## The Annals of Statistics

### Speed of Estimation in Positron Emission Tomography and Related Inverse Problems

#### Abstract

Several algorithms for image reconstruction in positron emission tomography (PET) have been described in the medical and statistical literature. We study a continuous idealization of the PET reconstruction problem, considered as an example of bivariate density estimation based on indirect observations. Given a large sample of indirect observations, we consider the size of the equivalent sample of observations, whose original exact positions would allow equally accurate estimation of the image of interest. Both for indirect and for direct observations, we establish exact minimax rates of convergence of estimation, for all possible estimators, over suitable smoothness classes of functions. A key technical device is a modulus of continuity appropriate to global function estimation. For indirect data and (in practice unobservable) direct data, the rates for mean integrated square error are $n^{-p/(p + 2)}$ and $(n/\log n)^{-p/(p + 1)}$, respectively, for densities in a class corresponding to bounded square-integrable $p$th derivatives. We obtain numerical values for equivalent sample sizes for minimax linear estimators using a slightly modified error criterion. Modifications of the model to incorporate attenuation and the third dimension effect do not affect the minimax rates. The approach of the paper is applicable to a wide class of linear inverse problems.

#### Article information

Source
Ann. Statist. Volume 18, Number 1 (1990), 251-280.

Dates
First available in Project Euclid: 12 April 2007

http://projecteuclid.org/euclid.aos/1176347500

Digital Object Identifier
doi:10.1214/aos/1176347500

Mathematical Reviews number (MathSciNet)
MR1041393

Zentralblatt MATH identifier
0699.62043

JSTOR