PubMed Health⌕ Search

Biomedical subjects

W Kucharczyk

Publications and source records attributed to W Kucharczyk.

At least 55 records · Page 3Linked to original sources
PubMed1990

Cause of signal loss in MR images of old hemorrhagic lesions.

Old hemorrhagic lesions in the brain are characteristically surrounded by a band of hemosiderin-containing tissue. This region is typically of low signal intensity on long-echo-time (TE) radio-frequency (RF) spin-echo magnetic resonance (MR) images and on gradient-echo MR images. To determine the cause of signal loss in this band, the authors measured the signal that arises from imaging such a region with use of an RF spin-echo technique with a 180 degrees pulse incrementally displaced from TE/2. The incremental loss of signal was small. Using an agar phantom containing iron particles, the authors also showed that signal loss results primarily from diffusion in magnetic gradients. They conclude that most signal loss in the dark band surrounding areas of late-stage hemorrhage arises from diffusion in areas of magnetic inhomogeneity.

Adult↗
PubMed1990

High resolution magnetic resonance imaging of vascular lesions at the skull base: a review.

Conventional spin-echo magnetic resonance imaging is now being used routinely for the evaluation of brain parenchyma. It has also proven to be an excellent modality for the diagnostic assessment of the larger cerebral blood vessels, typically those found in or adjacent to the skull base. It possesses sufficiently good spatial and contrast resolution to be used for the diagnosis of arterial thrombosis, atherosclerotic and "berry" aneurysms, arterial dissection and venous sinus occlusion in preference to computed tomography. It has reduced, but not eliminated, the need for confirmatory angiography for these indications.

Cerebral Arteries↗
PubMed1990

Making magnetic resonance images and beyond.

Magnetic resonance (MR), a comparatively new imaging method in Canada, is based on physical principles that are different from all current imaging methods. An understanding of these principles is therefore essential to appreciate the clinical capabilities and limitations of MR. Because MR is a multiparameter imaging method, the challenge of choosing appropriate imaging sequences must be addressed. The technical development of anatomical image formation is now almost complete, so future research will focus on the use of MR to obtain more than just spatial information. The quantitative measurement of relaxation times, chemical composition, flow and spectra hold great promise in extending the capabilities of MR beyond those of other imaging methods.

Humans↗
PubMed1989

MRI: when you can't afford not to.

Magnetic resonance technology offers vivid, lifelike imaging. Our experts advise when MRI is the standard of care and when it is not--or not yet--worth the cost.

Cost-Benefit Analysis↗
PubMed1989

Do we really need another localizing technique for parathyroid glands?

To evaluate magnetic resonance imaging (MRI) in the preoperative localization of abnormal parathyroid glands, we examined 16 patients with primary hyperparathyroidism at initial presentation with MRI and ultrasound of the neck. These studies were analyzed prospectively and compared with the findings at bilateral neck exploration. The surgeon was intentionally blinded to the imaging studies. MRI was accurate in the lateralizing of an abnormal gland in 21 of 32 sides (66 percent). Sensitivity was 65 percent and specificity was 66 percent. Ultrasound was accurate in 19 of 32 sides (59 percent). Sensitivity was 50 percent and specificity was 75 percent. The difference was not statistically significant. We do not believe that MRI is indicated prior to initial exploration in patients with primary hyperparathyroidism.

Humans↗
PubMed1989

Hypothalamic-pituitary region: magnetic resonance imaging.

Endocrine disorders of the hypothalamus and pituitary gland are often caused by lesions which can be accurately detected and delineated by MRI, often with specific findings. MRI has emerged as the imaging modality of choice for pathology of the hypothalamus and other suprasellar structures, and for extrasellar extension of pituitary tumours. The advantage is mainly based on the high contrast resolution, vascular visualization without the need for intravascular contrast and direct multiplanar imaging capability inherent with the technique. CT, however, enjoys much wider availability and better spatial resolution at present. CT is still the method used to detect pituitary microadenomas in most centres, although high field-strength MR scanners and gadolinium enhancement permit thinner sections with improved sensitivity in certain institutes. Further advances in MRI technology are expected to broaden its usefulness in endocrinology.

Humans↗
PubMed1989

T2 values in the human brain: comparison with quantitative assays of iron and ferritin.

Magnetic resonance (MR) imaging with a whole-body imager was performed in 10 fresh, unfixed whole human brains selected randomly from cadavers. All subjects were neurologically intact before death. T2 time constants were measured within the caudate nucleus, putamen, globus pallidus, cortical gray matter, subcortical white matter, and optic radiation. These regions were then excised, and T2 values were measured again with a 1.5-T MR spectrometer. Quantitative assays of iron, ferritin, and protein from these areas were then performed. Iron concentration varied significantly among brain regions, whereas ferritin and protein concentrations were constant among brain regions and among individuals. Neither iron nor ferritin concentration showed any consistent correlation with T2 values. Histologic examination of brain micro-sections with iron- and ferritin-specific stains of demonstrated poor correlation with biochemical assays of ferritin and iron concentrations. Results indicate that T2 values correlate poorly with iron and ferritin concentrations found in neurologically intact brains.

Adolescent↗
PubMed1989

Histochemical characterization and functional significance of the hyperintense signal on MR images of the posterior pituitary.

MR imaging of the pituitary fossa characteristically shows a well-circumscribed area of high signal intensity in the posterior lobe on T1-weighted images. We used a combination of high-field MR, electron microscopy, and histologic techniques in experimental animals to determine whether the hyperintensity of the posterior lobe might be functionally related to hormone neurosecretory processes, and to attempt to establish its chemical nature. Histologic sections of a dog's pituitary gland processed with lipid-specific markers showed intense staining in the posterior lobe but not in the anterior lobe, thus documenting the location of fat in the posterior pituitary. Administration of vasoactive drugs known to influence vasopressin secretion to anesthetized cats produced changes in the volume of high-intensity signal in the posterior pituitary. Subsequent electron microscopy showed a significant increase in posterior lobe glial cell lipid droplets and neurosecretory granules in dehydration-stimulated cats. The data suggest that the pituitary hyperintensity represents intracellular lipid signal in the glial cell pituicytes of the posterior lobe or neurosecretory granules containing vasopressin. The volume of the signal may, in turn, reflect the functional state of hormonal release from the neurohypophysis.

Animals↗
PubMed1989

MRI of the floor of the mouth, tongue and orohypopharynx.

Magnetic resonance is the imaging modality of choice for studies of the orohypopharynx, floor of the mouth, or tongue base. The superiority of MRI soft tissue contrast can demonstrate intra- and extraorgan spread of tumor beyond that of CT. Use of T1- and T2-weighted pulse sequences allows better discrimination of pathologic masses from fat or muscle than does CT. Multiplanar capabilities allow ease of examination in the preferred planes. Various sequences or planes of imaging may be chosen to tailor the examination to the anatomic region of interest. The use of Gd-DTPA with T1-weighted images should further improve diagnostic precision of tumor location and extension and may replace the need for the longer T2-weighted sequences. Gadolinium may help differentiate tumor recurrence from fibrosis in the post-radiation patient. New improvements in surface coil technology, motion and flow compensation imaging strategies, faster scan times, and spatial resolution will further advance MRI as the modality of choice for assessment of oropharyngeal, mouth, and tongue soft tissue masses.

Gadolinium↗
PubMed1988

Syrinx-like artifacts on MR images of the spinal cord.

Magnetic resonance (MR) imaging of the spinal cord frequently demonstrates, especially on sagittal sections, a central stripe that mimics a true syrinx. This syrinx-like manifestation of a truncation artifact occurs in objects having a width of only a few pixels and was demonstrated by calculations verified with phantom MR images. Healthy volunteers and two patients with a syrinx and cervical spondylosis, respectively, underwent MR imaging. By increasing the number of phase-encoding steps, decreasing the field of view, and switching phase- and frequency-encoding axes, the syrinx-like artifact can be eliminated.

Cervical Vertebrae↗
PubMed1987

Posterior pituitary gland: appearance on MR images in normal and pathologic states.

T1-weighted magnetic resonance (MR) images of the pituitary gland and sella turcica routinely demonstrate a region of high signal intensity in the neurohypophysis. High-resolution MR imaging studies of the sella turcica in 200 subjects with a normal or abnormal sella were analyzed. The hyperintensity was found in the images of about 90% of healthy subjects and patients with microadenoma, in only 43% of patients with macroadenoma, and in 12% of patients with empty sellae. The signal was absent in several patients with functional or anatomic abnormalities of the hypothalamic-hypophyseal axis. It is concluded that the high signal intensity in the posterior lobe of the pituitary gland is present in most healthy individuals and that its absence in many patients with large intrasellar masses and empty sellae is due to compression of posterior lobe tissue. Its absence in diabetes insipidus further suggests a relationship between hyperintensity and the functional status of the hypothalamic-hypophyseal axis.

Adenoma↗
PubMed1987

Rathke cleft cysts: CT, MR imaging, and pathologic features.

The authors retrospectively reviewed the clinical, computed tomography (CT), and magnetic resonance (MR) imaging findings in seven patients with pathologically proved Rathke cleft cysts. All the cysts were located in the anterior sella turcica or the anterior suprasellar cistern. Five cysts had both intra- and suprasellar components, one was entirely intrasellar, and the other was predominantly suprasellar in location. The size of the cysts ranged from 8 to 20 mm. CT scans demonstrated low-density homogeneous lesions in four cases. On MR images of three of these four cases, the cysts had the same intensity as cerebrospinal fluid on T1- and T2-weighted images, while in the fourth case, the cyst was hyperintense on the T1-weighted images. In the remaining three cases, CT showed slight hyperdensity relative to brain parenchyma, suggestive of contrast enhancement. MR showed signal heterogeneity of these lesions with focal components of diminished signal intensity of T2-weighted images. These same foci appeared iso- to slightly hyperintense on T1-weighted images.

Adult↗
PubMed1987

Magnetic resonance imaging of cerebral ischemia and infarction.

In summary, then, the major strength of MRI in evaluating cerebral ischemia is in the sensitivity that this methodology provides for detection of the disease process. However, it must be realized that edema is a nonspecific event related to various insults affecting the brain. There is still an uncertain capability of MRI in separating acute hemorrhagic from acute ischemic events. The superior sensitivity of MRI should help in investigations aimed at evaluating various forms of intervention in acute ischemia. Because some of these acute changes are at the biochemical rather than morphologic level, proton MRI alone probably will be insufficient to explore numerous variables. For this reason, the potential offered by MRS in cerebral ischemia research and in clinical settings is important. Vascular imaging is relatively complex. Several techniques show promising results but at the present time have poor resolution in comparison to ultrasound and angiography. For the immediate future, they will remain investigational.

Animals↗
PubMed1986

Spin-echo MR imaging of intracranial hemorrhage.

This retrospective study was performed to describe the appearance of intracranial hemorrhagic lesions on magnetic resonance (MR) imaging at 0.35 tesla using the spin-echo technique, and define the present clinical role of MRI in this particular pathology. Forty-eight examinations of forty-three patients with forty-seven intracranial hemorrhagic lesions (39 true hematomas and 8 hemorrhagic lesions mixed with other tissues) were reviewed for this study. Comparative CT studies were available for all the patients. In our limited experience with acute hematomas (less than 3 days old), low or isointense signal was seen with a short TR (0.5 s), but a relative increase in signal intensity was observed with a long TR (2.0 s). This appearance of acute hematoma was not specific. Chronic hematomas (more than 3 days old) were imaged as foci of bright signal intensity on both short and long TR. This pattern was characteristic of chronic hematoma. With a short TR (0.5 s), two hemorrhagic lesions (5 and 7 days old) were displayed as an isointense signal surrounded by a rim of high intensity signal. This peripheral zone most likely represented liquefaction at the clot's periphery and the initial formation of methemoglobin. T1 and T2 relaxation times were found to be very long for acute hematomas (first two days). T1 values of chronic hematomas (more than 3 days old) were comparatively short and in the same range as T1 of white matter. T2 values of chronic hematomas decreased also but remained very long.

Acute Disease↗
PubMed1986

Acute experimental cerebral ischemia: MR enhancement using Gd-DTPA.

The effects of a paramagnetic contrast agent, gadolinium-DTPA (Gd-DTPA), on magnetic resonance (MR) imaging of acute cerebral ischemia was investigated in a feline model of middle cerebral artery occlusion. Imaging was performed both before and after administration of an intravenous dose of 0.2 mmol/kg of Gd-DTPA. The animals were then sacrificed for pathologic correlation. No changes in intensity or relaxation times were noted before or after Gd-DTPA administration in two animals with 2 hours of occlusion. Infarcts were noted before and after contrast enhancement in all six cats with ischemia of greater than 16-hours duration. Gd-DTPA caused significant increase in intensity of infarct but not in that of normal cerebral tissue. Rapid enhancement was visible in infarcts of 16-24 hours, but such enhancement was slower in infarcts of 72-168 hours, presumably owing to slowed inflow caused by increased vasogenic edema in the latter group. Contrast enhancement of acute cerebral ischemic lesions with Gd-DTPA offers no improvement in sensitivity of MR imaging, although the conspicuity of the lesion may be improved. Additionally, contrast media may provide potential temporal and pathophysiological data for better characterization of cerebral ischemia.

Animals↗
PubMed1986

Pituitary adenomas: high-resolution MR imaging at 1.5 T.

The magnetic resonance (MR) images of 28 patients with surgically confirmed pituitary adenomas were retrospectively evaluated. The examinations were performed on a 1.5-T superconducting MR system using a multisection spin-echo technique with 3-mm-thick sections and a 256 X 256 matrix. T1- and T2-weighted images were obtained in sagittal and coronal planes. The MR findings were correlated with detailed operative reports and diagrams. There were 11 microadenomas and 17 macroadenomas. Ten of the microadenomas and all of the macroadenomas were accurately localized and their extent delineated, particularly on T1-weighted coronal sections. Adenomas typically appeared hypointense on T1-weighted coronal sections. The appearance on T2-weighted images was variable, and generally the lesions were less well seen. Involvement of parasellar structures, particularly the optic chiasm and cavernous sinuses, was accurately depicted. Cyst formation and hemorrhage could be characterized in some instances. In general, there was excellent correlation between MR imaging and operative findings.

Adenoma↗