) I n s t r AB Scanditronix, SwedenAbs t ra c 5 An automated blood sampling system h a s been constructed and evaluated. Two d i f f e r e n t d e t e c t o r u n i t s i n t h e blood sampling system a r e compared. Results from s t u d i e s of blood-brain b a r r i e r t r a n s f e r of a C -1

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The PC2048-15B is the brain version of the new generation of Scanditronix positron camera systems. It is based on a detection unit with 16 scintillating crystals mounted on 2 dual photomultiplier tubes. A system description is given and preliminary test results including spatial resolution, sensitivity to true and random coincidences, scatter correction, and count rate linearity are presented.

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Iterative reconstruction techniques have been shown to have superior noise characteristics compared to conventional filtered backprojection (FB). The main drawbacks of the iterative methods are the increased computational burden and the difficulty in establishing a stopping criterion and ensuring proper quantitation in different imaging situations. Using a combination of techniques, we have been able to reduce the time required for iterative reconstruction to a few times that of FB. We have also compared the quantitation properties of FB to those of additive and multiplicative iteration formulas, including the Maximum Likelihood method (ML). Without acceleration, all three tested methods gave quantitative results after 40 iterations, regardless of the number of counts in the data. However, with noisy data, the best images in a leastsquares sense were obtained after typically 10-20 iterations.