Emission tomography and image reconstruction

Abstract

In the early days of nuclear medicine, measurement of radioactivity administered into a human body was simply acquired by placing a Geiger counter over the desired region of interest. Further progress was undertaken using a rectilinear scanner. The breakthrough, as mentioned in Chap. 10, came from the development of the gamma camera and the use of the scintillation crystal coupled to photomultiplier tubes (PMTs). To this end, there was no available tool to measure the spatial extent of tracer distribution in three-dimensional (3D) fashion, and all measurements were confined to two-dimensional (2D) planar imaging. The third dimension is important to fully depict radiopharmaceutical uptake, hence enabling the interpreting physician to make a confident decision. Another feature of 3D imaging is the ability to quantify tracer concentrations more accurately than with 2D imaging. Tracer uptake, residence time, and clearance rates are important dynamics of tracer biodistribution in diseased and healthy tissues, in which temporal sampling is particularly useful for studying tracer or organ kinetics. Adding the time dimension to 2D planar imaging is important in some scintigraphic studies, such as renal scintigraphy and planar equilibrium radionuclide angiocardiography (ERNA). In the former case, kidney function is studied through a time course of about half an hour, dividing the examination time into two phases (perfusion and function) such that the first minute is assigned to depict organ perfusion while the rest of the study is used to assess renal function. In planar ERNA, the time dimension is essential to make snapshots of different phases of the heart cycle through identification of the R-R signal during heart contraction. This helps to obtain valuable information about heart motion and to assess its functional parameters. © 2011 Springer-Verlag Berlin Heidelberg.