Risk factors of non-arteritic anterior ischemic optic neuropathy (NAION): ocular or systemic

We retrospectively analyzed 22 patients with non-arteritic anterior ischemic optic neuropathy (NAION) seen at Chung-Ho memorial hospital between 1994 and 1996 to investigate the risk factors of NAION. The risk factors were divided into two groups: ocular and systemic. The ocular factors include refractive state, intraocular pressure, and cup-disk ratio of fellow eye. The systemic factors include diabetes, hypertension and cardiovascular diseases. The analysis revealed: (1) only 22.6% of patients with NAION have systemic risk factors; (2) intraocular pressure is not specific to NAION; (3) most of fellow eyes (72.6%) have cup-disk ratio not more than 0.1; and (4) most patients (90.9%) are hyperopic or emmetropic, only 9% of patients are myopic in either affected or fellow eyes. The statistical comparison between ocular (including cup-disk ratio and refractive state) and systemic factors is significant. The correlation with systemic factors in our study was not so high as previous study had reported. On the contrary, crowding effect of small cup-disk ratio, which induces a vicious circle of generally circulatory compromised disk, may play an important role in NAION. Besides, hyperopic or at least emmetropic eyes are more prone to NAION than myopic eyes. This may be due to lack of flattening of the temporal excavation, therefore adding a predisposing factor to a generally circulatory compromised disk. The risk factors associated with NAION seem more strongly correlated with ocular factors than with systemic factors.

Tumor characterization with dynamic contrast-enhanced MRI using MR contrast agents of various molecular weights

Dynamic contrast-enhanced MR imaging was used to measure the kinetics of enhancement in three different animal tumor models (Walker 256, R3230 AC, MCF7) using three different Gd complexes (Gd-DTPA, Gd-DTPA-24-cascade-polymer 30 kD, and polylysine-Gd-DTPA 50 kD). The three tumor models varied in growth rate, with the most rapid growth demonstrated by Walker 256 cells and the slowest growth occurring in the MCF7 cells. For each tumor, the kinetics of enhancement using polylysine-Gd-DTPA was analyzed using a pharmacokinetic model to estimate the vascular volume of the tumor. The rate of entry of the contrast agent into the interstitial space served as the measure of vascular permeability. The smallest molecular-weight agent, Gd-DTPA, could not provide information about vascular permeability. The intermediate and the largest agents both demonstrated that the faster-growing Walker 256 tumor had greater vascular permeability than did the slower-growing R3230 AC tumor. The degree of vascular permeability in the MCF7 tumor could not be assessed fairly due to insufficient statistics. The current study provides evidence supporting the hypothesis that more rapidly growing tumors have higher vascular permeability than do tumors that grow more slowly.

Pharmacokinetic changes induced by vasomodulators in kidneys, livers, muscles, and implanted tumors in rats as measured by dynamic Gd-DTPA-enhanced MRI

The effects of three physiologically different vasomodulators, angiotensin II (a vasoconstrictor), hydralazine (a vasodilator), and histamine (a permeability modulator), on the pharmaco-kinetics of entry of small molecules (measured by Gd-DTPA concentration) into normal and abnormal tissue were studied in rats implanted with R3230 AC tumors. Sequential dynamic Gd-DTPA-enhanced MRI studies, one before and one after vasomodulator administration, were performed, and the signal intensities of various tissues analyzed. Angiotensin II (6 micrograms/kg) reduced blood flow in tumors, but increased it in muscles. Hydralazine (5 mg/kg) reduced blood flow in tumors, kidneys, and livers, and slowed Gd-DTPA clearance from tumors, livers, and muscles. Histamine (25 micrograms/kg) increased renal blood flow, hastening Gd-DTPA clearance causing reduced measurable blood flow in tumors and muscles. By simultaneously monitoring the effects in various tissues, the pharmacokinetic effect of each drug in the entire body could be obtained.

[Unusual spontaneous dural cavernous sinus fistula between right external carotid artery and left cavernous sinus--a case report]

A 64 year-old female had left exophthalmos which resulted from a spontaneous dural cavernous sinus fistula between the right external carotid artery and left cavernous sinus. The left cavernous sinus was fed directly from internal maxillary branches of right external carotid artery with the sparing of right cavernous sinus and intracavernous sinus. Symptoms and signs of dural cavernous sinus fistula developed slowly in the left eye only. Although this kind of spontaneou dural cavernous sinus fistula is very rare. The possibility of arterial feeding from contralateral carotid artery should not be ignored in any patient that is suffered from dural cavernous sinus fistula while angiographic study is performed.

Regional comparison of tumor vascularity and permeability parameters measured by albumin-Gd-DTPA and Gd-DTPA

Sequential albumin-Gd-DTPA and Gd-DTPA dynamic enhancement studies were performed in an animal tumor model for the comparison of regional vascularity and permeability parameters measured by these two different sizes of contrast agents. The early albumin-Gd-DTPA enhancement arises from the vascular compartment, and the averaged signal enhancement derived from the first 3 to first 6 images postinjection can be reliably used to assess vascularity. The signal intensity in the images during the period of 5-10 min post-albumin-Gd-DTPA injection shows a steady linear variation. The intercept of the linear relationship is another indicator of the vascularity and the slope represents the tumor permeability to albumin-Gd-DTPA. The Gd-DTPA enhancement study was analyzed by a two-compartmental pharmacokinetic model to calculate the regional vascularity and permeability. The permeability parameters measured from albumin-Gd-DTPA and Gd-DTPA show an excellent correlation. The vascularity parameters measured from albumin-Gd-DTPA show good linear correlation with the low vascularity groups measured by Gd-DTPA, but show saturation for the high vascularity groups. The enhancement mechanisms for both contrast agents are discussed to relate the imaging parameters to the physiological variables.

Measurement of vascular volume fraction and blood-tissue permeability constants with a pharmacokinetic model: studies in rat muscle tumors with dynamic Gd-DTPA enhanced MRI

We propose a compartmental model to explain the signal enhancement curves following the bolus injection of Gd-DTPA. The model incorporates vascular volume fraction contribution, and the possibility of having different transport constants between the plasma and extravascular components. A Walker 256 carcinoma grown in rat muscle was used to demonstrate the capability of this model. Several different types of tissues were included in the measurements: normal, quickly enhanced, slowly enhanced, and necrotic tissues. Blood volume and blood-tissue permeability information can be derived from the dynamic contrast-enhanced MRI study employing the proposed model. In the tissue contrast enhancement curve, the initial rising slope after injection is related to the blood volume (or, vascular volume fraction), the maximum enhancement ratio is related to the uptake of tissue, and the decay rate is related to the clearance of tracer from tissue. The measured permeability constant is not the conventional permeability; instead they are contrast agents uptake and clearance rates, which are limited by the blood perfusion. These parameters can be used to characterize different enhancement patterns.

Use of Gore-Tex sling in brow suspension procedure

A variety of materials have been employed for brow suspension surgery for ptosis. Gore-Tex (expanded polytetrafluoroethylene ePTFE) has been used as vascular prosthesis. We have used cylinder Gore-Tex in brow suspension surgery for 15 ptotic eyelids (11 patients), including 10 eyes (8 patients) of congenital ptosis, 1 eye of traumatic ptosis in a young male, and 4 eyes (2 patients) of myogenic ptosis in elderly patients. All of the eyelids had minimal or absent levator muscle function, and drooped to cover the visual axes. The surgical technique for the 10 congenital ptotic eyelids was a modified Fox's method. The remaining 5 adult eyelids were operated by a modified Crawford's method, with interlocking of the two suspension bands at the lower apex of each triangle and direct suturing of the bands to the tarsal plate. The use of Gore-Tex in brow suspension makes it easy to adjust the height and contour of the operated eyelids. Patients were followed-up from 2 to 16 months (average 9.1 months) postoperatively. The only complication was granuloma formation at the most upper knot area in 5 patients (6 eyelids), one of which also had granuloma at the ipsilateral fornix with the Gore-Tex band cutting through the conjunctiva. One eyelid drooped due to knot granuloma and infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Statistical description of microcirculatory flow as measured with an MR method

Quantification of microcirculatory flow is important for the functional assessment of biologic systems. The authors describe a method of analyzing the dependence of the magnetic resonance (MR) signal intensity on microcirculatory flow. A gel bead phantom was used to simulate the randomly oriented flow capillaries, and the MR signal intensity of the phantom was studied at different flow velocities by using velocity-sensitized and -compensated spin-echo pulse sequences. A theoretical model based on the spin-phase phenomenon is proposed to elucidate the effect of flow on signal intensity. The velocity phase of a spin depends on its path and the corresponding velocity-encoding gradients. A Monte Carlo simulation was used to generate the path of a spin on the basis of a statistical model for flow through a random capillary network. From the velocity-phase distribution of a group of spins within a voxel, the signal attenuation due to flow can be calculated. The results of the statistical model and experimental measurements agreed well. Also, T1 and T2 effects in MR flow measurements were investigated. The current study provides a theoretical framework for understanding MR measurements of microcirculatory flow.

Susceptibility effects in porous media in the presence of flow

Magnetic resonance (MR) imaging of microvascular flow is an important topic in biomedicine because it permits access to the functional state of a biologic system. The internal heterogeneous magnetic field due to susceptibility differences within tissues is one of the factors that can affect signal intensity. A glass bead phantom simulating a porous medium was used to experimentally study the effect of the internal magnetic field on MR flow measurements. A physical model was developed to simulate the paths of the moving spins and the local magnetic field distribution in the medium to estimate the signal intensity with spin-phase analysis. The susceptibility variation inside the glass bead phantom was estimated by comparing the simulation results with the experimental data. Experiments were also performed with a tissue-simulating phantom, and the results indicated that the effect of the internal field inhomogeneity on in vivo microvascular flow measurements was negligible.

A new device of incentive spirometry

Incentive spirometry is a feedback system to encourage patients to take a deep breath and produce a sustained maximal inspiration (SMI) for the primary purpose of opening and stabilizing atelectatic areas of the lung. However, currently available incentive devices are not reusable, expensive, and emphasize inspiratory effort only. We have designed a new device of incentive spirometer based on pursed-lip breathing technique. The device consists of a piece of paper hanging on a frame. The patient is instructed to take a deep and slow inspiration followed by holding the breath for 5 seconds. Then, using pursed-lip technique, the patient generates a flow to keep the paper attached to a bar as long as possible. The duration of paper blowing is recorded and is compared with vital capacity. In the present study 96 cases were recorded. Vital capacity was correlated well with paper blowing time (multiple regression test r = 0.87, p less than 0.0001). The advantages of our device include (1) reusibility and less cost, (2) equal emphasis of both inspiration and expiration, and (3) being especially helpful for patients with chronic obstructive lung disease (COPD). This is a preliminary result and further clinical study is needed.

[Intraocular lens implantation at Kaohsiung Medical College]

Between March 1984 and December 1987, 993 cataractous eyes in 884 patients (462 males, 422 females) were operated on using intraocular lens implantation at the Kaohsiung Medical College Hospital. The age of the patients ranged from half year to 93 years, with an average of 61.9 years. Primary lens implantation was performed in 98.4% of the cases, secondary implantation in 1.6% of the cases. There were 6 cases were done by using the triple procedure (combined keratoplasty with cataract extraction and intraocular lens implantation). Among these 742 eyes followed-up for from one to 43 months, final vision could be corrected to 6/12 or better in 63.5% of the cases. While 64.4% of the cases of post-operation cylinder were less than 2 diopters, the final refraction showed that the spherical equivalent diopters were within 2 diopters in 61.7% of the cases. Complications in the anterior chamber lens group included pupillary changes (21.2%), pseudophakic bullous keratopathy or decompensation (13.5%), lens subluxation or dislocation (13.5%) and cystoid macular edema (5.8%). Complications in the posterior chamber lens group included pupillary changes (16.2%), posterior capsular thickening (3.2%), anterior or posterior synechiae (2.7%) and lens subluxation or dislocation (2.8%).

Passive optical detection of meteorological parameters in launch vehicle environments

New optical detection systems are being developed which combine conventional passive photometry with advanced data processing and statistical analysis methods. These crossed-beam detection systems can continuously monitor meteorological parameters in rocket or aircraft environments. The outputs from several photometers are analyzed by cross correlation techniques to retrieve the transit times or transit distance of light emitting, absorbing, or scattering particles between the photometer lines of sight. These transit times and distances are then transformed into wind components and turbulence levels for preselected altitudes. A continuous near real time display of these meteorological parameters is also under development.