High-Field Magnetic Resonance Imaging

Quantification of global cerebral atrophy in multiple sclerosis from 3T MRI using SPM: the role of misclassification errors

Purpose

We tested the validity of a freely available segmentation pipeline to measure compartmental brain volumes from 3T MRI in patients with multiple sclerosis (MS). Our primary focus was methodological to explore the effect of segmentation corrections on the clinical relevance of the output metrics.

Methods

Three-dimensional T1-weighted images were acquired to compare 61 MS patients to 30 age- and gender-matched normal controls (NC). We also tested the within patient MRI relationship to disability (eg, expanded disability status scale [EDSS] score) and cognition. Statistical parametric mapping v. 8 (SPM8)-derived gray matter (GMF), white matter (WMF), and total brain parenchyma fractions (BPF) were derived before and after correcting errors from T1 hypointense MS lesions and/or ineffective deep GM contouring.

Results

MS patients had lower GMF and BPF as compared to NC (P<.05). Cognitively impaired patients had lower BPF than cognitively preserved patients (P<.05). BPF was related to EDSS; BPF and GMF were related to disease duration (all P<.05). Errors caused bias in GMFs and WMFs but had no discernable influence on BPFs or any MRI-clinical associations.

Conclusions

We report the validity of a segmentation pipeline for the detection of MS-related brain atrophy with 3T MRI. Longitudinal studies are warranted to extend these results.

Ultrasound-triggered BSA/SPION hybrid nanoclusters for liver-specific magnetic resonance imaging

Nanoclusters of superparamagnetic iron oxide nanoparticles (SPION) are developed for liver-specific magnetic resonance imaging (MRI) by a unique synthesis route. The process is efficient, environmentally benign, and straight forward within five minutes. The clustering effect is triggered in the presence of bovine serum albumin (BSA) aqueous phase under ultrasonication condition. The hydrophobic SPION are densely self-assembled into BSA/SPION hybrid nanoclusters with a uniform size of ~86 nm. The as-prepared BSA/SPION hybrid nanoclusters are found to be biocompatible and stable. They exhibit high transverse relaxivity and longitudinal relaxivity in water (r(2) and r(1) values are 600.8 and 4.3 s(-1) per mM of Fe(3+), respectively). In vivo T(2)-weighted MRI shows excellent enhancement in liver with an imaging time-window up to 48 h. In vivo biodistribution study indicates a gradual excretion of the nanoclusters via hepatobiliary (HB) processing. No toxicity is observed in the in vivo and ex vivo experiments. The BSA/SPION hybrid nanoclusters present great potential in MRI as the liver-specific contrast agents (CAs).

Simultaneous typical and extraordinary imaging findings of AIDS-associated cytomegalovirus encephalitis

Encephalitis caused by cytomegalovirus (CMV) is a devastating disease that occurs mostly in profoundly immunocompromised individuals, particularly in the setting of advanced HIV infection or organ transplantation. Imaging findings in AIDS-associated cytomegalovirus encephalitis that have been described range from ventriculitis (more common) to solitary mass lesions (less common). We describe a fatal case of AIDS-associated cytomegalovirus encephalitis that included typical imaging findings but also atypical features with widespread, multifocal lesions demonstrating restricted diffusion on magnetic resonance imaging (MRI). It is likely that these diffusion abnormalities are appreciated due to changes in imaging technology from the pre-highly active antiretroviral therapy era in which the typical imaging findings of CMV encephalitis were first described. The differential diagnosis of widespread, multifocal lesions with restricted diffusion in the setting of AIDS should now include CMV encephalitis.

Time-of-flight magnetic resonance angiography of the canine brain at 3.0 Tesla and 7.0 Tesla

OBJECTIVE

To evaluate the ability of 2-D time-of-flight (ToF) magnetic resonance angiography (MRA) to depict intracranial vasculature and compare results obtained with 3.0- and 7.0-T scanners in dogs.

ANIMALS

5 healthy Beagles.

PROCEDURES

2-D ToF-MRA of the intracranial vasculature was obtained for each dog by use of a 3.0-T and a 7.0-T scanner. Quantitative assessment of the images was obtained by documentation of the visibility of major arteries comprising the cerebral arterial circle and their branches and recording the number of vessels visualized in the dorsal third of the brain. Qualitative assessment was established by evaluation of overall image quality and image artifacts.

RESULTS

Use of 3.0- and 7.0-T scanners allowed visualization of the larger vessels of the cerebral arterial circle. Use of a 7.0-T scanner was superior to use of a 3.0-T scanner in depiction of the first- and second-order arterial branches. Maximum-intensity projection images had a larger number of vessels when obtained by use of a 7.0-T scanner than with a 3.0-T scanner. Overall, image quality and artifacts were similar with both scanners.

CONCLUSIONS AND CLINICAL RELEVANCE

Visualization of the major intracranial arteries was comparable with 3.0- and 7.0-T scanners; the 7.0-T scanner was superior for visualizing smaller vessels. Results indicated that ToF-MRA is an easily performed imaging technique that can be included as part of a standard magnetic resonance imaging examination and should be included in the imaging protocol of dogs suspected of having cerebrovascular disease.