients with penile cancer.     

Whole-body MRI in children: current status and future applications

Whole-body MRI (WBMRI) is a novel technique that makes imaging of the whole patient in a manner similar to scintigraphy or positron emission tomography (PET) possible. Unlike the latter two methods, it is without exposure to radiation and thus gaining increasing importance and application in pediatrics. With the introduction of a moving tabletop, sequential movement of the patient through the magnet has become possible with automatic direct realignment of the images after acquisition. The common scan plane is coronal with additional planes being added depending on the indication. WBMRI is targeted for maximum coverage of the body within the shortest possible time using the minimum number of sequences. The evaluation of the bone marrow has been the primary indication thus inversion recovery sequences like STIR or TIRM are mostly used with the T1-weighted sequence being added variably. For correct evaluation of the bone marrow in the pediatric age group understanding normal pattern of marrow transformation is essential. The primary role of WBMRI has been in oncology for the detection of tumor spread and also for the follow-up and evaluation of complications. The initial comparative studies of WBMRI with scintigraphy and PET in children have shown the high diagnostic potential of WBMRI. Emerging potential applications of WBMRI include the evaluation for osteonecrosis, chronic multifocal recurrent osteomyelitis, myopathies, and generalized vascular malformations. Future use of WBMRI may incorporate non-accidental trauma, virtual autopsy, body fat mapping and diffusion-weighted imaging.     

Frontiers in musculoskeletal MRI: articular cartilage

The techniques and uses of MRI in current clinical practice, primarily as a means to detect morphologic abnormalities, are reviewed. Ongoing development of techniques that can improve morphologic assessment including techniques to increase spatial and contrast resolution is discussed, as are methods to measure cartilage volumes and thickness. Finally, several of the more widely studied techniques used to probe loss of the macromolecular structure of cartilage prior to the development of macroscopic defects are presented and compared.     

CT-colonography: current status and future directions in consideration of the technical evolution

Computertomography and with it CT-colonography evolves technically and also possibilities of data processing proceed rapidly. The current status of CTC can be summarized as follows:The method represents a true alternative to barium enema if technical conditions are given.CTC can be performed with excellent results immediately following an incomplete colonoscopy. In pretherapeutic diagnosis of colorectal carcinoma, CTC can be combined with a staging CT of the abdomen. The recent technical advances with new 16 row technology in image quality and data acquisition - mainly concerning the spatial and temporal resolution - are very promising. Developments in postprocessing of CT data can also contribute to a higher efficiency of labor. Alternative preparation schemata can lead to a more comfortable bowel cleansing and stool labeling can even avoid this procedure, resulting both in an even improved compliance. Radiation exposure in low dose technique is comparable to a double contrast barium enema and can be still reduced by optimisation of scanning parameters.The aim of the following article is (1 to give an overview of the current status of patient preparation, image acquisition and data processing; (2) to review recent clinical trials and experimental studies and to show future directions of CTC with regard to the clinical development.     

Clinical applications of PET/MRI: current status and future perspectives

Fully integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) scanners have been available for a few years. Since then, the number of scanner installations and published studies have been growing. While feasibility of integrated PET/MRI has been demonstrated for many clinical and preclinical imaging applications, now those applications where PET/MRI provides a clear benefit in comparison to the established reference standards need to be identified. The current data show that those particular applications demanding multiparametric imaging capabilities, high soft tissue contrast and/or lower radiation dose seem to benefit from this novel hybrid modality. Promising results have been obtained in whole-body cancer staging in non-small cell lung cancer and multiparametric tumor imaging. Furthermore, integrated PET/MRI appears to have added value in oncologic applications requiring high soft tissue contrast such as assessment of liver metastases of neuroendocrine tumors or prostate cancer imaging. Potential benefit of integrated PET/MRI has also been demonstrated for cardiac (i.e., myocardial viability, cardiac sarcoidosis) and brain (i.e., glioma grading, Alzheimer’s disease) imaging, where MRI is the predominant modality. The lower radiation dose compared to PET/computed tomography will be particularly valuable in the imaging of young patients with potentially curable diseases. However, further clinical studies and technical innovation on scanner hard- and software are needed. Also, agreements on adequate refunding of PET/MRI examinations need to be reached. Finally, the translation of new PET tracers from pre-clinical evaluation into clinical applications is expected to foster the entire field of hybrid PET imaging, including PET/MRI.Both positron emission tomography (PET) and magnetic resonance imaging (MRI) are well-established imaging modalities that have been clinically available for more than 30 years. However, the combination of PET and computed tomography (CT) into PET/CT has heralded a new era of hybrid imaging driven by the rapid ascend of PET/CT and the decline of stand-alone PET. The integration of PET and CT into a hybrid system provided added value that exceeds the sum of its parts, in particular fast and accurate attenuation correction and the combination of anatomical and molecular information.Inspired by the vast success of PET/CT, the combination of PET and MRI was an obvious goal. Therefore initial solutions comprised the software based co-registration and post-hoc fusion (1) of independently acquired PET and MRI data, as well as shared tabletop sequential PET and MRI acquisition (2, 3). While the integration of PET and CT into a hybrid system was challenging but technically feasible, the integration of PET and MRI was considered extremely demanding, if not impossible. Two main technical challenges that had to be solved: in the first place development of a PET insert that is compatible to high magnetic field strengths normally used in MRI, and vice versa development of a magnetic resonance (MR) scanner that guarantees a stable and homogenous magnetic field in the presence of a PET insert. Conventional PET detectors consist of scintillation crystals and photomultipliers, and the latter, being very sensitive to magnetic fields, cannot be used in integrated PET/MRI systems. Hence, one approach was to replace photomultipliers by avalanche photodiodes (APDs), which are insensitive to even strong magnetic fields (4). The scintillation crystals used in PET/MRI scanners are usually composed of lutetium ortho-oxysilicate, with the advantage of only minor disturbances of magnetic field homogeneity (Fig. 1). Next generation PET/MRI scanners could be based on silicon photomultiplier PET detectors, which showed better performance characteristics than the APDs and, in contrast to these, are capable of time-of-flight imaging (5). Secondly, the development of MR-based attenuation correction methods is necessary, as the commonly used method for attenuation correction in PET/CT systems, which is based on the absorption of X-rays, is not transferable to MRI. Hence, different methods for attenuation correction in PET/MRI systems have been proposed, one of which consists of segmentation of the attenuation map into four classes (background, lung tissue, fat, and soft tissue) (6). In principle, the MR-based attenuation map is created with a two-point Dixon sequence (7), providing water-only and fat-only images, which are combined and segmented to form an MR-based attenuation map. The method proved its technical feasibility with the limitation that in bone tissue and in its vicinity standardized uptake values (SUV) derived from PET/MRI systems might be erroneously underestimated when compared to SUVs derived from PET/CT (8). Therefore, SUVs derived from PET/MRI systems should be interpreted carefully until a larger experience with the new method of PET/MRI exists.Open in a separate windowFigure 1.Diagram of an integrated PET/MRI scanner with capability of simultaneous PET and MRI data acquisition. Image courtesy of Siemens Healthcare, Erlangen, Germany.In 2010, the first fully integrated whole-body PET/MR hybrid imaging system based on APD technology and MR-based attenuation correction became commercially available (Biograph mMR, Siemens Healthcare, Erlangen, Germany) (9). As of December 2013 more than 50 of these systems have been sold (>40 installed, 10 ordered) in Europe, North America, Asia, and Australia (10).     

Snowboarding injuries : current trends and future directions

Snowboarding has become one of the premier alpine sports. The past decade has seen the popularity of snowboarding increase dramatically and the recent Winter Olympic Games at Salt Lake City, USA, showcased the strong visual appeal of the sport and the youth-oriented lifestyle and culture that accompanies it. The injury profile of the sport has also undergone change along with technological advances in boot and binding systems and the changing demographics of the sports participants. Central to the development of injury-prevention strategies is knowledge of the profile of injuries that occur, understanding those who are at particular risk and, if possible, the biomechanical factors involved in each injury type. Snowboarding was initially considered a dangerous, uncontrolled, alpine sport - an opinion based on little or no scientific evidence. That evidence has rapidly grown over the past decade and we now know that snowboard injury rates are no different to those in skiing; however, the injury profile is different. The purpose of this review is to give some perspective to the current snowboard injury literature. It discusses not only the demographic profile of those injured and the type of injuries that occur, but also gives some insight into the progress that has occurred in determining the impact of specific prevention strategies, such as splints to prevent injuries to the wrist/forearm. The next decade will also see a greater understanding of the biomechanical forces involved in snowboard injuries, which may well impact on future technological advances. As the literature indicates, however, some things will not change, e.g. injuries are more likely to occur in beginners and lessons need to be reinforced as a fundamental aspect of any injury-prevention strategy.     

CT of pulmonary emphysema - current status, challenges, and future directions

Pulmonary emphysema is characterized by irreversible destruction of lung parenchyma. Emphysema is a major contributor to chronic obstructive pulmonary disease (COPD), which by itself is a major cause of morbidity and mortality in the western world. Computed tomography (CT) is an established method for the in-vivo analysis of emphysema. This review first details the pathological basis of emphysema and shows how the subtypes of emphysema can be characterized by CT. The review then shows how CT is used to quantify emphysema, and describes the requirements and foundations for quantification to be accurate. Finally, the review discusses new challenges and their potential solution, notably focused on multi-detector-row CT, and emphasizes the open questions that future research on CT of pulmonary emphysema will have to address.     

T2* mapping for articular cartilage assessment: principles,current applications,and future prospects

With advances in joint preservation surgery that are intended to alter the course of osteoarthritis by early intervention, accurate and reliable assessment of the cartilage status is critical. Biochemically sensitive MRI techniques can add robust biomarkers for disease onset and progression, and therefore, could be meaningful assessment tools for the diagnosis and follow-up of cartilage abnormalities. T2* mapping could be a good alternative because it would combine the benefits of biochemical cartilage evaluation with remarkable features including short imaging time and the ability of high-resolution three-dimensional cartilage evaluation—without the need for contrast media administration or special hardware. Several in vitro and in vivo studies, which have elaborated on the potential of cartilage T2* assessment in various cartilage disease patterns and grades of degeneration, have been reported. However, much remains to be understood and certain unresolved questions have become apparent with these studies that are crucial to the further application of this technique. This review summarizes the principles of the technique and current applications of T2* mapping for articular cartilage assessment. Limitations of recent studies are discussed and the potential implications for patient care are presented.