Molecular Imaging Insight - March 2008 - (Page 15) Addressing the challenges Molecular imaging within the field of pediatrics is challenging due to the very nature of the patient population. Children are inherently different than adults in their range of body sizes, behaviors and the rather unique types of diseases affecting them, says S. Ted Treves, MD, chief of Nuclear Medicine/PET at Children’s Hospital in Boston and professor of radiology and director of the Joint Program in nuclear medicine at Harvard Medical School. “One of the biggest challenges in imaging children is the need for high spatial resolution,” he says. “The equipment is normally designed for adult use and we have to adapt our techniques and equipment for the benefit of children.” Treves directs his research along two paths: optimizing the use of nuclear medicine in pediatrics with a recent focus on reducing radiation dose in children; and integrating modalities in medical imaging. An important challenge to pediatric imaging is obtaining high-quality studies using the lowest possible radiation dose, he adds. Improved use of technology combined with careful screening of indications can help lower radiation dose and still provide the necessary diagnostic information. One of the common dangers in treating children is over-treating disease, says Richard L. Wahl, MD, FACR, professor of nuclear medicine, director of nuclear medicine/PET facility, vice chair radiology for technology and business development at Johns Hopkins University School of Medicine in Baltimore. “Both under- and over-treatment can occur in children if you don’t have the right technology,” he says. While the combination of PET and CT is more potent than either alone, it is a good method to use to avoid many false positives and negatives on CT and to add specificity to PET. Helen R. Nadel, MD, pediatric radiologist, division head of nuclear medicine, British Columbia Children’s Hospital in Vancouver, Canada, agrees that it is necessary to accommodate the varying needs within pediatrics, while minimizing radiation exposure. “Given that we run the gamut of all age groups from newborns to the cusp of adulthood for the diseases we face in pediatrics, we cannot always standardize and set up one way to do a test for everyone,” Nadel says. Optimizing hybrid molecular imaging for pediatrics requires a little more flexibility and creativity in how tests are performed. Standardizing protocols can be a good start, but such protocols may require modification. “In nuclear medicine [there] is a movement toward optimized workflow and batch processing,” MolecularImaging.net she says. “We would love to do this in pediatrics, but when you deal with a population that can range from 5 pounds to 200 pounds, it is not possible. You cannot possibly do them the same way—you must adapt.” Clinical indications for PET/CT “Just because it is difficult, does not mean it is impossible for these technologies to make a difference in pediatrics,” says Wahl. These hybrid technologies are proving their value in pediatric neurology, orthopedics and oncology, Treves says. In neurology, PET fused with MR has proven an effective tool for the localization of focal epilepsy in the brain. “In addition, PET/MR fusion is effective for assessing the effect of therapy and also to detect the residual or recurrent brain tumor activity,” Treves says. “At Children’s Hospital Boston, PET/MR image fusion is considered a necessity and it is done routinely in all brain studies so that the anatomic-functional relationships can be assessed more easily. Emerging PET agents beyond FDG hold promise in improving the assessment of brain tumors in children.” It has been proven that PET’s metabolic assessment shows other areas of abnormality that cannot be detected by other modalities, 16 year old male, HLA-B27 which aids in surgical planning. “It positive; presents with back is proven but requires a dedicated pain. Bilateral pars defects on CT but only left L5 shows epilepsy surgery service that can increased activity. SPECT/CT act on the results,” Nadel says. confirms that only the left side Despite its proven ability, with the is a functionally significant abnormality. Source: British limited availability of PET/CT in Columbia Children’s Hospital. pediatrics, the British Columbia’s Children’s Hospital has been providing their assessment of children with other modalities such as functional MRI (fMRI), but Nadel admits this is an area of potential growth for PET. Treves says that PET/CT, using 18F sodium fluoride (18F NaF PET), a skeletal PET imaging agent, is being used in orthopedics and sports medicine to assess various bone disorders, osteomyelitis, bone tumors, non-accidental trauma, or any of the wellestablished indications of skeletal scintigraphy. “PET with 18F NaF has certain advantages including a high sensitivity, exquisite spatial resolution and rapid imaging at a similar radiation exposure to that of conventional skeletal scintigraphy,” he adds. “The combination of PET and CT provides improved lesion localization.” In the case of pediatric oncology, the majority of childhood cancers are clinically aggressive, high-grade tumors such as malignant lymphomas, bone and soft-tissue sarcomas, germ cell tumors and neuroblastoma. Pediatric cancer is a heterogeneous group of diseases and there is March 2008 | Molecular Imaging Insight 15 http://MolecularImaging.net
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