V-48 - A RENEWABLE SOURCE FOR TRANSMISSION SCANNING WITH PET

A Ge-68 (t(1/2) = 271 d) source is normally used to produce transmissi on images for PET studies. New PET scanners utilize two or three 10-15 mCi Ge-68 sources for this purpose. V-48 (t(1/2) = 15.98 d) has been investigated as an alternative to Ge-68 for routine transmission scann ing in PET. A target system has been developed to produce nearly homog eneous (+/- 10%) sources of 1 mCi/cm (10 mCi over 10 cm) using the Ti- 48(p, n)V-48 reaction (E(p) = 17 MeV). The target consists of a small diameter (3.17 mm) Ti tube (> 99.99% Ti, 73.7% Ti-48) Oriented at 6 de grees to the incident proton beam and held rigidly within a water cool ed aluminum target body. The Ti tube wall presents an effective target thickness of 8.5 mm to the grazing proton beam. The Ti tube is water cooled. Typical irradiations of 20 mu A for 120 min on the tube yield 10 mCi sources. Short-lived V-47 (t(1/2) = 32.6 min) and V-46 (t(1/2) = 422 ms) impurities are allowed to decay prior to utilizing the sourc e for routine PET transmission scanning. Ti tubes are reused to produc e new sources each week.