Added Value of 18 FDG Pet-scanner in Diagnosis and Management of Subclinical Rejection in Kidney Transplant Patients

The renal biopsy (RB) represents the gold-standard for the diagnosis of acute renal transplant rejection (AR), and allows early verification of a so-called "subclinical" rejection, ie without any clinical or biological abnormality detectable in a stable kidney transplant patient. The RB also makes it possible to certify a strictly normal renal histology and thus to motivate the withdrawal of corticosteroid therapy. It is this 3-month post-transplant protocol RB protocol that has been effective since 2007 at the CHU Liège. However, RB is an invasive procedure, contraindicated in patients taking anticoagulants, and carrying a significant risk of complications. The potential complications associated with RB motivate the identification and validation of other diagnostic means. In the present project, the investigators propose to study the relevance of positron emission tomography (PET), coupled with conventional tomography (CT), after intravenous injection of 18-fluoro-deoxy-glucose (18FDG) in the overall protocol of the renal transplant patient at 3 months post-transplant to: (i) allow protocol renal biopsy only in patients with suspicion of an acute rejection (ii) be a decision maker for withdrawal from corticosteroids in the absence of rejection In practice, the investigators suggest performing 18FDG PET / CT imaging on the day of the surveillance biopsy, which is systematically performed in all kidney transplant patients at University Hospital of Liège 3 months after transplant. The investigators are considering 3 scenarios: * Scenario 1. The renal biopsy shows signs of humoral rejection: the patient is excluded from the study and is treated "as usual" on the basis of the histological results. * Scenario 2. The renal biopsy does not show signs of humoral rejection but the 18FDG PET / CT shows a high metabolic activity of the graft (\> 2.4): the patient is treated "as usual" on the basis of histological findings. * Scenario 3. The renal biopsy does not show signs of humoral rejection and the 18FDG PET / CT shows a weak metabolic activity of the graft (\<2.4): the immunosuppressive treatment is gradually weaned off corticosteroids. This clinical research project is interested in a major health problem in the follow-up of renal transplant patients, and could make it possible to improve the management of a subclinical rejection of the renal transplant and to increase the withdrawal of corticosteroids including side effects are well known.