Optimization of signal detection in SPECT

Parallel-hole collimators of varying design are discussed, using the display signal-to-noise ratio of R.F. Wagner et al. (Med. Phys., vol.6, p.83-94, 1979) to obtain contrast-detail diagrams and analytical expressions for the signal-to-noise ratio in SPECT (single-photon-emission computed tomography). It is concluded: (1) that the detectability of deeply embedded small objects (more than ~10 cm deep) may be improved only slightly by improvements in the resolution and geometric efficiency of parallel-hole collimators; (2) that a long-bore collimator outperforms a low-energy general-purpose collimator for objects smaller than ~2 cm, but only to a minor degree; and (3) that for improvement of small object detectability by SPECT, the most fruitful technological pursuit would probably involve development of focused collimators.     

The 9-hexadecenoic and 11-octadecenoic acid content of natural fats and oils

The monoenoic methyl esters from numerous fats and oils which contained appreciablecis-9-hexadecenoic acid (cis-9-16∶1) were isolated by liquid-solid chromatography on silver nitrate-silica gel. Analysis of the monoenes by packed and capillary column gas-liquid chromatography showed that significant amounts ofcis-11-octadecenoic acid (cis-11-18∶1) were present in all samples. The amount ofcis-11-18∶1 found in the monoenoic methyl esters increased proportionally to logarithmic increases in thecis-9-16∶1 level. Most analyses reported in the literature also show this proportionality. This mathematical relationship suggests that chain elongation ofcis-9-16∶1 tocis-11-18∶1 is a biosynthetic pathway operative in a wide variety of species.     

反式 -1,4-聚异戊二烯相对分子质量的调节

采用负载钛本体沉淀聚合法,以氢气作链转移剂,制备了不同相对分子质量的反式-1,4-聚异戊二烯(TPI),讨论了老化、氢气调节及塑炼对其相对分子质量的影响,以及不同相对分子质量TPI的结构与性能。结果表明,本体系合成TPI的数均相对分子质量为(5～15)×104,相对分子质量分布为2.00～3.00;门尼粘度为20～120时,随着TPI相对分子质量的降低,其结晶速度提高,结晶度无明显变化,拉伸强度明显降低,扯断伸长率、屈服强度和邵尔A型硬度无明显变化。     

Mie scattering from a sonoluminescing air bubble in water

A single bubble of air in water can emit pulses of blue-white light that have durations of less than 50 ps while it is oscillating in an acoustic standing wave. The emission is called sonoluminescence. A knowledge of the bubble diameter throughout the cycle, and in particular near the time of sonoluminescence emission, can provide important information about the phenomenon. A new Mie scattering technique is developed to determine the size of the bubble through its expansion and collapse during the acoustic cycle. The technique does not rely on an independent means of calibration or on accurate measurements of the scattered intensity.     

Scientific sketching for collaborative VR visualization design

We present four studies investigating tools and methodologies for artist-scientist-technologist collaboration in designing multivariate, virtual reality (VR) visualizations. Design study 1 identifies the promise of 3D drawing-style interfaces for VR design and also establishes limitations of these tools with respect to precision and support for animation. Design study 2 explores animating artist-created visualization designs with scientific 3D fluid flow data. While results captured an accurate sense of flow that was advantageous as compared to the results of study 1, the potential for visual exploration using the design tools tested was limited. Design study 3 reveals the importance of a new 3D interface that overcomes the precision limitation found in study 1 while remaining accessible to artist collaborators. Drawing upon previous results, design study 4 engages collaborative teams in a design process that begins with traditional paper sketching and moves to animated, interactive, VR prototypes "sketched" by designers in VR using interactive 3D tools. Conclusions from these four studies identify important characteristics of effective artist-accessible VR visualization design tools and lead to a proposed formalized methodology for successful collaborative design that we expect to be useful in guiding future collaborations. We call this proposed methodology Scientific Sketching.     

Port Placement Planning in Robot-Assisted Coronary Artery Bypass

Properly selected port sites for robot-assisted coronary artery bypass graft (CABG) improve the efficiency and quality of these procedures. In clinical practice, surgeons select port locations using external anatomic landmarks to estimate a patient's internal anatomy. This paper proposes an automated approach to port selection based on a preoperative image of the patient, thus avoiding the need to estimate internal anatomy. Using this image as input, port sites are chosen from a grid of surgeon-approved options by defining a performance measure for each possible port triad. This measure seeks to minimize the weighted squared deviation of the instrument and endoscope angles from their optimal orientations at each internal surgical site. This performance measure proves insensitive to perturbations in both its weighting factors and moderate intraoperative displacements of the patient's internal anatomy. A validation study of this port site selection was performed. cardiac algorithm also Six surgeons dissected model vessels using the port triad selected by this algorithm with performance compared to dissection using a surgeon-selected port triad and a port triad template described by Tabaie et al., 1999. With the algorithm-selected ports, dissection speed increased by up to 43% (p = 0.046) with less overall vessel trauma. Thus, this algorithmic approach to port site selection has important clinical implications for robot-assisted CABG which warrant further investigation.