This study will focus on the use of repetitive Transcranial Magnetic Stimulation (rTMS) as a treatment of Obsessive Compulsive Disorder (OCD), which is a common illness that impairs quality of life and that can be hard to treat.

To precisely analyze the effects of rTMS on OCD, the investigators are going to plan a study comparing cerebral blood flow before and after rTMS treatment. The measuring will occur on the Orbito Frontal Cortex (OFC), whose role in OCD has already been shown by our team (Nauczyciel et al, 2014 in Translational Psychiatry), using Magnetic Resonance Imaging in Arterial Spin Labeling, an MRI method allowing to measure arteriola blood flow.

Our primary outcome is to show a significate difference between cerebral blood flow in OCD between one group of participants treated by rTMS and another one treated by placebo. The study will be double blinded with a placebo rTMS machine, monocentric and prospective, with participants suffering from OCD randomized between two groups.

Obsessive Compulsive Disorders (OCD) are a frequent and debilitating disease. Impact on daily life is usually important, with a high rate of mood and anxious comorbidities, such as Major Depressive Disorder occurring in half of these participants. The effects can be dramatic, leading to higher suicide rate in this population.

Guidelines for OCD treatment in France recommend the use of Serotonin Specific Recapture Inhibitors (SSRI) and Cognitive Behavioral Therapy (CBT), if possible simultaneously. However, those treatments are responsible for adverse effects for the first and not easily accessible for the second. Consequently, a non-negligible number of participants still suffers from symptoms of OCD with a non-optimal treatment.

Repetitive Transcranial Magnetic Stimulation (rTMS), a noninvasive neurostimulation method, has shown its usefulness in the treatment of mental illnesses. It has been authorized by the Food and Drugs Administration in the United States for the treatment of OCD. It represents an alternative method for helping those participants, but pattern of modifications over OCD pathophysiology has still to be unraveled.

In order to precisely analyze the effects of Low Frequency rTMS (LF rTMS) on OCD, the investigators designed a monocentric, prospective, double blind study comparing cerebral blood flow (CBF) before and after a rTMS treatment. Measurements will be performed on the Orbito Frontal Cortex (OFC), whose role in OCD has already been shown by our team (Nauczyciel et al, 2014 in Translational Psychiatry), using Magnetic Resonance Imaging (MRI) in Arterial Spin Labeling (ASL).

Inclusion criteria will be OCD diagnosis, age between 18 and 65, and the lack of counter indication to MRI and rTMS. Participants will firstly undergo MRI before treatment, along with a psychometric assessment. Participants will then receive a one-week rTMS treatment, with two sessions of fifteen minutes per day. Second MRI and evaluation will be performed 4 weeks after the end of the treatment.

Psychometric assessment will consist of MINI, YBOCS, CGI, MADRS, HAMA, and GAF, administered before and four weeks after treatment. The psychiatrist giving the assessment will be blind to the randomization of the patient, so will be the radiologist performing the MRI.

Our primary outcome is to show a significant difference between CBF in OCD in participants treated by rTMS versus participants treated by sham rTMS. A decrease of the CBF in the OFC is expected, in regards to the inhibitor effects of LF rTMS. This result will allow us to follow objectively the neurobiological effects of rTMS, developing the ability to plan more efficiently rTMS treatment for participants.

Inclusion Criteria:

• Participants over 18 to 65
• Score at YBOCS over 15
• Diagnosis of Obsessive Compulsive Disorder acknowledged by two psychiatrists using the DSM V criteria
• Patient is able to receive and understand information about the trial, and agrees to participate in the trial
• Indication of treatment by rTMS

Exclusion Criteria:

Related to MRI and / or rTMS:

• Cardiac Stimulator or Implantable Automatic Defibrillator
• Neurosurgical Clips
• Cochlear Implant
• Intra ocular or cranial metallic foreign body
• Endoprosthesis lasting from less than four weeks
• Ostheosynthesis material lasting from less than six weeks
• Claustrophobia

Other criteria:

• Pregnancy or breast feeding
• Unstable hemodynamics, acute respiratory failure, need for constant surveillance not possible during the MRI, precarious general condition
• Patient over legal protection, care without consent
• Active psychiatric pathology other than anxious or mood disorder
• Active severe somatic disease
• History of seizures or other neurologic pathologies (Parkinson's Disease, CVA, Alzheimer's Disease, Multiple Sclerosis, Lewy Body Dementia...)
• Patient without social security

Data about study protocol and clinical information will be available on request from other researchers. MRI raw data will not be shared but processed data is planned to be available.

Data will be available from the moment a scientific publication is accepted to 5 years later.

Access to data will be granted for researchers aiming to perform another analysis or to review the topic, or to perform a meta-analysis.

The masking model will use the same rTMS coil as the active group, bit with a 180° rotation, making the magnetic field face the opposite direction, and thus not being able to produce Neuromodulation on the patient. The stimulation intensity will be decreased at 30% of the motor threshold, to keep the characteristic sound of active rTMS. The patient will not know their group; neither will the investigator nor the rater. Only the rTMS performing technician will know the randomization group to be able to choose the right setting.