Whole-body MR/PET: applications in abdominal imaging

Over the last few decades it has been shown that novel technologies and technological progress rapidly change the working environment of radiologists and nuclear medicine physicians. Thus, new possibilities, e.g., in tumor staging and therapy monitoring, but also new challenges arise. Recently, it could be shown that the integration of magnetic resonance imaging (MRI) and positron emission tomography (PET) is technically possible. The evolvement of new dedicated hybrid MR/PET systems for whole-body imaging in humans offers new potential in multimodal imaging. Especially simultaneous measurement of PET and MRI datasets allows for insights in metabolic and functional processes, particularly in oncologic demands, but also in cardiovascular and cerebral imaging. In this work-in-progress review article, a technical summary including the method-inherent challenges are given. Furthermore, possible clinical applications and research interests are addressed.     

Perfusion MR imaging: basic principles and clinical applications

Dynamic contrast-enhanced perfusion MR imaging provides hemodynamic information that complements traditional structural imaging and is increasingly used in clinical practice to diagnose, manage, and understand brain tumors. Relative cerebral blood volume maps derived from perfusion MR imaging data provide quantifiable estimates of regional blood volume that can be used to grade gliomas, differentiate different brain tumor types, and distinguish tumors from non-neoplastic lesions. There are a few minor limitations of the dynamic contrastenhanced perfusion MR imaging technique-susceptibility artifacts, relative rather than absolute quantification of cerebral blood volume, and the inaccurate estimation of cerebral blood volume in patients in whom the blood-brain barrier has been severely disrupted or destroyed. Despite the minor potential pitfalls of the technique, inclusion of perfusion MR imaging as part of a routine evaluation of brain tumors can lead to improved diagnostic accuracy, understanding of tumor pathophysiology, and detection and quantification of tumor angiogenesis. With further work, perfusion MR imaging could be used to assess existing and novel cancer therapies that target blood vessels.     

心血管磁共振成像临床应用和新进展

近年来由于MRI的进展,现已成为医学成像技术的主要组成部分,心血管MRI已广泛、有效地应用于心脏、大血管、内脏和外周血管成像及诊治工作.本文简要叙述心血管MRI临床应用概况,如对胸主动脉疾患、缺血性心脏病、心肌病、心脏肿瘤、先心病、心包疾患和心脏瓣膜病的诊断评价等.重点讨论一些新进展,如MR心肌灌注成像和心肌存活的评价;MR冠脉造影和斑块成像;深静脉血栓和肺栓塞的MR诊断以及MR血管造影对腹主-髂股-下肢动脉狭窄性病变的诊断及效果分析.     

Black-blood MR angiography. Techniques, and clinical applications.

As there are limitations in WB-MR angiography, so there are limitations in BB-MR angiography. Vessel morphology is visualized by means of the innermost nonattenuated layer of tissue, which, under ideal conditions, coincides with the luminal surface of the vessel wall. Vessel morphology may be depicted inaccurately whenever a portion of the vessel wall is undetectable with the MR imaging technique used. In such cases, vessel segments with exaggerated lumen diameter may result at locations where tissues with either a very short T2 or a low proton density are present. Another phenomenon that could potentially degrade the accuracy of vessel depiction with BB techniques is the effect of slowly flowing blood near the vessel walls. Residual blood signal would result in apparent vessel narrowing. Preliminary clinical experience in the brain, however, suggests that this adverse effect is less prominent with a turbo-SE-based BB technique than with a TOF WB technique. BB-MR angiography data sets may also present image postprocessing difficulties arising from the isointensity between the vessels and other dark structures such as bones and air-filled cavities. A limitation that is more specific to hybrid-SE-based BB-MR pulse sequences, particularly for very high spatial resolution applications, stems from the comparatively high RF specific absorption rates that result from the intensive use of 180 degrees refocusing pulses. GRASE-based BB-MR techniques that generate a fraction of the RF energy constitute a promising alternative for very high spatial resolution applications. In summary, to be effective, a BB technique must produce strong signal attenuation from flowing spins, ideally to the level of the baseline noise. Simultaneously it should produce good depiction of tissues with the comparatively short T2s characteristic of vessel walls and muscle, hence the need to operate with the shortest possible TE. Finally, high spatial resolution combined with fast data acquisition are requisites for imaging small vessels in the presence of motion, such as the carotid arteries. The flow properties of BB-MR angiographic sequences that meet these criteria were reviewed for different anatomic locations.     

Cancer biomarkers: current issues and future directions

Cancer biomarkers and characteristics of an ideal biomarker for cancer are discussed in this review, as well as technologies for their detection. The focus of this article is on the use of biomarkers for anticancer drug development and clinical applications, including determination of prognosis as well as monitoring of response to therapy. Types of biomarkers include methylated DNA sequences, mitochondrial DNA and microRNA. Within clinical research, oncology is expected to have the largest gains from biomarkers over the next five to ten years. Development of personalized medicine for cancer is closely linked to biomarkers, which may serve as the basis for diagnosis, drug discovery and monitoring of diseases. A major challenge in development of cancer biomarkers will be the integration of proteomics with genomics and metabolomics data and their functional interpretation in conjunction with clinical data and epidemiology.     

Children with AIDS: issues and future directions

Throughout the history of nursing, the care of people with communicable disease has comprised a substantial part of nursing practice. With the advent of the acquired immunodeficiency syndrome (AIDS) epidemic in the early 1980s, nurses once again began caring for persons with infectious disease. Lack of knowledge about the disease process itself, as well as fear of exposure to the virus, continue to cause concern within the health care community. This article is intended to provide nurses with current information about AIDS in the pediatric population as well as its implications for nursing practice.     

Volumetric MR imaging of the liver and applications.

Recent improvements in MR technology have enabled the development of volumetric three-dimensional (3D) imaging methods for fat-suppressed T1-weighted images of the entire upper abdomen with pixel sizes of approximately 2 mm in all dimensions and with acquisition times of less than 25 seconds for breath-hold imaging. When performed with a timing scheme, dynamic contrast-enhanced volumetric imaging of the liver can be performed with selective imaging during the arterial phase and portal venous phase of enhancement. The volumetric data sets can be reconstructed in any oblique plane, enabling improved detection, localization, and characterization of small liver lesions. The combination of high-resolution isotropic pixels and accurate timing also permits angiographic reconstructions of the 3D images, producing MR angiography and venography that can be useful in therapeutic planning, such as for catheter-based interventions or surgical resections or transplantation. Additionally, with use of a hepatobiliary contrast agent such as mangafodipir, T1-weighted volumetric MR cholangiography can be performed in patients with nonobstructed systems for depiction of intrahepatic biliary anatomy.     

Neurocognitive sequelae of sickle cell disease: current issues and future directions.

Sickle cell disease is a genetic disorder with an autosomal recessive pattern of inheritance. This disease is most prevalent among those of African American and Mediterranean descent. Cerebral vascular accident (CVA) or stroke is one of the major complications of hemoglobin SS (Hgb SS) disease. CVA has implications for physical as well as neurocognitive function for children. Recent literature suggests that some children with sickle cell disease without overt signs of CVA may still have evidence of neurological deficit, both on magnetic resonance imaging and neurological examination. There is a growing body of knowledge that further aids in delineation of risk factors for CVA, silent infarct, and neurocognitive deficits in children with Hgb SS disease. More research is needed to continue to explore avenues for identification and intervention. The purpose of this article is to delineate areas of ongoing research in this important area.     

Coronary MR angiography clinical applications and potential for imaging coronary artery disease

Over the past decade, CMRA has emerged as a unique clinical imaging tool with applications in selected populations. Patients with suspected coronary artery anomalies and patients with Kawasaki disease and coronary aneurysms are among those for whom CMRA has demonstrated clinical usefulness. For assessment of patients with atherosclerotic CAD, CMRA is useful for detection of patency of bypass grafts. At centers with appropriate expertise and resources, CMRA also appears to be of value for exclusion of severe proximal multivessel CAD in selected patients. Data from multicenter trials will continue to define the clinical role of CMRA, particularly as it relates to assessment of CAD. Future developments and enhancements of CMRA promise better lumen and coronary artery wall imaging. This may become the new target in noninvasive evaluation of CAD.     

Setting up a clinical cardiac MR imaging program: practical issues and economics

Use of MR imaging to assess the heart has grown rapidly in recent years. MR imaging can assess cardiac anatomy, quantify ventricular and valvular function, identify regions of infarcted myocardium, and evaluate flow-limiting coronary artery stenoses better than any other single imaging modality. Despite its superior capabilities, cardiac MR imaging has yet to be adopted widely in clinical practice, in part because of the many obstacles to developing a clinical cardiac MR imaging program. The purpose of this article is to provide information that may be helpful in developing such a program. The information is based on the authors' experience in an inpatient hospital setting and an outpatient private practice. The recommendations reflect personal opinions and donot represent requirements of any organization or society unless otherwise indicated.     

Future directions in MR imaging of the female pelvis

New technology continues to change the field of MR imaging. This article describes select areas of technical development that are likely to have an increasing clinical impact on MR imaging of the female pelvis, including high-field imaging, parallel imaging, contrast agents, diffusion-weighted imaging and spectroscopy, and MR-guided intervention.     

Contrast agents in abdominal imaging: current and future directions

Magnetic resonance imaging is an established imaging method for the evaluation of the abdomen. Accurate assessment of the liver, spleen, pancreas, bile ducts, vascular structures, and retroperitoneal organs (eg, the kidneys, the collecting system, and the adrenals) are possible on MR imaging. The intravenous administration of MR contrast agents can frequently improve the examination and provide more specific diagnoses. The advent of more specific, "hepatobiliary" contrast agents has further improved the differential diagnostic process, particularly for MR imaging of the liver. The availability of orally administered MR contrast agents has further extended the range of abdominal applications, making MR imaging of the small bowel and the colon established imaging procedures.     

Diffusion-weighted magnetic resonance imaging in the upper abdomen: technical issues and clinical applications

Recent technological achievements have enabled the transposition of diffusion-weighted imaging (DWI) with good diagnostic quality into other body regions, especially the abdomen and pelvis. Many emerging and established applications are now being evaluated on the upper abdomen, the liver being the most studied organ. This article discusses imaging strategies for DWI on the upper abdomen, describes the clinical protocol, and reviews the most common clinical applications of DWI on solid abdominal organs.     

Principles of contrast-enhanced MR angiography. Basic and clinical applications

Contrast-enhanced MR angiography has several advantages in the clinical setting. One advantage is the shortening of T1 because the source of signal increase is resistant to signal losses caused by blood saturation, especially for in-plane flow as encountered in TOF MR angiography and PC MR angiography. This T1 reduction is clearly advantageous in obtaining images of tortuous vessels and stenotic regions. Because the contrast agent Gd-DTPA is well-tolerated and has no nephrotoxic effect, its use in patients with impaired renal function is widely accepted. It is also reported in the literature that the depiction of large aneurysms is markedly more simple with CE-MR angiography than with digital subtraction angiography because filling and subsequent washout of contrast material can be followed over a longer period of time. The main intrinsic advantage of CE-MR angiography compared with TOF and PC-MR angiography is its acquisition speed (because of ultra-short TRs) with comparable gradient performance. Also, the slice orientation can be chosen as the clinical situation dictates and needs rather than being uniformly perpendicular to blood flow, as was often necessary previously. The author considers CE-MR angiography a valuable development for vascular MR imaging. It is currently being compared with alternative methods in studies at several centers.     

Cardiac magnetic resonance imaging: current status and future directions

Cardiac MRI (CMR) provides a comprehensive evaluation of cardiac function and anatomy, as well as myocardial tissue characterization and perfusion. New data show the potential for CMR to analyze left ventricular diastolic function, coronary plaque and myocardial oxygen levels. A growing body of animal and clinical data on molecular imaging, hybrid imaging and interventional CMR holds promise for more widespread clinical application. Technological advances in body coils, 3-T systems, imaging sequences and novel applications such as T1 mapping will expand the application and quality of CMR.