Downstream effects of polypathology on neurodegeneration of medial temporal lobe subregions.

The medial temporal lobe (MTL) is a nidus for neurodegenerative pathologies and therefore an important region in which to study polypathology. We investigated associations between neurodegenerative pathologies and the thickness of different MTL subregions measured using high-resolution post-mortem MRI. Tau, TAR DNA-binding protein 43 (TDP-43), amyloid-ß and α-synuclein pathology were rated on a scale of 0 (absent)-3 (severe) in the hippocampus and entorhinal cortex (ERC) of 58 individuals with and without neurodegenerative diseases (median age 75.0 years, 60.3% male). Thickness measurements in ERC, Brodmann Area (BA) 35 and 36, parahippocampal cortex, subiculum, cornu ammonis (CA)1 and the stratum radiatum lacunosum moleculare (SRLM) were derived from 0.2 × 0.2 × 0.2 mm3 post-mortem MRI scans of excised MTL specimens from the contralateral hemisphere using a semi-automated approach. Spearman's rank correlations were performed between neurodegenerative pathologies and thickness, correcting for age, sex and hemisphere, including all four proteinopathies in the model. We found significant associations of (1) TDP-43 with thickness in all subregions (r = - 0.27 to r = - 0.46), and (2) tau with BA35 (r = - 0.31) and SRLM thickness (r = - 0.33). In amyloid-ß and TDP-43 negative cases, we found strong significant associations of tau with ERC (r = - 0.40), BA35 (r = - 0.55), subiculum (r = - 0.42) and CA1 thickness (r = - 0.47). This unique dataset shows widespread MTL atrophy in relation to TDP-43 pathology and atrophy in regions affected early in Braak stageing and tau pathology. Moreover, the strong association of tau with thickness in early Braak regions in the absence of amyloid-ß suggests a role of Primary Age-Related Tauopathy in neurodegeneration.

Real time magnetic resonance guided endomyocardial local delivery.

OBJECTIVE: To investigate the feasibility of targeting various areas of left ventricle myocardium under real time magnetic resonance (MR) imaging with a customised injection catheter equipped with a miniaturised coil. DESIGN: A needle injection catheter with a mounted resonant solenoid circuit (coil) at its tip was designed and constructed. A 1.5 T MR scanner with customised real time sequence combined with in-room scan running capabilities was used. With this system, various myocardial areas within the left ventricle were targeted and injected with a gadolinium-diethylenetriaminepentaacetic acid (DTPA) and Indian ink mixture. RESULTS: Real time sequencing at 10 frames/s allowed clear visualisation of the moving catheter and its transit through the aorta into the ventricle, as well as targeting of all ventricle wall segments without further image enhancement techniques. All injections were visualised by real time MR imaging and verified by gross pathology. CONCLUSION: The tracking device allowed real time in vivo visualisation of catheters in the aorta and left ventricle as well as precise targeting of myocardial areas. The use of this real time catheter tracking may enable precise and adequate delivery of agents for tissue regeneration.

Cardiac imaging at 4 Tesla.

Although higher magnetic field strength is a means to increase SNR in MRI, cardiac imaging has been difficult at high fields due to decreased RF penetration. Using a tailored cardiac coil constructed of two transmit surface coils with a four-element multicoil for signal reception, the authors demonstrate high-quality heart images acquired on a 4-T scanner. These images show an increase in SNR of approximately 2.5-fold over imaging at 1.5 T. This improvement in image quality can be used to increase in-plane resolution, reduce slice thickness, or reduce total scan time. Magn Reson Med 45:176-178, 2001.

A spiral volume coil for improved RF field homogeneity at high static magnetic field strength.

Biological samples have a high dielectric constant that can shorten RF wavelengths by a factor of 8 relative to the vacuum. At high field strengths, finite wavelength effects within larger samples are the dominant cause of RF field nonuniformity. A coil design is presented that can reduce and even eliminate this inhomogeneity; 4-T images in phantoms and in the head of a normal volunteer are presented, which demonstrate improved homogeneity relative to a standard coil. This coil design should aid in realizing the potential advantages of imaging large samples at high field strengths.

Respiratory sinus arrhythmia is a limited measure of cardiac parasympathetic control in man.

1. Respiratory modulation of cardiac parasympathetic activity and the relationship between respiratory sinus arrhythmia and parasympathetic control has been studied in twenty-nine conscious, healthy young adult subjects. 2. Changes in heart period in propranolol-treated subjects were taken as the measure of changes in cardiac parasympathetic activity; respiratory sinus arrhythmia was quantified as the difference between maximum and minimum heart periods in a given respiratory cycle; cardiac parasympathetic control was defined as the change in heart period after administration of a full dose of atropine. 3. During normal quiet breathing the inspiratory level of cardiac parasympathetic activity was not reduced to zero. The expiratory level was influenced by excitatory inputs whose activation was related to respiratory cycle length. 4. Slow breathing was associated with augmented sinus arrhythmia, but in different individuals the influence on minimum and maximum heart periods varied so that mean heart period was increased in some subjects but decreased in others. This occurred both in control conditions and after administration of a full dose of propranolol. 5. During normal breathing the correlation across subjects between respiratory sinus arrhythmia and parasympathetic control, although significant, was not close (r = 0.61). The relationship was not affected by beta-adrenergic blockade (r = 0.63). The strength of the correlation improved when multiple regression of respiratory sinus arrhythmia was performed on three variables: parasympathetic control, respiratory cycle length and tidal volume (R = 0.93). 6. It is concluded that in conscious human subjects the respiratory modulation of cardiac parasympathetic activity is different from that observed in the anaesthetized dog, and that variations in the amplitude of respiratory sinus arrhythmia do not necessarily reflect proportional changes in cardiac parasympathetic control.