Speaker
Prof.
Roberto Pani
(INFN)
Description
Radionuclide imaging is a common non-invasive technique used in the evaluation of
cardiac function and disease. Currently, planar and SPECT imaging are used in nuclear
cardiology to perform gated equilibrium blood pool imaging, myocardial perfusion
imaging and first-pass imaging. More than one-third of all nuclear imaging procedures
are cardiac imaging and most of these are myocardial perfusion SPECT studies.
Therefore, a SPECT system optimized for a dedicated to cardiac imaging could have a
significant impact on a large patient population. The standard clinical SPECT imaging
using a single-head gamma camera is obviously far from optimal.
Several commercial companies have introduced L-shaped camera systems specifically for
cardiac SPECT imaging. Although these systems double the coverage of a single-head
system and cut the acquisition time for a 180° acquisition in half, there is still a
large gap in detection coverage. Among the current systems, the 3-head configuration
provides the most complete detector coverage and therefore, the current 3-head
configuration with standard Anger cameras of 40 cm FoV is not exactly optimized
because it still allows a portion of emitted photons to escape undetected.
Intuitively, a cylindrical 2pi geometry should be the optimal configuration to catch
the maximum number of photons emitted from a body section.
Over the last 20 years several groups have shown interest and proposed designs using
cylindrical geometries for body and cardiac SPECT. However, the concept of using
cylindrical geometry for cardiac SPECT imaging is not straightforward and needs to
be examined carefully. Very recently INFN have proposed a new scintillation crystal
for SPECT: LaBR3:Ce. Its superior energy resolution (6.5% at 140 keV) and a short
scintillation decay time (16 ns), can allow high counting rate (more than three times
higher than NaI(Tl)) and high scatter rejection. It seems an election crystal for
cardiac SPECT where very high counting rate are required and a significant fraction
(30-40%) of photons detected have been scattered. Preliminary results on continuous
LaBr3:Ce have shown 1 mm intrinsic spatial resolution for a crystal thickness
corresponding to 80% efficiency at 140 keV photon energy. Measurements on thicker
crystals (1 cm) are going to verify spatial resolution values better than 2 mm with a
further increasing of detection efficiency of the system. To this aim INFN is
promoting a new design of a cylindrical geometry for cardiac SPECT based on LaBr3:Ce
detection module. Each module will have one continuous LaBr3:Ce crystal with
dimensions of 10cm x 20cm. The optimal crystal thickness (between 5 and 10 mm) is
under investigation. Scintillation light from the crystals will be collected by eight
2-in square Position Sensitive Photomultiplier Tubes Hamamatsu H8500 (PSPMTs)
optically coupled to each module via a glass window light guide. These modules are
designed to be components of a modular cylindrical single photon emission computed
tomography system suitable for cardiac imaging. All the 10 modules can be moved along
the radial direction and the ring itself, of about 70 cm diameter, can rotate to
obtain the required number of views as a function of chosen FoV. Modules can work
individually as 10 independent modules with 20cm x 10cm FoV each, viewing the heart
centered in the ring, or they can be coupled to form 5 detectors with a slant
collimator, with 40cm x 10cm FoV each. In addition, the ring geometry can vary its
size or it can form a L shaped camera to be positioned close to the heart to increase
system spatial resolution as required in the cardiac gene therapy imaging.
Therefore, high resolution collimation is required to compensate for the long target
distance at the expense of geometric efficiency. The expected maximum sensitivity of
the system is almost 2.7 cps/kBq (100 cps/microCi)with a maximum rate of 2 MHz and a
spatial resolution of 2.5 cm. The best spatial resolution would be around 4 mm.
Ultimately, the smallest ring geometry consists of 5 modules (20cm x 10cm FoV each)
defining a minimum ring diameter of 28 cm. It can be an unique system for paediatric
cardiac SPECT.
Author
Prof.
Roberto Pani
(INFN)