Biomedical Applications of Emission Tomography - Correction Techniques in Emission Tomography - page 20

therefore of great interest for basic research and clinical application. Several
radioligands are available to investigate the cardiac sympathetic nervous sys-
tem in patients using PET [9]. The most widely used for clinical research
is the catecholamine (\stress hormone") analog [ 11 C]meta-hydroxyephedrine
([ 11 C]mHED), which is taken up, released and taken up again by the nerve
endings. In principle, dynamic PET is able to quantify the eciency of the
catecholamine re-uptake and thereby assess nerve function. However, the use
of PET to image molecular targets such as transporters or receptors in small
animals imposes challenges not apparent in studies using metabolic tracers
such as [ 18 F]FDG which can be given at the high concentrations needed to
achieve good images. Scanner design aims to optimize both resolution and
sensitivity but in dedicated animal scanners resolution is often pursued at
the expense of sensitivity so that high doses of radioactivity and/or long ac-
quisition times are required. Recently, we were able to prove the feasibility
of assessing cardiac nerve function by dynamic PET [11]. In this study, the
radiolabelled catecholamine [ 11 C]mHED was injected intravenously into mice
and its pharmakokinetics followed by dynamic PET acquisitions. From the
mathematical analysis of the time-activity-curves generated from regions-of-
interest placed over the left ventricular myocardium, measures of the eciency
of the catecholamine uptake were calculated. The great potential of dynamic
PET is shown by injecting an uptake competitor of [ 11 C]mHED, metaraminol
after the injection of [ 11 C]mHED and while the animal was scanned dynam-
ically in PET. Competetion of [ 11 C]mHED binding by metaraminol can be
quantitatively assessed by the analysis of [ 11 C]mHED washout from the my-
ocardium (Figure 2.3). Since the object of interest, the murine heart, is small
and beating fast, correction methods for partial volume, spillover, motion, etc.
are of crucial importance to guarantee an optimal precision of quantification.
2.4.3.3 From mice to men|Non-invasive translational imaging of
inflammatory activity in graft-versus-host disease
As stated above, [ 18 F]FDG is the most commonly used tracer for PET
imaging in patients. Therefore, applying it in small animal PET to study
the diagnostic potential of a new application and translating the preclinical
findings into clinical research is a obvious and natural approach. An example
of this translational strategy is given here.
Gastrointestinal graft-versus-host disease (GvHD) is a common and poten-
tially life-threatening complication after hematopoietic stem cell transplanta-
tion (HSCT). Non-invasive tests for assessment of GvHD activity are desir-
able but lacking. Since GvHD is an inflammatory condition with inflammatory
cells infiltrating various organs such as the bowel and [ 18 F]FDG is known to
be taken up by inflammatory cells, we aimed at testing the ability to visualize
intestinal GvHD-associated inflammation in an allogeneic murine transplant
model by [ 18 F]FDG-PET in vivo [26]. A predominant localization of intesti-
nal GvHD to the colon was verified by histology and fluorescence reflectance