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Biomedical Imaging Magnetic Resonance Imaging
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
Susceptibility-weighted imaging (SWI) is a GRE-based technique with several enhancements to increase its sensitivity to tissue susceptibilities (Haacke et al. 2004). It can distinguish paramagnetic (e.g., hemorrhage/iron) from diamagnetic (e.g., calcification) lesions. It can also produce venograms based on the susceptibility differences. In quantitative susceptibility mapping (QSM), the phase information in GRE images is further analyzed to quantify susceptibility values using various mathematical methods (Wang and Liu 2015).
The Deep Brain Connectome
Published in Yu Chen, Babak Kateb, Neurophotonics and Brain Mapping, 2017
Ifije E. Ohiorhenuan, Vance L. Fredrickson, Mark A. Liker
While much progress has been made with respect to global patterns of connectivity, a similar analysis of connectivity of the basal ganglia and deep white matter tracts is still nascent (Lenglet et al. 2012). Due to their small size and proximity to other subcortical structures, imaging of the basal ganglia is challenging and relies on ultrahigh 7T MRI modalities that are not yet widely available (Keuken et al. 2014). Furthermore, the precise visualization of subcortical structures often requires novel MR sequences such as quantitative susceptibility mapping (Keuken et al. 2014). Consequently, the atlases of deep brain nuclei used for surgical planning are constructed from group-averaged MRI studies. Nevertheless, generating a basal ganglia and thalamic connectome for an individual is possible and has led to the identification and reconstruction of canonical basal ganglia pathways (Lenglet et al. 2012).
What is the potential of paramagnetic rim lesions as diagnostic indicators in multiple sclerosis?
Published in Expert Review of Neurotherapeutics, 2022
Maria Sofia Martire, Lucia Moiola, Maria Assunta Rocca, Massimo Filippi, Martina Absinta
Susceptibility-based MRI is exquisitely sensitive to magnetic properties of the tissue allowing the assessment of the tissue microstructure as well as iron content (i.e. iron-laden microglia of chronic active MS lesions). To date, different susceptibility-based imaging acquisition and post-processing methods have been applied for the detection of PRL. First, 2D T2*-weighted single gradient echo (GRE) or multi-echo gradient echo (ME-GRE) was used on 7 T MRI studies; later on, submillimetric segmented (multi-shot) echo-planar imaging (EPI) sequence [27] providing both magnitude and phase 3D images was applied at 3 T (Figure 1A). Using these sequences, PRL can be seen on magnitude images, however, with much less sensitivity than on phase images. Different post-processing techniques such as filtered unwrapped phase, susceptibility-weighted imaging (SWI), which can combine magnitude and phase contrast, and quantitative susceptibility mapping (QSM), which is a quantitative technique used to measure brain magnetic susceptibility [13,45], are commonly used to visualize PRL in research studies. Of note, QSM algorithms can remove dipole and other susceptibility artifacts more efficiently than other postprocessing techniques. Among these approaches, SWI is often utilized in clinical practice for brain bleeding detection and could foster a prompt use of PRL as a diagnostic biomarker.
Neuroimaging in hereditary spastic paraplegias: from qualitative cues to precision biomarkers
Published in Expert Review of Molecular Diagnostics, 2022
Grainne Mulkerrin, Marcondes C. França, Jasmin Lope, Ee Ling Tan, Peter Bede
It is noteworthy that more recent white matter techniques such as neurite orientation dispersion and density imaging (NODDI), diffusion kurtosis imaging (DKI), and high angular resolution diffusion imaging (HARDI) have not been applied to larger patient cohorts yet, despite their superior potential to characterize white matter integrity especially with regard to crossing fibers. Furthermore, novel multi-voxel whole-brain spectroscopy sequences that have been extensively used to other MNDs are yet to be applied to HSP [161,162]. Other imaging modalities, which have been extensively utilized in MNDs, such as connectomic approaches, quantitative susceptibility mapping (QSM), motor imagery-based fMRI, and texture analysis, are yet to be implemented in HSP [163–165]. Another stereotyped shortcoming of existing HSP imaging studies is the lack of relevant disease controls such as ALS or PLS, which would help to appraise the specificity of purported radiological signatures to HSP. Anatomically expanded activation patterns observed on task-based fMRI studies need to be interpreted with caution. There is a notion that slowly progressive neurodegenerative conditions and neurological syndromes with initial insult in childhood, such as post-poliomyelitis syndrome, may be associated with compensatory processes and structural adaptation, which may be detected by advanced imaging methods [166]. The existence of such adaptive or compensatory processes needs to be clarified in HSP. Contrary to other MNDs, these mechanisms have not been studied in HSP to date.
Clinical care and therapeutic trials in PLS
Published in Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration, 2020
Mary Kay Floeter, Deborah Warden, Dale Lange, James Wymer, Sabrina Paganoni, Hiroshi Mitsumoto
A variety of methods to image the motor cortex are being investigated as possible biomarkers for PLS and to measure progression of upper motor neuron disease. T2 hyperintensity within the corticospinal tract or atrophy of the precentral gyrus are often seen but their presence is variable. The correlation between quantitative imaging deficits and clinical deficits is not clear. Alterations found in diffusion tensor imaging measures of the corticospinal tract were unchanged over time in small longitudinal study (28). T2 hypo-intensity in PLS patients and T2*/R2* susceptibility measures correlate with microglial iron deposition in the middle and deep cortical layers on autopsy. They also qualitatively correlate with disease severity and progression (28–30). Of interest in this technique is that changes can be appreciated in specific regions of the homunculus that can be correlated with the clinical syndrome (Figure 1). Further, changes over time can be reflected in changes in quantitative susceptibility mapping (QSM) images to measure iron deposition. Although promising, validation with clinical progression is ongoing. Glial activation in patients with PLS has been identified but its role as a potential marker is uncertain (31).