Magnetization Transfer Of Water T2 Relaxation Components In Human Brain: Implications For T2-Based Segmentation Of Spectroscopic Volumes
Helms G, Piringer A
Magn Reson Imaging 2001 Jul;19(6):803-11
MR Research Center, Karolinska Hospital, Department of Clinical NeuroScience, Stockholm, Sweden
PMID# 11551720; UI# 21436127
BiExponential T2 relaxation of the localized water signal can be used for segmentation of Spectroscopic volumes.
To assess the specificity of the components an iterative relaxation measurement of the localized water signal.
(STEAM, 12 Echo times, geometric spacing from 30 ms to 2000 ms) was combined with Magnetization Transfer (MT) saturation.
40 single Lobe pulses, 12 ms duration, 1440 degrees nominal flip angle, 1 kHz offset, repeated every 30 ms.
Voxels (volume elements) including CSF were examined in Parietal Cortex and PeriVentricular Parietal White Matter (10 each).
As well as 13 voxels in Central White Matter and 16 T1-HypoIntense Non-Enhancing Multiple Sclerosis lesions without CSF inclusion.
BiExponential models (excluding Myelin water) were fitted to the relaxation data. In PeriVentricular VOIs the component of long T2 (1736 +/- 168 ms) that is attributed to CSF was not affected by MT.
In Cortical VOIs this component had markedly shorter T2's (961 +/- 239 ms) and showed both attenuation and prolongation with MT, indicating contributions from tissue.
MS lesions and Central WM showed a second tissue component of intermediate T2 (160-410 ms).
In MS lesions, however, markedly less MT of the intermediate component was found, which is consistent with decreased cellularity and exchange in a region that is large compared to Diffusion motion.
IntraVoxel And InterVoxel Coherence In Multiple Sclerosis Assessed Using Diffusion Tensor MRI
Cercignani M, Bozzali M, Iannucci G, Comi G, Filippi M
J Neurol 2002 Jul;249(7):875-83
Scientific Institute and University, Ospedale San Raffaele, NeuroImaging Research Unit, Dept. of NeuroScience, via Olgettina 60, 20132 Milan, Italy
PMID# 12140672; UI# 22135914
Previous Diffusion Tensor Magnetic Resonance Imaging (DT-MRI) studies reported Mean Diffusivity () and Fractional Anisotropy (FA) changes in lesions and Normal-Appearing White Matter (NAWM) of patients with Multiple Sclerosis (MS).
But, neglected the additional information which can be obtained by the analysis of the InterVoxel Coherence (C).
The present study is based on a large sample of patients with MS and it is aimed at assessing the potential role of C in the quantification of MS-related tissue damage of T2-visible lesions and NAWM.
We obtained dual-echo, T1-weighted and DT-MRI scans from 78 patients with Relapsing/Remitting (RR), Secondary/Progressive (SP), or Primary/Progressive (PP) MS and from 26 healthy volunteers.
We calculated, FA and C of T2-HyperIntense lesions, T1-IsoIntense lesions, T1-HypoIntense lesions and several areas of the NAWM.
and FA of the majority of NAWM regions studied from MS patients were different from the corresponding quantities of the White Matter from controls.
NAWM C from patients was lower than White Matter C from controls only for the Parietal PeriCallosal Areas.
SPMS patients had higher Corpus Callosum and lower Corpus Callosum FA and C than patients with either RRMS or PPMS.
Average lesion was higher, and average FA and C lower than the corresponding quantities measured in the NAWM.
Average T1-HypoIntense lesion was higher and average FA lower than the corresponding quantities of T1-IsoIntense lesions.
Whereas, average C of these two lesion populations were not different. SPMS had higher average lesion than both PPMS and RRMS patients.
NAWM and C of the Corpus Callosum were moderately correlated with disability.
This study confirms the role of DT-MRI metrics to identify MS lesions with different amounts of tissue damage and to detect diffuse changes in the NAWM.
It also shows that measuring C enables us to obtain additional information about tissue damage, which is complementary to that given by the analysis of and FA.
Correlations Between Structural CNS Damage And Functional MRI Changes In Primary/Progressive MS
Filippi M, Rocca MA, Falini A, Caputo D, Ghezzi A, Colombo B, Scotti G, Comi G
NeuroImage 2002 Mar;15(3):537-46
Scientific Institute and University Ospedale San Raffaele, NeuroImaging Research Unit, Milan, Italy
In patients with Primary/Progressive Multiple Sclerosis (PPMS), we investigated whether Brain and Cervical Cord structural changes in lesions and Normal-Appearing Brain Tissue (NABT).
Measured using Conventional, Magnetization Transfer (MT), and Diffusion Tensor (DT) MRI, are correlated with movement-associated Cortical activations measured using Functional Magnetic Resonance Imaging (fMRI).
From 26 right-handed PPMS patients and 15 right-handed, sex- and age-matched healthy controls, we obtained:
- Brain and Cervical Cord Dual-Echo scans and MT Ratio (MTR) maps
- Brain Mean Diffusivity () maps
- fMRI (flexion-extension of the last four fingers of the right hand)
All PPMS patients had no previous symptoms affecting their right upper limbs, which were functionally normal. Healthy volunteers showed more significant activation in the Ipsilateral Cerebellar Hemisphere than PPMS patients.
PPMS patients showed greater activation BiLaterally in the Superior Temporal Gyrus, IpsiLaterally in the Middle Frontal Gyrus, and, ContraLaterally in the Insula/Claustrum.
In PPMS patients, moderate to strong correlations (r values ranging from 0.59 to 0.68) were found between relative activations of Cortical Areas.
Located in a widespread network for Sensory-Motor and MultiModal integration and the severity of structural changes of the NABT (as measured using MT and DT MRI) and the severity of Cervical Cord damage (as measured using MT MRI).
This study shows that the pattern of Cortical activation of PPMS patients is different from that of normal controls even when performing a Motor Task with clinically unaffected limbs.
It also suggests that Cortical reorganization might be able to limit the consequences of MS injury in the Brain and Cervical Cord.
(c)2002 Elsevier Science (USA).
Highly Diffusion-Sensitized MRI Of Brain: Dissociation Of Gray And White Matter
Yoshiura T, Wu O, Zaheer A, Reese TG, Sorensen AG
Magn Reson Med 2001 May;45(5):734-40
Massachusetts General Hospital and Harvard Medical School, Department of Radiology, Boston, Massachusetts 02119, USA
The Brains of six healthy volunteers were scanned with a full Tensor Diffusion MRI technique to study the effect of a high b value on Diffusion-Weighted Images (DWIs). The b values ranged from 500 to 5000 s/mm(2).
IsoTropic DWIs, Trace Apparent Diffusion Coefficient (ADC) maps, and Fractional Anisotropy (FA) maps were created for each b value. As the b value increased, ADC decreased in both the Gray and White Matter.
Furthermore, ADC of the White Matter became lower than that of the Gray Matter, and, as a result, the White Matter became brighter than the Gray Matter in the IsoTropic DWIs.
Quantitative analysis showed that these changes were due to NonMonoExponential Diffusion signal decay of the Brain tissue, which was more prominent in White Matter than in Gray Matter.
There was no significant change in relation to the b value in the FA maps. High b value appears to have a dissociating effect on Gray and White Matter in DWIs.