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Biomedical subjects

W Kucharczyk

Publications and source records attributed to W Kucharczyk.

At least 91 records · Page 5Linked to original sources
PubMedDate not supplied

MR systems for image-guided therapy.

The use of MRI to guide and monitor interventional procedures requires the merging of surgical and MRI environments. The ideal magnet shape for homogeneity and efficiency is spherical, but this design provides no access. Opening the sphere to provide both patient and surgeon access suggests cylindrical or biplanar magnets. Cylindrical magnets have poor surgical access but provide good imaging capabilities, which can be used in conjunction with a neighboring but distinct surgical environment. Biplanar magnets provide more and better approaches to the patient, but generally with lower field strength. Vertical biplanar systems allows surgical approaches from above but reduce the access of support staff to the patient. A hybrid magnet design, which combines the benefits of both cylindrical and biplanar magnets, can provide increased access with simultaneous approach from two sides of the patient. Application-specific magnets can target a smaller region, leading to compact magnet designs that greatly expand access for both surgical intervention as well as patient support. As the field of interventional MRI matures, the suitability of each design to specific applications will be better understood, leading to more integrated system designs tailored to the needs of image-guided therapy.

Equipment Design↗
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MRI monitoring of interstitial microwave-induced heating and thermal lesions in rabbit brain in vivo.

The purpose of this experiment was to use MRI to monitor microwave heating and thermal damage of brain tissue in vivo. Interstitial microwave antennas were implanted into the cerebral hemispheres of seven anesthetized rabbits. Variable power of 30 to 100 W was applied for periods of 5 to 15 minutes and tissue temperature was monitored continuously. MR images were obtained throughout the procedure at 20-second intervals, using a spoiled gradient-echo sequence, without significant artifact. Magnitude, phase, and complex difference images all demonstrated temperature-related signal changes during heating. The findings were better visualized on the phase and complex difference images. Phase difference image analysis revealed an approximately linear relationship between phase change and temperature. Post-treatment thermal lesions measured up to 2.0 cm in size on pathologic specimens and exhibited a zonal pattern on spin-echo MR images.

Animals↗
PubMedDate not supplied

Very slow in-plane flow with gradient echo imaging.

It is well appreciated that gradient-echo imaging techniques with short recovery times are highly sensitive to flow. This article analyzes the effect of in-plane flow in gradient recalled acquisition in the steady state (GRASS). It is shown that there is loss of signal due to velocity-dependent dephasing effects at velo cities as slow as 0.2 mm per second. It is also shown that striations appear in GRASS images of flow phantoms. This effect, which has not been previously described, arises from a modulation of K-space in the phase-encoding direction during the transient approach to steady state. Although these bands can give the appearance of flow lines, they are completely artifactual and not readily interpretable. Thus, the appearance of in-plane fluid movement in clinical GRASS images is a complex combination of signal loss due to dephasing and artifactual banding. Therefore, the interpretation of flow in GRASS images should be attempted only with caution.

Humans↗
PubMedDate not supplied

Spontaneous dissection of the vertebral artery: MR findings.

Spontaneous (nontraumatic) dissection of the carotid and vertebral arteries, once thought to be rare, is being recognized and reported more frequently. We report one case of spontaneous dissection of the vertebral artery initially diagnosed by magnetic resonance imaging and subsequently confirmed by angiography.

Aortic Dissection↗
PubMedDate not supplied

Dimensions of the optic nerves, chiasm, and tracts: MR quantitative comparison between patients with optic atrophy and normals.

OBJECTIVE: The dimensions of the optic nerves, chiasm, and tracts were determined in normal patients and in patients with clinical evidence of optic atrophy to establish whether there was a significant difference between the two groups. MATERIALS AND METHODS: The authors analyzed thin section coronal MRI of 110 patients. Seventy-seven patients were normal, 20 had visual impairment without funduscopic evidence of optic atrophy, and 13 had visual impairment with funduscopic evidence of optic atrophy. RESULTS: The normal mean dimensions were (height x width): optic tracts 2.8 x 5.1 mm; nerves 3.0 x 5.9 mm; chiasm 3.5 x 15.0 mm. The mean dimensions in the optic atrophy group were significantly less (p < 0.01): optic tract 2.1 x 4.7 mm; nerve 2.7 x 5.8 mm; chiasm 2.6 x 12.6 mm. CONCLUSION: The reduced mean dimensions in the optic atrophy group are statistically significant but due to individual variability and errors inherent in measuring small structures, these measurements may be difficult to apply clinically. The most clinically useful measurement is the chiasm width. A width < 13.5 mm correlates well with funduscopic evidence of optic atrophy.

Adolescent↗
PubMedDate not supplied

Hypertrophic olivary degeneration: metaanalysis of the temporal evolution of MR findings.

BACKGROUND AND PURPOSE: Hypertrophic olivary degeneration (HOD) is usually caused by a lesion in the triangle of Guillain and Mollaret and presents clinically as palatal tremor. Although the imaging features have been well described, the temporal course of hypertrophy and T2 signal increase in the inferior olivary nucleus (ION) has not been fully characterized. Our purpose was to evaluate the time course of MR imaging features of HOD caused by a lesion within the triangle of Guillain and Mollaret. METHODS: The temporal progression of HOD in 45 patients with symptomatic palatal tremor was obtained by extrapolation of combined MR imaging data from six patients treated at our institution and 39 patients reported in the literature. The MR examinations and reports were reviewed for presence of hyperintense signal in the ION on T2-weighted images, hypertrophy of the ION, and an inciting lesion in the triangle of Guillain and Mollaret. The interval between the MR examination and the inciting lesion was determined. RESULTS: Increased olivary signal on T2-weighted images first appeared 1 month after the inciting lesion and persisted for at least 3 to 4 years. Olivary hypertrophy initially developed 6 months after the acute event and resolved by 3 to 4 years. CONCLUSION: Visible changes on MR images in the ION in patients with a lesion in the triangle of Guillain and Mollaret correlate well with the described sequential histopathologic findings.

Disease Progression↗
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Subacute necrotizing myelopathy: MR imaging in four pathologically proved cases.

This report describes the MR and correlative imaging findings of four histologically proved cases of subacute necrotizing myelopathy in which there was no evidence of a spinal dural arteriovenous fistula. Subacute necrotizing myelopathy is characterized clinically by progressive motor and sensory deterioration, and pathologically by necrosis in the spinal cord. Initial MR imaging showed focal enlargement of the spinal cord and nonspecific T1 and T2 lengthening. Rimlike enhancement was demonstrated in one case. Clinically, steroid therapy failed in all four patients. Follow-up MR scans showed two slightly enlarged lesions, one stable thoracolumbar lesion, and atrophy of a cervical lesion. Open spinal cord biopsies revealed foci of necrosis and abnormal parenchymal vessels with thickened hyalinized walls. A prolonged course distinguishes subacute necrotizing myelopathy from acute transverse myelitis, but the clinical course and imaging appearance are similar to those of intramedullary tumor. Rimlike rather than solid contrast enhancement may be a distinguishing feature. In the absence of a demonstrable spinal dural arteriovenous fistula, the radiologic differentiation of subacute necrotizing myelopathy from tumor is probably impossible, and biopsy establishes the correct diagnosis.

Acute Disease↗
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MR imaging of the brain in patients with diabetes insipidus.

Diabetes insipidus is a clinical syndrome characterized by the excretion of copious volumes of dilute urine combined with persistent intake of abnormally large quantities of fluid. There are two general forms of the disease, central (vasopressin deficient) and nephrogenic (vasopressin resistant). Diabetes insipidus of central origin most often results from lesions in the hypothalamic-neurohypophyseal axis. Twenty-six cases of central diabetes insipidus were evaluated with the use of high-field-strength MR imaging. A wide variety of precipitating conditions were found, including Langerhans cell histiocytosis, neoplasia, trauma, and infection. A thickened pituitary infundibulum was seen in most patients, and an absence of high intensity signal in the posterior pituitary lobe on T1-weighted images was seen in every case. Analysis of stalk morphology; associated brain findings; and correlation with the patient's age, sex, history, and radiographs of other body parts improved diagnostic specificity. When combined with clinical information, MR imaging is able to provide a specific diagnosis in almost all cases of central diabetes insipidus.

Adolescent↗
PubMedDate not supplied

The effect of phospholipid vesicles on the NMR relaxation of water: an explanation for the MR appearance of the neurohypophysis?

The normal neurohypophysis is hyperintense relative to brain and adenohypophysis on T1-weighted MR images, but the signal is not chemically shifted with respect to water. The source of the hyperintense MR signal in the normal neurohypophysis has been the subject of recent controversy. To date, an adequate biophysical explanation for the unusual imaging properties of the neurohypophysis has not been found. The purpose of this study was to investigate the effect of two chemical components of the neurohypophysis, phospholipids and vasopressin, on the MR signal. We synthesized phospholipid vesicles of the same size as those found in the neurohypophysis (100-200 nm) and quantitatively measured T1, T2, and chemical shift in a spectrometer at concentrations of 0-250 mg/ml of phospholipid. Imaging of the test materials was performed on a 1.5-T whole-body MR system using T1-weighted images, T2-weighted images, reduced bandwidth, and fat suppression techniques. The experiment was also performed with saline buffer, mineral oil, vasopressin, and vasopressin incorporated into the core of the phospholipid vesicles. We found that a solution containing phospholipid vesicles has T1 and T2 characteristics analogous to the neurohypophysis and that this solution exhibits a single peak that is not chemically shifted with respect to water. Vasopressin had no effect on the signal, neither in solution nor in the vesicles. We conclude that phospholipid acts as a relaxation enhancer of water protons and that the MR characteristics of the phospholipid vesicles can account for the observed MR properties of the neurohypophysis.

Humans↗
PubMedDate not supplied

MR imaging of acute experimental ischemia in cats.

The evolution of acute cerebral ischemia was documented by magnetic resonance (MR) imaging in 13 mongrel cats with occlusion of the middle cerebral artery through a transorbital approach. The animals were imaged under anesthesia at intervals from 30 min to 10 days after production of the lesion. An MR imager operating at 0.35 T was used with multislice, multi-spin-echo technique (TR = 500-2000 msec; TE = 28, 56 msec). The animals were sacrificed after imaging for pathologic correlation. Infarcts beyond 4 hr of age were visualized in all subjects. The earliest infarct was seen at 30 min (two cats) as an area of high signal intensity on T2-weighted images. In three other cats, however, 3-hr-old infarcts were not detectable. In one animal, a hemorrhage within a 1-week-old area of infarction was not characterized by MR imaging but was identified on CT scanning. The mass effect of the infarction appeared greatest at 2-4 days after infarction. The basal ganglia showed ischemic effects to best advantage. MR imaging offers previously unavailable sensitivity for the early noninvasive detection of cerebral ischemia in vivo.

Animals↗