Magnetic resonance. Principles and applications

Alterations of the Subchondral Bone in Osteoarthritis: Complying with Wolff's law

Osteoarthritis (OA) is a whole joint disease that is significantly related to abnormal mechanical loads. Subchondral bone alterations, during the evolution course of OA, are considered as a reflection of adaptation of the bone tissue to mechanical loads. However, some of these alterations are taken as detriment and paradoxical. What are these structure, composition, and mechanical property alterations or mechanical functions for are not quite clear. In this review, we evaluate the possibility that these alterations are used for maintaining joint function. With taking excessive load as a risk factor and under conditions of articular cartilage gradually loss its thickness and its function of evenly distributing load on subchondral bone plate, and applying poroelasticity. Moreover, Boussinesq's pressure bulb theory and bone optimal design principles are utilized for bone mechanics. We found that each subchondral bone alteration has its unique mechanical function in resisting loads and maintaining joint function, and these alterations comply with both bone optimal design principles and Wolff's law within a proper range.

Real time dynamic imaging and current targeted therapies in the war on cancer: a new paradigm

In biology, as every science student is made to learn, ontology recapitulates phylogeny. In medicine, however, oncology recapitulates polemology, the science of warfare: The medical establishment is transitioning from highly toxic poisons that kill rapidly dividing normal and malignant cells with little specificity to tailored therapies that target the tumors with the lethality of the therapeutic warhead. From the advent of the information age with the incorporation of high-tech intelligence, reconnaissance, and surveillance has resulted in "data fusion" where a wide range of information collected in near real-time can be used to redesign most of the treatment strategies currently used in the clinic. The medical community has begun to transition from the 'black box' of tumor therapy based solely on the clinical response to the 'glass box' of dynamic imaging designed to bring transparency to the clinical battlefield during treatment, thereby informing the therapeutic decision to 'retreat or repeat'. The tumor microenvironment is dynamic, constantly changing in response to therapeutic intervention, and therefore the therapeutic assessment must map to this variable and ever-changing landscape with dynamic and non-static imaging capabilities. The path to personalized medicine will require incorporation and integration of dynamic imaging at the bedside into clinical practice for real-time, interactive assessment of response to targeted therapies. The application of advanced real time imaging techniques along with current molecularly targeted anticancer therapies which alter cellular homeostasis and microenvironment can enhance therapeutic interventions in cancer patients and further improve the current status in clinical management of patients with advanced cancers.

Magnetic Resonance Imaging:Overview of the Technology and Medical Applications

The physical phenomenon of nuclear magnetic resonance (NMR) was first characterized almost forty years ago in 1946 by the simultaneous but independent experimental successes of American scientists Felix Bloch and Edward Purcell. Their discoveries prompted development of conventional NMR spectroscopy. a technique used to describe the molecular composition and behavior of chemical compounds. Twenty-five years later, in 1971, Damadian used NMR to demonstrate differences in the behavior of water in malignant and benign tissues, and he suggested that NMR possessed “many of the desirable features of an external probe for the detection of internal cancer” (7). In the same year, Lauterbur produced the first two-dimensional NMR image, a cross-sectional portrait of two tubes of water (25). The potential utility of this technique to medical imaging was obvious, and soon afterwards multiple researchers began development of clinical NMR imaging systems. The first human whole-body NMR scan was accomplished by 1977. Improvements in the scanning process and image quality continue with, as yet, no limits in sight. In this clinical context, NMR techniques have experienced a name change to the current prevailing appellation, magnetic resonance imaging (MRI).

Magnetic resonance imaging of pelvic tumors in children

Pelvic tumors in children may be large, complex and of unknown origin. Preoperative radiological information regarding tumor localization and extent becomes essential in these cases for proper staging and surgical planning. Magnetic resonance imaging (MRI) offers the ability to enhance the surgical preparation of children who present with a pelvic mass. Advantages of MRI over computerized tomography include improved soft tissue characterization, signal enhancement of neuroendocrine tumors and multiplanar imaging. These features better define the origin, size and extent of tumors. In addition, no ionizing radiation is required. Several examples of pelvic tumors are presented. The new anatomical information provided by MRI altered surgical planning previously based on computerized tomography findings alone.

Computed tomography versus magnetic resonance imaging and three-dimensional applications

An attempt has been made to simplify and to provide an understanding of some of the new modalities for evaluation of head and neck pathology. Both CT and MRI are complementary to each other: MRI being superior to CT in evaluating soft tissue, and CT being superior to MRI in assessing fine bony details and in identifying microcalcifications. MRI is the modality of choice for tumor evaluation because it has several advantages over CT in assessing the location, spread, and staging of the disease. HRCT scanning remains the procedure of choice in the evaluation of middle ear and base of the skull, and in the evaluation of benign sinonasal disease. CPA and IAC lesions are best evaluated by MRI. Three-dimensional surface reformations of axial CT scans enable the surgeon to plan the operative approach needed to reduce facial fractures and to repair cranial deformities.

The relevance of socioeconomic and health policy issues to clinical research. The case of MRI and neuroradiology

Magnetic resonance imaging (MRI) is a high-cost, new technology with great potential for improving patient care. The lack of a coherent public policy for MRI, or its predecessor computed tomography (CT), has caused considerable problems. Lack of an enunciated public policy has led to inconsistent reimbursement and reimbursement levels that develop in haphazard ways. Furthermore, diffusion has been unpredictable and has led to geographical excesses and deficiencies. Technology assessments of MRI, although numerous, have used inconsistent criteria to rate MRI's clinical efficacy. The lack of methodologically sound studies of MRI severely hampered early evaluation. This article examines these problems and suggests that the medical profession take a stronger leadership role in developing policies for expensive, promising new diagnostic technologies. The profession should promote, demand, and perform rigorous clinical evaluations of new technologies, and help develop a consensus regarding the criteria for what constitutes a clinically valuable advance in diagnostic technology.

NMR imaging in dentistry: relaxation and diffusion studies

Magnetic resonance imaging has been widely used for medical diagnosis in recent years. The knowledge of the proton spin-lattice relaxation time, T1, represents the basis for NMR imaging. In the present study, we measured T1 in saliva, gingival fluid, gingival blood, and inflamed gingiva by means of a pulsed NMR Fourier-transform spectrometer. From several measurements, we found the following average T1 values: in saliva, T1 = 2550 msec; in gingival fluid, T1 = 2085 msec; in gingival blood, T1 = 1515 msec; and in inflamed gingiva samples, T1 = 840 msec.

In addition, electron paramagnetic resonance imaging was used to demonstrate the in vitro diffusion processes of spin-labeled molecules into tooth enamel by application of the linear magnetic field gradient to a conventional EPR spectrometer. The diffusion coefficient for the nitroxide spin-labeled molecules into tooth enamel was evaluated as D = 10-7 cm2 sec-1.

Magnetic resonance imaging of the head and neck

Magnetic resonance imaging (MR) has already gained wide acceptance in the evaluation of intracranial and spinal canal abnormalities. MR also provides excellent resolution of certain tumors of the head and neck and is particularly useful for the evaluation of neoplasms in the vicinity of the skull base. The absence of a bone signal prevents the streaking artifact so troublesome with computerized axial tomography (CT) and allows better definition of tumor. MR does not use ionizing radiation and appears to be an innocuous imaging mode--thus multiple examinations in young patients are not objectionable with MR. The ability to obtain images in multiple planes by control of the magnetic gradients allows for axial, sagittal, and coronal imaging, without changing the supine position of the patient. Multiple projections are helpful in providing better preoperative assessment of the extent and size of certain neoplasms of the neck.

Computerized tomographic scan assessment of alcoholic brain damage and its potential reversibility

The assessment of alcoholic brain damage by computerized tomographic (CT) scanning is reviewed and discussed. Alcoholics showed greater cerebral atrophy than aged-matched neurological controls. Supratentorial atrophy measurements correlated significantly with some neurobehavioral assessment measures. The cerebral atrophy reversed in some subjects with maintained abstinence. Computerized assessment of cerebral spinal fluid volume (cerebral atrophy) and mean cerebral density showed decreased cerebral spinal fluid volume and increased cerebral density with maintained abstinence over 4 weeks in a group of 20 alcoholics. CT cerebellar measurements demonstrated atrophy in many subjects, but these measurements did not correlate with measures of ataxia, cognitive impairment, supratentorial atrophy measurements, or age. An example of a magnetic resonance imaging scan of an alcoholic is given. Its advantages in avoiding bony artifact for posterior fossa atrophy estimations and its potential for in vivo description and localization of central nervous system metabolic abnormalities in alcoholism are discussed.