Clinical nuclear magnetic resonance imaging of the body

NMR promises great advances in diagnosis and has delivered so much already that it is expected that in the future it will replace many applications of the currently used imaging modalities. Although x-ray computed tomography is continuing to advance in speed of scanning and resolving power, NMR will most likely soon eliminate its use in many studies of the central nervous system and also in many other areas of the body. The promise of combining topical spectroscopy with imaging is also exciting and should provide further information about metabolic processes of various organs. Progress in NMR is so rapid and the future is so bright that one of the great problems will be to develop a new breed of radiologists who are versatile in biochemistry, mathematics, and computers, as well as competent in morphologic anatomy and pathologic physiology. As time goes on, advances in NMR will be achieved only by teams of clinical and basic scientists encompassing multiple disciplines.     

Clinical magnetic resonance imaging with nuclear medicine correlation

The current role of magnetic resonance imaging (MRI) in different organ systems is discussed and compared to nuclear medicine and to other available clinical diagnostic modalities. The value of optimizing radiofrequency pulse sequence selection to provide additional tissue characterization is also described. The results of nuclear medicine and MRI studies in 56 patients are compared to evaluate the clinical diagnostic contribution of each imaging modality for various pathological processes. In addition, the state-of-the-art MRI systems and future development in MRI technology with its potential contribution is defined.     

Tomographic imaging with nuclear magnetic resonance

A technique is described for obtaining tomographic images of hydrogen distribution in animals using nuclear magnetic resonance (NMR). Resonant frequency is proportional to magnetic field strength, so that spatial resolution is achieved by frequency selection and magnetic field shaping. The results of scanning a phantom and two rats are presented.     

Urinary tract imaging by nuclear magnetic resonance

Nuclear magnetic resonance scanning has already found application in the urinary tract in man. It is a method of producing diagnostic images from the radiofrequency signals which can be elicited from hydrogen nuclei when the abdomen is placed in a strong magnetic field and subjected to pulses of RF energy. Computer-generated images depict the distribution of signal-emitting nuclei, modified by their relaxation times and macroscopic motion. The images are tomographic and have great potential flexibility in plane orientation. Normal anatomy, space-occupying lesions and lesions characterized by local edema have been visualized to date, and as clinical experience is accumulated, a much greater range of pathology promises to be detectable by this technique.     

Site planning for nuclear magnetic resonance imaging

The unique factors to be considered in selection of a site for a magnetic resonance imaging installation are addressed, with emphasis on the interaction of the magnet with its environment. The effect of ferrous objects on the magnet and the influence of the magnet on its surroundings are discussed. Design issues for magnetic shields are given.     

Urinary tract imaging by nuclear magnetic resonance

Nuclear magnetic resonance scanning has already found application in the urinary tract in man. It is a method of producing diagnostic images from the radiofrequency signals which can be elicited from hydrogen nuclei when the abdomen is placed in a strong magnetic field and subjected to pulses of RF energy. Computer-generated images depict the distribution of signal-emitting nuclei, modified by their relaxation times and macroscopic motion. The images are tomographic and have great potential flexibility in plane orientation. Normal anatomy, space-occupying lesions and lesions characterized by local edema have been visualized to date, and as clinical experience is accumulated, a much greater range of pathology promises to be detectable by this technique.     

Improvements in snap-shot nuclear magnetic resonance imaging

New variants of the ultra-high-speed echo-planar imaging technique have been used to obtain snap-shot images of adult patients and volunteers at 0.1 T. Modified pulsed-gradient sequences together with non-linear signal sampling and activity screened gradients have greatly improved the image quality obtainable by single-shot methods. A particular variant, modulus blipped echo-planar single-pulse technique (MBEST), although slightly slower than the blipped echo-planar single-pulse technique (BEST), is experimentally more robust and incorporates intrinsic T2 weighting. An account of these improvements together with some experimental results is presented.     

Burn injury by nuclear magnetic resonance imaging

Nuclear magnetic resonance imaging has become a standard diagnostic procedure in clinical medicine and is well known to have hazards for patients with pacemaker or metallic foreign bodies. Compared to CT, the frequency of MRI examinations is increasing due to the missing exposure of the patients by X-rays. Furthermore, high-field magnetic resonance tomograph (MRT) with 3 T has entered clinical practice, and 7-T systems are installed in multiple scientific institutions. On the other hand, the possibility of burn injuries has been reported only in very few cases.Based on a clinical finding of a burn injury in a 31-year-old male patient during a routine MRI of the lumbar spine with standard protocol, the MR scanner was checked and the examination was simulated in an animal model.The patient received a third-degree burn injury of the skin of the right hand and pelvis in a small region of skin contact. The subsequent control of the MRI scanner indicated no abnormal values for radiofrequency (RF) and power. In the subsequent animal experiment, comparable injuries could only be obtained by high RF power in a microwave stove.It is concluded that ‘tissue loops’ resulting from a contact between hand and pelvis must be avoided. With regard to forensic aspects, the need to inform patients of such a minimal risk can be avoided if the patients are adequately positioned using an isolating material between the hands and pelvis. These facts must be emphasized more in the future, if high-field MRI with stronger RF gradients is available in routine imaging.     

In vivo nuclear magnetic resonance imaging of lithium

Magnetic resonance imaging techniques have previously been applied to 1H, 23Na, 31P, and 19F nuclei. This is the first report of application of these techniques to 7Li. Lithium images of both aqueous phantoms and a rat abdomen are presented. Applications of this technique to humans are discussed.     

Microcomputer simulation of nuclear magnetic resonance imaging contrasts

The high information content of magnetic resonance images is due to the multiplicity of its parameters. However, this advantage introduces a difficulty in the interpretation of the contrast: an image is strongly modified according to the visualised parameters. The author proposes a micro-computer simulation program. After recalling the main intrinsic and extrinsic parameters, he shows how the program works and its interest as a pedagogic tool and as an aid for contrast optimisation of images as a function of the suspected pathology.     

A computer simulation of nuclear magnetic resonance imaging

A modular, user-friendly computer simulation of NMR imaging was created for the DEC VAX computer. This simulation is novel in that complex imaging phenomena, such as chemical shifts and flow, may be easily studied. Other features include spin warp and backprojection imaging, movie generation, and simulation of image contrast, composite pulse sequences, motion artifacts, aliasing, selective excitation, field inhomogeneity, noise and signal averaging. The simulation incorporates fast Fourier transform and graphics modules for processing and display of one- and two-dimensional images. Examples which illustrate features of the program are shown. The simulation is a useful tool for both the sophisticated and the beginning user of NMR imaging. It serves as a drawing board for studying MRI phenomena and a teaching program for demonstrating basic techniques.     

Analysis of eddy currents in nuclear magnetic resonance imaging

The eddy currents in nuclear magnetic resonance (NMR) imaging are analyzed from the solutions of Maxwell's equations and their effects are examined over various experimental conditions from whole-body diagnostic imaging to recently developed NMR microscopy. The analysis is focused mainly on the frequency characteristics and intensity variations of the eddy-current-induced field which depends on the overall system size, ratio of the gradient coil size to the magnet bore diameter, and the pulse-sequence-dependent parameters such as input current waveform and repetition time. From the analysis, the frequency response of the eddy-current-induced field is that of a high-pass filter whose cutoff frequency is inversely proportional to the square of the overall system size. The intensity ratio of the generated field to the induced field is not affected by the overall system size, but is sensitively related to the ratio of the gradient coil size to the magnet bore diameter.     

Visualization of brain infarction with nuclear magnetic resonance imaging

Summary Nine patients with cerebral or cerebellar hemispheric infarction and two patients with brain stem lesions were studied with NMR imaging in order to examine the lesion with different weightings on the various NMR parameters. The time interval between examination and the acute onset of the stroke varied from one day to six months. The lesions were clearly detected by the T₁ weighted inversion recovery sequence but the tissue contrast was better using the spin echo sequence with a long repetition rate and a long echo delay (SE_2000/100). In two patients the brain stem lesions were invisible with CT, but were easily depicted with NMR. In one of them the further progress of the lesion was also confirmed and visualized with the follow-up NMR study.     

Clinical applications of functional magnetic resonance imaging

Despite its immediate success as a tool for basic research, the clinical application of functional MRI(fMRI) is still limited. FMRI has proven useful for presurgical functional mapping of the eloquent cortices. Localization of the sensorimotor cortex by fMRI may be of relatively limited value because the sensorimotor cortex can often be readily localized by means of anatomical methods. In contrast, the language cortices may not be localized anatomically and the language dominant hemisphere has been determined by invasive Wada test. Previous reports have shown that fMRI can be a promising alternative to the Wada test. A recent clinical trial has suggested that fMRI can be used to diagnose Alzheimer's disease in its earliest stage, detecting subclinical deterioration of the memory function. FMRI may be useful to predict the future decline of memory in people with genetic risks. Monitoring of the functional recovery of post-stroke brains may be another promising clinical application of fMRI. FMRI has demonstrated functional reorganization of the brain that may be related to the restoration of motor and language functions.     

Clinical impact of shoulder magnetic resonance imaging

The clinical impact of magnetic resonance imaging (MRI) of the shoulder is dependent upon the clinical diagnosisand clinical indications for surgical management. MRI of the shoulder is very useful in defining the anatomic pathology associated with shoulder pain and disability. The clinical impact of MRI is improved when it is obtained under well defined criteria which should be based upon clinical treatment algorithms. Shoulder MRI is best used to define the anatomic pathology associated with rotator cuff tears and traumatic glenohumeral instability.     

Clinical impact of elbow magnetic resonance imaging

The elbow and its articulations are subject to tremendous forces during overhead sports. The elbow joint is vulnerable to a variety of injuries as a result of either acute traumatic events or chronic repetitive overuse. Elbow pathology in throwing athletes has been classified according to the mechanism of injury: medial tension overload, lateral compression, extension overload, and posterolateral rotatory instability. Given the complexity of these injuries, complete diagnosis and treatment requires a thorough evaluation of the elbow. This evaluation begins with a history and physical examination, an understanding of pathomechanics, and an assessment of normal and pathological anatomy. Imaging studies may be of assistance in defining this anatomy. The correlation of these imaging studies with clinical information is essential in the proper diagnosis and management of these complex injuries. This article presents the impact of elbow magnetic resonance imaging (MRI) for the clinical diagnosis of the three most common elbow disorders for which MRI has diagnostic efficacy in the athlete.