Biomedical subjects

Jacques A de Guise

Publications and source records attributed to Jacques A de Guise.

17 recordsLinked to original sources

PubMed2007

Optimization of spatial resolution for peripheral magnetic resonance angiography.

RATIONALE AND OBJECTIVES: To determine optimum spatial resolution when imaging peripheral arteries with magnetic resonance angiography (MRA). MATERIALS AND METHODS: Eight vessel diameters ranging from 1.0 to 8.0 mm were simulated in a vascular phantom. A total of 40 three-dimensional flash MRA sequences were acquired with incremental variations of fields of view, matrix size, and slice thickness. The accurately known eight diameters were combined pairwise to generate 22 "exact" degrees of stenosis ranging from 42% to 87%. Then, the diameters were measured in the MRA images by three independent observers and with quantitative angiography (QA) software and used to compute the degrees of stenosis corresponding to the 22 "exact" ones. The accuracy and reproducibility of vessel diameter measurements and stenosis calculations were assessed for vessel size ranging from 6 to 8 mm (iliac artery), 4 to 5 mm (femoro-popliteal arteries), and 1 to 3 mm (infrapopliteal arteries). Maximum pixel dimension and slice thickness to obtain a mean error in stenosis evaluation of less than 10% were determined by linear regression analysis. RESULTS: Mean errors on stenosis quantification were 8.8% +/- 6.3% for 6- to 8-mm vessels, 15.5% +/- 8.2% for 4- to 5-mm vessels, and 18.9% +/- 7.5% for 1- to 3-mm vessels. Mean errors on stenosis calculation were 12.3% +/- 8.2% for observers and 11.4% +/- 15.1% for QA software (P = .0342). To evaluate stenosis with a mean error of less than 10%, maximum pixel surface, the pixel size in the phase direction, and the slice thickness should be less than 1.56 mm2, 1.34 mm, 1.70 mm, respectively (voxel size 2.65 mm3) for 6- to 8-mm vessels; 1.31 mm2, 1.10 mm, 1.34 mm (voxel size 1.76 mm3), for 4- to 5-mm vessels; and 1.17 mm2, 0.90 mm, 0.9 mm (voxel size 1.05 mm3) for 1- to 3-mm vessels. CONCLUSION: Higher spatial resolution than currently used should be selected for imaging peripheral vessels.

Constriction, Pathologic↗

PubMed2006

Relation between the sagittal pelvic and lumbar spine geometries following surgical correction of adolescent idiopathic scoliosis.

Sagittal spinopelvic relations have been reported in adolescent idiopathic scoliosis (AIS), but there is little information on their effect following surgery. The objective of this study is to evaluate the relation between the pelvic and lumbar spine geometries following posterior spinal instrumentation and fusion (PSIF). Sixty patients with AIS undergoing PSIF were studied retrospectively. Thoracic kyphosis (TK), lumbar lordosis (LL), LL within and below fusion, pelvic incidence (PI), sacral slope (SS) and pelvic tilt (PT) were measured on preoperative and postoperative standing lateral radiographs. Significant postoperative correlations were found between PI and LL (r = 0.67), SS and LL (r = 0.90), PI and LL below fusion (r = 0.40), SS and LL below fusion (r = 0.48). Pelvic parameters did not influence LL within fusion. A strong correlation was found between LL below and within fusion (r = -0.76). The close interdependence between lumbar lordosis and pelvic geometry preoperatively is maintained postoperatively following PSIF. In the planning of surgery for AIS, it may be helpful to evaluate the sagittal pelvic morphology (PI) in addition to the spinal curves. Preoperative evaluation of the pelvic morphology could be used to optimize intraoperative positioning of the patient and to determine the optimal amount of LL that needs to be restored or preserved by the instrumentation, so that LL remains congruent with the pelvic morphology.

Adolescent↗

PubMed2006

Resolution enhancement in digital x-ray imaging.

We have developed a restoration method for radiographs that enhances image sharpness and reveals bone microstructures that were initially hidden in the soft-tissue glare. The method is two fold: the image is first deconvolved using the Richardson-Lucy algorithm and is then divided with a signal modelling the soft-tissue distribution to increase the overall contrast. Each step has its own merits but the power of the restoration method lies in their combination. The originality of the method is its reliance on a priori information at each step in the processing. We have measured and modelled analytically the point-spread function of a low-dose gas microstrip x-ray detector at several beam energies. We measured the relationship between the local image intensity and the noise variance for these images. The soft-tissue signal was also modelled using a minimum-curvature filtering technique. These results were then combined into an image deconvolution procedure that uses wavelet filtering to reduce restoration noise while keeping the enhanced small-scale features. The method was applied successfully to images of a human-torso phantom and improved the contrast of small details on the bones and in the soft tissues. We measured a mean 54% increase in signal to noise ratio and a mean 105% increase in contrast to noise ratio in the 70 and 140 kVp images we analysed. The method was designed to facilitate the analysis of radiographs by relying on two levels of visual inspection. The contrast of the full image is first enhanced by division with the signal modelling the soft-tissue distribution. Based on the result, a radiologist might decide to zoom in on a given image section. The full restoration method is then applied to that region of interest. Indeed, full image deconvolution is often unnecessary since enhanced small-scale details are not visible at large scale; only the section of interest is processed which is more efficient.

Algorithms↗

PubMed2006

Gesture standardization increases the reproducibility of 3D kinematic measurements of the knee joint.

BACKGROUND: The literature on the 3D kinematics of the knee suggests that the gesture accomplished during kinematic assessment might play a significant role in the values measured. The purpose of this study is to demonstrate that a standardized gesture leads to an increased reproducibility in 3D kinematic measurements of the knee. METHODS: Seventeen healthy male subjects performed series of knee-bends in standardized and unconstrained conditions while their left knee's 3D kinematics were recorded using an optical motion-recording system. Standardized knee-bends were performed in a specially designed structure stabilizing the shoulders, pelvis and feet. Coefficient of multiple correlation were calculated for the ascent and the descent phases of the knee-bends for the tibial rotation and abduction/adduction components of the knee movement. FINDINGS: Comparisons between coefficient of multiple correlation of the different gesture conditions showed a statistically significant increase in reproducibility for the tibial rotation during the standardized knee-bends. INTERPRETATION: It appears that gesture standardization is an interesting option to consider for precise kinematic assessment of the living human knee.

Adult↗

PubMed2006

Computerized assessment of sagittal curvatures of the spine: comparison between Cobb and tangent circles techniques.

OBJECTIVE: The tangent circles technique has been proposed as an alternative to the Cobb angle technique to assess sagittal curves of the spine. However, it has never been compared directly to the Cobb technique. This study compares the reproducibility and clinical relevance of the maximum Cobb angle and tangent circles techniques. METHOD: Standing sagittal radiographs of the spine of 10 adolescents with idiopathic scoliosis, 10 adolescents with spondylolisthesis, and 10 healthy adolescents were used. Thoracic kyphosis (TK) and lumbar lordosis (LL) were measured by 3 observers using the maximum Cobb angle and the tangent circles techniques. Intra- and interobserver intraclass correlation coefficients (ICCs) were calculated. RESULT: Intra- and interobserver ICCs for TK were 0.88 and 0.85, respectively, for the maximum Cobb angle technique, and 0.94 and 0.83, respectively, for the tangent circles technique. Intra- and interobserver ICCs for LL were 0.97 and 0.77, respectively, for the maximum Cobb angle technique, and 0.88 and 0.94, respectively, for the tangent circles technique. The 2 techniques were highly correlated for the measurement of the TK (r=0.93) and LL (r=0.88). CONCLUSION: Both techniques provide excellent intra- and interobserver reproducibility. Tangent circles technique may be a good alternative to the Cobb angle technique because it allows the evaluation of the global geometry of sagittal spinal curves, especially when there is limited visibility of bony structures on radiographs.

Adolescent↗

PubMed2006

Comparison of sacropelvic morphology between normal adolescents and subjects with adolescent idiopathic scoliosis.

Previous studies suggest that the pelvic morphology may be abnormal in adolescent idiopathic scoliosis. This study compares the sacropelvic morphology between normal adolescents and subjects with adolescent idiopathic scoliosis (AIS) in both sagittal and coronal planes. The sacropelvic morphology was assessed from the postero-anterior and lateral standing radiographs of 27 normal adolescents and 29 subjects with AIS presenting a major Cobb angle greater than 30 degrees . Sacropelvic morphology was characterized by 19 parameters in the sagittal plane and 26 parameters in the coronal plane. There was no difference in sacropelvic morphology between the two groups in the sagittal plane. In the coronal plane, significant differences were found for right pelvic length, right iliac height, left and right pubic length, left obturator foramen width, bicristal distance, bituberal distance, biacetabular distance, pubic symphysis width, pelvic inlet, and subpubic angle. There was no significant pelvic asymmetry in AIS subjects. This is the first study that specifically evaluates the sagittal and coronal sacropelvic morphology in AIS. The results suggest that the coronal sacropelvic morphology is distorted in AIS. A longitudinal study is required in order to evaluate the influence of sacropelvic morphology in the progression of AIS.

Adolescent↗

PubMed2006

Relation between the sagittal pelvic and lumbar spine geometries following surgical correction of adolescent idiopathic scoliosis: a preliminary study.

The influence of surgery on the relationship between the lumbar spine and the pelvis in adolescent idiopathic scoliosis (AIS) remains mostly unknown. The sagittal spinopelvic balance of 40 patients with AIS undergoing posterior spinal instrumentation and fusion was studied. After surgery, the total lumbar lordosis (LL) and the LL below fusion remained correlated to the sagittal pelvic geometry. LL within fusion, which is set by the instrumentation, was also related to the LL below fusion. This preliminary study shows that pelvic morphology probably has an important impact on the postoperative sagittal lumbar alignment. Evaluation of the sagittal pelvic geometry could therefore be useful in the preoperative planning of surgery for AIS. Further studies with more patients are still needed in order to confirm this hypothesis and to evaluate if the distal fusion level influences the spino-pelvic balance.

Adolescent↗

PubMed2005

3D elastic registration of vessel structures from IVUS data on biplane angiography.

RATIONALE AND OBJECTIVES: Planar angiograms and intravascular ultrasound (IVUS) imaging provide important insight for the evaluation of atherosclerotic diseases and blood flow abnormalities. The construction of realistic three-dimensional models is essential to efficiently follow the progression of arterial plaque. This requires an explicit localization of IVUS frames from angiograms. Because of the difficulties encountered when trying to track the position of an IVUS transducer, we propose an elastic registration approach that relies on a virtual catheter path. MATERIALS AND METHODS: Deformable surface models of the lumen and external wall are constructed from segmented IVUS contours. A crude registration is obtained using a three-dimensional vessel centerline, reconstructed from two calibrated angiograms. Robust optimization of the virtual catheter path, position, absolute orientation, and regulation of the external wall shape is performed until near-perfect alignment of the back-projected silhouettes on image edges is reached. RESULTS: Visual assessment of the reconstructed vessels showed a good superposition of virtual models on the angiograms. We measured a 0.4-mm residual error value. A preliminary study of convergence properties on 15 datasets showed that initial absolute orientation may affect the solution. However, for follow-ups, coherent solutions were found among datasets. CONCLUSION: The advantages of the virtual catheter path approach are demonstrated. Future work will look at ways to single out the true solution with a better use of the available information in both modalities and additional validation studies on improved datasets.

Algorithms↗

PubMed2005

Personalized body segment parameters from biplanar low-dose radiography.

Body segment parameters are essential data in biomechanics. They are usually computed with population-specific predictive equations from literature. Recently, medical imaging and video-based methods were also reported for personalized computation. However, these methods present limitations: some of them provide only two-dimensional measurements or external measurements, others require a lot of tomographic images for a three-dimensional (3-D) reconstruction. Therefore, an original method is proposed to compute personalized body segment parameters from biplanar radiography. Simultaneous low-dose frontal and sagittal radiographs were obtained with EOS system. The upper leg segments of eight young males and eight young females were studied. The personalized parameters computed from the biplanar radiographic 3-D reconstructions were compared to literature. The biplanar radiographic method was consistent with predictive equations based on gamma-ray scan and dual energy X-ray absorptiometry.

Algorithms↗

PubMed2005

Physical characteristics of a low-dose gas microstrip detector for orthopedic x-ray imaging.

A new scanning slit gas detector dedicated to orthopedic x-ray imaging is presented and evaluated in terms of its fundamental imaging characteristics. The system is based on the micromesh gaseous structure detector and achieves primary signal amplification through electronic avalanche in the gas. This feature, together with high quantum detection efficiency and fan-beam geometry, allows for imaging at low radiation levels. The system is composed of 1764 channels spanning a width of 44.8 cm and is capable of imaging an entire patient at speeds of up to 15 cm/s. The resolution was found to be anisotropic and significantly affected by the beam quality in the horizontal direction, but otherwise sufficient for orthopedic studies. As a consequence of line-by-line acquisition, the images contain some ripple components due to mechanical vibrations combined with variations in the x-ray tube output power. The reported detective quantum efficiency (DQE) values are relatively low (0.14 to 0.20 at 0.5 mm(-1)) as a consequence of a suboptimal collimation geometry. The DQE values were found to be unaffected by the exposure down to 7 microGy, suggesting that the system is quantum limited even for low radiation levels. A system composed of two orthogonal detectors is already in use and can produce dual-view full body scans at low doses. This device could contribute to reduce the risk of radiation induced cancer in sensitive clientele undergoing intensive x-ray procedures, like young scoliotic women.

Calibration↗

PubMed2004

Quantitative magnetic resonance imaging evaluation of knee osteoarthritis progression over two years and correlation with clinical symptoms and radiologic changes.

OBJECTIVE: To evaluate the change in osteoarthritic (OA) knee cartilage volume over a two-year period with the use of magnetic resonance imaging (MRI) and to correlate the MRI changes with radiologic changes. METHODS: Thirty-two patients with symptomatic knee OA underwent MRI of the knee at baseline and at 6, 12, 18, and 24 months. Loss of cartilage volumes were computed and contrasted with changes in clinical variables for OA and with standardized semiflexed knee radiographs at baseline at 1 and 2 years. RESULTS: Progression of cartilage loss at all followup points was statistically significant (P < 0.0001), with a mean +/- SD of 3.8 +/- 5.1% for global cartilage loss and 4.3 +/- 6.5% for medial compartment cartilage loss at 6 months, 3.6 +/- 5.1% and 4.2 +/- 7.5% at 12 months, and 6.1 +/- 7.2% and 7.6 +/- 8.6% at 24 months. Discriminant function analysis identified 2 groups of patients, those who progressed slowly (<2% of global cartilage loss; n = 21) and those who progressed rapidly (>15% of global cartilage loss; n = 11) over the 2 years of study. At baseline, there was a greater proportion of women (P = 0.001), a lower range of motion (P = 0.01), a greater circumference and higher level of pain (P = 0.05) and stiffness in the study knee, and a higher body mass index in the fast progressor group compared with the slow progressor group. No statistical correlation between loss of cartilage volume and radiographic changes was seen. CONCLUSION: Quantitative MRI can measure the progression of knee OA precisely and can help to identify patients with rapidly progressing disease. These findings indicate that MRI could be helpful in assessing the effects of treatment with structure-modifying agents in OA.

Arthrography↗

PubMed2004

Fast accurate stereoradiographic 3D-reconstruction of the spine using a combined geometric and statistic model.

OBJECTIVE: To describe and evaluate a fast accurate stereoradiographic 3D-reconstruction method of the spine. BACKGROUND: Stereoradiographic methods based on anatomical landmarks identification are the only ones providing information on 3D-deformities of the spine in a standing position, but require 2-4 h for the whole spine, making the method inadequate for clinical routine. METHODS: The proposed semi-automated method is based on (1) vertebral body volume reconstruction, (2) definition of a local referential associated to this volume, (3) reliable a priori knowledge of the vertebral shape using eight morphologic descriptors of the vertebral body to estimate, from a multiple linear regression, 21 3D-point coordinates per vertebra, (4) kriging of a 2000 points model with regard to the 21 points. The method was evaluated for vertebral orientation and shape accuracy. RESULTS: 3D models of the whole spine are obtained within 15 min. Manual vs. semi-automated reconstruction comparison yield similar accuracy regarding the CT-scan references. For vertebrae orientation, results were slightly different from the manual reconstruction method (however an absolute reference is lacking). CONCLUSION: The stereoradiographic 3D-reconstruction method allows for a significant reduction of the whole reconstruction time, with regard to previously described methods. Moreover, the accuracy was evaluated and was found to be comparable to the accuracy of previous methods. The results of this study show that stereoradiography could now be employed in routine clinical environment. RELEVANCE: 3D spine reconstruction from biplanar radiographs in standing position can be obtained using a fast and accurate method.

Algorithms↗

PubMed2003

Sagittal plane analysis of the spine and pelvis in adolescent idiopathic scoliosis according to the coronal curve type.

STUDY DESIGN: A retrospective study investigated the sagittal alignment in adolescent idiopathic scoliosis (AIS). OBJECTIVE: To evaluate the sagittal alignment of the spine and pelvis in adolescent idiopathic scoliosis on the basis of curve type. SUMMARY OF BACKGROUND DATA: The relation between the spine and pelvis highly influences the sagittal balance in adults. However, the sagittal alignment of the spine and pelvis in adolescent idiopathic scoliosis is poorly defined in the literature. METHODS: Five sagittal parameters were evaluated on lateral radiographs of 160 patients with adolescent idiopathic scoliosis: thoracic kyphosis, lumbar lordosis, sacral slope, pelvic tilt, and pelvic incidence. The patients were classified according to their coronal curve type. Analysis of variance was used to compare the parameters between the curve types, and Pearson coefficients were used to investigate the relation between all parameters (alpha = 0.05). RESULTS: The thoracic kyphosis was significantly lower for King I, II, and III curves than for lumbar curves. The lumbar lordosis was higher for lumbar curves, although not significantly. No significant change between the groups was observed for the sacral slope, pelvic tilt, or pelvic incidence. The pelvic incidence was significantly correlated with the lumbar lordosis, sacral slope, and pelvic tilt for all the groups. The lumbar lordosis was strongly related to the sacral slope in all cases, but not with the thoracic kyphosis, except in the case of thoracolumbar curves. CONCLUSIONS: Thoracic kyphosis depended mostly on the spinal deformity, whereas lumbar lordosis was influenced mainly by the pelvic configuration. The scoliotic curve type was not associated with a specific pattern of sagittal pelvic morphology and balance. The pelvic incidence found in this study was significantly higher than that reported in the literature for normal adolescents. The role of the pelvic incidence in the pathogenesis of adolescent idiopathic scoliosis needs to be explored in a longitudinal study involving patients with adolescent idiopathic scoliosis and normal adolescents.

Adolescent↗

PubMed2003

In vitro evaluation of combined graft deformation in anterior cruciate ligament reconstructions.

In this paper, we present a simple method of calculating deformation of an anterior cruciate ligament graft in combined elongation, bending and total twisting. We also report our results on these deformations for three types of ligament reconstruction in cadaver knees: two isometric reconstructions, using either a biological bone-patellar tendon-bone autograft or an artificial Trevira prosthesis, and modified over-the-top reconstruction with the prosthesis. The data show that the modified OTT technique produced elongation of the graft equivalent to that of the synthetic isometric technique, but significantly less than isometric reconstruction with the biological graft (p<0.05, ANOVA). Moreover, the grafts were subjected to bending and twisting.

Aged↗

PubMed2003

Computer-aided method for quantification of cartilage thickness and volume changes using MRI: validation study using a synthetic model.

The primary objective of this study was to develop a computer-aided method for the quantification of three-dimensional (3-D) cartilage changes over time in knees with osteoarthritis (OA). We introduced a local coordinate system (LCS) for the femoral and tibial cartilage boundaries that provides a standardized representation of cartilage geometry, thickness, and volume. The LCS can be registered in different data sets from the same patient so that results can be directly compared. Cartilage boundaries are segmented from 3-D magnetic resonance (MR) slices with a semi-automated method and transformed into offset-maps, defined by the LCS. Volumes and thickness are computed from these offset-maps. Further anatomical labeling allows focal volumes to be evaluated in predefined subregions. The accuracy of the automated behavior of the method was assessed, without any human intervention, using realistic, synthetic 3-D MR images of a human knee. The error in thickness evaluation is lower than 0.12 mm for the tibia and femur. Cartilage volumes in anatomical subregions show a coefficient of variation ranging from 0.11% to 0.32%. This method improves noninvasive 3-D analysis of cartilage thickness and volume and is well suited for in vivo follow-up clinical studies of OA knees.

Algorithms↗

PubMed2002

Quantitative comparison of three different types of anterior cruciate ligament reconstruction methods: laxity and 3-D kinematic measurements.

In this project, we compared knee laxity and 3-D knee kinematics after ACL reconstruction on cadaver knees using (1) bone-patellar tendon-bone two-tunnel; (2) synthetic ligament two-tunnel; and (3) synthetic ligament "over-the-top" technique. We used a computer assisted system, based on the acquisition of the knee's movement with magnetic sensors (Polhemus, Vermont, USA). The use of personalised three-dimensional (3D) models of the bones enabled us to ensure a reproducible measurement of three-dimensional kinematic and laxity parameters. Our results showed that even when knee laxity was restored to normal, 3D kinematic measurements revealed that the reconstructions tended to under or over-constrain the knee's movement. This study shows that 3D kinematics is a complementary measurement that can be useful to get a better comprehension of the knee's function after ligament reconstruction.

Aged↗

PubMed2002

Relation between the pelvis and the sagittal profile in adolescent idiopathic scoliosis: the influence of curve type.

Previous studies have shown a correlation between pelvic parameters and the lumbar lordosis in normal subjects and in scoliotic adults. This study investigates the relationship between pelvic and spinal geometries in the sagittal plane for adolescent idiopathic scoliosis (AIS) patients having various curve types. The study group was composed of 129 AIS patients classified according to their curve type: King I, King II, King III or lumbar curve. The SpineView software (Surgiview, France) was used to compute five parameters on sagittal x-rays: thoracic kyphosis (TK), lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT) and pelvic incidence (PI). The TK was significantly lower for King I, II and III curves as compared to the lumbar curves. The LL tended to be higher for patients having a major lumbar scoliotic (King I and lumbar) curve, although not significantly. No significant change between the groups was observed for the SS, PT and PI. The PI was significantly correlated to the LL, SS and PT for all groups. The SS was strongly related to the LL in all cases. However, no relationship was found between the TK and the LL in any group. This study showed that the TK mostly depends on the thoracic scoliotic curve and therefore on the shape and orientation of the vertebrae, which explains that many King I, II and III patients are hypokyphotic. Conversely, the LL is mainly influenced by the pelvic configuration. Since the pelvic parameters are similar for all groups, these parameters are not likely to be important in the development of a specific type of scoliotic curve.

Adolescent↗