Rigid motion artifact reduction in CT using extended difference function.

BACKGROUND: In computed tomography (CT), a patient motion would result in degraded spatial resolution and image artifacts. OBJECTIVE: To eliminate motion artifacts, this study presents a method to estimate the motion parameters from sinograms based on extended difference function. METHODS: Based on our previous work, we first divide the projection data into two parts according to view angles and take Radon transform. Then, we calculate the extended difference functions and search for the minimum points. The relative displacements can be determined by the minimum points, and the motion can be estimated by the relationships between the relative displacements and motion parameters. Finally, we introduce the estimated parameters into the reconstruction process to compensate for the motion effects. RESULTS: The simulation results show that the running times can reduce by about 30% than our previous work. In phantom experiments, the relative mean rotation excursion (RMRE) and relative mean translation excursion (RMTE) of the new method are lower than the conventional Helgason-Ludwig consistency condition (HLCC) based method and comparable to our previous work. Compare with the HLCC method, the root mean square error (RMSE) of the new method also reduces, while the Pearson correlation coefficient (CC) and mean structural similarity index (MSSIM) increase. CONCLUSIONS: The proposed new method yields the improved performance on accuracy of motion estimation with higher computational efficiency, and thus it can produce high-quality images.

Rigid motion artifact reduction in CT using frequency domain analysis.

BACKGROUND: It is often unrealistic to assume that the subject remains stationary during a computed tomography (CT) imaging scan. A patient rigid motion can be decomposed into a translation and a rotation around an origin. How to minimize the motion impact on image quality is important. OBJECTIVE: To eliminate artifacts caused by patient rigid motion during a CT scan, this study investigated a new method based on frequency domain analysis to estimate and compensate motion impact. METHODS: Motion parameters was first determined by the magnitude correlation of projections in frequency domain. Then, the estimated parameters were applied to compensate for the motion effects in the reconstruction process. Finally, this method was extended to helical CT. RESULTS: In fan-beam CT experiments, the simulation results showed that the proposed method was more accurate and faster on the performance of motion estimation than using Helgason-Ludwig consistency condition method (HLCC). Furthermore, the reconstructed images on both simulated and human head experiments indicated that the proposed method yielded superior results in artifact reduction. CONCLUSIONS: The proposed method is a new tool for patient motion compensation, with a potential for practical application. It is not only applicable to motion correction in fan-beam CT imaging, but also to helical CT.

Preparation and reactivity of a Ru(0) phosphino-carbene complex.

The reaction of the phosphino-carbene MeNC3H2NPtBu2 with RuHCl(CO)(PPh3)3 is shown to give facile access to the Ru(0) species (MeNC3H2NPtBu2)Ru(CO)(PPh3)2 (). This species undergoes oxidative addition of H2 and silanes to give (MeNC3H2NPtBu2)RuH2(CO)(PPh3)2, (MeNC3H2NPtBu2)Ru H(SiRPh2)(CO)(PPh3) (R = Ph 5, H 6) and (MeNC3H2NPtBu2) RuH(PhSi(SCH2CH2)2O)(CO)(PPh3) .

Projection domain denoising method based on dictionary learning for low-dose CT image reconstruction.

Reducing X-ray tube current is one of the widely used methods for decreasing the radiation dose. Unfortunately, the signal-to-noise ratio (SNR) of the projection data degrades simultaneously. To improve the quality of reconstructed images, a dictionary learning based penalized weighted least-squares (PWLS) approach is proposed for sinogram denoising. The weighted least-squares considers the statistical characteristic of noise and the penalty models the sparsity of sinogram based on dictionary learning. Then reconstruct CT image using filtered back projection (FBP) algorithm from the denoised sinogram. The proposed method is particularly suitable for the projection data with low SNR. Experimental results show that the proposed method can get high-quality CT images when the signal to noise ratio of projection data declines sharply.

1,1-Olefin-bridged bis-(2-indenyl) metallocenes of titanium and zirconium.

Tetrasubstituted alkenes bearing geminal 2-indenyl substituents--9-[bis(1H-inden-2-yl)methylidene]-9H-fluorene (6), 2,2'-(2,2-diphenylethene-1,1-diyl)-bis(1H-indene) (7), and 2,2'-(2-propylpent-1-ene-1,1-diyl)-bis(1H-indene) (8) have been synthesized and metallated to form a new class of ansa titanium and zirconium metallocene complexes containing a single sp(2)-hybridized carbon bridge. The synthesis of the tetramethylated bis-indenyl Zr-analog is described. In addition, the 1,1-bis-indenyl ethylene is prepared and the Zr complex is modified by olefin metathesis. X-ray structure analyses reveal strained η(5) sandwich complexes with highly open metal centers. These complexes have proven active in the polymerization of ethylene and its copolymerization with 1-hexene.

Syntheses of carbocyclic analogues of α-D-glucosamine, α-D-mannose, α-D-mannuronic acid, ß-L-idosamine, and ß-L-gulose.

A versatile synthesis of orthogonally protected derivatives of carba-α-D-glucosamine, carba-α-D-mannose, carba-α-D-mannuronic acid, carba-ß-L-idosamine, and carba-ß-L-gulose from methyl α-D-mannoside is described. Our synthetic strategy utilizes the palladium-promoted Ferrier carbocyclization and persistent butane-2,3-diacetal protection to produce a key chiral cyclohexanone intermediate, from which all five carbasugar derivatives can readily be obtained.

Total syntheses of (Sp)-(+)- and (Rp)-(-)-spiniferin-1, a pair of unusual natural products with planar chirality.

(S(p))-(+)-Spiniferin-1 and (R(p))-(-)-spiniferin-1, a pair of unusual marine natural products with planar chirality, were firstly synthesized via a polyfluoroalkanosulfonyl fluoride induced homoallylic carbocation rearrangement reaction. The chiral resolution and palladium-catalyzed ß-H elimination of allylic alcohol derivatives were considered as the key steps of these divergent syntheses.

Ester hydrogenation catalyzed by Ru-CNN pincer complexes.

We report new Ru-CNN pincer catalysts for ester hydrogenation under mild conditions.

Total synthesis of (±)-spiniferin-1 via a polyfluoroalkanosulfonyl fluoride induced homoallylic carbocation rearrangement reaction.

A facile total synthesis of marine natural product (±)-spiniferin-1 has been accomplished in eight steps with 28.9% overall yield, involving a rearrangement reaction initiated by polyfluoroalkanosulfonyl fluoride to construct the 1,6-methano[10]annulene core of the natural product as a key step.