Evi Theunissen

Visualisation of the kinetics of macrophage infiltration during experimental autoimmune encephalomyelitis by magnetic resonance imaging

Macrophages are considered to be the predominant effector cells in multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). Ultra small particles of iron oxide (USPIO) can be used to detect macrophage infiltrates in the CNS with magnetic resonance imaging (MRI). Here, we investigated whether the kinetics of lesion formation in EAE can be visualised by altering the time point of USPIO injection and the time interval between particle injection and MRI. When USPIO are systemically injected 24 h before MRI, hypo intense regions are detected in different brain regions depending on the disease stage. These regions correspond to sites of macrophage infiltration. A more complete visualisation of sites of inflammation is accomplished by USPIO injection at disease onset and postponing MRI to top of disease. This study demonstrates that the distribution pattern and amount of inflammatory lesions detected with USPIO, depends on timing of USPIO administration and subsequent MRI. These findings are important for a correct application and interpretation of USPIO dependent contrast imaging of CNS inflammation.

Tracking of myelin-reactive T cells in experimental autoimmune encephalomyelitis (EAE) animals using small particles of iron oxide and MRI

Myelin‐reactive T cells are responsible for initiating the cascade of autoreactive immune responses leading to the development of multiple sclerosis. For better insights into the disease mechanism, it is of major importance to have knowledge on the sites at which these cells are active during disease progression. Herein, we investigated the feasibility of tracking myelin‐reactive T cells, upon labelled with SPIO particles, in the central nervous system (CNS) of experimental autoimmune encephalomyelitis (EAE) animals by MRI. First, we determined the optimal labelling condition leading to a high particle uptake and minimal SPIO–Poly‐l‐lysine (PLL) aggregate formation using Prussian blue staining and inductively coupled plasma spectroscopy measurements. Results from labelling of myelin reactive T cells with low concentrations of SPIO particles (i.e. 25 µg/ml) combined with different concentrations of PLL (0–1.5 µg/ml) showed that increasing amounts of PLL led to augmented levels of free remnant SPIO‐PLL aggregates. In contrast, a low PLL concentration (i.e. 0.5 µg/ml) combined with high concentrations of SPIO (i.e. 400 µg Fe/ml) led to a high labelling efficiency with minimal amounts of aggregates. Second, the labelled myelin‐reactive T cells were transferred to control rats to induce EAE. At the occurrence of hindlimb paralysis, the SPIO labelled myelin‐reactive T cells were detected in the sacral part of the spinal cord and shown to be highly confined to this region. However, upon transfer in already primed rats, T cells were more widely distributed in the CNS and shown present in the spinal cord as well as in the brain. Our study demonstrates the feasibility of tracking SPIO labelled myelin‐reactive T cells in the spinal cord as well as the brain of EAE rats upon systemic administration. Furthermore, we provide data on the optimal labelling conditions for T cells leading to a high particle uptake and minimal aggregate formation. Copyright

Post-mortem assessment of rat spinal cord injury and white matter sparing using inversion recovery-supported proton density magnetic resonance imaging

Study design:This was an experimental study.Objectives:White matter sparing influences locomotor recovery after traumatic spinal cord injury (SCI). The objective of the present post-mortem magnetic resonance imaging (MRI) investigation was to assess the potential of a simple inversion recovery (IR) sequence in combination with high-resolution proton density (PD) images to selectively depict spared white matter after experimental SCI in the rat.Setting:This study was conducted at University of Liège and Centre Hospitalier Universitaire, Liège, Belgium and Hasselt University, Diepenbeek, Belgium.Methods:Post-mortem 9.4 tesla (T) MRI was obtained from five excised rat spines 2 months after compressive SCI. The locomotor recovery had been followed weekly using the standardized Basso–Beattie–Bresnahan scale. IR MRI was used to depict normal white matter as very hypo-intense. Preserved white matter, cord atrophy and lesion volume were assessed, and histology was used to confirm MRI data.Results:MRI showed lesion severity and white matter sparing in accordance with the degree of locomotor recovery. IR MRI enhanced detection of spared and injured white matter by selectively altering the signal of spared white matter. Even subtle white matter changes could be detected, increasing diagnostic accuracy as compared to PD alone. MRI accuracy was confirmed by histology.Conclusion:High-resolution IR-supported PD MRI provides useful micro-anatomical information about white matter damage and sparing in the post-mortem assessment of chronic rat SCI.

Rapid, postmortem 9.4 T MRI of spinal cord injury: correlation with histology and survival times.

High field magnetic resonance imaging (MRI) has been increasingly used to assess experimental spinal cord injury (SCI). In the present investigation, after partial spinal cord injury and excision of the whole spine, pathological changes of the spinal cord were studied in spinal cord-spine blocks, from the acute to the chronic state (24 h to 5 months). Using proton density (PD) weighted imaging parameters at a magnetic field strength of 9.4 tesla (T), acquisition times ranging from <1 to 10 h per specimen were used. High in-plane pixel resolution (68 and 38 microm, respectively) was obtained, as well as high signal-to-noise ratio (SNR), which is important for optimal contrast settings. The quality of the resulting MR images was demonstrated by comparison with histology. The cord and the lesion were shown in their anatomical surroundings, detecting cord swelling in the acute phase (24 h to 1 week) and cord atrophy at the chronic stage. Haemorrhage was detected as hypo-intense signal. Oedema, necrosis and scarring were hyper-intense but could not be distinguished. Histology confirmed that the anatomical delimitation of the lesion extent by MRI was precise, both with high and moderate resolution. The present investigation thus demonstrates the precision of spinal cord MRI at different survival delays after compressive partial SCI and establishes efficient imaging parameters for postmortem PD MRI.

Detailed Visualization of the Functional Regions of the Rat Pituitary Gland by High-Resolution T2-Weighted MRI

With 5 figures and 1 table