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Biomedical subjects

K R Davis

Publications and source records attributed to K R Davis.

At least 163 records · Page 9Linked to original sources
PubMedDate not supplied

Vertebral-basilar posterior cerebral territory stroke--delineation by proton nuclear magnetic resonance imaging.

We used three-dimensional proton NMR images to study ischemic infarction in the territory of the vertebral-basilar posterior cerebral circulation. The study includes sixteen cases, eight of which are presented in detail. In seven cases, the infarctions were secondary to demonstrable large artery occlusive disease -- vertebral, basilar, or posterior cerebral. In nine cases, the infarctions were secondary to what was presumably small vessel disease. In fifteen of the sixteen cases, NMR imaging could locate the infarct, inversion recovery and spin-echo pulse sequences being more sensitive than the saturation recovery pulse sequence. This efficiency rests on the high sensitivity of ischemic infarction to changes in T1 and T2 relaxation time, highlighted in the inversion recovery and spin-echo images, respectively. The additional advantages of the three-dimensional approach, and the lack of bone artifact, make NMR imaging superior to CT scanning in identifying areas of infarction in the territory of posterior cerebral circulation.

Adult↗
PubMedDate not supplied

The prognosis of carotid siphon stenosis.

We retrospectively reviewed the clinical course and angiograms of 15 patients with carotid siphon stenosis of 50% or greater. Fourteen had less than 50% stenosis at the origin of the ipsilateral internal carotid artery, and one had a greater degree of stenosis but underwent endarterectomy after an initial angiogram. Angiograms were examined for evidence of hemodynamic abnormalities in addition to residual lumen diameter. Seven patients initially had TIAs, 5 had strokes, and 3 were asymptomatic. In an average followup of 51 months (range 4-123 months) subsequent cerebral ischemic events occurred in 6 (40%), but only 1 had a stroke with a persisting neurological deficit that could be directly attributed to the siphon stenosis. Stenoses were hemodynamically significant by angiography in 5 of 7 TIA patients, and only 1 of 5 stroke patients. The incidence of subsequent ischemic events in this study was similar to 2 previous studies of siphon stenosis, however in this study most of the events ipsilateral to the siphon stenosis were TIAs or minor strokes. The association of hemodynamic angiographic abnormalities and initial TIAs but not strokes suggests that the mechanism producing ischemic symptoms may differ in patients with TIA and stroke who have carotid siphon stenosis.

Adult↗
PubMedDate not supplied

Limitations of computed tomography in the investigation of acoustic neuromas.

Seventy percent of 80 surgically proven acoustic neuromas were visualized on preoperative computed tomography (CT) scans. Many more tumors were seen on contrast enhanced scans than on unenhanced scans (55 vs 25). No intracanalicular tumors and only one of 15 tumors less than 2 cm in size were visualized on CT scan. Most medium size tumors (2.0-3.0 cm) and all large tumors (greater than 3.0 cm) were visualized on CT scan when optimal technique was used. Positive CT scans often replace more invasive diagnostic studies in the investigation of acoustic neuromas. Negative scans do not rule out tumors as intracanalicular, and small tumors are usually not visualized with current techniques. If there is clinical suspicion of an acoustic neuroma, positive contrast posterior fossa cisternography should be done when the CT scan is negative.

Evaluation Studies as Topic↗
PubMedDate not supplied

Giant intracranial aneurysms of the anterior circulation: clinical characteristics and diagnosis by computed tomography.

The computed tomography (CT) characteristics and clinical features of giant (globoid) aneurysms of the anterior circulation are reviewed. These lesions appear on the CT scan as smoothly encapsulated ovoid masses, within which a partially patent lumen is seen after the infusion of iodinated contrast material. With careful analysis of the CT scan it may be possible to differentiate giant internal carotid artery, anterior cerebral artery, and middle cerebral artery aneurysms from other parasellar and hemispheric lesions.

Adult↗
PubMedDate not supplied

The effectiveness of condoms in reducing heterosexual transmission of HIV.

CONTEXT: It is not established whether the condom is as effective at preventing heterosexual transmission of HIV as it is for preventing conception. An overall estimate of condom effectiveness for HIV prevention is needed. METHODS: Information on condom usage and HIV serology was obtained from 25 published studies of serodiscordant heterosexual couples. Condom usage was classified as always (in 100% of acts of intercourse), sometimes (1-99%, 0-99% or 1-100%) or never (0%). Studies were stratified by design, direction of transmission and condom usage group. Condom efficacy was calculated from the HIV transmission rates for always-users and never-users. RESULTS: For always-users, 12 cohort samples yielded a consistent HIV incidence of 0.9 per 100 person-years (95% confidence interval, 0.4-1.8). For 11 cohort samples of never-users, incidence was estimated at 6.8 per 100 person-years (95% confidence interval, 4.4-10.1) for male-to-female transmission, 5.9 per 100 (95% confidence interval, 1.5-15.1) for female-to-male transmission and 6.7 per 100 (95% confidence interval, 4.5-9.6) in samples that specified the direction of transmission. Generally, the condom's effectiveness at preventing HIV transmission is estimated to be 87%, but it may be as low as 60% or as high as 96%. CONCLUSIONS: Consistent use of condoms provides protection from HIV. The level of protection approximates 87%, with a range depending upon the incidence among condom nonusers. Thus, the condom's efficacy at reducing heterosexual transmission may be comparable to or slightly lower than its effectiveness at preventing pregnancy

Condoms↗
PubMedDate not supplied

Phase-contrast imaging of the parotid region.

Standard T1- and T2-weighted spin-echo acquisitions were compared with T1- and T2-weighted phase-contrast techniques in a series of 10 consecutive patients with parotid masses to assess the role of phase-contrast methods in the evaluation of lesions in the parotid fossa. Greater tissue-lesion contrast was obtained with phase-contrast methods in nine of 10 cases, allowing improved lesion visualization; however, an increase in lesion detectability was not observed in this series. Standard MR imaging methods are sufficient for imaging the parotid region in most cases, but can be quite time-consuming. Recommended screening of the parotid fossa that optimizes tissue-lesion contrast, lesion detectability, and imaging time is performed by combining a standard T1-weighted acquisition with a T1- or T2-weighted phase-contrast acquisition. Selection of a T1- or T2-weighted phase-contrast acquisition is determined by the T1 characteristics of the lesion.

Humans↗
PubMedDate not supplied

MR of hemorrhage: a new approach.

Using a modification of the partial saturation (PS) pulse sequence, we developed an MR method that permits the acquisition of highly T1- and T2-weighted images of the head and body in as little as 10 sec. The PS images, which were acquired at 0.6 T in a series of six patients with acute and subacute hemorrhage, showed a striking reduction in the signal intensity of hemorrhagic lesions. This effect, which is related to bulk magnetic susceptibility variations, was either minimal or absent on conventional T1- and T2-weighted spin-echo (SE) images. Our results suggest that high-field systems are not needed in order to image acute and subacute hemorrhage.

Brain Diseases↗
PubMedDate not supplied

The detection of intracranial calcifications by MR.

Twenty patients in whom CT had unequivocally demonstrated the presence of calcification in a diversity of lesions and who had undergone MR, performed at 0.6 T and with standard T1- and T2-weighted pulse sequences, were retrospectively studied to determine the MR signal-intensity characteristics of the calcifications and to assess the ability of MR to detect the presence of this abnormality. CT proved superior to MR in detecting and characterizing calcification. In seven of 20 cases, the apparent extent of calcification was equal by both imaging techniques, and in 13 of the 20 cases, CT showed more extensive abnormality. In five of the 20 cases, the calcifications were seen by MR as regions of profoundly reduced signal intensity, approximately equal to cortical bone, in all pulse sequences. In 12 of the 20 cases, the signal intensity was profoundly reduced in one or more, but not all, pulse sequences. T2-weighted pulse sequences were most sensitive in detecting calcification of signal void. Reviewed without knowledge of the CT findings, the MR images were interpreted as definitely indicative of the presence of calcification in three of the 20 cases. In seven of the 20 cases, the MR images raised the possibility of calcification but were less definitive than the CT findings. In 10 of the 20 cases, MR was judged indeterminate for the presence of calcification.

Adolescent↗
PubMedDate not supplied

Magnetic susceptibility effects secondary to out-of-plane air in fast MR scanning.

Areas of signal loss in brain overlying air-containing structures at the skull base are commonly observed on axial fast MR images. The nature of this effect, which can mimic the appearance of cerebral hemorrhage, is investigated in a phantom study and in a normal volunteer. The magnitude of the signal loss is found to be inversely related to the distance of the scanning plane from the air-containing structure and directly related to the echo time.

Brain↗
PubMedDate not supplied

Treatment of carotid cavernous fistulae or cavernous aneurysms associated with a persistent trigeminal artery: report of three cases.

One case of traumatic carotid cavernous fistula and two cases of cavernous aneurysm associated with a persistent trigeminal artery are reported. Since a significant rate of infarctions or hemorrhages in the vertebrobasilar territory is associated with PTA, we prefer to permanently occlude the PTA during treatment of a carotid cavernous fistula or a cavernous aneurysm if the trigeminal artery can be sacrificed without jeopardizing the basilar circulation. These three patients were cured without complications. The internal carotid artery could be preserved in only one case.

Adult↗
PubMedDate not supplied

Cholesterol granuloma of the petrous apex: MR and CT evaluation.

We reviewed the clinical, CT, and MR findings in seven consecutive patients who had a total of nine cholesterol granulomas. Preoperative MR scans were available for five of the seven patients; two patients were studied with MR after treatment only (one had a recurrent lesion and the other was asymptomatic at the time of study). Preoperative CT scans were available for all patients, except one patient who was examined after developing a symptomatic recurrence. All lesions were detected by both imaging methods. Seven preoperative lesions (five patients) and one symptomatic recurrence (one patient) demonstrated increased signal intensity of both T1- and T2-weighted MR images. Three surgically drained lesions (three patients) showed a marked reduction in signal intensity on T1-weighted images. Pre- and postoperative lesions had different patterns of signal intensity on the chemical-shift images, which were obtained in two instances. The MR appearance of cholesterol granuloma differs from that of most other lesions that occur in the petrous apex. CT did not differentiate between pre- and postoperative lesions in all cases, while MR demonstrated a dramatic change on T1-weighted images and chemical-shift studies. Our findings indicate that MR is more specific than CT in suggesting the correct diagnosis of cholesterol granuloma and that MR appears to be the technique of choice in the follow-up of previously treated patients.

Adult↗
PubMedDate not supplied

Selective arteriography of glomus tympanicum and jugulare tumors: techniques, normal and pathologic arterial anatomy.

Glomus tympanicum and jugulare tumors arise within the middle ear and jugular fossa, respectively, but often extend into the adjacent areas of the skull base and posterior fossa. Multiple branches of the external carotid, internal carotid, and vertebral arteries may contribute to the vascular supply of these lesions. The arteriograms of 15 patients with glomus tumors were correlated with the surgical findings to determine if selective arteriography could define precisely the involvement within the middle ear, jugular fossa, and mastoid. The arteriographic mapping correlated well with the surgical findings in nine of 13 cases that had surgery, but a few important limitations were found. Therefore, a new arteriographic projection, called a transcanalicular view, is proposed that separates the middle ear from the jugular fossa, allowing for better visualization and assessment of the tumor blush.

Angiography↗
PubMedDate not supplied

Cholinergic actions of metrizamide.

In a study of the possible mechanisms of the clinical side effects of metrizamide, it was applied to several in vitro model preparations. It was shown that, although high metrizamide concentrations are without noticeable effect on many basic neuronal functions, metrizamide does interfere with cholinergic mechanisms. At concentrations equivalent to, or significantly lower than, those probably achieved during clinical procedures, metrizamide is both an inhibitor of the enzyme acetylcholinesterase and an antagonist of cholinergic transmission. These data suggest the possibility that some of the side effects resulting from clinical procedures employing metrizamide may be explained by its actions on cholinergic synapses.

Acetylcholine↗
PubMedDate not supplied

Preliminary clinical results of proton (1H) imaging of cranial neoplasms: in vivo measurements of T1 and mobile proton density.

Proton nuclear magnetic resonance (NMR) images reflecting T1 relaxation time and approximating proton density were acquired and used to generate T1 rate (1/T1) maps. By region-of-interest selection, measurements of T1 relaxation time were made from discrete volumes of the imaging plane. Such techniques were applied to the study of human cranial neoplasia and associated conditions of differential diagnostic importance (e.g., postoperative changes, radiation necrosis). Inversion-recovery NMR images exhibit a high lesion-detection sensitivity. In all patients, the specificity of NMR imaging is low since all abnormal areas appear as lesions darker than surrounding normal brain, reflecting a decreased proton density, prolonged T1 values, or both. T1 relaxation times are prolonged within neoplastic foci; however, absolute T1 values overlap with those found in other lesions.

Astrocytoma↗
PubMedDate not supplied

Superselective injection of BCNU through a latex calibrated-leak balloon.

Carmustine (BCNU) has been used extensively to treat glioblastomas by injection through a catheter placed in the cervical internal carotid artery. The technique causes severe pain to the eye and has resulted in ipsilateral blindness. The use of a latex calibrated-leak balloon positioned above the ophthalmic artery in the internal carotid artery or in one of its branches appears to circumvent the ocular complications mentioned. At an infusion rate at 125 ml/hr the balloon does not inflate and does not occlude the artery. This new technique has been used to treat 10 patients without complications.

Brain Neoplasms↗