Biomedical Engineering Reference
In-Depth Information
Fig. 13.7.
Typical crystal photoemission probability as a function of time since
gamma absorption
Fig. 13.8.
Result of time correlation that enables the detection of the source of
gamma radiation
To find the exact location of positron emission, one must monitor all
gamma radiation reaching a pair of detectors on an axis at exactly the same
time and then cross-correlate all estimated arrival times. The emission loci
may be derived by measuring the TOF of the particle with respect to a refer-
ence point of known coordinates. The tomography of emissions may be con-
structed using conventional Fourier transform techniques in combination with
a mechanical system where a detector pair rotates around an axis longitudinal
to the cylindrical volume being probed (Fig. 13.8). The pair may be further
translated after each rotation cycle to complete a cylindrical scan. The litera-
ture on TOF imaging and gated sensors (both CCD and CMOS APS) is very
extensive, a few examples are found in [8, 21-23].
13.5 System Considerations
A SPC may be implemented in a number of ways. If the application requires
an array of simultaneously operating single photon detectors (SPDs), then
a SPAD array is a desirable alternative to PMT or SiAPD arrays in terms
of cost, power consumption, and miniaturization. Several demonstrations of
CMOS SPAD arrays exist in various technologies [8, 9, 24, 25]. The methods
