• contrast agents
• CT image quality
• micro-CT
• molecular imaging

Sub-millimeter Computed Tomography (micro-CT) is an essential tool to
study small animal models of human diseases. Micro-CT generally provides high-resolution anatomic information, either on its own or in conjuction
with functional imaging modalities such as Positron Emission Tomography
(PET) and Single-Photon Emission Computed Tomography (SPECT). The
increasing development of new contrast agents and the advanced applications of micro-CT, make possible to provide morpho-functional information
by translating preclinical models to clinical applications and pioneering new
ones. The main goal in micro-CT imaging is to obtain a high spatial resolution, while reducing the long scanning time and radiation dose. In fact, the
animal dose strongly depends on the scanning protocol and it should be kept
at low levels in order to enable longitudinal studies avoiding radiation-related
injuries.
This work falls into the wide research field of molecular imaging, where
collaboration between physicists, biologists, and chemists is very close.
The aim of this thesis is to evaluate the performance of the CT component of
a novel combined PET/CT scanner for preclinical imaging which is operating
at the Institute of Clinical Physiology of the National Research Council, in
Pisa.
In the first part of the thesis the physical background of CT and micro-
CT imaging is described. Then it focuses on IRIS CT components and the
related imaging perfomances. A digression on the contrast agents available
on the market for micro-CT imaging is then given, including a discussion on
the difference between water-soluble contrast agents and blood-pool contrast
agents. The relating properties reflecting on CT enhancement of animal
studies will be also examined.
In the second part, results of experimental measurements on the IRIS
CT are reported. More specifically, spatial resolution and micro-CT image
noise are evaluated as a function of the spatial frequency, in terms of the
Modulation Transfer Function (MTF) and Noise Power Spectrum (NPS), re-
spectively. As a new achievement of this work, the beam hardening artifact is
analyzed and a first correction of it is provided. Then the focus shifts on stu-
dies with contrast media. Phantom studies employing conventional contrast
agents based on iodine are reported. They have allowed the first investigations of the IRIS CT scanner high temporal resolution protocol, specifically
designed for dynamic (functional) imaging. Moreover the response to X-rays
of a novel nanoparticle-based contrast agent under development at the Center for Nanotechnology Innovation@Nest, Istituto Italiano di Tecnologia, is
first analyzed by means of phantom simulations. Simulations aimed to give
a replication of the real imaging process in order to foresee the experimental
results of phantom studies employing this novel contrast agent. The sensitivity of the IRIS CT scanner to nanoparticles was finally evaluated for all
tube voltages.
The results obtained from fast imaging protocols could represent the basis
of further analysis aimed to optimize the contrast agent injection protocol in
real dynamic acquisitions. Further investigations of these novel nanoparticle-based contrast agents are also needed in order to implement advanced preclinical applications of the IRIS CT with potential big impact on molecular imaging research, and, hopefully, potential translation to the clinical world.