Er:YAG laser irradiation to control the progression of enamel erosion: an in situ study.

This in situ study evaluated the effect of Er:YAG laser irradiation in controlling the progression of enamel erosion-like lesions. Fifty-six enamel slabs (330 KHN ± 10 %) with one fourth of the surface covered with resin composite (control area) were submitted to initial erosion-like lesion formation with citric acid. The slabs were divided into two groups: irradiated with Er:YAG laser and non-irradiated. Fourteen volunteers used an intraoral palatal appliance containing two slabs, in two phases of 5 days each. During the intraoral phase, in a crossed-over design, half of the volunteers immersed the appliance in citric acid while the other half used deionized water, both for 5 min, three times per day. Enamel wear was determined by an optical 3D profilometer. ANOVA revealed that when deionized water was used as immersion solution during the intraoral phase, lower values of wear were showed when compared with the groups that were eroded with citric acid, whether irradiated or non-irradiated with Er:YAG laser. When erosion with citric acid was performed, Er:YAG laser was not able to reduce enamel wear. Small changes on enamel surface were observed when it was irradiated with Er:YAG laser. It may be concluded that Er:YAG laser irradiation did not reduce the progression of erosive lesions on enamel submitted to in situ erosion with citric acid.

Bond durability in erbium:yttrium-aluminum-garnet laser-irradiated enamel.

This study sought to evaluate the influence of thermocycling and water storage on the microtensile bond strength of composite resin bonded to erbium:yttrium-aluminum-garnet (Er:YAG)-irradiated and bur-prepared enamel. Eighty bovine incisors were selected and sectioned. Specimens were ground to produce a flat enamel surface. Samples were randomly assigned according to cavity preparation device: (I) Er:YAG laser and (II) high-speed turbine, and were subsequently restored with composite resin. They were subdivided according to the duration of water storage (WS)/number of thermocycles (TCs): 24 h WS/no TCs; 7 days WS/500 TCs; 1 month WS/2,000 TCs; 6 months WS/12,000 TCs. The teeth were sectioned into 1.0 mm(2)-thick slabs and subjected to tensile stress in a universal testing machine. Data were submitted to two-way analysis of variance (ANOVA) and Tukey's test at a 0.05 significance level. The different periods of water storage and thermocycling did not influence the microtensile bond strength (microTBS) values in the Er:YAG laser-prepared groups. In bur-prepared enamel, the group submitted to 12,000 TCs/6 months' WS (IID) showed a significant decrease in bond strength values when compared to the group stored in water for 24 h and not submitted to thermocycling (IIA), but values were statistically similar to those obtained in all Er:YAG laser groups and in the bur- prepared groups degraded with 500 TCs/1 week WS (IIB) or 2,000 TCs/1 month WS (IIC). It may be concluded that adhesion of an etch-and-rinse adhesive to Er:YAG laser-irradiated enamel was not affected by the methods used to simulate degradation of the adhesive interface and was similar to adhesion in the bur-prepared groups in all periods of water storage and thermocycling.

Magnetic resonance imaging of the acute effects of interstitial neodymium:YAG laser irradiation on tissues.

RATIONALE AND OBJECTIVES: Laser irradiation therapy in deep tissues requires a monitoring method other than visual guidance. Magnetic resonance imaging (MRI) can be used for this purpose because it visualizes soft tissue structures and heat distribution. METHODS: The authors performed interstitial laser irradiations in rat livers with various laser outputs and measured the sizes of laser-induced lesions. MRI of these lesions was done ex vivo and compared with the histologic findings. Laser-induced lesions also were studied in rabbit brain, liver, and skeletal muscle to show the influences of tissue optical and thermal properties. Imaging of interstitial laser irradiation also was performed in vivo in rabbit brains. RESULTS: MRI depicted the laser-induced lesions produced with different laser outputs and tissue types. MRIs of rabbit brain in vivo effectively demonstrated the signal decrease during heating and acute tissue changes. CONCLUSION: MRI has potential for monitoring interstitial laser surgery or hyperthermia.

Differentiation of experimental white matter lesions using multiparametric magnetic resonance measurements.

The potential of multiparametric proton magnetic resonance (MR) measurements for characterizing white matter lesions was investigated. The authors compared acute experimental allergic encephalomyelitis (EAE), which is distinguished by inflammatory lesions, with an immunologically potentiated hyperacute form of the disease in which demyelinating lesions (DEM) also are present. Tissue samples containing cervical spinal cord and brain stem were excised and in vitro measurements of T1, T2, and two components of T2 were performed. Discriminant analysis was applied using MR parameters singly and in various combinations. When the disease was clearly manifested, discrimination between treated and normal animals was satisfactory with single parameters. The use of biexponential T2 components improved the distinction of normal from treated but asymptomatic animals, and differentiated between EAE and DEM. These results suggest that improved characterization of white matter lesions is possible with multiparametric MR in vivo, especially if sampling is performed with imaging and the T2 decay curves are obtained with a sufficient number of echoes to perform biexponential analysis.

Characterization of cerebral infarction by multicomponent analysis of transverse magnetization decay curves.

RATIONALE AND OBJECTIVES: Individual components of the transverse magnetization decay curve (TDC) were assessed for their ability to characterize ischemia in photochemically induced cerebral infarcts. METHODS: Fifty rats were randomly divided into equal-sized experimental and control groups, which were subdivided into groups studied at five different time points, ranging from 6 hours to 22 days. All the rats received transcalvarial irradiation with 560-nm light. Five rats in each time group also received a sensitizing dye before irradiation. In these latter animals, lesions of uniform size and location developed. Lesions were compared with tissue of similar volume and location from the contralateral cortex of the experimental animals and with tissue from both hemispheres of the control animals. TDCs of all the samples were measured and fit with mono- and bi-exponential functions. RESULTS: Unlike the control tissue, infarcted tissue displayed definitive two-component TDC behavior. The time course of the bi-exponential parameters yielded information unavailable from mono-exponential analyses. CONCLUSIONS: Bi-exponential analysis of TDCs may have diagnostic use as a more sensitive indicator of cerebral infarction than mono-exponential analyses.

Response to and control of destructive energy by magnetic resonance.

Magnetic resonance imaging techniques can be used to control and monitor the deposition of destructive energy. The authors evaluated the feasibility of phosphorus-31 magnetic resonance spectroscopy for the control, monitoring, and prediction of the three-dimensional extent of tissue destruction during interstitial laser surgery. Characteristic metabolic changes were demonstrated within the lesion and in the adjacent normal tissue during the deposition of thermal energy.

Cocaine- and methamphetamine-induced acute cerebral vasospasm: an angiographic study in rabbits.

Stroke is a frequently reported, though uncommon, complication of drug abuse, primarily cocaine. The pathogenesis is uncertain, although such cerebrovascular events may result from sympathetically mediated vasoconstriction of cerebral vessels. Amphetamine, another sympathomimetic amine that is commonly abused, may also cause strokes by producing cerebral vasospasm and/or vasculitis. Amphetamine and its derivatives are frequent adulterants of illegally obtained cocaine and may also be used concurrently; the effect(s) of this combination of drugs upon the cerebral vasculature is not known. Our aim was to develop an animal model that would enable us to study the ability of these drugs to produce acute cerebral vasospasm and to observe the response to IV administration of amphetamine and cocaine, either alone or together. Magnified basilar artery arteriograms were obtained in 12 New Zealand white rabbits before and after IV administration of cocaine, methamphetamine, or both, at various dosages. Low doses produced mild vasodilatation. At higher doses, the animals who received cocaine and methamphetamine alone showed little or no basilar artery spasm, but coadministration produced definite basilar artery vasospasm, reflecting a synergistic vasoconstrictive effect. If a similar response exists in the human cerebral vasculature, then this could help explain the cause of strokes associated with drug abuse.

Late reoperations after repair of tetralogy of Fallot.

Twenty-two patients underwent 23 late reoperations after total correction of tetralogy of Fallot from 1965 to 1990. Indications for reoperation included: isolated ventricular septal defect (VSD) in 9 patients (41%), isolated right ventricular outflow tract (RVOT) obstruction in 3 patients (13.7%), VSD associated with a RVOT obstruction in 7 patients (31.8%), aneurysm of the pericardial RVOT patch in 1 patient (4.5%), aortic insufficiency with a residual VSD in 1 patient (4.5%), and tricuspid regurgitation in 1 patient (4.5%). The reoperation consisted of closure of a residual VSD in 17 patients, relief of a RVOT gradient in 11, insertion of a RVOT valve in 4, tricuspid valve replacement in 1 (reoperated twice), aortic valve replacement in 1, and excision of a RVOT aneurysm in 1. Two patients died in hospital (9%) but there were no early deaths in the 11 patients reoperated upon after 1978. Mean follow-up period was 135 months. There were 2 late deaths. The actuarial 20-year survival was 87%. Of the surviving patients, 16 (89%) were in New York Heart Association class I, 1 (5.5%) was in class II, and one (5.5%) was in class III. One patient required a second reoperation for tricuspid bioprosthesis degeneration and 1 patient had moderate recurrent RVOT gradient due to calcified pulmonary bioprosthesis. This study tends to support the policy of recommending reoperation in the presence of surgically significant residual defects. Reoperation is associated with a low early mortality and good long-term results.

Combined heart and kidney transplantation: an effective therapeutic option--report of six cases.

Six cases of combined heart and kidney transplantation with organs from the same donor are reported. All six patients suffered from primary end-stage kidney disease, two chronic glomerulonephritis, two glomerulosclerosis, one chronic pyelonephritis and one with unknown etiology. Four patients were undergoing hemodialysis. Three patients had the diagnosis of ischemic heart disease, one dilated cardiomyopathy secondary to congenital heart disease, two idiopathic dilated cardiomyopathy. Five were males and one female. Ages ranged from 38 to 54 years. On-site or short-distance young donors with normal renal function and good cardiac function necessitating low inotropic support were selected. ABO compatibility was used exclusively. Orthotopic heart transplantation was performed first. During cardiopulmonary bypass, hemofiltration was used in four cases. Kidney transplantation was performed immediately after the closure of the chest. Diuresis was immediate in all cases. No cardiac rejection was documented at EMB. Renal function normalized within few days with no signs of kidney rejection. All six patients are alive and well with normal cardiac and renal function at a mean follow-up of 43 months. Patients and donors selection associated with a proper surgical strategy and prompt immunosuppressive therapy administration make the combined heart and kidney transplantation an effective therapeutic option.

Noninvasive arterial occlusion using MRI-guided focused ultrasound.

The purpose of this work was to test the hypothesis that reproducible and sustainable arterial occlusion can be induced by focused ultrasound energy deposition noninvasively within deep tissue. An MRI-compatible focused ultrasound transducer was used to sonicate a branch of the renal artery (diameter about 0.6 mm) in vivo (nine rabbits). An intravenous MRI contrast agent bolus was injected about 30 min and up to 7 days after the sonication. After follow-up, in vitro magnification x-ray angiograms were obtained and the kidneys were fixed in formaldehyde for histologic study. The ultrasound pulses resulted in complete cessation of blood flow, as shown by the gradient echo images. In seven of the nine rabbits, a wedge-shaped unenhanced area was seen at the part of the kidney that was perfused by the vessel after the contrast agent injection. This area extended laterally (outside of the sonicated volume) to the cortical surface of the kidney. The x-ray angiograms showed that the artery was completely occluded. Postmortem histologic evaluation showed an infarcted tissue volume corresponding to the wedge shape seen in the images. This study showed that appropriately focused ultrasound can be used to close arteries noninvasively. This finding has significant clinical potential.

Potential adverse effects of high-intensity focused ultrasound exposure on blood vessels in vivo.

The aim of the study was to evaluate the potential adverse effects of high intensity ultrasound exposure on blood vessels during noninvasive focused ultrasound surgery. A hydraulic MR-compatible positioning device was used to manipulate a focused ultrasound transducer (frequency 1.49 MHz, f-number = 0.8) in an MRI scanner. The system was used to sonicate a branch of the femoral artery and vein of 19 rabbits (26 thighs) in vivo at intensity levels above the threshold for transient cavitation; i.e., between 4400 and 8800 W cm-2 with multiple 1 s pulses stepped across the vessels (step size = 0.7 mm). The vessels were located and followed by MR angiography. In 13 rabbits, x-ray angiograms were also performed after the animals were euthanized. The results demonstrated that the 1 s high-intensity exposures caused the arteries to constrict at all exposure levels tested. At the intensity of 5800 W cm-2 and above, the MRI angiogram immediately after the sonications showed no flow. The x-ray angiograms (1-2 h later) showed that the blood vessels were open, but constricted to about 50% or less of their diameter. Both the MR and x-ray angiograms showed that the vessel diameters relaxed toward their initial diameter during the first week after sonication. In five cases, hemorrhage or vessel rupture was caused by the sonication. This study demonstrates that short, high-intensity focused ultrasound exposure can cause vessel spasm and hemorrhage when transient cavitation is present. This condition should be avoided during noninvasive focused ultrasound surgery.

In vivo characterization of cytotoxic intracellular edema by multicomponent analysis of transverse magnetization decay curves.

RATIONALE AND OBJECTIVES: We investigated the multicompartmental nature of T2 decay in a specific white matter edema model. METHODS: Triethyltin (TET) intoxication was produced in six male New Zealand White rabbits. Images were obtained over the 23-day study duration using a 64-echo Carr-Purcell-Meiboom-Gill (CPMG) sequence (repetition time = 3000 msec, echo time = 20 msec). T2 decay curves were extracted from 0.7 x 0.7 x 3.0 mm3 voxels in the corpus callosum and contiguous white matter tracts, cortex, thalamic nuclei, hypothalamic nuclei, and the masseter muscles. The curves were fit with biexponential functions. RESULTS: Increased signal intensity in the corpus callosum was evident 2-3 days after the first TET injection. At this time, a substantial slowly relaxing component appeared in the decay curves of the corpus callosum and, to a lesser extent, in the thalamus and hypothalamus. Changes in the rabbits' body weight, general physical condition, and neurologic state paralleled the growth and regression of the second, slowly relaxing component. CONCLUSION: The appearance and regression of a slowly decaying second component in the T2 decay curve is consistent with the formation and shrink-age of intracellular vesicles in the intramyelin sheaths of central white matter.

The vertebral canals in lumbar disc disease.

The sagittal dimensions of the five lumbar vertebral canals tend to be more shallow in patients operated for lumbar radiculopathy than in a group of controls. The more frequent occurrence of radiculopathy in patients with small canals can be explained by the requirement for only a small protrusion of intervertebral disc, or any other structural abnormality, to impinge the nerve. The sagittal diameter can be obtained easily from the lateral roentgenogram and, therefore, requires no invasive or expensive tests. This measurement can be quite helpful in interpreting myelographic defects and in planning and doing operations on patients with radiculopathy.

Combined surgical approach to coexistent carotid and coronary artery disease.

Combined coronary artery bypass and carotid endarterectomy were performed in 52 patients (mean age 61 years) between 1981 and 1990. Of these, 36 (69%) had functional class III-IV angina pectoris, 33 (63%) had triple-vessel disease, 36 (69%) had one, or more, previous myocardial infarctions, and 33 (63%) had an abnormal left ventricular function. In 4 cases, additional cardiac procedures were performed. Asymptomatic carotid stenosis was documented in 29 patients (56%) and the remaining 23 (44%) had experienced cerebrovascular symptoms. All patients had hemodynamically significant stenosis of at least one carotid artery, 17 (33%) had severe bilateral carotid artery stenosis, and 6 (11%) had an additional occlusion of the contralateral internal carotid artery. There were no early deaths. Perioperative morbidity included: myocardial infarction in 4 patients (7.7%) and neurological deficit in 3 (5.7%) but functional impairment was not permanent. Late results have been obtained for all 52 patients at a mean postoperative interval of 35 months. Four patients (7.7%) have died, and the 5 year life-table survival rate was 83%. At five years, actuarial curves showed 67% of patients to be free of all serious events or death. Late mortality and morbidity were related above all to the progression of the coronary artery disease. We concluded that simultaneous endarterectomy of significant carotid artery stenosis in candidates for coronary bypass can be done safely and considered as more practical for the patient.

Experimental treatment of cerebral vascular spasm secondary to subarachnoid hemorrhage.

Cerebral artery spasm following subarachnoid hemorrhage (SAH) is a major cause of morbidity and mortality. Treatment or prevention methods are most desirable. Using the basilar artery of the rabbit, cerebral arterial spasm was induced with an injection of 4 ml of autologous blood via cisternal puncture in six treated, four pre-treated and six control animals. Vertebral angiography was performed before and at ten, twenty, thirty and sixty minutes after the injection of blood was carried out, and the presence of spasm and its cause were followed in these animals. Pre-treated and treated subjects received 2 mg/kg of diltiazem (a calcium antagonist) either before and after the injection of blood, respectively. Analysis of vessel diameters by computer assisted densitometry showed that the treated group had a significant reduction of basilar artery spasm when compared to the control group, while in the pre-treated group, spasm was prevented.

Use of the retrograde "pull-through" technique.

A 50-year-old man, who 9 months earlier had undergone emergency operation for acute type I aortic dissection, was readmitted to our hospital with the diagnosis of an enlarging aneurysm of the false lumen involving the transverse arch and the proximal third of the descending thoracic aorta, due principally to redissection at the distal suture line of the ascending aortic graft. Replacement of the aortic arch and proximal descending thoracic aorta was performed by using the retrograde "pull-through" technique with hypothermic circulatory arrest and retrograde cerebral perfusion. Although circulatory arrest lasted 110 minutes, the patient was extubated on the 2nd postoperative day and had no central or peripheral neurologic damage. Mild, transitory renal dysfunction was observed in the 1st postoperative week, and the patient was discharged on the 18th postoperative day. He is asymtomatic at 15 postoperative months. Deep hypothermia and retrograde cerebral perfusion proved effective despite prolonged circulatory arrest. The retrograde "pull-through" technique is an effective method of replacing the entire thoracic aorta and should probably be considered for single-stage repair of acute type I aortic dissection with multiple intimal tears.

Papillary fibroelastoma of the mitral valve. A rare cause of embolic events.

A 66-year-old woman was admitted to our department with an 11-month history of multiple transient ischemic attacks and strokes. A 2-dimensional echocardiographic study revealed an intracardiac tumor attached both to the chordae and to the anterolateral papillary muscle of the mitral valve. The patient underwent excision of the tumor, which necessitated concomitant mitral valve replacement. She remains free of symptoms 1 year postoperatively, with no echocardiographic evidence of recurrence of the tumor. To date, 19 cases of surgically treated papillary fibroelastomas of the mitral valve have been reported in the English-language literature. We add the description of our case to emphasize the importance of this tumor as an identifiable and curable cause of cerebral and coronary embolization. The frequent occurrence of cardiac valve tumors suggests the use of 2-dimensional echocardiography in patients who are experiencing transient ischemic attacks or strokes, as well as in those who sustain a myocardial infarction despite normal coronary arteries at angiography. When papillary fibroelastoma is diagnosed, surgical treatment must be considered because of the high risk of embolization.

Successful resection of a tuberculous pseudoaneurysm of the descending thoracic aorta: case report and review of the literature.

An aneurysm of the descending thoracic aorta was found in a 55-year-old woman. She had hemoptysis, fever, and weight loss beginning 1 month before hospitalization. A miliary tuberculosis developed after angiography. The patient underwent surgical resection of the aneurysm, which proved to be tuberculous. The aortic wall was reconstructed with a Dacron patch. Antituberculosis pharmacotherapy, started before operation, was discontinued after 16 months of administration. The patient is doing well 19 months after operation. The English literature reports only 7 other cases of surgical treatment of tuberculous aneurysm of the thoracic aorta. According to previous reports, early surgical intervention, combined with preoperative and prolonged postoperative antituberculosis therapy and close postoperative follow-up, is mandatory in this group of patients.

Microhardness and SEM after CO(2) laser irradiation or fluoride treatment in human and bovine enamel.

BACKGROUND: It remains uncertain as to whether or not CO(2) laser is able to hinder demineralization of enamel. The possibility to use bovine instead of human teeth on anticariogenic studies with laser has not yet been determined. PURPOSE: To compare the ability of CO(2) laser and fluoride to inhibit caries-like lesions in human enamel and to test whether a similar pattern of response would hold for bovine enamel. STUDY DESIGN: Ninety-six enamel slabs (2 × 2 × 4 mm) (48 from bovine and 48 from human teeth) were randomly distributed according to surface treatment (n = 12): CO(2) laser, 5% sodium fluoride varnish (FV), 1.23% acidulated phosphate fluoride (APF) gel, or no treatment (control). Specimens were subjected to a 14-day in vitro cariogenic challenge. Microhardness (SMH) was measured at 30 µm from the surface. For ultrastructural analysis, additional 20 slabs of each substrate (n = 5) received the same treatment described earlier and were analyzed by SEM. RESULTS: ANOVA and Tukey test ascertained that CO(2) laser promoted the least mineral loss (SMH = 252(a)). Treatment with FV resulted in the second highest values (207(b)), which was followed by APF (172(c)). Untreated specimens performed the worst (154(d)). SEM showed no qualitative difference between human and bovine teeth. APF and control groups exhibited surfaces covered by the smear layer. A granulate precipitate were verified on FV group and fusion of enamel crystals were observed on lased-specimens. CONCLUSIONS: CO(2) laser may control caries progression more efficiently than fluoride sources and bovine teeth may be a suitable substitute for human teeth in studies of this nature.