Biomedical subjects

P Suetens

Publications and source records attributed to P Suetens.

At least 19 recordsLinked to original sources

PubMed2006

Intracorporeal rectal stapling following laparoscopic total mesorectal excision: overcoming a challenge.

BACKGROUND: Division of the rectum following total mesorectal excision (TME) using intracorporeal stapling devices is technically difficult due to their width and limited roticulation. More than one cartridge is often required and resultant wedging of the stump may be associated with an appreciable leak rate. METHODS: Three-dimensional reconstruction was performed of CT and MRI images from the lower abdomen of six patients undergoing laparoscopic TME using the Amira software environment. The stapling device was virtually reconstructed by in-house developed software, superimposed over the point of division of the rectum and the site of skin entry identified. RESULTS: The 45 degrees angulation of available roticulating stapling devices precludes perpendicular division of the rectum following laparoscopic TME. The optimal angulation for transverse rectal stapling varied between 62 degrees and 68 degrees . CONCLUSION: A roticulating stapler with minimum angulation of 65 degrees would achieve transverse division of the rectum following laparoscopic TME.

Aged↗

PubMed2006

Large-scale in-vivo Caucasian facial soft tissue thickness database for craniofacial reconstruction.

A large-scale study of facial soft tissue depths of Caucasian adults was conducted. Over a 2-years period, 967 Caucasian subjects of both sexes, varying age and varying body mass index (BMI) were studied. A user-friendly and mobile ultrasound-based system was used to measure, in about 20min per subject, the soft tissue thickness at 52 facial landmarks including most of the landmarks used in previous studies. This system was previously validated on repeatability and accuracy [S. De Greef, P. Claes, W. Mollemans, M. Loubele, D. Vandermeulen, P. Suetens, G. Willems, Semi-automated ultrasound facial soft tissue depth registration: method and validation. J. Forensic Sci. 50 (2005)]. The data of 510 women and 457 men were analyzed in order to update facial soft tissue depth charts of the contemporary Caucasian adult. Tables with the average thickness values for each landmark as well as the standard deviation and range, tabulated according to gender, age and BMI are reported. In addition, for each landmark and for both sexes separately, a multiple linear regression of thickness versus age and BMI is calculated. The lateral asymmetry of the face was analysed on an initial subset of 588 subjects showing negligible differences and thus warranting the unilateral measurements of the remaining subjects. The new dataset was statistically compared to three datasets for the Caucasian adults: the traditional datasets of Rhine and Moore [J.S. Rhine, C.E. Moore, Tables of facial tissue thickness of American Caucasoids in forensic anthropology. Maxwell Museum Technical series 1 (1984)] and Helmer [R. Helmer, Schädelidentifizierung durch elektronische bildmischung, Kriminalistik Verlag GmbH, Heidelberg, 1984] together with the most recent in vivo study by Manhein et al. [M.H. Manhein, G.A. Listi, R.E. Barsley, R. Musselman, N.E. Barrow, D.H. Ubelbaker, In vivo facial tissue depth measurements for children and adults. J. Forensic Sci. 45 (2000) 48-60]. The large-scale database presented in this paper offers a denser sampling of the facial soft tissue depths of a more representative subset of the actual Caucasian population over the different age and body posture subcategories. This database can be used as an updated chart for manual and computer-based craniofacial approximation and allows more refined analyses of the possible factors affecting facial soft tissue depth.

Adolescent↗

PubMed2006

Radiation dose vs. image quality for low-dose CT protocols of the head for maxillofacial surgery and oral implant planning.

The goal of this study was to determine the acquisition parameters for a low-dose multi-slice CT protocol and to compare the effective dose and the image quality of this low-dose protocol with the image quality of a clinical multi-slice CT protocol, routinely used for visualisation of the head. The low-dose protocol was derived from a clinical multi-slice CT protocol by lowering mA s and kV and increasing the pitch. The low-dose protocol yielded a dose reduction from 1.5 to 0.18 mSv for a multi-slice CT scan of the whole head, whereas noise in the low-dose CT images was increased. For bone segmentation, noise could be reduced by use of a non-linear edge preserving smoothing filter. Tests on ESP and skull phantom indicated that the accuracy of the measurements on low-dose CT is acceptable for image-based planning of maxillofacial and oral implant surgery, reducing the dose by a factor of 8.

Humans↗

PubMed2004

The nasopalatine canal revisited using 2D and 3D CT imaging.

OBJECTIVES: To assess the location, morphology and dimensions of the nasopalatine canal on two-dimensional and three-dimensional (2D and 3D) CT images. METHODS: Material included 34 spiral CT scans for pre-operative planning of implant placement in the maxilla. Scanning was performed using a standard exposure and patient positioning protocol. 2D and 3D spiral CT images were carefully examined for the location, morphology and dimensions of the nasopalatine canal by two independent observers. A comparison was made between 2D observations and a 2D/3D combined observation strategy (paired t-tests). RESULTS: The nasopalatine canal typically appeared as a canal with a mean (standard deviation (SD)) length of 8.1 (3.4) mm. Its palatal opening is the incisive foramen with a mean (SD) inner Ø of 4.6 (1.8) mm. At the level of the nasal floor often 2 (Y-canal morphology), but sometimes 3 or 4 openings could be observed. In particular cases, the canal showed up as a cylinder with only one nasal opening. The average (SD) maximum width of the nasopalatine canal structure at the level of the nasal floor was 4.9 (1.2) mm. The buccopalatal width of the jaw, anterior to the canal was 7.4 (2.6) mm. Interpretation of canal morphology was significantly different when comparing 2D image observation with a 2D/3D combined observation strategy. However, dimensional measurements of the canal were not significantly different for a 2D and a combined 2D/3D approach. CONCLUSIONS: The nasopalatine canal may show important anatomical variations, both with regard to morphology and dimensions. To avoid any potential complications during surgical procedures such as implant placement, a careful pre-operative observation is required. Cross-sectional imaging may be advocated to determine canal morphology and dimensions and to assess anterior bone width for potential implant placement buccally to the canal.

Adult↗

PubMed2003

Comparison of time-domain displacement estimators for two-dimensional RF tracking.

Techniques have been described in the literature to enable multidimensional strain rate estimation. They are based on multidimensional velocity estimation. One of the problems in obtaining robust lateral strain rate estimates is the fact that lateral velocity estimates are intrinsically noisier than axial ones. The aim of this study was to find the optimal estimator for tracking of the radiofrequency patterns both in axial and lateral directions. Performances of the following estimators were investigated using simulations: cross-correlation, normalized cross-correlation, sum of absolute differences and sum of squared differences. Two-dimensional (2-D) velocity estimation was not feasible using cross-correlation. However, normalized cross-correlation, sum of absolute differences and sum of squared differences showed accurate axial and lateral results. For smaller window lengths, sum of squared differences was found to be the preferred estimator for 2-D velocity estimation using a 1-D kernel.

Acoustics↗

PubMed2003

Temporal subtraction of thorax CR images using a statistical deformation model.

We propose a voxel-based nonrigid registration algorithm for temporal subtraction of two-dimensional thorax X-ray computed radiography images of the same subject. The deformation field is represented by a B-spline with a limited number of degrees of freedom, that allows global rib alignment to minimize subtraction artifacts within the lung field without obliterating interval changes of clinically relevant soft-tissue abnormalities. The spline parameters are constrained by a statistical deformation model that is learned from a training set of manually aligned image pairs using principal component analysis. Optimization proceeds along the transformation components rather then along the individual spline coefficients, using pattern intensity of the subtraction image within the automatically segmented lung field region as the criterion to be minimized and applying a simulated annealing strategy for global optimization in the presence of multiple local optima. The impact of different transformation models with varying number of deformation modes is evaluated on a training set of 26 images using a leave-one-out strategy and compared to the manual registration result in terms of criterion value and deformation error. Registration quality is assessed on a second set of validation images by a human expert rating each subtraction image on screen. In 85% of the cases, the registration is subjectively rated to be adequate for clinical use.

Algorithms↗

PubMed2002

Integrating images into a central medical information system.

Of the information items that must be easily available to the different actors involved in the care process, radiological images are not the least important. While until recently it was not feasible to include these into the medical information system, this situation has changed. Still, emphasis in PACS (Picture Archiving and Communication Systems) is primarily on the technological aspects. In this paper, in contrast, we stress the importance of integration of images into the overall workflow and into the overall medical record. We do so using illustrations from the PACS project of the University Hospitals Leuven. We briefly indicate that tight integration at the user interface level is needed, and that this requires more than standardized communication between subsystems.

Computer Systems↗

PubMed2002

Web-access to a central medical record to improve cooperation between hospital and referring physicians.

We set up Web-access to the central electronic medical record of the University Hospitals Leuven. Purpose was to enable external physicians to more actively participate in the care process as full members of the multidisciplinary treatment team. They get a view on the complete care process in the hospital, and can access results as these become available instead of being provided summary information post factum. This complements traditional electronic exchange between healthcare records. We report on technical setup and results from an extended pilot. We believe that this approach can enrich the discussion on how to provide the "global medical record".

Appointments and Schedules↗

PubMed2001

Automated segmentation of multiple sclerosis lesions by model outlier detection.

This paper presents a fully automated algorithm for segmentation of multiple sclerosis (MS) lesions from multispectral magnetic resonance (MR) images. The method performs intensity-based tissue classification using a stochastic model for normal brain images and simultaneously detects MS lesions as outliers that are not well explained by the model. It corrects for MR field inhomogeneities, estimates tissue-specific intensity models from the data itself, and incorporates contextual information in the classification using a Markov random field. The results of the automated method are compared with lesion delineations by human experts, showing a high total lesion load correlation. When the degree of spatial correspondence between segmentations is taken into account, considerable disagreement is found, both between expert segmentations, and between expert and automatic measurements.

Algorithms↗

PubMed2001

An iterative maximum-likelihood polychromatic algorithm for CT.

A new iterative maximum-likelihood reconstruction algorithm for X-ray computed tomography is presented. The algorithm prevents beam hardening artifacts by incorporating a polychromatic acquisition model. The continuous spectrum of the X-ray tube is modeled as a number of discrete energies. The energy dependence of the attenuation is taken into account by decomposing the linear attenuation coefficient into a photoelectric component and a Compton scatter component. The relative weight of these components is constrained based on prior material assumptions. Excellent results are obtained for simulations and for phantom measurements. Beam-hardening artifacts are effectively eliminated. The relation with existing algorithms is discussed. The results confirm that improving the acquisition model assumed by the reconstruction algorithm results in reduced artifacts. Preliminary results indicate that metal artifact reduction is a very promising application for this new algorithm.

Algorithms↗

PubMed2001

Parametric study of the peak negative acoustic pressure distribution within the image plane of a phased array transducer.

A study is presented in which the influence of pulse and transducer characteristics on the distribution of the peak negative acoustic pressure within the image plane of a phased array transducer is shown. First, the influence of the center frequency, the bandwidth of the transmitted pulse, the position of the focus point, and the properties of the phased array are investigated by computer simulation. These simulations show that both the maximal amplitude and the homogeneity of the distribution of the peak negative pressure within a sector image depend on these parameters. Most remarkably, they show that the maximal peak pressure does not necessarily occur on the geometrical symmetry axis of the array transducer but can occur at the outermost lateral lines of a sector image. Second, this effect is demonstrated experimentally by hydrophone measurements of the sound field produced by a standard, clinically used, 2.5-MHz phased array transducer. The experimental results agree well with the theoretical model. The relevance of this study for contrast echography and the safety measurements of ultrasound is discussed.

Acoustics↗

PubMed2000

An image-based 3D planning environment for hemicricolaryngectomy and reconstruction by tracheal autotransplantation.

OBJECTIVE: A new conservation method for unilateral glottal cancer with significant subglottal extension consists of a hemicricolaryngectomy and subsequent reconstruction of the laryngeal defect with a transferable patch of revascularized cervical trachea. In order to restore the three crucial functions of the larynx - airway patency, speech, and swallowing--the reconstructed larynx should resemble a situation with one paralyzed and one intact vocal fold at the glottal level. We hypothesize that this result can be achieved when the tracheal patch meets a typical surgical constraint--the so-called paramedian position at the glottal level - and when the patch is rigidly applied. This hypothesis was tested by developing and using an image-based planning system in a number of situations. MATERIALS AND METHODS: An image-based surgery simulator was developed according to the working hypothesis. To validate the transfer from planning towards actual surgery, a cadaver study was set up. Based on a patient case-study, the sufficiency of the hypothesis for obtaining good functional results was evaluated. Finally, post-operative images of patients who were doing well after being operated without pre-operative planning were compared with retrospective planning to check the necessity of the hypothesis in obtaining good functionality of the neolarynx. RESULTS: We were able to design an efficient surgery simulator. The transfer from planning towards actual surgery is accurate, and satisfactory functional results were obtained from the patient case-study. The results from the retrospective planning showed that the hypothesis is not necessary to obtain good functional results, and that the smallest possible resection is preferred from the oncological point of view. CONCLUSION: The working hypothesis is sufficient for good functional results, but is unnecessary and often undesirable from an oncological point of view. Important lessons are drawn concerning our long-term goal of pre-operative determination of the shape and position of a tracheal patch suitable for optimizing the (neo-) laryngeal functions.

Cadaver↗

PubMed2000

Remote myocardial dysfunction after acute anterior myocardial infarction: impact of left ventricular shape on regional function: a magnetic resonance myocardial tagging study.

OBJECTIVES: We sought to evaluate regional morphology and function in patients in their first week after having a reperfused anterior myocardial infarction (MI) using magnetic resonance (MR) myocardial tagging. BACKGROUND: The mechanism of myocardial dysfunction in the remote, noninfarct-related regions is an unresolved issue to date. METHODS: Sixteen patients with a first reperfused transmural anterior MI were studied with MR tagging at 5 +/- 2 days after the event, and the results were compared with those of an age-matched control group regions. The left ventricle (LV) was divided into infarct, adjacent and remote regions. Magnetic resonance tagging provided information on the regional ventricular morphology and function. RESULTS: Morphologically, an increase of the circumferential radius of curvature was found in the remote myocardium, whereas the longitudinal radius of curvature was increased in all regions of the LV. A significant increase in apical sphericity was also found. A significant reduction in strain and function was found not only in the infarct region, but also in the adjacent and remote myocardium. The loss in regional ejection fraction in the remote myocardium (61.4 +/- 11.7% in patients vs. 68.7 +/- 10.0% in control subjects, p < 0.0001) was related to a significant reduction of the longitudinal and circumferential strain, whereas systolic wall thickening was preserved. CONCLUSIONS: Remote myocardial dysfunction contributes significantly to the loss in global ventricular function. This could be secondary to morphologic changes in the infarct region, leading to an increased systolic longitudinal wall stress without loss of intrinsic contractility in the remote regions.

Adult↗

PubMed2000

High frame rate myocardial integrated backscatter. Does this change our understanding of this acoustic parameter?

AIMS: Integrated backscatter (IB) and its cyclic variation (CV) derived from radio-frequency (RF) data have been used as parameters to attempt myocardial tissue characterization. Prior imaging systems used to measure IB and its CV typically acquired data at frame rates of 20-30 Hz and at a resolution of 6-8 bits. If changes in IB levels are in part related to specific short-lived events, occurring within the cardiac cycle, this frame rate and resolution could have been too low to resolve adequately what might be a more complex data set. METHODS AND RESULTS: To investigate this possibility, we acquired real time two-dimensional (2D) myocardial IQ data (the 'in-phase quadrature' sampled RF data) at high frame rate (> 100 Hz), high dynamic resolution (theoretical 19-bit) and a sector angle of 20 degrees. Several consecutive heart cycles of myocardial data were acquired from individual cardiac walls in five closed chest dogs and 10 healthy, young volunteers at normal heart rates. On the reconstructed RF data regions of interest were indicated, and IB and its CV were calculated. The extracted high frame rate curves showed that the CV of IB is not a smooth sinusoidal-like curve, but is made up of multiple reproducible peaks and troughs with local minima and maxima which are temporally related to active or passive mechanical events, i.e. systolic contraction, early ventricular relaxation and ventricular filling due to atrial contraction. CONCLUSIONS: This study shows that increasing the rate of real-time RF data acquisition results in a more complex, reproducible IB curve. The resolved maxima and minima in IB levels are related to specific phases of the myocardial contraction. Furthermore, spectral analysis showed that IB curves acquired at normal heart rates contain information up to 40 Hz. Hence, cardiac imaging data sets used to analyse regional myocardial function obtained at frequencies lower than 80 frames per second can contain aliased information.

Adult↗

PubMed2000

Regional strain and strain rate measurements by cardiac ultrasound: principles, implementation and limitations.

The non-invasive quantification of regional myocardial function is an important goal in clinical cardiology. Myocardial thickening/thinning indices is one method of attempting to define regional myocardial function. A new ultrasonic method of quantifying regional deformation has been introduced based on the principles of 'strain' and 'strain rate' imaging. These new imaging modes introduce concepts derived from mechanical engineering which most echocardiographers are not familiar with. In order to maximally exploit these new techniques, an understanding of what they measure is indispensable. This paper will define each of these modalities in terms of physical principles and will give an introduction to the principles of data acquisition and processing required to implement ultrasonic strain and strain rate imaging. In addition, the current status of development of the technique and its limitations will be discussed, together with examples of potential clinical applications.

Biomedical Engineering↗

PubMed2000

Are changes in myocardial integrated backscatter restricted to the ischemic zone in acute induced ischemia? An in vivo animal study.

Integrated backscatter (IB) from a myocardial region, calculated from radiofrequency echocardiographic data, has been proposed as a useful parameter for investigating changes in myocardial tissue induced by ischemia. In 10 closed-chest dogs, 5 minutes of myocardial ischemia was induced by either a proximal occlusion of the circumflex coronary artery (CX) (5 dogs), resulting in extensive ischemia in the posterior wall, or by occluding the distal CX vessel (5 dogs) to produce a small localized ischemic zone in the posterior wall. High-resolution digital radiofrequency data from the whole left ventricular myocardium, in the imaging plane during one complete heart cycle, were acquired with a whole-image real-time acquisition approach. Regions in the septum and posterior wall (both ischemic tissue and, in the case of distal occlusions, tissue surrounding the ischemic zone) were chosen for analysis, and IB and cyclic variation (CV) of IB were calculated. Post occlusion, an increase in mean IB values was found in the ischemic segment. However, an increase in CV was also observed in the peri-ischemic zone for the distal CX occlusion and in the septum after proximal CX occlusion. These findings show that changes in CV are not restricted to the ischemic zone but may also occur in distal myocardium. This may be explained by changes in the regional contractile state and loading conditions of the "normal" myocardium, which are altered in response to the distal ischemia.

Animals↗

PubMed1999

Robustness of integrated backscatter for myocardial tissue characterization.

Integrated backscatter (IB) has been used for ultrasonic tissue characterization. To assess the potential variables in IB measurements, we performed both theoretical simulations and in vitro phantom measurements. First, we simulated data in which the scatterer position randomly was varied. IB values for the resulting images were calculated. Second, RF data from a tissue-mimicking phantom were acquired. Third, an adapted imaging approach, based on phase insensitivity, was evaluated. For both the simulations and phantom measurements, IB showed a standard deviation of +/-20%. These large deviations can be explained by variations in interference of signals and are not related to the state of the tissue. Small deviations in position of the scatterers resulted in important variations in IB. They must be taken into account and may limit the use of IB in cardiological applications. An improvement potentially can be obtained using phase insensitivity in new ultrasound processing schemes.

Computer Simulation↗

PubMed1999

Comparative evaluation of multiresolution optimization strategies for multimodality image registration by maximization of mutual information.

Maximization of mutual information of voxel intensities has been demonstrated to be a very powerful criterion for three-dimensional medical image registration, allowing robust and accurate fully automated affine registration of multimodal images in a variety of applications, without the need for segmentation or other preprocessing of the images. In this paper, we investigate the performance of various optimization methods and multiresolution strategies for maximization of mutual information, aiming at increasing registration speed when matching large high-resolution images. We show that mutual information is a continuous function of the affine registration parameters when appropriate interpolation is used and we derive analytic expressions of its derivatives that allow numerically exact evaluation of its gradient. Various multiresolution gradient- and non-gradient-based optimization strategies, such as Powell, simplex, steepest-descent, conjugate-gradient, quasi-Newton and Levenberg-Marquardt methods, are evaluated for registration of computed tomography (CT) and magnetic resonance images of the brain. Speed-ups of a factor of 3 on average compared to Powell's method at full resolution are achieved with similar precision and without a loss of robustness with the simplex, conjugate-gradient and Levenberg-Marquardt method using a two-level multiresolution scheme. Large data sets such as 256(2) x 128 MR and 512(2) x 48 CT images can be registered with subvoxel precision in <5 min CPU time on current workstations.

Algorithms↗