Biomedical subjects

R J van der Geest

Publications and source records attributed to R J van der Geest.

At least 19 recordsLinked to original sources

PubMed2005

Optimizing the automatic segmentation of the left ventricle in magnetic resonance images.

Automatic segmentation of the left ventricular (LV) myocardial borders in cardiovascular MR (CMR) images allows a significant speed-up of the procedure of quantifying LV function, and improves its reproducibility. The automated boundary delineation is usually based on a set of parameters that define the algorithms. Since the automatic segmentation algorithms are usually sensitive to the image quality and frequently depend heavily on the acquisition protocol, optimizing the parameters of the algorithm for such different protocols may be necessary to obtain optimal results. In other words, using a default set of parameters may be far from optimal for different scanners or protocols. For the MASS-software, for example, this means that a total of 14 parameters need to be optimized. This optimization is a difficult and labor-intensive process. To be able to more consistently and rapidly tune the parameters, an automated optimization system would be extremely desirable. In this paper we propose such an approach, which is based on genetic algorithms (GAs). The GA is an unsupervised iterative tool that generates new sets of parameters and converges toward an optimal set. We implemented and compared two different types of the genetic algorithms: a simple GA (SGA) and a steady state GA (2SGA). The difference between these two algorithms lies in the characteristics of the generated populations: "nonoverlapping populations" and "overlapping populations," respectively "nonoverlapping" population means that the two populations are disjoint, and "overlapping" means that the best parameters found in the previous generation are included in the present population. The performance of both algorithms was evaluated on twenty routinely obtained short-axis examinations (eleven examinations acquired with a steady-state free precession pulse sequence, and nine examinations with a gradient echo pulse sequence). The optimal parameters obtained with the GAs were used for the LV myocardial border delineation. Finally, the automatically outlined contours were compared to the gold standard--manually drawn contours by experts. The result of the comparison was expressed as a degree of similarity after a processing time of less than 72 h to a 59.5% of degree of similarity for SGA and a 66.7% of degree of similarity for 2SGA. In conclusion, genetic algorithms are very suitable to automatically tune the parameters of a border detection algorithm. Based on our data, the 2SGA was more suitable than the SGA method. This approach can be generalized to other optimization problems in medical image processing.

Algorithms↗

PubMed2004

Automatic segmentation and plaque characterization in atherosclerotic carotid artery MR images.

In vivo MRI provides a means to non-invasively image and assess the morphological features of atherosclerotic carotid arteries. To assess quantitatively the degree of vulnerability and the type of plaque, the contours of the lumen, outer boundary of the vessel wall and plaque components, need to be traced. Currently this is done manually, which is time-consuming and sensitive to inter- and intra-observer variability. The goal of this work was to develop an automated contour detection technique for tracing the lumen, outer boundary and plaque contours in carotid MR short-axis black-blood images. Seventeen patients with carotid atherosclerosis were imaged using high-resolution in vivo MRI, generating a total of 50 PD- and T1-weighted MR images. These images were automatically segmented using the algorithm presented in this work, which combines model-based segmentation and fuzzy clustering to detect the vessel wall, lumen and lipid core boundaries. The results demonstrate excellent correspondence between automatic and manual area measurements for lumen (r = 0.92) and outer (r = 0.91), and acceptable correspondence for fibrous cap thickness (r = 0.71). Though further optimization is required, our algorithm is a powerful tool for automatic detection of lumen and outer boundaries, and characterization of plaque in atherosclerotic vessels.

Aged↗

PubMed2004

Quantitative analysis of vascular images, in particular of abdominal aorta aneurysms from 3D CTA data sets.

This article presents a combination of well known image processing techniques to automatically segment CTA images of the Abdominal Aortic Aneurysm. Current results are that about 80% of the contours need no manual corrections. The remaining 20% fail due to calcified plaque close to the lumen border. After correction a 3D surface model is created from the 2D contours which is used as input for flow simulations and for parameter extraction of the AAA by clinicians for selecting the proper size and shape endograft, and to plan the placement procedure of this endograft in the patient.

Algorithms↗

PubMed2003

Automated segmentation and analysis of vascular structures in magnetic resonance angiographic images.

The accurate assessment of the presence and extent of vascular disease, and planning of vascular interventions based on MRA requires the determination of vessel dimensions. The current standard is based on measuring vessel diameters on maximum intensity projections (MIPs) using calipers. In order to increase the accuracy and reproducibility of the method, automated analysis of the 3D MR data is required. A novel method for automatically determining the trajectory of the vessel of interest, the luminal boundaries, and subsequent the vessel dimensions is presented. The automated segmentation in 3D uses deformable models, combined with knowledge of the acquisition protocol. The trajectory determination was tested on 20 in vivo studies of the abdomen and legs. In 93% the detected trajectory followed the vessel. The luminal boundary detection was validated on contrast-enhanced (CE) MRA images of five stenotic phantoms. The results from the automated analysis correlated very well with the true diameters of the phantoms used in the in vitro study (r = 0.999, P < 0.001). MRA and x-ray angiography (XA) of the phantoms also correlated well (r = 0.895, P < 0.001). The average unsigned difference between the MRA and XA measurements was 0.08 +/- 0.05 mm. In conclusion, the automated approach allows the accurate assessment of vessel dimensions in MRA images.

Abdomen↗

PubMed2001

Tumor diameter and volume assessed by magnetic resonance imaging in the prediction of outcome for invasive cervical cancer.

OBJECTIVE: The aim of this study was to evaluate the predictive value of pretherapeutic magnetic resonance imaging (MRI)-based measurements of tumor diameter and volume with regard to recurrent disease. METHODS: MRI on 0.5- or 1.5-T scanners was performed in 126 consecutive women with invasive carcinoma of the uterine cervix. Initial tumor diameter and volume were determined on T(2)-weighted images; volume was calculated by the standard technique of multiplying the sum of the areas by the slice thickness. Patients were treated by radical surgery, radiotherapy, or a combined approach based on clinical International Federation of Gynecology and Obstetrics (FIGO) stage and individual patient criteria. Clinical data (patient age and FIGO stage), MRI-derived tumor dimensions (diameter and volume), and histological findings (tumor invasion depth and lymph-node involvement) were associated and linked to patient outcome. RESULTS: MRI-based tumor diameter correlated strongly with histological tumor invasion depth and lymph-node status (P < 0.01 and P = 0.01) while tumor volume on MRI was significantly associated only with tumor invasion depth into adjacent tissues (P < 0.01). Univariate analysis demonstrated graphically that MRI-derived tumor diameter and volume and clinical FIGO stage are associated with progression-free survival. Correlation analysis showed a strong association between MRI-derived tumor diameter and volume on MRI (r = 68%, P < 0.01) and also demonstrated a correlation between tumor diameter on MRI and FIGO stage Ib (Ib1 versus Ib2) cervical tumors (r = 46.7%, P < 0.01). CONCLUSION: Tumor diameter and volume, determined by pretreatment MRI examinations, predict progression-free survival for patients with invasive cervical carcinoma. This study demonstrates the value of MRI as an adjunct to clinical evaluation of invasive cervical cancer, providing more complete assessment of morphological risk factors important in patient prognosis and treatment planning.

Adult↗

PubMed2001

Multistage hybrid active appearance model matching: segmentation of left and right ventricles in cardiac MR images.

A fully automated approach to segmentation of the left and right cardiac ventricles from magnetic resonance (MR) images is reported. A novel multistage hybrid appearance model methodology is presented in which a hybrid active shape model/active appearance model (AAM) stage helps avoid local minima of the matching function. This yields an overall more favorable matching result. An automated initialization method is introduced making the approach fully automated. Our method was trained in a set of 102 MR images and tested in a separate set of 60 images. In all testing cases, the matching resulted in a visually plausible and accurate mapping of the model to the image data. Average signed border positioning errors did not exceed 0.3 mm in any of the three determined contours-left-ventricular (LV) epicardium, LV and right-ventricular (RV) endocardium. The area measurements derived from the three contours correlated well with the independent standard (r = 0.96, 0.96, 0.90), with slopes and intercepts of the regression lines close to one and zero, respectively. Testing the reproducibility of the method demonstrated an unbiased performance with small range of error as assessed via Bland-Altman statistic. In direct border positioning error comparison, the multistage method significantly outperformed the conventional AAM (p < 0.001). The developed method promises to facilitate fully automated quantitative analysis of LV and RV morphology and function in clinical setting.

Computer Simulation↗

PubMed2001

Automated observer-independent acquisition of cardiac short-axis MR images: a pilot study.

The authors compared an automated observer-independent acquisition planning method for short-axis multisection multiphase cardiac magnetic resonance imaging studies with conventional manual image planning. Systematic and random differences and reproducibility of left ventricular function measurements and image geometry were evaluated in five healthy adult volunteers and 20 patient studies. Results with the automated planning method were as accurate and reproducible as those with the manual planning method.

Adult↗

PubMed2000

Right ventricular function in patients after acute myocardial infarction assessed with phase contrast MR velocity mapping encoded in three directions.

The purpose of the study was to assess global and regional myocardial function of the right ventricle (RV) with the use of phase contrast (PC) velocity mapping in patients after acute myocardial infarction. We examined 8 patients after acute myocardial wall infarction and 10 healthy volunteers for comparison. PC velocity mapping was performed in a single midventricular short-axis slice with velocity encoding in three different directions. RV displacement during systole in the through-plane direction differed significantly between patients and volunteers (P = 0.009). RV myocardial velocity in the through-plane and radial directions, evaluated at time of peak ejection rate, was significantly lower in patients than in healthy volunteers (P<0.05). RV abnormalities may be detected in patients after acute myocardial infarction using PC velocity mapping with velocity encoding in three different directions. Owing to their short acquisition times and relatively easy postprocessing, PC techniques are time-efficient and promising tools for the evaluation of RV function.

Adult↗

PubMed2000

Detection of areas with viable remnant tumor in postchemotherapy patients with Ewing's sarcoma by dynamic contrast-enhanced MRI using pharmacokinetic modeling.

An approach is presented for monitoring the effects of neoadjuvant chemotherapy in patients with Ewing's sarcoma using dynamic contrast-enhanced perfusion magnetic resonance (MR) images. For that purpose, we modify the three-compartment pharmacokinetic permeability model introduced by Tofts et al. (Magn Reson Med 1991;17:357-67) to a two-compartment model. Perfusion MR images acquired using an intravenous injection with Gadolinium (Gd-DTPA) are analyzed with this two-compartment pharmacokinetic model as well as the with an extended pharmacokinetic model that includes the (local) arrival time t(0) of the tracer as an endogenous (estimated) parameter. For each MR section, a wash-in parameter associated with each voxel is estimated twice by fitting each of the two pharmacokinetic models to the dynamic MR signal. A comparison of the two wash-in parametric images (global versus local arrival time) with matched histologic macroslices demonstrates a good correspondence between areas with viable remnant tumor and a high wash-in rate. This can be explained by the high number and permeability of the (leaking) capillaries in viable tumor tissue. The novel pharmacokinetic model based on a local arrival time of tracer results in the best fit of the wash-in rate, the most important factor discerning viable from nonviable tumor components. However, parameter estimates obtained with this model are also more sensitive to noise in the MR signal. The novel pharmacokinetic model resulted in a sensitivity between 0.22 and 0.60 and a specificity between 0.61 and 1. The model based on a global arrival time gave sensitivities between 0.33 and 0.77 and specificities between 0.58 and 0.99. Both statistics are computed as the fraction of correctly labeled voxels (viable or nonviable tumor) within a specified ROI, which delineates the tumor. We conclude that the added value of estimating the local arrival time of tracer first manifests itself for moderate noise levels in the MR signal. The novel pharmacokinetic model should moreover be preferred when pharmacokinetic modeling is applied on the average signal intensity within a ROI, where noise has less effect on the fitted parameters.

Adolescent↗

PubMed2000

Vessel diameter measurements in gadolinium contrast-enhanced three-dimensional MRA of peripheral arteries.

In this study, the possibilities for quantification of vessel diameters of peripheral arteries in gadolinium contrast-enhanced magnetic resonance angiography (Gd CE MRA) were evaluated. Absolute vessel diameter measurements were assessed objectively and semi-automatically in maximum intensity projections (MIPs) of contrast-enhanced T1-weighted 3D spoiled gradient-echo datasets, studied with digital subtraction techniques. In vivo, the complete peripheral arterial bed of six patients was studied, from the aorto-iliac bifurcation down to the distal run-off. By measuring the signal intensity (SI) over the lumen of a vessel in the MIP, an SI-plot was obtained. Next, the vessel boundaries were determined using a threshold algorithm; from these boundary points individual diameter values could be obtained along the trajectory of the vessel. In an in vitro study, an optimal threshold value of 30% of the range of SI-values between the background and the maximal SI in the vessel was obtained for accurate diameter measurement in Gd CE MRA (i.e., full-width 30%-maximum). Furthermore, the relationship between the accuracy of these measurements and the scan resolution was investigated. Accuracy was found to be acceptable (i.e., less than 10% over/underestimation) for vessel sizes covering at least 3 pixels. In six patients, diameters were measured in MIPs of the total datasets (i.e., D(T)) as well as in selective MIPs of the clipped datasets (i.e., D(S)) (n = 209). D(T) and D(S) were statistically significantly correlated (p < 0.01) with a Pearson correlation coefficient rP = 0.98. Measurements in the total MIPs yielded statistically significant (p < 0.01) smaller diameter values compared with measurements in selective MIPs, with a mean difference of 0.15 mm. Diameter values from the selective MIPs of the aorto-iliac arteries were also compared with diameter values measured at corresponding anatomic positions in X-ray angiograms of these patients (i.e., D(x)) (n = 70). D(X) and D(S) were statistically significantly correlated (p < 0.01) with a Pearson correlation coefficient rP = 0.92. Diameters measured in the selective MIPs were smaller than those measured in the X-ray angiograms (mean difference 0.49 mm) and this difference was statistically significant (p < 0.01). In conclusion, diameter values can be evaluated accurately in MIPs of vessels with at least 3 pixels in diameter, using the full-width 30%-maximum criterion.

Adult↗

PubMed2000

Quantification of global and regional ventricular function in cardiac magnetic resonance imaging.

One of the strong assets of cardiac magnetic resonance (CMR) is its ability to assess myocardial anatomy, structure, function, flow, and perfusion within a single examination. Quantification of global and regional function from magnetic resonance imaging (MRI) studies was shown to be accurate and reproducible in experimental and clinical research studies. With the advent of high-performance MRI scanners and newly developed pulse sequences, image acquisition times have been reduced considerably in recent years. However, the clinical use of CMR remains limited for various reasons. Among these limitations is that the amount of images obtained in a typical cardiac examination is so large that visual and especially quantitative image analysis is tedious and time consuming. There is an urgent need for optimized dedicated software tools featuring highly automated contour detection and optimized display capabilities to present the quantitative results to the physician in an orderly fashion, thus facilitating clinical decision making. This article focuses on the state of the art in CMR postprocessing techniques for quantitative assessment of global and regional function.

Female↗

PubMed1999

Blood pool contrast agent CMD-A2-Gd-DOTA-enhanced MR imaging of infarcted myocardium in pigs.

The purpose of this study was to assess the ability of the new blood pool contrast agent meglumine-carboxymethyldextran-ethylenediamino-gadoterate (CMD-A2-Gd-DOTA) to depict acute occlusive myocardial infarction (AMI). First-pass gradient-echo and delayed spin-echo magnetic resonance imaging (MRI) was performed 5 days after induction of AMI in a pig model. MRI was correlated with pathology. First-pass imaging with CMD-A2-Gd-DOTA allowed detection of infarcted myocardium in all pigs (n = 7). The infarction was recognized as a black spot on MRI as well as on a parametric image. The signal intensity (SI) amplitudes of normal versus infarcted myocardium were 80.55 +/- 18.61 versus 8.48 +/- 15.50 on MRI and 81.62 +/- 18.50 versus 1.61 +/- 3.73 on the parametric image (both P values < 0.001. The contrast ratio between normal and infarcted myocardium was not significantly improved on spin-echo MRI, suggesting largely intact vascular integrity outside the occluded area. CMD-A2-Gd-DOTA is useful for depicting occlusive myocardial infarction by first-pass MRI. Spin-echo imaging is promising in assessing vascular integrity. J. Magn. Reson. Imaging 1999;10:170-177.

Analysis of Variance↗

PubMed1999

Quantification in cardiac MRI.

Magnetic resonance imaging (MRI) offers several acquisition techniques for precise and highly reproducible assessment of global and regional ventricular function, flow, and perfusion at rest and under pharmacological or physical stress conditions. Recent advances in hardware and software have resulted in strong improvement of image quality and in a significant decrease in the required imaging time for each of these acquisitions. Several aspects of heart disease can be studied by combining multiple MRI techniques in a single examination. Such a comprehensive examination could replace a number of other imaging procedures, such as diagnostic X-ray angiography, echocardiography, and scintigraphy, which would be beneficial for the patient and cost effective. Despite the advances in MRI, quantitative image analysis often still relies on manual tracing of contours in the images, which is a time-consuming and tedious procedure that limits the clinical applicability of cardiovascular MRI. Reliable automated or semi-automated image analysis software would be very helpful to overcome the limitations associated with manual image processing. In this paper the developments directed toward automated quantitative image analysis and semi-automated contour detection for cardiovascular MR imaging are reviewed. J. Magn. Reson. Imaging 1999; 10:602-608.

Animals↗

PubMed1999

Scan optimization of gadolinium contrast-enhanced three-dimensional MRA of peripheral arteries with multiple bolus injections and in vitro validation of stenosis quantification.

In this study, a T1-weighted three-dimensional (3D) spoiled gradient-echo scanning protocol was developed to image the complete arterial system of the pelvis and both legs along their entire length in patients with peripheral arterial disease. Three adjacent stations were to be acquired consecutively, with some overlap, to image the entire area of interest; per station one gadolinium (Gd) contrast bolus would be administered. In an in vitro phantom study, the scanning protocol was optimized. The optimal flip angle was found to be 50 degrees. Also, the optimal scan delay was chosen to be equal to the arrival time of the contrast bolus, thereby minimizing artifacts. Three contrast bolus injections showed sufficient enhancement of the vessels after image subtraction. Finally, stenosis quantification by manual caliper was performed by five observers in the magnetic resonance angiography (MRA) images and correlated with the percent diameter reduction determined by quantitative angiography from corresponding X-ray images. The MRA measurements were reproducible, and intra- and interobserver variabilities were statistically non-significant (p=0.54 and p=0.12, respectively). Stenosis quantification performed by four observers showed a good correlation with the X-ray-derived values (rp > 0.90, p < 0.02); the results from one observer were not significantly correlated. Five patients with proven peripheral disease were investigated with this new MRA scanning protocol, using standard hardware and software. The images were of good quality, which allowed adequate clinical evaluation; the original diagnoses obtained from X-ray examinations, were confirmed with MRA. In conclusion, peripheral arterial disease can be evaluated adequately with this magnetic resonance scanning protocol.

Adult↗

PubMed1999

Gadolinium contrast-enhanced three-dimensional MRA of peripheral arteries with multiple bolus injection: scan optimization in vitro and in vivo.

In this study, a scanning protocol was developed to image the arterial bed of the pelvis and both legs along their entire length in patients with peripheral arterial disease, using standard hard- and software. Three adjacent stations are acquired consecutively, with some small overlap; per station; one Gadolinium contrast bolus is administered. The scanning protocol was optimized in an in vitro phantom study. The optimal flip angle was found to be 50 degrees. Also, the optimal scan delay was chosen to be equal to the arrival time of the contrast bolus thereby minimizing artifacts. Three contrast bolus injections showed sufficient enhancement of the vessels after image subtraction. Finally, stenosis quantification by manual caliper was performed by five observers in the MRA images and correlated with the percent diameter reduction determined by quantitative angiography from corresponding X-ray images. The results of the MRA measurements were reproducible and intra- and inter-observer variabilities were statistically non-significant (p = 0.54 and p = 0.12, respectively). Stenosis quantification performed by four observers showed a good correlation with the X-ray derived values (rp > 0.90, p < 0.02); the results from one observer were not significantly correlated. Five patients with proven peripheral disease were investigated with this new MRA scanning protocol. The images were of good quality which allowed adequate clinical evaluation; the original diagnoses obtained from X-ray examinations, were confirmed with MRA. In conclusion, peripheral arterial disease can be evaluated adequately with this MR scanning protocol.

Adult↗

PubMed1999

MRI-derived left ventricular function parameters and mass in healthy young adults: relation with gender and body size.

PURPOSE: To obtain normal values of left ventricular (LV) end-diastolic volume (EDV), stroke volume (SV), cardiac output (CO) and LV mass, in relation to gender, weight (W), length (L) and body surface area (BSA). METHODS: Sixty-one healthy volunteers (32 male, 22.4 +/- 2.2 years) were examined, weight was 70.9 +/- 12.2 kg, length was 1.78 +/- 0.09 m, BSA was 1.88 +/- 0.19 m2. Segmented k-space breathhold cine MRI was used to obtain a stack of parallel short-axis images, from which LV volumes and end-diastolic mass were derived by slice summation. Four different body size indices were studied: W, L, L2 and BSA. RESULTS: After indexing for L, L2 and BSA, the gender differences in all LV parameters are still persisting. After indexing for W, gender differences persist for EDV and EDM, but are no longer observed for SV and CO. Separate regression analyses for males and females were performed. EDV, SV, CO and EDM correlated significantly with each body size index, both in males and in females. L or BSA were in general better predictors for LV parameters than W. Linear regression equations of EDV (ml) vs. L(m) were for males: EDV = 275 x L - 359 and for females: EDV = 190 x L - 215. Equations of SV(ml) vs. L were for males: SV = 186 x L - 237 and for females: SV = 118 x L - 121. Equations of LV mass(g) vs. L were for males: Mass = 175 x L - 179 and for females: Mass = 65.8 x L - 10.9. CONCLUSION: Most gender differences in LV parameters remain even after correction for body size indices. Normal reference values for LV parameters are given in relation to body size indices, by calculating regression coefficients separately for males and females. These normal values serve to obtain more accurate reference values for a patient with given gender, weight and length, and thus to improve the differentiation between normal and abnormal LV parameters.

Adult↗

PubMed1999

Stenosis quantification from post-stenotic signal loss in phase-contrast MRA datasets of flow phantoms and renal arteries.

In this study a semi-automated and observer-independent algorithm for quantifying post-stenotic signal loss (PSL) in 3D phase-contrast (PC) magnetic resonance angiography (MRA) of patients with renal artery stenosis is presented. This algorithm was developed on MRA datasets of stenotic phantoms, which were included in a flow circuit with stationary flows. The length and the severity of the PSL (incorporating both length and degree of PSL) in the maximum intensity projections (MIPs) of MRA datasets were proposed for quantifying stenoses. The algorithm was tested in renal arteries of ten patients with renal artery stenosis and seven healthy volunteers. Digital subtraction angiography (DSA) was performed in the patients and served as the gold standard. Stenosis severity showed better correlation with the severity of the PSL than with the length, both for in vitro as in vivo. Spearman correlation coefficients (rS) showed statistically significant correlations between the severity of the PSL and parameters determined by DSA, i.e. percent diameter stenosis (rS = 0.90). The length of the PSL showed no correlation with the diameter stenosis (rS = 0.37).

Adult↗

PubMed1999

Anatomical model matching with fuzzy implicit surfaces for segmentation of thoracic volume scans.

Many segmentation methods for thoracic volume data require manual input in the form of a seed point, initial contour, volume of interest etc. The aim of the work presented here is to further automate this segmentation initialization step. In this paper an anatomical modeling and matching method is proposed to coarsely segment thoracic volume data into anatomically labeled regions. An anatomical model of the thorax is constructed in two steps: 1) individual organs are modeled with blended fuzzy implicit surfaces and 2) the single organ models are grouped into a tree structure with a solid modeling technique named constructive solid geometry (CSG). The combination of CSG with fuzzy implicit surfaces allows a hierarchical scene description by means of a boundary model, which characterizes the scene volume as a boundary potential function. From this boundary potential, an energy function is defined which is minimal when the model is registered to the tissue-air transitions in thoracic magnetic resonance imaging (MRI) data. This allows automatic registration in three steps: feature detection, initial positioning and energy minimization. The model matching has been validated in phantom simulations and on 15 clinical thoracic volume scans from different subjects. In 13 of these sets the matching method accurately partitioned the image volumes into a set of volumes of interest for the heart, lungs, cardiac ventricles, and thorax outlines. The method is applicable to segmentation of various types of thoracic MR-images, provided that a large part of the thorax is contained in the image volume.

Heart↗