Nuclear medicine and multimodality imaging of pediatric neuroblastoma

Neuroblastoma is an embryonic tumor of the peripheral sympathetic nervous system and is metastatic or high risk for relapse in nearly 50% of cases. Therefore, exact staging with radiological and nuclear medicine imaging methods is crucial for defining the adequate therapeutic choice. Tumor cells express the norepinephrine transporter, which makes metaiodobenzylguanidine (MIBG), an analogue of norepinephrine, an ideal tumor specific agent for imaging. MIBG imaging has several disadvantages, such as limited spatial resolution, limited sensitivity in small lesions and the need for two or even more acquisition sessions. Most of these limitations can be overcome with positron emission tomography (PET) using [F-18]2-fluoro-2-deoxyglucose [FDG]. Furthermore, new tracers, such as fluorodopa or somatostatin receptor agonists, have been tested for imaging neuroblastoma recently. However, MIBG scintigraphy and PET alone are not sufficient for operative or biopsy planning. In this regard, a combination with morphological imaging is indispensable. This article will discuss strategies for primary and follow-up diagnosis in neuroblastoma using different nuclear medicine and radiological imaging methods as well as multimodality imaging.

ISMRM workshop on fat-water separation: insights, applications and progress in MRI

Approximately 130 attendees convened on February 19-22, 2012 for the first ISMRM-sponsored workshop on water-fat imaging. The motivation to host this meeting was driven by the increasing number of research publications on this topic over the past decade. The scientific program included an historical perspective and a discussion of the clinical relevance of water-fat MRI, a technical description of multiecho pulse sequences, a review of data acquisition and reconstruction algorithms, a summary of the confounding factors that influence quantitative fat measurements and the importance of MRI-based biomarkers, a description of applications in the heart, liver, pancreas, abdomen, spine, pelvis, and muscles, an overview of the implications of fat in diabetes and obesity, a discussion on MR spectroscopy, a review of childhood obesity, the efficacy of lifestyle interventional studies, and the role of brown adipose tissue, and an outlook on federal funding opportunities from the National Institutes of Health.

Response assessment in oncology: limitations of anatomic response criteria in the era of tailored treatments

Evaluation of tumor response is a vital element in clinical oncology research, particularly in the development of new drugs. Tumor response also plays a significant role in treatment decisions made by clinicians in practice. The underlying concept of tumor response, however, was developed as a result of limited understanding of tumor biology coupled with restricted availability of both effective treatments and imaging modalities. In recent years, impressive advances have been made in the treatment of cancer. Groundbreaking advances in our understanding of the molecular biology of tumor growth and proliferation have been made. New biologic agents have been approved for the treatment of several malignancies and, in many cases, biomarkers have been identified that can help predict those patients who will benefit. Pre-operative chemotherapy is now established for a number of tumor types. Modern imaging technologies allowing functional characterization of tumors have been introduced into clinical practice. In this new therapeutic landscape, the existing concept of tumor response risks becoming an anachronism, and revision of the criteria used to define tumor response is warranted. In this paper, we critically review the limitations of the classic criteria for tumor response assessment, and briefly discuss the potential role of alternative methodologies in providing a new, functional definition of tumor response.

CT and MRI in monitoring response: state-of-the-art and future developments

The present review is aimed at updating the reader with the current role of computed tomography (CT) and magnetic resonance imaging (MRI) in the evaluation of tumor response, contextualizing the imaging methods advantages and limitations. CT has been the most frequent and widely adopted diagnostic tool. The main advantages of such method include wide availability, high reproducibility, capability to contemporarily evaluate soft tissues, bone and lung parenchyma, besides being easy to perform. Its main limitation is related to the use of ionizing radiation. MRI has emerged as a feasible alternative to CT, particularly in patients with contraindications to the use of iodinated contrast agents, with advantages related to its high soft tissues contrast. The disadvantages are based on its operational complexity and the many technical variables involved which may influence and compromise the reproducibility and broad implementation of the method. New criteria for evaluation of tumor response have recently been proposed, contemplating lately developed drugs and therapeutic strategies that demand the utilization of functional parameters. In this context, the technological developments incorporated in the CT and MRI imaging techniques, such as perfusion analysis, diffusion studies (DW-RM) and MR spectroscopy (MRS), among others, have provided relevant information regarding the tumor response to targeted therapies, anticipating dimensional alterations and guiding physicians in the course of the treatment. Despite such developments, further efforts are needed to establish reproducible protocols, functional response criteria and time intervals for response evaluation in order to allow a definitive incorporation of these new technologies in the assessment of tumor response.

(18)F-FDG-PET/CT in evaluating response to therapy in solid tumors: where we are and where we can go

In the past, enormous public and private investments have been made to reduce cancer incidence and mortality. Despite some improvements over the last 10 years, the overall outcome of the "war on cancer" has been disappointing. Among the reasons for this limited success is our inability to determine, whether the therapeutic target is present, and whether the target is reached by the drug. A further important issue is our limited ability to correctly assess response to treatment early after start of therapy which would allow for more individualized treatment approaches. PET and PET/CT with the glucose analogue 2'-[(18)F]-fluoro-2'-deoxy-D-glucose (FDG) are increasingly used to assess response to therapy in patients, and a converging large body of evidence is emerging that suggests that changes in glucose utilization during therapy can be used to predict clinical outcome. In this article we provide an overview of the utility of (18)F-FDG PET/CT imaging for early monitoring of cancer therapy and address current and future challenges for its more widespread adoption. First, we discuss general requirements that any imaging modality must meet to provide valid and valuable treatment response assessment. We will then review the strengths and limitations of CT (RECIST) and PET based response criteria. Finally, we will examine the role of FDG-PET/(CT) imaging for response assessments in solid tumors.

Therapy response assessment in radiotherapy of lung cancer

Radiotherapy represents an important therapeutic modality in the treatment of lung cancer. Treatment response assessment after high-dose radiotherapy with or without concurrent chemotherapy using conventional imaging methods is limited since normal tissue appearance might resemble tumour recurrence very close. Positron emission tomography (PET) based imaging has been introduced in this situation with great enthusiasm and provides useful additional information on the biologic characteristics of the irradiated region, be it tumour or healthy lung tissue, provided some marginal conditions are taken into account. Furthermore, biologic imaging seems highly appealing for treatment guidance especially during treatment protocols including multimodality approaches with neoadjuvant intent. Treatment response might not only serve as a surrogate marker for pathological remission but for overall prognosis as well. Within this context, the optimal time point and the best parameter to evaluate remain issues of continuing debate. This review is aimed to give an overview of the current state of the scientific knowledge.

Use of PET/CT to evaluate response to therapy in lymphoma

(18)F-FDG-PET is a well established standard procedure for most lymphoma subtypes. In particular the advantage of metabolic imaging stands in its strong predictivity in response. Indeed PET scan has been incorporated into revised response criteria for aggressive lymphomas and recommended to be performed at baseline and after therapy. At the same time, several ongoing clinical trials are investigating the value of treatment adaptation based on interim PET (PETi) results for Hodgkin Lymphoma (HL) and aggressive Non-Hodgkin Lymphoma (NHL). On the other hand, scientific literature provides limited detailed information regarding the numerous non aggressive NHL subtypes. Usually indolent NHL are typically less FDG avid, furthermore their long natural history and high incidence of recurrence decreases the clinical impact of a potential risk-adapted or response-adapted approach. We reviewed, from a nuclear medicine point of view and a clinical point of interest, evidence for the use of FDG-PET in monitoring early and end treatment response.

Functional and molecular imaging with MRI: potential applications in paediatric radiology

MRI is a very versatile tool for noninvasive imaging and it is particularly attractive as an imaging technique in paediatric patients given the absence of ionizing radiation. Recent advances in the field of MRI have enabled tissue function to be probed noninvasively, and increasingly MRI is being used to assess cellular and molecular processes. For example, dynamic contrast-enhanced MRI has been used to assess tissue vascularity, diffusion-weighted imaging can quantify molecular movements of water in tissue compartments and MR spectroscopy provides a quantitative assessment of metabolite levels. A number of targeted contrast agents have been developed that bind specifically to receptors on the vascular endothelium or cell surface and there are several MR methods for labelling cells and tracking cellular movements. Hyperpolarization techniques have the capability of massively increasing the sensitivity of MRI and these have been used to image tissue pH, successful response to drug treatment as well as imaging the microstructure of the lungs. Although there are many challenges to be overcome before these techniques can be translated into routine paediatric imaging, they could potentially be used to aid diagnosis, predict disease outcome, target biopsies and determine treatment response noninvasively.

Molecular imaging in oncology: the acceptance of PET/CT and the emergence of MR/PET imaging

In the last decade, PET-only systems have been phased out and replaced with PET-CT systems. This merger of a functional and anatomical imaging modality turned out to be extremely useful in clinical practice. Currently, PET-CT is a major diagnostic tool in oncology. At the dawn of the merger of MRI and PET, another breakthrough in clinical imaging is expected. The combination of these imaging modalities is challenging, but has particular features such as imaging biological processes at the same time in specific body locations.

[New developments in computer-assisted surgery (CAS). From intraoperative imaging to ultrasound-based navigation]

Ever faster processor capacity is having an impact on computer-assisted or computer-aided surgery (CAS). The fusion of different imaging modalities enables functional data such as PET-CT, for example, to be available in image-guided surgery. Referencing of image data is the key to precise navigation. Intraoperative data acquisition is a new approach to improving accuracy. Thus, intraoperative CT conducted under navigational support enables automatic referencing of up-to-date image data. Alternatively, intraoperative magnetic resonance imaging or intraoperative sonography can be performed. Ultrasound systems have already been successfully integrated in existing navigational systems to compensate for intraoperative tissue shifting. Ultrasound systems may play a role in the future as a single modality in image-guided surgery in soft tissue of the neck and skull bone.

Temporal subtraction chest radiography

Radiologist are commonly required to compare a sequence of two or more chest radiographs of a given patient obtained over a period of time, which may range from a few hours to many years. In such cases, the task is one of detecting interval change. In the case of patients who have had a previous chest radiograph, an opportunity exists to enhance selectively areas of interval change, including regions with new or altered pathology, by using the previous radiographs as a subtraction mask. With temporal subtraction, the previous image is superimposed and registered with the current image, using automated two-dimensional warping to compensate for any differences in positioning. A "difference image" is then created, by subtracting the previous from the current radiograph. In this temporal subtraction image, areas that are unchanged appear as uniform gray, while regions of new opacity, such as due to pneumonia or cancer, appear as prominent dark foci on a lighter background. By cancelling out the complex anatomical background, temporal subtraction can provide dramatically enhanced visibility of new areas of disease.

Advances in multimodality imaging through a hybrid PET/MRI system

The development of integrated imaging systems for magnetic resonance imaging (MRI) and positron emission tomography (PET) is currently being explored in a number of laboratories and industrial settings. PET/MRI scanners for both preclinical and human research applications are being developed. PET/MRI overcomes many limitations of PET/computed tomography (CT), such as limited tissue contrast and high radiation doses delivered to the patient or the animal being studied. In addition, recent PET/MRI designs allow for simultaneous rather than sequential acquisition of PET and MRI data, which could not have been achieved through a combination of PET and CT scanners. In a combined PET/CT scanner, while both scanners share a common patient bed, they are hard-wired back-to-back and therefore do not allow simultaneous data acquisition. While PET/MRI offers the possibility of novel imaging strategies, it also creates considerable challenges for acquiring artifact-free images from both modalities. In this review, we discuss motivations, challenges, and potential research applications of developing PET/MRI technology. A brief overview of both MRI and PET is presented and preclinical and clinical applications of PET/MRI are identified. Finally, issues and concerns about image quality, clinical practice, and economic feasibility are discussed.

Revolutionary impact of PET and PET-CT on the day-to-day practice of medicine and its great potential for improving future health care

In this communication, we present an overview of the impact and advantages of PET and PET-CT fusion imaging in the practice of medicine. We also discuss the evolution of this promising molecular imaging technique since its inception and the future prospects of the combined structure-function approach. Superior contrast resolution, accurate quantification and above all optimal image quality aid in improved diagnosis of many serious disorders including cancer. We speculate that this powerful imaging approach will almost completely replace most other conventional methods in the future. Currently, 18[F]-fluorode- -oxyglucose (FDG) is the main radiopharmaceutical employed for PET studies around the globe. With the availability of high quality PET images on a routine basis in most centres around the world and the likelihood that several other useful PET tracers will be approved in the near future for routine clinical applications, this technique will likely become essential in almost any medical disorder.

[Combination of radiological and nuclear medical imaging in animals: an overview about today's possibilities]

Molecular imaging of small animals has made considerable progress in the last years. Various research fields are interested in imaging small animals due to the lower numbers of animals per experiment. This has advantages with respect to financial, ethical and research aspects. Non-invasive imaging allows examination of one animal several times during the same experiment. This makes it possible to follow a pathological process in the same animal over time. However, the radiological methods used such as magnetic resonance imaging or computed tomography as well as the nuclear medicine methods such as single photon emission computed tomography or positron emission tomography suffer from disadvantages. Molecular aspects are limited in the radiological methods while anatomical localization is difficult in nuclear medicine. The fusion of these methods leads to additional information. This review shows today's possibilities with their advantages as well as disadvantages.

Single-photon emission computed tomography/computed tomography: basic instrumentation and innovations

Correlation of the anatomical and functional information presented by single-photon emission computed tomography (SPECT) and computed tomography (CT) can aid in the decision-making process by enabling better localization and definition of organs and lesions and improving the precision of surgical biopsies. Technical developments over the past 20 years have led to the development of better software techniques for image fusion and, more recently, to the development of modern SPECT/CT systems. While image fusion techniques have been in clinical use for many years, the first commercial SPECT/CT system was only developed in 1999. Following the commercial success of PET/CT systems that employed multidetector CT (MDCT) scanners, there has been renewed interest in the development of comparable SPECT/CT systems. This has resulted in the development of a range of SPECT/CT devices varying from a simple CT add-on to a conventional SPECT system that can provide low-dose CT images to a full MDCT scanner integrated with a SPECT system. The advantages of combining SPECT with CT are numerous and are primarily due to the anatomic referencing and the attenuation correction capabilities of CT. Depending on system design, there are varying technical issues surrounding the different SPECT/CT devices, ranging from cost, radiation dose, planning, and siting requirements to system-specific issues such as table sag and CT artifacts due to patient motion. Motion artifacts should be less prevalent with the faster acquisition times of modern scanners, but are still problematic in the thorax and have not yet been fully resolved as they pertain to the use of CT data for cardiac attenuation correction. As this technology matures, we can expect to see a range of SPECT/CT devices available on the market that range from low-dose 1-4 slice inexpensive CT upgrades of conventional SPECT systems, to SPECT systems incorporating 64 or 128 slices CT scanners. The cost of the high-end CT scanners will exceed the cost of the SPECT scanner and hence the justification for such devices will be heavily dependent on clear demonstration of their value in clinical practice.

Contemporary adrenal scintigraphy

INTRODUCTION

High-resolution computed tomography (CT) and magnetic resonance (MR) imaging have replaced scintigraphy as primary imaging modalities for the evaluation of adrenal diseases.

DISCUSSION

Thin-slice CT, CT contrast washout studies and MR pulse sequences specifically designed to identify adrenal lipid content have radically changed the approach to anatomic imaging and provide unique insight into the physical characteristics of the adrenals. With a confirmed biochemical diagnosis, further evaluation is often unnecessary, especially in diagnostic localization of diseases of the adrenal cortex. However, despite the exquisite detail afforded by anatomy-based imaging, there are not infrequently clinical situations in which the functional insight provided by scintigraphy is crucial to identify adrenal dysfunction and to assist in localization of adrenocortical and adrenomedullary disease. The introduction of hybrid PET/CT and SPECT/CT, modalities that directly integrate anatomic and functional information, redefine the radiotracer principle in the larger context of high-resolution anatomic imaging. Instead of becoming obsolete, scintigraphy is an element of a device that combines it with CT or MR to allow a direct correlation between function and anatomy, whereby the combination creates a more powerful diagnostic tool than the separate component modalities.

PET/CT and radiotherapy

This article reviews the state of the art of PET/CT applications in radiotherapy, specifically its use in disease staging, patient selection, treatment planning and treatment evaluation. Diseases for which radiotherapy with radical intent is indicated will be considered, as well as those in which PET/CT may actually change the course of disease. The methodological and technological aspects of PET/CT in radiotherapy are discussed, focusing on the problem of target volume definition with CT and PET functional imaging and the problem of tumor motion with respect to imaging and dose delivery.

Technology improvements for image-guided and minimally invasive spine procedures

This paper reports on technology developments aimed at improving the state of the art for image-guided minimally invasive spine procedures. Back pain is a major health problem with serious economic consequences. Minimally invasive procedures to treat back pain are rapidly growing in popularity due to improvements in technique and the substantially reduced trauma to the patient versus open spinal surgery. Image guidance is an enabling technology for minimally invasive procedures, but technical problems remain that may limit the wider applicability of these techniques. The paper begins with a discussion of low back pain and the potential shortcomings of open back surgery. The advantages of minimally invasive procedures are enumerated, followed by a list of technical problems that must be overcome to enable the more widespread dissemination of these techniques. The technical problems include improved intraoperative imaging, fusion of images from multiple modalities, the visualization of oblique paths, percutaneous spine tracking, mechanical instrument guidance, and software architectures for technology integration. Technical developments to address some of these problems are discussed next. The discussion includes intraoperative computerized tomography (CT) imaging, magnetic resonance imaging (MRI)/CT image registration, three-dimensional (3-D) visualization, optical localization, and robotics for percutaneous instrument placement. Finally, the paper concludes by presenting several representative clinical applications: biopsy, vertebroplasty, nerve and facet blocks, and shunt placement. The program presented here is a first step to developing the physician-assist systems of the future, which will incorporate visualization, tracking, and robotics to enable the precision placement and manipulation of instruments with minimal trauma to the patient.

Implications of PET based molecular imaging on the current and future practice of medicine

The last quarter century has witnessed the introduction of a variety of powerful techniques that have allowed visualization of organ structure and function with exquisite detail. This in turn has brought about a true revolution in the day-to-day practice of medicine. Structural imaging with x-ray computerized tomography and magnetic resonance imaging has added tremendously to many areas of medicine, including preoperative evaluation of patients. Many surgical procedures have been replaced by minimally invasive techniques, which have become a reality only because of the availability of modern imaging modalities. However, despite such accomplishments, structural imaging is quite insensitive for detecting early disease in which there often are no gross structural alterations in organ anatomy. Therefore, these modalities should be complemented by methodologies that can detect abnormalities at the molecular and cellular levels. The introduction of [(18)F]-fluorodeoxyglucose positron emission tomography (FDG-PET) in 1976 as a molecular imaging technique clearly has shown the power of this approach for treating a multitude of serious disorders. The impact of FDG-PET has been particularly impressive in patients with cancer diagnosis, for whom it has become important in staging, monitoring response to treatment, and detecting recurrence. In this review, we emphasize the role of FDG-PET in the assessment of central nervous system maladies, malignant neoplastic processes, infectious and inflammatory diseases, and cardiovascular disorders. New radiotracers are being developed and promise to expand further the list of indications for PET. These include novel tracers for cancer diagnosis and treatment capable of detecting hypoxia and angiogenesis. Prospects for developing new tracers for imaging other organ diseases also appear very promising.

PET/CT: panacea, redundancy, or something in between?

In the past decade, the integration of anatomic imaging and functional imaging has emerged as a new and promising diagnostic tool. Developments in software provided methods to integrate various modalities, such as PET, CT, MRI, and MR spectroscopy. The introduction of combined PET/CT scanners has boosted image fusion in this specific field and raised high expectations. Image fusion can be performed at 3 different levels: visual fusion, software fusion, and hardware fusion, each having strengths, weaknesses, and issues inherent to technique. Visual fusion is the traditional side-by-side reviewing of 2 separate modalities. Software image fusion provides evaluation of 2 modalities in 1 integrated image set. True hardware fusion of PET and CT does not exist at present. Currently, hardware fusion refers to a PET/CT scanner that consists of separate scanners, which positioned in line at a fixed distance, with projection of the PET image over the CT image. The suggested superiority of hardware fusion with these so-called hybrid PET/CT scanners over software fusion has sparked debate. Because scientific data that unequivocally show that state-of-the-art software fusion is less accurate than hardware fusion (as provided in hybrid PET/CT scanners) are unavailable, the primacy of a combined PET/CT scanner over stand-alone PET and CT is more a matter of belief than of science. Further research comparing the overall performance of PET/CT scanners with that of separate scanners with software for image fusion is much needed. The continuous development of better software for image fusion and respiratory and cardiac gating is also needed, not only for PET and CT imaging but also for fusion of PET with MRI and CT with MRI.

PET/CT today and tomorrow

Accurate anatomic localization of functional abnormalities seen with PET is known to be problematic. Even though nonspecific tracers such as 18F-FDG visualize certain normal anatomic structures, the spatial resolution is generally inadequate for localization of pathology. Combining PET with a high-resolution anatomic imaging modality such as CT can resolve the localization issue, as long as the images from the two modalities are accurately coregistered. However, software-based registration techniques have difficulty accounting for differences in patient positioning and involuntary movement of internal organs, often necessitating labor-intensive nonlinear mapping that may not converge to a satisfactory result. Acquiring both CT and PET images in the same scanner obviates the need for software registration and routinely provides accurately aligned images of anatomy and function in a single scan.

DISCUSSION

A CT scanner positioned in tandem with a PET scanner and with a common patient couch and operating console has recently been explored as a solution to anatomic and functional image registration. Axial translation of the couch between the two modalities enables both CT and PET data to be acquired during a single imaging session. In addition, the CT images can be used to generate noiseless attenuation correction factors for the PET emission data. By minimizing patient movement between the CT and PET scans, and after accounting for the axial separation of the two modalities, accurately registered anatomic and functional images can be obtained. Since the introduction of the first PET/CT prototype a little over 5 years ago, several thousand cancer patients have been scanned on combined PET/CT devices. In the past 3 years, a number of commercial designs have become available featuring multidetector spiral CT scanners and high-performance PET devices. Initial experience has demonstrated an increased level of accuracy and confidence in the interpretation of the combined study compared with separate readings, particularly in the ability to distinguish pathology from normal physiologic uptake and to precisely localize abnormal foci.

CONCLUSION

Combined PET/CT scanners represent an important evolution in technology that is helping to bring molecular imaging to the forefront in cancer diagnosis, staging, and therapy monitoring.

[Clinical value of digital subtraction angiography in cardiology--current status and future prospects]

Advances in digital technology have made the digital processing of X-ray images possible. The principles of processing, which can be traced back to the early origin of radiology, are characterized by the aims "image enhancement" and "functional imaging". These principles have been routinely applied in digital subtraction angiography (DSA) for visualization of non-moving vessels. DSA is used with caution in cardiology mainly because methodical problems caused by the motion of the background structures. In order to assess the clinical relevance of DSA to cardiology the following questions will be answered: Which structures can be visualized? How large is the error of the parameters determined by DSA? What is the clinical relevance of these parameters? What are the advantages of DSA with regard to the examination procedure? Using DSA the left ventricle can be visualized at rest and during exercise by intravenous injection of contrast medium. The examination procedure can easily be combined with measurements of pulmonary arterial pressure. The errors of left ventricular parameters amount to: ventricular volumes: +/- 12- +/- 18 ml; ejection fraction: +/- 8%; ventricular diameters: +/- 7- +/- 13%; wall volume: +/- 48 ml; wall thickness: +/- 1.6 mm. The image quality of aorto-coronary bypass grafts visualized by intravenously injected contrast medium is sufficient to decide whether the grafts are patent or occluded. The visualization of the proximal segments of coronary arteries by intravenous injection of contrast medium is reported in rare cases.(ABSTRACT TRUNCATED AT 250 WORDS)