10 GHz pulse repetition rate Er:Yb:glass laser modelocked with quantum dot semiconductor saturable absorber mirror.

Semiconductor saturable absorber mirror (SESAM) modelocked high pulse repetition rate (≥10 GHz) diode-pumped solid-state lasers are proven as an enabling technology for high data rate coherent communication systems owing to their low noise and high pulse-to-pulse optical phase-coherence. Compared to quantum well, quantum dot (QD)-based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the first 10 GHz pulse repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting 2 ps pulse width from an Er-doped glass oscillator (ERGO). The 10 GHz ERGO laser is modelocked with InAs/GaAs QD-SESAM with saturation fluence as low as 9 µJ/cm2.

Green-diode-pumped femtosecond Ti:Sapphire laser with up to 450 mW average power.

We investigate power-scaling of green-diode-pumped Ti:Sapphire lasers in continuous-wave (CW) and mode-locked operation. In a first configuration with a total pump power of up to 2 W incident onto the crystal, we achieved a CW power of up to 440 mW and self-starting mode-locking with up to 200 mW average power in 68-fs pulses using semiconductor saturable absorber mirror (SESAM) as saturable absorber. In a second configuration with up to 3 W of pump power incident onto the crystal, we achieved up to 650 mW in CW operation and up to 450 mW in 58-fs pulses using Kerr-lens mode-locking (KLM). The shortest pulse duration was 39 fs, which was achieved at 350 mW average power using KLM. The mode-locked laser generates a pulse train at repetition rates around 400 MHz. No complex cooling system is required: neither the SESAM nor the Ti:Sapphire crystal is actively cooled, only air cooling is applied to the pump diodes using a small fan. Because of mass production for laser displays, we expect that prices for green laser diodes will become very favorable in the near future, opening the door for low-cost Ti:Sapphire lasers. This will be highly attractive for potential mass applications such as biomedical imaging and sensing.

Low repetition rate SESAM modelocked VECSEL using an extendable active multipass-cavity approach.

Ultrafast VECSELs are compact pulsed laser sources with more flexibility in the emission wavelength compared to diode-pumped solid-state lasers. Typically, the reduction of the pulse repetition rate is a straightforward method to increase both pulse energy and peak power. However, the relatively short carrier lifetime of semiconductor gain materials of a few nanoseconds sets a lower limit to the repetition rate of passively modelocked VECSELs. This fast gain recovery combined with low pulse repetition rates leads to the buildup of multiple pulses in the cavity. Therefore, we applied an active multipass approach with which demonstrate fundamental modelocking at a repetition rate of 253 MHz with 400 mW average output power in 11.3 ps pulses.

Carbon dioxide as an angioscopic medium. Comparison to various methods of saline delivery.

The limitations of angiography, when it is used as the sole method of vascular assessment, are increasingly apparent as vascular intervention becomes more sophisticated. Angioscopy could be an adjunctive diagnostic modality by differentiating among thrombus, dissection, and atheroma, and by monitoring the response to therapy. However, angioscopy requires a blood-free field for adequate visibility, and this may be difficult to obtain. The feasibility of carbon dioxide (CO2) and various saline delivery methods for clarifying the viewing field for percutaneous angioscopy was investigated. Angioscopy of femoral and iliac arteries on nine dogs was performed. Saline was infused by hand injection, pressure bag infusion, or mechanical power injection, and CO2 gas was injected using a special gas injector. The clarity of the viewing field was graded for each medium and method. Excellent quality antegrade femoral angioscopy was obtained with CO2. The superiority of CO2 injection in comparison with power-injected saline approached statistical significance (P = .06). Power-injected CO2 and power saline were superior to hand-injected or pressure bag-injected saline for maintaining sufficient visibility. Retrograde iliac angioscopy was possible without inflow occlusion, but required high flow rates (only possible with power-injected saline or CO2). CO2 injected under controlled circumstances holds promise as a medium to improve angioscopic visibility.

Effects of carbon dioxide arterial infusion on hepatic biochemistry and histology in a rabbit model.

RATIONALE AND OBJECTIVES: The objective of this study was to determine the effect of carbon dioxide (CO2) infusion on hepatic biochemistry and histology in a rabbit model. METHODS: The study population consisted of 24 anesthetized rabbits that received hepatic infusion of either CO2 or saline (control) at doses of 10 mL/kg, comparable with those doses used in human clinical trials. Blood for clinical chemistry analysis was collected at baseline, 1 hour, 24 hours, and 168 hours (7 days) postprocedure. The rabbits were killed at 7 days postprocedure and the liver examined histologically for hepatic damage. RESULTS: There were no significant differences between the CO2 and the control groups in dorsal, ventral, and dorsal/ventral scores. Increases in alanine, an important indicator of hepatocellular membrane injury, in the CO2 group were significantly greater at 1 hour and 24 hours posttreatment (P = 0.037 and 0.013). However, the mean levels at 168 hours (7 days) were not significantly different (P = 0.22). The increases at 1 and 24 hours were small, transient, and considered clinically insignificant. CONCLUSION: No long-term hepatic effects in these animals were suggested by biochemical and histological examinations.

Detection of acute intracerebral hemorrhage on MR imaging: ineffectiveness of prolonged interecho interval pulse sequences.

MR imaging at 0.6 T was performed in 22 patients with acute (less than 7 days) intracranial hemorrhage to determine the efficacy of prolongation of the interecho interval, which has been demonstrated to enhance T2 shortening in vitro, as a method to improve the detection of hemorrhage in clinical imaging. The protocol included 750/33 (TR/TE), 2150/60,120 (short interecho interval of 60 msec), and 2150/120 (long interecho interval of 120 msec) sequences. Visual comparisons of the 2150/120 images obtained with the short and long interecho intervals demonstrated no difference in the degree of hypointensity in 21 of 22 cases. Quantitative comparisons demonstrated no statistically significant difference in the degree of maximal hypointensity, in the ease of detectability of hypointensity, or in the overall image contrast in 16 of 22 cases. We conclude that prolongation of the interecho interval is not a clinically useful technique to improve the detection of acute hemorrhage.

Computed tomographic changes of hypertensive encephalopathy.

Computed tomographic (CT) scans were evaluated in 11 patients with acute hypertensive encephalopathy. Hypertensive encephalopathy is characterized by an acute, severe rise in blood pressure associated with headache, nausea, vomiting, altered mental status, and focal neurologic deficits, and rapid improvement after control of blood pressure. The systolic blood pressure range is 200-280 mm Hg; diastolic is 130-170 mm Hg. The most common CT finding was white-matter edema, diffuse or focal, affecting the supratentorial compartment in all cases and the infratentorial compartment in eight. These changes resolved after the blood pressure was lowered in all six patients studied by follow-up CT. Permanent areas of infarction were demonstrated in three patients. These abnormalities are correlated with the neuropathologic findings in hypertensive encephalopathy.

MR imaging of acute intracranial hemorrhage: findings on sequential spin-echo and gradient-echo images in a dog model.

Seven intraparenchymal hematomas (four venous and three arterial) were placed in the brains of six dogs in order to study the MR appearance of acute hemorrhage and to evaluate the effects of several variables on the signal intensity of the hematoma. MR imaging at 0.6 and 1.5 T was performed by using standard short and long TR spin-echo and low-flip-angle gradient-echo sequences. Sequential examinations were performed during the first week following hematoma creation. MR findings were compared with CT and postmortem examinations. Three patterns of signal intensity were observed, which varied according to the size (small vs large) and location (parenchymal vs intraventricular) of the hematomas. The small parenchymal hematomas did not undergo evolutionary changes. On short TR scans they were isointense at both field strengths, and therefore not detectable; on long TR scans these hematomas were of variable intensity at 1.5 T and were hyperintense at 0.6 T. On gradient-echo scans, they were hypointense at all times at both field strengths. The large parenchymal hematomas underwent evolutionary changes typical of those seen in clinical imaging. On short TR scans they were initially isointense and became hyperintense 1-3 days later. Long TR scans demonstrated initial hyperintensity, followed by the development of hypointensity within 12 hr in the venous hematomas and within 60 hr in the arterial hematoma. The intensity changes on long TR scans were seen at both 0.6 and 1.5 T, but occurred sooner and to a greater degree at 1.5 T. Gradient-echo imaging of these large lesions demonstrated hypointensity at all times at both field strengths. The intraventricular hemorrhages demonstrated more rapid development of hyperintensity on short TR scans and slower and less pronounced development of hypointensity on long TR scans compared with the parenchymal clots in the same animal. Gradient-echo imaging of the intraventricular hemorrhages demonstrated hypointensity at all times at both field strengths. A multifactorial hypothesis is proposed to explain the differences in intensity between venous, arterial, and intraventricular blood. Gradient-echo sequences should prove to be highly useful in detecting and delineating hemorrhages and are recommended for the MR protocol of patients with acute neurologic ictus and suspected hemorrhage.

Intraspinal extension of an air cyst of the lung: case report.

We report the diagnostic evaluation and treatment of a cystic paraspinal and epidural lesion originally thought to be a neurofibroma or an arachnoid cyst. Intraoperatively, the lesion was found to be an air cyst of the lung that was successfully ligated.

Symptomatic lumbar epidural varices. Report of two cases.

Lumbar epidural varices have been infrequently described in the literature and rarely accepted as a primary pathophysiological entity. The authors' total experience with symptomatic lumbar epidural varices over the last 15 years includes four cases (incidence 0.067% of all lumbar spine operations), two of which are described in detail in this paper. The mechanism for their formation is proposed: central disc herniations obstruct the anterior epidural venous flow leading to anterolateral caudal venous distention. Subsequent venous endothelial injury predisposes to varying degrees of phlebothrombosis. Decompression of partially thrombosed varices may occur during operative discectomy or spontaneously during regression of the nonoperated disc prolapse. Regression of the central disc herniation may also explain the "disappearing disc" phenomenon, in which patients with clinical and radiographic evidence of apparently large caudal disc herniations exhibit clinical and radiographic resolution. Magnetic resonance (MR) imaging characteristics of the epidural varix depend upon the degree of thrombosis within this anomaly. A thrombosed varix is hyperintense on T1-weighted, proton-density, and T2-weighted images, whereas flowing blood is hypointense. The variable hypo- and hyperintensity on the T2-weighted MR imaging sequences correlate with a partially patent lumen within the varix.

The effect of cadmium and other metals on vascular smooth muscle of the dogfish shark, Squalus acanthias.

The effect of Cd2+ and related metals (Ni2+, Hg2+, Pb2+, Co2+, Sn2+ Cu2+ and Zn2+) on vascular tension was studied using isolated rings of endothelium-free, smooth muscle from the ventral aorta of the shark, Squalus acanthias. Both Cd2+ and Ni2+ produced significant vasoconstriction at concentrations at or above 10(-6) M (112 and 59 ppb, respectively); the other metals were either marginally constrictive (Hg2+ and Sn2+) or were without effect (Pb2+, Co2+, Cu2+, and Zn2+). We suggest that previously published vascular effects of Hg2+ and Pb2+ may have been secondary to responses of the vascular endothelium, and that the role of Ni2+ in hypertension should be investigated further. Our data indicate that the effects of metals on this vascular smooth muscle are specific and not generic. Moreover, this system could be utilized to investigate the mechanisms of metal-induced vasoconstriction.

The effect of atropine on cadmium- and nickel-induced constriction of vascular smooth muscle of the dogfish shark ventral aorta.

We investigated the effect of blockade of muscarinic, cholinergic receptors by atropine on the Cd2(+)- and Ni2(+)-induced vasoconstriction of rings of endothelium-free, vascular smooth muscle from the ventral aorta of the dogfish shark, Squalus acanthias. Atropine reduced the Cd2(+)-induced vasoconstriction by approximately 50%, but did not alter the Ni2(+)-induced vasoconstriction, suggesting that the vasoactivity of these two metals may be, at least partially, via different pathways. In addition, this is the first demonstration that one component of Cd2+ vaso-toxicity may be via stimulation of muscarinic receptors.

Detection of hemorrhage in acute cerebral infarction. Evaluation with spin-echo and gradient-echo MRI.

We investigated the efficacy of magnetic resonance imaging (MRI) in the detection and delineation of acute hemorrhagic cerebral infarction and evaluated the role of gradient-echo imaging in these patients. This study was performed prospectively. Entry criteria were: (1) Clinical evidence of acute supratentorial infarction later confirmed by at least one imaging study, and (2) unenhanced computed tomography (CT) and MRI scans performed within 72 hours of ictus. The first 50 patients who met these criteria were included. Comparison of CT and spin-echo (SE) and gradient-echo (GE) MRI at 0.6 T for the visualization of infarction and for the detection or exclusion of hemorrhage were done. There were no cases in which CT was superior to MRI for the diagnosis of either bland or hemorrhagic infarction. All 50 infarcts were detected on long TR SE MRI and 30/50 on GE scans. Eighteen infarcts were judged to be hemorrhagic on the basis of well-established CT and MRI criteria. In all these cases, hemorrhage was most obvious on GE scans as focal areas of marked hypointensity, including 10 cases in which SE MRI and CT demonstrated subtle, equivocal, or no evidence of hemorrhage. In addition, GE MRI allowed for the exclusion of hemorrhage in five cases with equivocal findings of hemorrhage on long TR SE MRI. GE MRI is a valuable adjunct to SE sequences for the detection or exclusion of hemorrhage in acute infarcts with equivocal or mild intensity changes on SE MRI. With further improvements in fast-scanning techniques and a greater understanding of the pathophysiology and clinical implications of hemorrhagic infarction, it may be possible to replace CT with a combination of SE and GE MRI as the primary imaging modality in the evaluation of acute infarction.

The neuroimaging features of the cardiolipin antibody syndrome.

The purpose of our study was to define the neuroimaging features of the cardiolipin antibody syndrome. Thirty-eight patients with elevated anticardiolipin antibody titers were studied with magnetic resonance imaging or computed tomography or both. Two patients underwent cerebral angiography. All patients had recurrent transient ischemic attacks, amaurosis, or strokes. One patient had normal imaging findings. The remaining patients had a combination of infarction and atrophy. Focal infarcts, the most common finding, were seen in 32 patients. Cerebral atrophy was seen in 26 patients and was the only radiographic finding in 5. Angiography demonstrated dramatic abnormalities in the distal portions of the anterior and posterior circulations, with multiple stenosis and occlusions and extensive pial and transdural collateral networks. The cardiolipin antibody syndrome should be suspected in young patients with transient ischemic attacks or strokes in the absence of the usual risk factors for cerebrovascular disease. The presence of raised anticardiolipin antibody titers or the cardiolipin antibody syndrome in patients with lupus, in those with other connective tissue diseases, and in patients without overt manifestations of an autoimmune disorder should be viewed as a risk factor for future ischemic cerebrovascular events. Further understanding of the precise role of these antibodies in the pathogenesis of vascular thrombosis may lead to a better understanding of the mechanisms underlying certain forms of stroke.

1.55 µm InAs/GaAs quantum dots and high repetition rate quantum dot SESAM mode-locked laser.

High pulse repetition rate (≥ 10 GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10 GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting ∼2 ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices.

Soliton mode-locked Er:Yb:glass laser.

We report on a simple diode-pumped passively mode-locked Er:Yb:glass laser generating transform-limited 1536-nm solitons of 255-fs duration with a repetition rate of 50 MHz and average power of 58 mW. We also discuss timing jitter and the trade-off between short pulses and high output power in these lasers.