Prospects for advancing nuclear cardiology by means of new detector designs

Abstract

In the March/April issue of the Journal, there is a fascinating article by Slomka et al 1 reporting advances in SPECT detector design and image reconstruction techniques. In this essay we shall outline briefly the physical principles that have made these innovations possible and explore ways in which diagnosing cardiac disease may be advanced with this new technology. First, it is useful to understand how it has become possible to improve Nuclear Cardiology image quality. Usually, for any given technology, such as Anger camera tomograms reconstructed by filtered backprojection, improving one property of an image causes degradation of other image properties; for instance, improving signal-to-noise ratio by applying a stronger spatial filter decreases image contrast and spatial resolution. 2 In order to achieve a genuine improvement in image quality it is necessary to replace an older technology with a newer one. One way to accomplish this is to replace filtered backprojection reconstruction approaches with more sophisticated iterative reconstruction algorithms; another approach is to replace the Anger cameras with superior data collecting devices. Ultimately, the reliability of scintigrams is inseparably connected to the amount of information associated with each detected gamma ray. Anger cameras consist of a single large NaI(Tl) crystal with a bank of many photomultiplier tubes and a collimator. Some of the recent improvements in image quality have come about by replacing the NaI(Tl) crystal with a solid state device, such as CZT and CSI(Tl) crystals, which provide considerably more information for each detected gamma ray. For instance, every time a 140 keV gamma ray scintillates in a NaI(Tl) crystal, it produces 5,600 light photons, which are converted to 700 photoelectrons, which then must be amplified in a photomultiplier tube to produce an electronic signal suitable for information processing. 3 The greatest factor contributing to Anger