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.

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.

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.

MR-based temperature monitoring for hot saline injection therapy.

We applied magnetic resonance (MR) phase mapping methods to monitor the thermal frequency shift of water in order to study temperature changes from percutaneous hot saline injection therapy (PSIT) using in vitro swine livers and in vivo rabbit livers. The thermal coefficients calculated from the shifts of the water frequency with thermocouple based temperature measurements were -0.0085 +/- 0.0019 ppm/ degrees C for the in vitro studies and -0.0089 ppm/ degrees C for the in vivo studies. The error range was estimated to be +/- 3 degrees C and +/- 4.5 degrees C, respectively. Color-coded temperature maps were compared with macroscopic lesion sizes of the specimen. Regions defined using a 20 degrees C elevation in the initial images following hot saline injection (around 55 degrees C in absolute temperature) closely correlated with visible coagulation in size. We conclude that MR temperature monitoring of PSIT is quite feasible and may be helpful in expanding the clinical use of this thermal therapeutic tool for liver tumors.

Tolterodine-warfarin drug interaction.

OBJECTIVE: To report two cases of warfarin therapy in which the addition of tolterodine resulted in prolonged international normalized ratios (INRs). CASE SUMMARY: Two patients, each receiving warfarin for stroke prophylaxis in association with chronic atrial fibrillation, developed adverse effects after the initiation of tolterodine for urinary disorders. Other medications for concurrent medical diagnoses had remained unchanged. One patient had an episode of prostatitis, which was treated with levofloxacin immediately prior to tolterodine initiation. The warfarin dosage had remained constant for many weeks in both patients prior to and during the tolterodine trials. In each patient, the initiation of tolterodine was associated with a significant increase in the patient's INR measured 10-14 days later. Thus, tolterodine was ineffective in both patients and was discontinued one to two days before the elevated INRs were determined during routine clinic visits. INRs determined approximately two weeks after tolterodine was discontinued were similar to those obtained during the period before the use of the drug; the warfarin dosage remained unchanged. Rechallenge with tolterodine was not attempted in either patient. DISCUSSION: Several aspects of the reported cases support the validity of a proposed drug interaction when tolterodine is initiated in a patient stabilized on warfarin therapy. The temporal association of the course of tolterodine with an elevated INR, the return to the previous warfarin dose-INR response relationship after tolterodine discontinuation, and the absence of other causes for the elevated INR were factors found in both patients. Possible mechanisms to explain the suggested drug interaction are explored. CONCLUSIONS: Until further data are available, clinicians should be vigilant for a possible drug interaction when tolterodine therapy is initiated in a patient maintained on warfarin therapy.

Brain edema development after MRI-guided focused ultrasound treatment.

The aim of this study was to investigate a potential technique for image-guided minimally invasive neurosurgical interventions. Focused ultrasound (FUS) delivers thermal energy without an invasive probe, penetrating the dura mater, entering through the cerebrospinal fluid (CSF) space, or harming intervening brain tissue. We applied continuous on-line monitoring by MRI to demonstrate the effect of the thermal intervention on the brain tissue. For this, seven rabbits had a part of their skull removed to create access for the FUS beam into the brain through an acoustic window of 11 mm in diameter. Dura was left intact and skin was sutured. One week later, the rabbits were sonicated for 3 seconds with 21 W acoustic power, and the FUS focus was visualized with a temperature-sensitive T1-weighted MRI pulse sequence. The tissue reaction was documented over 7 days with T2-weighted images of the brain. The initial area of the central low signal intensity in the axial plane was .4+/-.3 mm2, and for the bright hyperintensity surrounding the lesion, it was 2.3+/-.6 mm2 (n = 7). In the coronal plane, the corresponding values were .4+/-.1 mm2 and 3.4+/-.9 mm2 (n = 5). The developing brain edema culminated 48 hours later and thereafter diminished during the next 5 days. Histology revealed a central necrosis in the white matter surrounded by edematous tissue with inflammatory cells. In summary, the image-guided thermal ablation technique described here produced a relatively small lesion in the white matter at the targeted location. This was accomplished without opening the dura or the need for a stereotactical device. MRI allowed on-line monitoring of the lesion setting and the deposition of thermal energy and demonstrated the tissue damage after the thermal injury.

Heart transplantation 1985-1998: 13-years experience at Angelo De Gasperis Cardio-Thoracic Department-Milan.

BACKGROUND: After 13 years of transplant experience in our center, we analyzed the results in the overall population and in particular subgroups of heart transplant recipients. We tried to identify risk factors for both early (3 months) and late (over 3 months) mortality after heart transplantation. METHODS: The data on 461 patients transplanted from November 1985-June 1998 were reviewed. To study risk factors for mortality, the results for 313 patients operated on from June 1985-June 1995 were studied and analyzed with a multivariate logistic regression and Cox's proportional hazard model. Seventy pre-, intra- and postoperative variables were considered including patient demographics, clinical status, hemodynamic parameters, donor characteristics, donor-recipient HLA mismatches, complications, and immunosuppressive protocols. We also compared results for patients transplanted from 1985-1991 (Group 1) and from 1992-1998 (Group II) to assess improvements due to changes in indications and in perioperative treatments. RESULTS: Overall mortality in the entire population was 20.2% (93/461). The 30-day, 3-month and late mortality rates were 8.0%, 10.2%, 11.1%, respectively. Group II mortality rates were 6.5%, 8.5% and 6.8%, respectively, despite a significant increase in Status I patients (20.6% in Group I vs 49.0% in Group II, p = 0.0001). The main causes of death were graft failure (24.7%), cardiac allograft vasculopathy (18.3%), and infection (16.1%). The mean follow-up of the 414 recipients who survived more than 3 months was 54.0 +/- 37.3 months. Actuarial survival was 87.4%, 79.2% and 68.9% at one, 5 and 10 years, respectively. The difference in the 5-year actuarial survival rates between Group I and Group II patients was statistically significant (73.5% vs 83.9%, p = 0.0135). The transpulmonary gradient, right atrial pressure and mid-high doses of donor inotropic support were identified as independent risk factors for early mortality. The number of moderate rejections at biopsy and early posttransplant infections were identified as independent risk factors for late mortality. The results of patients transplanted while on ventricular assist devices, urgent and elective patients and combined heart and kidney transplants were also reported. CONCLUSIONS: The overall results of our 13-year experience are very satisfying in relation to early and late mortality, with a significant favorable trend between patients transplanted in the early era (1985-1991) and those transplanted in the recent era (1992-1998). Pulmonary hypertension and elevated preoperative right filling pressure appear to indicate a significantly increased risk of early death and only marginally influence late survival, which is principally influenced by severe postoperative complications. Good results were achieved in combined heart and kidney transplantation and among patients who deteriorated during the waiting period and were supported with ventricular assist devices. The early and late outcomes for urgent (status I) and elective (status II) heart transplant patients were comparable.

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.

Thermal effects of focused ultrasound on the brain: determination with MR imaging.

PURPOSE: To determine the feasibility of the use of temperature-sensitive magnetic resonance (MR) imaging for the detection of local temperature elevations at the focus of a low-power ultrasound beam in the brain. MATERIALS AND METHODS: The brains in 28 rabbits were sonicated at acoustic power levels of 3.5-17.5 W. Four to five different locations were sonicated at different acoustic power levels in each rabbit. MR images were obtained 2 hours, 48 hours, 10 days, and 23 days after the sonications, depending on when the animals were sacrificed. Histologic evaluation of whole brain was performed. RESULTS: Forty of 43 (93%) of the lowest-power (3.5-W) sonications were visible on temperature-sensitive MR images and did not result in any short- or long-term histologic or MR imaging evidence of tissue damage. A contrast-to-noise ratio of approximately 6 and a temperature elevation of 7 degrees-8 degrees C were observed. CONCLUSION: Temperature elevations induced by means of focused ultrasound exposures that do not cause damage in the in vivo rabbit brain can be detected at temperature-sensitive MR imaging.

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.

MR appearance and spectral features of injected ethanol in the liver: implication for fast MR-guided percutaneous ethanol injection therapy.

PURPOSE: Our goal was to evaluate several fast MR strategies for monitoring ethanol distributions so that percutaneous ethanol injection might be guided with MRI. METHOD: Fast RF spoiled GRE sequences (SPGR) and T2-weighted rapid acquisition with relaxation enhancement (RARE) sequences with and without spectroscopic-quality water suppression techniques were assessed for their ability to depict the distribution of injected ethanol in ex vivo pig liver. A line scan Carr-Purcell-Meiboom-Gill spectroscopic imaging sequence was used to validate observations and measure spectral relaxation characteristics of the ethanol signal in liver. Injected deuterated ethanol was also tested as an alternative possibility to depict the distribution of ethanol. RESULTS: The water-suppressed T2-weighted RARE sequence depicted the distribution of ethanol better than other sequences. Deuterated ethanol appeared as a signal void on all sequences. CONCLUSION: Water-suppressed T2-weighted RARE sequences could be useful to rapidly monitor MR-guided PEI.

Optimization of spoiled gradient-echo phase imaging for in vivo localization of a focused ultrasound beam.

The parameters of a spoiled gradient-echo (SPGR) pulse sequence have been optimized for in vivo localization of a focused ultrasound beam. Temperature elevation was measured by using the proton resonance frequency shift technique, and the phase difference signal-to-noise ratio (SNR delta phi) was estimated in skeletal muscle and kidney cortex in 10 rabbits. Optimized parameters included the echo time equivalent to T2* of the tissue, the longest repetition time possible with a 20-s sonication, and the flip angle equivalent to the Ernst angle. Optimal SPGR phase imaging can detect a sonication beam with a peak phase difference of 0.55 radian, which corresponds to a temperature elevation of 7.3 degrees C. The sonication beam can be localized within one voxel (0.6 x 0.6 x 5 mm3) at power levels that are below the threshold for thermal damage of the tissue.

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.

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.

MR monitoring of focused ultrasonic surgery of renal cortex: experimental and simulation studies.

The aim of the study was to test the hypothesis that magnetic resonance (MR) imaging-guided and -monitored noninvasive ultrasonic surgery can be performed in highly perfused tissues from outside the body. A simulation study was performed to evaluate the optimal sonication parameters. An MR-compatible positioning device was then used to manipulate a focused ultrasound transducer in an MR imager, which was used to sonicate kidneys of five rabbits at various power levels and different durations. Temperature elevation during sonication was monitored with a T1-weighted spoiled gradient-echo sequence. The simulation study demonstrated that a sharply focused transducer and relatively short sonication times (30 seconds or less) are necessary to prevent damage to the overlying skin and muscle tissue, which have a much lower blood perfusion rate than kidney. The experiments showed that the imaging sequence was sensitive enough to show temperature elevation during sonication, thereby indicating the location of the beam focus. Histologic evaluations showed that kidney necrosis could be consistently induced without damage to overlying skin and muscle. The study demonstrated that highly perfused tissues such as the renal cortex can be coagulated from outside the body with focused ultrasound and that MR imaging can be used to guide and monitor this 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.

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.

[Magnetic resonance in postoperative evaluation of aortic dissection]. / La Risonanza Magnetica nella valutazione postoperatoria della dissecazione aortica.

The value of MRI was investigated in the demonstration of residual alterations and postoperative complications of aortic dissection. October 1988 to December 1992, fifty-nine patients were examined with MRI. The series consisted of 53 patients affected with type A and 6 with type B aortic dissection, all of them surgically treated. The following parameters were studied: 1) aortic dilatation above and 2) below the prosthesis, 3) redissection, 4) persistent intimal flap, 5) origin of abdominal vessels from the false lumen and 6) study of supra-aortic vessels. Twelve of 59 patients were considered normal since all parameters were negative. The aorta was dilated in 19 patients distal to the graft and in 4 proximal to it. Redissection was observed in 33 of 59 patients. Residual intimal flap was clearly demonstrated in 33 of 59 patients; the state of the false lumen was clearly depicted in 12 patients with SE images alone and in 18 of the extant 21 with phase imaging. In 11 of 59 patients abdominal vessels originated from the false lumen. In 53 of 59 patients supra-aortic vessels were clearly demonstrated and appeared to be involved in 10 patients. In 6 cases MRI failed to yield enough information. In our experience MRI is the method of choice for monitoring the aorta after surgical dissection to detect changes and complications and therefore choose the most appropriate treatment.

MR monitoring during cryotherapy in the liver: predictability of histologic outcome.

For well-controlled application of cryotherapy to focal liver lesions, real-time monitoring is necessary to limit the final necrotic effect in the treated area. In this study, near real-time magnetic resonance (MR) monitoring images of normal rabbit liver were obtained during the freezing procedure. The MR-monitored, freezing-induced lesions were followed with MR images for up to 3 weeks. Corresponding histologic samples were also obtained over the same time period. Our results indicate that MR images obtained during the freezing procedure can adequately depict the area of final necrosis. Furthermore, histologic changes at each stage of lesion development correlated well with MR signal intensities on follow-up images. With the development of an MR-compatible cryogen probe, MR imaging may prove to be a robust method for monitoring, controlling, and following up cryotherapy in the liver.