Visual acuity: calculating appropriate averages.

Controversy surrounds the averaging of visual acuity scores. We examine this debate and provide a series of guidelines and worked examples to enable investigators to select an average (e.g.

MR imaging of blood oxygenation-dependent changes in focal renal ischemia and transplanted liver tumor in rat.

The potential of using fast magnetic resonance (MR) imaging in conjunction with apnea-induced blood deoxygenation for the noninvasive monitoring of relative perfusion in the rat abdomen has been studied with two experimental models: glycerol-induced focal renal ischemia and transplanted liver tumor. Gradient-echo echo-planar imaging (GRE-EPI) (TE of 20 msec at 2T) of liver and kidney was performed before, during, and after a 60-second apnea episode and then was followed in the same rat by contrast-enhanced (a) GRE-EPI and (b) T1-weighted spin-echo imaging (TR msec/TE msec = 200/6) with polylysine-(gadolinium-DTPA [diethylenetriaminepentaacetic acid]). The results indicate that a noninvasive vascular challenge due to apnea can be used for the detection of focal tissue perfusion abnormalities in rat kidney and liver tumor.

Rapid MR imaging of a vascular challenge to focal ischemia in cat brain.

Deoxygenated blood was effectively used as a magnetic resonance (MR) susceptibility contrast agent to distinguish perfused and nonperfused (ischemic) regions in a focal ischemia model in cat brain at 2T. Modulation of cerebral blood oxygenation levels in response to apnea was followed in real time with T2*-weighted (gradient-recalled) echo-planar MR imaging. Signal loss in the T2*-weighted images occurred only in perfused tissues as blood became globally deoxygenated.

Accuracy of Goldmann tonometry in clinical practice.

The intra- and inter-observer variability of Goldmann applanation tonometry was studied in 8 hospital tonometrists, 4 of whom received brief revision training in tonometer use. Intraocular pressure (IOP) measurements were obtained from 16 glaucoma patients. Over a series of four readings taken from individual eyes, intraocular pressure did not significantly vary.

Cerebrovascular transit characteristics of DyDTPA-BMA and GdDTPA-BMA on normal and ischemic cat brain.

Purpose: To compare the efficacy of two nonionic T2*-shortening contrast agents, DyDTPA-BMA dysprodiamide injection and GdDTPA-BMA gadodiamide injection, as perfusion-sensitive MR imaging agents in normal and acutely ischemic brain.

Methods: The magnetic susceptibility effects of intravenous injections of 0.10-0.

Endogenous susceptibility contrast in myocardium during apnea measured using gradient recalled echo planar imaging.

Gradient recalled echo planar imaging was used to monitor changes in myocardial and left ventricular chamber blood intensity during apnea in rats. Significant signal loss in both blood (to 62 +/- 5% and 51 +/- 6% of baseline) and myocardium (to 79 +/- 2% and 76 +/- 3% of baseline) was observed at 45 and 90 s apnea while O2 saturation decreased from 98 +/- 1% to 62 +/- 7% and 36 +/- 9%, respectively. These results show that myocardial intensity is modulated by alterations in blood oxygenation.

Echo-planar MR imaging of normal and ischemic myocardium with gadodiamide injection.

Rapid echo-planar (EP) magnetic resonance (MR) imaging was used to monitor the first pass of a bolus of gadodiamide injection in the hearts of normal rats and rats subjected to left coronary artery occlusion. Inversion-recovery EP imaging combined with a low dose (0.05 mmol/kg) of the contrast agent caused signal enhancement of normal myocardium from 19% +/- 4 to 63% +/- 5 (mean +/- 1 standard error of the mean) of fully relaxed intensity at the peak of the bolus but only slight increase in signal intensity of the ischemic zone.

Comparison of the Keeler Pulsair 2000 non-contact tonometer with Goldmann applanation.

The Pulsair 2000 non-contact tonometer (Keeler Ltd, UK) is compared with the Goldmann applanation tonometer. Data from 80 eyes were acquired by four experienced observers. A linear regression analysis showed the relationship between the instruments to be: Pulsair = 0.

Cytotoxic brain edema: assessment with diffusion-weighted MR imaging.

To determine whether cytotoxic brain edema is associated with a decrease in diffusion, it was induced in rats, in the absence of ischemia, with an established model of acute hyponatremic encephalopathy. Cytotoxic brain edema secondary to acute hyponatremia was induced with intraperitoneal injections of 2.5% dextrose in water and subcutaneous injection of arginine-vasopressin.

Magnetic resonance imaging demonstration of pharmacologic-induced myocardial vasodilatation using a macromolecular gadolinium contrast agent.

Rationale And Objectives: Adenosine is a potent vasodilator used clinically in nuclear scintigraphy to assess coronary artery reserves. The potential to identify this vasodilating effect of adenosine using magnetic resonance imaging (MRI), which is superior in spatial resolution to nuclear scintigraphy, combined with a blood-pool MRI contrast agent, was investigated in normal rats.

Methods: Groups of Sprague-Dawley rats received successive infusions of either adenosine (3 mg/kg/minute; n = 7) or dipyridamole (negative control; up to 1.

Real-time observation of transient focal ischemia and hyperemia in cat brain.

Gradient-recalled echo-planar (T2*-weighted) imaging was used to noninvasively monitor regional blood oxygenation state changes in real time during transient episodes of focal ischemia in cat brain. Varying ischemic intervals (12 s to 30 min) were caused by middle cerebral artery occlusion. A rapid signal drop was noted upon occlusion, due to deoxygenation of static blood in the ischemic tissues.

Contrast-enhanced MR imaging of the lung: assessments of ventilation and perfusion.

The use of aerosolized gadopentetate dimeglumine to define regional lung ventilation and of intravenously administered polylysine-(gadopentetate dimeglumine)40 to assess regional lung perfusion was investigated. In 10 healthy rats who breathed aerosolized gadopentetate dimeglumine (0.25 mol/L) for 5 minutes, pulmonary signal intensity increased diffusely in both lungs by more than 70%.

Preferential looking--clinical lessons.

Preferential looking-based tests of acuity have been available for over a decade. The authors discuss their use in clinical practice, particularly in three groups in whom acuity could not be quantified by traditional means: normal infants, and young children who are either mentally retarded, or who have visual disorders. Preferential looking (PL) testing has increased our understanding of the natural history of visual pathway disorders and has revealed certain patterns of acuity development.

Optimization of capillary zone electrophoresis/electrospray ionization parameters for the mass spectrometry and tandem mass spectrometry analysis of peptides.

The solution chemistry conditions necessary for optimum analysis of peptides by capillary zone electrophoresis (CZE)/electrospray ionization mass spectrometry and CZE electrospray ionization tandem mass spectrometry have been studied. To maximize the signal-to-noise ratio of the spectra it was found necessary to use acidic CZE buffers of low ionic strength. This not only increases the total ion current, but it also serves to fully protonate the peptides, minimizing the distribution of ion current across the ensemble of possible charge states.

Detection of zonal renal ischemia with contrast-enhanced MR imaging with a macromolecular blood pool contrast agent.

The potential of magnetic resonance (MR) imaging enhanced with albumin-(gadolinium diethylenetriaminepentaacetic acid [DTPA])35, a macromolecular blood pool marker, for detection of focal changes in renal perfusion was studied in a myoglobinuric acute renal failure (ARF) model in the rat. T1-weighted spin-echo postcontrast images of injured kidneys at 3 hours after glycerol injection showed three distinct zones: a strongly enhanced outer cortex, a low-intensity inner cortex, and a strongly enhanced medulla. The distinct band of low intensity in the inner cortex indicated zonal decreased blood volume, corresponding to published microsphere data showing zonal low perfusion in the inner cortex.

Magnetic resonance imaging detection of an experimental pulmonary perfusion deficit using a macromolecular contrast agent. Polylysine-gadolinium-DTPA40.

Rationale And Objectives: This study was designed to evaluate the potential of a blood-pool magnetic resonance (MR) contrast agent, polylysine-gadolinium-DTPA40 (polylysine-Gd-DTPA40) for detecting pulmonary perfusion defects.

Materials And Methods: Pulmonary emboli were induced in 10 rats by venous injection of 0.2 mL of air.

Light and retinopathy of prematurity: does retinal location offer a clue?

Nursery illumination has been implicated in the pathogenesis of retinopathy of prematurity (ROP), although the results of recent studies are conflicting. The data base for this article is a prospective ROP study on 607 infants of birth weight less than or equal to 1700 g including 35 larger siblings from multiple births when 1 infant fulfilled the birth weight criteria. Retinopathy commences preferentially in the nasal retina of the most immature neonate and is less likely to develop, or its onset is delayed, in the superior and inferior regions.

Thrombolytic therapy: a case study.

Nursing care for Mr J evolved around his actual and potential problems. The actual problems were: an alteration in comfort (chest pain) related to myocardial ischemia, decreased cardiac output related to reperfusion dysrhythmias, and knowledge deficit regarding treatment with thrombolytic therapy. The potential problems were: fluid volume deficit related to lysis of clots in the cerebral vasculature, and alteration in myocardial tissue perfusion related to reocclusion of the coronary artery.

Iron-dextran as a magnetic susceptibility contrast agent: flow-related contrast effects in the T2-weighted spin-echo MRI of normal rat and cat brain.

Iron-dextran (1 mmol Fe/kg) was used as an intravascular, paramagnetic contrast agent in rat and cat brain in conventional spin-echo T2-weighted (TR 2800/TE 100) 1H magnetic resonance imaging. The resulting images displayed differential decreases (30-50%) in intensity whose pattern was similar to that obtained with the superparamagnetic particulate iron oxide AMI-25 (0.18 mmol Fe/kg).

Hypercarbia-induced changes in cerebral blood volume in the cat: a 1H MRI and intravascular contrast agent study.

Cerebral blood volume changes with arterial carbon dioxide were monitored by proton T1-weighted MR images following administration of the intravascular contrast agent Gd-DTPA labeled with human serum albumin. Without MR contrast, no significant image intensity changes were observed with PaCO2. Following contrast, regional brain image intensities increased significantly over control (0% inspired CO2) in cortical gray, white, and basal ganglia regions with increasing PaCO2 and returned to control intensities upon return to 0% inspired CO2.

Differentiation of capillary leak and hydrostatic pulmonary edema with a macromolecular MR imaging contrast agent.

The ability of a macromolecular contrast agent (polylysine-[gadopentetate dimeglumine]40) to allow distinction of pulmonary capillary leak from hydrostatic pulmonary edema was investigated. Capillary leak edema was induced in 12 rats by means of venous injection of oleic acid; hydrostatic pulmonary edema was induced in 10 rats by means of continuous infusion of 0.9% sodium chloride.