tailieunhanh - Pediatric Chest Imaging - part 7

thể hiện tín hiệu hơi sáng hơn cơ bắp bình thường. Trên T2W, các tín hiệu của tuyến ức bình thường sáng hơn nhiều so với tín hiệu của cơ, tương tự như vậy khi bão hòa chất béo được sử dụng. Tín hiệu không đồng nhất của tuyến ức nên được coi là bệnh lý. Các mô tuyến ức tiết lộ giảm đồng nhất về cường độ pha phản đối | PEDIATRIC MEDIASTINAL MASSES IMAGING EVALUATION 329 demonstrate slightly brighter signal than normal muscle. On T2-weighted images the signal of the normal thymus is much brighter than the signal of the muscle likewise when fat saturation is used. Inhomogeneous signal of the thymus should be considered pathologic. The thymic tissue revealed homogeneous decrease in intensity on opposed-phase MR images relative to that seen on in-phase images of healthy volunteers and two patients with hyperplastic thymus. Chemical-shift MR imaging may be useful in identifying normal thymic tissue and the hyperplastic thymus in early adulthood 13 . Various radiopharmaceuticals localize in the thymus. Gallium 67 67Ga citrate uptake has been shown in as many as 61 of children younger than 2 years of age with lymphoid and nonlymphoid tumors. Thymic 67Ga uptake is most often seen after chemotherapy. This reflects the presence of activated thymic lymphocytes as part of the immunologic response that leads to hyperplasia 14 . 67Ga uptake may also occur in children stressed by illness 15 16 . Iodine 131 uptake has been shown to occur in hyperplastic thymus that does not contain ectopic thyroid tissue or metastatic foci 17 . The presence of somatostatin receptors in the thymus accounts for the occasional visualization of a normal thymus in children who undergo imaging with indium 111 pentetreotide 18 19 . There is increased uptake of 2- fluorine 18 -fluoro-2-deoxy-D-glucose FDG in the normal thymus gland of patients between the ages of 2 and 13 years 20 21 . Most of the patients studied had positron emission tomography PET scans for various oncologic conditions and had no known or suspected thymus abnormality. This uptake assumes an important role when evaluating mediastinal uptake in whole-body PET scans in pediatric oncology patients to avoid false-positive interpretation. Previous treatment with a high dose of radioiodine and chemotherapy may contribute to visualization of a normal thymus