Biomedical subjects

Wen-Tung Wang

Publications and source records attributed to Wen-Tung Wang.

3 recordsLinked to original sources

PubMed2005

A modified projection reconstruction trajectory for reduction of undersampling artifacts.

PURPOSE: To reduce undersampling artifacts for a given number of repetitions of the projection reconstruction (PR) sequence by modifying its k-space trajectory to sample more mid-frequencies while reducing the sampling coverage of the peripheral spatial frequencies. MATERIALS AND METHODS: The single k-space spoke measured per repetition in the standard PR was modified so that one complete and two partial spokes were measured per repetition but with decreased k-space extent. The point spread functions (PSFs) and undersampling artifacts of the modified PR were compared with those of the standard PR for various numbers of projections. Phantom and in vivo images were used to assess the relative performance. RESULTS: PSF analysis indicated that the modified PR method provided reduced undersampling artifacts with somewhat reduced spatial resolution. The phantom and in vivo images corroborated this. CONCLUSION: The modified PR trajectory provides reduced undersampling artifact vs. the standard PR, particularly when the number of projections is limited and the artifact level is high.

Artifacts↗

PubMed2005

Effect of attenuation correction on lesion detection using a hybrid PET system.

OBJECTIVE: The purpose of this study was to investigate the effect of attenuation correction (AC) on lesion detection for a hybrid PET system. MATERIAL AND METHOD: Experimental list-mode data were acquired from hot spheres inside a uniform cylindrical phantom with an elliptical cross-section using a Siemens E. CAM+ dual-camera hybrid PET system. Spheres with inner diameters of 0.8- and 1-cm and the cylindrical phantom were filled with F-18 to simulate lesions with lesion-to-background (L/B) ratios of 14:1 and 8:1, respectively, found in clinical PET studies. The list-mode data of each sphere size were regrouped into sinograms with peak-to-peak energy window settings at 30% and 20% for the 0.8- and 1-cm diameter lesion, respectively. They were then rebinned using the single slice rebinning method. Attenuation correction was applied assuming uniform attenuation. The sinograms with and without AC were reconstructed using 5 iterations of OS-EM algorithm with 8 angles/ subset and postfiltered with a Butterworth filter with n = 5 and fc = 0.52 cycles/cm. Human observer performance study and localization receiver operating characteristic (LROC) analysis were used to evaluate the reconstructed images for maximum lesion detection. Average areas under the LROC curves (A(LROC)) across 8 observers obtained with and without AC were determined. The null hypothesis that there was no difference between with AC and without AC was tested using a two-tailed t-test with 95% confidence interval. RESULTS: The results indicated that for the 0. 8-cm lesion with 14:1 L/B ratio, the A(LROC) decreases from 0.66 to 0.62 when AC is applied as compared to without AC andfrom 0.69 to 0.63 for the 1.0-cm lesion with 8:1 L/ B ratio, but no statistical significant difference (p > 0. 05). CONCLUSION: The authors conclude that for a phantom with hot lesions embedded in a uniform background, AC decreases lesion detectability compared to without AC using a hybrid PET system for small lesion sizes.

Humans↗

PubMed2002

Efficient simulation of SPECT down-scatter including photon interactions with crystal and lead.

A major image degrading factor in simultaneous Dual Isotope (DI) SPECT or simultaneous Emission-Transmission (ECT-TCT) imaging, is the detection of photons emitted by the higher energy isotope in the energy window used for imaging the lower energy isotope. In Tc-99m/Tl-201 DI-SPECT typically tens of percents of the total detected down-scatter is caused by lead x rays. In Tc-99m/Gd-153 ECT-TCT, a comparable fraction of the down-scatter originates from Tc-99m photons which only partly deposit their energy in the detector crystal (i.e., due to crystal interactions). Efficient simulation methods which model down-scatter can be used to optimize DI-SPECT or ECT-TCT imaging acquisition or reconstruction protocols. In this paper we adapt a previously proposed efficient down-scatter simulation method, to include the interactions of photons with the detector crystal and collimator lead. To this end, point spread function tables including crystal and lead interactions are precalculated. Subsequently, photons are traced through the patient body until their last scatter position, and the precalculated responses are used to project the photons onto the detector plane, while photon attenuation in the patient is taken into account. The approach is evaluated by comparing simulated Tc-99m down-scatter projections with measured projections. Incorporation of photon interaction with crystal and lead leads to significantly improved accuracy of the shape of down-scatter responses, while differences in total counts between simulated and measured projections typically decrease from tens of percents to a couple of percents. Calculating 60 down-scatter projections of an extended distribution on a 64 x 64 x 64 grid takes about three minutes on a PC with two 1.2 GHz processors. We conclude that accurate and efficient simulation of down-scatter is now possible including the major effects of the nonuniform mass density of the patient as well as photon interactions with the crystal and collimator lead.

Biophysical Phenomena↗