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D W Chakeres

Publications and source records attributed to D W Chakeres.

63 records · Page 4Linked to original sources
PubMedDate not supplied

High-resolution 3DFT MR imaging of the endolymphatic duct and soft tissues of the otic capsule.

This study compares the visualization of otic capsule anatomy by thin-section three-dimensional Fourier transformation (3DFT) MR imaging with that by high-resolution CT. The osseous margins of the otic capsule are delineated by high-resolution CT, while MR displays the soft-tissue structures. Routine two-dimensional Fourier transformation (2DFT) spin-echo MR techniques have been limited by slice thickness and signal to noise. Previous longer TE 3DFT gradient-echo MR images of the otic structures have been degraded by magnetic susceptibility effects, which limit spatial resolution and decrease signal to noise. These effects are especially prevalent in the otic capsule, where small soft-tissue structures interface with surrounding air and bone. We developed a high-resolution 3DFT MR technique to image five normal subjects. MR images were compared with high-resolution CT images of the same subjects. Axial, sagittal, and coronal 3DFT gradient-echo MR images with a short TR/TE and 15 degrees flip angle were acquired on a General Electric 1.5-T Signa unit using a 3-in. circular, receive-only surface coil. Axial, sagittal, and coronal 1.5-mm-thick contiguous high-resolution CT bone-algorithm images were obtained also. There was a high correlation between the MR and CT findings. The 3DFT MR images demonstrated significantly higher spatial resolution and soft-tissue detail than the high-resolution CT images did. For example, the endolymphatic duct was seen on twice the number of consecutive sagittal and axial MR slices. Other soft-tissue otic capsule structures routinely seen on the 3DFT MR images included the entire facial nerve, membranous labyrinth including cochlea, and tensor tympani muscle. This study demonstrates a new high-resolution 3DFT MR technique for visualizing the soft-tissue microstructures of the otic capsule and achieves a level of spatial resolution beyond that possible with high-resolution CT.

Adult↗
PubMedDate not supplied

Acute subarachnoid hemorrhage: in vitro comparison of magnetic resonance and computed tomography.

The computed tomographic (CT) attenuation values and magnetic resonance (MR) signal intensities of simulated acute subarachnoid hemorrhage were compared systematically. In vitro MR and CT measurements (T1, T2, and Hounsfield units) were made of mixtures of normal human cerebrospinal fluid (CSF) and normal heparinized blood, ranging from 0% to 100% by volume. The mixtures were measured in a plexiglass phantom with a Siemens DR3 CT scanner for attenuation measurements (Hounsfield units) and in the Baylor Bruker Instruments Proton Scanner (6-MHz) using inversion-recovery and spin-echo pulse sequence techniques for T1- and T2-calculated relaxation times. A PRAXIS II (10.7 MHz permanent magnet) nonimaging unit was used to measure the relaxation times of the CSF/blood mixtures independently for comparison. The Hounsfield measurements of the densest parts of the layered mixtures showed increasing values with increasing amounts of hemorrhage (0% blood, 0 H; 100% blood, 66 H) in a nonlinear pattern. The T1 times of the mixtures decreased with increasing amounts of blood, ranging from 2200 msec to 500 msec for 100% CSF and 100% blood, respectively. The inverse of the T1 relaxation times was proportional to the percentage of blood. The T2 data for the mixtures were similar in character to the T1 relaxation times, except for shorter T2 times at high concentrations of blood. It was concluded the MRI distinguishes varying blood/CSF mixtures on the basis of relaxation times better than does CT on the basis of Hounsfield units. CT still has an imaging advantage, since high-concentration hemorrhage is clearly different from normal brain, while concentrated acute subarachnoid blood has relaxation times similar to normal brain and is nearly isointense on MRI.

Acute Disease↗
PubMedDate not supplied

MR imaging of acute spinal cord trauma.

The thoracic spinal cords of five mongrel dogs were imaged with a 1.5 T MR scanner before and after trauma induced by a well-established method of spinal cord impaction that produces central cord hemorrhagic necrosis. The anesthetized dogs were studied acutely with a 5-in. circular surface coil, 12-cm field of view, sagittal and axial partial-saturation (TR = 600, TE = 25 msec) and spin-echo (TR = 2000, TE = 25-100 msec) techniques. One normal dog was used as a control. The cords were surgically removed and histologically examined. Direct correlation of the pathologic findings and imaging data showed that at the level of trauma there was obliteration of epidural fat and CSF spaces secondary to central cord hemorrhage and edema. The traumatized cords expanded to fill the bony canal, and there was loss of visualization of the internal anatomy of the cord (gray- and white-matter structures). We conclude that MR can accurately identify cord hemorrhage and edema within a few hours of spinal trauma.

Animals↗
PubMedDate not supplied

Clinical significance of partial volume averaging of the temporal bone.

The effects of partial volume averaging on computed tomographic images of temporal bone structures were evaluated. The models chosen for study included a cadaver stapes, two metallic prosthetic stapes, and a formalin-fixed temporal bone. The studies measured the changes in apparent dimension and Hounsfield units with incremental filling of voxels with metallic densities, changes in the angle of tomographic section in relation to small bony structures, and the effects of soft-tissue silhouetting. The clinical significance of these changes is demonstrated by examples of this phenomenon seen in actual patient examinations. This study confirms that partial volume averaging is one of the primary limitations in resolution of small structures of the temporal bone.

Evaluation Studies as Topic↗
PubMedDate not supplied

Normal and pathologic radiographic anatomy of the motor innervation of the face.

Facial motor disorders, including facial paralysis, myokymia, dyskinesia, and hemifacial spasm, are common clinical problems in which radiographic evaluation plays a crucial role. Since every segment of the motor innervation of the face from the brain to the parotid gland can now be seen radiographically, radiologists must understand the normal anatomy, the common pathologic lesions at each level, and the clinical findings that help localize the abnormality so that the most sensitive and accurate radiographic approach can be planned. Though computed tomography alone allows for visualization of every segment, other methods such as cisternography, angiography, polytomography, sialography, and magnetic resonance imaging are complementary in specific disorders.

Aged↗
PubMedDate not supplied

MR of head and neck adenopathy in asymptomatic HIV-seropositive men.

PURPOSE: Adenopathy is a well-known component of AIDS-related complex. Our goal was to determine whether asymptomatic HIV-infected persons have characteristic findings of head and neck adenopathy on MR imaging and whether there is an association between the MR findings and the CD4 lymphocyte counts. METHODS: We blindly and retrospectively evaluated the distribution and size of lymphadenopathy seen on screening MR examinations that were performed on 50 asymptomatic HIV-positive male subjects and 50 age-matched HIV-negative control subjects. We also correlated the imaging findings in HIV-seropositive and -seronegative subjects with their CD4 counts. RESULTS: The HIV-positive subjects had a higher incidence of adenopathy compared with the controls. Statistically significant differences were found between the groups in size and number of neck lymph nodes, thickness of the adenoids, size of high, deep cervical-retropharyngeal lymph nodes, and presence of parotid abnormalities. We found a correlation between increasing lymph node size and decreasing CD4 levels. CONCLUSION: We conclude that HIV-positive asymptomatic patients have a high incidence of head and neck abnormalities including lymphadenopathy, and alteration in their CD4 counts not commonly seen in seronegative control subjects.

Adult↗
PubMedDate not supplied

The extracranial facial nerve: high resolution three-dimensional Fourier transform MR imaging.

PURPOSE: To investigate the use of high-resolution three-dimensional Fourier transform gradient-echo MR in evaluation of the extracranial facial nerve. METHODS: Nine normal subjects and one clinical patient were scanned. Several imaging parameters, including echo time, field-of-view, and the use of Gd-DTPA, were manipulated to determine the optimal technique. Adequate results were obtained in less than 7 minutes acquisition time using a T1-weighted (50/5.3) gradient-echo technique, with a 30 degree flip angle, a 12-cm field of view, 128 x 256 matrix, and 28 or 60 1.0-mm-thick contiguous sections. RESULTS: Gd-DTPA administration was not found useful in identifying the normal extracranial facial nerve. The proximal extracranial facial nerve was seen as a branching low signal intensity tubular structure on 10 to 20 contiguous images in all five volunteers in which this optimal technique was employed. Postprocessing of the images to produce curved oblique planar reconstructed images was useful to display long segments of the facial nerve on a single image. CONCLUSION: Our experience with high resolution three-dimensional Fourier transform MR imaging indicates that it can consistently demonstrate the intraparotid facial nerve on multiple contiguous images.

Adult↗