European Radiology

Carpenter, T. A.; Williams, E. J.

doi: 10.1007/s003300050787pmid: 10415231

There have been remarkable advances in the hardware used for nuclear magnetic resonance imaging scanners. These advances have enabled an extraordinary range of sophisticated magnetic resonance MR sequences to be performed routinely. This paper focuses on the following particular aspects: (a) Magnet system. Advances in magnet technology have allowed superconducting magnets which are low maintenance and have excellent homogeneity and very small stray field footprints. (b) Gradient system. Optimisation of gradient design has allowed gradient coils which provide excellent field for spatial encoding, have reduced diameter and have technology to minimise the effects of eddy currents. These coils can now routinely provide the strength and switching rate required by modern imaging methods. (c) Radio-frequency (RF) system. The advances in digital electronics can now provide RF electronics which have low noise characteristics, high accuracy and improved stability, which are all essential to the formation of excellent images. The use of surface coils has increased with the availability of phased-array systems, which are ideal for spinal work. (d) Computer system. The largest advance in technology has been in the supporting computer hardware which is now affordable, reliable and with performance to match the processing requirements demanded by present imaging sequences.

Hennig, J.

doi: 10.1007/s003300050788pmid: 10415232

The k-space algorithm offers a comprehensive way for classification and understanding of the imaging properties of all commonly used MR sequences. This presentation describes the basic concepts of k-space and its most relevant properties for MR imaging. The ramifications of k-space sampling is discussed for the most commonly used groups of MR sequences including gradient-echo techniques, echo-planar imaging, spin echo, and rapid acquisition relation enhanced imaging (e. g., turbo spin echo, fast spin echo). In addition, the basic problems and properties of sequences based on non-rectilinear k-space sampling, such as spiral imaging, are discussed. Their artifact behavior is significantly different from rectilinear scans, which project all imperfections along the phase-encoding directions, whereas the artifact produced by spirals are more complex and not always easily recognizable as such. An understanding of the k-space sampling offers important insight into the basic properties of a given sequence regarding signal-to-noise ratio, image distortion, resolution and contrast. It is demonstrated that the ultimate limitation in imaging speed is given by the loss of signal-to-noise ratio inherent to faster data sampling.

Nitz, W. R.; Reimer, P.

doi: 10.1007/s003300050789pmid: 10415233

This paper is a brief introduction to tissue-specific parameters and the utilization of various MR imaging sequences to display these parameters in order to differentiate normal from pathologic tissue and function. The three dominant tissue-specific parameters discussed are proton density, longitudinal relaxation time T1, and transverse relaxation time T2. For the utilization of gradient-echo sequences, transverse relaxation time T2* is introduced, more dependent on the environment or tissue interfaces than on the tissue itself. Another tissue-specific parameter is the concentration of macromolecules and their hydration layers as targeted with magnetization transfer imaging. Still another tissue-specific parameter is the chemical environment. Functional parameters that influence the contrast are diffusion, perfusion, flow, or motion. The sequence-related utilization of these tissue-specific parameters start with magnetization preparation as in spectral suppression of fat signal, relaxation-dependent elimination of fat or cerebrospinal fluid (CSF) signal, simple inversion pulse, magnetization transfer saturation, or diffusion weighting. Possible contrast mechanisms for the tissue-specific parameters are discussed for each of the commonly used sequences, whether of spin-echo type or of gradient-echo type, with or without magnetization preparation, conventional single-echo acquisition, or contemporary multiecho acquisition.

Sartor, K.

doi: 10.1007/s003300050790pmid: 10415234

The radiologic modality that most likely provides the imaging information needed in a patient suspected of having a brain tumor is MR imaging. A brain tumor can be reliably ruled out if the MR examination is performed properly and experts interpret the results as negative. If there is a tumor, however, its exact location and topography must be determined. Important for therapy and prognosis are also tumor properties such as histologic type and grade, as well as effects on adjacent brain structures. Although potentially a noninvasive method of in vivo neuropathology, MR is still far from being sufficiently specific, as dissimilar lesions may look the same despite the use of refined imaging protocols. The evolution of MR imaging continues, however, making further methodologic improvement likely. Presently, advanced methods, such as diffusion- and perfusion-weighted MR imaging, functional MR imaging, neuronavigation based on MR imaging data, and the use of MR imaging during surgery (intraoperative MR imaging), influence the way patients are treated. Likewise, follow-up imaging (monitoring) of tumor patients by MR has become more effective, and experience has shown how to distinguish reactive changes from recurrent tumor. In the future, MR imaging may gain importance in the development of novel therapeutic concepts.

Wilms, G.; Demaerel, P.; Bosmans, H.; Marchal, G.

doi: 10.1007/s003300050791pmid: 10415235

Due to flow-void phenomena, MRI is of great value in the demonstration of cerebral aneurysms and vascular malformations as well as of related parenchymal changes and hemorrhagic complications. Magnetic resonance angiography can produce vascular images which are of importance in the diagnosis and follow-up of the lesions.

Forsting, M.

doi: 10.1007/s003300050792pmid: 10415236

Metabolic disorders of the brain are rare, complex and confusing. The diagnostic modality of choice nowadays is MRI. The high diagnostic sensitivity, however, is coupled with a lack of specificity and usually results in the depiction of similar appearing but clinically diverse white matter processes. For this reason it is essential to perform the MRI as early as possible during the course of the disease and to keep in close contact to the referring clinician to optimize image interpretation. Another precondition is to know the natural course of brain myelination and to know how this appears on the individual MR machine with different parameters. In some diseases like phenylketonuria MRI seems to be an excellent tool to monitor dietary treatment and patient compliance. In patients after radio- and / or chemotherapy MRI reveals the radiation induced leucencephalopathy and can usually differentiate between a recurrent malignancy.

Tyrrell, P. N. M.; Cassar-Pullicino, V. N.; McCall, I. W.

doi: 10.1007/s003300050793pmid: 10415237

Spinal infection is a significant cause of morbidity. Despite advances in antibiotic treatment regimens, the incidence is not decreasing due at least in part to an increase in 'at-risk' populations, namely the elderly and the immunocompromised. Prompt diagnosis is greatly facilitated by early and appropriate imaging techniques together with microbiological assessment following culture from blood, needle aspirate and biopsy material. This article gives an overview of imaging of spinal infection with an emphasis on MR imaging, which has greatly contributed to early diagnosis, thus allowing implementation of timely appropriate treatment.

Abd El Bagi, M. E.; Sammak, B. M.; Al Shahed, M. S.; Yousef, B. A.; Demuren, O. A.; Al Jared, M.; Thagafi, M. A. Al

doi: 10.1007/s003300050794pmid: 10415238

Bone infections are usually due to haematogenous spread from distant infected organs. Spread of local sepsis or contamination of open wounds are less frequent routes of infection. The commonest cause of osteomyelitis is Staphylococcus aureus. The term rare bone infections refers to diseases where only a few percent affect bone or diseases which are essentially rare; these include bacteria, fungi, parasites and non-specific conditions. Common examples are tuberculosis, salmonellosis, brucellosis, hydatidosis, madura, actinomycosis, aspergillosis and American fungal infections. Certain bone infections have become exceedingly rare, particularly atypical mycobacteria, viral embryopathies and spirochaetes. Rare bone infections are encountered in many parts of the world commonly in the tropics and in the U. S. Immunocompromise and ease of travel can lead to increased incidence. A high index of clinical suspicion is necessary for diagnosis. Specific laboratory diagnosis is not always possible. Radiographs, computed tomography, isotope studies and magnetic resonance are useful but may not make the diagnosis. Aspiration or biopsy is necessary. Rare bone infections may simulate non-infective bone lesions.

Sánchez-Márquez, A.; Gil-García, M.; Valls, C.; Portabella-Blavia, F.; Narváez-Garcia, J.; Andía-Navarro, E.; Pozuelo-Segura, O.

doi: 10.1007/s003300050795pmid: 10415239

Sports-related injuries of the lower extremity are frequent. Before magnetic resonance (MR) imaging was available, ultrasound, radionuclide scintigraphy and computed tomography were used to evaluate muscle trauma. Although relatively inexpensive, these imaging modalities are limited by their low specificity. The high degree of soft tissue contrast and multiplanar capability of MR imaging, allow direct visualization as well as characterization of traumatic muscle lesions. This pictorial review highlights the spectrum of traumatic muscle lesions on MRI, with emphasis on its typical appearances.

Roca, M.; Mota, J.; Giraldo, P.; García Erce, J. A.

doi: 10.1007/s003300050796pmid: 10415240

Systemic mastocytosis (SM) is an abnormal proliferation of mast cells, located in different structures: skin, bone marrow, spleen, liver and lymph nodes. Magnetic resonance imaging was prospectively performed in ten patients diagnosed by bone marrow biopsy in order to describe the different patterns of bone marrow involvement. Coronal T1-weighted spin-echo images were obtained in vertebral, pelvic, humeral and femoral bones. Depending on the extension of the cell infiltration, three patterns of bone marrow involvement were used: normal/no involvement (N), non-homogeneous (NH) and homogeneous (H). All ten patients presented bone infiltration. The patterns observed were: spine (50 % NH, 50 % H), pelvis (70 % NH), humerus 100(NH) and femur 40 % (NH). T1-weighted MR imaging is a sensitive technique for detecting marrow abnormalities in patients with systemic mastocytosis. There is no correlation between percentage of mast cells in bone marrow biopsy and extent or pattern of bone marrow involvement.