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Sabine Van Huffel

Publications and source records attributed to Sabine Van Huffel.

At least 19 recordsLinked to original sources

An automated quantitation of short echo time MRS spectra in an open source software environment: AQSES.

This paper describes a new quantitation method called AQSES for short echo time magnetic resonance spectra. This method is embedded in a software package available online from www.esat.kuleuven.be/sista/members/biomed/new/ with a graphical user interface, under an open source license, which means that the source code is freely available and easy to adapt to specific needs of the user. The quantitation problem is mathematically formulated as a separable nonlinear least-squares fitting problem, which is numerically solved using a modified variable-projection procedure. A macromolecular baseline is incorporated into the fit via nonparametric modelling, efficiently implemented using penalized splines. Unwanted components such as residual water are removed with a maximum-phase FIR filter. Constraints on the phases, dampings and frequencies of the metabolites can be imposed. AQSES has been tested on simulated MR spectra with several types of disturbance and on short echo time in vivo proton MR spectra. Results show that AQSES is robust, easy to use and very flexible.

Humans↗

Determination of dominant simulated spindle frequency with different methods.

Accurate analysis of EEG sleep spindle frequency is challenging. The frequency content of true sleep spindles is not known. Therefore, simulated spindle activity was studied in the present work. Five types of simulated test signals were designed, all containing a dominant spindle represented by a 13-Hz sine wave as such or with a waxing and waning pattern accompanied by a secondary spindle activity in three test signals. Background EEG was included in four test signals, modeled either as small additional sinusoids across the spindle frequency range or as filtered Gaussian noise segments. The purpose of this study was to investigate how accurately the dominant spindle frequency of 13 Hz could be resolved with different methods in the presence of the interfering waveforms. A matching pursuit (MP) based approach, discrete Fourier transform (DFT) with Hanning windowing with and without zero padding, Hankel total least squares (HTLS) and wavelet methods were compared in the analyses. MP method provided best overall performance, followed closely by DFT with zero padding. Comparative studies like this are important to decide the method of choice in clinical sleep EEG analysis.

Algorithms↗

Quantification of prostate MRSI data by model-based time domain fitting and frequency domain analysis.

This paper compares two spectral processing methods for obtaining quantitative measures from in vivo prostate spectra, evaluates their effectiveness, and discusses the necessary modifications for accurate results. A frequency domain analysis (FDA) method based on peak integration was compared with a time domain fitting (TDF) method, a model-based nonlinear least squares fitting algorithm. The accuracy of both methods at estimating the choline + creatine + polyamines to citrate ratio (CCP:C) was tested using Monte Carlo simulations, empirical phantom MRSI data and in vivo MRSI data. The paper discusses the different approaches employed to achieve the quantification of the overlapping choline, creatine and polyamine resonances. Monte Carlo simulations showed induced biases on the estimated CCP:C ratios. Both methods were successful in identifying tumor tissue, provided that the CCP:C ratio was greater than a given (normal) threshold. Both methods predicted the same voxel condition in 94% of the in vivo voxels (68 out of 72). Both TDF and FDA methods had the ability to identify malignant voxels in an artifact-free case study using the estimated CCP:C ratio. Comparing the ratios estimated by the TDF and the FDA, the methods predicted the same spectrum type in 17 out of 18 voxels of the in vivo case study (94.4%).

Algorithms↗

Canonical correlation analysis applied to remove muscle artifacts from the electroencephalogram.

The electroencephalogram (EEG) is often contaminated by muscle artifacts. In this paper, a new method for muscle artifact removal in EEG is presented, based on canonical correlation analysis (CCA) as a blind source separation (BSS) technique. This method is demonstrated on a synthetic data set. The method outperformed a low-pass filter with different cutoff frequencies and an independent component analysis (ICA)-based technique for muscle artifact removal. In addition, the method is applied on a real ictal EEG recording contaminated with muscle artifacts. The proposed method removed successfully the muscle artifact without altering the recorded underlying ictal activity.

Action Potentials↗

Ultrasound characteristics of different types of adnexal malignancies.

OBJECTIVE: To describe ultrasound characteristics of adnexal malignancies, i.e., borderline ovarian tumors, primary invasive ovarian epithelial cancer stage 1, primary invasive ovarian epithelial cancer stages 2-4, rare types of malignancy, and metastatic tumors. METHODS: In a prospective international study involving nine European ultrasound centers, 1,066 women with a pelvic mass judged to be of adnexal origin underwent transvaginal gray scale and color Doppler ultrasound examination by a skilled examiner before surgery. A standardized examination technique and predefined definitions of ultrasound characteristics were used. RESULTS: Of 1,066 masses, 266 were malignant and are included: 55 ovarian borderline tumors, 144 primary invasive epithelial ovarian cancers (42 stage 1, 102 stages 2-4), 25 rare malignancies, and 42 metastatic tumors. Most (56%) metastatic tumors and most (60%) rare types of tumor were solid and richly vascularized at color Doppler ultrasound examination (on a scale ranging from 1 to 4, color score based on subjective evaluation was 3 or 4 in 88% and 86%, respectively). Borderline ovarian tumors and stage 1 primary invasive ovarian epithelial cancers differed from stages 2-4 primary invasive ovarian epithelial cancers: they were larger (median volume 375 ml and 695 ml vs. 209 ml; P = 0.0213 and 0.0001), a larger proportion contained papillary projections (64% and 67% vs. 41%; P = 0.0072 and 0.0054), they were more often multilocular cysts without solid components (18% and 14% vs. 2%; P < 0.0017 and 0.0204), but they were less often purely solid (5% and 7% vs. 38%; P <or= 0.0001 and 0.0005). With increasing degree of invasiveness - from borderline epithelial ovarian tumors via stage 1 invasive epithelial ovarian tumors to stages 2-4 invasive epithelial ovarian tumors - ascites became more common (9% vs. 31% vs. 61%; P = 0.0082, <0.0001, and 0.0017), and, among tumors with solid components (n = 179), the proportion of tumor consisting of solid tissue increased (median 2%-10%-34%; P = 0.0212, <0.0001, and 0.0003). CONCLUSION: Papillary projections are characteristic of borderline tumors and stage 1 primary invasive epithelial ovarian cancer. A small proportion of solid tissue at ultrasound examination makes a malignant mass more likely to be a borderline tumor or a stage 1 epithelial ovarian cancer than an advanced ovarian cancer, a metastasis, or a rare type of tumor.

Adnexal Diseases↗

Logistic regression model to distinguish between the benign and malignant adnexal mass before surgery: a multicenter study by the International Ovarian Tumor Analysis Group.

PURPOSE: To collect data for the development of a more universally useful logistic regression model to distinguish between a malignant and benign adnexal tumor before surgery. PATIENTS AND METHODS: Patients had at least one persistent mass. More than 50 clinical and sonographic end points were defined and recorded for analysis. The outcome measure was the histologic classification of excised tissues as malignant or benign. RESULTS: Data from 1,066 patients recruited from nine European centers were included in the analysis; 800 patients (75%) had benign tumors and 266 (25%) had malignant tumors. The most useful independent prognostic variables for the logistic regression model were as follows: (1) personal history of ovarian cancer, (2) hormonal therapy, (3) age, (4) maximum diameter of lesion, (5) pain, (6) ascites, (7) blood flow within a solid papillary projection, (8) presence of an entirely solid tumor, (9) maximal diameter of solid component, (10) irregular internal cyst walls, (11) acoustic shadows, and (12) a color score of intratumoral blood flow. The model containing all 12 variables (M1) gave an area under the receiver operating characteristic curve of 0.95 for the development data set (n = 754 patients). The corresponding value for the test data set (n = 312 patients) was 0.94; and a probability cutoff value of .10 gave a sensitivity of 93% and a specificity of 76%. CONCLUSION: Because the model was constructed from multicenter data, it is more likely to be generally applicable. The effectiveness of the model will be tested prospectively at different centers.

Adnexal Diseases↗

The accuracy of transvaginal ultrasonography for the diagnosis of ectopic pregnancy prior to surgery.

BACKGROUND: To evaluate the accuracy of transvaginal ultrasonography (TVS) for the detection of ectopic pregnancies (EPs) in women undergoing surgery for presumed ectopic pregnancy. METHODS: A prospective, observational study. Women were diagnosed with an EP using TVS if any of the following were noted in the adnexal region: (i) an inhomogeneous mass or blob sign adjacent to the ovary and moving separately from the ovary; or (ii) a mass with a hyper-echoic ring around the gestational sac or bagel sign; or (iii) a gestational sac with a fetal pole with or without cardiac activity. The final diagnosis was based on the findings at surgery and subsequent histology of removed tissues. RESULTS: 6621 consecutive women underwent TVS during the study; 200/6621 (3.0%) women were diagnosed as having an EP using TVS. Forty-eight non-surgically managed women were excluded from the analysis. 85.5% of women presented with symptoms and 14.5% were asymptomatic. In 88 (57.9%) cases an inhomogeneous mass or blob sign was visualized and in 20 cases (13.2%) an embryo +/- cardiac activity. Thirty-one (20.4%) had a hyper-echoic ring in the adnexa. In 11 (7.2%) cases there was no evidence of either an intra-uterine (IUP) or EP on ultrasound. Two (1.3%) IUPs were subsequently diagnosed as heterotopic pregnancies. There was no association between the presenting complaints and TVS findings. 152 surgical procedures were performed. In 5.9% (9/152) of these cases no EPs were confirmed in fallopian tube or pelvis at laparoscopy. In 9.1% (13/143) of cases an EP was visualized at surgery when not seen on the index ultrasound scan. The sensitivity and specificity of TVS to detect EP were 90.9% and 99.9%, respectively, with positive and negative predictive values of 93.5% and 99.8%, respectively. CONCLUSIONS: 90.9% of ectopic pregnancies in this study population can be accurately diagnosed using TVS prior to surgery. The diagnosis of an ectopic pregnancy should be based on the positive visualization of an adnexal mass using TVS. This should in turn result in a decrease in the number of false positive laparoscopies.

Adult↗

Tissue segmentation and classification of MRSI data using canonical correlation analysis.

In this article an accurate and efficient technique for tissue typing is presented. The proposed technique is based on Canonical Correlation Analysis, a statistical method able to simultaneously exploit the spectral and spatial information characterizing the Magnetic Resonance Spectroscopic Imaging (MRSI) data. Recently, Canonical Correlation Analysis has been successfully applied to other types of biomedical data, such as functional MRI data. Here, Canonical Correlation Analysis is adapted for MRSI data processing in order to retrieve in an accurate and efficient way the possible tissue types that characterize the organ under investigation. The potential and limitations of the new technique have been investigated by using simulated as well as in vivo prostate MRSI data, and extensive studies demonstrate a high accuracy, robustness, and efficiency. Moreover, the performance of Canonical Correlation Analysis has been compared to that of ordinary correlation analysis. The test results show that Canonical Correlation Analysis performs best in terms of accuracy and robustness.

Algorithms↗

Modeling common dynamics in multichannel signals with applications to artifact and background removal in EEG recordings.

Removing artifacts and background electroencephaloraphy (EEG) from multichannel interictal and ictal EEG has become a major research topic in EEG signal processing in recent years. We applied for this purpose a recently developed subspace-based method for modeling the common dynamics in multichannel signals. When the epileptiform activity is common in the majority of channels and the artifacts appear only in a few channels the proposed method can be used to remove the latter. The performance of the method was tested on simulated data for different noise levels. For high noise levels the method was still able to identify the common dynamics. In addition, the method was applied to real life EEG recordings containing interictal and ictal activity contaminated with muscle artifact. The muscle artifacts were removed successfully. For both the synthetic data and the analyzed real life data the results were compared with the results obtained with principal component analysis (PCA). In both cases, the proposed method performed better than PCA.

Action Potentials↗

Measurement of the liver tissue oxygenation by near-infrared spectroscopy.

OBJECTIVE: To study the relation between the liver tissue oxygenation index (TOI), transcutaneously measured with spatially resolved spectroscopy (a new method of near-infrared spectroscopy or NIRS), the mixed venous oxygen saturation and the blood flow in the different parts of the splanchnic circulation in newborn piglets. DESIGN: Tissue oxygenation index of the liver was measured in six newborn piglets at 33 degrees C, 35 degrees C, 37 degrees C and after a decrease in arterial carbon dioxide pressure (PaCO(2)). MEASUREMENTS: Mixed venous oxygen saturation, blood gas analysis and peripheral oxygen saturation were measured at each step. Gastric, proximal jejunal, midgut, distal ileal, splenic and hepatic arterial blood flow were measured by injection of coloured microspheres into the left atrium. NIRS optodes were attached to the skin over the liver and TOI was calculated. RESULTS: No significant changes of TOI of the liver were seen during the increase in temperature or change in PaCO(2). TOI correlated well with mixed venous oxygen saturation (r=0.85), the mid-ileal blood flow (r=0.57) and the distal ileal blood flow (r=0.72). CONCLUSIONS: Measurement of the TOI of the liver might be a non-invasive way to measure the distal ileal blood flow.

Animals↗

Acute effects of tamoxifen and third-generation aromatase inhibitors on menopausal symptoms of breast cancer patients.

Endocrine treatments of breast cancer patients antagonize estrogen and may lead to consequences of estrogen deprivation including menopausal symptoms. We analyzed the changes in frequency and severity of menopausal symptoms in patients receiving tamoxifen or aromatase inhibitors and identified factors influencing these symptoms. One hundred and eighty-one consecutive postmenopausal breast cancer patients scheduled to start endocrine treatment were included in this prospective study. A menopause symptom questionnaire covering vasomotor, atrophic, psychological, cognitive and somatic symptoms was filled in at baseline, and after 1 and 3 months of therapy. Both first-line tamoxifen and aromatase inhibitors induced an increase in the occurrence and severity of hot flashes (p<0.0001 and p=0.014, respectively). Musculoskeletal pain and dyspareunia significantly increased under first-line non-steroidal aromatase inhibitors (p=0.0039 and p=0.001, respectively), while patients under tamoxifen had significant decrease in sexual interest (p< or =0.0001). Younger age was associated with more hot flashes and vaginal dryness at baseline, and after 1 and 3 months of therapy (all p<0.02). We conclude that there are significant differences between the early effects of tamoxifen and aromatase inhibitors on menopausal symptoms of breast cancer patients. Our results underscore the need for safe and effective non-hormonal interventions to alleviate vasomotor and musculoskeletal symptoms which were the most prevalent and severe symptoms.

Anastrozole↗

Using prior knowledge in SVD-based parameter estimation for magnetic resonance spectroscopy--the ATP example.

We introduce the knowledge-based singular value decomposition (KNOB-SVD) method for exploiting prior knowledge in magnetic resonance (MR) spectroscopy based on the SVD of the data matrix. More specifically, we assume that the MR data are well modeled by the superposition of a given number of exponentially damped sinusoidal components and that the dampings alphakappa, frequencies omegakappa, and complex amplitudes rhokappa of some components satisfy the following relations: alphakappa = alpha (alpha = unknown), omegakappa = omega + (kappa- 1)delta (omega = unknown, delta = known), and rhokappa = Ckapparho (rho = unknown, ckappa = known real constants). The adenosine triphosphate (ATP) complex, which has one triple peak and two double peaks whose dampings, frequencies, and amplitudes may in some cases be known to satisfy the above type of relations, is used as a vehicle for describing our SVD-based method throughout the paper. By means of numerical examples, we show that our method provides more accurate parameter estimates than a commonly used general-purpose SVD-based method and a previously suggested prior knowledge-based SVD method.

Adenosine Triphosphate↗

Nonlinear analysis of heart rate variability in infants with apparent life-threatening events.

Some studies have shown that neonates having experienced an Apparent Life-Threatening Event (ALTE) have an increased risk of dying of the Sudden Infant Death Syndrome (SIDS). In this study the heart rate variability in neonates has been analyzed through a study of the long range correlations and scale invariance (self-similarity) in their cardiac rhythm. The goal is to see whether it is possible to distinguish normal infants from infants with ALTEs using the previously mentioned nonlinear measures of the heart rate variability. Twelve ALTE infants are included in this study. To determine the degree to which these neonates suffer from ALTEs two examinations are performed: a polysomnography and home monitoring. Using the nonlinear measures obtained from the nonlinear analysis of the heart rate variability, the group suffering most from ALTEs can clearly be separated from the other neonates.

Heart↗

Measurement of tissue oxygenation index during the first three days in premature born infants.

No normal values of tissue oxygenation index (TOI) of the brain are known regarding premature born infants. We measured TOI, a measure for the cerebral hemoglobin oxygen saturation, on the head of 15 preterm infants with a median postmenstrual age of 28 weeks (interquartile range (IQR) between 26-29 weeks) with spatially resolved spectroscopy (NIRO 300, Hamamatsu) during the first three days of life. Infants with intra-ventricular hemorrhage or periventricular leucomalacia before the first measurement, as shown by ultrasound, were excluded. The first measurement was done within the first 6 hours of life, the second and third measurement at, respectively, 24 and 48 hours after this first measurement. The mean TOI was calculated if saturation did not change by more than 5% for at least 30 minutes. Other parameters measured were PaO2, PCO2, pH, mean arterial blood pressure, heart rate, hemoglobin, glycemia and peripheral oxygen saturation. There was a significant increase of TOI after 24 (p < 0.05) and 48 (p < 0.001) hours. The median TOI on the first day was 57% (95% CI: 54-65.7), 66.1% on the second day (95%CI: 61.9-82.3%) and 76.1% on the third day (95%CI 67.8-80.1%). No correlation was found between TOI and peripheral oxygen saturation, blood pressure, PaO2, PaCO2 and hemoglobin concentration after multiple regression analysis. TOI increases in the first three days in premature born babies. The increase of TOI is not due to an increase of oxygenation or mean arterial blood pressure. In our opinion, it reflects the increase in cerebral blood flow during the first three days.

Adult↗

Quantitation of the concordance between cerebral intravascular oxygenation and mean arterial blood pressure for the detection of impaired autoregulation.

Since some important forms of brain injury in premature infants are caused in considerable part by disturbances in cerebral blood flow (CBF), it is important to be able to detect whether the cerebrovascular autoregulation, the mechanism by which CBF is maintained constant despite alterations in mean arterial blood pressure (MAP), is working properly. A recent study suggested that concordant changes in MAP and cerebral intravascular oxygenation (HbD), measured non-invasively by near-infrared spectroscopy (NIRS) as the difference between the concentration changes of oxygenated hemoglobin (HbO2) and deoxygenated hemoglobin (Hb), reflect impaired cerebrovascular autoregulation. Consequently, premature infants with impaired cerebrovascular autoregulation could be identified by simultaneous, continuous measurements of HbD and MAP. From several premature babies, MAP, HbD and arterial oxygen saturation (SaO2) were measured simultaneously at the University Hospital Leuven, Belgium. The concordance between MAP and HbD was quantitated using three different measures, among which a newly developed measure that looks for similarity of the dynamics between signals. Some preliminary results obtained from the measured data are given.

Blood Pressure↗

Frequency-domain method based on the singular value decomposition for frequency-selective NMR spectroscopy.

In several applications of NMR spectroscopy the user is interested only in the components lying in a small frequency band of the spectrum. A frequency selective analysis deals precisely with this kind of NMR spectroscopy: parameter estimation of only those spectroscopic components that lie in a preselected frequency band of the NMR data spectrum, with as little interference as possible from the out-of-band components and in a computationally efficient way. In this paper we introduce a frequency-domain singular value decomposition (SVD)-based method for frequency selective spectroscopy that is computationally simple, statistically accurate, and which has a firm theoretical basis. To illustrate the good performance of the proposed method we present a number of numerical examples for both simulated and in vitro NMR data.

Algorithms↗

Ultrasound assessment of endometrial thickness and endometrial polyps in women on hormonal replacement therapy.

OBJECTIVE: This study was performed to evaluate the thickness and the sonographic features of the endometrium in postmenopausal women on hormone replacement therapy (HRT). STUDY DESIGN: This prospective study was based on 483 vaginal ultrasound examinations performed in 238 consecutive postmenopausal women on HRT. RESULTS: Endometrial polyps were diagnosed by ultrasound in 16.3% of the patients; 43.6% were asymptomatic. In the nonpolyp group, a significant difference in endometrial thickness between sequential and continuous schemes was found. In sequential HRT, a three-layer ultrasound pattern of the endometrium was seen in 47% of the women in the estrogen-alone phase of cycle versus 11% in the estrogen-progestogen phase. CONCLUSION: Patients on HRT need other reference values for endometrial thickness compared with postmenopausal women without HRT. In women on sequential HRT, a transvaginal sonographic evaluation performed in the estrogen-alone phase of cycle may optimize the accuracy for focal lesion detection. The significance of the incidental finding of polyps in an important number of asymptomatic women on HRT remains unsettled.

Endometrial Neoplasms↗

A subspace time-domain algorithm for automated NMR spectral normalization.

Recently, two methods have been proposed for quantitatively comparing NMR spectra of control and treated samples, in order to examine the possible occurring variations in cell metabolism and/or structure in response to numerous physical, chemical, and biological agents. These methods are the maximum superposition normalization algorithm (MaSNAl) and the minimum rank normalization algorithm (MiRaNAl). In this paper a new subspace-based time-domain normalization algorithm, denoted by SuTdNAl (subspace time-domain normalization algorithm), is presented. By the determination of the intersection of the column spaces of two Hankel matrices, the common signal poles and further on the components having proportionally varying amplitudes are detected. The method has the advantage that it is computationally less intensive than the MaSNAl and the MiRaNAl. Furthermore, no approximate estimate of the normalization factor is required. The algorithm was tested by Monte Carlo simulations on a set of simulation signals. It was shown that the SuTdNAl has a statistical performance similar to that of the MiRaNAl, which itself is an improvement over the MaSNAl. Furthermore, two samples of known contents are compared with the MiRaNAl, the SuTdNAl, and an older method using a standard. Finally, the SuTdNAl is tested on a realistic simulation example derived from an in vitro measurement on cells.

Journal Article↗