Image Reconstruction in Light-Sheet Microscopy: Spatially Varying Deconvolution and Mixed Noise

We study the problem of deconvolution for light-sheet microscopy, where the data is corrupted by spatially varying blur and a combination of Poisson and Gaussian noise. The spatial variation of the point spread function of a light-sheet microscope is determined by the interaction between the excitation sheet and the detection objective PSF. We introduce a model of the image formation process that incorporates this interaction and we formulate a variational model that accounts for the combination of Poisson and Gaussian noise through a data fidelity term consisting of the infimal convolution of the single noise fidelities, first introduced in L. Calatroni et al. (SIAM J Imaging Sci 10(3):1196-1233, 2017). We establish convergence rates and a discrepancy principle for the infimal convolution fidelity and the inverse problem is solved by applying the primal-dual hybrid gradient (PDHG) algorithm in a novel way. Numerical experiments performed on simulated and real data show superior reconstruction results in comparison with other methods.

MAVS polymers smaller than 80 nm induce mitochondrial membrane remodeling and interferon signaling

Double‐stranded RNA (dsRNA) is a potent proinflammatory signature of viral infection and is sensed primarily by RIG‐I‐like receptors (RLRs). Oligomerization of RLRs following binding to cytosolic dsRNA activates and nucleates self‐assembly of the mitochondrial antiviral‐signaling protein (MAVS). In the current signaling model, the caspase recruitment domains of MAVS form helical fibrils that self‐propagate like prions to promote signaling complex assembly. However, there is no conclusive evidence that MAVS forms fibrils in cells or with the transmembrane anchor present. We show here with super‐resolution light microscopy that MAVS activation by dsRNA induces mitochondrial membrane remodeling. Quantitative image analysis at imaging resolutions as high as 32 nm shows that in the cellular context, MAVS signaling complexes and the fibrils within them are smaller than 80 nm. The transmembrane domain of MAVS is required for its membrane remodeling, interferon signaling, and proapoptotic activities. We conclude that membrane tethering of MAVS restrains its polymerization and contributes to mitochondrial remodeling and apoptosis upon dsRNA sensing.

Correlations between the surface ECG and the intracavitary electrocardiogram in typical atrial flutter

Typical atrial flutter (cavo-tricuspid isthmus-dependent) has as an electrophysiological substrate a macro-reentry circuit localized in the right atrium. Depending on the right atrial depolarization sequence, the rotation of the macro-reentry circuit can be counterclockwise (with an inferior to superior activation of the right atrium free wall and superior to inferior activation of the interatrial septum), characterized by negative F waves in inferior leads (DII, DIII, aVF) and V6, and positive in V1 on the surface electrogram (ECG), or clockwise (with a superior to inferior activation of the right atrium free wall and inferior to superior activation of the interatrial septum) characterized by positive F waves in inferior leads (DII, DIII, aVF) and V6, and negative in V1. Nevertheless, it is considered that for the diagnosis of the typical or atypical nature of this arrhythmia, the surface ECG has limited value. The purpose of this study was to compare the relationship between the flutter rotation sequence determined by the intracavitary electrogram and the morphology of the F waves on the surface ECG.

METHODS

The study included 387 patients admitted to the Cardiology - Rehabilitation Hospital from Cluj-Napoca between January 2007 and May 2010, diagnosed with typical atrial flutter during an electrophysiological study. Using the intracavitary electrograms the flutter rotation sequence was determined (clockwise or counterclockwise). The F waves' aspect on the surface ECG in leads DII, DIII, aVF, aVL, V1 and V6 was then analyzed.

RESULTS

One hundred and fifty two patients (39.3%) were diagnosed with clockwise atrial flutter and 235 patients (60.7%) with counterclockwise atrial flutter. The positive predictive value (PPV) of negative F waves in inferior leads and positive in V1 was, in the case of counterclockwise atrial flutter 98%; the negative predictive value (NPV) was 79%; sensitivity (Se) was 83% and specificity (Sp) was 97%. For typical clockwise atrial flutter, the PPV of the positive F waves in the inferior leads and negative in V1 was 94% (p < 0.001); the NPV was 85%; Se was 73% and Sp was 97%.

CONCLUSION

The surface ECG has a high value in determining the macroreentry circuit rotation sequence in the case of typical atrial flutter.

Microarray analysis at single-molecule resolution

Bioanalytical chip-based assays have been enormously improved in sensitivity in the recent years; detection of trace amounts of substances down to the level of individual fluorescent molecules has become state-of-the-art technology. The impact of such detection methods, however, has yet not fully been exploited, mainly due to a lack of appropriate mathematical tools for robust data analysis. One particular example relates to the analysis of microarray data. While classical microarray analysis works at resolutions of 2-20 microm and quantifies the abundance of target molecules by determining average pixel intensities, a novel high-resolution approach directly visualizes individual bound molecules as diffraction-limited peaks. The now possible quantification via counting is less susceptible to labeling artifacts and background noise. We have developed an approach for the analysis of high-resolution microarray images. First, it consists of a single-molecule detection step, based on undecimated wavelet transforms, and second, a spot identification step via spatial statistics approach (corresponding to the segmentation step in the classical microarray analysis). The detection method was tested on simulated images with a concentration range of 0.001 to 0.5 molecules per square micrometer and signal-to-noise ratio (SNR) between 0.9 and 31.6. For SNR above 15, the false negatives relative error was below 15%. Separation of foreground/background is proved reliable, in case foreground density exceeds background by a factor of 2. The method has also been applied to real data from high-resolution microarray measurements.

The role of radiofrequency ablation as a first line therapy in the treatment of atrial flutter

Cavo-tricuspid isthmus radiofrequency (RF) ablation is an efficient option in the treatment of atrial flutter. In the case of a well-tolerated, first episode of atrial flutter, it has a class II indication, level of evidence B, the current first-line therapeutic option being electrical cardioversion, pharmacological cardioversion or atrial overdrive pacing followed by long-term antiarrhythmic therapy. The purpose of this study was to evaluate, in a prospective manner, the recurrence rate of these two different therapeutic options after the treatment of a first episode of atrial flutter.

MATERIAL AND METHODS

Between January 2007 and May 2009, for 99 patients admitted to the hospital for a first episode of atrial flutter, cardioversion was attempted either by RF ablation (group 1-42 patients), or by electrical cardioversion, pharmacological cardioversion or atrial overdrive pacing followed by long-term Amiodarone therapy (group 21-57 patients). We compared the recurrence rate of atrial flutter in the 2 groups after a follow-up period of one year.

RESULTS

In group 1, sinus rhythm was achieved in all patients, with bidirectional isthmic block being obtained for 37 patients (88.1%). In group 2, conversion to sinus rhythm was obtained in all cases. The recurrence rate was 6 times higher in group 2 vs group 1 (57.9% = 33 patients vs 9.5% = 4 patients) (p = 0.01).

CONCLUSION

RF ablation should be considered as a therapeutic option in the treatment of the first episode of atrial flutter, due to its significant efficiency in maintaining sinus rhythm and to its low recurrence rate.

[The recovery of work capacity within the framework of short-term antitubercular chemotherapy]

The authors compare the results of chemotherapy reflected in the proportion of recoveries of work capacity and the number of retired persons in two groups of patients--one including 102 cases treated between 1970 and 1971 by a 3/6 regimen, and another one including 91 patients treated in 1986 by a modern intensive 3 + 3 regimen. The data indicate better results with the 1986 lot as compared with the 1970-1971 lot. In the 1986 group there were no fatalities and the persons that recovered their work capacity represented 90.1% of the total. By contrast, in the group treated between 1970 and 1971 there were two fatalities and only 84.3% of all the patients did recover the work capacity. The number of retired persons decrease from 11.7% in the first group to 7.7% in the second. Temporary incapacity decreased from an average of 321 days to an average of 267 days in the second group. All these results were obtained by shortening the treatment from an average of 9 months to an average of 6 months.

Structural and catalytic properties of L-alanine dehydrogenase from Bacillus cereus

Alanine dehydrogenase from Bacillus cereus, a non-allosteric enzyme composed of six identical subunits, was purified to homogeneity by chromatography on blue-Sepharose and Sepharose 6B-CL. Like other pyridine-linked dehydrogenases, alanine dehydrogenase is inhibited by Cibacron blue, competitively with respect to NADH and noncompetitively with respect to pyruvate. The enzyme was inactivated by 0.1 M glycine/HCl (pH 2) and reactivated by 0.1 M phosphate (pH 8) supplemented with NAD+ or NADH. The reactivation was characterized by sigmoidal kinetics indicating a complex mechanism involving rate-limiting folding and association steps. Cibacron blue interfered with renaturation, presumably by competition with NADH. Chromatography on Sepharose 6B-CL of the partially renatured alanine dehydrogenase led to the separation of several intermediates, but only the hexamer was characterized by enzymatic activity. By immobilization on Sepharose 4B, alanine dehydrogenase from B. cereus retained 66% of the specific activity of the soluble enzyme. After denaturation of immobilized alanine dehydrogenase with 7 M urea, 37% of the initial protein was still bound to Sepharose, indicating that on the average the hexamer was attached to the matrix via, at most, two subunits. The ability of the denatured, immobilized subunits to pick up subunits from solution shows their capacity to fold back to the native conformation after urea treatment. The formation of "hybrids" between subunits of enzyme from B. cereus and Bacillus subtilis demonstrates the close resemblance of the tertiary and quaternary structures of alanine dehydrogenases from these species.

Catalytic properties of Sepharose-bound L-alanine dehydrogenase from Bacillus cereus

(1) L-Alanine dehydrogenase from Bacillus cereus was purified by a two-step chromatographic procedure involving Cibacron-Blue 3G-A Sepharose 4B-CL, and Sepharose 6B-CL, and immobilized on CNBr-activated Sepharose 4B. (2) Following immobilization via two of the six subunits, L-alanine dehydrogenase retained 66% of the specific activity of the soluble enzyme. The affinity of the immobilized enzyme for NH4+, pyruvate and L-alanine, was not different to that of the soluble form. The Km of the Sepharose-bound L-alanine dehydrogenase for pyridine coenzymes was 6-8-times higher than in the soluble case. (3) The stability of L-alanine dehydrogenase towards urea or thermal denaturation was increased by immobilization. (4) The incubation at 37 degrees C for 24 h of the immobilized L-alanine dehydrogenase with 3 M NH4Cl/NH4OH buffer (pH 9) released 70% of the enzyme. The specific activity and the affinity of the 'solubilized' L-alanine dehydrogenase for the pyridine coenzymes was the same as that obtained with the original, soluble L-alanine dehydrogenase.