Diagnostic imaging at its centennial: the past,the present and the future.

Since the discovery of x-rays by Wilhelm Conrad Röntgen 100 years ago, diagnostic imaging has profoundly influenced the practice of medicine. As a result of discoveries during this period, ultrasonography, nuclear imaging, computed tomography and magnetic resonance imaging, as well as conventional radiography, have assumed a major role in diagnostic medicine. In addition to their traditional role in diagnosis, imaging techniques are becoming an increasingly important factor in innovative treatment methods, and this role is likely to expand. In the current climate of rising health care costs, radiologists and other health care providers who use imaging must increasingly account to health care funders for the cost-effectiveness of imaging in relation to other diagnostic and interventional techniques. They must also assure minimum standards of quality and training, and determine the appropriate role for diagnostic imaging in health care systems of the future.     

Current imaging paradigms in radiation oncology

The technological revolution in imaging during recent decades has transformed the way image-guided radiation therapy is performed. Anatomical imaging (plain radiography, computed tomography, magnetic resonance imaging) greatly improved the accuracy of delineating target structures and has formed the foundation of 3D-based radiation treatment. However, the treatment planning paradigm in radiation oncology is beginning to shift toward a more biological and molecular approach as advances in biochemistry, molecular biology, and technology have made functional imaging (positron emission tomography, nuclear magnetic resonance spectroscopy, optical imaging) of physiological processes in tumors more feasible and practical. This review provides an overview of the role of current imaging strategies in radiation oncology, with a focus on functional imaging modalities, as it relates to staging and molecular profiling (cellular proliferation, apoptosis, angiogenesis, hypoxia, receptor status) of tumors, defining radiation target volumes, and assessing therapeutic response. In addition, obstacles such as imaging-pathological validation, optimal timing of post-therapy scans, spatial and temporal evolution of tumors, and lack of clinical outcome studies are discussed that must be overcome before a new era of functional imaging-guided therapy becomes a clinical reality.     

Multimodal optical imaging

The recent resurgence of interest in the use of intravital microscopy in lung research is a manifestation of extraordinary progress in visual imaging and optical microscopy. This review evaluates the tools and instrumentation available for a number of imaging modalities, with particular attention to recent technological advances, and addresses recent progress in use of optical imaging techniques in basic pulmonary research.1 Limitations of existing methods and anticipated future developments are also identified. Although there have also been major advances made in the use of magnetic resonance imaging, positron emission tomography, and X-ray and computed tomography to image intact lungs and while these technologies have been instrumental in advancing the diagnosis and treatment of patients, the purpose of this review is to outline developing optical methods that can be evaluated for use in basic research in pulmonary biology.     

Imaging radiation-induced normal tissue injury

Technological developments in radiation therapy and other cancer therapies have led to a progressive increase in five-year survival rates over the last few decades. Although acute effects have been largely minimized by both technical advances and medical interventions, late effects remain a concern. Indeed, the need to identify those individuals who will develop radiation-induced late effects, and to develop interventions to prevent or ameliorate these late effects is a critical area of radiobiology research. In the last two decades, preclinical studies have clearly established that late radiation injury can be prevented/ameliorated by pharmacological therapies aimed at modulating the cascade of events leading to the clinical expression of radiation-induced late effects. These insights have been accompanied by significant technological advances in imaging that are moving radiation oncology and normal tissue radiobiology from disciplines driven by anatomy and macrostructure to ones in which important quantitative functional, microstructural, and metabolic data can be noninvasively and serially determined. In the current article, we review use of positron emission tomography (PET), single photon emission tomography (SPECT), magnetic resonance (MR) imaging and MR spectroscopy to generate pathophysiological and functional data in the central nervous system, lung, and heart that offer the promise of, (1) identifying individuals who are at risk of developing radiation-induced late effects, and (2) monitoring the efficacy of interventions to prevent/ameliorate them.     

多功能磁共振造影剂研究进展

磁共振成像技术因对人体无创、任意方向断层扫描三维图像且分辨率较高、提供形态与功能两方面诊断评价等突出优点,成为了临床上用于疾病诊断的重要手段之一。临床上使用磁共振造影剂可以提高成像的分辨率和灵敏度,提高图像质量,增强对比度和可读性。但是,各种成像技术由于实现原理不同,具有各自的优势和缺陷,靠传统单一的诊断模式无法提供疾病的全面信息,因而在对各种复杂疾病进行诊断时会受到一定的限制。因此,将磁共振成像与其他成像技术如CT成像、超声成像等联合起来使用,则可以达到优势互补的效果,能为疾病的临床诊断提供更快捷精确的信息,同时可将磁共振成像与各种治疗方式结合在一起,即开发基于磁共振成像的诊断治疗一体化试剂,以实现对疾病的即时治疗和实时监控。本文主要介绍了磁共振成像造影剂的原理和种类,并且综述了目前国内外在基于磁共振成像的多功能造影剂/诊疗制剂这一领域的研究进展,最后就未来可能的研究方向进行了展望。     

Molecular mechanisms for Alzheimer's disease: implications for neuroimaging and therapeutics

Alzheimer's disease is a progressive neurodegenerative disorder characterised by the gradual onset of dementia. The pathological hallmarks of the disease are beta-amyloid (Abeta) plaques, neurofibrillary tangles, synaptic loss and reactive gliosis. The current therapeutic effort is directed towards developing drugs that reduce Abeta burden or toxicity by inhibiting secretase cleavage, Abeta aggregation, Abeta toxicity, Abeta metal interactions or by promoting Abeta clearance. A number of clinical trials are currently in progress based on these different therapeutic strategies and they should indicate which, if any, of these approaches will be efficacious. Current diagnosis of Alzheimer's disease is made by clinical, neuropsychologic and neuroimaging assessments. Routine structural neuroimaging evaluation with computed tomography and magnetic resonance imaging is based on non-specific features such as atrophy, a late feature in the progression of the disease, hence the crucial importance of developing new approaches for early and specific recognition at the prodromal stages of Alzheimer's disease. Functional neuroimaging techniques such as functional magnetic resonance imaging, magnetic resonance spectroscopy, positron emission tomography and single photon emission computed tomography, possibly in conjunction with other related Abeta biomarkers in plasma and CSF, could prove to be valuable in the differential diagnosis of Alzheimer's disease, as well as in assessing prognosis. With the advent of new therapeutic strategies there is increasing interest in the development of magnetic resonance imaging contrast agents and positron emission tomography and single photon emission computed tomography radioligands that will permit the assessment of Abeta burden in vivo.     

缺血性心肌病的多模态心血管影像学方法进展

近年来,超声(ultrasound, US)、CT冠状动脉造影(CT coronary angiography, CCTA)、血管内超声(intravenous ultrasound,IVUS)、光学相干断层成像(optical coherence tomography, OCT)、多层螺旋CT成像(multi-slice computed tomography, MSCT)、单光子发射计算机断层成像(single-photon emission computed tomography, SPECT)、正电子发射计算机断层成像(positron emission computed tomography, PET)及心脏磁共振(cardiac magnetic resonance, CMR)等多种心血管成像技术能够提供与冠脉病变及心肌形态和功能相关的解剖学、血流动力学、细胞生物学及病理生理学等方面的重要信息,在缺血性心肌病的临床诊疗及预后评估中发挥着日益重要的作用。然而,如何恰当选择的多模态心血管影像技术是临床医师面临的一大难题。因此,本文在归纳总结主要心血管成像技术临床应用进展的基础上,对多模态心血管影像学在缺血性心肌病相关的冠脉解剖与斑块成像、心肌功能、心肌灌注及心肌活性显像中的临床应用价值进行综述。旨在帮助临床医师客观认识各种成像技术的优势与不足,从而制定最优化的选择方案。     

Magnetic resonance tomography of temporomandibular joint

The paper shows the place of magnetic resonance imaging among other radiation diagnostic techniques in detecting abnormal changes in the temporomandibular joint. The authors' own data were based on the results of 315 examinations. The paper describes the technical features of examination of the joint and shows it possible to visualize different anatomic structures on T1-, T2- and Pd-weighted images. It also indicates the diagnostic potentialities of magnetic resonance imaging in identifying abnormal changes in the joint in its diseases and lesions. This has allowed the authors to show what is indicated for magnetic resonance imaging of the temporomandibular joint and that it is necessary to develop an algorithm of radiation diagnosis for patients with different clinical forms of joint diseases.     

Comparison of magnetic resonance imaging and computed tomography in suspected lesions in the posterior cranial fossa.

OBJECTIVE--To compare computed tomography and magnetic resonance imaging in investigating patients suspected of having a lesion in the posterior cranial fossa. DESIGN--Randomised allocation of newly referred patients to undergo either computed tomography or magnetic resonance imaging; the alternative investigation was performed subsequently only in response to a request from the referring doctor. SETTING--A regional neuroscience centre serving 2.7 million. PATIENTS--1020 Patients recruited between April 1986 and December 1987, all suspected by neurologists, neurosurgeons, or other specialists of having a lesion in the posterior fossa and referred for neuroradiology. The groups allocated to undergo computed tomography or magnetic resonance imaging were well matched in distributions of age, sex, specialty of referring doctor, investigation as an inpatient or an outpatient, suspected site of lesion, and presumed disease process; the referring doctor''s confidence in the initial clinical diagnosis was also similar. INTERVENTIONS--After the patients had been imaged by either computed tomography or magnetic resonance (using a resistive magnet of 0.15 T) doctors were given the radiologist''s report and a form asking if they considered that imaging with the alternative technique was necessary and, if so, why; it also asked for their current diagnoses and their confidence in them. MAIN OUTCOME MEASURES--Number of requests for the alternative method of investigation. Assessment of characteristics of patients for whom further imaging was requested and lesions that were suspected initially and how the results of the second imaging affected clinicians'' and radiologists'' opinions. RESULTS--Ninety three of the 501 patients who initially underwent computed tomography were referred subsequently for magnetic resonance imaging whereas only 28 of the 493 patients who initially underwent magnetic resonance imaging were referred subsequently for computed tomography. Over the study the number of patients referred for magnetic resonance imaging after computed tomography increased but requests for computed tomography after magnetic resonance imaging decreased. The reason that clinicians gave most commonly for requesting further imaging by magnetic resonance was that the results of the initial computed tomography failed to exclude their suspected diagnosis (64 patients). This was less common in patients investigated initially by magnetic resonance imaging (eight patients). Management of 28 patients (6%) imaged initially with computed tomography and 12 patients (2%) imaged initially with magnetic resonance was changed on the basis of the results of the alternative imaging. CONCLUSIONS--Magnetic resonance imaging provided doctors with the information required to manage patients suspected of having a lesion in the posterior fossa more commonly than computed tomography, but computed tomography alone was satisfactory in 80% of cases...     

Airway imaging in disease: Gimmick or useful tool?

Airway remodeling is an important pathophysiological mechanism in a variety of chronic airway diseases. Historically investigators have had to use invasive techniques such as histological examination of excised tissue to study airway wall structure. The last several years has seen a proliferation of relatively noninvasive techniques to assess the airway branching pattern, wall thickness, and more recently, airway wall tissue components. These methods include computed tomography, magnetic resonance imaging, and optical coherence tomography. These new imaging technologies have become popular because to understand the physiology of lung disease it is important we understand the underlying anatomy. However, these new approaches are not standardized or available in all centers so a review of their validity and clinical utility is appropriate. This review documents how investigators are working hard to correct for inconsistencies between techniques so that they become more accepted and utilized in clinical settings. These new imaging techniques are very likely to play a frontline role in the study of lung disease and will, hopefully, allow clinicians and investigators to better understand disease pathogenesis and to design and assess new therapeutic interventions.     

A realistic utilization of nanotechnology in molecular imaging and targeted radiotherapy of solid tumors

Precise dose delivery to malignant tissue in radiotherapy is of paramount importance for treatment efficacy while minimizing morbidity of surrounding normal tissues. Current conventional imaging techniques, such as magnetic resonance imaging (MRI) and computerized tomography (CT), are used to define the three-dimensional shape and volume of the tumor for radiation therapy. In many cases, these radiographic imaging (RI) techniques are ambiguous or provide limited information with regard to tumor margins and histopathology. Molecular imaging (MI) modalities, such as positron emission tomography (PET) and single photon-emission computed-tomography (SPECT) that can characterize tumor tissue, are rapidly becoming routine in radiation therapy. However, their inherent low spatial resolution impedes tumor delineation for the purposes of radiation treatment planning. This review will focus on applications of nanotechnology to synergize imaging modalities in order to accurately highlight, as well as subsequently target, tumor cells. Furthermore, using such nano-agents for imaging, simultaneous coupling of novel therapeutics including radiosensitizers can be delivered specifically to the tumor to maximize tumor cell killing while sparing normal tissue.     

The developing role of cytokines for imaging inflammation and infection

The diagnosis of inflammatory processes is an important goal in medicine. In some cases the diagnosis is easy, based on the clinical history and the physical examination of the patient. Other cases are more difficult to diagnose because they are asymptomatic or with non-specific symptoms. Thus, several imaging techniques have been developed for the diagnosis of inflammatory processes, from the simple X-ray to the more sophisticated computerised tomography, magnetic resonance imaging and nuclear medicine scan. They provide different information and their role in different diseases will be discussed in this review with particular emphasis on the expanding field of the use of radiolabelled cytokines for imaging infection/inflammation. So far, IL-1, IL-1ra, IL-2, IL-6, IL-8, IL-10, IL-12 p40, G-CSF, IFN-gamma and EGF have been radiolabelled for in vivo targetting of different leukocyte subsets with promising results for their clinical use.     

Clinical examination or whole-body magnetic resonance imaging: the Holy Grail of spondyloarthritis imaging

Whole-body magnetic resonance imaging allows acquisition of diagnostic images in the shortest scan time, leading to better patient compliance and artifact-free images. Methods of clinical examination of the anterior chest wall joints vary between physician groups and consideration of the rules of rib motion is suggested. The type of joint and its synovial lining may also aid imaging/clinical correlation. This well-written study by experts in the field with a standardized design and methodology allows good scientific analysis and suggests the advantages of whole-body magnetic resonance imaging in anterior chest wall imaging. Selection of clinical examination criteria and specific joints may have had an influence on the study results and the lack of association reported.     

Advances in magnetic resonance imaging of lung physiology.

This review presents an overview of some recent magnetic resonance imaging (MRI) techniques for measuring aspects of local physiology in the lung. MRI is noninvasive, relatively high resolution, and does not expose subjects to ionizing radiation. Conventional MRI of the lung suffers from low signal intensity caused by the low proton density and the large degree of microscopic field inhomogeneity that degrades the magnetic resonance signal and interferes with image acquisition. However, in recent years, there have been rapid advances in both hardware and software design, allowing these difficulties to be minimized. This review focuses on some newer techniques that measure regional perfusion, ventilation, gas diffusion, ventilation-to-perfusion ratio, partial pressure of oxygen, and lung water. These techniques include contrast-enhanced and arterial spin-labeling techniques for measuring perfusion, hyperpolarized gas techniques for measuring regional ventilation, and apparent diffusion coefficient and multiecho and gradient echo techniques for measuring proton density and lung water. Some of the major advantages and disadvantages of each technique are discussed. In addition, some of the physiological issues associated with making measurements are discussed, along with strategies for understanding large and complex data sets.     

Oesophageal carcinoma demonstrated by whole-body nuclear magnetic resonance imaging.

The quality of the images produced by nuclear magnetic resonance (NMR) imaging has steadily improved over the past five years. Images of the head, thorax, and abdomen have clearly shown the normal anatomy. A clinical trial of NMR imaging has therefore been started in Aberdeen to assess its diagnostic accuracy and compare it with conventional radiography and other imaging technique. The first patient examined by whole-body NMR imaging had carcinoma of the oesophagus diagnosed on barium meal examination. A technetium-99m-sulphur colloid liver scan also showed hepatic metastases. NMR imaging showed a large tumour in the lower third of the oesophagus, and areas of increased proton spin-lattice relaxation time (T1) on a section through the liver corresponded with the metastases shown on the radionuclide scan. Increased areas of T1 were present in some vertebrae, and a technetium-99m bone scan confirmed the presence of bone metastases. The NMR images in this patient compared well with the images from other techniques. The continuing clinical trial may show that NMR is an accurate diagnostic aid which will complement existing techniques for diagnosing intrathoracic and intra-abdominal conditions.     

The evolution of medical imaging: from Geiger counters to MRI--a personal saga

This article traces the evolution of medical imaging, from the crude images of the thyroid gland obtained using Geiger and scintillation counters, to the automatic scanners built to image brain tumors and organs, to gamma cameras, to digital imaging. A computed tomography scanner built in Aberdeen in the late 1960s led to the present-day gamma-camera tomographs, the main workhorse of nuclear medicine. The gradual evolution of the steps needed for clinical magnetic resonance imaging (MRI) are described, along with the rapid development of this novel form of body imaging. A brief account is also given of the present-day use of MRI in clinical medicine worldwide, with some modern cutting-edge applications, and its possible future.     

Magnetic resonance imaging and spectroscopy of prostate cancer

Magnetic resonance imaging may improve the staging of prostate cancer compared with clinical evaluation alone, computerized tomography, or transrectal ultrasound, and it allows simultaneous and detailed evaluation of prostatic, periprostatic, and pelvic anatomy. Endorectal magnetic resonance imaging and magnetic resonance spectroscopic imaging (endoMRI/MRSI) allow better visualization of the zonal anatomy of the prostate and better delineation of tumor location, volume, and extent (stage). Metabolic criteria used to identify and localize prostate cancer with endoMRI/MRSI have been standardized, thus improving the accuracy of the examination and limiting interobserver variations in interpretation. Evidence is now emerging that endoMRI/MRSI may also be helpful in assessing response to prostate cancer treatment, most commonly with radiation and/or androgen-deprivation therapy.     

Computed tomography and magnetic resonance imaging in the diagnosis of accessory nasal sinuses, upper jaw and nasal cavity tumors

Radiation studies, including computed tomography (CT) and magnetic resonance imaging (MRI), revealed that these techniques can accurately determine the site of a tumor, the borders of its spread to the adjacent anatomic structures. They also revealed the features of CT in detecting osseous structural destruction and the advantage of MRI in visualizing the soft tissue component of a neoplasm and in distinguishing the degree of contrast of tumor tissue and concurrent secondary inflammation. The accuracy of CT and MRI for small tumors is 45-80 and 29% higher than that of X-ray study and traditional tomography, respectively. The potentialities of all radiation diagnostic techniques for over 3.0-cm tumors are equal.     

Introduction to the special issue on molecular imaging in radiation biology

Molecular imaging is an evolving science that is concerned with the development of novel imaging probes and biomarkers that can be used to non-invasively image molecular and cellular processes. This special issue approaches molecular imaging in the context of radiation research, focusing on biomarkers and imaging methods that provide measurable signals that can assist in the quantification of radiation-induced effects of living systems at the physical, chemical and biological levels. The potential to image molecular changes in response to a radiation insult opens new and exciting opportunities for a more profound understanding of radiation biology, with the possibility of translation of these techniques to radiotherapy practice. This special issue brings together 14 reviews dedicated to the use of molecular imaging in the field of radiation research. The initial three reviews are introductory overviews of the key molecular imaging modalities: magnetic resonance, nuclear and optical. This is followed by 11 reviews each focusing on a specialist area within the field of radiation research. These include: hypoxia and perfusion, tissue metabolism, normal tissue injury, cell death and viability, receptor targeting and nanotechnology, reporter genes, reactive oxygen species (ROS), and biological dosimetry. Over the preceding decade, molecular imaging brought significant new advances to our understanding of every area of radiation biology. This special issue shows us these advances and points to the vibrant future of our field armed with these new capabilities.     

Measurement of subclinical atherosclerosis: beyond risk factor assessment

PURPOSE OF REVIEW: Assessment of subclinical atherosclerosis using the current available noninvasive imaging modalities holds promise for individual cardiovascular risk management and monitoring efficacy of therapeutic interventions (i.e. surrogate end-points). The present review addresses benefits and limitations of flow-mediated dilatation, intima-media thickness, electron-beam computed tomography and magnetic resonance coronary angiography. RECENT FINDINGS: Both carotid intima-media thickness and peripheral flow-mediated dilatation correlate inversely with cardiovascular risk factors and coronary artery disease. They have been shown to carry predictive value for future cardiovascular events, but clinical application of both intima-media thickness and flow-mediated dilatation demands further methodological maturation of these techniques. Intima thickening has been successfully targeted in numerous intervention trials, but determination of an explicit threshold value beyond which cardiovascular risk significantly increases will facilitate its utility as a routine clinical tool. Electron-beam computed tomography can accurately detect and quantify coronary artery calcification (an established marker of the total coronary plaque burden). However, lack of evidence of its additional predictive power for future coronary events warrants for further research. Finally, magnetic resonance coronary angiography appears to be a promising technique, integrating both functional and anatomical aspects of coronary artery disease. Properly designed studies are needed to determine its value in clinical practice. SUMMARY: Various noninvasive imaging techniques have recently emerged that may find applications in clinical research. However, before widespread clinical utilization, further technical refinement of all of the cited imaging modalities is mandatory. It will be a challenge over the coming few years to clarify whether improvements in surrogate end-points can directly be translated into improved outcomes.