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Biomedical subjects

D W Chakeres

Publications and source records attributed to D W Chakeres.

At least 55 records · Page 3Linked to original sources
PubMed1984

Paragangliomas of the temporal bone: high-resolution CT studies.

Seventeen patients with 15 surgically proved paragangliomas involving the temporal bone and parapharyngeal spaces were examined with high-resolution computed tomography (CT). Scans were obtained in multiple axial (0 degree, 30 degrees) and coronal (70 degrees, 105 degrees) section planes using 1.5-mm collimation and table incrementation. The purpose of this study was to demonstrate the utility of HRCT in assessing tumor extent and size, with particular emphasis on intrinsic temporal bone invasion. The most characteristic HRCT signs of paraganglioma include: jugular fossa expansion, soft-tissue mass in the hypotympanum and sinus tympani, permeation of the infracochlear surface, dural ballooning adjacent to the jugular fossa (indicative of epidural tumor), anterior displacement of parapharyngeal fat planes, and extension into the proximal aspect of the eustachian canal. It is concluded that HRCT is the single most efficacious examination to determine tumor extent, especially when intratemporal invasion has occurred, and to define other additional clinically unsuspected lesions.

Diagnosis, Differential↗
PubMed1984

The Meckel cave: computed tomographic study. Part I: Normal anatomy; Part II: Pathology.

A formalin-fixed cadaver head with air filling the cisternal and ventricular spaces was scanned by high-resolution computed tomography (CT) in multiple planes (axial, coronal, and sagittal) through the Meckel cave. Correlation of the CT appearance of the Meckel cave was made with an anatomic dissection and whole-head band saw cross-sections. The appearance of the Meckel caves in normal patients was defined using similar high-resolution CT technique with intravenous and intrathecal contrast enhancement. CT techniques allowed consistent and accurate definition of the Meckel cave, the fifth cranial nerve, and adjacent anatomic structures. CT findings of 13 patients with lesions of the Meckel cave are also reviewed, including six trigeminal schwannomas, three meningiomas, two secondary tumors, one glioma, and one congenital fatty tumor. Surgical confirmation was present in 11 cases. Diagnosis and determination of the extent of Meckel cave lesions is possible with the use of high-resolution CT.

Carotid Artery, Internal↗
PubMed1984

Cerebral angiography: a device to reduce exposure to the eye lens.

A simple inexpensive eyeshield, made of thin sheets of lead apron material laminated to a 5- X 15-cm sheet of x-ray film base, which is taped to the temple nearest the lateral x-ray tube prior to the completion of standard simultaneous biplane posteroanterior (PA) and lateral angiograms, results in a significant reduction in radiation exposure to the lens of the eye. The shield protects the eye lens without significantly imparing the quality of the radiographs. Compared with reported radiation exposure for standard cerebral vascular angiography, use of this device can produce a 20-fold drop in radiation exposure to the lens.

Cerebral Angiography↗
PubMed1984

CT of ear structures: a tailored approach.

A major advance in imaging of the ear structures has occurred with the development of high-resolution, thin-section computed tomography. The purpose of this article is to explain a technique tailored to the CT evaluation of specific anatomic structures. The normal CT anatomy of the ear is demonstrated.

Carotid Artery, Internal↗
PubMed1983

Computed tomography demonstration of a hypothalamic metastasis.

This case report describes a patient who presented with panhypopituitarism secondary to hypothalamic metastasis. A primary hypothalamic abnormality was suggested by computed tomographic (CT) demonstration of a small enhancing circular mass centered within the hypothalamus. Sellar radiographs and cerebral angiography were normal.

Aged↗
PubMed1983

A systematic technique for comprehensive evaluation of the temporal bone by computed tomography.

A systematic method for comprehensive visualization of the temporal bone structures using thin-section, high-resolution computed tomography (CT) was developed. In relation to the anthropologic baseline (0 degrees), four separate tomographic planes of 0 degrees, 30 degrees, 70 degrees, and 105 degrees were each found to optimize different aspects of temporal bone evaluation with significant reduction in the radiation dose to the lens. Virtually all patients were able to maintain the necessary head positioning that allows for both direct coronal and axial sections. It is concluded that in the majority of cases, thin-section, high-resolution CT can replace polytomography, although the examinations may be complementary in the evaluation of certain abnormalities.

Cornea↗
PubMed1983

Brainstem and related structures: normal CT anatomy using direct longitudinal scanning with metrizamide cisternography.

A method for direct longitudinal imaging of the cisternal spaces surrounding the brainstem and related structures by CT was developed for use with metrizamide. Multiple 1.5-mm or 5-mm sections were obtained at a 70 degrees angle to the anthropologic baseline, allowing excellent visualization of the brainstem, the cranial nerves, the parasellar structures, and the cerebellum. Thin section, high resolution CT scans of a formalin-fixed normal cadaver head were obtained, and the specimen was then dissected in the same tomographic plane for correlation with normal anatomy. The technique described produces a simple, highly accurate evaluation of the normal and pathologic anatomy of the brainstem and adjacent structures. The method of study allows for visualization of structures and relationships previously unattainable by any other clinical radiographic imaging technique.

Brain Stem↗
PubMedDate not supplied

Optimization of submillimeter-resolution MR imaging methods for the inner ear.

Submillimeter-resolution magnetic resonance (MR) imaging of the inner ear is valuable for diagnosis and treatment planning. Its main advantage for investigations of underlying disease is that it can directly depict the fluid spaces of the membranous labyrinth rather than define only the bony canal, as does computed tomography. A systematic evaluation of factors influencing high-resolution three-dimensional (3D) gradient-echo imaging of the inner ear with a standard clinical MR system is presented. This includes the evaluation of various radio-frequency coils, the design of steady-state pulse sequences, and the optimization of acquisition parameters. A quantitative analysis was facilitated by computer simulations and image processing. The highest signal-to-noise ratio for the membranous labyrinth was obtained with a single 3-inch (7.6-cm) receiver coil and a 3D GRASS (gradient-recalled acquisition in the steady state) sequence with the minimal achievable TR msec/TE msec of 25/7 and a 40 degrees--60 degrees flip angle, which yielded acceptable images with minimal voxel volumes of 0.1 mm3 in 14 minutes.

Ear, Inner↗
PubMedDate not supplied

A segment-interleaved motion-compensated acquisition in the steady state (SIMCAST) technique for high resolution imaging of the inner ear.

MRI, with ever-increasing spatial resolution, recently has depicted progressively more anatomic details of the inner ear and is playing an important role in the diagnostic evaluation of patients with sensorineural hearing loss. We present a three-dimensional (3D) segment-interleaved, motion-compensated acquisition in steady state (SIMCAST) sequence that allows further increase in spatial resolution in reasonable scan times minimizing artifacts due to susceptibility and motion. The sequence uses gradient moment nulling over TR and segmented interleaved acquisition of multiple data sets with different radiofrequency (RF) phase-cycling schemes. Combination of data from multiple acquisitions by averaging and maximum intensity projection were compared. Images of phantoms and in vivo inner ears were obtained with both full and fractional echoes and compared with other high resolution techniques such as three-dimensional gradient-echo and two-dimensional (2D) and three-dimensional fast spin-echo (FSE) sequences. The new sequence achieves improved signal-to-noise ratio (SNR) and spatial resolution resulting in improved depiction of inner ear structures.

Adult↗
PubMedDate not supplied

Clivus fracture: CT demonstration.

A transverse fracture of the clivus through the region of the fused sphenooccipital synchondrosis involving the carotid canals was studied by CT. The patient also had bilateral temporal bone fractures with otorrhea and a carotid cavernous fistula. The literature related to clivus fractures is reviewed.

Accidents, Traffic↗
PubMedDate not supplied

Human leptomeningeal and cortical vascular anatomy of the cerebral cortex at 8 Tesla.

PURPOSE: The purpose of this work was to describe the human leptomeningeal and cortical vascular anatomy as seen at high resolution on an 8 T UHFMRI system. METHOD: With a 1024 x 1024 matrix, axial gradient echo images of the cerebral cortex were acquired on a human volunteer at 8 T with TR 500 ms, TE 16 ms, flip angle 22.5 degrees, bandwidth 53 kHz, and slice thickness 2.84 mm. The same subject was evaluated at 1.5 T using similar parameters. The images were then reviewed in detail and compared with known cortical and leptomeningeal vascular anatomy. RESULTS: Two hundred forty micron in-plane resolution images of the human brain were acquired at 8 T without evident artifact from susceptibility distortions, RF penetration, or dielectric resonances. The CSF, gray matter, and white matter structures were well discerned. The microscopic leptomeningeal vascular anatomy was well visualized, and the course of small perforating cortical vessels could be followed from the cortical surface to the white matter junction. CONCLUSION: Initial 8 T images of the brain demonstrate detailed leptomeningeal and cortical vascular anatomy.

Arachnoid↗
PubMedDate not supplied

High resolution MRI of the deep brain vascular anatomy at 8 Tesla: susceptibility-based enhancement of the venous structures.

PURPOSE: The purpose of this work was to describe the deep vascular anatomy of the human brain using high resolution MR gradient echo imaging at 8 T. METHOD: Gradient echo images were acquired from the human head using a transverse electromagnetic resonator operating in quadrature and tuned to 340 MHz. Typical acquisition parameters were as follows: matrix = 1,024 x 1,024, flip angle = 45 degrees, TR = 750 ms, TE = 17 ms, FOV = 20 cm, slice thickness = 2 mm. This resulted in an in-plane resolution of approximately 200 microm. Images were analyzed, and vascular structures were identified on the basis of location and course. RESULTS: High resolution ultra high field magnetic resonance imaging (UHFMRI) enabled the visualization of many small vessels deep within the brain. These vessels were typically detected as signal voids, and the majority represented veins. The prevalence of the venous vasculature was attributed largely to the magnetic susceptibility of deoxyhemoglobin. It was possible to identify venous structures expected to measure below 100 microm in size. Perforating venous drainage within the deep gray structures was identified along with their parent vessels. The course of arterial perforators was more difficult to follow and not as readily identified as their venous counterparts. CONCLUSION: The application of high resolution gradient echo methods in UHFMRI provides a unique detailed view of particularly the deep venous vasculature of the human brain.

Arteries↗
PubMedDate not supplied

High resolution MRI of the deep gray nuclei at 8 Tesla.

PURPOSE: High resolution MR images obtained from a normal human volunteer at 8 T are utilized to describe the appearance of iron-containing deep gray nuclei at this field strength. METHOD: High resolution (1,024 x 1,024 matrix) near-axial gradient echo images of the deep gray nuclei were acquired on a human volunteer by using an 8 T scanner. The images were acquired using a transverse electromagnetic resonator operating in quadrature. The following parameters were utilized: TR = 750 ms, TE = 17 ms, flip angle = 45 degrees, receiver bandwidth = 50 kHz, slice thickness = 2 mm, FOV = 20 cm. The 8 T images were reviewed and correlated to the known anatomy of the deep nuclei by comparing them with images observed at lower field strength, published diagrams, and histologic sections. In addition, the appearance of the nuclei was related to the known imaging characteristics of brain iron at lower fields. RESULTS: The caudate, globus pallidus, putamen, thalami, substantia nigra, and red nuclei were clearly identified. The structures with the highest levels of iron, the globus pallidus, substantia nigra, and red nuclei, demonstrated significantly decreased signal, providing a map of iron distribution in the human brain. CONCLUSION: Preliminary imaging at 8 T demonstrates the ability to acquire ultra high resolution images of the deep nuclei, with signal characteristics believed to represent the distribution of brain iron. This may prove to be important in the early diagnosis of several neurodegenerative disorders.

Adult↗
PubMedDate not supplied

High resolution MRI of the brainstem at 8 T.

A recently developed ultra high field MRI system operating at 8 T (UHFMRI) was applied for brainstem imaging. UHFMRI was performed in five healthy volunteers (three men, two women; age range 34--46 years). Sagittal and axial slices were obtained with the following settings: GE, TR 750--1,000 ms, TE 7-9 ms, FOV 20 cm, matrix 1,024 x 1,024 or 512 x 512 points, slice thickness 2 mm, resolution 195 or 390 microm/pixel. The brainstem structures were assigned based on anatomy and course. Images with good signal strength and homogeneity were acquired from the midbrain and the pons. Main intraaxial structures could be directly visualized. The periaqueductal gray matter and nuclei had higher signal intensity than the predominantly white matter structures such as the corticobulbar/corticopontine/corticospinal tracts, the sensory lemnisci, and the medial longitudinal fasciculus. Structures with high iron content such as the substantia nigra and the red nucleus were seen as prominent signal hypointensities. Numerous vessels traversing the brainstem including small perforators were also distinguished. It is concluded that UHFMRI enables the acquisition of high quality images of the upper brainstem with details approaching that of histologic specimen.

Adult↗
PubMedDate not supplied

Canine abdominal MRI at 8 Tesla: initial experience with conventional gradient-recalled echo and rapid acquisition with relaxation enhancement (RARE) techniques.

PURPOSE: In this manuscript, we present our initial experience with MRI of the abdomen at 8 T of canine subjects both alive and dead. Our hypothesis is that abdominal imaging at 8 T should be possible and should demonstrate unique information. To our knowledge, this is the first description of imaging characteristics of the abdomen at such field strengths using a human MR scanner. METHOD: An 8 T, 80 cm magnet housed in our department since 1998 was used for our study. GRE and rapid acquisition by relaxation enhancement (RARE) pulse sequences were selected to give reasonable slice profiles with relatively low power. Three dogs were imaged alive and after being killed. RESULTS: Our initial results show excellent signal-to-noise ratio and good RF penetration. Structures in the center of the abdomen were well visualized. Homogeneous signal was noted throughout each image without dielectric resonance artifact. Magnetic susceptibility artifacts were most severe on the GRE sequences. On the GRE sequences, the images appeared relatively T2 weighted. Signal voids were seen due to gas in the lung and bowel and susceptibility artifact at subcutaneous fat-muscle boundaries. The liver and spleen showed similar signal intensity, hypointense to subcutaneous muscle at low TE values. There was little internal anatomy of the liver or spleen visible except for the vessels. The kidney, in contrast, demonstrated very good internal structure with visualization of the cortex and medulla. Linear signal voids were depicted in the expected location of normal renal vascular anatomy on the GRE sequences. On the RARE sequences, the images also appeared T2 weighted. Magnetic susceptibility artifacts at subcutaneous fat-muscle boundaries were absent. Signal voids were noted in vessels with blood flow and gas. The liver and spleen were of similar signal intensity and slightly hypointense to muscle. The kidney and pancreas were of higher signal intensity than liver and subcutaneous muscle. The gallbladder wall demonstrated a striated pattern of two layers, with an inner hypointense and an outer hyperintense layer on the RARE sequence. The gastric wall demonstrated a striated pattern of five layers on the RARE sequence. CONCLUSION: Images of the dog abdomen with the world's first ultra high field 8 T magnet show robust image quality and excellent spatial resolution. Image contrast is greatest on the RARE sequence, and susceptibility artifact is strongest on the GRE sequence.

Abdomen↗