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Biomedical subjects

A S Smith

Publications and source records attributed to A S Smith.

At least 37 records · Page 2Linked to original sources
PubMed1990

Intracranial chemical-shift artifacts on MR images of the brain: observations and relation to sampling bandwidth.

The purpose of this study was to evaluate the presence of chemical-shift artifacts on cranial MR and to illustrate the interrelationship among chemical-shift artifacts, variable acquisition parameters, and field strength. Measurements of chemical-shift artifacts were performed on scans obtained from a volunteer imaged in a 1.5-T General Electric system at bandwidths of 8, 16, and 32 kHz, using a 24-cm field of view and an 8-kHz bandwidth with a 48-cm field of view. Chemical-shift displacements at 8 kHz were 6.6 and 14.2 mm at the respective fields of view. Retrospective review was also performed in 77 cases of cranial MR performed on a 1.4-T Technicare unit for the presence and source of chemical-shift artifact on spin-density and T2-weighted images. Most data reviewed showed no significant interference of chemical-shift artifacts on cranial images. An artifactual subdural fluid collection was a common artifact (n = 30/77). When present, this was due to shift of fat signal from subcutaneous tissues onto the brain in patients younger than 10 years old (n = 4/10) and correlated with the distance between brain and subcutaneous fat of less than the linear value of the chemical shift. When this artifact was present in adults (n = 25/67), it was due to shift of the medullary fat signal across the inner table of the skull. The latter also occurred in one child under 10. Apparent location shifts, consistent with the displacement expected from the chemical-shift artifact, were noted in five of five cases of intracranial lipoma. In one of these, the chemical-shift artifact disguised the presence of a large associated vessel. The method of calculating the linear displacement of chemical-shift artifact is reviewed, and the interrelationship of machine parameters and chemical-shift artifact is illustrated. Chemical-shift artifact increases proportionally with field strength and field of view. Increasing the bandwidth to decrease chemical-shift artifact has a resultant penalty in signal to noise but allows a lower time to echo. A lower time to echo can also be accomplished without increasing the bandwidth if asymmetric sampling is used. Awareness of the relationships among chemical-shift artifacts, acquisition parameters, and field strengths can result in a more tailored examination when the chemical-shift artifact is going to be a significant factor. In addition, interpreter error can be avoided by awareness of these relationships when reviewing images from outside institutions.

Adolescent↗
PubMed1989

Magnetic resonance imaging of disturbances in neuronal migration: illustration of an embryologic process.

Twenty-three cases of suspected congenital anomalies involving disorders of cortical proliferation, migration or cortication were retrospectively collected over an 18 month period. Pathologic confirmation was present in five cases. The theoretical sequential stages of cortical development are discussed as keys to the interpretation of MR images of anomalies resulting from arrest of the developmental process. MRI is the imaging modality of choice for suspected defects of cortex formation since it distinguishes gray from white matter, delineates the corticomedullary junction, records details of cortical surfaces, detects abnormal white matter, identifies heterotopias and records unrelated congenital abnormalities. Histopathologic confirmation of two cases of isolated heterotopia and three cases of polymicrogyria were available. Comparative images of MR, CT and pathologic specimens are presented.

Brain↗
PubMed1989

High-signal periventricular lesions in patients with sarcoidosis: neurosarcoidosis or multiple sclerosis?

The vast majority of periventricular abnormalities visualized with MR imaging in patients less than 50 years old represents multiple sclerosis (MS) lesions. There are many other causes of periventricular lesions, most of which can be differentiated from MS on the basis of history and physical or MR findings. Five cases of biopsy- or Kveim test-proved sarcoidosis with MR findings consistent with MS are reported. Each of these patients, diagnosed as having sarcoidosis, had symptoms identical to those seen in MS. Although these patients have not had histologic characterization of the intraparenchymal lesions seen on MR, they illustrate the difficulty of differentiating sarcoidosis with CNS involvement from MS in some patients on the basis of clinical, radiographic, electrodiagnostic, or CSF testing. This series contributes to a growing body of evidence that neurosarcoidosis probably should be included in the differential diagnosis of isolated periventricular lesions in patients less than 50 years old.

Adult↗
PubMed1989

MR imaging characteristics of tuberculous spondylitis vs vertebral osteomyelitis.

Retrospective evaluation was made of four patients with tuberculous spondylitis who had been studied by MR with T1- and T2-weighted images in the sagittal plane and spin-density-weighted images in the axial plane. Evaluation was made of the distribution of abnormal signals within the body and posterior elements of the vertebrae, the intervertebral disk, and the associated paraspinal and epidural areas. In two of the cases, three-level involvement was seen with noninvolvement of intervening disks; metastases were misdiagnosed. One patient had anterior/inferior erosion of the vertebral body without visualization of the disk. The last patient had the more typical MR characteristics of intervertebral disk infection. Plain film examination showed only degenerative changes in three of the four cases. MR revealed more extensive involvement than the plain films did. Involvement of the posterior element and posterior vertebral body was prominent in three of the four cases. This is a significant finding since these patients are more likely to have neurologic symptoms and require laminectomy. Follow-up examinations in two cases showed increased signal on T1-weighted images, suggesting infiltration of hemopoietic marrow with fat, as has been described for degenerative osteoarthritis. The anatomy of the microcirculation of the vertebral body is related to the patterns of vertebral osteomyelitis, and discrepancies can be seen between the findings in our cases and the MR criteria previously noted for pyogenic vertebral osteomyelitis. The MR findings in our patients generally were more typical of neoplasm than of infection. These findings may reflect the characteristics of the tuberculous organism relative to the age-dependent pattern of vertebral microcirculation. Correct diagnosis of tuberculous spondylitis in young to middle-aged adults requires correlation of MR and clinical findings.

Adolescent↗
PubMed1988

Association of heterotopic gray matter with seizures: MR imaging. Work in progress.

Heterotopic gray matter, which previously had been associated with severe congenital malformations of the brain and developmental delay, was found without these associated conditions. The authors found ten cases of heterotopic gray matter on magnetic resonance (MR) images. The lesions had a signal intensity that was isointense compared with that of gray matter on T1, spin-density, and T2-weighted images. Nine of the ten cases were associated with a seizure disorder. The tenth case, discovered during a workup for metastatic lung disease, was confirmed with pathologic studies. Heterotopic gray matter is the presence of cortical neurons in an abnormal location, which may be periventricular (nodular) or within the white matter (laminar). A knowledge of heterotopic gray matter and its association with seizures may prevent the misinterpretation of findings on MR images.

Adolescent↗
PubMed1985

Magnetic resonance with marked T2-weighted images: improved demonstration of brain lesions, tumor, and edema.

The object of this study was to determine the sensitivity of magnetic resonance (MR) for imaging intracranial lesions with heavily T2-weighted images compared with that of computed tomographic (CT) and T1-weighted images. Fifty-five patients with known intracranial pathology consisting of primary neurogenic tumors, brain infarcts, demyelinating disease, and metastases were studied by MR and CT. Patients were studied with either 0.6 or 1.5 T systems with T1- and T2-weighted radiofrequency pulse sequences. The heavily T2-weighted images were found to be superior to the T1-weighted images in terms of sensitivity, with 168 lesions found versus 86 by CT and 104 by T1-weighted imaging.

Brain Edema↗
PubMedDate not supplied

Lumen definition in MR angiography.

Factors affecting blood vessel lumen definition for two-dimensional and three-dimensional inflow magnetic resonance (MR) imaging methods are considered. Vessel definition is affected (a) by the amount of dephasing of the blood in the vessels, both for uncompensated and velocity-compensated gradients; (b) by the image reconstruction technique (normal Fourier reconstruction when asymmetric echoes are collected or a maximum-intensity projection technique in post-processing); (c) by loss of signal due to T2* dephasing; (d) by misregistration; (e) by vessel wall motion; and (f) by partial-volume effects. The first two factors were found to dominate for resolution on the order of 1 mm3. To overcome these dephasing problems, the authors developed asymmetric echo, velocity-compensated sequences with TEs as short as 4.8 msec. The data were then reconstructed with an iterative partial Fourier algorithm, enabling improved lumen definition to be obtained in phantoms and in vivo.

Artifacts↗
PubMedDate not supplied

Gadolinium-enhanced high-resolution MR angiography with adaptive vessel tracking: preliminary results in the intracranial circulation.

To overcome problems associated with poor contrast between vessels and background tissue in time-of-flight magnetic resonance angiography, the role of intravenous gadopentetate dimeglumine in conjunction with a postprocessing adaptive vessel tracking scheme was studied. Vessel tracking makes it possible to discriminate arteries from veins, to prevent problems associated with other bright tissues on maximum-intensity projections, and to increase the signal-to-noise ratio. Short, asymmetric, velocity-compensated field echoes were used in conjunction with high-resolution imaging techniques to spatially discriminate between adjacent vessels and stationary background tissue. Gadopentetate dimeglumine was shown to be useful for visualization of small vessels, aneurysms, and regions of slow flow, when used with this post-processing scheme.

Adolescent↗
PubMedDate not supplied

Automated local maximum-intensity projection with three-dimensional vessel tracking.

Despite the simplicity and widespread acceptance of the maximum-intensity-projection (MIP) technique for displaying three-dimensional (3D) magnetic resonance angiographic data, several disadvantages are associated with MIP as it is applied to all of the 3D data. These include elevated noise level, reduced contrast between small vessels and background tissue, and the inability to distinguish arteries from veins. The authors have developed a 3D vessel tracking method combined with a local MIP around a given vessel to complement conventional MIP and alleviate these problems. The method is referred to as a traveling MIP (TMIP). TMIP was evaluated in both patients and healthy volunteers. The results indicate that TMIP provides better contrast between vessels and background tissue, better lumen definition, and better vascular visualization than either MIP or vessel tracking alone.

Algorithms↗
PubMedDate not supplied

Patient participation in changing behaviors.

Individuals who did not participate in an organized cardiac rehabilitation program were interviewed to discover how they made lifestyle changes after a cardiac illness. The themes obtained from the analysis of the interview data were consistent with the components of Barrett's nursing theory of power as knowing participation in change. Implications for professional nursing practice related to the themes are described.

Health Behavior↗
PubMedDate not supplied

Periventricular involvement in CNS lymphomatoid granulomatosis: MR demonstration.

We report a case of intracranial lymphomatoid granulomatosis shown by magnetic resonance (MR) as a focal periventricular lesion. The patient had an undulant clinical course manifested by multiple peripheral and cranial neuropathies. Both the clinical course and the MR findings were difficult to differentiate from an unusual presentation of multiple sclerosis. Autopsy correlation was obtained after the patient succumbed to cardiopulmonary arrest during status epilepticus.

Adult↗
PubMedDate not supplied

Estimation of maxillary alveolar cleft volume by three-dimensional CT.

Reconstruction of cleft lip and palate deformities is a challenging problem involving a variety of the subspecialties of surgery, dentistry, and medicine as well as radiology. This paper outlines the contribution of three-dimensional CT to preoperative treatment planning for bone grafting of a maxillary cleft alveolus.

Adolescent↗
PubMedDate not supplied

MR angiography of Takayasu arteritis.

We describe MR angiographic findings utilizing a three-dimensional time-of-flight technique and compare the results with angiography in a case of suspected Takayasu arteritis involving vessels to the neck and upper extremities.

Adult↗
PubMedDate not supplied

Use of the delayed mask for improved demonstration of aneurysms on intraarterial DSA.

PURPOSE: We retrospectively explored the use of the delayed mask technique for intraarterial digital subtraction angiography (IADSA) to demonstrate the anatomy of aneurysm necks. METHODS: The delayed mask technique was utilized in 22 patients who had craniotomies for aneurysms demonstrated at angiography. The operative notes were compared to the angiographic findings of both the traditionally masked IADSA and the delayed mask IADSA. In addition, an in vitro model was constructed to examine the relationship between the size of the aneurysm neck and the ability to indirectly define its anatomy by demonstrating the flow jet. RESULTS: In 12 of 22 cases, the delayed mask technique demonstrated a systolic jet that was not demonstrated by traditional subtraction techniques. In nine of 12 cases, the delayed mask technique gave more specific information regarding the size, location, and orientation of the aneurysm neck. CONCLUSION: The delayed mask technique can add important information regarding the anatomy of aneurysm without adding time or risk to the procedure.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Diagnosis of ruptured intracranial dermoid cyst: value MR over CT.

The CT and MR findings of seven patients with pathologically proved ruptured dermoid cysts were reviewed to analyze the MR characteristics and to see if MR evaluation had significant advantages over CT. In six cases, both CT and MR identified fatty material in the CSF spaces. Hemorrhage complicated preoperative diagnosis in one case. Patterns of extraaxial fat distribution were as follows: intraventricular fat/CSF levels (three patients), generalized subarachnoid spread (six patients), and localized subarachnoid spread with sulcal widening (one patient). There was no correlation between fat distribution and clinical symptoms. MR showed the vascular involvement better than CT did in five of seven cases, and showed extension of the cysts into the skull base in two cases. Signal intensity of the solid mass was low on T1-weighted MR images and inhomogeneously high on T2-weighted images, which correlated pathologically with the presence of crystal cholesterol, hair, sebaceous glands, and epithelial cells in all cases. On MR, brain parenchyma showed little edema or other reaction to the masses, which were typically large. The value of MR over CT in the examination of ruptured dermoid cysts is the conspicuity of the extent of subarachnoid spread, involvement of the extraaxial structures, and evidence of vascular compromise, which can obviate angiography. MR had no advantage over CT in making the initial diagnosis of ruptured dermoid, but it would be the preferred preoperative study.

Adult↗
PubMedDate not supplied

MR of ballistic materials: imaging artifacts and potential hazards.

The most common ballistic materials available in the urban setting were studied for their MR effects on deflection force, rotation, heating, and imaging artifacts at 1.5 T to determine the potential efficacy and safety for imaging patients with ballistic injuries. The 28 missiles tested covered the range of bullet types and materials suggested by the Cleveland Police Department. The deflection force was measured by the New method. Rotation was evaluated 30 min after bullets had been placed in a 10% (weight per weight) ballistic gelatin designed to simulate brain tissue, with the long axis of the bullet placed parallel and perpendicular to the Z axis of the magnet. Heating was measured with alcohol thermometers by imaging for 1 hr alternatively with gradient-echo and spin-echo sequences (RF absorption = 0.033 and 0.326 w/kg respectively). Image artifacts on routine sequences were evaluated. All the steel-containing bullets except for the Winchester armor-piercing 38 caliber exhibited deflection. A nonsteel 7.38-mm Mauser also deflected. Deflection range was 514 to 15,504 dynes. Rotation occurred when the bullets were not parallel to the Z axis. Temperature changes were not significant. Deflecting projectiles resulted in obliteration of the image. The artifacts from other projectiles were small but varied by content. The artifact of the Winchester armor-piercing 38-caliber bullet was similar to those without steel. Bullets that contain steel or ferromagnetic contaminates such as nickel can be rotated within the MR unit.(ABSTRACT TRUNCATED AT 250 WORDS)

Firearms↗