A novel approach to dementia: high-resolution 1H MRI of the human hippocampus performed at 21.1 T

A volume birdcage coil with an adjustable sliding tuner ring for neuroimaging in high field vertical magnets: ex and in vivo applications at 21.1T

A tunable 900 MHz transmit/receive volume coil was constructed for ¹H MR imaging of biological samples in a 21.1 T vertical bore magnet. To accommodate a diverse range of specimen and RF loads at such a high frequency, a sliding-ring adaptation of a low-pass birdcage was implemented through simultaneous alteration of distributed capacitance. To make efficient use of the constrained space inside the vertical bore, a modular probe design was implemented with a bottom-adjustable tuning and matching apparatus. The sliding ring coil displays good homogeneity and sufficient tuning range for different samples of various dimensions representing large span of RF loads. High resolution in vivo and ex vivo images of large rats (up to 350 g), mice and human postmortem tissues were obtained to demonstrate coil functionality and to provide examples of potential applications at 21.1 T.

[Magnetic resonance imaging with 21.1 T and pathological correlations--diffuse Lewy body disease]

We investigated fixed basal ganglia specimens, including globus pallidus and putamen, with 21.1-Tesla MRI allowing us to achieve a microscopic level resolution from a patient with pathologically confirmed dementia with Lewy bodies (DLB) and a neurologically normal control case. We acquired T2 and T2 * weighted images that demonstrated diffuse and patchy lower intensities in the basal ganglia compared to control. There are several paramagnetic substances in brain tissue that could potentially reduce both T2 and T2 * relaxation times, including ferritin, iron (Fe3+), manganese, copper and others. Because iron is most abundant, low intensities on T2 and T2 * weighted images most likely reflect iron deposition. Iron, especially Fe3+, deposition was visible in the pathological specimens stained with Prussian blue after images were obtained. Although radiological-pathological comparisons are not straightforward with respect to either the MRI signal or relaxation quantification, there appears to be a correlation between the relative increase in iron as assessed by Prussian blue staining and the decrease in T2 * value between the DLB and control specimens. As such, this exceptionally high field MRI technique may provide details about the role that iron deposition plays either directly or indirectly as a biomarker in neurodegenerative processes.

Hippocampal sulcal cavities: prevalence, risk factors and relationship to memory impairment

While hippocampal volumes have been extensively examined in neuropsychiatric disorders and ageing, small areas of signal variation within the hippocampus commonly observed on MRI, described as hippocampal sulcal cavities (HSCs), have received less attention. We review the published literature on HSCs to examine their prevalence, putative aetiological factors such as hypertension, and possible cognitive correlates. HSCs were reported in 77% (66% weighted mean) of patients with memory disorders and 48% (47% weighted mean) of controls, and the prevalence increased with age in healthy subjects (r=0.64, p=0.047). A number of studies reported hypertension as a risk factor, and related their presence to poorer memory function. Further work is needed to fully understand the clinical significance of these lesions.