Pierre Malick Koulibaly

Bio: Pierre Malick Koulibaly is an academic researcher from University of Nice Sophia Antipolis. The author has contributed to research in topics: Iterative reconstruction & Imaging phantom. The author has an hindex of 13, co-authored 20 publications receiving 1023 citations.

European multicentre database of healthy controls for [123I]FP-CIT SPECT (ENC-DAT): age-related effects, gender differences and evaluation of different methods of analysis

Abstract: Dopamine transporter (DAT) imaging with [123I]FP-CIT (DaTSCAN) is an established diagnostic tool in parkinsonism and dementia Although qualitative assessment criteria are available, DAT quantification is important for research and for completion of a diagnostic evaluation One critical aspect of quantification is the availability of normative data, considering possible age and gender effects on DAT availability The aim of the European Normal Control Database of DaTSCAN (ENC-DAT) study was to generate a large database of [123I]FP-CIT SPECT scans in healthy controls SPECT data from 139 healthy controls (74 men, 65 women; age range 20 – 83 years, mean 53 years) acquired in 13 different centres were included Images were reconstructed using the ordered-subset expectation-maximization algorithm without correction (NOACSC), with attenuation correction (AC), and with both attenuation and scatter correction using the triple-energy window method (ACSC) Region-of-interest analysis was performed using the BRASS software (caudate and putamen), and the Southampton method (striatum) The outcome measure was the specific binding ratio (SBR) A significant effect of age on SBR was found for all data Gender had a significant effect on SBR in the caudate and putamen for the NOACSC and AC data, and only in the left caudate for the ACSC data (BRASS method) Significant effects of age and gender on striatal SBR were observed for all data analysed with the Southampton method Overall, there was a significant age-related decline in SBR of between 4 % and 67 % per decade This study provides a large database of [123I]FP-CIT SPECT scans in healthy controls across a wide age range and with balanced gender representation Higher DAT availability was found in women than in men An average age-related decline in DAT availability of 55 % per decade was found for both genders, in agreement with previous reports The data collected in this study may serve as a reference database for nuclear medicine centres and for clinical trials using [123I]FP-CIT SPECT as the imaging marker

Brain perfusion in Alzheimer's disease with and without apathy: a SPECT study with statistical parametric mapping analysis.

Abstract: Alzheimer's disease (AD) is clinically characterized by cognitive symptoms that, in combination with behavioral disturbances, significantly interfere with activities of daily living. These behavioral disorders contribute to the clinical heterogeneity of the disease and probably express different pathophysiological processes. Apathy is one of the most frequent behavioral disorders in AD. The aim of this study was to evaluate brain perfusion of AD patients with and without apathy (as determined by the Neuropsychiatric Inventory) compared with that in healthy elderly subjects. A total of 15 AD patients without apathy (AD/NA; mean age 76.6) and 15 AD patients with apathy (AD/A; mean age 77.6) were studied. Brain perfusion was measured by 99mTc-labeled bicisate (ECD) single-photon emission tomography (ECD SPECT). The images of the two AD subgroups were compared by means of statistical parametric mapping (SPM 99) to corresponding images of 11 healthy elderly control subjects (obtained from the Society of Nuclear Medicine database). Compared with the healthy elderly subjects, the apathy-free AD subgroup had significantly lower perfusion of inferior temporal regions (left fusiform gyrus, left parahippocampal area) and occipital regions (left gyrus lingualis). The apathy subgroup had significantly decreased perfusion of the left anterior cingulate, the right inferior and medial gyrus frontalis, the left orbitofrontal gyrus and the right gyrus lingualis. The differences in the brain areas with reduced perfusion between the apathy-free subjects (mainly the posterior regions) and the apathetic subjects (mainly the anterior regions) indicate that behavioral disorders such as apathy participate in the heterogeneity of brain perfusion in AD.

Quantitative accuracy of dopaminergic neurotransmission imaging with (123)I SPECT.

Abstract: 123I-Labeled radiotracers are suitable for in vivo imaging of the dopaminergic system by SPECT. However, precise measurement of striatal uptake is limited by scatter, attenuation, and the finite spatial resolution of the camera. We studied the quantitative accuracy that can be achieved with 123I SPECT of the dopaminergic neurotransmission system. Methods: Using a Monte Carlo simulation and brain phantom experiments, we studied the biases in brain and striatal absolute uptake estimates and in binding potential (BP) values for different processing schemes with corrections for attenuation, scatter, and the partial-volume effect. Results: Without any correction, brain activity was underestimated by at least 65%, and absolute striatal activity measured in regions corresponding to the anatomic contours of the striata was underestimated by about 90%. With scatter and attenuation corrections only, estimated brain activity was accurate within 10%; however, striatal activity remained underestimated by about 50%, and BP values were underestimated by more than 50%. When combined with attenuation and scatter corrections, anatomically guided partial-volume effect correction (PVC) reduced the biases in striatal activity estimates and in BP values to about 10%. PVC reliability was affected by errors in registering SPECT with anatomic images, in segmenting anatomic images, and in estimating the spatial resolution. With registration errors of 1 voxel (2.1 2.1 3.6 mm3) in all directions and of 15° around the axial direction, PVC still improved the accuracy of striatal activity and BP estimates compared with scatter and attenuation corrections alone, the errors being within 25%. A 50% overestimation of the striatal volume yielded an approximate 30% change in striatal activity estimates with respect to no overestimation but still provided striatal activity estimates that were more accurate than those obtained without PVC (average errors 1 SD were 22.5% 1.0% with PVC and 49.0% 5.5% without PVC). A 2-mm error in the spatial resolution estimate changed the striatal activity and BP estimates by no more than 10%. Conclusion: Accurate estimates of striatal uptake

Model-based respiratory motion compensation for emission tomography image reconstruction.

Abstract: In emission tomography imaging, respiratory motion causes artifacts in lungs and cardiac reconstructed images, which lead to misinterpretations, imprecise diagnosis, impairing of fusion with other modalities, etc. Solutions like respiratory gating, correlated dynamic PET techniques, list-mode data based techniques and others have been tested, which lead to improvements over the spatial activity distribution in lungs lesions, but which have the disadvantages of requiring additional instrumentation or the need of discarding part of the projection data used for reconstruction. The objective of this study is to incorporate respiratory motion compensation directly into the image reconstruction process, without any additional acquisition protocol consideration. To this end, we propose an extension to the maximum likelihood expectation maximization (MLEM) algorithm that includes a respiratory motion model, which takes into account the displacements and volume deformations produced by the respiratory motion during the data acquisition process. We present results from synthetic simulations incorporating real respiratory motion as well as from phantom and patient data.

Partial-Volume Effect in PET Tumor Imaging

Abstract: PET has the invaluable advantage of being intrinsically quantitative, enabling accurate measurements of tracer concentrations in vivo. In PET tumor imaging, indices characterizing tumor uptake, such as standardized uptake values, are becoming increasingly important, especially in the context of monitoring the response to therapy. However, when tracer uptake in small tumors is measured, large biases can be introduced by the partial-volume effect (PVE). The purposes of this article are to explain what PVE is and to describe its consequences in PET tumor imaging. The parameters on which PVE depends are reviewed. Actions that can be taken to reduce the errors attributable to PVE are described. Various PVE correction schemes are presented, and their applicability to PET tumor imaging is discussed.

Deterministic edge-preserving regularization in computed imaging

Abstract: Many image processing problems are ill-posed and must be regularized. Usually, a roughness penalty is imposed on the solution. The difficulty is to avoid the smoothing of edges, which are very important attributes of the image. In this paper, we first give conditions for the design of such an edge-preserving regularization. Under these conditions, we show that it is possible to introduce an auxiliary variable whose role is twofold. First, it marks the discontinuities and ensures their preservation from smoothing. Second, it makes the criterion half-quadratic. The optimization is then easier. We propose a deterministic strategy, based on alternate minimizations on the image and the auxiliary variable. This leads to the definition of an original reconstruction algorithm, called ARTUR. Some theoretical properties of ARTUR are discussed. Experimental results illustrate the behavior of the algorithm. These results are shown in the field of 2D single photon emission tomography, but this method can be applied in a large number of applications in image processing.

A review of partial volume correction techniques for emission tomography and their applications in neurology, cardiology and oncology

Abstract: Accurate quantification in PET and SPECT requires correction for a number of physical factors, such as photon attenuation, Compton scattering and random coincidences (in PET). Another factor affecting quantification is the limited spatial resolution. While considerable effort has gone into development of routine correction techniques for the former factors, less attention has been paid to the latter. Spatial resolution-related effects, referred to as 'partial volume effects' (PVEs), depend not only on the characteristics of the imaging system but also on the object and activity distribution. Spatial and/or temporal variations in PVE can often be confounding factors. Partial volume correction (PVC) could in theory be achieved by some kind of inverse filtering technique, reversing the effect of the system PSF. However, these methods are limited, and usually lead to noise-amplification or image artefacts. Some form of regularization is therefore needed, and this can be achieved using information from co-registered anatomical images, such as CT or MRI. The purpose of this paper is to enhance understanding of PVEs and to review possible approaches for PVC. We also present a review of clinical applications of PVC within the fields of neurology, cardiology and oncology, including specific examples.