Magnetic resonance annual最新文献

In the short time that MRI has been available, it has become apparent that one of the more important nonneurologic applications is in imaging the musculoskeletal system. MRI is effective at providing high-contrast images with acceptable spatial resolution for a variety of bone marrow disorders, soft tissue masses, osseous tumors, and muscle diseases. The multiplanar aspect of the method is a great advantage and promises to be a major reason why MRI will be selected instead of CT for many examinations. Currently, it appears that MRI is a leading method of detecting ischemic necrosis of the femoral head and determining the extent of soft tissue masses and bone tumors. Surface coil technology promises better resolution of small parts such as the wrist and temporomandibular joint. Phosphorous spectroscopy should make important contributions to our basic understanding of normal and altered muscle energy metabolism as well as providing a safe method of following the course and therapy of muscle diseases. It is anticipated that MRI will have an important position among the variety of imaging tests for musculoskeletal diseases.

The many varied effects of blood flow seen with different kinds of conventional MRI techniques can be understood as the result of three basic underlying mechanisms: washout of saturated spins, washout of excited spins, and phase shifts due to motion of excited spins along magnetic field gradients. These effects can be applied in various modified MRI techniques that have been proposed for the measurement of blood in blood vessels, although none have yet been put into routine clinical practice. The measurement of tissue perfusion with MRI remains a more difficult but very desirable goal.

MRS made especially versatile with current technology of multinuclear coils and time interlacing of signals is appropriately suited to multifaceted tumor biochemistry, where growth is a key metabolic feature. The established results that bioenergetics and lipid metabolite concentrations show a variety of responses in tumor growth and remission in response to anticancer procedures add a further novel dimension to tumor studies by MRS. Finally, the versatility of the multinuclear MRS approach seems most appropriate to the varied nature of cancer.

There is, of course, an intense activity directed at the improvement of MR imaging capabilities. Surface-coil techniques offer the possibility of improving the SNR sufficiently to permit the reduction of pixel sizes to values that would not be possible with conventional head and body coils. The successful application of surface-coil techniques to MR imaging suggests that this technique will be widely used in future MR imaging systems. This provides a fertile field for new research. This includes opportunities for mathematical and physical research into optimizing coil design. It also includes many opportunities for clinical research into the utilization of surface coils and high resolution MR imaging.

It is obvious that MRI has assumed a prominent role in the evaluation of disease in the brain and spine. However, CT has not been totally replaced in the evaluation of the CNS, and probably still remains the imaging modality of choice for most applications outside the CNS. Given a choice of CT or MRI in the evaluation of the CNS, certain recommendations can be made on the basis of the specific indication. It should be emphasized that these recommendations are quite dependent on the current level of technology and are thus subject to change. While not always based on rigorous comparisons, they represent a distillation of our own clinical experience (over 6,000 patients) and that of others. There is obviously a significant overlap between CT and MRI in their clinical applications in the CNS. For this reason, the recommendations in Table 1 are listed in descending order of preference, i.e., strong preference at the top, weaker preference at the bottom. In the brain MRI is indicated for the exclusion of early disease on the basis of its greater sensitivity. It is particularly useful in the posterior and middle fossae, where CT is limited by beam-hardening artifact from bone. MRI is preferred for the evaluation of MS and other diseases in the periventricular region, e.g., deep white matter infarcts and interstitial edema caused by hydrocephalus. Small extraaxial fluid collections are better seen by MRI than CT, particularly in the middle and posterior cranial fossae and at the vertex. Evaluation of the craniovertebral junction is enhanced by the ability to image directly in the sagittal plane. While MRI has clearly preempted many applications, CT is still the examination of choice in several clinical settings. Patients on respirators and those with cardiac pacemakers or intracranial aneurysm clips are currently excluded from MRI. Bone detail is better evaluated by CT; thus trauma victims with fractures and patients with suspected osseous abnormalities of the temporal bones should be studied by CT. Acute trauma patients are better studied by CT because they frequently cannot be sedated and therefore may not be able to lie motionless for the 5 to 20 min required for acquisition. In addition, trauma patients and those with acute strokes where hemorrhage is suspected should be studied by CT, where the blood can be specifically identified. The higher spatial resolution and shorter scan time of CT currently make it the examination of choice in the orbit and in the evaluation of suspected pituitary microadenomas.(ABSTRACT TRUNCATED AT 400 WORDS)