Biomedical Engineering Reference
In-Depth Information
The existence of positively charged electrons (positrons) was postulated
by Paul Dirac in 1928, based on Einstein's theory of relativity and the equa-
tions of quantum mechanics [7]. It was first observed experimentally by Carl
Anderson in 1932 [8], for which he was awarded the Nobel Prize for Physics
in 1936. The phenomenon of positron annihilation that gives rise to gamma
rays was observed by Joliot [9] and Thibaud [10] in 1933. It was shown later
that, in general, two photons are simultaneously emitted in almost exactly op-
posite directions whenever a positron passes through matter [11]. The use of
positron emitters for medical imaging purposes was first suggested by Wrenn
et al.
[12] and Sweet [13] in the early 1950s. The first successful positron imag-
ing device was described by Brownell and Sweet [14]. The system was used
for two-dimensional imaging of positron-emitting radionuclides (copper-64 and
arsenic-75) distribution to locate brain tumors in human, using a pair of NaI(Tl)
detectors. In 1963, Kuhl and Edwards introduced the concept of transverse- and
longitudinal-section scanning with single-photon emitting radionuclides [15] and
a device (Mark IV scanner), which consisted of a square array of 32 NaI(T1) de-
tectors, was built later for constructing images by superimposing multiple cross
sections of transverse axial scans [16]. Although the reconstruction method
was very primitive and the reconstructed images were severely blurred, the
development of PET was accelerated by the introduction of transverse axial
X-ray CT for radiography by Cormack and Hounsfield [1-3]. There have also
been a number of techniques developed for performing emission tomography
during the early 1970s [17-19], but all of these approaches were limited by inade-
quate mathematical reconstruction algorithms, insufficient angular sampling fre-
quency, image distortions due to photon attenuation and some other statistical
limitations.
The first positron computed tomograph was developed in 1975 by Ter-
Pogossian
et al.
[20]. This system was referred to as positron emission transax-
ial tomography (PETT II), which consisted of a hexagonal array of NaI(T1)
detectors connected in coincidence between opposite pairs. The filtered-
backprojection (FBP) reconstruction method was adopted in that system, and
the quality of the reconstructed images was markedly improved. The first whole-
body positron computed tomograph (PETT III) was developed shortly thereafter
and it was used in human studies [21-24]. This system was subsequently re-
designed and manufactured by EG&G/ORTEC as the commercial PET scanner,
ECAT [25].
