Associations of quantitative susceptibility mapping with Alzheimer's disease clinical and imaging markers

Abstract

Altered iron metabolism has been hypothesized to be associated with Alzheimer’s disease pathology, and prior work has shown associations between iron load and beta amyloid plaques. Quantitative susceptibility mapping (QSM) is a recently popularized MR technique to infer local tissue susceptibility secondary to the presence of iron as well as other minerals. Greater QSM values imply greater iron concentration in tissue. QSM has been used to study relationships between cerebral iron load and established markers of Alzheimer’s disease, however relationships remain unclear. In this work we study QSM signal characteristics and associations between susceptibility measured on QSM and established clinical and imaging markers of Alzheimer’s disease. The study included 421 participants (234 male, median age 70 years, range 34–97 years) from the Mayo Clinic Study of Aging and Alzheimer’s Disease Research Center; 296 (70%) had a diagnosis of cognitively unimpaired, 69 (16%) mild cognitive impairment, and 56 (13%) amnestic dementia. All participants had multi-echo gradient recalled echo imaging, PiB amyloid PET, and Tauvid tau PET. Variance components analysis showed that variation in cortical susceptibility across participants was low. Linear regression models were fit to assess associations with regional susceptibility. Expected increases in susceptibility were found with older age and cognitive impairment in the deep and inferior gray nuclei (pallidum, putamen, substantia nigra, subthalamic nucleus) (betas: 0.0017 to 0.0053 ppm for a 10 year increase in age, p = 0.03 to < 0.001; betas: 0.0021 to 0.0058 ppm for a 5 point decrease in Short Test of Mental Status, p = 0.003 to p < 0.001). Effect sizes in cortical regions were smaller, and the age associations were generally negative. Higher susceptibility was significantly associated with higher amyloid PET SUVR in the pallidum and putamen (betas: 0.0029 and 0.0012 ppm for a 20% increase in amyloid PET, p = 0.05 and 0.02, respectively), higher tau PET in the basal ganglia with the largest effect size in the pallidum (0.0082 ppm for a 20% increase in tau PET, p < 0.001), and with lower cortical gray matter volume in the medial temporal lobe (0.0006 ppm for a 20% decrease in volume, p = 0.03). Overall, these findings suggest that susceptibility in the deep and inferior gray nuclei, particularly the pallidum and putamen, may be a marker of cognitive decline, amyloid deposition, and off-target binding of the tau ligand. Although iron has been demonstrated in amyloid plaques and in association with neurodegeneration, it is of insufficient quantity to be reliably detected in the cortex using this implementation of QSM.

Iron Deposition in Gray Matter Nuclei of Patients With Intracranial Artery Stenosis: A Quantitative Susceptibility Mapping Study

“…Consistently, previous research has confirmed that the susceptibility evaluated by QSM was positively correlated with chemically determined iron concentration in brain tissue, particularly in deep GM nuclei (16). Moreover, many studies indicated increased iron-related susceptibility in brain tissues, as assessed by QSM, in various neurological diseases, such as AD, PD, Huntington's Disease (HD), and amyotrophic lateral sclerosis (30)(31)(32)(33). Therefore, it is reliable to apply non-invasive QSM imaging to investigate the changes of iron content in deep GM nuclei for patients with long-term ACAS and PCAS.…”

Iron Homeostasis Disorder and Alzheimer’s Disease

“…Moreover, by detecting the level of antioxidant protein in the hippocampus and amygdala, the level of oxidative stress in these two regions was found to be much higher than other regions. Moreover, the oxidative stress caused by iron accumulation will enhance the activity of IRP1, resulting in the enhancement of iron absorption through TfR1 and the increase in intracellular free iron level by reducing the concentration of ferritin-H and ferritin-L, which further enhances intracellular oxidative stress [93,98]. Based on magnetic resonance imaging (MRI) technology [99], it was found that iron accumulation may further lead to the deposition of Aβ amyloid and the formation of neurofibrillary tangles in the brain of AD patients.…”

Lewy Body Dementias: A Coin with Two Sides?

“…Studies evaluating the correlation between cognitive impairment in PD and the load of iron content [132,133] have identified that QSM increases covary with (1) MoCA scores in the hippocampus and thalamus; (2) poorer visual function and higher dementia risk scores in parietal, frontal, and medial occipital cortices; and (3) higher UPDRS-III scores in the putamen (all p < 0.05) [133]. QSM has also been used in AD [134], showing positive associations between susceptibility and amyloid PET in the pallidum and putamen, but with variable results regarding cortical areas. Overall, these findings suggest that QSM may be useful to track cognitive changes in PD; however, no studies analyzing patients with DLB are available [135].…”

“…SWI: Nigrosome 1 "swallow tail sign" differentiates DLB from AD with sensitivity (80%) [125]. QSM: Positive associations between susceptibility and amyloid PET in the pallidum and putamen of AD [134]. No studies in DLB.…”