Biomedical subjects

Chih-Wei Chang

Publications and source records attributed to Chih-Wei Chang.

4 recordsLinked to original sources

PubMed2006

Kinematic navigation in total knee replacement--experience from the first 50 cases.

BACKGROUND/PURPOSE: Proper alignment of the prosthesis is critical in total knee replacement (TKR) to minimize long-term wear, risk of osteolysis, and loosening of the prosthesis. This study examined the accuracy of lower limb alignment obtained using a kinematic navigation system for TKR, and the extra time needed to adopt this system. METHODS: From August 2002 to April 2003, 71 patients with knee osteoarthritis underwent 79 primary TKR operations by the same surgical team. Fifty of these operations were performed with the aid of the CT-free kinematic navigation system, and the remaining 29 were performed with conventional manual methods. Results, including operation time, radiographic alignment of the prosthesis and complications, for the two groups were compared. RESULTS: Patients in the kinematic navigation group achieved better accuracy in the coronal plane than the conventional group in terms of postoperative mechanical axis (1.89 +/- 0.63 degrees vs. 3.38 +/- 1.07 degrees ). Less variation was noted in the navigation group (femur: SD 1.88 degrees vs. 7.12 degrees ; tibia: SD 1.54 degrees vs. 2.99 degrees ), although the difference in the mean values was not significant (p = 0.475 and 0.55, respectively). The operation time (from skin to skin) in the navigation group (100.6 +/- 4.3 minutes) was longer than that in the conventional group (92.7 +/- 5.1 minutes; p = 0.027). Two perioperative fractures occurred in the navigation group, both of which were attributed to patient factors as opposed to operation procedures. No major complications such as infection or pulmonary embolism occurred during this study. CONCLUSION: Use of a kinematic navigation system in TKR provides better accuracy than conventional manual methods. The technique is easy to use, has a short learning curve, and requires an additional operation time of less than 10 minutes. Precise alignment can be achieved with the aid of navigation in most cases.

Aged↗

PubMed2005

Relaxation dynamics and structural characterization of organic nanoparticles with enhanced emission.

With a reprecipitation method, we prepared fluorescent organic nanoparticles of 1,4-di[(E)-2-phenyl-1-propenyl]benzene (PPB) that feature weak emission in solution but exhibit blue-shifted absorption and strong emission as aggregates. Picosecond fluorescent transients of these PPB nanoparticles showed biexponential decay, described with a consecutive kinetic model involving two emissive states. X-ray diffraction patterns of PPB nanocrystals indicate long-range packing structures of two types, one the same as in a single crystal and the other not yet determined. PPB molecules in a crystal show an arrangement of a herringbone type with three benzene rings in a PPB unit being nearly planar and two methyl groups of the unit pointing along the same direction, in contrast to the twisted structure of an isolated PPB molecule. Fluorescence transients of PPB on a femtosecond scale indicate an efficient channel for isomerization that is activated for free PPB in solution but inhibited in PPB forming nanoparticles, demonstrating the significance of molecular geometry and twisting motions that affect the relaxation dynamics in the excited state. The versatile techniques combined in this work provide strong evidence to improve our understanding of optical properties in organic nanoparticles dependent on size.

Journal Article↗

PubMed2004

Photoisomerization dynamics of azobenzene in solution with S1 excitation: a femtosecond fluorescence anisotropy study.

Measurements of anisotropy of femtosecond fluorescence after direct excitation of the S1(n,pi*) state of azobenzene in hexane and ethylene glycol solutions have been carried out to address the controversy about inversion and rotation in the mechanism of photoisomerization. The observed anisotropies in hexane decay to a nonzero asymptotic level with a relaxation period the same as that for slow decay of the corresponding biexponential transient; this effect is attributed to involvement of the out-of-plane CNNC-torsional motion on approach to a twisted conical intersection along the "rotation channel" that depolarizes the original in-plane transition moment. In contrast, when the rotational channel becomes substantially hindered in ethylene glycol, the anisotropies show no discernible decay feature, but the corresponding transients show prominent decays attributed to involvement of in-plane symmetric motions; the latter approach a planar-sloped conical intersection along a "concerted inversion channel" for efficient internal conversion through vibronic coupling. The proposed mechanism is consistent with theoretical calculations and rationalizes both results on quantum yields and ultrafast observations.

Journal Article↗

PubMed2004

Transcranial echo-guided transsphenoidal surgical approach for the removal of large macroadenomas.

OBJECT: Transsphenoidal surgery for the removal of macroadenomas has some disadvantages, including the risk of performing procedures without adequate visualization, difficulties in estimating the amount of residual tumor, and the risk of injuring major vessels. To overcome these disadvantages, the authors have developed transcranial echo-guided transsphenoidal surgery. METHODS: Three patients with large macroadenomas and two patients with irregularly shaped macroadenomas were selected for this operation. In addition to standard preparations for transsphenoidal surgery, in each case the right frontal bone was trephined and an echo probe was inserted transdurally through the trephination hole. During tumor removal, brightness-mode echo images and Doppler color flow images were obtained. The echo images allowed for real-time visualization of the tumor and surrounding brain structures including major arteries and the cisterns; histological heterogeneities of the tumor could also be appreciated. The tumors were removed safely and maximal tumor removal was achieved. CONCLUSIONS: Transcranial echo-guided transsphenoidal surgery provides real-time visualization of tumor removal. The method enhances the safety of this surgery, maximizes the removal of the tumor, and is inexpensive.

Adenoma↗