Comparing 3T and 1.5T MRI for Mapping Hippocampal Atrophy in the Alzheimer's Disease Neuroimaging Initiative

Abstract

BACKGROUND AND PURPOSE Prior MR imaging studies, primarily at 1.5T, established hippocampal atrophy as a biomarker for Alzheimer disease. 3T MR imaging offers a higher contrast and signal-to-noise ratio, yet distortions and intensity uniformity are harder to control. We applied our automated hippocampal segmentation technique to 1.5T and 3T MR imaging data, to determine whether hippocampal atrophy detection was enhanced at 3T. MATERIALS AND METHODS We analyzed baseline MR imaging data from 166 subjects from the Alzheimer’s Disease Neuroimaging Initiative-1 (37 with Alzheimer disease, 76 with mild cognitive impairment, and 53 healthy controls) scanned at 1.5T and 3T. Using multiple linear regression, we analyzed the effect of clinical diagnosis on hippocampal radial distance, while adjusting for sex. 3D statistical maps were adjusted for multiple comparisons by using permutation-based statistics at a threshold of P < .01. RESULTS Bilaterally significant radial distance differences in the areas corresponding to the cornu ammonis 1, cornu ammonis 2, and subiculum were detected for Alzheimer disease versus healthy controls and mild cognitive impairment versus healthy controls at 1.5T and more profoundly at 3T. Comparison of Alzheimer disease with mild cognitive impairment did not reveal significant differences at either field strength. Subjects who converted from mild cognitive impairment to Alzheimer disease within 3 years of the baseline scan versus nonconverters showed significant differences in the area corresponding to cornu ammonis 1 of the right hippocampus at 3T but not at 1.5T. CONCLUSIONS While hippocampal atrophy patterns in diagnostic comparisons were similar at 1.5T and 3T, 3T showed a superior signal-to-noise ratio and detected atrophy with greater effect size compared with 1.5T.

Whole Brain Volume Measured from 1.5T versus 3T MRI in Healthy Subjects and Patients with Multiple Sclerosis

“…In a previous study, Jovicich and colleagues computed brain structure volumes from various scan protocols at both 1.5T and 3T and showed that field strength may bias the measurement of gray matter areas. In addition, Chow and colleagues showed a superior signal‐to‐noise ratio and a greater effect size in detecting hippocampal atrophy in patients with Alzheimer's disease or mild cognitive impairment as compared to NC at 3T versus 1.5T. Examination of our segmentation maps indicated that the 1.5T images produced lower tissue contrast.…”

Five-Year Longitudinal Brain Volume Change in Healthy Elders at Genetic Risk for Alzheimer’s Disease

“…Most of the previously published longitudinal studies (Table 1) were conducted at 1.5T [7, 8, 10–14]. The superior signal to noise ratio associated with 3T [47, 48] is critical for delineating hippocampal subfields [49]. …”

7T MRI for neurodegenerative dementias in vivo: a systematic review of the literature

“…Postmortem studies suggest early involvement of ERC, subiculum, CA1 and dentate gyrus in AD,41 and hippocampal atrophy is well established as a biomarker for AD 42. It is possible to delineate the subfields of the hippocampus using 3T MRI in vivo; at 1.5T and 3T CA1, CA2 and subiculum atrophy (using both field strengths to image the same participants) was found in AD but not in MCI 17. In this paper, improved SNR and greater effect sizes were noted at 3T (compared with 1.5T), suggesting that a similar further improvement might be seen with an increase of B 0 to 7T.…”

“…Neuroimaging dementia research is largely concerned with the discovery of new biomarkers with such aims as earlier diagnosis, identification of ‘at-risk’ individuals and those with ‘prodromal’ dementia syndromes, monitoring of disease progression and identification of new treatment targets by illuminating the natural history of the disease in vivo. Increasing static field strength (B 0 ) from 1.5T to 3T has allowed imaging of macro and microstructures in the brain, for example, analysis of whole hippocampal volumes and differentiation between hippocampal subfield volumes in health and disease 17. However, even at 3T, MRI voxels typically measure millimetres.…”