PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Experimental validation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources
PubMedDate not supplied

Experimental validation of an automated edge-detection method for a simultaneous determination of the endocardial and epicardial borders in short-axis cardiac MR images: application in normal volunteers.

The goal of this study was to put together several techniques of image segmentation to provide a reliable assessment of the left ventricular mass with short-axis cardiac MR images. No initial manual input was required for this process based on region growing, gradient detection, and adaptive thresholding. A comparison between actual mass and automatic assessment was implemented with 9 minipigs that underwent spin-echo MR imaging. Fifteen normal volunteers were studied with a fast-gradient-echo sequence. The automatic segmentation was then controlled by three trained observers. Actual mass and automatic segmentation were strongly correlated (r = .97 with P < .01). For normal volunteers, the standard error of estimation of the automatic assessment (12 g) compared well with the average myocardial mass (120 +/- 30 g) and the interobserver reproducibility of the manual assessment (9 g). These results allow the application of this method to the quantification of the left ventricular function and mass in clinical practice.

Adult↗
PubMed2007

Experimental validation of noninvasive referencing in navigated procedures on long bones.

Navigation procedures in orthopedic surgery require fixation of reference markers to the anatomic region of interest. Inadequate fixation might lead to micromotion or loosening of the reference marker, consequently causing registration failures or errors in navigation. Osseous rigid fixation is usually achieved by minimally invasive Schanz screws or pins. The goal of this study was to evaluate a non invasive external fixation device, a headband so far used in cranial navigation, as an alternative invasive fixation technique to reference markers in the femur. A common navigation system with an adapted trauma software application was used to track the positions of the soft tissue-attached headband relative to an invasive reference marker on the femur during manipulations of the thigh. Relative translative and rotational movements of the headband were measured during defined movements of the hip and knee and manipulations of the headband itself. The results revealed high translative and rotational movements, up to 6 mm and 3 degrees , respectively, due to minor manipulations of the affected lower extremity. Noninvasive soft tissue fixation with a headband does not allow rigid fixation for accurate navigated registration or operative procedures at the femur. Necessary intraoperative movements or manipulations would cause substantial registration failures. Invasive fixation techniques with screws or pins are still the method of choice.

Bone Screws↗
PubMed2026

Bioinformatics Analysis and Experimental Validation of Key Genes Associated With Hypoxia and Ischemia in Myocardial Infarction.

BACKGROUND: This study aimed to screen and identify core hypoxia-ischemia-related genes associated with myocardial infarction (MI). METHOD: Two transcriptomic datasets, GSE97320 and GSE48060, were retrieved from the Gene Expression Omnibus (GEO) database. After data integration and batch effect elimination, differential expression analysis was performed to screen differentially expressed genes (DEGs), and the corresponding visualization analysis was conducted. Hypoxia-ischemia-related genes were acquired from the GeneCards database; hypoxia-ischemia related genes (HIRGs) were subsequently identified by intersecting the retrieved genes with screened DEGs. Gene Ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were implemented to explore the biological functions and underlying signaling pathways of HIRGs. A combination of protein-protein interaction (PPI) network analysis and random forest (RF) algorithm was applied to screen hub genes from HIRGs. The external GEO dataset GSE66360 was utilized to validate the expression patterns of candidate hub genes. Furthermore, an acute myocardial infarction (AMI) mouse model was established, and quantitative real-time polymerase chain reaction (qPCR) was performed to detect the mRNA expression levels of hub genes in myocardial tissues for in&#xa0;vivo validation. RESULTS: A total of 633 DEGs and 308 hypoxia-ischemia-related genes were screened in the present study, among which 21 overlapping HIRGs were obtained. PLAUR and IL1B were finally identified as two hub genes from HIRGs based on PPI network and random forest algorithm. The qPCR results revealed that the expression levels of PLAUR and IL1B were significantly upregulated in the AMI group compared with the sham operation group (p&#x2009;<&#x2009;0.05). CONCLUSION: The present findings demonstrated that PLAUR and IL1B serve as pivotal genes involved in the pathological hypoxia-ischemia process of AMI. These two genes may act as novel biomarkers and promising therapeutic targets for the recognition and clinical intervention of hypoxia-ischemia injury following AMI.

Myocardial Infarction↗
PubMed1995

Noninvasive quantitative method for measuring isovolumetric bladder pressure and urethral resistance in the male: I. Experimental validation of the theory.

Noninvasive measurement of intravesical pressure, impulsive flow rate, and localized urethral resistance is achieved by clamping the penis immediately above the glans with a pneumatic cuff and then instructing the patient to initiate voiding. The cuff is then deflated slowly until urinary flow of at least 1 ml/s is detected and is then released rapidly to permit unimpeded flow. Cuff pressure, voided volume, and flow rate are recorded as functions of time. From the resulting tracings it is possible to determine the isovolumetric bladder pressure, the impulsive flow rate, and the flow pattern specific to the test. We studied 53 male patients demonstrating that data thus obtained are reproducible and that the cuff pressure at the initiation of voiding does measure the bladder pressure at this moment. We then modeled the lower urinary tract by an analog electrical circuit which facilitated the analysis of the urodynamic data. This analysis suggests that it is possible to separate the effects of bladder dysfunction from the effects of urethral resistance and to localize the resistance to the proximal or distal urethra without invasive testing.

Aged↗
PubMed2002

An experimental validation of orphan genes of Buchnera, a symbiont of aphids.

Although Buchnera sp. APS, an intracellular symbiont of pea aphids, is a close relative of Escherichia coli, its genome has been extensively modified because of its prolonged intracellular life. In our previous studies on the Buchnera genome, computer analysis predicted three "orphan" genes, yba2, yba3, and yba4, which are open reading frames (ORFs) with no homologs in the database. In this paper, we successfully validated all these orphan genes by RT-PCR and Northern hybridization. The present study also revealed that yba3 and yba4 formed an operon, suggesting that they function in concert. Sequences around transcriptional start sites suggests that these genes are under the control of sigma 70. In view of codon usage and AT bias observed in these genes, it is likely that Buchnera have maintained them for an evolutionarily long time.

Amino Acid Sequence↗
PubMed1993

Experimental validation of a new quantitative method for the analysis of infarct size by cardiac perfusion tomography (SPECT).

Using global constraints and dynamic programming, a new model-based segmentation algorithm was developed to determine myocardial borders and basal plane. The segmented image is transformed to a countrate polar map and the infarct size (I.S.) is determined by comparison with a reference polar map. In order to evaluate our method the algorithm was applied to heart phantoms, to software simulations and to animal studies. In the last experiments, Tc-99m Sestamibi was used as a perfusion agent. The total myocardial volume and infarct size of a Jasczack phantom were overestimated, especially when I.S. was expressed in absolute rather than relative values. It was proven by software simulations of cardiac Spect studies that those errors were mainly due to finite resolution effects causing a clear overestimation of myocardial thickness. Implementation of a constant thickness in the algorithm resulted in a much better correlation with actual values. In a dog experiment the size of total myocardial volume of the area at risk during occlusion and of the final infarct size after thrombolysis was correlated with the histologic values obtained by planimetry after TTC staining. In 8 studies, an excellent correlation between the histologic area at risk versus the estimated perfusion defects was obtained (r = 0.97). The automatic delineation of myocardial borders and valve plane was excellent even when perfusion defects were present. Manual intervention was only necessary in certain slices where a clear overlap between liver and myocardium was present in the dog studies. Segmental polar maps expressing count rate and volume information provided a visual and quantitative tool to evaluate the influence of thrombolysis in acute ligation experiments. It is concluded that the new algorithm is ready to be used in a clinical environment for the quantitative evaluation of perfusion defects after acute myocardial infarction and for the follow-up of the therapeutic strategy.

Animals↗
PubMedDate not supplied

Experimental validation of methods for the measurement of coronary sinus blood flow in man.

The measurement accuracy of clinically applicable methods for blood flow measurement in coronary sinus -- continuous local thermodilution (LTD), differential pressure (DP), ultrasonic Doppler (US) and the electromagnetic flow measurement method (EMF) -- was examined in 15 anaesthetized closed chest dogs with left ventricle weights between 150 and 200 g. The LTD, DP, US and the EMF were examined in each experiment in the two following arrangements. 1. In coronary sinus -- left jugular vein by-pass: This arrangement allowed four reference methods for measurement of coronary sinus blood flow (CBF). 2. In "clinical" position, without by-pass, which allowed two reference methods for CBF measurements. The results on the measurement accuracy of the LTD, DP and US are, depending on the measurement arrangement, contradictory. In the by-pass arrangement 1 there was observed a good agreement of the LTD, DP and US CBF values with the reference values. In the "clinical" position, without by-pass 2 the measurement accuracy of LTD was not sufficient for exact measurement of CBF and derived parameters. The examined velocity tip flow probes (US, DP) gave no correlation with the reference methods. US and DP are even for semiquantitative estimation of CBF unsuitable. The EMF tip flow probe was for the CBF measurement unsuitable, because of disturbance by the electrical activity of myocardium.

Animals↗
PubMed2005

Quantification of aortic elasticity: development and experimental validation of a method using computed tomography.

Aortic distensibility depending on aortic cross-sectional area changes is an important parameter for the grading of vascular diseases. This study measured aortic area changes by multidetector computed tomography. An image reconstruction algorithm was developed to assess aorta diameter and area as a function of the cardiac cycle with sufficient time resolution along the entire length of the aorta by four-detector row computed tomography. The algorithm was tested on porcine aortic specimens and compared with an optical reference method. The error of the relative vessel area change comparing the two methods was found to be about 3%. Initial tests on patient datasets indicate that clinical application is feasible. The proposed method has the advantage that it can easily be integrated into a modified routine CT angiography study and allows the measurement of aortic cross-sectional area changes.

Anatomy, Cross-Sectional↗
PubMed2006

Blood flow in compliant arteries: an effective viscoelastic reduced model, numerics, and experimental validation.

The focus of this work is on modeling blood flow in medium-to-large systemic arteries assuming cylindrical geometry, axially symmetric flow, and viscoelasticity of arterial walls. The aim was to develop a reduced model that would capture certain physical phenomena that have been neglected in the derivation of the standard axially symmetric one-dimensional models, while at the same time keeping the numerical simulations fast and simple, utilizing one-dimensional algorithms. The viscous Navier-Stokes equations were used to describe the flow and the linearly viscoelastic membrane equations to model the mechanical properties of arterial walls. Using asymptotic and homogenization theory, a novel closed, "one-and-a-half dimensional" model was obtained. In contrast with the standard one-dimensional model, the new model captures: (1) the viscous dissipation of the fluid, (2) the viscoelastic nature of the blood flow - vessel wall interaction, (3) the hysteresis loop in the viscoelastic arterial walls dynamics, and (4) two-dimensional flow effects to the leading-order accuracy. A numerical solver based on the 1D-Finite Element Method was developed and the numerical simulations were compared with the ultrasound imaging and Doppler flow loop measurements. Less than 3% of difference in the velocity and less than 1% of difference in the maximum diameter was detected, showing excellent agreement between the model and the experiment.

Algorithms↗
PubMed1987

Determination of left ventricular ejection fraction by computer densitometric analysis of digital subtraction angiography: experimental validation and correlation with area-length methods.

Conventional methods for calculating left ventricular (LV) ejection fraction (EF) require accurate edge definition and geometric assumptions, which may be compromised in the presence of dyssynergy. Computer densitometric analysis (CDA) of digital subtraction angiography offers the potential for calculation of EF, independent of LV shape, by comparing summated brightness for regions of interest at end diastole and end systole. Therefore, the accuracy of CDA was validated for 2 mechanical heart models of differing geometry, spherical and rectangular. Both models confirmed the close correlation between calculated and measured EF (r = 0.98 and r = 0.99, respectively). Subsequently, the CDA was compared with single and biplane area-length EF calculations in 72 patients, half with a previous myocardial infarction. In patients without previous myocardial infarction, CDA correlated closely with both single-plane and biplane EF (r = 0.91 and 0.93, respectively). The close correlation was maintained regardless of whether CDA was applied to direct LV injection or intravenous digital subtraction angiography. However, in 36 patients with previous myocardial infarction, CDA correlated less closely with single-plane (r = 0.74) than with biplane (r = 0.86) area-length EF. Thus, CDA permits calculation of EF without geometric assumptions, and may be superior to the area-length method in patients with LV dyssynergy after myocardial infarction.

Adult↗
PubMed1993

A chemical shift selective inversion recovery sequence for fat-suppressed MRI: theory and experimental validation.

Fat-suppression techniques are used extensively in routine proton nuclear magnetic resonance imaging to produce images free from chemical shift artifacts and dynamic range problems. A hybrid fat-suppression sequence is studied which combines the principle of short time inversion recovery with chemical shift selective imaging. The aim of this study is to provide a theoretical understanding of the role of the sequence parameters, as well as to compare this hybrid sequence with its most closely related conventional fat-suppression techniques, namely selective pre-saturation and short time inversion recovery (STIR) imaging. The hybrid technique is shown to be robust in normal use, and more tolerant than the conventional methods to mis-settings of parameters such as inversion time, as well as tip angle and frequency bandwidth of the fat selective pulse.

Abdomen↗
PubMed1990

Doppler echocardiographic quantitation of cross-sectional area under various hemodynamic conditions: an experimental validation in a canine model of supravalvular aortic stenosis.

The hemodynamic effects on cross-sectional area calculated with the continuity equation were assessed in canine experiments. In 13 open chest dogs, 46 supravalvular aortic stenoses were created by aortic root banding. The cross-sectional area of the stenosis was calculated by Doppler echocardiography with application of the continuity equation before and after the following hemodynamic interventions: protocol 1, atrial pacing at 90, 120, 150 and 180 beats/min after sinus node crush; protocol 2, preload reduction by mild and severe clamping of the inferior vena cava; and protocol 3, afterload augmentation by mild and severe clamping of the descending aorta. In each observation, a dimension of the stenosis was directly measured by two-dimensional echocardiography, and the cross-sectional area was determined as a reference standard. As a result of the hemodynamic interventions, significant changes were observed in stroke volume and pressure gradient (protocol 1), in cardiac output, stroke volume and pressure gradient (protocol 2) and in heart rate, cardiac output and pressure gradient (protocol 3). Despite these changes in hemodynamic variables, the Doppler-derived cross-sectional area showed no significant change for a given stenosis. In addition, areas calculated with the continuity equation (x) agreed well with those determined by two-dimensional echocardiography (y) (r = 0.96, p less than 0.001, y = 0.97x + 0.02, SEE = +/- 0.06 cm2). Thus, it is concluded that Doppler echocardiography with application of the continuity equation accurately predicts the stenotic cross-sectional area over a wide range of hemodynamic conditions in supravalvular aortic stenosis.

Animals↗
PubMed2024

Genome-wide association studies with experimental validation identify a protective role for B lymphocytes against chronic post-surgical pain.

BACKGROUND: Chronic post-surgical pain (CPSP) significantly impacts patients' recovery and quality of life. Although environmental risk factors are well-established, genetic risk remains less understood. METHODS: A meta-analysis of genome-wide association studies followed by partitioned heritability was performed on 1350 individuals across five surgery types: hysterectomy, mastectomy, abdominal, hernia, and knee. In subsequent animal studies, withdrawal thresholds to evoked mechanical stimulation were measured in Rag1 null mutant and wild-type mice after plantar incision and laparotomy. Cell sorting by flow cytometry tracked recruitment of immune cell types. RESULTS: We discovered 77 genome-wide significant single-nucleotide polymorphism (SNP) hits, distributed among 24 loci and 244 genes. Meta-analysis of all cohorts estimated a SNP-based narrow-sense heritability for CPSP at &#x223c;39%, indicating a substantial genetic contribution. Partitioned heritability analysis across a wide variety of tissues revealed enrichment of heritability in immune system-related genes, particularly those associated with B and T cells. Rag1 null mutant mice lacking both T and B cells exhibited exacerbated and prolonged allodynia up to 42 days after surgery, which was rescued by B-cell transfer. Recruitment patterns of B cells but not T cells differed significantly during the first 7 days after injury in the footpad, lymph nodes, and dorsal root ganglia. CONCLUSIONS: These findings suggest a key protective role for the adaptive immune system in the development of chronic post-surgical pain.

Animals↗
PubMed2005

Lipid monolayers on Hg as a valid experimental model for lipid membranes under electrical fields.

Monolayers spread on Hg drops are shown as a suitable experimental set up to study the influence of external electric fields on the structure of lipid membranes. The electrical response exhibits a sharp transition at 24 degrees C, the transition temperature of DMPC. In addition, voltammetric response of monolayers of mixtures of DMPC/DMPE adsorbed on mercury, shows a similar trend to that found for dipole potential of monolayers of the same composition spread on an air-solution interface. It is concluded that a lipid monolayer adsorbed in a mercury-solution interface, has comparable properties as those found in other experimental models of lipid membranes in similar conditions. In addition, they constitute an ideal set up to study the effect of electrical fields on the dynamic conformation of lipids as a function of packing change produced by the condensation in the gel state or by the interaction of polar head groups.

Chemical Phenomena↗