Susceptibility Weighted Imaging (SWI) Study On Brain Iron Metabolism In Healthy Volunteers And Multiple Sclerosis Patients

Objectiveâ‘ to establish a evolution pattern of putative iron concentration in the deep grey nuclei and white matter calculated by the phase value in susceptibility weighted imaging (SWI) as a function of age, gender and hemisphere in healthy human brains.â‘¡to quantificationally measure the phase value in cerebral grey nuclei, demyelinating plaques and normal-appearance white matter (NAWM) in MS patients, and to determine the correlation between iron deposit and perfusion, then to exploit a biomarker for monitoring the evolvement of diseases.Materials and methods1.100 healthy adults (20-69 yr.;mean=44.26 yr) were performed with a 3D gradient echo sequence SWI. Each grey structure was divided into two parts, the high iron content region (Râ…¡) and the low iron content region (Râ… ). The total phase value (PHt), phase value of Râ…¡region (PHRâ…¡) and area of Râ…¡region (ARâ…¡) were respectively evaluated as proxy variables for iron content in bilateral head of caudate nucleus (HCN), globus pallidus(GP), putamen(PUT), substantia nigra(SN), red nucleus(RN), thalamus(THA) and pulvinar thalamus(PT) as a function of age, gender and hemisphere. The total phase values were also measured and assessed in bilateral frontal white matter(FWM), parietal white matter(PWM) and occipital white matter (OWM).2.The PHt, PHRâ…¡and ARâ…¡in bilateral HCN,GP,PUT,SN,RN,THA and PT were compared between MS patients (31 cases) and age-matched healthy controls (30 cases). Moreover, the correlations between these phase data and disease course as well as EDSS scores were respectively analyzed.3. SWI features of MS plaques were assessed and classified, and then the evolution of phase value and perfusion parameters in the plaques was further evaluated with in-house SPIN software. Besides, the phase values in the normal appearance white matter (NAWM) of the MS patients were compared with those of the controls, whose correlation with the disease time as well as EDSS scores were also evaluated.Results1. In the healthy adults, significant linear correlations between putative iron contents (derived from PHt, PHRâ…¡and ARâ…¡) and age were present in all grey nuclei except bilateral HCN and PUT, in which iron content dramatically increased after 40 years old (P<0.05). The phase values in bilateral PWM and OWM significantly decreased over age (P<0.05). Furthermore, the phase values in HCN and RN were significantly different between bilateral hemispheres (P<0.05)2. Compared with the controls, the PHt, PHRâ…¡and ARâ…¡of the bilateral GP, PUT, HCN, RN, SN, THA and PT generally decreased in the MS patients, and significant differences were observed in bilateral RN,SN and PT (P<0.05). The PHRâ…¡of bilateral SN in SP-MS group was obviously lower that in RR-MS group (P<0.05) Both of PHRâ…¡and ARâ…¡of the bilateral SN, GP and PT significantly correlated with EDSS (P<0.05)3. The round or oval hypointense foci with or without small veins was considered as the characteristical finding of MS plaques. Among 21 cases of MS patients with MR follow-up (interval:2.0 months-20.0 months),6 cases (28.57%, mean interval=7.0 months) developed hypointense plaques within the foci initially appeared as abnormal small vessels, of which the evolution pattern of phase values was in consistent with those of rCBF and rCBV (P<0.05)4. In comparison with the controls, the phase values of NAWM surrounding MS plaques were significantly lower in the MS group (P<0.05). Pearson correlation analysis revealed a significant correlation between the phase values of bilateral parietal NAWM and EDSS(P<0.05). As for the bilateral parietal and frontal NAWM, their phase values also significantly correlated with the rCBF (P<0.05)Conclusion1. In the healthy adults, iron deposits in grey nuclei and white matter showed an age dependent manner and increased dramatically after 40 years old.2. Uneven iron distribution within the grey nuclei should be highlighted. The measurements of Râ…¡phase and Râ…¡area have more significance in the evaluation of iron metabolism in healthy and morbid brain than the total phase value.3. Iron accumulation of the grey nuclei in the MS group significantly increased in comparison with the controls. SP-MS group had an increased iron deposition than the RR-MS group.4. The significant correlation between Râ…¡data and EDSS indicated that phase value was capable of monitoring the evolvement of diseases in MS patients. 5. The hypointense foci with or without small veins was considered as the characteristical finding of MS plaques. Presence of abnormal small vessels without definite hypointensity in the realm of plaques was regarded as the initial change of MS plaques. The excessive iron accumulation in the plaque following the gradual reduction of cerebral perfusion indicated the occurrence of irreversible injury.6. The phase values of NAWM in the MS patients varied with the cerebral perfusion, which also correlated with the EDSS, and could be used to predict the outcome of MS patients.