Comparison of PET and Proton MRS Imaging to Evaluate Pediatric Brain Tumor Activity

Overview

This study in children and young adults will compare two types of imaging, positron emission tomography (\[(18)F\]-DG PET) and proton magnetic resonance spectroscopy ((1)H-MRSI), to determine activity of a brain tumor or abnormal tissue in the brain following treatment for a brain tumor. Children with brain tumors are generally followed with magnetic resonance imaging (MRI) scans to evaluate response to treatment. However, because MRI only provides information on the structure of the brain, it may difficult to tell if an abnormal finding is due to tumor, swelling, scar tissue, or dead tissue. (1)H-MRSI and \[(18)F\]-DG PET, on the other hand, provide information on the metabolic activity of brain lesions. These two methods will be compared and evaluated for their ability to provide important additional information on childhood brain tumors. Patients between 1 and 21 years of age with a brain tumor or brain tissue abnormality following treatment for a brain tumor may be eligible for this study. Candidates will be screened with a medical history and physical examination, pregnancy test in women who are able to become pregnant, and a blood test for glucose. Participants will undergo the following procedures: (1)H-MRSI - This test is similar to MRI and is done in the same scanning machine. In MRI, scans of the brain are obtained by applying a strong magnetic field and then collecting the signals released from water after the magnetic field is changed. Pictures of the brain are then obtained by computer analysis of these signals. In (1)H-MRSI, the computer blocks the signal from water to get information on brain chemicals that can indicate whether an abnormality is tumor or dead tissue. Both MRI and MRI and (1)H-MRSI are done in this study. For these tests, the child lies on a stretcher that moves into the scanner - a narrow metal cylinder with a strong magnetic field. The child's head is placed in a headrest to prevent movement during the scan. He or she will hear loud thumping noises caused by the electrical switching of the magnetic field. A contrast agent is given through an intravenous (IV) catheter (plastic tube placed in an arm vein) or through a central line if one is in place. The contrast material brightens the images to provide a clearer picture of abnormalities. Children who have difficulty holding still or being in a scanning machine are given medications by an anesthesiologist to make them sleep through the procedure. Children who are awake during the procedure can communicate with the MRI technician at all times and ask to be removed from the scanner at any time. The MRI and (1)H-MRSI take 1-1/2 to 2 hours to complete. \[(18)F\]-DG PET - For this test, \[(18)F\]-DG (a radioactive form of glucose) is injected into the patient's arm vein through a catheter, followed by the PET scan, similar to a very open MRI scan without the noise. The PET scan tells how active the patient's tumor is by tracking the radioactive glucose. All cells use glucose, but cells with increased metabolism, such as cancer cells, use more glucose than normal cells. After the glucose injection, the patient lies quietly in a darkened room for 30 minutes, after which he or she is asked to urinate to help reduce the dose of radiation to the bladder. Then, the scan begins. When the scan is finished (after about 1 hour), the child is asked to urinate again and then every 3 to 4 hours for the rest of the day. Patients remain in the study for 2 years unless they withdraw, become pregnant, or require sedation but can no longer use an anesthetic. MRI and 1H-MRSI scans may be repeated every few months during the study period, if necessary. Only one PET scan is done each year.