Annotated bibliography.
Explore the source record for details and available documents.
Brain Diseases↗
Biomedical subjects
A D Elster
Publications and source records attributed to A D Elster.
Improved detection of gadolinium enhancement using magnetization transfer imaging.
Magnetization transfer (MT) imaging is a new MR imaging technique in which off-resonance radiofrequency pulses are used to selectively saturate protons in macromolecules. This saturation effect is transferred subsequently (by dipolar and chemical exchange interactions) to protons in free water, thereby altering tissue relaxation times and modulating image contrast. Gadolinium enhancement is not significantly mediated by macromolecular interactions and is, therefore, not suppressed by MT pulses. The theory underlying the use of the MT technique is presented, with examples of its clinical usefulness in improving contrast enhancement for a variety of central nervous system diseases.
Brain↗
Magnetic resonance contrast enhancement in cerebral infarction.
Contrast enhancement may aid significantly in the diagnosis, dating, and grading of cerebral infarctions. On MR imaging, four patterns of contrast enhancement may be distinguished: intravascular, meningeal, transitional, and parenchymal. Each pattern has a different appearance, time course, and clinical significance. The anatomic and physiologic mechanisms that give rise to these distinct types of contrast enhancement in cerebral infarction are discussed.
Brain↗
Skull-base foramina of the middle cranial fossa: reassessment of normal variation with high-resolution CT.
PURPOSE: To evaluate by means of high-resolution CT the anatomic variations of the middle cranial fossa foramen. METHODS: We examined 123 CT studies of the temporal bone in patients with no evidence of disease that might alter foraminal anatomy. A checklist of known variants and suspected structures was used as each case was systematically examined for the presence or absence of these foramina; variations in size, shape, and location; and relationship of structures to each other. Inclusion criteria were established to eliminate error. RESULTS: The foramen rotundum had a constant appearance. We identified the inferior rotundal canal in 16% of patients and the lateral rotundal canal in 8%. The foramen of Vesalius was present, at least unilaterally, in 80% of our cases. Asymmetry of the foramen of Vesalius did not indicate disease in our patient group. We did not find an inverse relationship between the size of the foramen of Vesalius and that of the ipsilateral foramen ovale. We found variations in the size and shape of the foramen ovale and its confluence with the foramen spinosum (n = 2) and the foramen of Vesalius (n = 8). We did not find an inverse relationship between the size of the foramen ovale and that of the foramen spinosum. The canaliculus innominatus for the lesser superficial petrosal nerve was identified in 16.3% of our patients. Variations of the foramen spinosum that we found include a medial bony defect (26.8%) and absence (3.2%). CONCLUSION: Although it is unlikely that well-formed foramen will be misinterpreted as diseased, it is nonetheless important to recognize foraminal variants and associated neurovascular anatomy.
Adolescent↗
Intraocular silicone oil: in vitro and in vivo MR and CT characteristics.
PURPOSE: To describe the CT and MR characteristics of intraocular silicone oil (polydimethylsiloxane), which is used with increasing frequency to treat complicated retinal detachments. METHODS: CT was performed on a silicone oil/water phantom and on a patient with retinal detachments secondary to cytomegalovirus retinitis, treated by bilateral intraocular injections of silicone oil. CT appearance and CT number of silicone oil were evaluated. Proton MR spectroscopy was performed with a 200-MHz spectrometer on a sample of polydimethylsiloxane within a tube of deuterated water. MR imaging was performed on a silicone oil/water phantom and on two patients with retinal detachments treated with silicone oil injection. RESULTS: Silicone oil is relatively radiodense; its CT attenuation is approximately 130 HU. On spectroscopy, silicone oil gave a single peak at 0.33 ppm. Relative to water silicone oil was hyperintense on T1-weighted images and hypointense on spin-density and T2-weighted images. Estimated T1 and T2 were 716 msec and 68 msec, respectively. Chemical shift artifacts were seen on MR images and were exaggerated when a narrow sampling bandwidth was used. In clinical cases spectral saturation pulses normally used for lipid suppression could be adjusted to saturate only the silicone resonance; in this way, the chemical shift artifact was eliminated. CONCLUSION: Intraocular silicone oil has unique imaging characteristics with which radiologists must become familiar. These characteristics include high attenuation on CT and hyperintensity on T1-weighted MR, both of which may mimic hemorrhage. Elimination of the prominent chemical shift artifact on MR with selective saturation of the silicone resonance improves evaluation of the globe.
AIDS-Related Opportunistic Infections↗
Annotated bibliography.
Explore the source record for details and available documents.
Diagnostic Imaging↗
Bacterial and viral parenchymal infections of the brain.
Magnetic resonance imaging (MRI) has been proven to aid in the early detection and diagnosis of parenchymal infections of the brain. Pyogenic brain abscess, herpes encephalitis, Listeria rhombencephalitis, and Rasmussen's syndrome are examined in this article. Imaging characteristics, epidemiology, clinical presentations, therapies, and pathologic findings are discussed.
Bacterial Infections↗
Imaging of the sella: anatomy and pathology.
The hypophysis cerebri, or pituitary gland, is a complex neuroendocrine organ involved in the control of a variety of homeostatic mechanisms. Subtleties in the internal anatomy of this gland are now becoming appreciated, such as the topographic arrangements of pituitary cell types and specializations in its regional microcirculation. A large number of potential lesions may affect the pituitary, including tumors (adenomas, Rathke cleft cysts, and craniopharyngiomas), inflammatory processes (adenohypophysitis, infections), and vascular lesions (apoplexy, infarction). Diseases isolated to the posterior lobe and stalk (eg, pituitary dwarfism, choristoma, diabetes insipidus) are also well recognized. Modern radiologic techniques like computed tomography (CT) and magnetic resonance (MR) imaging have provided new insights into the morphologic changes of the gland that occur both in health and in a variety of diseases. The picture of the gland that has emerged from this research is a dynamic one: The pituitary undergoes dramatic changes in size and shape throughout life that must be recognized when assessing it for pathologic change.
Adenoma↗
Large-tip-angle spin-echo imaging. Theory and applications.
RATIONALE AND OBJECTIVES: Tissue contrast phenomenology was investigated analytically and clinically for a class of magnetic resonance (MR) pulse sequences we call large-tip-angle (LTA) spin-echo (SE) imaging. In comparison to traditional SE sequences (denoted 90 degrees-180 degrees-echo), the LTA sequence is of the form alpha degrees-180 degrees-echo, where 90 degrees < alpha < 180 degrees. Theoretical analysis shows that appropriately designed LTA sequences can selectively boost the MR signal by 10%-150% in substances whose spin lattice (T1) relaxation values equal or exceed the sequence repetition time (TR). This unique contrast behavior potentially allows one to reduce TR (and hence imaging time) by 30% to 50% while maintaining constant T2-weighted contrast or contrast-to-noise within an image. METHODS: Preliminary clinical testing of LTA sequences was performed in 60 patients with a wide range of cranial, spinal, musculoskeletal, and abdominal pathologies. Large-tip-angle images (1,500/80/130 degrees) were blindly and prospectively compared to conventional (2,600/80/90 degrees) SE images. RESULTS: Principal diagnoses were concordant between the readers in all cases, although minor variances in detail features were noted in 6 (10%) of 60 cases. Large-tip-angle sequences revealed small cystic areas in two cerebral neoplasms and in a herniated disk which were not apparent on the standard SE images. However, the LTA images were rated to be "noisier" by visual assessment in 43 of 60 cases, the exception being for abdominal examinations, where respiratory and peristaltic artifacts were judged more severe on the standard SE sequences. CONCLUSIONS: Large-tip-angle SE imaging is an interesting technique capable of improving image contrast and signal from lesions with long T1 values when the sequence repetition time (TR) is short.
Brain↗
Gradient-echo MR imaging: techniques and acronyms.
This overview briefly traces the history and nomenclature of gradient-recalled-echo (GRE) techniques used in magnetic resonance (MR) imaging. GRE sequences, which are now offered commercially by 11 major manufacturers of MR imagers, are presented to illustrate their structural similarities and subtle differences in implementation. A classification scheme is proposed for these sequences employing a vendor-independent nomenclature. A glossary of GRE abbreviations and acronyms found in the current MR marketplace also is presented.
Abbreviations as Topic↗
Modern imaging of the pituitary.
Explore the source record for details and available documents.
Adenoma↗
Routine use of gadopentetate dimeglumine in cranial MR imaging of patients with AIDS.
Explore the source record for details and available documents.
Acquired Immunodeficiency Syndrome↗
Autosomal recessive osteopetrosis: bone marrow imaging.
Technetium-99m sulfur colloid scintigraphy was performed prospectively in 12 infants and children with autosomal recessive osteopetrosis, to correlate the appearance of bone marrow stores with advancing age. Baseline images were obtained in all patients, and one to five follow-up images were obtained in eight patients after they began therapy with calcitriol, interferon-gamma, or both. Conventional radiography was performed along with the nuclear studies in all cases. Magnetic resonance (MR) images of the head or lower extremities were also obtained in six patients and were correlated with the scintigraphic findings. Patterns of abnormal distribution of bone marrow appeared to be age-dependent. In patients younger than 1 year, marrow stores were primarily in the skull base and at the ends of the long bones. In patients aged 3-5 years, marrow stores shifted to the diaphyseal regions of long bones and to the calvarium. In the appendicular skeleton, areas of greatest bone marrow activity corresponded to regions of relative decreased opacity on radiographs and areas of intermediate or high signal intensity on T2-weighted MR images. The skull base showed appreciable marrow activity in spite of densely sclerotic bone on radiographs.
Bone Marrow↗
Cranial imaging in autosomal recessive osteopetrosis. Part I. Facial bones and calvarium.
Cranial imaging studies (radiographs, computed tomographic [CT] scans, magnetic resonance [MR] images, and bone marrow scintigrams) in 13 infants and children with autosomally recessive osteopetrosis were reviewed to characterize patterns of facial and calvarial involvement at presentation and with progression of disease. In the mandible, a characteristic triangular opacity representing calcification within the secondary condylar cartilage ossification center was seen in 10 of the 13 patients. Defective dentition with incomplete enamel formation and/or caries was encountered in all patients. The paranasal sinuses were poorly pneumatized in all patients, but the ethmoid sinuses tended to be the least severely affected. Hypertelorism was present in five of the 13 patients, with a characteristic "space-alien" appearance on frontal radiographs. In younger patients, the calvarium demonstrated a high-attenuation inner table, a broad, low-attenuation diploic space, and a less high-attenuation outer table at CT. In three older children, a "hair-on-end" appearance was seen, which, at bone marrow scintigraphy, corresponded to areas of marked hematopoietic activity. Regions of sclerotic bone demonstrated low signal intensity on both T1- and T2-weighted MR images; areas containing marrow had intermediate signal intensity. These many new radiologic features of osteopetrosis are related to its pathophysiologic characteristics.
Child↗
Cranial imaging in autosomal recessive osteopetrosis. Part II. Skull base and brain.
The authors reviewed cranial imaging studies (radiographs, computed tomographic scans, and magnetic resonance [MR] images) in 13 infants and children with the autosomal recessive form of osteopetrosis to characterize patterns of skull base, brain, and cranial nerve involvement at presentation and with progression of disease. Marked sclerosis and deposition of osteopetrotic bone was noted along the anterior (but not posterior) occipitomastoid suture (n = 8), at the basioccipital-exoccipital synchondrosis (n = 9), and along the sphenooccipital synchondrosis (n = 8). Endobones, presumably representing unresorbed primitive ossification centers, were seen in the sphenoidal body and basioccipital bone in 11 of the 13 patients. Marked cupping at the basioccipital-exoccipital synchondrosis was observed in three. Neurologic deficits included blindness (n = 11), conductive hearing loss (n = 11), and facial nerve palsies (n = 4). Delayed myelination was seen with MR imaging in two of five retarded infants, including one with a documented coexisting neuronal storage defect. Prominent extracerebral cerebrospinal fluid spaces were present over the frontal lobes in five of the eight developmentally normal patients, representing either subclinical parenchymal disease or a phenomenon related to discordant growth rates between skull and brain.
Brain↗