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Biomedical subjects

R D Tien

Publications and source records attributed to R D Tien.

At least 55 records · Page 3Linked to original sources
PubMed1994

Terminal syringohydromyelia and occult spinal dysraphism.

Terminal syringohydromyelia is a cystic dilatation of the lower third of the spinal cord. The authors describe its incidence and characteristics, its frequent association with occult spinal dysraphism, and its clinical significance and need for surgical treatment. All 143 cases of occult spinal dysraphism treated at the Duke University Medical Center between 1972 and 1992 were reviewed. A terminal syrinx was found in 24 (27%) of the 90 cases that were evaluated by magnetic resonance (MR) imaging. In contrast three (6.2%) of 48 cases evaluated by myelography and postmyelographic computerized tomography had a syrinx documented. The relative radiographic severity of the different syringes was estimated by using measurements of the syrinx and spinal cord on the MR images, classifying the cysts into large and small. Large syringes were frequently symptomatic, commonly presenting with pain, motor and sensory deficits of the lower extremities, scoliosis, and bowel and bladder dysfunction. Terminal syringohydromyelia with occult spinal dysraphic lesions was most often associated with tethered spinal cord from a tight filum terminale in the presence of an anorectal anomaly (67% of cases), meningocele manqué (54%), and diastematomyelia (38%). An infrequent association was seen with other spinal cord anomalies. The results of surgical management of terminal syringohydromyelia were analyzed, highlighting the necessity and effectiveness of shunting the large cysts, especially in the setting of a progressive symptomatology. Of the 11 patients with shunts who underwent MR imaging, 10 showed either complete or significant resolution of the syrinx; all five patients who had presented with pain (mainly back pain) showed complete resolution of the pain after shunting; finally, one-third of patients with shunt placement had significant postoperative improvement in their neurological examination, whereas none worsened. It is stressed that terminal syringohydromyelia is an important pathological entity that should be considered in patients with occult spinal dysraphism, and treated surgically when clinically or radiographically significant.

Adolescent↗
PubMed1994

Sellar and parasellar lesions involving the skull base.

Lesions of the central skull base, most notably the sphenoid bone, commonly originate from the endocranial soft tissues. Although most commonly identified with pituitary macroadenomas, skull base erosion, destruction, and remodeling may be seen with a variety of congenital, neoplastic, cystic, vascular, and inflammatory lesions involving the sellar and parasellar soft tissues.

Bone Diseases↗
PubMed1993

Comparison of serial PET and MRI scans in a pediatric patient with a brainstem glioma.

Profound clinical deficits may be associated with insults to the brainstem, making management of patients with brainstem gliomas very complex. Small changes in the radiographic appearance of a brainstem tumor may be associated with significant clinical deterioration. Furthermore, both magnetic resonance imaging and computed tomography are frequently unable to differentiate between therapy-related tissue reactions and progressive tumor. Two clinical scenarios particularly difficult to resolve include: (1) transient radiographic and clinical deterioration following hyperfractionated radiotherapy, and (2) clinical deterioration in a patient who has failed initial therapy, but has stable radiographic findings following a second therapy. We report a child with a pontine glioma whose tumor progression was demonstrated more convincingly with a 18F-deoxyglucose positron emission scan than with magnetic resonance imaging. PET scans may be helpful in confirming that tumor progression is responsible for clinical deterioration in a patient whose MRI scans remain stable.

Brain Neoplasms↗
PubMed1993

Pulsatile motion artifact reduction in 3D steady-state-free-precession-echo brain imaging.

An image can be made from the echo of a steady-state-free-precession and pulse sequences for this purpose have been implemented on various commercial systems under such names as "CE-FAST" and "SSFP" (herein generically termed SSFP-Echo). Such sequences can be employed to achieve strong T2-weighting with reduced T2* effects, but are limited by their sensitivity to flow and motion which produce artifacts. Simple considerations indicate that this sensitivity is primarily related to the (implementation-dependent) moments of the imaging gradients. In this work, MR imaging of the brain using a standard implementation of the sequence with large moment "crusher" gradients on the slice select axis (to dephase the FID of the SSFP) is compared to a modified implementation with reduced moment gradient pulses and different radiofrequency (RF) phase cycling. Asymmetric echo acquisition and narrowed bandwidth was used to further reduce gradient moments. The sensitivity of this sequence to flow and motion artifacts, especially for motion perpendicular to the slice, is thus expected to be significantly reduced. The modified sequence was found to have flow and motion artifacts reduced by a factor of five in the axial plane and a factor of two in the coronal plane. These modifications can thus significantly reduce the flow and motion artifacts commonly seen in conventional images of the SSFP echo with little or no penalty in scan time or signal-to-noise ratio.

Artifacts↗
PubMed1993

Three dimensional MR gradient recalled echo imaging of the inner ear: comparison of FID and echo imaging techniques.

The detailed structures of the inner ear make this region a diagnostic challenge for radiologists. Thin section high resolution CT is the "gold standard" for studies of the fine bony detail of the inner ear. Although CT can delineate bony structures, fine soft tissue details surrounded by CSF/endolymph (such as nerves in the internal auditory canal) are not easily identified. Conventional MR spin-echo T2-weighted images provide good image contrast for such structures, but the current commercially available minimum slice thickness of approximately 2-3 mm is too thick for the inner ear. Volume gradient recalled echo (GRE) MR imaging techniques can be used to achieve thin slices (< 2 mm) while maintaining adequate contrast for detailed examination. In the work reported here a volume GRE sequence that images the echo formed in a steady-state-free-precession (termed "CE-FAST" or "SSFP" on various commercial MRI systems and called SSFP-echo in this work) was used to image inner ear structures. This technique was compared with images generated using conventional volume GRE techniques (GRASS). While small flip angle volume GRE imaging has been used for inner ear imaging previously, the low contrast typical of such density weighting makes it difficult to distinguish soft tissue structures from surrounding CSF/endolymph. In this work, contrast-to-noise ratios (CNR) between CSF/endolymph and brain parenchyma were compared between the sequences at 15 degrees, 30 degrees, 60 degrees, and 90 degrees flip angles. The SSFP-echo sequence produced higher CNR for such structures and consistently outperformed GRASS sequences at flip angles of 30 degrees, 60 degrees, and 90 degrees.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Normal brain F-18 FDG-PET and MRI anatomy.

Image registration techniques will become increasingly important in correlative multimodality imaging. In the case of PET, a structural imaging study can be invaluable in correlating structure metabolism relationships. A registered brain atlas of PET and MRI has been developed by the authors that allows clinicians, residents, fellows, and others to refer to a structural abnormality on MRI or metabolic abnormality on PET and correlate it neuro-anatomically.

Brain↗
PubMed1993

Complex partial seizures and mesial temporal sclerosis: evaluation with fast spin-echo MR imaging.

PURPOSE: This study was performed to determine the sensitivity and specificity of fast spin-echo (FSE) magnetic resonance (MR) imaging in detecting mesial temporal sclerosis. MATERIALS AND METHODS: Twenty-one patients with a diagnosis of complex partial seizures were studied. Criteria for abnormality included visual detection of hippocampal MR signal abnormality and atrophy or significantly decreased hippocampal volume determined by using MR morphometric techniques. RESULTS: The overall sensitivity and specificity of MR imaging in demonstrating correct lateralization of seizure focus were both 100%. The positive predictive value of FSE MR imaging was 100%. The negative predictive value was 50%. CONCLUSION: The authors recommend FSE MR imaging of the hippocampus as the imaging technique of choice in the evaluation of patients with complex partial seizures for mesial temporal sclerosis.

Adult↗
PubMed1993

Mesenrhombencephalitis: MR findings in nine patients.

OBJECTIVE: Mesenrhombencephalitis is a serious form of brainstem inflammation predominantly involving the deep and vital portions of the brain, that is, the mesencephalon (midbrain) and rhombencephalon (pons, medulla). Mesenrhombencephalitis is difficult to diagnose on the basis of clinical and laboratory findings alone, and access to this portion of the brain for surgical biopsy carries high morbidity. We describe the MR appearance of mesenrhombencephalitis and correlate the imaging findings with clinical information. MATERIALS AND METHODS: Unenhanced and contrast-enhanced MR images of nine patients with mesenrhombencephalitis were reviewed retrospectively and correlated with clinical, laboratory, and pathologic data. The patients were categorized according to the cause of the disease: three had herpes simplex, one had Listeria monocytogenes, and five had mesenrhombencephalitis of undetermined cause. The three patients with clinical and MR evidence of herpes simplex mesenrhombencephalitis (one confirmed by brain biopsy) were comatose at presentation, with cranial nerve abnormalities in two and seizures in one. One patient with L. monocytogenes (established by blood culture) had cranial nerve palsies, fever, and pain in the ear. Five additional patients had headache (three), fever (three), nausea and vomiting (four), cranial nerve palsies (three), coma (two), and hyporeflexia (one) or hyperreflexia (four). Brain biopsy performed in two patients revealed chronic inflammation of unspecified cause; in one, it was compatible with viral encephalitis. RESULTS: MR images in three patients with herpes simplex mesenrhombencephalitis showed T2 signal hyperintensity in the midbrain (two), pons (one), medulla (one), and temporal lobes (three). Parenchymal foci of hemorrhage (methemoglobin, one patient) and leptomeningeal enhancement (one patient) were identified in the temporal lobes. T2-weighted MR images in one patient with L. monocytogenes showed signal hyperintensity in the brainstem, vermis, midbrain, and internal capsules. On T1-weighted images, low signal was present in these areas, which enhanced with paramagnetic contrast agents. In the remaining five patients, T2-weighted MR images showed patchy signal hyperintensity in the pons, medulla, and thalamus in three each and in the midbrain and temporal lobes in one each. T1-weighted MR images showed normal findings (two) or signal hypointensity in the thalamus and pons in one patient each. Areas of leptomeningeal and parenchymal enhancement were identified in one patient each. Brainstem swelling was seen in three patients, one of whom had petechial hemorrhage in the pons and hydrocephalus. CONCLUSION: Mesenrhombencephalitis is a serious illness that is diagnosed by a combination of imaging, clinical, laboratory, and pathologic studies. MR imaging may be crucial to the early diagnosis of this illness, and radiologists must be familiar with this uncommon entity and its MR findings in order to make timely diagnoses and facilitate treatment.

Adult↗
PubMed1993

Herpesvirus infections of the CNS: MR findings.

Herpesvirus infections of the CNS are prevalent in all segments of the population, and are an important health care issue. The family of herpesviruses consists of a large group of double-stranded DNA viruses that includes herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2), cytomegalovirus, Epstein-Barr virus, varicella-zoster virus, B virus, herpesvirus 6, and herpesvirus 7. In addition to producing infection when the host initially acquires the virus, an important property shared by these viruses is the ability to produce latent infection and to be reactivated.

Central Nervous System↗
PubMed1993

The dementias: correlation of clinical features, pathophysiology, and neuroradiology.

Current methods of neuroimaging have revolutionized the examination of patients with dementia. Clinical examination of these patients has identified cortical and subcortical patterns of dementia. Each of these patterns can be caused by various diseases. Mixed patterns also occur and also have several possible causes. Neuroimaging can be quite useful in confirming the clinical assessment of the pattern of dementia and in further refining the diagnosis. We review the pathophysiologic basis of and the clinical and neuroimaging findings in dementia, both cortical and subcortical. The roles of neuroimaging in diagnosis, prognostic assessment, and treatment evaluation are discussed.

Adult↗
PubMed1992

Practical choices of fast spin echo pulse sequence parameters: clinically useful proton density and T2-weighted contrasts.

With the development of fast spin echo (FSE) MRI techniques, T2-weighted images of the brain may be obtained much more quickly than when using conventional spin echo techniques (CSE), because made the individual echoes on the FSE pulse sequence are phase encoded, allowing acquisition of the same spatial information as in CSE with less excitations. The pulse sequence parameters (echo train length, bandwidth, echo spacing) are discussed. Images were obtained on four volunteers using both CSE and FSE while varying repetition time, echo time and matrix. Comparison for signal intensity gray-white differentiation, fat and CSE signal, arifacts and vascular resolution showed that FSE images comparable in quality to those of CSE can be obtained in less than half the time. A practical choice of FSE parameters is recommended for clinical use. However, artifacts, possibly related to CSF and vascular pulsation, of which the radiologist should be aware, were identified on the FSE images.

Artifacts↗
PubMed1992

Fat-suppression MR imaging in neuroradiology: techniques and clinical application.

Fat-suppression techniques are useful in MR imaging to eliminate strong signals from fatty tissues that interfere with signals from adjacent areas. Various methods of fat suppression have been devised, but when suppression of fat is used in combination with contrast enhancement employing paramagnetic agents (e.g., gadopentetate dimeglumine), the definition of normal anatomic structures is significantly improved, enhancing lesions become more conspicuous, and lesional margins are better defined in regions of the body with large amounts of fat, whose signal is suppressed. Contrast-enhanced fat-suppressed T1-weighted images provide more information than do conventional MR images. In this review, several types of fat-suppression techniques and their clinical applications in neuroradiology are described. Gadopentetate dimeglumine-enhanced, fat-suppressed T1-weighted images appear to have significant advantages over conventional T1-weighted contrast-enhanced images and should replace them in imaging regions of the body where large amounts of fat are present.

Adipose Tissue↗