Adlayer-Free Large-Area Single Crystal Graphene Grown on a Cu(111) Foil.

To date, thousands of publications have reported chemical vapor deposition growth of "single layer" graphene, but none of them has described truly single layer graphene over large area because a fraction of the area has adlayers. It is found that the amount of subsurface carbon (leading to additional nuclei) in Cu foils directly correlates with the extent of adlayer growth. Annealing in hydrogen gas atmosphere depletes the subsurface carbon in the Cu foil. Adlayer-free single crystal and polycrystalline single layer graphene films are grown on Cu(111) and polycrystalline Cu foils containing no subsurface carbon, respectively. This single crystal graphene contains parallel, centimeter-long ≈100 nm wide "folds," separated by 20 to 50 µm, while folds (and wrinkles) are distributed quasi-randomly in the polycrystalline graphene film. High-performance field-effect transistors are readily fabricated in the large regions between adjacent parallel folds in the adlayer-free single crystal graphene film.

Camphor-Enabled Transfer and Mechanical Testing of Centimeter-Scale Ultrathin Films.

Camphor is used to transfer centimeter-scale ultrathin films onto custom-designed substrates for mechanical (tensile) testing. Compared to traditional transfer methods using dissolving/peeling to remove the support-layers, camphor is sublimed away in air at low temperature, thereby avoiding additional stress on the as-transferred films. Large-area ultrathin films can be transferred onto hollow substrates without damage by this method. Tensile measurements are made on centimeter-scale 300 nm-thick graphene oxide film specimens, much thinner than the ≈2 µm minimum thickness of macroscale graphene-oxide films previously reported. Tensile tests were also done on two different types of large-area samples of adlayer free CVD-grown single-layer graphene supported by a ≈100 nm thick polycarbonate film; graphene stiffens this sample significantly, thus the intrinsic mechanical response of the graphene can be extracted. This is the first tensile measurement of centimeter-scale monolayer graphene films. The Young's modulus of polycrystalline graphene ranges from 637 to 793 GPa, while for near single-crystal graphene, it ranges from 728 to 908 GPa (folds parallel to the tensile loading direction) and from 683 to 775 GPa (folds orthogonal to the tensile loading direction), demonstrating the mechanical performance of large-area graphene in a size scale relevant to many applications.

Numerical Simulation of the Effect of Sodium Profile on Cardiovascular Response to Hemodialysis

PURPOSE: We developed a numerical model that predicts cardiovascular system response to hemodialysis, focusing on the effect of sodium profile during treatment. MATERIALS and METHODS: The model consists of a 2-compartment solute kinetics model, 3-compartment body fluid model, and 12-lumped-parameter representation of the cardiovascular circulation model connected to set-point models of the arterial baroreflexes. The solute kinetics model includes the dynamics of solutes in the intracellular and extracellular pools and a fluid balance model for the intracellular, interstitial, and plasma volumes. Perturbation due to hemodialysis treatment induces a pressure change in the blood vessels and the arterial baroreceptors then trigger control mechanisms (autoregulation system). These in turn alter heart rate, systemic arterial resistance, and cardiac contractility. The model parameters are based largely on the reported values. RESULTS: We present the results obtained by numerical simulations of cardiovascular response during hemodialysis with 3 different dialysate sodium concentration profiles. In each case, dialysate sodium concentration profile was first calculated using an inverse algorithm according to plasma sodium concentration profiles, and then the percentage changes in each compartment pressure, heart rate, and systolic ventricular compliance and systemic arterial resistance during hemodialysis were determined. A plasma concentration with an upward convex curve profile produced a cardiovascular response more stable than linear or downward convex curves. CONCLUSION: By conducting numerical tests of dialysis/cardivascular models for various treatment profiles and creating a database from the results, it should be possible to estimate an optimal sodium profile for each patient.

Pseudo-organ boundary conditions applied to a computational fluid dynamics model of the human aorta.

In three-dimensional numerical studies of the aorta, it is difficult to apply proper boundary conditions at the end of each major aortic branch because of interactions between blood and organs. Organs and body parts were assumed to be likened to cylindrically shaped porous media, so-called pseudo-organs, and treated in the computational domain as forms of hemodynamic resistance. Permeability functions were determined from two-dimensional axisymmetric computations of each aortic branch and these functions were then used in an unsteady three-dimensional simulation of the complete aorta. Substantially accurate cardiac output (5.91 L/min) and blood distributions to the major branches were predicted.

Nonlinear matching measure for the analysis of on-off type DNA microarray images.

We propose a new nonlinear matching measure for automatic analysis of the on-off type DNA microarray images in which the hybridized spots are detected by a template-matching method. The proposed measure is obtained by binary thresholding over the entire template region and taking the number of white pixels inside the spotted area. This measure is compared with the normalized covariance method in terms of classifying the ability to successfully locate markers. The proposed measure was evaluated for scanned images of human papillomavirus (HPV) DNA microarrays where locating markers is a critical issue because of the small number of spots. The targeting spots of HPV DNA chips are designed for genotyping twenty-two types of the human papillomavirus. The proposed measure is proven to give a more discriminative response, reducing the missed cases of successful marker location. The locating accuracy of the proposed method is also shown to have the same performance as that of the normalized covariance.

Computational analysis of the three-dimensional hemodynamics of the blood sac in the twin-pulse life-support system.

Blood flow in the twin-pulse life-support system (T-PLS) pulsatile blood pump was simulated using a three-dimensional rigid body-fluid-solid interaction model. This model can delineate the blood flow in the T-PLS resulting from operation of a moving actuator. The numerical method used in this study was a commercial finite element package called ADINA. We used a contact and fluid-solid interaction model to compute the blood hemodynamics in the sac. Blood flow is generated by the motion of the actuator, which strongly interacts with the solid material surrounding the blood. To obtain basic bioengineering data on the optimum operation of the T-PLS, we simulated four models in which the actuator moved at different speeds and investigated both the flow pattern and the distribution of shear stress. During the contraction phase, a strong axial flow is observed around the outlet, whereas there is stagnant flow around the inlet. The maximum shear stress in each model depends on the operation mode; however, all four models have similar flow rates. The sinusoidal mode exhibited the lowest maximum shear stress and is thus considered the most efficient of the four operating modes.

Application of the Pulsatile Cardiopulmonary Bypass in Animal Model / 대한흉부외과학회지

BACKGROUND: Currently, the cardiopulmonary machine with non-pulsatile pumps, which are low in internal circuit pressure and cause little damage to blood cells, is widely used. However, a great number of experimental studies shows that pulsatile perfusions are more useful than non-pulsatile counterparts in many areas, such as hemodynamic, metabolism, organ functions, and micro-circulation. Yet, many concerns relating to pulsatile cardiopulmonary machines, such as high internal circuit pressure and blood cell damage, have long hindered the development of pulsatile cardiopulmonary machines. Against this backdrop, this study focuses on the safety and effectiveness of the pulsatile cardiopulmonary machines developed by a domestic research lab. MATERIAL AND METHOD: The dual-pulsatile cardiopulmonary bypass experiment with total extracorporeal circulation was conducted on six calves. Extracorporeal circulation was provided between superior/inferior vena cava and aorta. The membrane oxygenator, which was placed between the left and right pumps, was used for blood oxygenation. Circulation took four hours. Arterial blood gas analysis and blood tests were also conducted. Plasma hemoglobin levels were calculated, while pulse pressure and internal circuit pressure were carefully observed. Measurement was taken five times; once before the operation of the cardiopulmonary bypass, and after its operation it was taken every hour for four hours. RESULT: Through the arterial blood gas analysis, PCO2 and pH remained within normal levels. PO2 in arterial blood showed enough oxygenation of over 100 mmHg. The level of plasma hemoglobin, which had total cardiopulmonary circulation, steadily increased to 15.87+/-5.63 mg/dl after four hours passed, but remained below 20 mg/dl. There was no obvious abnormal findings in blood test. Systolic blood pressure which was at 97.5+/-5.7 mmHg during the pre-circulation contraction period, was maintained over 100 mmHg as time passed. Moreover, diastolic blood pressure was 72.2+/-7.7 mmHg during the expansion period and well kept at the appropriate level with time passing by. Average blood pressure which was 83+/-9.2 mmHg before circulation, increased as time passed, while pump flow was maintained over 3.3 L/min. Blood pressure fluctuation during total extracorporeal circulation showed a similar level of arterial blood pressure of pre-circulation heart. CONCLUSION: In the experiment mentioned above, pulsatile cardiopulmonary machines using the doual-pulsatile structure provided effective pulsatile blood flow with little damage in blood cells, showing excellence in the aspects of hematology and hemodynamic. Therefore, it is expected that the pulsatile cardiopulmonary machine, if it becomes a standard cardiopulmonary machine in all heart operations, will provide stable blood flow to end-organs.

The Long-Term Clinical Results of a Platelet Glycoprotein IIb/IIIa Receptor Blocker (Abciximab : ReoPro(R)) Coated Stent in Patients with Acute Myocardial Infarction

BACKGROUND AND OBJECTIVES: The inhibition of coronary restenosis with an Abciximab (ReoPro(R))-coated stent has previously been reported by us. This study investigated the clinical outcomes of patients with acute myocardial infarction (AMI) treated with ReoPro-coated stents. SUBJECTS AND METHOD: A prospective randomized trial was conducted to compare two types of stent for the revascularization in 63 patients [Group I (ReoPro(r)-coated stent):n=32, 53.7+/-11.8 years, 27 male, and Group II (control stent):n=31, 55.4+/-12.1 years, 27 male] with AMI. The primary effective end points were major adverse coronary events (MACE):cardiac death, acute myocardial infarction, target lesion revascularization (TLR), in-stent restenosis and late lumen loss at the 1 year clinical and angiographic follow-ups. RESULTS: Baseline clinical characteristics and diameters of stenosis and the minimal luminal diameters were no different between the two groups. There was one myocardial infarction and revascularization during the hospital stay in group II. Follow-up coronary angiograms were performed in 71.9 (23/32) and 77.4% (24/31) of groups I and II, respectively. The diameter of stenosis and late loss were significantly lower in group I than group II (19.4+/-5.1 vs. 34.8+/-5.9%, p=0.013;and 0.39+/-0.26 vs. 0.89+/-0.45 mm;p=0.008, respectively). However, the restenosis rates were no different between the two groups (21.7 vs. 37.5%, p=0.341). One year clinical follow-ups were possible in 98.4% (62/63), and there were two AMI found in group II, but none in group I. The TLR rates and total MACE of group I were relatively lower compared with group II [12.9 (4/31) vs. 29.0% (9/31);p=0.122 and 12.9 (4/31) vs. 35.5% (11/31), p=0.038, respectively]. CONCLUSION: The ReoPro(R)-coated stent was safe, with no stent thrombosis, and effective in patients with AMI.

Cadaver Fitting Test of Mechanical Circulatory Assist Device Including Korean Artificial Heart (AnyHeart) in Korea / 대한해부학회지

Preclinical cadaver fitting study is paramount in the development of various implantable medical devices. It helps to evaluate the fitness of the size, shape, structure of the devices in the human anatomy, to locate the most optimal site for implantation, and to develope the clinically available surgical techniques. The purpose of this study was to observe the anatomical feasibility of Korean artificial heart (AnyHeart) in 12 human cadavers after obtaining the permission from the Korea University Anatomical Research Committee. The observation was focused on proper position of the artificial heart in various thoracic incisions (median sternotomy, right thoracotomy, left thoracotomy, transsternal incision), localization of inflow as well and outflow tract, cannulation sites, and so on. Results showed that Korean artificial heart had excellent anatomical feasibility in the human body and that a novel surgical technique of right thoracotomy approach was proved to be clinically applicable. Conclusively, the above results will provide the rationales of clinical trial and demonstrate the significance of human cadaver study in development of implantable medical devices.

Surgical Technique for Korean Artificial Heart(AnyHeart) Implantation Using a Right Thoracotomy Approach / 대한흉부외과학회지

BACKGROUND: The surgical technique for biventricular assist device(BVAD) implantation has mainly consisted of cannulation procedures. A median sternotomy has been the technique of choice as it gives a surgeon an excellent exposure of the heart. However, considering that most patients require a future sternotomy or already have a previous sternotomy, sternotomy-related complication remains a major concern in BVAD implantation. Based on this consideration as well as the clinical experiences of conventional heart surgery, the authors have hypothesized that the cardiac chambers for BVAD cannulation can be approached from the right side of the heart. The purpose of this study to develop a novel surgical technique of right thoracotomy for BVAD implantation in an animal study. MATERIAL AND METHOD: For last two years, 16 (11 calves, 3 canines, and 2 sheep) out of 30 experimental animals with AnyHeart implantation underwent a right thoracotomy. The device was used as an implantable BVAD in 14 animals, a wearable BVAD in 1, and an implantable LVAD in 1. The chest cavity was entered through the 4th intercostal space or the 5th periosteal bed. As for the BVAD use, a right inflow cannula was inserted into the right atrial free wall and a right outflow cannula was grafted onto the main pulmonary artery. A left inflow cannula was inserted into the interatrial groove and a left outflow cannula was grafted on the innominate artery of the ascending aorta. The connecting tubeswere brought out through the thoracotomy wound and connected to the pump located in the subcutaneous pocket at the right flank. RESULT: Except for the 5 animals for a fitting test or during the early learning curve, all recovered smoothly from the procedures. The inflow drainage allowed the pump output 6.5 L/min at the maximum with 3-3.5 L/min in an average. Of the survivors, there noted no procedure-related mortality or morbidity. Necropsy findings demonstrated the well-positioned cannula tips in the each cardiac chamber. CONCLUSION: The technique of right thoracotomy approach in AnyHeart implantation is simple, safe, and reproducible. As it can avoid sternotomy-orresternotomy-related complications, the authors suggest a right thoracotomy approach as one of the techniques for BVAD implantation. The technique would also be suggested as an alternatitve for a median sternotomy in a certain group of patients with various VAD implantations.

Effects of an Extra-corporeal Life Support System Using a Dual Pulsatile Pump

PURPOSE: The purpose of this study was to observe and compare the changes in the patterns of hemodynamic and blood profiles on the circuit of Extra-corporeal life support system (ECLS) by using a dual pulsatile pump (T-PLS). METHODS: An acute heart failure model using partial pulmonary artery banding was constructed in 12 piglets (20 -25kg). The animals were divided into centrifugal (n=6) and dual pulsatile pump (n=6) group. Each animal was placed on an ECLS system with a membrane oxygenator bypassing the right atrium and the aorta for 2 hours under general anesthesia. The parameters mainly observed were intra-circuit pressure changes, arterial pulsatility (pulse pressure), plasma free hemoglobin, hemodynamic changes, and other blood profiles. The parameters obtained just prior to the bypass were compared with the corresponding parameters obtained two hours after the bypass. RESULTS: Before bypass, the parameters were statistically the same between the groups. Two hours after the bypass, no significant differences were observed between the groups in ABGA, VBGA, AST/ALT, BUN/Cr, and electrolytes; the plasma free hemoglobin was 14.8+/-4.7 g/dl in the dual pulsatile group and 19.1+/-9.1 g/dl in the centrifugal group (p=NS). The pulse pressure was higher in the dual pulsatile pump than in the centrifugal pump group (35+/-8 vs. 11+/-7 mmHg, p=0.0253 mmHg). The highest circuit pressure was generated at the inlet of the membrane oxygenator and was higher in the dual pulsatile group than in the centrifugal group (173+/-12 mmHg vs. 222+/-8 mmHg, p=0.0000). CONCLUSION: The results demonstrate that a dual pulsating mechanism lessens blood cell trauma while providing physiologic pulsatile blood flow. The ECLS system using a dual pulsatile pump (T-PLS) can be useed as an effective and safe driving motor for an ECLS.

A Clinical Experience of Korean Artificial Heart(AnyHeart) / 대한흉부외과학회지

Korean artificial heart(AnyHeart) is a single-pieced and implantable bi-ventricular pulsatile pump adapting a moving actuator mechanism. The authors report a case of clinical application of AnyHeart as a life-saving device for the patients with end-stage heart disease combined with biventricular failure.

Clinical Observation on Exogeneous Endophthalmitis

PURPOSE: To evaluate the effectiveness of intravitreous injection of Vancomycin and Amikacin in exogenous endophthalmitis (before culture results are obtained), and the relationship between such empirical therapy and results of culture, susceptibilities of cultured organism to antibiotics, and visual prognosis. METHODS: The authors conducted a retrospective study of 23 patients (23 eyes) who had been treated for endophthalmitis between May 1996 and November 2000. RESULTS: The final vision was 0.15 and better in 18 eyes out of 23 eyes, and 5 eyes reported vision worse than 0.1. Endophthalmitis was associated with cataract surgery in 15 eyes, ocular traumja in 7 eyes, filtration surgery in 1 eye. Eyes with posttraumatic endophthalmitis had worse visual prognosis. When smear and culture was performed, 14 out of 23 eyes were tested positive, and all the obtained microorganisms showed sensitivity to vancomycin and amikacin. The results were similar between Gram positive and negative bacteria. When the onset of symptoms was within 1 week after intraocular operation, and when the patients with ocular trauma reported to the hospital within two days, the prognosis was relatively better. The use of intravitreous antibiotics alone yielded similar results compared to the use of combined systemic antibiotics. Two out of 5 eyes which underwent vitrectomy and 16 out of 18 eyes which did not undergo vitrectomy reported final vision of 0.15 or better. CONCLUSIONS: When endophthalmitis is suspected, one should immediately perform diagnostic workup and the patient is immediately given intravitreous injection of vancomycin and amikacin. When smear and culture results are obtained later on, one can modify and improve the treatment modalities in an attempt to improve visual prognosis.

Application of th Total Artificial Heart as an Implantable Biventricular Assist Device by Left Thoracotomy in an Ovine Model / 대한흉부외과학회지

BACKGROUND: The purpose of this study was to investigate the possibility of using the moving-actuator type total artificial heart as a biventricular assist device(BVAD) and to establish a safe and effective animal model for the implantation of a BVAD. MATERIAL AND METHOD: Seven Corridale sheep were used in this study wherein left thoracotomy was performed. The left and right outflow cannulas were anastomosed to the descending thoracic aorta and the main pulmonary artery, and the left and right inflow cannulas were inserted to the left atrium and the right atrial appendage. The devices were positioned in the preperitoneal pocket in 4 sheep, in the left pleural cavity in 2 sheep, and externally in 1 sheep. The aPTT was maintained between the 2 and 2.5 times the range that of the baseline. RESULT: Cannulation was carried out successfully in all cases. There was no case of operative death or immediate postoperative death. Three sheep expired postoperatively on the 2nd day because of thromboembolism, an artificial ventilator accident, and device and respiratory failure. Three other sheep died postoperatively on the 4th day because of acute renal and respiratory failure following thromboembolism. One sheep survived for 28 days. Experimentation on this animal terminated due to an electrical short-circuit caused by motor wire erosion. Thrombi were found on the valves of 4 out of 7 animals, especially on the connection between valves and the device. However , there was no thrombus in the cannulas. CONCLUSION: In conclusion, left thoracotomy for insertion of 4 cannulas and placement of device in the preperitoneal space is the safe and effective operative technique in ovine for testing in-vivo biocompatibility of the BVAD. Furthermore, it may be possible to use a moving-actuator type total artificial heart as a BVAD if technical improvements for reducing thromboembolism are carried out.

Simulation of the Effects of Long-term Implantation of Biventricular Assist Device on the Hemodynamic Parameters in Heart Failure

BACKGROUND AND OBJECTIVES: Ventricular assist device(VAD) was developed for the bridge to cardiac transplantation, but the current research trends proceed to the purpose of bridge to cardiac recovery. We investigated the effects of long-term VAD implantation on the hemodynamic parameters related to the prognosis of heart failure by simulation to provide the preclinical and clinical applicability. MATERIAL AND METHODS: A moving-actuator type artificial heart developed by Seoul National University Artificial Heart Laboratory was used as a model of biventricular assist device. We set initial values of hemodynamic parameters according to the guideline of VAD implantation, and performed simulation of the change of hemodynamic variables related to successful device weaning and the prognosis of heart failure. RESULTS: Cardiac indices (CIs) at 1 hour and 6 months after VAD implantation were 2.98 l/min/m2 and 2.60 l/min/m2, respectively. Systolic/diastolic/mean aorta pressure were 121/84/99 mmHg at 6 months after VAD implantation. During pump-off state at 6 month, each value of hemodynamic parameters were as follows: CI 2.53 l/min/m2, pulmonary capillary wedge pressure 10 mmHg, left ventricular end-diastolic volume 105 ml, left ventricular ejection fraction 0.58, mean aorta pressure 84 mmHg, end-systolic wall stress 108 kdyn/cm2. Peak rate of change of power(peak dPWR(t)/dt) was 5.62x108 dyneXcm/s2 after 6-month VAD implantation. In a real VAD-implanted patient, simulation data were partly compatible with real hemodynamic data, especially in the aspects of predicting VAD weaning. CONCLUSION:Long-term VAD implantation partially improved the values of hemodynamic parameters related to the prognosis, and this simulation results will provide the basic concept and applicability of clinical trial for end-stage heart failure.

On the Use of Neural Networks for the Risk Factor Analysis of NIDDM / 대한의료정보학회지

There were many cases to apply artificial intelligence to medicine. Neural networks are nonparametric pattern recognition techniques that can be used to model complex relationships. In this paper, we present the analysis of the risk factors of the noninsulin-dependent diabetes mellitus using the artificial neural network and the logistic regression model. First, we developed five prediction models using artificial neural networks and a logistic regression model with the data of Yonchon study of diabetes mellitus. Next, we measured each area under the ROC(Receiver-Operating Characteristic) plots for the performance, and results re followings; multilayer perceptron with seventeen variables(MLP17) was 0.7608, multilayer perceptron with seven variables(MLP7) was 0.7664, radial basis function network with seventeen variables(RBF17) was 0.7919, radial basis function network with seven variables(RBF7) was 0.7715 and logistic regression model(REG7) was 0.8343. All of the variables used are seventeen, and seven variables for neural networks(MLP7 and RBF7) were selected by logistic regression model. The order of higher risk variables in the neural networks(slope) did not completely agree with that in the logistic regression model(odds ratio). However, all of the four higher risk variables that were significant in the statistic model(0.05) also had large slopes(0.3) in the neural network model. And our neural network model also display the influence of another variables in development of the noninsulin-dependent diabetes mellitus.

MR Angiography of Stenosis and Aneurysm Models in the Pulsatile Flow: Variation with Imaging Parameters and Concentration of Contrast Media

PURPOSE: The image quality of magnetic resonance angiography (MRA) varies according to the imaging techniques applied and the parameters affected by blood flow patterns, as well as by the shape of the blood vessels. This study was designed to assess the influence on signal intensity and its distribution of the geometry of these vessels, the imaging parameters, and the concentration of contrast media in MRA of stenosis and aneurysm models. MATERIALS AND METHODS: MRA was performed in stenosis and aneurysm models made of glass tubes, using pulsatile flow with viscosity and flow profile similar to those of blood. Slice and maximum intensity projection (MIP) images were obtained using various imaging techniques and parameters ; there was variation in repetition time, flip angle, imaging planes, and concentrations of contrast media. On slice images of three-dimensional (3D) time-of-flight (TOF) techniques, flow signal intensity was measured at five locations in the models, and contrast ratio was calculated as the difference between flow signal intensity (SI) and background signal intensity (SIb) divided by background signal intensity or (SI-SIb)/SIb. MIP images obtained by various techniques and using various parameters were also analyzed, with emphasis in the stenosis model on demonstrated degree of stenosis, severity of signal void and image distortion, and in the aneurysm model, on degree of visualization, distortion of contour and distribution of signals. RESULTS: In 3D TOF, the shortest TR (36 msec) and the largest FA (50 degree) resulted in the highest contrast ratio, but larger flip angles did not effectively demonstrate the demonstration of the peripheral part of the aneurysm . Loss of signal was most prominent in images of the stenosis model obtained with parallel or oblique planes to the flow direction. The two-dimensional TOF technique also caused signal void in stenosis, but precisely demonstrated the aneurysm, with dense opacification of the peripheral part. The phase contrast technique showed some distortions in the imaging of stenosis, and partial opacification of ananeurysm. Contrast enhanced imaging offered no advantages in the imaging of the stenosis, but was excellent for demonstration of the aneurysm. CONCLUSION: This study demonstrates a spectrum of MRA images of stenosis and aneurysm model according to variation in imaging parameters and the concentration of contrast media.

A Study of Doppler Waveform Using Pulsatile Flow Model

PURPOSE: Through the construction of a pulsatile flow model using an artificial heart pump and stenosis to demonstrate triphasic Doppler waveform, which simulates in vivo conditions, and to evaluate the relationship between Doppler waveform and vascular compliance. MATERIALS AND METHODS: The flow model was constructed using a flowmeter, rubber tube, glass tube with stenosis, and artificial heart pump. Doppler study was carried out at the prestenotic, poststenotic, and distal segments; compliance was changed by changing the length of the rubber tube. RESULTS: With increasing proximal compliance, Doppler waveforms show decreasing peak velocity of the first phase and slightly delayed acceleration time, but the waveform itself did not change significantly. Distal compliance influenced the second phase, and was important for the formation of pulsus tardus and parvus, which without poststenotic vascular compliance, did not develop. The peak velocity of the first phase was inversely proportional to proximal compliance, and those of the second and third phases were directly proportional to distal compliance. CONCLUSION: After constructing this pulsatile flow model, we were able to explain the relationship between vascular compliance and Doppler waveform, and also better understand the formation of pulsus tardus and parvus.

In Vivo Single Voxel 1H MR Spectroscopy in Cerebral Glioma

PURPOSE: To assess the metabolite ratios in gliomas to determine whether the metabolic information obtained by using by using in vivo single vexel 1H magnetic resonance spectroscopy(MRS) can be used as a marker for the grading of malignancy. MATERIALS AND METHODS: A total of 28 1H MR spectra from brain tumors in 27 patients with pathologically-proven gliomas were recorded. Seven patients had low grade gliomas (grade II astrocytoma in three, oligodendroglioma in three and mixed glioma in one), six had anaplastic gliomas (grade III astrocytoma in three and oligodendroglioma in three), and 14 had glioblastoma multiformes (grade IV), 1H MRS was performed on a 1.5T MRunit using PRESS sequence with a TR of 2000ms, a TE of 270 or 135ms and a voxel size of cm for all spectra. Relative lactate levels, NAA/Cho, NAA/Cr and Cho/Cr ratios were measured based on the peak heights of each resonance and compared among gliomas. RESULTS: Most tumors demonstrated decreased NAA, elevated Cho and lactate. Relatively high lactate and Cho levels and markedly decreased NAA level were more frequently observed in the high grade gliomas than in low grade gliomas. Marked elevation of lactate level in the solid component of the tumor was mostly observed in high grade gliomas. In a patient with gliomatosis cerebri, 1H MRS demonstrated a spectral pattern of tumor in filtration in an area that on MR images was apparently normal. However, NAA/Cr, NAA/Cho and Cho/Cr ratios did not significantly correlate, however, with the histologic grading of malignancy. Because of the partial volume effect, the heterogeneity of tumors containing solid and cystic or necrotic components within avoxel limited the interpretation of 1H MRS data for the grading of malignancy. CONCLUSION: The results suggest that in some patients in vivo single voxel 1H MRS may be useful for grading the malignancy of gliomas and evaluating the exact extent of tumors. In solid gliomas, the relative level of lactate appears to be a good markerfor the grading of malignancy.