Central intra-lesional iron deposits as a possible novel imaging marker at 7 Tesla MRI in Susac Syndrome - an exploratory study

BACKGROUND: Susac syndrome (SuS) is a rare autoimmune disease that leads to hearing impairment, visual field deficits, and encephalopathy due to an occlusion of precapillary arterioles in the brain, retina, and inner ear. Given the potentially disastrous outcome and difficulties in distinguishing SuS from its differential diagnoses, such as multiple sclerosis (MS), our exploratory study aimed at identifying potential new SuS-specific neuroimaging markers. METHODS: Seven patients with a definite diagnosis of SuS underwent magnetic resonance imaging (MRI) at 7 Tesla (7T), including T2* weighted and quantitative susceptibility mapping (QSM) sequences. T2 weighted hyperintense lesions were analyzed with regard to number, volume, localization, central vein sign, T1 hypointensity, and focal iron deposits in the center of SuS lesions ("iron dots"). Seven T MRI datasets from the same institute, comprising 75 patients with, among others, MS, served as controls. RESULTS: The "iron dot" sign was present in 71.4% (5/7) of the SuS patients, compared to 0% in our control cohort. Thus, sensitivity was 71.4% and specificity 100%. A central vein sign was only incidentally detected. CONCLUSION: We are the first to demonstrate this type of "iron dot" lesions on highly resolving 7T T2*w and QSM images in vivo as a promising neuroimaging marker of SuS, corroborating previous histopathological ex vivo findings

Acoustic cardiac triggering: a practical solution for synchronization and gating of cardiovascular magnetic resonance at 7 Tesla

<p>Abstract</p> <p>Background</p> <p>To demonstrate the applicability of acoustic cardiac triggering (ACT) for imaging of the heart at ultrahigh magnetic fields (7.0 T) by comparing phonocardiogram, conventional vector electrocardiogram (ECG) and traditional pulse oximetry (POX) triggered 2D CINE acquisitions together with (i) a qualitative image quality analysis, (ii) an assessment of the left ventricular function parameter and (iii) an examination of trigger reliability and trigger detection variance derived from the signal waveforms.</p> <p>Results</p> <p>ECG was susceptible to severe distortions at 7.0 T. POX and ACT provided waveforms free of interferences from electromagnetic fields or from magneto-hydrodynamic effects. Frequent R-wave mis-registration occurred in ECG-triggered acquisitions with a failure rate of up to 30% resulting in cardiac motion induced artifacts. ACT and POX triggering produced images free of cardiac motion artefacts. ECG showed a severe jitter in the R-wave detection. POX also showed a trigger jitter of approximately Δt = 72 ms which is equivalent to two cardiac phases. ACT showed a jitter of approximately Δt = 5 ms only. ECG waveforms revealed a standard deviation for the cardiac trigger offset larger than that observed for ACT or POX waveforms.</p> <p>Image quality assessment showed that ACT substantially improved image quality as compared to ECG (image quality score at end-diastole: ECG = 1.7 ± 0.5, ACT = 2.4 ± 0.5, p = 0.04) while the comparison between ECG vs. POX gated acquisitions showed no significant differences in image quality (image quality score: ECG = 1.7 ± 0.5, POX = 2.0 ± 0.5, p = 0.34).</p> <p>Conclusions</p> <p>The applicability of acoustic triggering for cardiac CINE imaging at 7.0 T was demonstrated. ACT's trigger reliability and fidelity are superior to that of ECG and POX. ACT promises to be beneficial for cardiovascular magnetic resonance at ultra-high field strengths including 7.0 T.</p

Oscillating steady states

The signal formation and properties of steady-state free precession (SSFP) in combination with alternating RF pulse phases or alternating spin precession is analyzed. Simulations and experiments demonstrate that the amplitudes of SSFP echo paths are significantly influenced by application of alternating phases either via the exciting RF pulse or via some external mechanism producing alternating spin precession. The influence of alternating phases on echo amplitudes is different for different echo paths. The primary SSFP echo paths F0− and F0+ exhibit a signal reduction whereas higher-order echoes F−1− and F1+ show a signal increase upon application of oscillating phases. This behavior can be described using a simple perturbation theory applied to the frequency response profile of balanced SSFP combined with a final signal integration over one balanced SSFP band. The high sensitivity of SSFP echo amplitudes to alternating RF pulse phases or precession is exemplarily used to detect and visualize propagating transverse acoustic shear waves. Detection of flow or alternating currents are further possibilities to apply this unique feature of SSFP

Young Investigator Awards Finalist: Balanced Alternating Steady-State Elastography

A novel, balanced alternating steady-state elastography (BASEL) technique is proposed for visualization of propagating transverse acoustic shear waves. A conventional balanced steady-state free precession (b-SSFP) sequence was modified such that the dynamic equilibrium becomes very sensitive to small cyclic displacements, generating two distinct &ndash; alternating &ndash; steady states. Experiments with tissue-like agarose gel phantoms demonstrate that the novel sequence offers a scan time reduction of at least one order of magnitude for comparable sensitivity compared to standard MRE methods

Balanced alternating steady-state elastography

A conventional balanced steady-state free precession (b-SSFP) sequence scheme was modified such that the dynamic equilibrium becomes very sensitive to small cyclic displacements, generating two distinct and alternating steady states. This novel technique is proposed for the visualization of propagating transverse acoustic shear waves, as used in MR elastography (MRE) to determine the mechanical properties of materials or in vivo soft tissue. Experiments with tissue-like agarose gel phantoms and simulations demonstrate that the novel sequence offers an increase in phase sensitivity by about one order in magnitude compared to standard motion-encoding methods. In addition, the new method benefits from the very short acquisition times achieved by b-SSFP protocols