Biomedical subjects

D B Hackney

Publications and source records attributed to D B Hackney.

At least 91 records · Page 5Linked to original sources

PubMed1987

Subacute intracranial hemorrhage: contribution of spin density to appearance on spin-echo MR images.

The T2 and pseudodensity (proportional to proton density) of intracranial hemorrhages and normal white matter were calculated. The mean T2 (+/- standard deviation) was 120 +/- 62 for hemorrhage and 61 +/- 11 for white matter. Pseudodensity values were normalized to a white matter value of 1, and the value for hemorrhage was 1.56 +/- 0.28. These values were used to determine which components of hemorrhage-white matter contrast are due to T1, T2, and density. The results indicate that on spin-echo (SE) images obtained with a long repetition time (TR)/short echo time (TE) (2,500/0-20 [TR msec/TE msec]), the contrast is mainly due to density differences, with a modest T2 contribution on 20-msec-TE images and nearly no T1 component. At 600/0-20, the contrast continues to be largely determined by density differences, again with a modest T2 component on 20-msec-TE images. If the T1 of hemorrhage is extremely short, the T1 component of contrast on 600/0-20 SE images will be somewhat greater than the density component. Because contrast on short TR/short TE images may be largely or entirely determined by pseudodensity or T2, it is inaccurate to refer to 600/20 images as "T1-weighted". The assumption that high signal intensity at this sequence implies a "short T1" will lead to misleading conclusions.

Brain↗

PubMed1987

Surface-coil MR of orbital pseudotumor.

Fifteen patients with clinical presentations compatible with idiopathic inflammatory orbital pseudotumor were examined by CT and MR imaging to determine if MR could add specificity to the CT appearance of this entity. MR was performed on a 1.5 T system, using surface-coil and head-coil techniques. Idiopathic pseudotumor was confirmed in nine patients on the basis of response to steroid therapy in the absence of local cause or systemic illness. One other patient had biopsy-proven idiopathic pseudotumor. Five patients proved to have other orbital entities, including metastases, infectious myositis, hemorrhage, and orbital sarcoid. In all 10 patients with confirmed pseudotumor, CT and MR were abnormal. MR abnormalities in 10 of 10 patients with pseudotumor were hypointense to fat and isointense to muscle on T1-weighted images. On T2-weighted images the lesions of pseudotumor were isointense or only minimally hyperintense to fat in nine of 10 cases; in one case, the enlarged muscle was markedly hyperintense to fat. The MR signal intensity of pseudotumor was similar to that found in infectious myositis and sarcoid. These findings contrasted to the MR appearance of the other disease entities examined. Metastases appeared markedly hyperintense to fat on T2-weighted images, while hematoma was hyperintense to muscle and isointense to fat on T1-weighted images and markedly hyperintense to fat on T2-weighted images. In our preliminary series, surface-coil MR appears to add specificity to the CT appearance of orbital pseudotumor.

Adolescent↗

PubMed1986

The value of magnetic resonance imaging in treatment planning of nasopharyngeal carcinoma.

Seven patients with AJCC Stage T4 nasopharyngeal carcinoma underwent both computed tomographic (CT) and magnetic resonance (MR) examinations prior to radiation therapy treatment planning. Lateral tumor extension into the infratemporal fossa was visualized by MR as less extensive in three cases than suggested by CT, as was inferior extension into the parapharyngeal soft tissues in three cases. MR clarified uncertainties on CT regarding involvement of the pontine cistern in three patients and of the cavernous sinus in two patients. Posterior extension of tumor was underestimated by CT in four of six cases shown by MR to involve the clivus. MR appeared superior in evaluating the presence of parenchymal brain involvement in three cases. The margins of the final boost treatment fields dictated by MR findings differed measurably from those derived from CT in six of seven cases. These findings lend support for greater utilization of MR in treatment planning of nasopharyngeal carcinoma.

Adolescent↗

PubMed1986

Occult cerebral vascular malformations: high-field MR imaging.

Occult cerebral vascular malformations (OCVMs) have characteristic appearances on high-field magnetic resonance (MR) images. These consist of circumscribed regions of low intensity, most prominent on T2-weighted images and representing hemosiderin deposits. Interspersed within most of these lesions are multiple areas of various signal intensity patterns, which correspond to hematomas in different stages of evolution and to fibrous regions containing calcium as well as hemosiderin. Forty-six lesions were found in 19 patients (34 supratentorial and 12 infratentorial). The supratentorial lesions tended to be subcortical or periventricular. Computed tomography depicted 24 of the 46 lesions demonstrated by high-field MR. Comparison of images obtained with both low-field MR (0.12 T and 0.35 T) and high-field MR (1.5 T) revealed that high-field MR imaging was superior in depicting OCVMs. High-field MR appears to be both sensitive and specific for OCVMs and may obviate the need for possible biopsy of these lesions.

Adolescent↗

PubMed1986

Corpus callosum and limbic system: neuroanatomic MR evaluation of developmental anomalies.

Agenesis of the corpus callosum is a complex malformation of the brain that has been associated with varying degrees of limbic system maldevelopment. We retrospectively reviewed the records of 11 patients with callosal agenesis (seven total, four partial) who underwent magnetic resonance (MR) imaging, with particular attention to the associated malformations of the limbic system. Comparison was made with selected images from MR examinations of healthy volunteers and with necropsy specimens from other patients with callosal agenesis. Ten of 11 patients demonstrated limbic anomalies (severe motion artifact precluded evaluation of these structures in one patient). MR depicted not only the abnormalities intrinsic to callosal agenesis but also the frequently associated malformations of the limbic system.

Agenesis of Corpus Callosum↗

PubMed1986

Intracranial meningiomas: high-field MR imaging.

Twenty-five newly diagnosed intracranial meningiomas were evaluated with magnetic resonance (MR) imaging at 1.5 T, and findings were correlated with those of computed tomography (CT), angiography, and tumor histology. Meningiomas were generally hypointense on T1-weighted images and hyperintense on T2-weighted images relative to cerebral white matter. In comparison with the cortex, they were hypointense or isointense on T1-weighted images and isointense or hyperintense on T2-weighted images. A heterogeneous texture produced by tumor vascularity, calcifications, cystic foci, or an intrinsic speckled or mottled pattern was observed in all but the smallest lesions. An interface between meningioma and brain was uniformly present and consisted of a cerebro-spinal fluid cleft, vascular rim, or dural margin. Large meningiomas were associated with arcuate displacement and compression of adjacent gyri. MR imaging was superior to CT in defining extracerebral tumor location, tumor vascularity, arterial encasement, and venous sinus invasion. No correlation was found between the appearance on MR images and the pathologic classification.

Adolescent↗

PubMed1986

Hemorrhage and edema in acute spinal cord compression: demonstration by MR imaging.

Until the development of magnetic resonance (MR) imaging there was no nondestructive technique for monitoring the pathologic response to acute spinal cord trauma. The characteristic findings of hemorrhage, necrosis, and edema have been well described in animal models. We used a 1.4-T, animal imaging system to study acute cord contusions in rats. Contusions were induced by means of extradural aneurysm clip compression, and imaging was performed 3-5 hours after injury with short and long spin-echo (SE) sequences. Animals were killed immediately after imaging, and the gross anatomic and histologic findings were correlated with image appearances. On long SE sequences edema appeared as an area of high signal intensity that extended proximal and distal to the site of contusion. At the contusion site there was focal intraparenchymal hemorrhage which had low signal intensity on T2-weighted images, presumably owing to deoxyhemoglobin. MR imaging can be used to assess pathologic changes resulting from acute cord contusion and to aid in differentiating irreversible damage (hemorrhage) from potentially reversible edema.

Acute Disease↗

PubMed1986

Head injury: early results of comparing CT and high-field MR.

The sensitivity and specificity of CT and high-field MR (1.5 T) were compared in an evaluation of 30 patients with head injuries (eight acute, 15 subacute, and seven chronic). By using T1- and T2-weighted images, it was possible to detect various stages of hemorrhages and their separation from edema. In the acute category, both CT and MR showed acute hemorrhagic lesions, but only MR demonstrated coexisting chronic hematomas or small hypothalamic or brainstem infarctions. MR was far superior to CT in the detection and characterization of subacute injuries, including shearing injuries, hemorrhagic and nonhemorrhagic contusions, and subdural hematomas. In chronic injury, atrophy was demonstrated by both techniques, but only MR showed parenchymal abnormalities and old hemorrhages. Its ease in monitoring patients and its greater speed make CT the procedure of choice for the evaluation of acute cases. CT also provides information that is useful in deciding between surgery and medical management. However, the more precise anatomic depiction of MR and its sensitivity to parenchymal abnormalities make MR the key to correct prognosis in patients with subacute or chronic injury.

Accidents, Traffic↗

PubMed1986

Magnetic resonance imaging of cerebral aneurysm.

Twenty patients with congenital cerebral aneurysms, studied on a 1.5 tesla MR unit, were also evaluated by angiography and/or computed tomography (CT) in order to establish the relative sensitivity of magnetic resonance imaging (MRI) in the demonstration of such aneurysms. Of the 27 aneurysms found on MRI, all but 4 were seen without the aid of the angiographic study. The four seen in retrospect included 3 out of 4 in the smallest size category (less than 5 x 5 mm) and one in next larger (5 x 5 mm to 10 x 10 mm). When more than one aneurysm was present or when an aneurysm and an arteriovenous malformation was present, MRI proved to be useful in demonstrating which bled. The presence of both subacute and acute clot identified the lesions that had bled.

Adolescent↗

PubMed1986

Magnetic resonance imaging of dural venous sinus invasion, occlusion and thrombosis.

Seventeen patients were found to have involvement of the dural venous sinuses on magnetic resonance imaging (MRI). In 7, there was tumor invasion through the dural coverings and in 10 thrombosis occurred as a result of various causes. MRI shows tumor in the sinus as a signal producing mass replacing the normal hypointensity of rapidly flowing blood. Disruption of the hypointense leaves of the enveloping dura is also well shown by MRI. Intravascular clotting, whether in the chemical state of deoxyhemoglobin or intra- or extracellular methemoglobin can be characterized by MRI operating at high field (1.5 tesla). MRI is now the non-invasive diagnostic modality of choice in evaluation of the dural venous sinuses.

Adolescent↗

PubMed1986

High field magnetic resonance evaluation of acoustic neurinomas.

Eight acoustic neurinomas were studied with magnetic resonance imaging (MRI) at 1.5 tesla utilizing spin-echo T1 and T2 weighted images (WI). T1 WI identified the tumors best and provided more exacting anatomic relationships particularly for small lesions than did T2 WI. Intracanalicular tumors are well defined. All tumors were hypointense on T1 WI but were usually heterogeneous and had variable intensity on T2 WI. Several lesions became obscured on T2 WI because of isointensity with the adjacent cerebellum or CSF. High signal to noise ratio at 1.5 tesla permits thin section imaging (3 mm) at relatively short imaging times. T1 MRI was considerably superior to CT for the detection and anatomic definition of acoustic neurinomas.

Humans↗

PubMed1986

Magnetic resonance imaging of traumatic sinus and mastoid bleeding.

Magnetic resonance imaging (MRI) characterized intrasinus hemorrhage in 8 out of 10 patients with computed tomography (CT) evidence of post-traumatic sinus opacification. Fractures of sinus walls were demonstrated as disruptions in the hypointense line of the bony wall, as displacement of this line, or by increased signal from blood or sinus effusion within the fracture. Seven patients with fractures of the temporal bone were more difficult to evaluate because of the hypointensity of air trapped within the fracture line mimicing the bony wall and that within the middle ear mimicing the ossicles; 1.5 tesla MR proved superior to CT in demonstrating associated extra- and intracerebral hemorrhage.

Hemorrhage↗

PubMed1986

Magnetic resonance imaging of hemorrhagic conditions.

There is a stereotyped progression in the appearance of hemorrhage or thrombosis in magnetic resonance imaging performed at 1.5 tesla (T). This progression begins with low intensity on T2 weighted images (WI), and progresses to high intensity on T1 and T2 WI associated eventually, in some cases, with peripheral low intensity on T2 WI. Depending upon the etiology and location of hemorrhage or thrombosis the latter hypointensity on T2 WI may or may not be present. Hemorrhages occurring in regions of the brain not having an intact blood-brain barrier do not usually display persistence of low intensity. Regardless of etiology, consistent patterns in the evolution of hemorrhage may be observed on MR.

Brain↗

PubMed1986

Magnetic resonance imaging of the pediatric spinal cord and canal.

Of 105 pediatric patients studied on a 1.5 tesla MR unit for clinical suspicion of spinal disease 69.5 per cent of studies were positive. Magnetic resonance imaging (MRI) was successfully performed on all patients, from newborn up. MRI replaced invasive studies such as myelography and intrathecally enhanced computed tomography (CT) in all disease categories except for subarachnoid drop metastasis, spinal arteriovenous malformation and arachnoiditis. Conventional CT and radiography of the spine were complementary in disease processes where bony detail was important.

Adolescent↗

PubMed1983

Effects of contrast media on pulmonary hemodynamics: comparison of ionic and non-ionic agents.

Hemodynamic effects of pulmonary arterial injections of ionic (sodium methylglucamine diatrizoate) and non-ionic contrast media (iohexol) were compared in 9 anesthetized dogs which were maintained with an open thorax in a resting control state. Both were found to increase pulmonary arterial pressure and cardiac output. In addition, both resulted in decreased systemic vascular resistance, though the effect was significantly less with the non-ionic agent. Aortic pressure did not change with the non-ionic agent but fell drastically with the ionic agent. Contrary to prevailing beliefs, the predominant response of the pulmonary circulation to contrast media was a fall rather than a rise in pulmonary vascular resistance.

Animals↗

PubMed1983

Extravascular lung water: effects of ionic and nonionic contrast media.

The effects of right atrial injections of Renografin 76 (meglumine diatrizoate), hypertonic (5%) sodium chloride, and iohexol, a new nonionic contrast medium, on sequential measures of left atrial pressure and extravascular lung water in anesthetized dogs were studied. Renografin 76 caused significant transient elevations of extravascular lung water; control levels were reestablished at 15-20 minutes after injection. These changes occurred in the absence of significant changes in left atrial pressure. Iohexol reduced extravascular lung water slightly while hypertonic saline transiently increased it. The increased extravascular lung water after right atrial injections of ionic contrast medium can only partially be explained by the tonicity of the medium. This increase was not observed with nonionic medium, suggesting that nonionic media may be preferable imaging agents in patients with underlying lung or heart disease, and may be more suitable for digital intravenous examinations.

Animals↗

PubMedDate not supplied

Dependence of apparent diffusion coefficients on axonal spacing, membrane permeability, and diffusion time in spinal cord white matter.

We used a numerical simulation of water self-diffusion among permeable cylinders to predict the dependence of MR-based apparent diffusion coefficients in white matter on axonal separation, barrier permeability, and diffusion time (T). The transverse apparent diffusion coefficient (tADC), calculated with simulated diffusion-sensitizing gradients perpendicular to the axon fibers, remains a function of T down to diffusion times as short as .1 microsec for a range of diffusion barrier permeability. As the diffusion time lengthens, the response of tADC depends on axon diameter, with decreases in tADC occurring earliest, and most dramatically, for the smallest fiber diameter simulated (2 microm). For a given axonal separation, asymptotic values of ADC are determined by permeability alone and are the same for 2-microm and 11-microm fibers of equal membrane permeability. The effect of increased relative intracellular volume is manifested primarily in a decrease in tADC at short T. Increases in interaxonal spacing increase the tADC at asymptotically long diffusion times and reduce the dependence on permeability. However, at the widest plausible axonal separations, permeability remains an important determinant of tADC. These simulations may enhance interpretation of measured tADC in the context of the underlying physiologic and structural changes at the cellular level that accompany white-matter disease.

Animals↗

PubMedDate not supplied

MR diagnosis of acute disseminated encephalomyelitis.

High-field magnetic resonance (MR) imaging was performed in three patients with clinically diagnosed acute disseminated encephalomyelitis (ADEM). Contrast enhanced CT was normal in all cases. Magnetic resonance demonstrated multiple foci of demyelination in the brain stem, cerebrum, and cerebellum. Lesions were characteristic, in that they were relatively few in number, frequently present in the brain stem and posterior fossa, nonhemorrhagic, asymmetric, and easily correlated with clinical symptoms and signs. Follow-up MR in one patient who had clinically improved after steroid therapy showed marked resolution of previously documented lesions. Typical MR findings in combination with the appropriate clinical presentation can confirm the diagnosis of ADEM, obviate other more invasive diagnostic tests, identify the extent and sites of involvement, and follow response to therapy.

Adult↗