J P Vallée

Hôpitaux Universitaires de Genève, Genève, Geneva, Switzerland

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Publications (26)53.11 Total impact

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    Journal of Cardiovascular Magnetic Resonance 02/2012; 14 Suppl 1:P60. · 4.44 Impact Factor
  • 97th Annual Meeting of the Swiss Society of Radiology; 01/2010
  • Proceedings of 24th International Congress and Exhibition of Computer Assisted Radiology and Surgery (CARS2010); 01/2010
  • 18th Scientific Meeting & Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM'10); 01/2010
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    ABSTRACT: Introduction Marginal kidneys must be reanimated before their transplantation. Reanimation is conduced with hypothermic pulsatile perfusion. The tests used generally to demonstrate the viability is the vascular resistance which is not convenient for everybody. We have developed a magnetic resonance compatible perfusional technology allowing us to test the organs during the perfusion by Gd-perfusion MRI. Methods and results We have used pigs’ kidneys with no warm ischemic time to establish the basis in a normal kidney. After an eight-hour hypothermic pulsatile perfusion, kidneys are submitted to a Gd perfusion. First, we measure the anatomy of the vessels, then the distribution of Gd in the kidney. We obtain simultaneously a dynamic study of the organs where T0 represents the Gd bolus arrival in the cortex and TP the maximum saturation time of Gd. Conclusion We have observed that a normal T0 is inferior to 30 s and TP is inferior to one minute. We have compared these values with ATP resynthesis in these organs and found that they correlate. We hope for the future through that predictive use of Gd-MRI to avoid the clinical use of “too” marginal kidneys or the discard of good kidneys but not corresponding with the vascular resistance theory.
    Progrès en Urologie. 05/2009; 19(5):307–312.
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    17th Scientific Meeting & Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM'09); 01/2009
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    ABSTRACT: The aim of this study was to measure the myocardial area at risk in rat, using MRI and manganese injection during a coronary occlusion/reperfusion model at 1.5T. A sequential protocol with occlusion and MnCl2 injection immediately followed by MRI was used with the assumption that MnCl2-induced contrast persistence is enough to accurately image the area at risk 90 min after occlusion. A total of 15 adult rats underwent a single 30-min episode of coronary occlusion followed by reperfusion. MnCl2 was injected (25 micromol/kg) at the beginning of the occlusion for 11 rats (group 1) and 6 h after reperfusion for four animals (group 2). A deficit of signal enhancement was observed in all rats. Hypoenhancement area in group 1 was correlated to the area at risk delineated by methylene blue (r=0.96, P<0.0001) whereas in group 2 it was correlated to the infarct area given by triphenyltetrazolium chloride (TTC) solution (r=0.98, P=0.003). The area at risk size was significantly correlated with left ventricle ejection fraction (LVEF), end-systolic volume and anterolateral wall thickening. This work demonstrates that hypoenhanced zone obtained after manganese injection during occlusion represents the area at risk and not only the infarct zone.
    Magnetic Resonance in Medicine 06/2008; 59(6):1422-30. · 3.27 Impact Factor
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    ABSTRACT: Cardiovascular magnetic resonance has been shown to provide high data quality for myocardial perfusion assessment. However, to analyze the perfusion data, some signal processing and modeling is needed to correct for motion related artifacts and limited spatial resolution. This study describes a method based on system identification, allowing, after a first step of image registration, to integrate and correct the partial volume effect in the myocardium perfusion quantification. This method is then applied to patients with coronary artery disease or hypertrophic obstructive cardiomyopathy.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2007; 2007:4492-5.
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    ABSTRACT: The overall goal was to study cardiovascular function in small animals using a clinical 1.5-T MR scanner optimizing a fast gradient-echo cine sequence to obtain high spatial and temporal resolution. Normal rat hearts (n = 9) were imaged using a 1.5-T MR scanner with a spiral fast gradient-echo (fast field echo for Philips scanners) sequence, three Cartesian fast gradient-echo (turbo field echo for Philips scanners) sequences with different in-plane resolution, and with and without flow compensation and half-Fourier acquisition. The hearts of four rats were then excised and left-ventricle mass was weighed. Inter- and intra-observer variability analysis was performed for magnetic resonance imaging (MRI) measurements. Half-Fourier acquisition with flow compensation gave the best sequence in terms of image quality, spatial as well as temporal resolution, and suppression of flow artifact. Ejection fraction was 71 +/- 4% with less than 5% inter- and intra-observer variability. A good correlation was found between MRI-calculated left-ventricular mass and wet weight. Using optimized sequences on a clinical 1.5-T MR scanner can provide accurate quantification of cardiac function in small animals and can promote cardiovascular research on small animals at 1.5-T.
    MAGMA Magnetic Resonance Materials in Physics Biology and Medicine 09/2006; 19(3):144-51. · 1.86 Impact Factor
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    ABSTRACT: To compare MRI and MRA with Doppler-echocardiography (DE) in native and postoperative aortic coarctation, define the best MR protocol for its evaluation, compare MR with surgical findings in native coarctation. 136 MR studies were performed in 121 patients divided in two groups: Group I, 55 preoperative; group II, 81 postoperative. In group I, all had DE and surgery was performed in 35 cases. In group II, DE was available for comparison in 71 cases. MR study comprised: spin-echo, cine, velocity-encoded cine (VEC) sequences and 3D contrast-enhanced MRA. In group I, diagnosis of coarctation was made by DE in 33 cases and suspicion of coarctation and/or aortic arch hypoplasia in 18 cases. Aortic arch was not well demonstrated in 3 cases and DE missed one case. There was a close correlation between VEC MRI and Doppler gradient estimates across the coarctation, between MRI aortic arch diameters and surgery but a poor correlation in isthmic measurements. In group II, DE detected a normal isthmic region in 31 out of 35 cases. Postoperative anomalies (recoarctation, aortic arch hypoplasia, kinking, pseudoaneurysm) were not demonstrated with DE in 50% of cases. MRI is superior to DE for pre and post-treatment evaluation of aortic coarctation. An optimal MR protocol is proposed. Internal measurement of the narrowing does not correspond to the external aspect of the surgical narrowing.
    The International Journal of Cardiovascular Imaging 01/2006; 22(3-4):457-75. · 2.65 Impact Factor
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    ABSTRACT: PurposeTo investigate a balanced steady state free precession sequence (b-SSFP) under a large range of conditions and to compare its performance with other types of gradient echo sequences for dynamic imaging.Materials and Methods Balanced turbo field echo (b-TFE; Philips Medical Systems, Best, The Netherlands) was investigated in vitro at a range of T2/T1 along with T1-contrast enhanced turbo field echo (T1-TFE) and turbo field echo (TFE) so that a comparison could be made. Performance was quantified in terms of the initial slope of the signal-to-noise ratio (SNR) vs. 1/T1 curve (sensitivity) and the range of 1/T1 before signal saturation (contrast dynamic range [CDR]).ResultsThe b-TFE sequence was found to best perform, in terms of an optimal CDR, with a 90° flip angle (FA), saturation preparation, and short inversion time. Using these parameters, the sensitivity was also higher than that of the TFE sequence and T1-TFE sequence under their respective optimal conditions. For detection of small changes in contrast agent concentration (0.0–0.1 mM), b-TFE was also found to be the sequence of choice, with optimized parameters as follows, 90° FA, shortest TR/TE, and no magnetization preparation. The smallest matrices gave the highest signal sensitivity for all three sequences.Conclusion The CDR of b-TFE was much narrower than that of T1-TFE but could be widened under optimized conditions. The sensitivity of the b-TFE technique was the highest of the three sequences under all conditions tested. J. Magn. Reson. Imaging 2004;20:1030–1038. © 2004 Wiley-Liss, Inc.
    Journal of Magnetic Resonance Imaging 11/2004; 20(6):1030 - 1038. · 2.57 Impact Factor
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    ABSTRACT: We investigated the specificity of superparamagnetic iron oxide (SPIO)-enhanced T1-weighted spin-echo (SE) magnetic resonance (MR) images for the characterization of liver hemangiomas. When imaging liver hemangiomas, which are the most frequent benign liver tumors, a method with very high specificity is required, which will obviate other studies, follow-up, or invasive diagnostic procedures such as percutaneous biopsy. Eighty-three lesions were examined by MR imaging at 1.5 T before and after intravenous injection of SPIO particles. Lesions were categorized as follows according to the final diagnosis: 37 hemangiomas, nine focal nodular hyperplasias (FNHs), 19 hepatocellular carcinomas (HCCs), and 18 metastases. Their signal intensity values were normalized to muscle and compared. The only lesions showing a significant increase in signal intensity ratio (lesion to muscle) on postcontrast T1-weighted SE images were hemangiomas (p < 0.001). The signal intensity ratio of hemangiomas increased on average by 70%. Based on receiver operating characteristic analysis and using a cutoff level of 50% signal increase, the specificity and sensitivity of SPIO-enhanced MR imaging for the characterization of hemangiomas would be 100% and 70%, respectively. The T1 effect of SPIO particles can help differentiate hemangiomas from other focal liver lesions such as FNHs, HCCs, and metastases and may obviate biopsy. When using SPIO particles for liver imaging, it is useful to add a T1-weighted sequence to T2-weighted images, thereby providing additional information for lesion characterization.
    Abdominal Imaging 01/2004; 29(1):60-70. · 1.91 Impact Factor
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    ABSTRACT: Purpose:To improve the quantification of myocardial perfusion by registering the time series of magnetic resonance (MR) images with injection of gadolinium.Materials and Methods:Eight patients underwent MR scans to perform myocardial perfusion exam. Two short axis views of the left ventricle (LV) were acquired in free breathing. Two masks for performing the spatial registration of the images were evaluated. The registration was based on pixel intensity in a multi-resolution scheme. The efficiency of this correction was evaluated by calculating geometric residual displacement of the LV and by fitting the data to a compartment model fit with two parameters: K1, the blood-to-myocardium transfer coefficient, and Vd, the distribution volume of the contrast media.Results:The registration stage allowed a decrease in the observed motion of the LV from more than 1.98 ± 0.68 mm to less than 0.56 ± 0.18 mm (mean ± SD). Variability obtained in the perfusion analysis decreased from 46 ± 103% to 5± 4% for K1 parameter and from 18 ± 21% to 5 ± 5% for Vd parameter.Conclusion:As with manual correction, this automatic motion correction leads to accurate perfusion parameters in dynamic cardiac MR imaging after contrast agent injection. This automatic stage requires placing only one mask over one frame of the perfusion study instead of manually shifting each image to fit a reference image of the perfusion study. J. Magn. Reson. Imaging 2003;18:160–168. © 2003 Wiley-Liss, Inc.
    Journal of Magnetic Resonance Imaging 07/2003; 18(2):160 - 168. · 2.57 Impact Factor
  • European Urology Supplements - EUR UROL SUPPL. 01/2003; 2(1):76-76.
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    ABSTRACT: The purpose of this study was to investigate the influence of the fast gradient-recalled echo (GRE) sequence parameters on the contrast dynamic range and signal sensitivity, to optimize the magnetic resonance (MR) sequence for contrast media pharmacokinetic assessment. Effects of the fast low-angle shot (FLASH), Fast acquisition at steady rate (FAST), and radiofrequency-spoiled (RF)-FAST sequence parameters were studied in vitro. The FAST sequence had the highest sensitivity in low gadolinium (Gd) concentration. The FLASH and RF-FAST sequences had a larger contrast dynamic range, but the FLASH images contained side band artifacts. Increasing the flip angle to 90 degrees raised the sensitivity of the FAST sequence and the contrast dynamic range of the RF-FAST sequence. The shortest possible TE was optimal for both contrast dynamics and imaging time. TI had an influence on the sensitivity of the FAST sequence only for small acquisition matrices. This study indicates the optimal parameters for contrast dynamics (RF-FAST, 90 degrees flip angle, shortest possible TE) and sensitivity (FAST, 90 degrees flip angle, long TI(eff)).
    Journal of Magnetic Resonance Imaging 01/2002; 14(6):771-8. · 2.57 Impact Factor
  • L M Bidaut, J P Vallée
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    ABSTRACT: Cardiac dynamic magnetic resonance imaging (MRI) after contrast media injection suffers from motion induced by free breathing during acquisition. This work presents an automated approach for motion correction of the heart. The registration is based on the multipass/multiresolution iterative minimizing of intrinsic differences between each image and a reference image coupled to a two-dimensional/3 parameters rigid body correction. The efficiency of this correction method was evaluated with anatomical landmarks, various cost functions, and for a compartment model fit of the data with 2 parameters: K1, the blood to myocardium transfer coefficient; and Vd, the distribution volume of the contrast media. The variability of K1 and Vd, derived from the fit of the registered images (using the manual correction as a gold standard), was significantly reduced by comparison with the variability obtained from the uncorrected images (P < 0.04). This motion correction method also clearly improves the analysis of dynamic cardiac MRI after contrast media injection in comparison to manual correction.
    Journal of Magnetic Resonance Imaging 05/2001; 13(4):648-55. · 2.57 Impact Factor
  • Luc M. Bidaut PhD, Jean‐Paul Vallée
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    ABSTRACT: Cardiac dynamic magnetic resonance imaging (MRI) after contrast media injection suffers from motion induced by free breathing during acquisition. This work presents an automated approach for motion correction of the heart. The registration is based on the multipass/multiresolution iterative minimizing of intrinsic differences between each image and a reference image coupled to a two-dimensional/3 parameters rigid body correction. The efficiency of this correction method was evaluated with anatomical landmarks, various cost functions, and for a compartment model fit of the data with 2 parameters: K1, the blood to myocardium transfer coefficient; and Vd, the distribution volume of the contrast media. The variability of K1 and Vd, derived from the fit of the registered images (using the manual correction as a gold standard), was significantly reduced by comparison with the variability obtained from the uncorrected images (P < 0.04). This motion correction method also clearly improves the analysis of dynamic cardiac MRI after contrast media injection in comparison to manual correction. J. Magn. Reson. Imaging 2001;13:648–655. © 2001 Wiley-Liss, Inc.
    Journal of Magnetic Resonance Imaging 03/2001; 13(4):648 - 655. · 2.57 Impact Factor
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    ABSTRACT: To evaluate the potential of an iron oxide-based MR contrast agent for the detection and delineation of experimental liver tumors during the early vascular phase of the compound. Superparamagnetic blood pool agent (SBPA) was administered intravenously to rabbits bearing VX2 tumors. Images were acquired before the injection, immediately after, and 1 or 3 weeks later. The variations of signal intensity were measured in the tumors and in several tissues for various T1-weighted spin-echo, T2-weighted fast spin-echo, and T2-weighted gradient-recalled-echo sequences. Fourteen and 12 of the 16 tumors were detected immediately after SBPA injection using, respectively, the T2-weighted fast spin-echo and T2-weighted gradient-recalled-echo sequences. A significant decrease in signal intensity was observed in well-perfused organs, and blood signal was abolished even at the lowest injected dose and using a T1-weighted sequence. In the late phase, the loss in signal intensity of the liver was even more pronounced. The dominant T2 effect of SBPA induces an increase in the tumor-to-liver and tumor-to-blood contrast during the vascular phase, improving the detection of the tumors and allowing the distinction between small lesions and vessels through plane. This effect on the liver signal persists for several days because of the incorporation of SBPA in the reticuloendothelial system.
    Investigative Radiology 02/2001; 36(1):15-21. · 5.46 Impact Factor
  • J P Vallée, F Lazeyras, H G Khan, F Terrier
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    ABSTRACT: The aim of this study was to demonstrate the feasibility of the absolute renal blood flow quantification using MRI and injection of contrast media. Using a T1-weighted fast gradient sequence following an intravenous bolus injection of Gd-DTPA, dynamic images of the kidney were obtained in patients with well-functioning native kidneys (n = 7) or transplant (n = 9), with significant renal artery stenosis (n = 4) and with renal failure (n = 7). After signal intensity calibration, the absolute renal perfusion was equal to the wash-in slope of the renal transit curve divided by the contrast medium concentration at the peak of the bolus in the aorta. The cortical blood flow was 2.54+/-1.16 ml/min per gram in well-functioning kidneys decreasing to 1.09+/-0.75 ml/min per gram in case of renal artery stenosis (p = 0.04) and to 0.51+/-0.34 ml/min per gram in case of renal failure (P<0.001). These measurements were in agreement with previous results obtained by other methods. A standard MRI imaging sequence and a simple model can provide realistic quantitative data on renal perfusion. This work justifies further studies to compare this model with a gold standard for renal blood flow measurements.
    European Radiology 01/2000; 10(8):1245-52. · 4.34 Impact Factor
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    ABSTRACT: The authors evaluated the artifacts observed on myocardial perfusion curves derived from an inversion-prepared fast gradient-echo (GRE) imaging sequence in dogs after injection of a gadolinium-based contrast agent. Six mongrel dogs were divided into three groups. In groups 1 and 2, anesthesia was maintained with pentobarbital. Group 2 also received an intravenous injection of atropine (0.03 mg/kg). In group 3, anesthesia was maintained with isoflurane (1.0%). Imaging was performed on a 1.5-T magnetic resonance (MR) imaging unit (one section per heart beat, a 30 x 15-cm field of view, 10-mm section thickness, and 64-kHz bandwidth). Region-of-interest (ROI) markers were placed on the blood pool of the left intraventricular cavity, anterior wall of the left ventricle, and anterior to the chest wall to track respiratory motion. In group 1, the signal intensity (SI) periodically increased during each inspiration due to respiratory sinus arrhythmia. The relation between the SI increase and the variation of the delay between images was demonstrated in vitro and by computer simulations. No periodic increase of the SI was observed when regular cardiac rhythm was maintained by pharmacologic inhibition of the vagal-mediated chronotropic response with either the addition of atropine to pentobarbital or the use of isoflurane as the anesthetic agent. In an inversion-prepared fast GRE sequence, respiratory sinus arrhythmia can induce periodic SI increase by varying the respiratory rate interval and delay between images.
    Academic Radiology 10/1999; 6(9):512-20. · 1.91 Impact Factor

Publication Stats

426 Citations
53.11 Total Impact Points

Institutions

  • 2000–2009
    • Hôpitaux Universitaires de Genève
      • Service de radiologie
      Genève, Geneva, Switzerland
  • 1997–2008
    • University of Geneva
      • • Department of Radiology and Medical Informatics
      • • Division of Radio-oncology
      Genève, Geneva, Switzerland
  • 2007
    • Haute école de gestion de Genève
      Genève, Geneva, Switzerland
  • 1997–1999
    • Duke University Medical Center
      • Department of Radiology
      Durham, NC, United States